+N1548 December 2, 2010 ISO/IEC 9899:201x +N1548 Committee Draft -- December 2, 2010 ISO/IEC 9899:201x @@ -9,7 +10,10 @@ INTERNATIONAL STANDARD (C)ISO/IEC ISO/IEC 9 -Programming languages -- C ++ +Programming languages -- C
+ABSTRACT @@ -36,26871 +40,33398 @@ relevant patent rights of which they are aware and to provide supporting documen Changes from the previous draft (N1256) are indicated by ''diff marks'' in the right margin: deleted text is marked with ''*'', new or changed text with '' ''. - - - - -[page i] - - - -[page ii] - -Contents -Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii -Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii -1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -2. Normative references . . . . . . . . . . . . . . . . . . . . . . . 2 -3. Terms, definitions, and symbols . . . . . . . . . . . . . . . . . . . 3 -4. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . . 8 -5. Environment . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 5.1 Conceptual models . . . . . . . . . . . . . . . . . . . . . 10 - 5.1.1 Translation environment . . . . . . . . . . . . . . . . 10 - 5.1.2 Execution environments . . . . . . . . . . . . . . . . 12 - 5.2 Environmental considerations . . . . . . . . . . . . . . . . . 22 - 5.2.1 Character sets . . . . . . . . . . . . . . . . . . . . 22 - 5.2.2 Character display semantics . . . . . . . . . . . . . . 24 - 5.2.3 Signals and interrupts . . . . . . . . . . . . . . . . . 25 - 5.2.4 Environmental limits . . . . . . . . . . . . . . . . . 25 -6. Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 6.1 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 6.2 Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 6.2.1 Scopes of identifiers . . . . . . . . . . . . . . . . . 35 - 6.2.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 36 - 6.2.3 Name spaces of identifiers . . . . . . . . . . . . . . . 37 - 6.2.4 Storage durations of objects . . . . . . . . . . . . . . 38 - 6.2.5 Types . . . . . . . . . . . . . . . . . . . . . . . 39 - 6.2.6 Representations of types . . . . . . . . . . . . . . . . 44 - 6.2.7 Compatible type and composite type . . . . . . . . . . . 47 - 6.2.8 Alignment of objects . . . . . . . . . . . . . . . . . 48 - 6.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 50 - 6.3.1 Arithmetic operands . . . . . . . . . . . . . . . . . 50 - 6.3.2 Other operands . . . . . . . . . . . . . . . . . . . 54 - 6.4 Lexical elements . . . . . . . . . . . . . . . . . . . . . . 57 - 6.4.1 Keywords . . . . . . . . . . . . . . . . . . . . . . 58 - 6.4.2 Identifiers . . . . . . . . . . . . . . . . . . . . . . 59 - 6.4.3 Universal character names . . . . . . . . . . . . . . . 61 - 6.4.4 Constants . . . . . . . . . . . . . . . . . . . . . . 62 - 6.4.5 String literals . . . . . . . . . . . . . . . . . . . . 70 - 6.4.6 Punctuators . . . . . . . . . . . . . . . . . . . . . 72 - 6.4.7 Header names . . . . . . . . . . . . . . . . . . . . 73 - 6.4.8 Preprocessing numbers . . . . . . . . . . . . . . . . 74 - 6.4.9 Comments . . . . . . . . . . . . . . . . . . . . . 75 - - -[page iii] - - 6.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . 76 - 6.5.1 Primary expressions . . . . . . . . . . . . . . . . . 78 - 6.5.2 Postfix operators . . . . . . . . . . . . . . . . . . . 79 - 6.5.3 Unary operators . . . . . . . . . . . . . . . . . . . 88 - 6.5.4 Cast operators . . . . . . . . . . . . . . . . . . . . 91 - 6.5.5 Multiplicative operators . . . . . . . . . . . . . . . . 92 - 6.5.6 Additive operators . . . . . . . . . . . . . . . . . . 92 - 6.5.7 Bitwise shift operators . . . . . . . . . . . . . . . . . 94 - 6.5.8 Relational operators . . . . . . . . . . . . . . . . . . 95 - 6.5.9 Equality operators . . . . . . . . . . . . . . . . . . 96 - 6.5.10 Bitwise AND operator . . . . . . . . . . . . . . . . . 97 - 6.5.11 Bitwise exclusive OR operator . . . . . . . . . . . . . 98 - 6.5.12 Bitwise inclusive OR operator . . . . . . . . . . . . . . 98 - 6.5.13 Logical AND operator . . . . . . . . . . . . . . . . . 99 - 6.5.14 Logical OR operator . . . . . . . . . . . . . . . . . 99 - 6.5.15 Conditional operator . . . . . . . . . . . . . . . . . 100 - 6.5.16 Assignment operators . . . . . . . . . . . . . . . . . 101 - 6.5.17 Comma operator . . . . . . . . . . . . . . . . . . . 104 - 6.6 Constant expressions . . . . . . . . . . . . . . . . . . . . . 105 - 6.7 Declarations . . . . . . . . . . . . . . . . . . . . . . . . 107 - 6.7.1 Storage-class specifiers . . . . . . . . . . . . . . . . 108 - 6.7.2 Type specifiers . . . . . . . . . . . . . . . . . . . . 109 - 6.7.3 Type qualifiers . . . . . . . . . . . . . . . . . . . . 120 - 6.7.4 Function specifiers . . . . . . . . . . . . . . . . . . 124 - 6.7.5 Alignment specifier . . . . . . . . . . . . . . . . . . 126 - 6.7.6 Declarators . . . . . . . . . . . . . . . . . . . . . 127 - 6.7.7 Type names . . . . . . . . . . . . . . . . . . . . . 135 - 6.7.8 Type definitions . . . . . . . . . . . . . . . . . . . 136 - 6.7.9 Initialization . . . . . . . . . . . . . . . . . . . . 138 - 6.7.10 Static assertions . . . . . . . . . . . . . . . . . . . 144 - 6.8 Statements and blocks . . . . . . . . . . . . . . . . . . . . 145 - 6.8.1 Labeled statements . . . . . . . . . . . . . . . . . . 145 - 6.8.2 Compound statement . . . . . . . . . . . . . . . . . 146 - 6.8.3 Expression and null statements . . . . . . . . . . . . . 146 - 6.8.4 Selection statements . . . . . . . . . . . . . . . . . 147 - 6.8.5 Iteration statements . . . . . . . . . . . . . . . . . . 149 - 6.8.6 Jump statements . . . . . . . . . . . . . . . . . . . 150 - 6.9 External definitions . . . . . . . . . . . . . . . . . . . . . 154 - 6.9.1 Function definitions . . . . . . . . . . . . . . . . . . 155 - 6.9.2 External object definitions . . . . . . . . . . . . . . . 157 - 6.10 Preprocessing directives . . . . . . . . . . . . . . . . . . . 159 - 6.10.1 Conditional inclusion . . . . . . . . . . . . . . . . . 161 - 6.10.2 Source file inclusion . . . . . . . . . . . . . . . . . 163 - 6.10.3 Macro replacement . . . . . . . . . . . . . . . . . . 165 - - -[page iv] - - 6.10.4 Line control . . . . . . . . . . . . . . . . . . . . . 172 - 6.10.5 Error directive . . . . . . . . . . . . . . . . . . . . 173 - 6.10.6 Pragma directive . . . . . . . . . . . . . . . . . . . 173 - 6.10.7 Null directive . . . . . . . . . . . . . . . . . . . . 174 - 6.10.8 Predefined macro names . . . . . . . . . . . . . . . . 174 - 6.10.9 Pragma operator . . . . . . . . . . . . . . . . . . . 176 - 6.11 Future language directions . . . . . . . . . . . . . . . . . . 178 - 6.11.1 Floating types . . . . . . . . . . . . . . . . . . . . 178 - 6.11.2 Linkages of identifiers . . . . . . . . . . . . . . . . . 178 - 6.11.3 External names . . . . . . . . . . . . . . . . . . . 178 - 6.11.4 Character escape sequences . . . . . . . . . . . . . . 178 - 6.11.5 Storage-class specifiers . . . . . . . . . . . . . . . . 178 - 6.11.6 Function declarators . . . . . . . . . . . . . . . . . 178 - 6.11.7 Function definitions . . . . . . . . . . . . . . . . . . 178 - 6.11.8 Pragma directives . . . . . . . . . . . . . . . . . . 178 - 6.11.9 Predefined macro names . . . . . . . . . . . . . . . . 178 -7. Library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 - 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 179 - 7.1.1 Definitions of terms . . . . . . . . . . . . . . . . . . 179 - 7.1.2 Standard headers . . . . . . . . . . . . . . . . . . . 180 - 7.1.3 Reserved identifiers . . . . . . . . . . . . . . . . . . 181 - 7.1.4 Use of library functions . . . . . . . . . . . . . . . . 182 - 7.2 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 185 - 7.2.1 Program diagnostics . . . . . . . . . . . . . . . . . 185 - 7.3 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 187 - 7.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 187 - 7.3.2 Conventions . . . . . . . . . . . . . . . . . . . . . 188 - 7.3.3 Branch cuts . . . . . . . . . . . . . . . . . . . . . 188 - 7.3.4 The CX_LIMITED_RANGE pragma . . . . . . . . . . . 188 - 7.3.5 Trigonometric functions . . . . . . . . . . . . . . . . 189 - 7.3.6 Hyperbolic functions . . . . . . . . . . . . . . . . . 191 - 7.3.7 Exponential and logarithmic functions . . . . . . . . . . 193 - 7.3.8 Power and absolute-value functions . . . . . . . . . . . 194 - 7.3.9 Manipulation functions . . . . . . . . . . . . . . . . 195 - 7.4 Character handling <ctype.h> . . . . . . . . . . . . . . . . 199 - 7.4.1 Character classification functions . . . . . . . . . . . . 199 - 7.4.2 Character case mapping functions . . . . . . . . . . . . 202 - 7.5 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 204 - 7.6 Floating-point environment <fenv.h> . . . . . . . . . . . . . 205 - 7.6.1 The FENV_ACCESS pragma . . . . . . . . . . . . . . 207 - 7.6.2 Floating-point exceptions . . . . . . . . . . . . . . . 208 - 7.6.3 Rounding . . . . . . . . . . . . . . . . . . . . . . 211 - 7.6.4 Environment . . . . . . . . . . . . . . . . . . . . 212 - 7.7 Characteristics of floating types <float.h> . . . . . . . . . . . 215 - -[page v] - - 7.8 Format conversion of integer types <inttypes.h> . . . . . . . . 216 - 7.8.1 Macros for format specifiers . . . . . . . . . . . . . . 216 - 7.8.2 Functions for greatest-width integer types . . . . . . . . . 217 - 7.9 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 220 - 7.10 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 221 - 7.11 Localization <locale.h> . . . . . . . . . . . . . . . . . . 222 - 7.11.1 Locale control . . . . . . . . . . . . . . . . . . . . 223 - 7.11.2 Numeric formatting convention inquiry . . . . . . . . . . 224 - 7.12 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 230 - 7.12.1 Treatment of error conditions . . . . . . . . . . . . . . 232 - 7.12.2 The FP_CONTRACT pragma . . . . . . . . . . . . . . 234 - 7.12.3 Classification macros . . . . . . . . . . . . . . . . . 234 - 7.12.4 Trigonometric functions . . . . . . . . . . . . . . . . 237 - 7.12.5 Hyperbolic functions . . . . . . . . . . . . . . . . . 239 - 7.12.6 Exponential and logarithmic functions . . . . . . . . . . 241 - 7.12.7 Power and absolute-value functions . . . . . . . . . . . 246 - 7.12.8 Error and gamma functions . . . . . . . . . . . . . . . 248 - 7.12.9 Nearest integer functions . . . . . . . . . . . . . . . . 250 - 7.12.10 Remainder functions . . . . . . . . . . . . . . . . . 253 - 7.12.11 Manipulation functions . . . . . . . . . . . . . . . . 254 - 7.12.12 Maximum, minimum, and positive difference functions . . . 256 - 7.12.13 Floating multiply-add . . . . . . . . . . . . . . . . . 257 - 7.12.14 Comparison macros . . . . . . . . . . . . . . . . . . 258 - 7.13 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 261 - 7.13.1 Save calling environment . . . . . . . . . . . . . . . 261 - 7.13.2 Restore calling environment . . . . . . . . . . . . . . 262 - 7.14 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 264 - 7.14.1 Specify signal handling . . . . . . . . . . . . . . . . 265 - 7.14.2 Send signal . . . . . . . . . . . . . . . . . . . . . 266 - 7.15 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 267 - 7.16 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 268 - 7.16.1 Variable argument list access macros . . . . . . . . . . . 268 - 7.17 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 272 - 7.17.1 Introduction . . . . . . . . . . . . . . . . . . . . . 272 - 7.17.2 Initialization . . . . . . . . . . . . . . . . . . . . 273 - 7.17.3 Order and consistency . . . . . . . . . . . . . . . . . 274 - 7.17.4 Fences . . . . . . . . . . . . . . . . . . . . . . . 277 - 7.17.5 Lock-free property . . . . . . . . . . . . . . . . . . 278 - 7.17.6 Atomic integer and address types . . . . . . . . . . . . 279 - 7.17.7 Operations on atomic types . . . . . . . . . . . . . . . 281 - 7.17.8 Atomic flag type and operations . . . . . . . . . . . . . 284 - 7.18 Boolean type and values <stdbool.h> . . . . . . . . . . . . 286 - 7.19 Common definitions <stddef.h> . . . . . . . . . . . . . . . 287 - 7.20 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 289 - - -[page vi] - - 7.20.1 Integer types . . . . . . . . . . . . . . . . . . . . 289 - 7.20.2 Limits of specified-width integer types . . . . . . . . . . 291 - 7.20.3 Limits of other integer types . . . . . . . . . . . . . . 293 - 7.20.4 Macros for integer constants . . . . . . . . . . . . . . 294 - 7.21 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 296 - 7.21.1 Introduction . . . . . . . . . . . . . . . . . . . . . 296 - 7.21.2 Streams . . . . . . . . . . . . . . . . . . . . . . 298 - 7.21.3 Files . . . . . . . . . . . . . . . . . . . . . . . . 300 - 7.21.4 Operations on files . . . . . . . . . . . . . . . . . . 302 - 7.21.5 File access functions . . . . . . . . . . . . . . . . . 304 - 7.21.6 Formatted input/output functions . . . . . . . . . . . . 309 - 7.21.7 Character input/output functions . . . . . . . . . . . . . 330 - 7.21.8 Direct input/output functions . . . . . . . . . . . . . . 334 - 7.21.9 File positioning functions . . . . . . . . . . . . . . . 335 - 7.21.10 Error-handling functions . . . . . . . . . . . . . . . . 338 - 7.22 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 340 - 7.22.1 Numeric conversion functions . . . . . . . . . . . . . . 341 - 7.22.2 Pseudo-random sequence generation functions . . . . . . . 346 - 7.22.3 Memory management functions . . . . . . . . . . . . . 347 - 7.22.4 Communication with the environment . . . . . . . . . . 349 - 7.22.5 Searching and sorting utilities . . . . . . . . . . . . . . 353 - 7.22.6 Integer arithmetic functions . . . . . . . . . . . . . . 355 - 7.22.7 Multibyte/wide character conversion functions . . . . . . . 356 - 7.22.8 Multibyte/wide string conversion functions . . . . . . . . 358 - 7.23 String handling <string.h> . . . . . . . . . . . . . . . . . 360 - 7.23.1 String function conventions . . . . . . . . . . . . . . . 360 - 7.23.2 Copying functions . . . . . . . . . . . . . . . . . . 360 - 7.23.3 Concatenation functions . . . . . . . . . . . . . . . . 362 - 7.23.4 Comparison functions . . . . . . . . . . . . . . . . . 363 - 7.23.5 Search functions . . . . . . . . . . . . . . . . . . . 365 - 7.23.6 Miscellaneous functions . . . . . . . . . . . . . . . . 368 - 7.24 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 370 - 7.25 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 373 - 7.25.1 Introduction . . . . . . . . . . . . . . . . . . . . . 373 - 7.25.2 Initialization functions . . . . . . . . . . . . . . . . . 375 - 7.25.3 Condition variable functions . . . . . . . . . . . . . . 375 - 7.25.4 Mutex functions . . . . . . . . . . . . . . . . . . . 377 - 7.25.5 Thread functions . . . . . . . . . . . . . . . . . . . 380 - 7.25.6 Thread-specific storage functions . . . . . . . . . . . . 382 - 7.25.7 Time functions . . . . . . . . . . . . . . . . . . . . 384 - 7.26 Date and time <time.h> . . . . . . . . . . . . . . . . . . 385 - 7.26.1 Components of time . . . . . . . . . . . . . . . . . 385 - 7.26.2 Time manipulation functions . . . . . . . . . . . . . . 386 - 7.26.3 Time conversion functions . . . . . . . . . . . . . . . 388 - - -[page vii] - - 7.27 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 395 - 7.27.1 Restartable multibyte/wide character conversion functions . . 395 - 7.28 Extended multibyte and wide character utilities <wchar.h> . . . . . 399 - 7.28.1 Introduction . . . . . . . . . . . . . . . . . . . . . 399 - 7.28.2 Formatted wide character input/output functions . . . . . . 400 - 7.28.3 Wide character input/output functions . . . . . . . . . . 418 - 7.28.4 General wide string utilities . . . . . . . . . . . . . . 422 - 7.28.4.1 Wide string numeric conversion functions . . . . . 423 - 7.28.4.2 Wide string copying functions . . . . . . . . . . 427 - 7.28.4.3 Wide string concatenation functions . . . . . . . 429 - 7.28.4.4 Wide string comparison functions . . . . . . . . 430 - 7.28.4.5 Wide string search functions . . . . . . . . . . 432 - 7.28.4.6 Miscellaneous functions . . . . . . . . . . . . 436 - 7.28.5 Wide character time conversion functions . . . . . . . . . 436 - 7.28.6 Extended multibyte/wide character conversion utilities . . . . 437 - 7.28.6.1 Single-byte/wide character conversion functions . . . 438 - 7.28.6.2 Conversion state functions . . . . . . . . . . . 438 - 7.28.6.3 Restartable multibyte/wide character conversion - functions . . . . . . . . . . . . . . . . . . 439 - 7.28.6.4 Restartable multibyte/wide string conversion - functions . . . . . . . . . . . . . . . . . . 441 - 7.29 Wide character classification and mapping utilities <wctype.h> . . . 444 - 7.29.1 Introduction . . . . . . . . . . . . . . . . . . . . . 444 - 7.29.2 Wide character classification utilities . . . . . . . . . . . 445 - 7.29.2.1 Wide character classification functions . . . . . . 445 - 7.29.2.2 Extensible wide character classification - functions . . . . . . . . . . . . . . . . . . 448 - 7.29.3 Wide character case mapping utilities . . . . . . . . . . . 450 - 7.29.3.1 Wide character case mapping functions . . . . . . 450 - 7.29.3.2 Extensible wide character case mapping - functions . . . . . . . . . . . . . . . . . . 450 - 7.30 Future library directions . . . . . . . . . . . . . . . . . . . 452 - 7.30.1 Complex arithmetic <complex.h> . . . . . . . . . . . 452 - 7.30.2 Character handling <ctype.h> . . . . . . . . . . . . 452 - 7.30.3 Errors <errno.h> . . . . . . . . . . . . . . . . . 452 - 7.30.4 Format conversion of integer types <inttypes.h> . . . . 452 - 7.30.5 Localization <locale.h> . . . . . . . . . . . . . . 452 - 7.30.6 Signal handling <signal.h> . . . . . . . . . . . . . 452 - 7.30.7 Boolean type and values <stdbool.h> . . . . . . . . . 452 - 7.30.8 Integer types <stdint.h> . . . . . . . . . . . . . . 452 - 7.30.9 Input/output <stdio.h> . . . . . . . . . . . . . . . 453 - 7.30.10 General utilities <stdlib.h> . . . . . . . . . . . . . 453 - 7.30.11 String handling <string.h> . . . . . . . . . . . . . 453 - - - -[page viii] - - 7.30.12 Extended multibyte and wide character utilities - <wchar.h> . . . . . . . . . . . . . . . . . . . . 453 - 7.30.13 Wide character classification and mapping utilities - <wctype.h> . . . . . . . . . . . . . . . . . . . . 453 -Annex A (informative) Language syntax summary . . . . . . . . . . . . 454 - A.1 Lexical grammar . . . . . . . . . . . . . . . . . . . . . . 454 - A.2 Phrase structure grammar . . . . . . . . . . . . . . . . . . . 461 - A.3 Preprocessing directives . . . . . . . . . . . . . . . . . . . 469 -Annex B (informative) Library summary . . . . . . . . . . . . . . . . 471 - B.1 Diagnostics <assert.h> . . . . . . . . . . . . . . . . . . 471 - B.2 Complex <complex.h> . . . . . . . . . . . . . . . . . . . 471 - B.3 Character handling <ctype.h> . . . . . . . . . . . . . . . . 473 - B.4 Errors <errno.h> . . . . . . . . . . . . . . . . . . . . . 473 - B.5 Floating-point environment <fenv.h> . . . . . . . . . . . . . 473 - B.6 Characteristics of floating types <float.h> . . . . . . . . . . . 474 - B.7 Format conversion of integer types <inttypes.h> . . . . . . . . 474 - B.8 Alternative spellings <iso646.h> . . . . . . . . . . . . . . . 475 - B.9 Sizes of integer types <limits.h> . . . . . . . . . . . . . . 475 - B.10 Localization <locale.h> . . . . . . . . . . . . . . . . . . 475 - B.11 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 475 - B.12 Nonlocal jumps <setjmp.h> . . . . . . . . . . . . . . . . 480 - B.13 Signal handling <signal.h> . . . . . . . . . . . . . . . . . 480 - B.14 Alignment <stdalign.h> . . . . . . . . . . . . . . . . . 481 - B.15 Variable arguments <stdarg.h> . . . . . . . . . . . . . . . 481 - B.16 Atomics <stdatomic.h> . . . . . . . . . . . . . . . . . . 481 - B.17 Boolean type and values <stdbool.h> . . . . . . . . . . . . 483 - B.18 Common definitions <stddef.h> . . . . . . . . . . . . . . . 483 - B.19 Integer types <stdint.h> . . . . . . . . . . . . . . . . . . 483 - B.20 Input/output <stdio.h> . . . . . . . . . . . . . . . . . . 484 - B.21 General utilities <stdlib.h> . . . . . . . . . . . . . . . . 487 - B.22 String handling <string.h> . . . . . . . . . . . . . . . . . 489 - B.23 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 491 - B.24 Threads <threads.h> . . . . . . . . . . . . . . . . . . . 491 - B.25 Date and time <time.h> . . . . . . . . . . . . . . . . . . 492 - B.26 Unicode utilities <uchar.h> . . . . . . . . . . . . . . . . . 493 - B.27 Extended multibyte/wide character utilities <wchar.h> . . . . . . 493 - B.28 Wide character classification and mapping utilities <wctype.h> . . . 498 -Annex C (informative) Sequence points . . . . . . . . . . . . . . . . . 499 -Annex D (normative) Universal character names for identifiers . . . . . . . 500 - D.1 Ranges of characters allowed . . . . . . . . . . . . . . . . . 500 - D.2 Ranges of characters disallowed initially . . . . . . . . . . . . . 500 -Annex E (informative) Implementation limits . . . . . . . . . . . . . . 501 - -[page ix] - -Annex F (normative) IEC 60559 floating-point arithmetic . . . . . . . . . . 503 - F.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 503 - F.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 503 - F.3 Operators and functions . . . . . . . . . . . . . . . . . . . 504 - F.4 Floating to integer conversion . . . . . . . . . . . . . . . . . 506 - F.5 Binary-decimal conversion . . . . . . . . . . . . . . . . . . 506 - F.6 The return statement . . . . . . . . . . . . . . . . . . . . 507 - F.7 Contracted expressions . . . . . . . . . . . . . . . . . . . . 507 - F.8 Floating-point environment . . . . . . . . . . . . . . . . . . 507 - F.9 Optimization . . . . . . . . . . . . . . . . . . . . . . . . 510 - F.10 Mathematics <math.h> . . . . . . . . . . . . . . . . . . . 513 - F.10.1 Trigonometric functions . . . . . . . . . . . . . . . . 514 - F.10.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 516 - F.10.3 Exponential and logarithmic functions . . . . . . . . . . 516 - F.10.4 Power and absolute value functions . . . . . . . . . . . 520 - F.10.5 Error and gamma functions . . . . . . . . . . . . . . . 521 - F.10.6 Nearest integer functions . . . . . . . . . . . . . . . . 522 - F.10.7 Remainder functions . . . . . . . . . . . . . . . . . 524 - F.10.8 Manipulation functions . . . . . . . . . . . . . . . . 525 - F.10.9 Maximum, minimum, and positive difference functions . . . 526 - F.10.10 Floating multiply-add . . . . . . . . . . . . . . . . . 526 - F.10.11 Comparison macros . . . . . . . . . . . . . . . . . . 527 -Annex G (normative) IEC 60559-compatible complex arithmetic . . . . . . . 528 - G.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 528 - G.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 528 - G.3 Conventions . . . . . . . . . . . . . . . . . . . . . . . . 528 - G.4 Conversions . . . . . . . . . . . . . . . . . . . . . . . . 529 - G.4.1 Imaginary types . . . . . . . . . . . . . . . . . . . 529 - G.4.2 Real and imaginary . . . . . . . . . . . . . . . . . . 529 - G.4.3 Imaginary and complex . . . . . . . . . . . . . . . . 529 - G.5 Binary operators . . . . . . . . . . . . . . . . . . . . . . 529 - G.5.1 Multiplicative operators . . . . . . . . . . . . . . . . 530 - G.5.2 Additive operators . . . . . . . . . . . . . . . . . . 533 - G.6 Complex arithmetic <complex.h> . . . . . . . . . . . . . . 533 - G.6.1 Trigonometric functions . . . . . . . . . . . . . . . . 535 - G.6.2 Hyperbolic functions . . . . . . . . . . . . . . . . . 535 - G.6.3 Exponential and logarithmic functions . . . . . . . . . . 539 - G.6.4 Power and absolute-value functions . . . . . . . . . . . 540 - G.7 Type-generic math <tgmath.h> . . . . . . . . . . . . . . . 541 -Annex H (informative) Language independent arithmetic . . . . . . . . . . 542 - H.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 542 - H.2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 542 - H.3 Notification . . . . . . . . . . . . . . . . . . . . . . . . 546 - - -[page x] - -Annex I (informative) Common warnings . . . . . . . . . . . . . . . . 548 -Annex J (informative) Portability issues . . . . . . . . . . . . . . . . . 550 - J.1 Unspecified behavior . . . . . . . . . . . . . . . . . . . . . 550 - J.2 Undefined behavior . . . . . . . . . . . . . . . . . . . . . 553 - J.3 Implementation-defined behavior . . . . . . . . . . . . . . . . 566 - J.4 Locale-specific behavior . . . . . . . . . . . . . . . . . . . 574 - J.5 Common extensions . . . . . . . . . . . . . . . . . . . . . 575 -Annex K (normative) Bounds-checking interfaces . . . . . . . . . . . . . 578 - K.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 578 - K.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 579 - K.3 Library . . . . . . . . . . . . . . . . . . . . . . . . . . 579 - K.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . 579 - K.3.1.1 Standard headers . . . . . . . . . . . . . . . 579 - K.3.1.2 Reserved identifiers . . . . . . . . . . . . . . 580 - K.3.1.3 Use of errno . . . . . . . . . . . . . . . . . 580 - K.3.1.4 Runtime-constraint violations . . . . . . . . . . 580 - K.3.2 Errors <errno.h> . . . . . . . . . . . . . . . . . 581 - K.3.3 Common definitions <stddef.h> . . . . . . . . . . . 581 - K.3.4 Integer types <stdint.h> . . . . . . . . . . . . . . 581 - K.3.5 Input/output <stdio.h> . . . . . . . . . . . . . . . 582 - K.3.5.1 Operations on files . . . . . . . . . . . . . . 582 - K.3.5.2 File access functions . . . . . . . . . . . . . . 584 - K.3.5.3 Formatted input/output functions . . . . . . . . . 587 - K.3.5.4 Character input/output functions . . . . . . . . . 598 - K.3.6 General utilities <stdlib.h> . . . . . . . . . . . . . 600 - K.3.6.1 Runtime-constraint handling . . . . . . . . . . 600 - K.3.6.2 Communication with the environment . . . . . . . 602 - K.3.6.3 Searching and sorting utilities . . . . . . . . . . 603 - K.3.6.4 Multibyte/wide character conversion functions . . . 606 - K.3.6.5 Multibyte/wide string conversion functions . . . . . 607 - K.3.7 String handling <string.h> . . . . . . . . . . . . . 610 - K.3.7.1 Copying functions . . . . . . . . . . . . . . 610 - K.3.7.2 Concatenation functions . . . . . . . . . . . . 613 - K.3.7.3 Search functions . . . . . . . . . . . . . . . 616 - K.3.7.4 Miscellaneous functions . . . . . . . . . . . . 617 - K.3.8 Date and time <time.h> . . . . . . . . . . . . . . . 620 - K.3.8.1 Components of time . . . . . . . . . . . . . . 620 - K.3.8.2 Time conversion functions . . . . . . . . . . . 620 - K.3.9 Extended multibyte and wide character utilities - <wchar.h> . . . . . . . . . . . . . . . . . . . . 623 - K.3.9.1 Formatted wide character input/output functions . . . 624 - K.3.9.2 General wide string utilities . . . . . . . . . . . 635 - - - -[page xi] - - K.3.9.3 Extended multibyte/wide character conversion - utilities . . . . . . . . . . . . . . . . . . . 643 -Annex L (normative) Analyzability . . . . . . . . . . . . . . . . . . 648 - L.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 648 - L.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 648 - L.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 649 -Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 -Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653 - - - - -[page xii] (Contents) - - Foreword -1 ISO (the International Organization for Standardization) and IEC (the International - Electrotechnical Commission) form the specialized system for worldwide - standardization. National bodies that are member of ISO or IEC participate in the - development of International Standards through technical committees established by the - respective organization to deal with particular fields of technical activity. ISO and IEC - technical committees collaborate in fields of mutual interest. Other international - organizations, governmental and non-governmental, in liaison with ISO and IEC, also - take part in the work. -2 International Standards are drafted in accordance with the rules given in the ISO/IEC - Directives, Part 2. This International Standard was drafted in accordance with the fifth - edition (2004). -3 In the field of information technology, ISO and IEC have established a joint technical - committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical - committee are circulated to national bodies for voting. Publication as an International - Standard requires approval by at least 75% of the national bodies casting a vote. -4 Attention is drawn to the possibility that some of the elements of this document may be - the subject of patent rights. ISO and IEC shall not be held responsible for identifying any - or all such patent rights. -5 This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1, - Information technology, Subcommittee SC 22, Programming languages, their - environments and system software interfaces. The Working Group responsible for this - standard (WG 14) maintains a site on the World Wide Web at http://www.open- - std.org/JTC1/SC22/WG14/ containing additional information relevant to this - standard such as a Rationale for many of the decisions made during its preparation and a - log of Defect Reports and Responses. -6 This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as - corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and - ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include: - -- conditional (optional) features (including some that were previously mandatory) - -- support for multiple threads of execution including an improved memory sequencing - model, atomic objects, and thread-local storage (<stdatomic.h> and - <threads.h>) - -- additional floating-point characteristic macros (<float.h>) - -- querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>) - -- Unicode characters and strings (<uchar.h>) (originally specified in - ISO/IEC TR 19769:2004) - -- type-generic expressions - - -[page xiii] (Contents) - - -- static assertions - -- anonymous structures and unions - -- no-return functions - -- macros to create complex numbers (<complex.h>) - -- support for opening files for exclusive access - -- removed the gets function (<stdio.h>) - -- added the aligned_alloc, at_quick_exit, and quick_exit functions - (<stdlib.h>) - -- (conditional) support for bounds-checking interfaces (originally specified in - ISO/IEC TR 24731-1:2007) - -- (conditional) support for analyzability -7 Major changes in the second edition included: - -- restricted character set support via digraphs and <iso646.h> (originally specified - in AMD1) - -- wide character library support in <wchar.h> and <wctype.h> (originally - specified in AMD1) - -- more precise aliasing rules via effective type - -- restricted pointers - -- variable length arrays - -- flexible array members - -- static and type qualifiers in parameter array declarators - -- complex (and imaginary) support in <complex.h> - -- type-generic math macros in <tgmath.h> - -- the long long int type and library functions - -- increased minimum translation limits - -- additional floating-point characteristics in <float.h> - -- remove implicit int - -- reliable integer division - -- universal character names (\u and \U) - -- extended identifiers - -- hexadecimal floating-point constants and %a and %A printf/scanf conversion - specifiers - - - -[page xiv] (Contents) - --- compound literals --- designated initializers --- // comments --- extended integer types and library functions in <inttypes.h> and <stdint.h> --- remove implicit function declaration --- preprocessor arithmetic done in intmax_t/uintmax_t --- mixed declarations and code --- new block scopes for selection and iteration statements --- integer constant type rules --- integer promotion rules --- macros with a variable number of arguments --- the vscanf family of functions in <stdio.h> and <wchar.h> --- additional math library functions in <math.h> --- treatment of error conditions by math library functions (math_errhandling) --- floating-point environment access in <fenv.h> --- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support --- trailing comma allowed in enum declaration --- %lf conversion specifier allowed in printf --- inline functions --- the snprintf family of functions in <stdio.h> --- boolean type in <stdbool.h> --- idempotent type qualifiers --- empty macro arguments --- new structure type compatibility rules (tag compatibility) --- additional predefined macro names --- _Pragma preprocessing operator --- standard pragmas --- __func__ predefined identifier --- va_copy macro --- additional strftime conversion specifiers --- LIA compatibility annex - - -[page xv] (Contents) - - -- deprecate ungetc at the beginning of a binary file - -- remove deprecation of aliased array parameters - -- conversion of array to pointer not limited to lvalues - -- relaxed constraints on aggregate and union initialization - -- relaxed restrictions on portable header names - -- return without expression not permitted in function that returns a value (and vice - versa) -8 Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H, * - I, J, the bibliography, and the index are for information only. In accordance with Part 2 of - the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples - are also for information only. - - - - -[page xvi] (Contents) - - Introduction -1 With the introduction of new devices and extended character sets, new features may be - added to this International Standard. Subclauses in the language and library clauses warn - implementors and programmers of usages which, though valid in themselves, may - conflict with future additions. -2 Certain features are obsolescent, which means that they may be considered for - withdrawal in future revisions of this International Standard. They are retained because - of their widespread use, but their use in new implementations (for implementation - features) or new programs (for language [6.11] or library features [7.30]) is discouraged. -3 This International Standard is divided into four major subdivisions: - -- preliminary elements (clauses 1-4); - -- the characteristics of environments that translate and execute C programs (clause 5); - -- the language syntax, constraints, and semantics (clause 6); - -- the library facilities (clause 7). -4 Examples are provided to illustrate possible forms of the constructions described. - Footnotes are provided to emphasize consequences of the rules described in that - subclause or elsewhere in this International Standard. References are used to refer to - other related subclauses. Recommendations are provided to give advice or guidance to - implementors. Annexes provide additional information and summarize the information - contained in this International Standard. A bibliography lists documents that were - referred to during the preparation of the standard. -5 The language clause (clause 6) is derived from ''The C Reference Manual''. -6 The library clause (clause 7) is based on the 1984 /usr/group Standard. - - - - -[page xvii] (Contents) - - - -[page xviii] (Contents) - - - - Programming languages -- C - - - - 1. Scope -1 This International Standard specifies the form and establishes the interpretation of - programs written in the C programming language.1) It specifies - -- the representation of C programs; - -- the syntax and constraints of the C language; - -- the semantic rules for interpreting C programs; - -- the representation of input data to be processed by C programs; - -- the representation of output data produced by C programs; - -- the restrictions and limits imposed by a conforming implementation of C. -2 This International Standard does not specify - -- the mechanism by which C programs are transformed for use by a data-processing - system; - -- the mechanism by which C programs are invoked for use by a data-processing - system; - -- the mechanism by which input data are transformed for use by a C program; - -- the mechanism by which output data are transformed after being produced by a C - program; - -- the size or complexity of a program and its data that will exceed the capacity of any - specific data-processing system or the capacity of a particular processor; - -- all minimal requirements of a data-processing system that is capable of supporting a - conforming implementation. - - - 1) This International Standard is designed to promote the portability of C programs among a variety of - data-processing systems. It is intended for use by implementors and programmers. - -[page 1] (Contents) - - - 2. Normative references -1 The following referenced documents are indispensable for the application of this - document. For dated references, only the edition cited applies. For undated references, - the latest edition of the referenced document (including any amendments) applies. -2 ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for - use in the physical sciences and technology. -3 ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information - interchange. -4 ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental - terms. -5 ISO 4217, Codes for the representation of currencies and funds. -6 ISO 8601, Data elements and interchange formats -- Information interchange -- - Representation of dates and times. -7 ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded - Character Set (UCS). -8 IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously - designated IEC 559:1989). - - - - -[page 2] (Contents) - - - 3. Terms, definitions, and symbols -1 For the purposes of this International Standard, the following definitions apply. Other - terms are defined where they appear in italic type or on the left side of a syntax rule. - Terms explicitly defined in this International Standard are not to be presumed to refer - implicitly to similar terms defined elsewhere. Terms not defined in this International - Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not - defined in this International Standard are to be interpreted according to ISO 31-11. - 3.1 -1 access - <execution-time action> to read or modify the value of an object -2 NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used. - -3 NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value. - -4 NOTE 3 Expressions that are not evaluated do not access objects. - - 3.2 -1 alignment - requirement that objects of a particular type be located on storage boundaries with - addresses that are particular multiples of a byte address - 3.3 -1 argument - actual argument - actual parameter (deprecated) - expression in the comma-separated list bounded by the parentheses in a function call - expression, or a sequence of preprocessing tokens in the comma-separated list bounded - by the parentheses in a function-like macro invocation - 3.4 -1 behavior - external appearance or action - 3.4.1 -1 implementation-defined behavior - unspecified behavior where each implementation documents how the choice is made -2 EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit - when a signed integer is shifted right. - - 3.4.2 -1 locale-specific behavior - behavior that depends on local conventions of nationality, culture, and language that each - implementation documents - - -[page 3] (Contents) - -2 EXAMPLE An example of locale-specific behavior is whether the islower function returns true for - characters other than the 26 lowercase Latin letters. - - 3.4.3 -1 undefined behavior - behavior, upon use of a nonportable or erroneous program construct or of erroneous data, - for which this International Standard imposes no requirements -2 NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable - results, to behaving during translation or program execution in a documented manner characteristic of the - environment (with or without the issuance of a diagnostic message), to terminating a translation or - execution (with the issuance of a diagnostic message). - -3 EXAMPLE An example of undefined behavior is the behavior on integer overflow. - - 3.4.4 -1 unspecified behavior - use of an unspecified value, or other behavior where this International Standard provides - two or more possibilities and imposes no further requirements on which is chosen in any - instance -2 EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are - evaluated. - - 3.5 -1 bit - unit of data storage in the execution environment large enough to hold an object that may - have one of two values -2 NOTE It need not be possible to express the address of each individual bit of an object. - - 3.6 -1 byte - addressable unit of data storage large enough to hold any member of the basic character - set of the execution environment -2 NOTE 1 It is possible to express the address of each individual byte of an object uniquely. - -3 NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation- - defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order - bit. - - 3.7 -1 character - <abstract> member of a set of elements used for the organization, control, or - representation of data - 3.7.1 -1 character - single-byte character - <C> bit representation that fits in a byte -[page 4] (Contents) - - 3.7.2 -1 multibyte character - sequence of one or more bytes representing a member of the extended character set of - either the source or the execution environment -2 NOTE The extended character set is a superset of the basic character set. - - 3.7.3 -1 wide character - bit representation that fits in an object of type wchar_t, capable of representing any - character in the current locale - 3.8 -1 constraint - restriction, either syntactic or semantic, by which the exposition of language elements is - to be interpreted - 3.9 -1 correctly rounded result - representation in the result format that is nearest in value, subject to the current rounding - mode, to what the result would be given unlimited range and precision - 3.10 -1 diagnostic message - message belonging to an implementation-defined subset of the implementation's message - output - 3.11 -1 forward reference - reference to a later subclause of this International Standard that contains additional - information relevant to this subclause - 3.12 -1 implementation - particular set of software, running in a particular translation environment under particular - control options, that performs translation of programs for, and supports execution of - functions in, a particular execution environment - 3.13 -1 implementation limit - restriction imposed upon programs by the implementation - 3.14 -1 memory location - either an object of scalar type, or a maximal sequence of adjacent bit-fields all having - nonzero width - -[page 5] (Contents) - -2 NOTE 1 Two threads of execution can update and access separate memory locations without interfering - with each other. - -3 NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same - applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the - two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member - declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all - members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those - intervening bit-fields happen to be. - -4 EXAMPLE A structure declared as - struct { - char a; - int b:5, c:11, :0, d:8; - struct { int ee:8; } e; - } - contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate - memory locations, and can be modified concurrently without interfering with each other. The bit-fields b - and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently - modified, but b and a, for example, can be. - - 3.15 -1 object - region of data storage in the execution environment, the contents of which can represent - values -2 NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1. - - 3.16 -1 parameter - formal parameter - formal argument (deprecated) - object declared as part of a function declaration or definition that acquires a value on - entry to the function, or an identifier from the comma-separated list bounded by the - parentheses immediately following the macro name in a function-like macro definition - 3.17 -1 recommended practice - specification that is strongly recommended as being in keeping with the intent of the - standard, but that may be impractical for some implementations - 3.18 -1 runtime-constraint - requirement on a program when calling a library function -2 NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and - need not be diagnosed at translation time. - -3 NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime- - constraints for a library function are not violated by the program; see K.3.1.4. - -[page 6] (Contents) - - 3.19 -1 value - precise meaning of the contents of an object when interpreted as having a specific type - 3.19.1 -1 implementation-defined value - unspecified value where each implementation documents how the choice is made - 3.19.2 -1 indeterminate value - either an unspecified value or a trap representation - 3.19.3 -1 unspecified value - valid value of the relevant type where this International Standard imposes no - requirements on which value is chosen in any instance -2 NOTE An unspecified value cannot be a trap representation. - - 3.19.4 -1 trap representation - an object representation that need not represent a value of the object type - 3.19.5 -1 perform a trap - interrupt execution of the program such that no further operations are performed -2 NOTE In this International Standard, when the word ''trap'' is not immediately followed by - ''representation'', this is the intended usage.2) - - 3.20 -1 [^ x^] - ceiling of x: the least integer greater than or equal to x -2 EXAMPLE [^2.4^] is 3, [^-2.4^] is -2. - - 3.21 -1 [_ x_] - floor of x: the greatest integer less than or equal to x -2 EXAMPLE [_2.4_] is 2, [_-2.4_] is -3. - - - - - 2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap - representation might perform a trap but is not required to (see 6.2.6.1). - -[page 7] (Contents) - - - 4. Conformance -1 In this International Standard, ''shall'' is to be interpreted as a requirement on an - implementation or on a program; conversely, ''shall not'' is to be interpreted as a - prohibition. -2 If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime- - constraint is violated, the behavior is undefined. Undefined behavior is otherwise - indicated in this International Standard by the words ''undefined behavior'' or by the - omission of any explicit definition of behavior. There is no difference in emphasis among - these three; they all describe ''behavior that is undefined''. -3 A program that is correct in all other aspects, operating on correct data, containing - unspecified behavior shall be a correct program and act in accordance with 5.1.2.3. -4 The implementation shall not successfully translate a preprocessing translation unit - containing a #error preprocessing directive unless it is part of a group skipped by - conditional inclusion. -5 A strictly conforming program shall use only those features of the language and library - specified in this International Standard.3) It shall not produce output dependent on any - unspecified, undefined, or implementation-defined behavior, and shall not exceed any - minimum implementation limit. -6 The two forms of conforming implementation are hosted and freestanding. A conforming - hosted implementation shall accept any strictly conforming program. A conforming - freestanding implementation shall accept any strictly conforming program that does not - use complex types and in which the use of the features specified in the library clause - (clause 7) is confined to the contents of the standard headers <float.h>, - <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>, - <stddef.h>, and <stdint.h>. A conforming implementation may have extensions - (including additional library functions), provided they do not alter the behavior of any - strictly conforming program.4) - - - - 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded - by an appropriate conditional inclusion preprocessing directive using the related macro. For example: - #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */ - /* ... */ - fesetround(FE_UPWARD); - /* ... */ - #endif - - 4) This implies that a conforming implementation reserves no identifiers other than those explicitly - reserved in this International Standard. - -[page 8] (Contents) - -7 A conforming program is one that is acceptable to a conforming implementation.5) -8 An implementation shall be accompanied by a document that defines all implementation- - defined and locale-specific characteristics and all extensions. - Forward references: conditional inclusion (6.10.1), error directive (6.10.5), - characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h> - (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15), - variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h> - (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20). - - - - - 5) Strictly conforming programs are intended to be maximally portable among conforming - implementations. Conforming programs may depend upon nonportable features of a conforming - implementation. - -[page 9] (Contents) - - - 5. Environment -1 An implementation translates C source files and executes C programs in two data- - processing-system environments, which will be called the translation environment and - the execution environment in this International Standard. Their characteristics define and - constrain the results of executing conforming C programs constructed according to the - syntactic and semantic rules for conforming implementations. - Forward references: In this clause, only a few of many possible forward references - have been noted. - 5.1 Conceptual models - 5.1.1 Translation environment - 5.1.1.1 Program structure -1 A C program need not all be translated at the same time. The text of the program is kept - in units called source files, (or preprocessing files) in this International Standard. A - source file together with all the headers and source files included via the preprocessing - directive #include is known as a preprocessing translation unit. After preprocessing, a - preprocessing translation unit is called a translation unit. Previously translated translation - units may be preserved individually or in libraries. The separate translation units of a - program communicate by (for example) calls to functions whose identifiers have external - linkage, manipulation of objects whose identifiers have external linkage, or manipulation - of data files. Translation units may be separately translated and then later linked to - produce an executable program. - Forward references: linkages of identifiers (6.2.2), external definitions (6.9), - preprocessing directives (6.10). - 5.1.1.2 Translation phases -1 The precedence among the syntax rules of translation is specified by the following - phases.6) - 1. Physical source file multibyte characters are mapped, in an implementation- - defined manner, to the source character set (introducing new-line characters for - end-of-line indicators) if necessary. Trigraph sequences are replaced by - corresponding single-character internal representations. - - - - 6) Implementations shall behave as if these separate phases occur, even though many are typically folded - together in practice. Source files, translation units, and translated translation units need not - necessarily be stored as files, nor need there be any one-to-one correspondence between these entities - and any external representation. The description is conceptual only, and does not specify any - particular implementation. - -[page 10] (Contents) - - 2. Each instance of a backslash character (\) immediately followed by a new-line - character is deleted, splicing physical source lines to form logical source lines. - Only the last backslash on any physical source line shall be eligible for being part - of such a splice. A source file that is not empty shall end in a new-line character, - which shall not be immediately preceded by a backslash character before any such - splicing takes place. - 3. The source file is decomposed into preprocessing tokens7) and sequences of - white-space characters (including comments). A source file shall not end in a - partial preprocessing token or in a partial comment. Each comment is replaced by - one space character. New-line characters are retained. Whether each nonempty - sequence of white-space characters other than new-line is retained or replaced by - one space character is implementation-defined. - 4. Preprocessing directives are executed, macro invocations are expanded, and - _Pragma unary operator expressions are executed. If a character sequence that - matches the syntax of a universal character name is produced by token - concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing - directive causes the named header or source file to be processed from phase 1 - through phase 4, recursively. All preprocessing directives are then deleted. - 5. Each source character set member and escape sequence in character constants and - string literals is converted to the corresponding member of the execution character - set; if there is no corresponding member, it is converted to an implementation- - defined member other than the null (wide) character.8) - 6. Adjacent string literal tokens are concatenated. - 7. White-space characters separating tokens are no longer significant. Each - preprocessing token is converted into a token. The resulting tokens are - syntactically and semantically analyzed and translated as a translation unit. - 8. All external object and function references are resolved. Library components are - linked to satisfy external references to functions and objects not defined in the - current translation. All such translator output is collected into a program image - which contains information needed for execution in its execution environment. -Forward references: universal character names (6.4.3), lexical elements (6.4), -preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9). - - - -7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is - context-dependent. For example, see the handling of < within a #include preprocessing directive. -8) An implementation need not convert all non-corresponding source characters to the same execution - character. - -[page 11] (Contents) - - 5.1.1.3 Diagnostics -1 A conforming implementation shall produce at least one diagnostic message (identified in - an implementation-defined manner) if a preprocessing translation unit or translation unit - contains a violation of any syntax rule or constraint, even if the behavior is also explicitly - specified as undefined or implementation-defined. Diagnostic messages need not be - produced in other circumstances.9) -2 EXAMPLE An implementation shall issue a diagnostic for the translation unit: - char i; - int i; - because in those cases where wording in this International Standard describes the behavior for a construct - as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed. - - 5.1.2 Execution environments -1 Two execution environments are defined: freestanding and hosted. In both cases, - program startup occurs when a designated C function is called by the execution - environment. All objects with static storage duration shall be initialized (set to their - initial values) before program startup. The manner and timing of such initialization are - otherwise unspecified. Program termination returns control to the execution - environment. - Forward references: storage durations of objects (6.2.4), initialization (6.7.9). - 5.1.2.1 Freestanding environment -1 In a freestanding environment (in which C program execution may take place without any - benefit of an operating system), the name and type of the function called at program - startup are implementation-defined. Any library facilities available to a freestanding - program, other than the minimal set required by clause 4, are implementation-defined. -2 The effect of program termination in a freestanding environment is implementation- - defined. - 5.1.2.2 Hosted environment -1 A hosted environment need not be provided, but shall conform to the following - specifications if present. - - - - - 9) The intent is that an implementation should identify the nature of, and where possible localize, each - violation. Of course, an implementation is free to produce any number of diagnostics as long as a - valid program is still correctly translated. It may also successfully translate an invalid program. - -[page 12] (Contents) - - 5.1.2.2.1 Program startup -1 The function called at program startup is named main. The implementation declares no - prototype for this function. It shall be defined with a return type of int and with no - parameters: - int main(void) { /* ... */ } - or with two parameters (referred to here as argc and argv, though any names may be - used, as they are local to the function in which they are declared): - int main(int argc, char *argv[]) { /* ... */ } - or equivalent;10) or in some other implementation-defined manner. -2 If they are declared, the parameters to the main function shall obey the following - constraints: - -- The value of argc shall be nonnegative. - -- argv[argc] shall be a null pointer. - -- If the value of argc is greater than zero, the array members argv[0] through - argv[argc-1] inclusive shall contain pointers to strings, which are given - implementation-defined values by the host environment prior to program startup. The - intent is to supply to the program information determined prior to program startup - from elsewhere in the hosted environment. If the host environment is not capable of - supplying strings with letters in both uppercase and lowercase, the implementation - shall ensure that the strings are received in lowercase. - -- If the value of argc is greater than zero, the string pointed to by argv[0] - represents the program name; argv[0][0] shall be the null character if the - program name is not available from the host environment. If the value of argc is - greater than one, the strings pointed to by argv[1] through argv[argc-1] - represent the program parameters. - -- The parameters argc and argv and the strings pointed to by the argv array shall - be modifiable by the program, and retain their last-stored values between program - startup and program termination. - 5.1.2.2.2 Program execution -1 In a hosted environment, a program may use all the functions, macros, type definitions, - and objects described in the library clause (clause 7). - - - - - 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as - char ** argv, and so on. - -[page 13] (Contents) - - 5.1.2.2.3 Program termination -1 If the return type of the main function is a type compatible with int, a return from the - initial call to the main function is equivalent to calling the exit function with the value - returned by the main function as its argument;11) reaching the } that terminates the - main function returns a value of 0. If the return type is not compatible with int, the - termination status returned to the host environment is unspecified. - Forward references: definition of terms (7.1.1), the exit function (7.22.4.4). - 5.1.2.3 Program execution -1 The semantic descriptions in this International Standard describe the behavior of an - abstract machine in which issues of optimization are irrelevant. -2 Accessing a volatile object, modifying an object, modifying a file, or calling a function - that does any of those operations are all side effects,12) which are changes in the state of - the execution environment. Evaluation of an expression in general includes both value - computations and initiation of side effects. Value computation for an lvalue expression - includes determining the identity of the designated object. -3 Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations - executed by a single thread, which induces a partial order among those evaluations. - Given any two evaluations A and B, if A is sequenced before B, then the execution of A - shall precede the execution of B. (Conversely, if A is sequenced before B, then B is - sequenced after A.) If A is not sequenced before or after B, then A and B are - unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced - either before or after B, but it is unspecified which.13) The presence of a sequence point - between the evaluation of expressions A and B implies that every value computation and - side effect associated with A is sequenced before every value computation and side effect - associated with B. (A summary of the sequence points is given in annex C.) -4 In the abstract machine, all expressions are evaluated as specified by the semantics. An - actual implementation need not evaluate part of an expression if it can deduce that its - value is not used and that no needed side effects are produced (including any caused by - - 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main - will have ended in the former case, even where they would not have in the latter. - 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status - flags and control modes. Floating-point operations implicitly set the status flags; modes affect result - values of floating-point operations. Implementations that support such floating-point state are - required to regard changes to it as side effects -- see annex F for details. The floating-point - environment library <fenv.h> provides a programming facility for indicating when these side - effects matter, freeing the implementations in other cases. - 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations - cannot interleave, but can be executed in any order. - -[page 14] (Contents) - - calling a function or accessing a volatile object). -5 When the processing of the abstract machine is interrupted by receipt of a signal, the - values of objects that are neither lock-free atomic objects nor of type volatile - sig_atomic_t are unspecified, and the value of any object that is modified by the - handler that is neither a lock-free atomic object nor of type volatile - sig_atomic_t becomes undefined. -6 The least requirements on a conforming implementation are: - -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract - machine. - -- At program termination, all data written into files shall be identical to the result that - execution of the program according to the abstract semantics would have produced. - -- The input and output dynamics of interactive devices shall take place as specified in - 7.21.3. The intent of these requirements is that unbuffered or line-buffered output - appear as soon as possible, to ensure that prompting messages actually appear prior to - a program waiting for input. - This is the observable behavior of the program. -7 What constitutes an interactive device is implementation-defined. -8 More stringent correspondences between abstract and actual semantics may be defined by - each implementation. -9 EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual - semantics: at every sequence point, the values of the actual objects would agree with those specified by the - abstract semantics. The keyword volatile would then be redundant. -10 Alternatively, an implementation might perform various optimizations within each translation unit, such - that the actual semantics would agree with the abstract semantics only when making function calls across - translation unit boundaries. In such an implementation, at the time of each function entry and function - return where the calling function and the called function are in different translation units, the values of all - externally linked objects and of all objects accessible via pointers therein would agree with the abstract - semantics. Furthermore, at the time of each such function entry the values of the parameters of the called - function and of all objects accessible via pointers therein would agree with the abstract semantics. In this - type of implementation, objects referred to by interrupt service routines activated by the signal function - would require explicit specification of volatile storage, as well as other implementation-defined - restrictions. - -11 EXAMPLE 2 In executing the fragment - char c1, c2; - /* ... */ - c1 = c1 + c2; - the ''integer promotions'' require that the abstract machine promote the value of each variable to int size - and then add the two ints and truncate the sum. Provided the addition of two chars can be done without - overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only - produce the same result, possibly omitting the promotions. - -[page 15] (Contents) - -12 EXAMPLE 3 Similarly, in the fragment - float f1, f2; - double d; - /* ... */ - f1 = f2 * d; - the multiplication may be executed using single-precision arithmetic if the implementation can ascertain - that the result would be the same as if it were executed using double-precision arithmetic (for example, if d - were replaced by the constant 2.0, which has type double). - -13 EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate - semantics. Values are independent of whether they are represented in a register or in memory. For - example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load - is required to round to the precision of the storage type. In particular, casts and assignments are required to - perform their specified conversion. For the fragment - double d1, d2; - float f; - d1 = f = expression; - d2 = (float) expression; - the values assigned to d1 and d2 are required to have been converted to float. - -14 EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in - precision as well as range. The implementation cannot generally apply the mathematical associative rules - for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of - overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to - rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real - numbers are often not valid (see F.9). - double x, y, z; - /* ... */ - x = (x * y) * z; // not equivalent to x *= y * z; - z = (x - y) + y ; // not equivalent to z = x; - z = x + x * y; // not equivalent to z = x * (1.0 + y); - y = x / 5.0; // not equivalent to y = x * 0.2; - -15 EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment - int a, b; - /* ... */ - a = a + 32760 + b + 5; - the expression statement behaves exactly the same as - a = (((a + 32760) + b) + 5); - due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is - next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in - which overflows produce an explicit trap and in which the range of values representable by an int is - [-32768, +32767], the implementation cannot rewrite this expression as - a = ((a + b) + 32765); - since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap - while the original expression would not; nor can the expression be rewritten either as - - -[page 16] (Contents) - - a = ((a + 32765) + b); - or - a = (a + (b + 32765)); - since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine - in which overflow silently generates some value and where positive and negative overflows cancel, the - above expression statement can be rewritten by the implementation in any of the above ways because the - same result will occur. - -16 EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the - following fragment - #include <stdio.h> - int sum; - char *p; - /* ... */ - sum = sum * 10 - '0' + (*p++ = getchar()); - the expression statement is grouped as if it were written as - sum = (((sum * 10) - '0') + ((*(p++)) = (getchar()))); - but the actual increment of p can occur at any time between the previous sequence point and the next - sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned - value. - - Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the - signal function (7.14), files (7.21.3). - 5.1.2.4 Multi-threaded executions and data races -1 Under a hosted implementation, a program can have more than one thread of execution - (or thread) running concurrently. The execution of each thread proceeds as defined by - the remainder of this standard. The execution of the entire program consists of an - execution of all of its threads.14) Under a freestanding implementation, it is - implementation-defined whether a program can have more than one thread of execution. -2 The value of an object visible to a thread T at a particular point is the initial value of the - object, a value stored in the object by T , or a value stored in the object by another thread, - according to the rules below. -3 NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by - the desire to support atomic operations with explicit and detailed visibility constraints. However, it also - implicitly supports a simpler view for more restricted programs. - -4 Two expression evaluations conflict if one of them modifies a memory location and the - other one reads or modifies the same memory location. - - - - - 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of - atomic operations, for example, allow executions inconsistent with a simple interleaving as described - below. - -[page 17] (Contents) - -5 The library defines a number of atomic operations (7.17) and operations on mutexes - (7.25.4) that are specially identified as synchronization operations. These operations play - a special role in making assignments in one thread visible to another. A synchronization - operation on one or more memory locations is either an acquire operation, a release - operation, both an acquire and release operation, or a consume operation. A - synchronization operation without an associated memory location is a fence and can be - either an acquire fence, a release fence, or both an acquire and release fence. In addition, - there are relaxed atomic operations, which are not synchronization operations, and - atomic read-modify-write operations, which have special characteristics. -6 NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations - composing the mutex. Correspondingly, a call that releases the same mutex will perform a release - operation on those same locations. Informally, performing a release operation on A forces prior side effects - on other memory locations to become visible to other threads that later perform an acquire or consume - operation on A. We do not include relaxed atomic operations as synchronization operations although, like - synchronization operations, they cannot contribute to data races. - -7 All modifications to a particular atomic object M occur in some particular total order, - called the modification order of M. If A and B are modifications of an atomic object M, - and A happens before B, then A shall precede B in the modification order of M, which is - defined below. -8 NOTE 3 This states that the modification orders must respect the ''happens before'' relation. - -9 NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be - combined into a single total order for all objects. In general this will be impossible since different threads - may observe modifications to different variables in inconsistent orders. - -10 A release sequence on an atomic object M is a maximal contiguous sub-sequence of side - effects in the modification order of M, where the first operation is a release and every - subsequent operation either is performed by the same thread that performed the release or - is an atomic read-modify-write operation. -11 Certain library calls synchronize with other library calls performed by another thread. In - particular, an atomic operation A that performs a release operation on an object M - synchronizes with an atomic operation B that performs an acquire operation on M and - reads a value written by any side effect in the release sequence headed by A. -12 NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as - described below. Such a requirement would sometimes interfere with efficient implementation. - -13 NOTE 6 The specifications of the synchronization operations define when one reads the value written by - another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total - order. Each mutex acquisition ''reads the value written'' by the last mutex release. - -14 An evaluation A carries a dependency 15) to an evaluation B if: - - - 15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly - strictly intra-thread. - -[page 18] (Contents) - - -- the value of A is used as an operand of B, unless: - o B is an invocation of the kill_dependency macro, - - o A is the left operand of a && or || operator, - - o A is the left operand of a ? : operator, or - - o A is the left operand of a , operator; - or - -- A writes a scalar object or bit-field M, B reads from M the value written by A, and A - is sequenced before B, or - -- for some evaluation X, A carries a dependency to X and X carries a dependency to B. -15 An evaluation A is dependency-ordered before16) an evaluation B if: - -- A performs a release operation on an atomic object M, and B performs a consume - operation on M and reads a value written by any side effect in the release sequence - headed by A, or - -- for some evaluation X, A is dependency-ordered before X and X carries a - dependency to B. -16 An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A - is dependency-ordered before B, or, for some evaluation X: - -- A synchronizes with X and X is sequenced before B, - -- A is sequenced before X and X inter-thread happens before B, or - -- A inter-thread happens before X and X inter-thread happens before B. -17 NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced - before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The - first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed - by ''sequenced before''. The reason for this limitation is that a consume operation participating in a - ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this - consume operation actually carries a dependency. The reason that this limitation applies only to the end of - such a concatenation is that any subsequent release operation will provide the required ordering for a prior - consume operation. The second exception is that a concatenation is not permitted to consist entirely of - ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be - transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships - consisting entirely of ''sequenced before''. - -18 An evaluation A happens before an evaluation B if A is sequenced before B or A inter- - thread happens before B. - - - - 16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses - release/consume in place of release/acquire. - -[page 19] (Contents) - -19 A visible side effect A on an object M with respect to a value computation B of M - satisfies the conditions: - -- A happens before B, and - -- there is no other side effect X to M such that A happens before X and X happens - before B. - The value of a non-atomic scalar object M, as determined by evaluation B, shall be the - value stored by the visible side effect A. -20 NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data - race and the behavior is undefined. - -21 NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually - detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable - restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent) - execution. - -22 The visible sequence of side effects on an atomic object M, with respect to a value - computation B of M, is a maximal contiguous sub-sequence of side effects in the - modification order of M, where the first side effect is visible with respect to B, and for - every subsequent side effect, it is not the case that B happens before it. The value of an - atomic object M, as determined by evaluation B, shall be the value stored by some - operation in the visible sequence of M with respect to B. Furthermore, if a value - computation A of an atomic object M happens before a value computation B of M, and - the value computed by A corresponds to the value stored by side effect X, then the value - computed by B shall either equal the value computed by A, or be the value stored by side - effect Y , where Y follows X in the modification order of M. -23 NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if - both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee - provided by most hardware available to C atomic operations. - -24 NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the - values observed by loads of atomics, which we are restricting here. The intended reading is that there must - exist an association of atomic loads with modifications they observe that, together with suitably chosen - modification orders and the ''happens before'' relation derived as described above, satisfy the resulting - constraints as imposed here. - -25 The execution of a program contains a data race if it contains two conflicting actions in - different threads, at least one of which is not atomic, and neither happens before the - other. Any such data race results in undefined behavior. -26 NOTE 12 It can be shown that programs that correctly use simple mutexes and - memory_order_seq_cst operations to prevent all data races, and use no other synchronization - operations, behave as though the operations executed by their constituent threads were simply interleaved, - with each value computation of an object being the last value stored in that interleaving. This is normally - referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data- - race-free programs cannot observe most program transformations that do not change single-threaded - program semantics. In fact, most single-threaded program transformations continue to be allowed, since - any program that behaves differently as a result must contain undefined behavior. - -[page 20] (Contents) - -27 NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location - that would not be modified by the abstract machine are generally precluded by this standard, since such an - assignment might overwrite another assignment by a different thread in cases in which an abstract machine - execution would not have encountered a data race. This includes implementations of data member - assignment that overwrite adjacent members in separate memory locations. We also generally preclude - reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the - "visible sequence" rules. - -28 NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may - not preserve the semantics of the program as defined in this standard, since they potentially introduce a data - race. However, they are typically valid in the context of an optimizing compiler that targets a specific - machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that - is not tolerant of races or provides hardware race detection. - - - - -[page 21] (Contents) - - 5.2 Environmental considerations - 5.2.1 Character sets -1 Two sets of characters and their associated collating sequences shall be defined: the set in - which source files are written (the source character set), and the set interpreted in the - execution environment (the execution character set). Each set is further divided into a - basic character set, whose contents are given by this subclause, and a set of zero or more - locale-specific members (which are not members of the basic character set) called - extended characters. The combined set is also called the extended character set. The - values of the members of the execution character set are implementation-defined. -2 In a character constant or string literal, members of the execution character set shall be - represented by corresponding members of the source character set or by escape - sequences consisting of the backslash \ followed by one or more characters. A byte with - all bits set to 0, called the null character, shall exist in the basic execution character set; it - is used to terminate a character string. -3 Both the basic source and basic execution character sets shall have the following - members: the 26 uppercase letters of the Latin alphabet - A B C D E F G H I J K L M - N O P Q R S T U V W X Y Z - the 26 lowercase letters of the Latin alphabet - a b c d e f g h i j k l m - n o p q r s t u v w x y z - the 10 decimal digits - 0 1 2 3 4 5 6 7 8 9 - the following 29 graphic characters - ! " # % & ' ( ) * + , - . / : - ; < = > ? [ \ ] ^ _ { | } ~ - the space character, and control characters representing horizontal tab, vertical tab, and - form feed. The representation of each member of the source and execution basic - character sets shall fit in a byte. In both the source and execution basic character sets, the - value of each character after 0 in the above list of decimal digits shall be one greater than - the value of the previous. In source files, there shall be some way of indicating the end of - each line of text; this International Standard treats such an end-of-line indicator as if it - were a single new-line character. In the basic execution character set, there shall be - control characters representing alert, backspace, carriage return, and new line. If any - other characters are encountered in a source file (except in an identifier, a character - constant, a string literal, a header name, a comment, or a preprocessing token that is never - -[page 22] (Contents) - - converted to a token), the behavior is undefined. -4 A letter is an uppercase letter or a lowercase letter as defined above; in this International - Standard the term does not include other characters that are letters in other alphabets. -5 The universal character name construct provides a way to name other characters. - Forward references: universal character names (6.4.3), character constants (6.4.4.4), - preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1). - 5.2.1.1 Trigraph sequences -1 Before any other processing takes place, each occurrence of one of the following - sequences of three characters (called trigraph sequences17)) is replaced with the - corresponding single character. - ??= # ??) ] ??! | - ??( [ ??' ^ ??> } - ??/ \ ??< { ??- ~ - No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed - above is not changed. -2 EXAMPLE 1 - ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??) - becomes - #define arraycheck(a, b) a[b] || b[a] - -3 EXAMPLE 2 The following source line - printf("Eh???/n"); - becomes (after replacement of the trigraph sequence ??/) - printf("Eh?\n"); - - 5.2.1.2 Multibyte characters -1 The source character set may contain multibyte characters, used to represent members of - the extended character set. The execution character set may also contain multibyte - characters, which need not have the same encoding as for the source character set. For - both character sets, the following shall hold: - -- The basic character set shall be present and each character shall be encoded as a - single byte. - -- The presence, meaning, and representation of any additional members is locale- - specific. - - 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as - described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set. - -[page 23] (Contents) - - -- A multibyte character set may have a state-dependent encoding, wherein each - sequence of multibyte characters begins in an initial shift state and enters other - locale-specific shift states when specific multibyte characters are encountered in the - sequence. While in the initial shift state, all single-byte characters retain their usual - interpretation and do not alter the shift state. The interpretation for subsequent bytes - in the sequence is a function of the current shift state. - -- A byte with all bits zero shall be interpreted as a null character independent of shift - state. Such a byte shall not occur as part of any other multibyte character. -2 For source files, the following shall hold: - -- An identifier, comment, string literal, character constant, or header name shall begin - and end in the initial shift state. - -- An identifier, comment, string literal, character constant, or header name shall consist - of a sequence of valid multibyte characters. - 5.2.2 Character display semantics -1 The active position is that location on a display device where the next character output by - the fputc function would appear. The intent of writing a printing character (as defined - by the isprint function) to a display device is to display a graphic representation of - that character at the active position and then advance the active position to the next - position on the current line. The direction of writing is locale-specific. If the active - position is at the final position of a line (if there is one), the behavior of the display device - is unspecified. -2 Alphabetic escape sequences representing nongraphic characters in the execution - character set are intended to produce actions on display devices as follows: - \a (alert) Produces an audible or visible alert without changing the active position. - \b (backspace) Moves the active position to the previous position on the current line. If - the active position is at the initial position of a line, the behavior of the display - device is unspecified. - \f ( form feed) Moves the active position to the initial position at the start of the next - logical page. - \n (new line) Moves the active position to the initial position of the next line. - \r (carriage return) Moves the active position to the initial position of the current line. - \t (horizontal tab) Moves the active position to the next horizontal tabulation position - on the current line. If the active position is at or past the last defined horizontal - tabulation position, the behavior of the display device is unspecified. - \v (vertical tab) Moves the active position to the initial position of the next vertical - tabulation position. If the active position is at or past the last defined vertical -[page 24] (Contents) - - tabulation position, the behavior of the display device is unspecified. -3 Each of these escape sequences shall produce a unique implementation-defined value - which can be stored in a single char object. The external representations in a text file - need not be identical to the internal representations, and are outside the scope of this - International Standard. - Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3). - 5.2.3 Signals and interrupts -1 Functions shall be implemented such that they may be interrupted at any time by a signal, - or may be called by a signal handler, or both, with no alteration to earlier, but still active, - invocations' control flow (after the interruption), function return values, or objects with - automatic storage duration. All such objects shall be maintained outside the function - image (the instructions that compose the executable representation of a function) on a - per-invocation basis. - 5.2.4 Environmental limits -1 Both the translation and execution environments constrain the implementation of - language translators and libraries. The following summarizes the language-related - environmental limits on a conforming implementation; the library-related limits are - discussed in clause 7. - 5.2.4.1 Translation limits -1 The implementation shall be able to translate and execute at least one program that - contains at least one instance of every one of the following limits:18) - -- 127 nesting levels of blocks - -- 63 nesting levels of conditional inclusion - -- 12 pointer, array, and function declarators (in any combinations) modifying an - arithmetic, structure, union, or void type in a declaration - -- 63 nesting levels of parenthesized declarators within a full declarator - -- 63 nesting levels of parenthesized expressions within a full expression - -- 63 significant initial characters in an internal identifier or a macro name (each - universal character name or extended source character is considered a single - character) - -- 31 significant initial characters in an external identifier (each universal character name - specifying a short identifier of 0000FFFF or less is considered 6 characters, each - - - 18) Implementations should avoid imposing fixed translation limits whenever possible. - -[page 25] (Contents) - - universal character name specifying a short identifier of 00010000 or more is - considered 10 characters, and each extended source character is considered the same - number of characters as the corresponding universal character name, if any)19) - -- 4095 external identifiers in one translation unit - -- 511 identifiers with block scope declared in one block - -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit - -- 127 parameters in one function definition - -- 127 arguments in one function call - -- 127 parameters in one macro definition - -- 127 arguments in one macro invocation - -- 4095 characters in a logical source line - -- 4095 characters in a string literal (after concatenation) - -- 65535 bytes in an object (in a hosted environment only) - -- 15 nesting levels for #included files - -- 1023 case labels for a switch statement (excluding those for any nested switch - statements) - -- 1023 members in a single structure or union - -- 1023 enumeration constants in a single enumeration - -- 63 levels of nested structure or union definitions in a single struct-declaration-list - 5.2.4.2 Numerical limits -1 An implementation is required to document all the limits specified in this subclause, - which are specified in the headers <limits.h> and <float.h>. Additional limits are - specified in <stdint.h>. - Forward references: integer types <stdint.h> (7.20). - 5.2.4.2.1 Sizes of integer types <limits.h> -1 The values given below shall be replaced by constant expressions suitable for use in #if - preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the - following shall be replaced by expressions that have the same type as would an - expression that is an object of the corresponding type converted according to the integer - promotions. Their implementation-defined values shall be equal or greater in magnitude - - - 19) See ''future language directions'' (6.11.3). - -[page 26] (Contents) - -(absolute value) to those shown, with the same sign. --- number of bits for smallest object that is not a bit-field (byte) - CHAR_BIT 8 --- minimum value for an object of type signed char - SCHAR_MIN -127 // -(27 - 1) --- maximum value for an object of type signed char - SCHAR_MAX +127 // 27 - 1 --- maximum value for an object of type unsigned char - UCHAR_MAX 255 // 28 - 1 --- minimum value for an object of type char - CHAR_MIN see below --- maximum value for an object of type char - CHAR_MAX see below --- maximum number of bytes in a multibyte character, for any supported locale - MB_LEN_MAX 1 --- minimum value for an object of type short int - SHRT_MIN -32767 // -(215 - 1) --- maximum value for an object of type short int - SHRT_MAX +32767 // 215 - 1 --- maximum value for an object of type unsigned short int - USHRT_MAX 65535 // 216 - 1 --- minimum value for an object of type int - INT_MIN -32767 // -(215 - 1) --- maximum value for an object of type int - INT_MAX +32767 // 215 - 1 --- maximum value for an object of type unsigned int - UINT_MAX 65535 // 216 - 1 --- minimum value for an object of type long int - LONG_MIN -2147483647 // -(231 - 1) --- maximum value for an object of type long int - LONG_MAX +2147483647 // 231 - 1 --- maximum value for an object of type unsigned long int - ULONG_MAX 4294967295 // 232 - 1 - - -[page 27] (Contents) - - -- minimum value for an object of type long long int - LLONG_MIN -9223372036854775807 // -(263 - 1) - -- maximum value for an object of type long long int - LLONG_MAX +9223372036854775807 // 263 - 1 - -- maximum value for an object of type unsigned long long int - ULLONG_MAX 18446744073709551615 // 264 - 1 -2 If the value of an object of type char is treated as a signed integer when used in an - expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the - value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of - CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of - UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1. - Forward references: representations of types (6.2.6), conditional inclusion (6.10.1). - 5.2.4.2.2 Characteristics of floating types <float.h> -1 The characteristics of floating types are defined in terms of a model that describes a - representation of floating-point numbers and values that provide information about an - implementation's floating-point arithmetic.21) The following parameters are used to - define the model for each floating-point type: - s sign ((+-)1) - b base or radix of exponent representation (an integer > 1) - e exponent (an integer between a minimum emin and a maximum emax ) - p precision (the number of base-b digits in the significand) - fk nonnegative integers less than b (the significand digits) -2 A floating-point number (x) is defined by the following model: - p - x = sb e (Sum) f k b-k , - k=1 - emin <= e <= emax - -3 In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be - able to contain other kinds of floating-point numbers, such as subnormal floating-point - numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0, - e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and - NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates - through almost every arithmetic operation without raising a floating-point exception; a - signaling NaN generally raises a floating-point exception when occurring as an - - - 20) See 6.2.5. - 21) The floating-point model is intended to clarify the description of each floating-point characteristic and - does not require the floating-point arithmetic of the implementation to be identical. - -[page 28] (Contents) - - arithmetic operand.22) -4 An implementation may give zero and values that are not floating-point numbers (such as - infinities and NaNs) a sign or may leave them unsigned. Wherever such values are - unsigned, any requirement in this International Standard to retrieve the sign shall produce - an unspecified sign, and any requirement to set the sign shall be ignored. -5 The minimum range of representable values for a floating type is the most negative finite - floating-point number representable in that type through the most positive finite floating- - point number representable in that type. In addition, if negative infinity is representable - in a type, the range of that type is extended to all negative real numbers; likewise, if - positive infinity is representable in a type, the range of that type is extended to all positive - real numbers. -6 The accuracy of the floating-point operations (+, -, *, /) and of the library functions in - <math.h> and <complex.h> that return floating-point results is implementation- - defined, as is the accuracy of the conversion between floating-point internal - representations and string representations performed by the library functions in - <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the - accuracy is unknown. -7 All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant - expressions suitable for use in #if preprocessing directives; all floating values shall be - constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX, - and FLT_ROUNDS have separate names for all three floating-point types. The floating- - point model representation is provided for all values except FLT_EVAL_METHOD and - FLT_ROUNDS. -8 The rounding mode for floating-point addition is characterized by the implementation- - defined value of FLT_ROUNDS:23) - -1 indeterminable - 0 toward zero - 1 to nearest - 2 toward positive infinity - 3 toward negative infinity - All other values for FLT_ROUNDS characterize implementation-defined rounding - behavior. - - - 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support - IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with - similar behavior. - 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through - the function fesetround in <fenv.h>. - -[page 29] (Contents) - -9 Except for assignment and cast (which remove all extra range and precision), the values - yielded by operators with floating operands and values subject to the usual arithmetic - conversions and of floating constants are evaluated to a format whose range and precision - may be greater than required by the type. The use of evaluation formats is characterized - by the implementation-defined value of FLT_EVAL_METHOD:24) - -1 indeterminable; - 0 evaluate all operations and constants just to the range and precision of the - type; - 1 evaluate operations and constants of type float and double to the - range and precision of the double type, evaluate long double - operations and constants to the range and precision of the long double - type; - 2 evaluate all operations and constants to the range and precision of the - long double type. - All other negative values for FLT_EVAL_METHOD characterize implementation-defined - behavior. -10 The presence or absence of subnormal numbers is characterized by the implementation- - defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and - LDBL_HAS_SUBNORM: - -1 indeterminable25) - 0 absent26) (type does not support subnormal numbers) - 1 present (type does support subnormal numbers) -11 The values given in the following list shall be replaced by constant expressions with - implementation-defined values that are greater or equal in magnitude (absolute value) to - those shown, with the same sign: - -- radix of exponent representation, b - FLT_RADIX 2 - - - - - 24) The evaluation method determines evaluation formats of expressions involving all floating types, not - just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float - _Complex operands is represented in the double _Complex format, and its parts are evaluated to - double. - 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret - subnormal representations as zero, nor as nonzero. - 26) Characterization as absent is intended if no floating-point operations produce subnormal results from - non-subnormal inputs, even if the type format includes representations of subnormal numbers. - -[page 30] (Contents) - --- number of base-FLT_RADIX digits in the floating-point significand, p - FLT_MANT_DIG - DBL_MANT_DIG - LDBL_MANT_DIG --- number of decimal digits, n, such that any floating-point number with p radix b digits - can be rounded to a floating-point number with n decimal digits and back again - without change to the value, - { p log10 b if b is a power of 10 - { - { [^1 + p log10 b^] otherwise - FLT_DECIMAL_DIG 6 - DBL_DECIMAL_DIG 10 - LDBL_DECIMAL_DIG 10 --- number of decimal digits, n, such that any floating-point number in the widest - supported floating type with pmax radix b digits can be rounded to a floating-point - number with n decimal digits and back again without change to the value, - { pmax log10 b if b is a power of 10 - { - { [^1 + pmax log10 b^] otherwise - DECIMAL_DIG 10 --- number of decimal digits, q, such that any floating-point number with q decimal digits - can be rounded into a floating-point number with p radix b digits and back again - without change to the q decimal digits, - { p log10 b if b is a power of 10 - { - { [_( p - 1) log10 b_] otherwise - FLT_DIG 6 - DBL_DIG 10 - LDBL_DIG 10 --- minimum negative integer such that FLT_RADIX raised to one less than that power is - a normalized floating-point number, emin - FLT_MIN_EXP - DBL_MIN_EXP - LDBL_MIN_EXP - - - - -[page 31] (Contents) - - -- minimum negative integer such that 10 raised to that power is in the range of - normalized floating-point numbers, [^log10 b emin -1 ^] - [ ] - FLT_MIN_10_EXP -37 - DBL_MIN_10_EXP -37 - LDBL_MIN_10_EXP -37 - -- maximum integer such that FLT_RADIX raised to one less than that power is a - representable finite floating-point number, emax - FLT_MAX_EXP - DBL_MAX_EXP - LDBL_MAX_EXP - -- maximum integer such that 10 raised to that power is in the range of representable - finite floating-point numbers, [_log10 ((1 - b- p )b emax )_] - FLT_MAX_10_EXP +37 - DBL_MAX_10_EXP +37 - LDBL_MAX_10_EXP +37 -12 The values given in the following list shall be replaced by constant expressions with - implementation-defined values that are greater than or equal to those shown: - -- maximum representable finite floating-point number, (1 - b- p )b emax - FLT_MAX 1E+37 - DBL_MAX 1E+37 - LDBL_MAX 1E+37 -13 The values given in the following list shall be replaced by constant expressions with - implementation-defined (positive) values that are less than or equal to those shown: - -- the difference between 1 and the least value greater than 1 that is representable in the - given floating point type, b1- p - FLT_EPSILON 1E-5 - DBL_EPSILON 1E-9 - LDBL_EPSILON 1E-9 - -- minimum normalized positive floating-point number, b emin -1 - FLT_MIN 1E-37 - DBL_MIN 1E-37 - LDBL_MIN 1E-37 - - - - -[page 32] (Contents) - - -- minimum positive floating-point number27) - FLT_TRUE_MIN 1E-37 - DBL_TRUE_MIN 1E-37 - LDBL_TRUE_MIN 1E-37 - Recommended practice -14 Conversion from (at least) double to decimal with DECIMAL_DIG digits and back - should be the identity function. -15 EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum - requirements of this International Standard, and the appropriate values in a <float.h> header for type - float: - 6 - x = s16e (Sum) f k 16-k , - k=1 - -31 <= e <= +32 - - FLT_RADIX 16 - FLT_MANT_DIG 6 - FLT_EPSILON 9.53674316E-07F - FLT_DECIMAL_DIG 9 - FLT_DIG 6 - FLT_MIN_EXP -31 - FLT_MIN 2.93873588E-39F - FLT_MIN_10_EXP -38 - FLT_MAX_EXP +32 - FLT_MAX 3.40282347E+38F - FLT_MAX_10_EXP +38 - -16 EXAMPLE 2 The following describes floating-point representations that also meet the requirements for - single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a - <float.h> header for types float and double: - 24 - x f = s2e (Sum) f k 2-k , - k=1 - -125 <= e <= +128 - - 53 - x d = s2e (Sum) f k 2-k , - k=1 - -1021 <= e <= +1024 - - FLT_RADIX 2 - DECIMAL_DIG 17 - FLT_MANT_DIG 24 - FLT_EPSILON 1.19209290E-07F // decimal constant - FLT_EPSILON 0X1P-23F // hex constant - FLT_DECIMAL_DIG 9 - - - 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a - positive number no greater than the minimum normalized positive number for the type. - 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent - limits are one less than shown here. - -[page 33] (Contents) - - FLT_DIG 6 - FLT_MIN_EXP -125 - FLT_MIN 1.17549435E-38F // decimal constant - FLT_MIN 0X1P-126F // hex constant - FLT_TRUE_MIN 1.40129846E-45F // decimal constant - FLT_TRUE_MIN 0X1P-149F // hex constant - FLT_HAS_SUBNORM 1 - FLT_MIN_10_EXP -37 - FLT_MAX_EXP +128 - FLT_MAX 3.40282347E+38F // decimal constant - FLT_MAX 0X1.fffffeP127F // hex constant - FLT_MAX_10_EXP +38 - DBL_MANT_DIG 53 - DBL_EPSILON 2.2204460492503131E-16 // decimal constant - DBL_EPSILON 0X1P-52 // hex constant - DBL_DECIMAL_DIG 17 - DBL_DIG 15 - DBL_MIN_EXP -1021 - DBL_MIN 2.2250738585072014E-308 // decimal constant - DBL_MIN 0X1P-1022 // hex constant - DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant - DBL_TRUE_MIN 0X1P-1074 // hex constant - DBL_HAS_SUBNORM 1 - DBL_MIN_10_EXP -307 - DBL_MAX_EXP +1024 - DBL_MAX 1.7976931348623157E+308 // decimal constant - DBL_MAX 0X1.fffffffffffffP1023 // hex constant - DBL_MAX_10_EXP +308 -If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For -example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of -precision), then DECIMAL_DIG would be 21. - -Forward references: conditional inclusion (6.10.1), complex arithmetic -<complex.h> (7.3), extended multibyte and wide character utilities <wchar.h> -(7.28), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h> -(7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12). - - - - -[page 34] (Contents) - - - 6. Language - 6.1 Notation -1 In the syntax notation used in this clause, syntactic categories (nonterminals) are - indicated by italic type, and literal words and character set members (terminals) by bold - type. A colon (:) following a nonterminal introduces its definition. Alternative - definitions are listed on separate lines, except when prefaced by the words ''one of''. An - optional symbol is indicated by the subscript ''opt'', so that - { expressionopt } - indicates an optional expression enclosed in braces. -2 When syntactic categories are referred to in the main text, they are not italicized and - words are separated by spaces instead of hyphens. -3 A summary of the language syntax is given in annex A. - 6.2 Concepts - 6.2.1 Scopes of identifiers -1 An identifier can denote an object; a function; a tag or a member of a structure, union, or - enumeration; a typedef name; a label name; a macro name; or a macro parameter. The - same identifier can denote different entities at different points in the program. A member - of an enumeration is called an enumeration constant. Macro names and macro - parameters are not considered further here, because prior to the semantic phase of - program translation any occurrences of macro names in the source file are replaced by the - preprocessing token sequences that constitute their macro definitions. -2 For each different entity that an identifier designates, the identifier is visible (i.e., can be - used) only within a region of program text called its scope. Different entities designated - by the same identifier either have different scopes, or are in different name spaces. There - are four kinds of scopes: function, file, block, and function prototype. (A function - prototype is a declaration of a function that declares the types of its parameters.) -3 A label name is the only kind of identifier that has function scope. It can be used (in a - goto statement) anywhere in the function in which it appears, and is declared implicitly - by its syntactic appearance (followed by a : and a statement). -4 Every other identifier has scope determined by the placement of its declaration (in a - declarator or type specifier). If the declarator or type specifier that declares the identifier - appears outside of any block or list of parameters, the identifier has file scope, which - terminates at the end of the translation unit. If the declarator or type specifier that - declares the identifier appears inside a block or within the list of parameter declarations in - a function definition, the identifier has block scope, which terminates at the end of the - associated block. If the declarator or type specifier that declares the identifier appears - -[page 35] (Contents) - - within the list of parameter declarations in a function prototype (not part of a function - definition), the identifier has function prototype scope, which terminates at the end of the - function declarator. If an identifier designates two different entities in the same name - space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end - strictly before the scope of the other entity (the outer scope). Within the inner scope, the - identifier designates the entity declared in the inner scope; the entity declared in the outer - scope is hidden (and not visible) within the inner scope. -5 Unless explicitly stated otherwise, where this International Standard uses the term - ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the - entity in the relevant name space whose declaration is visible at the point the identifier - occurs. -6 Two identifiers have the same scope if and only if their scopes terminate at the same - point. -7 Structure, union, and enumeration tags have scope that begins just after the appearance of - the tag in a type specifier that declares the tag. Each enumeration constant has scope that - begins just after the appearance of its defining enumerator in an enumerator list. Any - other identifier has scope that begins just after the completion of its declarator. -8 As a special case, a type name (which is not a declaration of an identifier) is considered to - have a scope that begins just after the place within the type name where the omitted - identifier would appear were it not omitted. - Forward references: declarations (6.7), function calls (6.5.2.2), function definitions - (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3), - source file inclusion (6.10.2), statements (6.8). - 6.2.2 Linkages of identifiers -1 An identifier declared in different scopes or in the same scope more than once can be - made to refer to the same object or function by a process called linkage.29) There are - three kinds of linkage: external, internal, and none. -2 In the set of translation units and libraries that constitutes an entire program, each - declaration of a particular identifier with external linkage denotes the same object or - function. Within one translation unit, each declaration of an identifier with internal - linkage denotes the same object or function. Each declaration of an identifier with no - linkage denotes a unique entity. -3 If the declaration of a file scope identifier for an object or a function contains the storage- - class specifier static, the identifier has internal linkage.30) - - - - 29) There is no linkage between different identifiers. - -[page 36] (Contents) - -4 For an identifier declared with the storage-class specifier extern in a scope in which a - prior declaration of that identifier is visible,31) if the prior declaration specifies internal or - external linkage, the linkage of the identifier at the later declaration is the same as the - linkage specified at the prior declaration. If no prior declaration is visible, or if the prior - declaration specifies no linkage, then the identifier has external linkage. -5 If the declaration of an identifier for a function has no storage-class specifier, its linkage - is determined exactly as if it were declared with the storage-class specifier extern. If - the declaration of an identifier for an object has file scope and no storage-class specifier, - its linkage is external. -6 The following identifiers have no linkage: an identifier declared to be anything other than - an object or a function; an identifier declared to be a function parameter; a block scope - identifier for an object declared without the storage-class specifier extern. -7 If, within a translation unit, the same identifier appears with both internal and external - linkage, the behavior is undefined. - Forward references: declarations (6.7), expressions (6.5), external definitions (6.9), - statements (6.8). - 6.2.3 Name spaces of identifiers -1 If more than one declaration of a particular identifier is visible at any point in a - translation unit, the syntactic context disambiguates uses that refer to different entities. - Thus, there are separate name spaces for various categories of identifiers, as follows: - -- label names (disambiguated by the syntax of the label declaration and use); - -- the tags of structures, unions, and enumerations (disambiguated by following any32) - of the keywords struct, union, or enum); - -- the members of structures or unions; each structure or union has a separate name - space for its members (disambiguated by the type of the expression used to access the - member via the . or -> operator); - -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as - enumeration constants). - Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1), - structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags - (6.7.2.3), the goto statement (6.8.6.1). - - 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see - 6.7.1. - 31) As specified in 6.2.1, the later declaration might hide the prior declaration. - 32) There is only one name space for tags even though three are possible. - -[page 37] (Contents) - - 6.2.4 Storage durations of objects -1 An object has a storage duration that determines its lifetime. There are four storage - durations: static, thread, automatic, and allocated. Allocated storage is described in - 7.22.3. -2 The lifetime of an object is the portion of program execution during which storage is - guaranteed to be reserved for it. An object exists, has a constant address,33) and retains - its last-stored value throughout its lifetime.34) If an object is referred to outside of its - lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when - the object it points to (or just past) reaches the end of its lifetime. -3 An object whose identifier is declared without the storage-class specifier - _Thread_local, and either with external or internal linkage or with the storage-class - specifier static, has static storage duration. Its lifetime is the entire execution of the - program and its stored value is initialized only once, prior to program startup. -4 An object whose identifier is declared with the storage-class specifier _Thread_local - has thread storage duration. Its lifetime is the entire execution of the thread for which it - is created, and its stored value is initialized when the thread is started. There is a distinct - object per thread, and use of the declared name in an expression refers to the object - associated with the thread evaluating the expression. The result of attempting to - indirectly access an object with thread storage duration from a thread other than the one - with which the object is associated is implementation-defined. -5 An object whose identifier is declared with no linkage and without the storage-class - specifier static has automatic storage duration, as do some compound literals. The - result of attempting to indirectly access an object with automatic storage duration from a - thread other than the one with which the object is associated is implementation-defined. -6 For such an object that does not have a variable length array type, its lifetime extends - from entry into the block with which it is associated until execution of that block ends in - any way. (Entering an enclosed block or calling a function suspends, but does not end, - execution of the current block.) If the block is entered recursively, a new instance of the - object is created each time. The initial value of the object is indeterminate. If an - initialization is specified for the object, it is performed each time the declaration or - compound literal is reached in the execution of the block; otherwise, the value becomes - indeterminate each time the declaration is reached. - - - - 33) The term ''constant address'' means that two pointers to the object constructed at possibly different - times will compare equal. The address may be different during two different executions of the same - program. - 34) In the case of a volatile object, the last store need not be explicit in the program. - -[page 38] (Contents) - -7 For such an object that does have a variable length array type, its lifetime extends from - the declaration of the object until execution of the program leaves the scope of the - declaration.35) If the scope is entered recursively, a new instance of the object is created - each time. The initial value of the object is indeterminate. -8 A non-lvalue expression with structure or union type, where the structure or union - contains a member with array type (including, recursively, members of all contained - structures and unions) refers to an object with automatic storage duration and temporary - lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the - value of the expression. Its lifetime ends when the evaluation of the containing full - expression or full declarator ends. Any attempt to modify an object with temporary - lifetime results in undefined behavior. - Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators - (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8). - 6.2.5 Types -1 The meaning of a value stored in an object or returned by a function is determined by the - type of the expression used to access it. (An identifier declared to be an object is the - simplest such expression; the type is specified in the declaration of the identifier.) Types - are partitioned into object types (types that describe objects) and function types (types - that describe functions). At various points within a translation unit an object type may be - incomplete (lacking sufficient information to determine the size of objects of that type) or - complete (having sufficient information).37) -2 An object declared as type _Bool is large enough to store the values 0 and 1. -3 An object declared as type char is large enough to store any member of the basic - execution character set. If a member of the basic execution character set is stored in a - char object, its value is guaranteed to be nonnegative. If any other character is stored in - a char object, the resulting value is implementation-defined but shall be within the range - of values that can be represented in that type. -4 There are five standard signed integer types, designated as signed char, short - int, int, long int, and long long int. (These and other types may be - designated in several additional ways, as described in 6.7.2.) There may also be - implementation-defined extended signed integer types.38) The standard and extended - signed integer types are collectively called signed integer types.39) - - 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an - embedded block prior to the declaration, leaves the scope of the declaration. - 36) The address of such an object is taken implicitly when an array member is accessed. - 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at - different points within a translation unit. - -[page 39] (Contents) - -5 An object declared as type signed char occupies the same amount of storage as a - ''plain'' char object. A ''plain'' int object has the natural size suggested by the - architecture of the execution environment (large enough to contain any value in the range - INT_MIN to INT_MAX as defined in the header <limits.h>). -6 For each of the signed integer types, there is a corresponding (but different) unsigned - integer type (designated with the keyword unsigned) that uses the same amount of - storage (including sign information) and has the same alignment requirements. The type - _Bool and the unsigned integer types that correspond to the standard signed integer - types are the standard unsigned integer types. The unsigned integer types that - correspond to the extended signed integer types are the extended unsigned integer types. - The standard and extended unsigned integer types are collectively called unsigned integer - types.40) -7 The standard signed integer types and standard unsigned integer types are collectively - called the standard integer types, the extended signed integer types and extended - unsigned integer types are collectively called the extended integer types. -8 For any two integer types with the same signedness and different integer conversion rank - (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a - subrange of the values of the other type. -9 The range of nonnegative values of a signed integer type is a subrange of the - corresponding unsigned integer type, and the representation of the same value in each - type is the same.41) A computation involving unsigned operands can never overflow, - because a result that cannot be represented by the resulting unsigned integer type is - reduced modulo the number that is one greater than the largest value that can be - represented by the resulting type. -10 There are three real floating types, designated as float, double, and long - double.42) The set of values of the type float is a subset of the set of values of the - type double; the set of values of the type double is a subset of the set of values of the - type long double. - - - 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as - described in 7.1.3. - 39) Therefore, any statement in this Standard about signed integer types also applies to the extended - signed integer types. - 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended - unsigned integer types. - 41) The same representation and alignment requirements are meant to imply interchangeability as - arguments to functions, return values from functions, and members of unions. - 42) See ''future language directions'' (6.11.1). - -[page 40] (Contents) - -11 There are three complex types, designated as float _Complex, double - _Complex, and long double _Complex.43) (Complex types are a conditional - feature that implementations need not support; see 6.10.8.3.) The real floating and - complex types are collectively called the floating types. -12 For each floating type there is a corresponding real type, which is always a real floating - type. For real floating types, it is the same type. For complex types, it is the type given - by deleting the keyword _Complex from the type name. -13 Each complex type has the same representation and alignment requirements as an array - type containing exactly two elements of the corresponding real type; the first element is - equal to the real part, and the second element to the imaginary part, of the complex - number. -14 The type char, the signed and unsigned integer types, and the floating types are - collectively called the basic types. The basic types are complete object types. Even if the - implementation defines two or more basic types to have the same representation, they are - nevertheless different types.44) -15 The three types char, signed char, and unsigned char are collectively called - the character types. The implementation shall define char to have the same range, - representation, and behavior as either signed char or unsigned char.45) -16 An enumeration comprises a set of named integer constant values. Each distinct - enumeration constitutes a different enumerated type. -17 The type char, the signed and unsigned integer types, and the enumerated types are - collectively called integer types. The integer and real floating types are collectively called - real types. -18 Integer and floating types are collectively called arithmetic types. Each arithmetic type - belongs to one type domain: the real type domain comprises the real types, the complex - type domain comprises the complex types. -19 The void type comprises an empty set of values; it is an incomplete object type that - cannot be completed. - - - - 43) A specification for imaginary types is in annex G. - 44) An implementation may define new keywords that provide alternative ways to designate a basic (or - any other) type; this does not violate the requirement that all basic types be different. - Implementation-defined keywords shall have the form of an identifier reserved for any use as - described in 7.1.3. - 45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be - used to distinguish the two options. Irrespective of the choice made, char is a separate type from the - other two and is not compatible with either. - -[page 41] (Contents) - -20 Any number of derived types can be constructed from the object and function types, as - follows: - -- An array type describes a contiguously allocated nonempty set of objects with a - particular member object type, called the element type. The element type shall be - complete whenever the array type is specified. Array types are characterized by their - element type and by the number of elements in the array. An array type is said to be - derived from its element type, and if its element type is T , the array type is sometimes - called ''array of T ''. The construction of an array type from an element type is called - ''array type derivation''. - -- A structure type describes a sequentially allocated nonempty set of member objects - (and, in certain circumstances, an incomplete array), each of which has an optionally - specified name and possibly distinct type. - -- A union type describes an overlapping nonempty set of member objects, each of - which has an optionally specified name and possibly distinct type. - -- A function type describes a function with specified return type. A function type is - characterized by its return type and the number and types of its parameters. A - function type is said to be derived from its return type, and if its return type is T , the - function type is sometimes called ''function returning T ''. The construction of a - function type from a return type is called ''function type derivation''. - -- A pointer type may be derived from a function type or an object type, called the - referenced type. A pointer type describes an object whose value provides a reference - to an entity of the referenced type. A pointer type derived from the referenced type T - is sometimes called ''pointer to T ''. The construction of a pointer type from a - referenced type is called ''pointer type derivation''. A pointer type is a complete - object type. - -- An atomic type describes the type designated by the construct _Atomic ( type- - name ). (Atomic types are a conditional feature that implementations need not - support; see 6.10.8.3.) - These methods of constructing derived types can be applied recursively. -21 Arithmetic types and pointer types are collectively called scalar types. Array and - structure types are collectively called aggregate types.46) -22 An array type of unknown size is an incomplete type. It is completed, for an identifier of - that type, by specifying the size in a later declaration (with internal or external linkage). - A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete - - - 46) Note that aggregate type does not include union type because an object with union type can only - contain one member at a time. - -[page 42] (Contents) - - type. It is completed, for all declarations of that type, by declaring the same structure or - union tag with its defining content later in the same scope. -23 A type has known constant size if the type is not incomplete and is not a variable length - array type. -24 Array, function, and pointer types are collectively called derived declarator types. A - declarator type derivation from a type T is the construction of a derived declarator type - from T by the application of an array-type, a function-type, or a pointer-type derivation to - T. -25 A type is characterized by its type category, which is either the outermost derivation of a - derived type (as noted above in the construction of derived types), or the type itself if the - type consists of no derived types. -26 Any type so far mentioned is an unqualified type. Each unqualified type has several - qualified versions of its type,47) corresponding to the combinations of one, two, or all - three of the const, volatile, and restrict qualifiers. The qualified or unqualified - versions of a type are distinct types that belong to the same type category and have the - same representation and alignment requirements.48) A derived type is not qualified by the - qualifiers (if any) of the type from which it is derived. -27 Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier - designates an atomic type. The size, representation, and alignment of an atomic type - need not be the same as those of the corresponding unqualified type. Therefore, this - Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the - atomic version of a type is permitted along with the other qualified versions of a type. - The phrase ''qualified or unqualified type'', without specific mention of atomic, does not - include the atomic types. -28 A pointer to void shall have the same representation and alignment requirements as a - pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of - compatible types shall have the same representation and alignment requirements. All - pointers to structure types shall have the same representation and alignment requirements - as each other. All pointers to union types shall have the same representation and - alignment requirements as each other. Pointers to other types need not have the same - representation or alignment requirements. -29 EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is - pointer, not a floating type. The const-qualified version of this type is designated as ''float * const'' - whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const- - - - 47) See 6.7.3 regarding qualified array and function types. - 48) The same representation and alignment requirements are meant to imply interchangeability as - arguments to functions, return values from functions, and members of unions. - -[page 43] (Contents) - - qualified float'' and is a pointer to a qualified type. - -30 EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to - function returning struct tag''. The array has length five and the function has a single parameter of type - float. Its type category is array. - - Forward references: compatible type and composite type (6.2.7), declarations (6.7). - 6.2.6 Representations of types - 6.2.6.1 General -1 The representations of all types are unspecified except as stated in this subclause. -2 Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, - the number, order, and encoding of which are either explicitly specified or - implementation-defined. -3 Values stored in unsigned bit-fields and objects of type unsigned char shall be - represented using a pure binary notation.49) -4 Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT - bits, where n is the size of an object of that type, in bytes. The value may be copied into - an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is - called the object representation of the value. Values stored in bit-fields consist of m bits, - where m is the size specified for the bit-field. The object representation is the set of m - bits the bit-field comprises in the addressable storage unit holding it. Two values (other - than NaNs) with the same object representation compare equal, but values that compare - equal may have different object representations. -5 Certain object representations need not represent a value of the object type. If the stored - value of an object has such a representation and is read by an lvalue expression that does - not have character type, the behavior is undefined. If such a representation is produced - by a side effect that modifies all or any part of the object by an lvalue expression that - does not have character type, the behavior is undefined.50) Such a representation is called - a trap representation. -6 When a value is stored in an object of structure or union type, including in a member - object, the bytes of the object representation that correspond to any padding bytes take - unspecified values.51) The value of a structure or union object is never a trap - - - 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values - represented by successive bits are additive, begin with 1, and are multiplied by successive integral - powers of 2, except perhaps the bit with the highest position. (Adapted from the American National - Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of - type unsigned char range from 0 to 2 - CHAR_BIT - - 1. - 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined - behavior, but the value of the variable cannot be used until a proper value is stored in it. - -[page 44] (Contents) - - representation, even though the value of a member of the structure or union object may be - a trap representation. -7 When a value is stored in a member of an object of union type, the bytes of the object - representation that do not correspond to that member but do correspond to other members - take unspecified values. -8 Where an operator is applied to a value that has more than one object representation, - which object representation is used shall not affect the value of the result.52) Where a - value is stored in an object using a type that has more than one object representation for - that value, it is unspecified which representation is used, but a trap representation shall - not be generated. -9 Loads and stores of objects with atomic types are done with - memory_order_seq_cst semantics. - Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function - designators (6.3.2.1), order and consistency (7.17.3). - 6.2.6.2 Integer types -1 For unsigned integer types other than unsigned char, the bits of the object - representation shall be divided into two groups: value bits and padding bits (there need - not be any of the latter). If there are N value bits, each bit shall represent a different - power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of - representing values from 0 to 2 N - 1 using a pure binary representation; this shall be - known as the value representation. The values of any padding bits are unspecified.53) -2 For signed integer types, the bits of the object representation shall be divided into three - groups: value bits, padding bits, and the sign bit. There need not be any padding bits; - signed char shall not have any padding bits. There shall be exactly one sign bit. - Each bit that is a value bit shall have the same value as the same bit in the object - representation of the corresponding unsigned type (if there are M value bits in the signed - type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect - - 51) Thus, for example, structure assignment need not copy any padding bits. - 52) It is possible for objects x and y with the same effective type T to have the same value when they are - accessed as objects of type T, but to have different values in other contexts. In particular, if == is - defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0. - Furthermore, x == y does not necessarily imply that x and y have the same value; other operations - on values of type T may distinguish between them. - 53) Some combinations of padding bits might generate trap representations, for example, if one padding - bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap - representation other than as part of an exceptional condition such as an overflow, and this cannot occur - with unsigned types. All other combinations of padding bits are alternative object representations of - the value specified by the value bits. - -[page 45] (Contents) - - the resulting value. If the sign bit is one, the value shall be modified in one of the - following ways: - -- the corresponding value with sign bit 0 is negated (sign and magnitude); - -- the sign bit has the value -(2 M ) (two's complement); - -- the sign bit has the value -(2 M - 1) (ones' complement). - Which of these applies is implementation-defined, as is whether the value with sign bit 1 - and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones' - complement), is a trap representation or a normal value. In the case of sign and - magnitude and ones' complement, if this representation is a normal value it is called a - negative zero. -3 If the implementation supports negative zeros, they shall be generated only by: - -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value; - -- the +, -, *, /, and % operators where one operand is a negative zero and the result is - zero; - -- compound assignment operators based on the above cases. - It is unspecified whether these cases actually generate a negative zero or a normal zero, - and whether a negative zero becomes a normal zero when stored in an object. -4 If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<, - and >> operators with operands that would produce such a value is undefined. -5 The values of any padding bits are unspecified.54) A valid (non-trap) object representation - of a signed integer type where the sign bit is zero is a valid object representation of the - corresponding unsigned type, and shall represent the same value. For any integer type, - the object representation where all the bits are zero shall be a representation of the value - zero in that type. -6 The precision of an integer type is the number of bits it uses to represent values, - excluding any sign and padding bits. The width of an integer type is the same but - including any sign bit; thus for unsigned integer types the two values are the same, while - for signed integer types the width is one greater than the precision. - - - - - 54) Some combinations of padding bits might generate trap representations, for example, if one padding - bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap - representation other than as part of an exceptional condition such as an overflow. All other - combinations of padding bits are alternative object representations of the value specified by the value - bits. - -[page 46] (Contents) - - 6.2.7 Compatible type and composite type -1 Two types have compatible type if their types are the same. Additional rules for - determining whether two types are compatible are described in 6.7.2 for type specifiers, - in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure, - union, or enumerated types declared in separate translation units are compatible if their - tags and members satisfy the following requirements: If one is declared with a tag, the - other shall be declared with the same tag. If both are completed anywhere within their - respective translation units, then the following additional requirements apply: there shall - be a one-to-one correspondence between their members such that each pair of - corresponding members are declared with compatible types; if one member of the pair is - declared with an alignment specifier, the other is declared with an equivalent alignment - specifier; and if one member of the pair is declared with a name, the other is declared - with the same name. For two structures, corresponding members shall be declared in the - same order. For two structures or unions, corresponding bit-fields shall have the same - widths. For two enumerations, corresponding members shall have the same values. -2 All declarations that refer to the same object or function shall have compatible type; - otherwise, the behavior is undefined. -3 A composite type can be constructed from two types that are compatible; it is a type that - is compatible with both of the two types and satisfies the following conditions: - -- If both types are array types, the following rules are applied: - o If one type is an array of known constant size, the composite type is an array of - that size. - o Otherwise, if one type is a variable length array whose size is specified by an - expression that is not evaluated, the behavior is undefined. - o Otherwise, if one type is a variable length array whose size is specified, the - composite type is a variable length array of that size. - o Otherwise, if one type is a variable length array of unspecified size, the composite - type is a variable length array of unspecified size. - o Otherwise, both types are arrays of unknown size and the composite type is an - array of unknown size. - The element type of the composite type is the composite type of the two element - types. - -- If only one type is a function type with a parameter type list (a function prototype), - the composite type is a function prototype with the parameter type list. - - - 55) Two types need not be identical to be compatible. - -[page 47] (Contents) - - -- If both types are function types with parameter type lists, the type of each parameter - in the composite parameter type list is the composite type of the corresponding - parameters. - These rules apply recursively to the types from which the two types are derived. -4 For an identifier with internal or external linkage declared in a scope in which a prior - declaration of that identifier is visible,56) if the prior declaration specifies internal or - external linkage, the type of the identifier at the later declaration becomes the composite - type. - Forward references: array declarators (6.7.6.2). -5 EXAMPLE Given the following two file scope declarations: - int f(int (*)(), double (*)[3]); - int f(int (*)(char *), double (*)[]); - The resulting composite type for the function is: - int f(int (*)(char *), double (*)[3]); - - 6.2.8 Alignment of objects -1 Complete object types have alignment requirements which place restrictions on the - addresses at which objects of that type may be allocated. An alignment is an - implementation-defined integer value representing the number of bytes between - successive addresses at which a given object can be allocated. An object type imposes an - alignment requirement on every object of that type: stricter alignment can be requested - using the _Alignas keyword. -2 A fundamental alignment is represented by an alignment less than or equal to the greatest - alignment supported by the implementation in all contexts, which is equal to - alignof(max_align_t). -3 An extended alignment is represented by an alignment greater than - alignof(max_align_t). It is implementation-defined whether any extended - alignments are supported and the contexts in which they are supported. A type having an - extended alignment requirement is an over-aligned type.57) -4 Alignments are represented as values of the type size_t. Valid alignments include only - those values returned by an alignof expression for fundamental types, plus an - additional implementation-defined set of values, which may be empty. Every valid - alignment value shall be a nonnegative integral power of two. - - - 56) As specified in 6.2.1, the later declaration might hide the prior declaration. - 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended - alignment has been applied. - -[page 48] (Contents) - -5 Alignments have an order from weaker to stronger or stricter alignments. Stricter - alignments have larger alignment values. An address that satisfies an alignment - requirement also satisfies any weaker valid alignment requirement. -6 The alignment requirement of a complete type can be queried using an alignof - expression. The types char, signed char, and unsigned char shall have the - weakest alignment requirement. -7 Comparing alignments is meaningful and provides the obvious results: - -- Two alignments are equal when their numeric values are equal. - -- Two alignments are different when their numeric values are not equal. - -- When an alignment is larger than another it represents a stricter alignment. - - - - -[page 49] (Contents) - - 6.3 Conversions -1 Several operators convert operand values from one type to another automatically. This - subclause specifies the result required from such an implicit conversion, as well as those - that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes - the conversions performed by most ordinary operators; it is supplemented as required by - the discussion of each operator in 6.5. -2 Conversion of an operand value to a compatible type causes no change to the value or the - representation. - Forward references: cast operators (6.5.4). - 6.3.1 Arithmetic operands - 6.3.1.1 Boolean, characters, and integers -1 Every integer type has an integer conversion rank defined as follows: - -- No two signed integer types shall have the same rank, even if they have the same - representation. - -- The rank of a signed integer type shall be greater than the rank of any signed integer - type with less precision. - -- The rank of long long int shall be greater than the rank of long int, which - shall be greater than the rank of int, which shall be greater than the rank of short - int, which shall be greater than the rank of signed char. - -- The rank of any unsigned integer type shall equal the rank of the corresponding - signed integer type, if any. - -- The rank of any standard integer type shall be greater than the rank of any extended - integer type with the same width. - -- The rank of char shall equal the rank of signed char and unsigned char. - -- The rank of _Bool shall be less than the rank of all other standard integer types. - -- The rank of any enumerated type shall equal the rank of the compatible integer type - (see 6.7.2.2). - -- The rank of any extended signed integer type relative to another extended signed - integer type with the same precision is implementation-defined, but still subject to the - other rules for determining the integer conversion rank. - -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has - greater rank than T3, then T1 has greater rank than T3. -2 The following may be used in an expression wherever an int or unsigned int may - be used: - -[page 50] (Contents) - - -- An object or expression with an integer type (other than int or unsigned int) - whose integer conversion rank is less than or equal to the rank of int and - unsigned int. - -- A bit-field of type _Bool, int, signed int, or unsigned int. - If an int can represent all values of the original type (as restricted by the width, for a - bit-field), the value is converted to an int; otherwise, it is converted to an unsigned - int. These are called the integer promotions.58) All other types are unchanged by the - integer promotions. -3 The integer promotions preserve value including sign. As discussed earlier, whether a - ''plain'' char is treated as signed is implementation-defined. - Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers - (6.7.2.1). - 6.3.1.2 Boolean type -1 When any scalar value is converted to _Bool, the result is 0 if the value compares equal - to 0; otherwise, the result is 1.59) - 6.3.1.3 Signed and unsigned integers -1 When a value with integer type is converted to another integer type other than _Bool, if - the value can be represented by the new type, it is unchanged. -2 Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or - subtracting one more than the maximum value that can be represented in the new type - until the value is in the range of the new type.60) -3 Otherwise, the new type is signed and the value cannot be represented in it; either the - result is implementation-defined or an implementation-defined signal is raised. - 6.3.1.4 Real floating and integer -1 When a finite value of real floating type is converted to an integer type other than _Bool, - the fractional part is discarded (i.e., the value is truncated toward zero). If the value of - the integral part cannot be represented by the integer type, the behavior is undefined.61) - - - 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain - argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the - shift operators, as specified by their respective subclauses. - 59) NaNs do not compare equal to 0 and thus convert to 1. - 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression. - 61) The remaindering operation performed when a value of integer type is converted to unsigned type - need not be performed when a value of real floating type is converted to unsigned type. Thus, the - range of portable real floating values is (-1, Utype_MAX+1). - -[page 51] (Contents) - -2 When a value of integer type is converted to a real floating type, if the value being - converted can be represented exactly in the new type, it is unchanged. If the value being - converted is in the range of values that can be represented but cannot be represented - exactly, the result is either the nearest higher or nearest lower representable value, chosen - in an implementation-defined manner. If the value being converted is outside the range of - values that can be represented, the behavior is undefined. Results of some implicit - conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that - required by the new type. - 6.3.1.5 Real floating types -1 When a value of real floating type is converted to a real floating type, if the value being - converted can be represented exactly in the new type, it is unchanged. If the value being - converted is in the range of values that can be represented but cannot be represented - exactly, the result is either the nearest higher or nearest lower representable value, chosen - in an implementation-defined manner. If the value being converted is outside the range of - values that can be represented, the behavior is undefined. Results of some implicit - conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that - required by the new type. - 6.3.1.6 Complex types -1 When a value of complex type is converted to another complex type, both the real and - imaginary parts follow the conversion rules for the corresponding real types. - 6.3.1.7 Real and complex -1 When a value of real type is converted to a complex type, the real part of the complex - result value is determined by the rules of conversion to the corresponding real type and - the imaginary part of the complex result value is a positive zero or an unsigned zero. -2 When a value of complex type is converted to a real type, the imaginary part of the - complex value is discarded and the value of the real part is converted according to the - conversion rules for the corresponding real type. - 6.3.1.8 Usual arithmetic conversions -1 Many operators that expect operands of arithmetic type cause conversions and yield result - types in a similar way. The purpose is to determine a common real type for the operands - and result. For the specified operands, each operand is converted, without change of type - domain, to a type whose corresponding real type is the common real type. Unless - explicitly stated otherwise, the common real type is also the corresponding real type of - the result, whose type domain is the type domain of the operands if they are the same, - and complex otherwise. This pattern is called the usual arithmetic conversions: - First, if the corresponding real type of either operand is long double, the other - operand is converted, without change of type domain, to a type whose - -[page 52] (Contents) - - corresponding real type is long double. - Otherwise, if the corresponding real type of either operand is double, the other - operand is converted, without change of type domain, to a type whose - corresponding real type is double. - Otherwise, if the corresponding real type of either operand is float, the other - operand is converted, without change of type domain, to a type whose - corresponding real type is float.62) - Otherwise, the integer promotions are performed on both operands. Then the - following rules are applied to the promoted operands: - If both operands have the same type, then no further conversion is needed. - Otherwise, if both operands have signed integer types or both have unsigned - integer types, the operand with the type of lesser integer conversion rank is - converted to the type of the operand with greater rank. - Otherwise, if the operand that has unsigned integer type has rank greater or - equal to the rank of the type of the other operand, then the operand with - signed integer type is converted to the type of the operand with unsigned - integer type. - Otherwise, if the type of the operand with signed integer type can represent - all of the values of the type of the operand with unsigned integer type, then - the operand with unsigned integer type is converted to the type of the - operand with signed integer type. - Otherwise, both operands are converted to the unsigned integer type - corresponding to the type of the operand with signed integer type. -2 The values of floating operands and of the results of floating expressions may be - represented in greater precision and range than that required by the type; the types are not - changed thereby.63) - - - - - 62) For example, addition of a double _Complex and a float entails just the conversion of the - float operand to double (and yields a double _Complex result). - 63) The cast and assignment operators are still required to remove extra range and precision. - -[page 53] (Contents) - - 6.3.2 Other operands - 6.3.2.1 Lvalues, arrays, and function designators -1 An lvalue is an expression (with an object type other than void) that potentially - designates an object;64) if an lvalue does not designate an object when it is evaluated, the - behavior is undefined. When an object is said to have a particular type, the type is - specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that - does not have array type, does not have an incomplete type, does not have a const- - qualified type, and if it is a structure or union, does not have any member (including, - recursively, any member or element of all contained aggregates or unions) with a const- - qualified type. -2 Except when it is the operand of the sizeof operator, the unary & operator, the ++ - operator, the -- operator, or the left operand of the . operator or an assignment operator, - an lvalue that does not have array type is converted to the value stored in the designated - object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has - qualified type, the value has the unqualified version of the type of the lvalue; additionally, - if the lvalue has atomic type, the value has the non-atomic version of the type of the - lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete - type and does not have array type, the behavior is undefined. If the lvalue designates an - object of automatic storage duration that could have been declared with the register - storage class (never had its address taken), and that object is uninitialized (not declared - with an initializer and no assignment to it has been performed prior to use), the behavior - is undefined. -3 Except when it is the operand of the sizeof operator or the unary & operator, or is a - string literal used to initialize an array, an expression that has type ''array of type'' is - converted to an expression with type ''pointer to type'' that points to the initial element of - the array object and is not an lvalue. If the array object has register storage class, the - behavior is undefined. -4 A function designator is an expression that has function type. Except when it is the - operand of the sizeof operator65) or the unary & operator, a function designator with - type ''function returning type'' is converted to an expression that has type ''pointer to - - - 64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left - operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an - object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described - as the ''value of an expression''. - An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary - expression that is a pointer to an object, *E is an lvalue that designates the object to which E points. - 65) Because this conversion does not occur, the operand of the sizeof operator remains a function - designator and violates the constraint in 6.5.3.4. - -[page 54] (Contents) - - function returning type''. - Forward references: address and indirection operators (6.5.3.2), assignment operators - (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix - increment and decrement operators (6.5.2.4), prefix increment and decrement operators - (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3). - 6.3.2.2 void -1 The (nonexistent) value of a void expression (an expression that has type void) shall not - be used in any way, and implicit or explicit conversions (except to void) shall not be - applied to such an expression. If an expression of any other type is evaluated as a void - expression, its value or designator is discarded. (A void expression is evaluated for its - side effects.) - 6.3.2.3 Pointers -1 A pointer to void may be converted to or from a pointer to any object type. A pointer to - any object type may be converted to a pointer to void and back again; the result shall - compare equal to the original pointer. -2 For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to - the q-qualified version of the type; the values stored in the original and converted pointers - shall compare equal. -3 An integer constant expression with the value 0, or such an expression cast to type - void *, is called a null pointer constant.66) If a null pointer constant is converted to a - pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal - to a pointer to any object or function. -4 Conversion of a null pointer to another pointer type yields a null pointer of that type. - Any two null pointers shall compare equal. -5 An integer may be converted to any pointer type. Except as previously specified, the - result is implementation-defined, might not be correctly aligned, might not point to an - entity of the referenced type, and might be a trap representation.67) -6 Any pointer type may be converted to an integer type. Except as previously specified, the - result is implementation-defined. If the result cannot be represented in the integer type, - the behavior is undefined. The result need not be in the range of values of any integer - type. - - - - - 66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19. - 67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to - be consistent with the addressing structure of the execution environment. - -[page 55] (Contents) - -7 A pointer to an object type may be converted to a pointer to a different object type. If the - resulting pointer is not correctly aligned68) for the referenced type, the behavior is - undefined. Otherwise, when converted back again, the result shall compare equal to the - original pointer. When a pointer to an object is converted to a pointer to a character type, - the result points to the lowest addressed byte of the object. Successive increments of the - result, up to the size of the object, yield pointers to the remaining bytes of the object. -8 A pointer to a function of one type may be converted to a pointer to a function of another - type and back again; the result shall compare equal to the original pointer. If a converted - pointer is used to call a function whose type is not compatible with the referenced type, - the behavior is undefined. - Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types - capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1). - - - - - 68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a - pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is - correctly aligned for a pointer to type C. - -[page 56] (Contents) - - 6.4 Lexical elements - Syntax -1 token: - keyword - identifier - constant - string-literal - punctuator - preprocessing-token: - header-name - identifier - pp-number - character-constant - string-literal - punctuator - each non-white-space character that cannot be one of the above - Constraints -2 Each preprocessing token that is converted to a token shall have the lexical form of a - keyword, an identifier, a constant, a string literal, or a punctuator. - Semantics -3 A token is the minimal lexical element of the language in translation phases 7 and 8. The - categories of tokens are: keywords, identifiers, constants, string literals, and punctuators. - A preprocessing token is the minimal lexical element of the language in translation - phases 3 through 6. The categories of preprocessing tokens are: header names, - identifiers, preprocessing numbers, character constants, string literals, punctuators, and - single non-white-space characters that do not lexically match the other preprocessing - token categories.69) If a ' or a " character matches the last category, the behavior is - undefined. Preprocessing tokens can be separated by white space; this consists of - comments (described later), or white-space characters (space, horizontal tab, new-line, - vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances - during translation phase 4, white space (or the absence thereof) serves as more than - preprocessing token separation. White space may appear within a preprocessing token - only as part of a header name or between the quotation characters in a character constant - or string literal. - - - - 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot - occur in source files. - -[page 57] (Contents) - -4 If the input stream has been parsed into preprocessing tokens up to a given character, the - next preprocessing token is the longest sequence of characters that could constitute a - preprocessing token. There is one exception to this rule: header name preprocessing - tokens are recognized only within #include preprocessing directives and in - implementation-defined locations within #pragma directives. In such contexts, a - sequence of characters that could be either a header name or a string literal is recognized - as the former. -5 EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a - valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex - might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program - fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or - not E is a macro name. - -6 EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on - increment operators, even though the parse x ++ + ++ y might yield a correct expression. - - Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5), - floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix - increment and decrement operators (6.5.2.4), prefix increment and decrement operators - (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals - (6.4.5). - 6.4.1 Keywords - Syntax -1 keyword: one of - alignof goto union - auto if unsigned - break inline void - case int volatile - char long while - const register _Alignas - continue restrict _Atomic - default return _Bool - do short _Complex - double signed _Generic - else sizeof _Imaginary - enum static _Noreturn - extern struct _Static_assert - float switch _Thread_local - for typedef - Semantics -2 The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as - keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for -[page 58] (Contents) - - specifying imaginary types.70) - 6.4.2 Identifiers - 6.4.2.1 General - Syntax -1 identifier: - identifier-nondigit - identifier identifier-nondigit - identifier digit - identifier-nondigit: - nondigit - universal-character-name - other implementation-defined characters - nondigit: one of - _ a b c d e f g h i j k l m - n o p q r s t u v w x y z - A B C D E F G H I J K L M - N O P Q R S T U V W X Y Z - digit: one of - 0 1 2 3 4 5 6 7 8 9 - Semantics -2 An identifier is a sequence of nondigit characters (including the underscore _, the - lowercase and uppercase Latin letters, and other characters) and digits, which designates - one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct. - There is no specific limit on the maximum length of an identifier. -3 Each universal character name in an identifier shall designate a character whose encoding - in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character - shall not be a universal character name designating a character whose encoding falls into - one of the ranges specified in D.2. An implementation may allow multibyte characters - that are not part of the basic source character set to appear in identifiers; which characters - and their correspondence to universal character names is implementation-defined. - - - - 70) One possible specification for imaginary types appears in annex G. - 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character - name may be used in forming valid external identifiers. For example, some otherwise unused - character or sequence of characters may be used to encode the \u in a universal character name. - Extended characters may produce a long external identifier. - -[page 59] (Contents) - -4 When preprocessing tokens are converted to tokens during translation phase 7, if a - preprocessing token could be converted to either a keyword or an identifier, it is converted - to a keyword. - Implementation limits -5 As discussed in 5.2.4.1, an implementation may limit the number of significant initial - characters in an identifier; the limit for an external name (an identifier that has external - linkage) may be more restrictive than that for an internal name (a macro name or an - identifier that does not have external linkage). The number of significant characters in an - identifier is implementation-defined. -6 Any identifiers that differ in a significant character are different identifiers. If two - identifiers differ only in nonsignificant characters, the behavior is undefined. - Forward references: universal character names (6.4.3), macro replacement (6.10.3). - 6.4.2.2 Predefined identifiers - Semantics -1 The identifier __func__ shall be implicitly declared by the translator as if, - immediately following the opening brace of each function definition, the declaration - static const char __func__[] = "function-name"; - appeared, where function-name is the name of the lexically-enclosing function.72) -2 This name is encoded as if the implicit declaration had been written in the source - character set and then translated into the execution character set as indicated in translation - phase 5. -3 EXAMPLE Consider the code fragment: - #include <stdio.h> - void myfunc(void) - { - printf("%s\n", __func__); - /* ... */ - } - Each time the function is called, it will print to the standard output stream: - myfunc - - Forward references: function definitions (6.9.1). - - - - - 72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other - identifier is explicitly declared using the name __func__, the behavior is undefined. - -[page 60] (Contents) - - 6.4.3 Universal character names - Syntax -1 universal-character-name: - \u hex-quad - \U hex-quad hex-quad - hex-quad: - hexadecimal-digit hexadecimal-digit - hexadecimal-digit hexadecimal-digit - Constraints -2 A universal character name shall not specify a character whose short identifier is less than - 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through - DFFF inclusive.73) - Description -3 Universal character names may be used in identifiers, character constants, and string - literals to designate characters that are not in the basic character set. - Semantics -4 The universal character name \Unnnnnnnn designates the character whose eight-digit - short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal - character name \unnnn designates the character whose four-digit short identifier is nnnn - (and whose eight-digit short identifier is 0000nnnn). - - - - - 73) The disallowed characters are the characters in the basic character set and the code positions reserved - by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by - UTF-16). - - 74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997. - -[page 61] (Contents) - - 6.4.4 Constants - Syntax -1 constant: - integer-constant - floating-constant - enumeration-constant - character-constant - Constraints -2 Each constant shall have a type and the value of a constant shall be in the range of - representable values for its type. - Semantics -3 Each constant has a type, determined by its form and value, as detailed later. - 6.4.4.1 Integer constants - Syntax -1 integer-constant: - decimal-constant integer-suffixopt - octal-constant integer-suffixopt - hexadecimal-constant integer-suffixopt - decimal-constant: - nonzero-digit - decimal-constant digit - octal-constant: - 0 - octal-constant octal-digit - hexadecimal-constant: - hexadecimal-prefix hexadecimal-digit - hexadecimal-constant hexadecimal-digit - hexadecimal-prefix: one of - 0x 0X - nonzero-digit: one of - 1 2 3 4 5 6 7 8 9 - octal-digit: one of - 0 1 2 3 4 5 6 7 - - - - -[page 62] (Contents) - - hexadecimal-digit: one of - 0 1 2 3 4 5 6 7 8 9 - a b c d e f - A B C D E F - integer-suffix: - unsigned-suffix long-suffixopt - unsigned-suffix long-long-suffix - long-suffix unsigned-suffixopt - long-long-suffix unsigned-suffixopt - unsigned-suffix: one of - u U - long-suffix: one of - l L - long-long-suffix: one of - ll LL - Description -2 An integer constant begins with a digit, but has no period or exponent part. It may have a - prefix that specifies its base and a suffix that specifies its type. -3 A decimal constant begins with a nonzero digit and consists of a sequence of decimal - digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the - digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed - by a sequence of the decimal digits and the letters a (or A) through f (or F) with values - 10 through 15 respectively. - Semantics -4 The value of a decimal constant is computed base 10; that of an octal constant, base 8; - that of a hexadecimal constant, base 16. The lexically first digit is the most significant. -5 The type of an integer constant is the first of the corresponding list in which its value can - be represented. - - - - -[page 63] (Contents) - - Octal or Hexadecimal - Suffix Decimal Constant Constant - - none int int - long int unsigned int - long long int long int - unsigned long int - long long int - unsigned long long int - - u or U unsigned int unsigned int - unsigned long int unsigned long int - unsigned long long int unsigned long long int - - l or L long int long int - long long int unsigned long int - long long int - unsigned long long int - - Both u or U unsigned long int unsigned long int - and l or L unsigned long long int unsigned long long int - - ll or LL long long int long long int - unsigned long long int - - Both u or U unsigned long long int unsigned long long int - and ll or LL -6 If an integer constant cannot be represented by any type in its list, it may have an - extended integer type, if the extended integer type can represent its value. If all of the - types in the list for the constant are signed, the extended integer type shall be signed. If - all of the types in the list for the constant are unsigned, the extended integer type shall be - unsigned. If the list contains both signed and unsigned types, the extended integer type - may be signed or unsigned. If an integer constant cannot be represented by any type in - its list and has no extended integer type, then the integer constant has no type. - - - - -[page 64] (Contents) - - 6.4.4.2 Floating constants - Syntax -1 floating-constant: - decimal-floating-constant - hexadecimal-floating-constant - decimal-floating-constant: - fractional-constant exponent-partopt floating-suffixopt - digit-sequence exponent-part floating-suffixopt - hexadecimal-floating-constant: - hexadecimal-prefix hexadecimal-fractional-constant - binary-exponent-part floating-suffixopt - hexadecimal-prefix hexadecimal-digit-sequence - binary-exponent-part floating-suffixopt - fractional-constant: - digit-sequenceopt . digit-sequence - digit-sequence . - exponent-part: - e signopt digit-sequence - E signopt digit-sequence - sign: one of - + - - digit-sequence: - digit - digit-sequence digit - hexadecimal-fractional-constant: - hexadecimal-digit-sequenceopt . - hexadecimal-digit-sequence - hexadecimal-digit-sequence . - binary-exponent-part: - p signopt digit-sequence - P signopt digit-sequence - hexadecimal-digit-sequence: - hexadecimal-digit - hexadecimal-digit-sequence hexadecimal-digit - floating-suffix: one of - f l F L - -[page 65] (Contents) - - Description -2 A floating constant has a significand part that may be followed by an exponent part and a - suffix that specifies its type. The components of the significand part may include a digit - sequence representing the whole-number part, followed by a period (.), followed by a - digit sequence representing the fraction part. The components of the exponent part are an - e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence. - Either the whole-number part or the fraction part has to be present; for decimal floating - constants, either the period or the exponent part has to be present. - Semantics -3 The significand part is interpreted as a (decimal or hexadecimal) rational number; the - digit sequence in the exponent part is interpreted as a decimal integer. For decimal - floating constants, the exponent indicates the power of 10 by which the significand part is - to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2 - by which the significand part is to be scaled. For decimal floating constants, and also for - hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either - the nearest representable value, or the larger or smaller representable value immediately - adjacent to the nearest representable value, chosen in an implementation-defined manner. - For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is - correctly rounded. -4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has - type float. If suffixed by the letter l or L, it has type long double. -5 Floating constants are converted to internal format as if at translation-time. The - conversion of a floating constant shall not raise an exceptional condition or a floating- - point exception at execution time. All floating constants of the same source form75) shall - convert to the same internal format with the same value. - Recommended practice -6 The implementation should produce a diagnostic message if a hexadecimal constant - cannot be represented exactly in its evaluation format; the implementation should then - proceed with the translation of the program. -7 The translation-time conversion of floating constants should match the execution-time - conversion of character strings by library functions, such as strtod, given matching - inputs suitable for both conversions, the same result format, and default execution-time - rounding.76) - - 75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not - convert to the same internal format and value. - 76) The specification for the library functions recommends more accurate conversion than required for - floating constants (see 7.22.1.3). - -[page 66] (Contents) - - 6.4.4.3 Enumeration constants - Syntax -1 enumeration-constant: - identifier - Semantics -2 An identifier declared as an enumeration constant has type int. - Forward references: enumeration specifiers (6.7.2.2). - 6.4.4.4 Character constants - Syntax -1 character-constant: - ' c-char-sequence ' - L' c-char-sequence ' - u' c-char-sequence ' - U' c-char-sequence ' - c-char-sequence: - c-char - c-char-sequence c-char - c-char: - any member of the source character set except - the single-quote ', backslash \, or new-line character - escape-sequence - escape-sequence: - simple-escape-sequence - octal-escape-sequence - hexadecimal-escape-sequence - universal-character-name - simple-escape-sequence: one of - \' \" \? \\ - \a \b \f \n \r \t \v - octal-escape-sequence: - \ octal-digit - \ octal-digit octal-digit - \ octal-digit octal-digit octal-digit - - - - -[page 67] (Contents) - - hexadecimal-escape-sequence: - \x hexadecimal-digit - hexadecimal-escape-sequence hexadecimal-digit - Description -2 An integer character constant is a sequence of one or more multibyte characters enclosed - in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the - letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are - any members of the source character set; they are mapped in an implementation-defined - manner to members of the execution character set. -3 The single-quote ', the double-quote ", the question-mark ?, the backslash \, and - arbitrary integer values are representable according to the following table of escape - sequences: - single quote ' \' - double quote " \" - question mark ? \? - backslash \ \\ - octal character \octal digits - hexadecimal character \x hexadecimal digits -4 The double-quote " and question-mark ? are representable either by themselves or by the - escape sequences \" and \?, respectively, but the single-quote ' and the backslash \ - shall be represented, respectively, by the escape sequences \' and \\. -5 The octal digits that follow the backslash in an octal escape sequence are taken to be part - of the construction of a single character for an integer character constant or of a single - wide character for a wide character constant. The numerical value of the octal integer so - formed specifies the value of the desired character or wide character. -6 The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape - sequence are taken to be part of the construction of a single character for an integer - character constant or of a single wide character for a wide character constant. The - numerical value of the hexadecimal integer so formed specifies the value of the desired - character or wide character. -7 Each octal or hexadecimal escape sequence is the longest sequence of characters that can - constitute the escape sequence. -8 In addition, characters not in the basic character set are representable by universal - character names and certain nongraphic characters are representable by escape sequences - consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t, - and \v.77) - - - -[page 68] (Contents) - - Constraints -9 The value of an octal or hexadecimal escape sequence shall be in the range of - representable values for the corresponding type: - Prefix Corresponding Type - none unsigned char - L the unsigned type corresponding to wchar_t - u char16_t - U char32_t - Semantics -10 An integer character constant has type int. The value of an integer character constant - containing a single character that maps to a single-byte execution character is the - numerical value of the representation of the mapped character interpreted as an integer. - The value of an integer character constant containing more than one character (e.g., - 'ab'), or containing a character or escape sequence that does not map to a single-byte - execution character, is implementation-defined. If an integer character constant contains - a single character or escape sequence, its value is the one that results when an object with - type char whose value is that of the single character or escape sequence is converted to - type int. -11 A wide character constant prefixed by the letter L has type wchar_t, an integer type - defined in the <stddef.h> header; a wide character constant prefixed by the letter u or - U has type char16_t or char32_t, respectively, unsigned integer types defined in the - <uchar.h> header. The value of a wide character constant containing a single - multibyte character that maps to a single member of the extended execution character set - is the wide character corresponding to that multibyte character, as defined by the - mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an - implementation-defined current locale. The value of a wide character constant containing - more than one multibyte character or a single multibyte character that maps to multiple - members of the extended execution character set, or containing a multibyte character or - escape sequence not represented in the extended execution character set, is - implementation-defined. -12 EXAMPLE 1 The construction '\0' is commonly used to represent the null character. - -13 EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight - bits for objects that have type char. In an implementation in which type char has the same range of - values as signed char, the integer character constant '\xFF' has the value -1; if type char has the - same range of values as unsigned char, the character constant '\xFF' has the value +255. - - - - - 77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash, - the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4). - -[page 69] (Contents) - -14 EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123' - specifies an integer character constant containing only one character, since a hexadecimal escape sequence - is terminated only by a non-hexadecimal character. To specify an integer character constant containing the - two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal - escape sequence is terminated after three octal digits. (The value of this two-character integer character - constant is implementation-defined.) - -15 EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction - L'\1234' specifies the implementation-defined value that results from the combination of the values - 0123 and '4'. - - Forward references: common definitions <stddef.h> (7.19), the mbtowc function - (7.22.7.2), Unicode utilities <uchar.h> (7.27). - 6.4.5 String literals - Syntax -1 string-literal: - encoding-prefixopt " s-char-sequenceopt " - encoding-prefix: - u8 - u - U - L - s-char-sequence: - s-char - s-char-sequence s-char - s-char: - any member of the source character set except - the double-quote ", backslash \, or new-line character - escape-sequence - Constraints -2 A sequence of adjacent string literal tokens shall not include both a wide string literal and - a UTF-8 string literal. - Description -3 A character string literal is a sequence of zero or more multibyte characters enclosed in - double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8. - A wide string literal is the same, except prefixed by the letter L, u, or U. -4 The same considerations apply to each element of the sequence in a string literal as if it - were in an integer character constant (for a character or UTF-8 string literal) or a wide - character constant (for a wide string literal), except that the single-quote ' is - representable either by itself or by the escape sequence \', but the double-quote " shall -[page 70] (Contents) - - be represented by the escape sequence \". - Semantics -5 In translation phase 6, the multibyte character sequences specified by any sequence of - adjacent character and identically-prefixed string literal tokens are concatenated into a - single multibyte character sequence. If any of the tokens has an encoding prefix, the - resulting multibyte character sequence is treated as having the same prefix; otherwise, it - is treated as a character string literal. Whether differently-prefixed wide string literal - tokens can be concatenated and, if so, the treatment of the resulting multibyte character - sequence are implementation-defined. -6 In translation phase 7, a byte or code of value zero is appended to each multibyte - character sequence that results from a string literal or literals.78) The multibyte character - sequence is then used to initialize an array of static storage duration and length just - sufficient to contain the sequence. For character string literals, the array elements have - type char, and are initialized with the individual bytes of the multibyte character - sequence. For UTF-8 string literals, the array elements have type char, and are - initialized with the characters of the multibyte character sequence, as encoded in UTF-8. - For wide string literals prefixed by the letter L, the array elements have type wchar_t - and are initialized with the sequence of wide characters corresponding to the multibyte - character sequence, as defined by the mbstowcs function with an implementation- - defined current locale. For wide string literals prefixed by the letter u or U, the array - elements have type char16_t or char32_t, respectively, and are initialized with the - sequence of wide characters corresponding to the multibyte character sequence, as - defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for - its type, with an implementation-defined current locale. The value of a string literal - containing a multibyte character or escape sequence not represented in the execution - character set is implementation-defined. -7 It is unspecified whether these arrays are distinct provided their elements have the - appropriate values. If the program attempts to modify such an array, the behavior is - undefined. -8 EXAMPLE 1 This pair of adjacent character string literals - "\x12" "3" - produces a single character string literal containing the two characters whose values are '\x12' and '3', - because escape sequences are converted into single members of the execution character set just prior to - adjacent string literal concatenation. - -9 EXAMPLE 2 Each of the sequences of adjacent string literal tokens - - - - 78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a - \0 escape sequence. - -[page 71] (Contents) - - "a" "b" L"c" - "a" L"b" "c" - L"a" "b" L"c" - L"a" L"b" L"c" - is equivalent to the string literal - L"abc" - Likewise, each of the sequences - "a" "b" u"c" - "a" u"b" "c" - u"a" "b" u"c" - u"a" u"b" u"c" - is equivalent to - u"abc" - - Forward references: common definitions <stddef.h> (7.19), the mbstowcs - function (7.22.8.1), Unicode utilities <uchar.h> (7.27). - 6.4.6 Punctuators - Syntax -1 punctuator: one of - [ ] ( ) { } . -> - ++ -- & * + - ~ ! - / % << >> < > <= >= == != ^ | && || - ? : ; ... - = *= /= %= += -= <<= >>= &= ^= |= - , # ## - <: :> <% %> %: %:%: - Semantics -2 A punctuator is a symbol that has independent syntactic and semantic significance. - Depending on context, it may specify an operation to be performed (which in turn may - yield a value or a function designator, produce a side effect, or some combination thereof) - in which case it is known as an operator (other forms of operator also exist in some - contexts). An operand is an entity on which an operator acts. - - - - -[page 72] (Contents) - -3 In all aspects of the language, the six tokens79) - <: :> <% %> %: %:%: - behave, respectively, the same as the six tokens - [ ] { } # ## - except for their spelling.80) - Forward references: expressions (6.5), declarations (6.7), preprocessing directives - (6.10), statements (6.8). - 6.4.7 Header names - Syntax -1 header-name: - < h-char-sequence > - " q-char-sequence " - h-char-sequence: - h-char - h-char-sequence h-char - h-char: - any member of the source character set except - the new-line character and > - q-char-sequence: - q-char - q-char-sequence q-char - q-char: - any member of the source character set except - the new-line character and " - Semantics -2 The sequences in both forms of header names are mapped in an implementation-defined - manner to headers or external source file names as specified in 6.10.2. -3 If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters, - the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the - - - - - 79) These tokens are sometimes called ''digraphs''. - 80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely - interchanged. - -[page 73] (Contents) - - sequence between the " delimiters, the behavior is undefined.81) Header name - preprocessing tokens are recognized only within #include preprocessing directives and - in implementation-defined locations within #pragma directives.82) -4 EXAMPLE The following sequence of characters: - 0x3<1/a.h>1e2 - #include <1/a.h> - #define const.member@$ - forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited - by a { on the left and a } on the right). - {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2} - {#}{include} {<1/a.h>} - {#}{define} {const}{.}{member}{@}{$} - - Forward references: source file inclusion (6.10.2). - 6.4.8 Preprocessing numbers - Syntax -1 pp-number: - digit - . digit - pp-number digit - pp-number identifier-nondigit - pp-number e sign - pp-number E sign - pp-number p sign - pp-number P sign - pp-number . - Description -2 A preprocessing number begins with a digit optionally preceded by a period (.) and may - be followed by valid identifier characters and the character sequences e+, e-, E+, E-, - p+, p-, P+, or P-. -3 Preprocessing number tokens lexically include all floating and integer constant tokens. - Semantics -4 A preprocessing number does not have type or a value; it acquires both after a successful - conversion (as part of translation phase 7) to a floating constant token or an integer - constant token. - - - 81) Thus, sequences of characters that resemble escape sequences cause undefined behavior. - 82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9. - -[page 74] (Contents) - - 6.4.9 Comments -1 Except within a character constant, a string literal, or a comment, the characters /* - introduce a comment. The contents of such a comment are examined only to identify - multibyte characters and to find the characters */ that terminate it.83) -2 Except within a character constant, a string literal, or a comment, the characters // - introduce a comment that includes all multibyte characters up to, but not including, the - next new-line character. The contents of such a comment are examined only to identify - multibyte characters and to find the terminating new-line character. -3 EXAMPLE - "a//b" // four-character string literal - #include "//e" // undefined behavior - // */ // comment, not syntax error - f = g/**//h; // equivalent to f = g / h; - //\ - i(); // part of a two-line comment - /\ - / j(); // part of a two-line comment - #define glue(x,y) x##y - glue(/,/) k(); // syntax error, not comment - /*//*/ l(); // equivalent to l(); - m = n//**/o - + p; // equivalent to m = n + p; - - - - - 83) Thus, /* ... */ comments do not nest. - -[page 75] (Contents) - - 6.5 Expressions -1 An expression is a sequence of operators and operands that specifies computation of a - value, or that designates an object or a function, or that generates side effects, or that - performs a combination thereof. The value computations of the operands of an operator - are sequenced before the value computation of the result of the operator. -2 If a side effect on a scalar object is unsequenced relative to either a different side effect - on the same scalar object or a value computation using the value of the same scalar - object, the behavior is undefined. If there are multiple allowable orderings of the - subexpressions of an expression, the behavior is undefined if such an unsequenced side - effect occurs in any of the orderings.84) -3 The grouping of operators and operands is indicated by the syntax.85) Except as specified - later, side effects and value computations of subexpressions are unsequenced.86) * -4 Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, - collectively described as bitwise operators) are required to have operands that have - integer type. These operators yield values that depend on the internal representations of - integers, and have implementation-defined and undefined aspects for signed types. -5 If an exceptional condition occurs during the evaluation of an expression (that is, if the - result is not mathematically defined or not in the range of representable values for its - type), the behavior is undefined. - - - - 84) This paragraph renders undefined statement expressions such as - i = ++i + 1; - a[i++] = i; - while allowing - i = i + 1; - a[i] = i; - - 85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same - as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the - expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in - 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators - (6.5.3), and an operand contained between any of the following pairs of operators: grouping - parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and - the conditional operator ? : (6.5.15). - Within each major subclause, the operators have the same precedence. Left- or right-associativity is - indicated in each subclause by the syntax for the expressions discussed therein. - 86) In an expression that is evaluated more than once during the execution of a program, unsequenced and - indeterminately sequenced evaluations of its subexpressions need not be performed consistently in - different evaluations. - -[page 76] (Contents) - -6 The effective type of an object for an access to its stored value is the declared type of the - object, if any.87) If a value is stored into an object having no declared type through an - lvalue having a type that is not a character type, then the type of the lvalue becomes the - effective type of the object for that access and for subsequent accesses that do not modify - the stored value. If a value is copied into an object having no declared type using - memcpy or memmove, or is copied as an array of character type, then the effective type - of the modified object for that access and for subsequent accesses that do not modify the - value is the effective type of the object from which the value is copied, if it has one. For - all other accesses to an object having no declared type, the effective type of the object is - simply the type of the lvalue used for the access. -7 An object shall have its stored value accessed only by an lvalue expression that has one of - the following types:88) - -- a type compatible with the effective type of the object, - -- a qualified version of a type compatible with the effective type of the object, - -- a type that is the signed or unsigned type corresponding to the effective type of the - object, - -- a type that is the signed or unsigned type corresponding to a qualified version of the - effective type of the object, - -- an aggregate or union type that includes one of the aforementioned types among its - members (including, recursively, a member of a subaggregate or contained union), or - -- a character type. -8 A floating expression may be contracted, that is, evaluated as though it were a single - operation, thereby omitting rounding errors implied by the source code and the - expression evaluation method.89) The FP_CONTRACT pragma in <math.h> provides a - way to disallow contracted expressions. Otherwise, whether and how expressions are - contracted is implementation-defined.90) - Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2). - - - 87) Allocated objects have no declared type. - 88) The intent of this list is to specify those circumstances in which an object may or may not be aliased. - 89) The intermediate operations in the contracted expression are evaluated as if to infinite precision and - range, while the final operation is rounded to the format determined by the expression evaluation - method. A contracted expression might also omit the raising of floating-point exceptions. - 90) This license is specifically intended to allow implementations to exploit fast machine instructions that - combine multiple C operators. As contractions potentially undermine predictability, and can even - decrease accuracy for containing expressions, their use needs to be well-defined and clearly - documented. - -[page 77] (Contents) - - 6.5.1 Primary expressions - Syntax -1 primary-expression: - identifier - constant - string-literal - ( expression ) - generic-selection - Semantics -2 An identifier is a primary expression, provided it has been declared as designating an - object (in which case it is an lvalue) or a function (in which case it is a function - designator).91) -3 A constant is a primary expression. Its type depends on its form and value, as detailed in - 6.4.4. -4 A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5. -5 A parenthesized expression is a primary expression. Its type and value are identical to - those of the unparenthesized expression. It is an lvalue, a function designator, or a void - expression if the unparenthesized expression is, respectively, an lvalue, a function - designator, or a void expression. - Forward references: declarations (6.7). - 6.5.1.1 Generic selection - Syntax -1 generic-selection: - _Generic ( assignment-expression , generic-assoc-list ) - generic-assoc-list: - generic-association - generic-assoc-list , generic-association - generic-association: - type-name : assignment-expression - default : assignment-expression - Constraints -2 A generic selection shall have no more than one default generic association. The type - name in a generic association shall specify a complete object type other than a variably - - 91) Thus, an undeclared identifier is a violation of the syntax. - -[page 78] (Contents) - - modified type. No two generic associations in the same generic selection shall specify - compatible types. The controlling expression of a generic selection shall have type - compatible with at most one of the types named in its generic association list. If a - generic selection has no default generic association, its controlling expression shall - have type compatible with exactly one of the types named in its generic association list. - Semantics -3 The controlling expression of a generic selection is not evaluated. If a generic selection - has a generic association with a type name that is compatible with the type of the - controlling expression, then the result expression of the generic selection is the - expression in that generic association. Otherwise, the result expression of the generic - selection is the expression in the default generic association. None of the expressions - from any other generic association of the generic selection is evaluated. -4 The type and value of a generic selection are identical to those of its result expression. It - is an lvalue, a function designator, or a void expression if its result expression is, - respectively, an lvalue, a function designator, or a void expression. -5 EXAMPLE The cbrt type-generic macro could be implemented as follows: - #define cbrt(X) _Generic((X), \ - long double: cbrtl, \ - default: cbrt, \ - float: cbrtf \ - )(X) - - 6.5.2 Postfix operators - Syntax -1 postfix-expression: - primary-expression - postfix-expression [ expression ] - postfix-expression ( argument-expression-listopt ) - postfix-expression . identifier - postfix-expression -> identifier - postfix-expression ++ - postfix-expression -- - ( type-name ) { initializer-list } - ( type-name ) { initializer-list , } - argument-expression-list: - assignment-expression - argument-expression-list , assignment-expression - - - - -[page 79] (Contents) - - 6.5.2.1 Array subscripting - Constraints -1 One of the expressions shall have type ''pointer to complete object type'', the other - expression shall have integer type, and the result has type ''type''. - Semantics -2 A postfix expression followed by an expression in square brackets [] is a subscripted - designation of an element of an array object. The definition of the subscript operator [] - is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that - apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the - initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th - element of E1 (counting from zero). -3 Successive subscript operators designate an element of a multidimensional array object. - If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as - other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with - dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or - implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional - array, which itself is converted into a pointer if used as other than an lvalue. It follows - from this that arrays are stored in row-major order (last subscript varies fastest). -4 EXAMPLE Consider the array object defined by the declaration - int x[3][5]; - Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an - array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to - a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually - entails multiplying i by the size of the object to which the pointer points, namely an array of five int - objects. The results are added and indirection is applied to yield an array of five ints. When used in the - expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j] - yields an int. - - Forward references: additive operators (6.5.6), address and indirection operators - (6.5.3.2), array declarators (6.7.6.2). - 6.5.2.2 Function calls - Constraints -1 The expression that denotes the called function92) shall have type pointer to function - returning void or returning a complete object type other than an array type. -2 If the expression that denotes the called function has a type that includes a prototype, the - number of arguments shall agree with the number of parameters. Each argument shall - - - 92) Most often, this is the result of converting an identifier that is a function designator. - -[page 80] (Contents) - - have a type such that its value may be assigned to an object with the unqualified version - of the type of its corresponding parameter. - Semantics -3 A postfix expression followed by parentheses () containing a possibly empty, comma- - separated list of expressions is a function call. The postfix expression denotes the called - function. The list of expressions specifies the arguments to the function. -4 An argument may be an expression of any complete object type. In preparing for the call - to a function, the arguments are evaluated, and each parameter is assigned the value of the - corresponding argument.93) -5 If the expression that denotes the called function has type pointer to function returning an - object type, the function call expression has the same type as that object type, and has the - value determined as specified in 6.8.6.4. Otherwise, the function call has type void. * -6 If the expression that denotes the called function has a type that does not include a - prototype, the integer promotions are performed on each argument, and arguments that - have type float are promoted to double. These are called the default argument - promotions. If the number of arguments does not equal the number of parameters, the - behavior is undefined. If the function is defined with a type that includes a prototype, and - either the prototype ends with an ellipsis (, ...) or the types of the arguments after - promotion are not compatible with the types of the parameters, the behavior is undefined. - If the function is defined with a type that does not include a prototype, and the types of - the arguments after promotion are not compatible with those of the parameters after - promotion, the behavior is undefined, except for the following cases: - -- one promoted type is a signed integer type, the other promoted type is the - corresponding unsigned integer type, and the value is representable in both types; - -- both types are pointers to qualified or unqualified versions of a character type or - void. -7 If the expression that denotes the called function has a type that does include a prototype, - the arguments are implicitly converted, as if by assignment, to the types of the - corresponding parameters, taking the type of each parameter to be the unqualified version - of its declared type. The ellipsis notation in a function prototype declarator causes - argument type conversion to stop after the last declared parameter. The default argument - promotions are performed on trailing arguments. - - - - 93) A function may change the values of its parameters, but these changes cannot affect the values of the - arguments. On the other hand, it is possible to pass a pointer to an object, and the function may - change the value of the object pointed to. A parameter declared to have array or function type is - adjusted to have a pointer type as described in 6.9.1. - -[page 81] (Contents) - -8 No other conversions are performed implicitly; in particular, the number and types of - arguments are not compared with those of the parameters in a function definition that - does not include a function prototype declarator. -9 If the function is defined with a type that is not compatible with the type (of the - expression) pointed to by the expression that denotes the called function, the behavior is - undefined. -10 There is a sequence point after the evaluations of the function designator and the actual - arguments but before the actual call. Every evaluation in the calling function (including - other function calls) that is not otherwise specifically sequenced before or after the - execution of the body of the called function is indeterminately sequenced with respect to - the execution of the called function.94) -11 Recursive function calls shall be permitted, both directly and indirectly through any chain - of other functions. -12 EXAMPLE In the function call - (*pf[f1()]) (f2(), f3() + f4()) - the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before - the function pointed to by pf[f1()] is called. - - Forward references: function declarators (including prototypes) (6.7.6.3), function - definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1). - 6.5.2.3 Structure and union members - Constraints -1 The first operand of the . operator shall have an atomic, qualified, or unqualified - structure or union type, and the second operand shall name a member of that type. -2 The first operand of the -> operator shall have type ''pointer to atomic, qualified, or - unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the - second operand shall name a member of the type pointed to. - Semantics -3 A postfix expression followed by the . operator and an identifier designates a member of - a structure or union object. The value is that of the named member,95) and is an lvalue if - the first expression is an lvalue. If the first expression has qualified type, the result has - the so-qualified version of the type of the designated member. - - 94) In other words, function executions do not ''interleave'' with each other. - 95) If the member used to read the contents of a union object is not the same as the member last used to - store a value in the object, the appropriate part of the object representation of the value is reinterpreted - as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type - punning''). This might be a trap representation. - -[page 82] (Contents) - -4 A postfix expression followed by the -> operator and an identifier designates a member - of a structure or union object. The value is that of the named member of the object to - which the first expression points, and is an lvalue.96) If the first expression is a pointer to - a qualified type, the result has the so-qualified version of the type of the designated - member. -5 Accessing a member of an atomic structure or union object results in undefined - behavior.97) -6 One special guarantee is made in order to simplify the use of unions: if a union contains - several structures that share a common initial sequence (see below), and if the union - object currently contains one of these structures, it is permitted to inspect the common - initial part of any of them anywhere that a declaration of the completed type of the union - is visible. Two structures share a common initial sequence if corresponding members - have compatible types (and, for bit-fields, the same widths) for a sequence of one or more - initial members. -7 EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or - union, f().x is a valid postfix expression but is not an lvalue. - -8 EXAMPLE 2 In: - struct s { int i; const int ci; }; - struct s s; - const struct s cs; - volatile struct s vs; - the various members have the types: - s.i int - s.ci const int - cs.i const int - cs.ci const int - vs.i volatile int - vs.ci volatile const int - - - - - 96) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to - its operand), the expression (&E)->MOS is the same as E.MOS. - 97) For example, a data race would occur if access to the entire structure or union in one thread conflicts - with access to a member from another thread, where at least one access is a modification. Members - can be safely accessed using a non-atomic object which is assigned to or from the atomic object. - -[page 83] (Contents) - -9 EXAMPLE 3 The following is a valid fragment: - union { - struct { - int alltypes; - } n; - struct { - int type; - int intnode; - } ni; - struct { - int type; - double doublenode; - } nf; - } u; - u.nf.type = 1; - u.nf.doublenode = 3.14; - /* ... */ - if (u.n.alltypes == 1) - if (sin(u.nf.doublenode) == 0.0) - /* ... */ - The following is not a valid fragment (because the union type is not visible within function f): - struct t1 { int m; }; - struct t2 { int m; }; - int f(struct t1 *p1, struct t2 *p2) - { - if (p1->m < 0) - p2->m = -p2->m; - return p1->m; - } - int g() - { - union { - struct t1 s1; - struct t2 s2; - } u; - /* ... */ - return f(&u.s1, &u.s2); - } - - Forward references: address and indirection operators (6.5.3.2), structure and union - specifiers (6.7.2.1). - - - - -[page 84] (Contents) - - 6.5.2.4 Postfix increment and decrement operators - Constraints -1 The operand of the postfix increment or decrement operator shall have atomic, qualified, - or unqualified real or pointer type, and shall be a modifiable lvalue. - Semantics -2 The result of the postfix ++ operator is the value of the operand. As a side effect, the - value of the operand object is incremented (that is, the value 1 of the appropriate type is - added to it). See the discussions of additive operators and compound assignment for - information on constraints, types, and conversions and the effects of operations on - pointers. The value computation of the result is sequenced before the side effect of - updating the stored value of the operand. With respect to an indeterminately-sequenced - function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object - with atomic type is a read-modify-write operation with memory_order_seq_cst - memory order semantics.98) -3 The postfix -- operator is analogous to the postfix ++ operator, except that the value of - the operand is decremented (that is, the value 1 of the appropriate type is subtracted from - it). - Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). - 6.5.2.5 Compound literals - Constraints -1 The type name shall specify a complete object type or an array of unknown size, but not a - variable length array type. -2 All the constraints for initializer lists in 6.7.9 also apply to compound literals. - Semantics -3 A postfix expression that consists of a parenthesized type name followed by a brace- - enclosed list of initializers is a compound literal. It provides an unnamed object whose - value is given by the initializer list.99) - - - 98) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence - where T is the type of E: - T tmp; - T result = E; - do { - tmp = result + 1; - } while (!atomic_compare_exchange_strong(&E, &result, tmp)); - with result being the result of the operation. - -[page 85] (Contents) - -4 If the type name specifies an array of unknown size, the size is determined by the - initializer list as specified in 6.7.9, and the type of the compound literal is that of the - completed array type. Otherwise (when the type name specifies an object type), the type - of the compound literal is that specified by the type name. In either case, the result is an - lvalue. -5 The value of the compound literal is that of an unnamed object initialized by the - initializer list. If the compound literal occurs outside the body of a function, the object - has static storage duration; otherwise, it has automatic storage duration associated with - the enclosing block. -6 All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100) -7 String literals, and compound literals with const-qualified types, need not designate - distinct objects.101) -8 EXAMPLE 1 The file scope definition - int *p = (int []){2, 4}; - initializes p to point to the first element of an array of two ints, the first having the value two and the - second, four. The expressions in this compound literal are required to be constant. The unnamed object - has static storage duration. - -9 EXAMPLE 2 In contrast, in - void f(void) - { - int *p; - /*...*/ - p = (int [2]){*p}; - /*...*/ - } - p is assigned the address of the first element of an array of two ints, the first having the value previously - pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The - unnamed object has automatic storage duration. - -10 EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects - created using compound literals can be passed to functions without depending on member order: - drawline((struct point){.x=1, .y=1}, - (struct point){.x=3, .y=4}); - Or, if drawline instead expected pointers to struct point: - - - - 99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types - or void only, and the result of a cast expression is not an lvalue. - 100) For example, subobjects without explicit initializers are initialized to zero. - 101) This allows implementations to share storage for string literals and constant compound literals with - the same or overlapping representations. - -[page 86] (Contents) - - drawline(&(struct point){.x=1, .y=1}, - &(struct point){.x=3, .y=4}); - -11 EXAMPLE 4 A read-only compound literal can be specified through constructions like: - (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6} - -12 EXAMPLE 5 The following three expressions have different meanings: - "/tmp/fileXXXXXX" - (char []){"/tmp/fileXXXXXX"} - (const char []){"/tmp/fileXXXXXX"} - The first always has static storage duration and has type array of char, but need not be modifiable; the last - two have automatic storage duration when they occur within the body of a function, and the first of these - two is modifiable. - -13 EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory - and can even be shared. For example, - (const char []){"abc"} == "abc" - might yield 1 if the literals' storage is shared. - -14 EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly - linked object. For example, there is no way to write a self-referential compound literal that could be used - as the function argument in place of the named object endless_zeros below: - struct int_list { int car; struct int_list *cdr; }; - struct int_list endless_zeros = {0, &endless_zeros}; - eval(endless_zeros); - -15 EXAMPLE 8 Each compound literal creates only a single object in a given scope: - struct s { int i; }; - int f (void) - { - struct s *p = 0, *q; - int j = 0; - again: - q = p, p = &((struct s){ j++ }); - if (j < 2) goto again; - return p == q && q->i == 1; - } - The function f() always returns the value 1. -16 Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the - lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would - have an indeterminate value, which would result in undefined behavior. - - Forward references: type names (6.7.7), initialization (6.7.9). - - - - -[page 87] (Contents) - - 6.5.3 Unary operators - Syntax -1 unary-expression: - postfix-expression - ++ unary-expression - -- unary-expression - unary-operator cast-expression - sizeof unary-expression - sizeof ( type-name ) - alignof ( type-name ) - unary-operator: one of - & * + - ~ ! - 6.5.3.1 Prefix increment and decrement operators - Constraints -1 The operand of the prefix increment or decrement operator shall have atomic, qualified, - or unqualified real or pointer type, and shall be a modifiable lvalue. - Semantics -2 The value of the operand of the prefix ++ operator is incremented. The result is the new - value of the operand after incrementation. The expression ++E is equivalent to (E+=1). - See the discussions of additive operators and compound assignment for information on - constraints, types, side effects, and conversions and the effects of operations on pointers. -3 The prefix -- operator is analogous to the prefix ++ operator, except that the value of the - operand is decremented. - Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). - 6.5.3.2 Address and indirection operators - Constraints -1 The operand of the unary & operator shall be either a function designator, the result of a - [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is - not declared with the register storage-class specifier. -2 The operand of the unary * operator shall have pointer type. - Semantics -3 The unary & operator yields the address of its operand. If the operand has type ''type'', - the result has type ''pointer to type''. If the operand is the result of a unary * operator, - neither that operator nor the & operator is evaluated and the result is as if both were - omitted, except that the constraints on the operators still apply and the result is not an - -[page 88] (Contents) - - lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor - the unary * that is implied by the [] is evaluated and the result is as if the & operator - were removed and the [] operator were changed to a + operator. Otherwise, the result is - a pointer to the object or function designated by its operand. -4 The unary * operator denotes indirection. If the operand points to a function, the result is - a function designator; if it points to an object, the result is an lvalue designating the - object. If the operand has type ''pointer to type'', the result has type ''type''. If an - invalid value has been assigned to the pointer, the behavior of the unary * operator is - undefined.102) - Forward references: storage-class specifiers (6.7.1), structure and union specifiers - (6.7.2.1). - 6.5.3.3 Unary arithmetic operators - Constraints -1 The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, - integer type; of the ! operator, scalar type. - Semantics -2 The result of the unary + operator is the value of its (promoted) operand. The integer - promotions are performed on the operand, and the result has the promoted type. -3 The result of the unary - operator is the negative of its (promoted) operand. The integer - promotions are performed on the operand, and the result has the promoted type. -4 The result of the ~ operator is the bitwise complement of its (promoted) operand (that is, - each bit in the result is set if and only if the corresponding bit in the converted operand is - not set). The integer promotions are performed on the operand, and the result has the - promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent - to the maximum value representable in that type minus E. -5 The result of the logical negation operator ! is 0 if the value of its operand compares - unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. - The expression !E is equivalent to (0==E). - - - - 102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is - always true that if E is a function designator or an lvalue that is a valid operand of the unary & - operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of - an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. - Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an - address inappropriately aligned for the type of object pointed to, and the address of an object after the - end of its lifetime. - -[page 89] (Contents) - - 6.5.3.4 The sizeof and alignof operators - Constraints -1 The sizeof operator shall not be applied to an expression that has function type or an - incomplete type, to the parenthesized name of such a type, or to an expression that - designates a bit-field member. The alignof operator shall not be applied to a function - type or an incomplete type. - Semantics -2 The sizeof operator yields the size (in bytes) of its operand, which may be an - expression or the parenthesized name of a type. The size is determined from the type of - the operand. The result is an integer. If the type of the operand is a variable length array - type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an - integer constant. -3 The alignof operator yields the alignment requirement of its operand type. The result - is an integer constant. When applied to an array type, the result is the alignment - requirement of the element type. -4 When sizeof is applied to an operand that has type char, unsigned char, or - signed char, (or a qualified version thereof) the result is 1. When applied to an - operand that has array type, the result is the total number of bytes in the array.103) When - applied to an operand that has structure or union type, the result is the total number of - bytes in such an object, including internal and trailing padding. -5 The value of the result of both operators is implementation-defined, and its type (an - unsigned integer type) is size_t, defined in <stddef.h> (and other headers). -6 EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage - allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to - allocate and return a pointer to void. For example: - extern void *alloc(size_t); - double *dp = alloc(sizeof *dp); - The implementation of the alloc function should ensure that its return value is aligned suitably for - conversion to a pointer to double. - -7 EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array: - sizeof array / sizeof array[0] - -8 EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a - function: - #include <stddef.h> - - - - 103) When applied to a parameter declared to have array or function type, the sizeof operator yields the - size of the adjusted (pointer) type (see 6.9.1). - -[page 90] (Contents) - - size_t fsize3(int n) - { - char b[n+3]; // variable length array - return sizeof b; // execution time sizeof - } - int main() - { - size_t size; - size = fsize3(10); // fsize3 returns 13 - return 0; - } - - Forward references: common definitions <stddef.h> (7.19), declarations (6.7), - structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2). - 6.5.4 Cast operators - Syntax -1 cast-expression: - unary-expression - ( type-name ) cast-expression - Constraints -2 Unless the type name specifies a void type, the type name shall specify atomic, qualified, - or unqualified scalar type, and the operand shall have scalar type. -3 Conversions that involve pointers, other than where permitted by the constraints of - 6.5.16.1, shall be specified by means of an explicit cast. -4 A pointer type shall not be converted to any floating type. A floating type shall not be - converted to any pointer type. - Semantics -5 Preceding an expression by a parenthesized type name converts the value of the - expression to the named type. This construction is called a cast.104) A cast that specifies - no conversion has no effect on the type or value of an expression. -6 If the value of the expression is represented with greater precision or range than required - by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the - type of the expression is the same as the named type and removes any extra range and - precision. - Forward references: equality operators (6.5.9), function declarators (including - prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7). - - 104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the - unqualified version of the type. - -[page 91] (Contents) - - 6.5.5 Multiplicative operators - Syntax -1 multiplicative-expression: - cast-expression - multiplicative-expression * cast-expression - multiplicative-expression / cast-expression - multiplicative-expression % cast-expression - Constraints -2 Each of the operands shall have arithmetic type. The operands of the % operator shall - have integer type. - Semantics -3 The usual arithmetic conversions are performed on the operands. -4 The result of the binary * operator is the product of the operands. -5 The result of the / operator is the quotient from the division of the first operand by the - second; the result of the % operator is the remainder. In both operations, if the value of - the second operand is zero, the behavior is undefined. -6 When integers are divided, the result of the / operator is the algebraic quotient with any - fractional part discarded.105) If the quotient a/b is representable, the expression - (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is - undefined. - 6.5.6 Additive operators - Syntax -1 additive-expression: - multiplicative-expression - additive-expression + multiplicative-expression - additive-expression - multiplicative-expression - Constraints -2 For addition, either both operands shall have arithmetic type, or one operand shall be a - pointer to a complete object type and the other shall have integer type. (Incrementing is - equivalent to adding 1.) -3 For subtraction, one of the following shall hold: - - - - - 105) This is often called ''truncation toward zero''. - -[page 92] (Contents) - - -- both operands have arithmetic type; - -- both operands are pointers to qualified or unqualified versions of compatible complete - object types; or - -- the left operand is a pointer to a complete object type and the right operand has - integer type. - (Decrementing is equivalent to subtracting 1.) - Semantics -4 If both operands have arithmetic type, the usual arithmetic conversions are performed on - them. -5 The result of the binary + operator is the sum of the operands. -6 The result of the binary - operator is the difference resulting from the subtraction of the - second operand from the first. -7 For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. -8 When an expression that has integer type is added to or subtracted from a pointer, the - result has the type of the pointer operand. If the pointer operand points to an element of - an array object, and the array is large enough, the result points to an element offset from - the original element such that the difference of the subscripts of the resulting and original - array elements equals the integer expression. In other words, if the expression P points to - the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and - (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of - the array object, provided they exist. Moreover, if the expression P points to the last - element of an array object, the expression (P)+1 points one past the last element of the - array object, and if the expression Q points one past the last element of an array object, - the expression (Q)-1 points to the last element of the array object. If both the pointer - operand and the result point to elements of the same array object, or one past the last - element of the array object, the evaluation shall not produce an overflow; otherwise, the - behavior is undefined. If the result points one past the last element of the array object, it - shall not be used as the operand of a unary * operator that is evaluated. -9 When two pointers are subtracted, both shall point to elements of the same array object, - or one past the last element of the array object; the result is the difference of the - subscripts of the two array elements. The size of the result is implementation-defined, - and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. - If the result is not representable in an object of that type, the behavior is undefined. In - other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of - an array object, the expression (P)-(Q) has the value i-j provided the value fits in an - -[page 93] (Contents) - - object of type ptrdiff_t. Moreover, if the expression P points either to an element of - an array object or one past the last element of an array object, and the expression Q points - to the last element of the same array object, the expression ((Q)+1)-(P) has the same - value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the - expression P points one past the last element of the array object, even though the - expression (Q)+1 does not point to an element of the array object.106) -10 EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types. - { - int n = 4, m = 3; - int a[n][m]; - int (*p)[m] = a; // p == &a[0] - p += 1; // p == &a[1] - (*p)[2] = 99; // a[1][2] == 99 - n = p - a; // n == 1 - } -11 If array a in the above example were declared to be an array of known constant size, and pointer p were - declared to be a pointer to an array of the same known constant size (pointing to a), the results would be - the same. - - Forward references: array declarators (6.7.6.2), common definitions <stddef.h> - (7.19). - 6.5.7 Bitwise shift operators - Syntax -1 shift-expression: - additive-expression - shift-expression << additive-expression - shift-expression >> additive-expression - Constraints -2 Each of the operands shall have integer type. - Semantics -3 The integer promotions are performed on each of the operands. The type of the result is - that of the promoted left operand. If the value of the right operand is negative or is - - 106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In - this scheme the integer expression added to or subtracted from the converted pointer is first multiplied - by the size of the object originally pointed to, and the resulting pointer is converted back to the - original type. For pointer subtraction, the result of the difference between the character pointers is - similarly divided by the size of the object originally pointed to. - When viewed in this way, an implementation need only provide one extra byte (which may overlap - another object in the program) just after the end of the object in order to satisfy the ''one past the last - element'' requirements. - -[page 94] (Contents) - - greater than or equal to the width of the promoted left operand, the behavior is undefined. -4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with - zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo - one more than the maximum value representable in the result type. If E1 has a signed - type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is - the resulting value; otherwise, the behavior is undefined. -5 The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type - or if E1 has a signed type and a nonnegative value, the value of the result is the integral - part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the - resulting value is implementation-defined. - 6.5.8 Relational operators - Syntax -1 relational-expression: - shift-expression - relational-expression < shift-expression - relational-expression > shift-expression - relational-expression <= shift-expression - relational-expression >= shift-expression - Constraints -2 One of the following shall hold: - -- both operands have real type; or * - -- both operands are pointers to qualified or unqualified versions of compatible object - types. - Semantics -3 If both of the operands have arithmetic type, the usual arithmetic conversions are - performed. -4 For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. -5 When two pointers are compared, the result depends on the relative locations in the - address space of the objects pointed to. If two pointers to object types both point to the - same object, or both point one past the last element of the same array object, they - compare equal. If the objects pointed to are members of the same aggregate object, - pointers to structure members declared later compare greater than pointers to members - declared earlier in the structure, and pointers to array elements with larger subscript - values compare greater than pointers to elements of the same array with lower subscript - -[page 95] (Contents) - - values. All pointers to members of the same union object compare equal. If the - expression P points to an element of an array object and the expression Q points to the - last element of the same array object, the pointer expression Q+1 compares greater than - P. In all other cases, the behavior is undefined. -6 Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= - (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is - false.107) The result has type int. - 6.5.9 Equality operators - Syntax -1 equality-expression: - relational-expression - equality-expression == relational-expression - equality-expression != relational-expression - Constraints -2 One of the following shall hold: - -- both operands have arithmetic type; - -- both operands are pointers to qualified or unqualified versions of compatible types; - -- one operand is a pointer to an object type and the other is a pointer to a qualified or - unqualified version of void; or - -- one operand is a pointer and the other is a null pointer constant. - Semantics -3 The == (equal to) and != (not equal to) operators are analogous to the relational - operators except for their lower precedence.108) Each of the operators yields 1 if the - specified relation is true and 0 if it is false. The result has type int. For any pair of - operands, exactly one of the relations is true. -4 If both of the operands have arithmetic type, the usual arithmetic conversions are - performed. Values of complex types are equal if and only if both their real parts are equal - and also their imaginary parts are equal. Any two values of arithmetic types from - different type domains are equal if and only if the results of their conversions to the - (complex) result type determined by the usual arithmetic conversions are equal. - - - - 107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it - means (a<b)<c; in other words, ''if a is less than b, compare 1 to c; otherwise, compare 0 to c''. - 108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value. - -[page 96] (Contents) - -5 Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a - null pointer constant, the null pointer constant is converted to the type of the pointer. If - one operand is a pointer to an object type and the other is a pointer to a qualified or - unqualified version of void, the former is converted to the type of the latter. -6 Two pointers compare equal if and only if both are null pointers, both are pointers to the - same object (including a pointer to an object and a subobject at its beginning) or function, - both are pointers to one past the last element of the same array object, or one is a pointer - to one past the end of one array object and the other is a pointer to the start of a different - array object that happens to immediately follow the first array object in the address - space.109) -7 For the purposes of these operators, a pointer to an object that is not an element of an - array behaves the same as a pointer to the first element of an array of length one with the - type of the object as its element type. - 6.5.10 Bitwise AND operator - Syntax -1 AND-expression: - equality-expression - AND-expression & equality-expression - Constraints -2 Each of the operands shall have integer type. - Semantics -3 The usual arithmetic conversions are performed on the operands. -4 The result of the binary & operator is the bitwise AND of the operands (that is, each bit in - the result is set if and only if each of the corresponding bits in the converted operands is - set). - - - - - 109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or - adjacent members of a structure with no padding between them, or because the implementation chose - to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses - outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined - behavior. - -[page 97] (Contents) - - 6.5.11 Bitwise exclusive OR operator - Syntax -1 exclusive-OR-expression: - AND-expression - exclusive-OR-expression ^ AND-expression - Constraints -2 Each of the operands shall have integer type. - Semantics -3 The usual arithmetic conversions are performed on the operands. -4 The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit - in the result is set if and only if exactly one of the corresponding bits in the converted - operands is set). - 6.5.12 Bitwise inclusive OR operator - Syntax -1 inclusive-OR-expression: - exclusive-OR-expression - inclusive-OR-expression | exclusive-OR-expression - Constraints -2 Each of the operands shall have integer type. - Semantics -3 The usual arithmetic conversions are performed on the operands. -4 The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in - the result is set if and only if at least one of the corresponding bits in the converted - operands is set). - - - - -[page 98] (Contents) - - 6.5.13 Logical AND operator - Syntax -1 logical-AND-expression: - inclusive-OR-expression - logical-AND-expression && inclusive-OR-expression - Constraints -2 Each of the operands shall have scalar type. - Semantics -3 The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it - yields 0. The result has type int. -4 Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation; - if the second operand is evaluated, there is a sequence point between the evaluations of - the first and second operands. If the first operand compares equal to 0, the second - operand is not evaluated. - 6.5.14 Logical OR operator - Syntax -1 logical-OR-expression: - logical-AND-expression - logical-OR-expression || logical-AND-expression - Constraints -2 Each of the operands shall have scalar type. - Semantics -3 The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it - yields 0. The result has type int. -4 Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the - second operand is evaluated, there is a sequence point between the evaluations of the first - and second operands. If the first operand compares unequal to 0, the second operand is - not evaluated. - - - - -[page 99] (Contents) - - 6.5.15 Conditional operator - Syntax -1 conditional-expression: - logical-OR-expression - logical-OR-expression ? expression : conditional-expression - Constraints -2 The first operand shall have scalar type. -3 One of the following shall hold for the second and third operands: - -- both operands have arithmetic type; - -- both operands have the same structure or union type; - -- both operands have void type; - -- both operands are pointers to qualified or unqualified versions of compatible types; - -- one operand is a pointer and the other is a null pointer constant; or - -- one operand is a pointer to an object type and the other is a pointer to a qualified or - unqualified version of void. - Semantics -4 The first operand is evaluated; there is a sequence point between its evaluation and the - evaluation of the second or third operand (whichever is evaluated). The second operand - is evaluated only if the first compares unequal to 0; the third operand is evaluated only if - the first compares equal to 0; the result is the value of the second or third operand - (whichever is evaluated), converted to the type described below.110) * -5 If both the second and third operands have arithmetic type, the result type that would be - determined by the usual arithmetic conversions, were they applied to those two operands, - is the type of the result. If both the operands have structure or union type, the result has - that type. If both operands have void type, the result has void type. -6 If both the second and third operands are pointers or one is a null pointer constant and the - other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers - of the types referenced by both operands. Furthermore, if both operands are pointers to - compatible types or to differently qualified versions of compatible types, the result type is - a pointer to an appropriately qualified version of the composite type; if one operand is a - null pointer constant, the result has the type of the other operand; otherwise, one operand - is a pointer to void or a qualified version of void, in which case the result type is a - pointer to an appropriately qualified version of void. - - 110) A conditional expression does not yield an lvalue. - -[page 100] (Contents) - -7 EXAMPLE The common type that results when the second and third operands are pointers is determined - in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two - pointers have compatible types. -8 Given the declarations - const void *c_vp; - void *vp; - const int *c_ip; - volatile int *v_ip; - int *ip; - const char *c_cp; - the third column in the following table is the common type that is the result of a conditional expression in - which the first two columns are the second and third operands (in either order): - c_vp c_ip const void * - v_ip 0 volatile int * - c_ip v_ip const volatile int * - vp c_cp const void * - ip c_ip const int * - vp ip void * - - 6.5.16 Assignment operators - Syntax -1 assignment-expression: - conditional-expression - unary-expression assignment-operator assignment-expression - assignment-operator: one of - = *= /= %= += -= <<= >>= &= ^= |= - Constraints -2 An assignment operator shall have a modifiable lvalue as its left operand. - Semantics -3 An assignment operator stores a value in the object designated by the left operand. An - assignment expression has the value of the left operand after the assignment,111) but is not - an lvalue. The type of an assignment expression is the type the left operand would have - after lvalue conversion. The side effect of updating the stored value of the left operand is - sequenced after the value computations of the left and right operands. The evaluations of - the operands are unsequenced. - - - - - 111) The implementation is permitted to read the object to determine the value but is not required to, even - when the object has volatile-qualified type. - -[page 101] (Contents) - - 6.5.16.1 Simple assignment - Constraints -1 One of the following shall hold:112) - -- the left operand has atomic, qualified, or unqualified arithmetic type, and the right has - arithmetic type; - -- the left operand has an atomic, qualified, or unqualified version of a structure or union - type compatible with the type of the right; - -- the left operand has atomic, qualified, or unqualified pointer type, and (considering - the type the left operand would have after lvalue conversion) both operands are - pointers to qualified or unqualified versions of compatible types, and the type pointed - to by the left has all the qualifiers of the type pointed to by the right; - -- the left operand has atomic, qualified, or unqualified pointer type, and (considering - the type the left operand would have after lvalue conversion) one operand is a pointer - to an object type, and the other is a pointer to a qualified or unqualified version of - void, and the type pointed to by the left has all the qualifiers of the type pointed to - by the right; - -- the left operand is an atomic, qualified, or unqualified pointer, and the right is a null - pointer constant; or - -- the left operand has type atomic, qualified, or unqualified _Bool, and the right is a - pointer. - Semantics -2 In simple assignment (=), the value of the right operand is converted to the type of the - assignment expression and replaces the value stored in the object designated by the left - operand. -3 If the value being stored in an object is read from another object that overlaps in any way - the storage of the first object, then the overlap shall be exact and the two objects shall - have qualified or unqualified versions of a compatible type; otherwise, the behavior is - undefined. -4 EXAMPLE 1 In the program fragment - - - - - 112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion - (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type - qualifiers that were applied to the type category of the expression (for example, it removes const but - not volatile from the type int volatile * const). - -[page 102] (Contents) - - int f(void); - char c; + + ++ +Contents
+
+ ISO (the International Organization for Standardization) and IEC (the International + Electrotechnical Commission) form the specialized system for worldwide + standardization. National bodies that are member of ISO or IEC participate in the + development of International Standards through technical committees established by the + respective organization to deal with particular fields of technical activity. ISO and IEC + technical committees collaborate in fields of mutual interest. Other international + organizations, governmental and non-governmental, in liaison with ISO and IEC, also + take part in the work. +
+ International Standards are drafted in accordance with the rules given in the ISO/IEC + Directives, Part 2. This International Standard was drafted in accordance with the fifth + edition (2004). +
+ In the field of information technology, ISO and IEC have established a joint technical + committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical + committee are circulated to national bodies for voting. Publication as an International + Standard requires approval by at least 75% of the national bodies casting a vote. +
+ Attention is drawn to the possibility that some of the elements of this document may be + the subject of patent rights. ISO and IEC shall not be held responsible for identifying any + or all such patent rights. +
+ This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1, + Information technology, Subcommittee SC 22, Programming languages, their + environments and system software interfaces. The Working Group responsible for this + standard (WG 14) maintains a site on the World Wide Web at http://www.open- + std.org/JTC1/SC22/WG14/ containing additional information relevant to this + standard such as a Rationale for many of the decisions made during its preparation and a + log of Defect Reports and Responses. +
+ This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as + corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and + ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include: +
+ Major changes in the second edition included: +
+ Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H, * + I, J, the bibliography, and the index are for information only. In accordance with Part 2 of + the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples + are also for information only. + + +
+ With the introduction of new devices and extended character sets, new features may be + added to this International Standard. Subclauses in the language and library clauses warn + implementors and programmers of usages which, though valid in themselves, may + conflict with future additions. +
+ Certain features are obsolescent, which means that they may be considered for + withdrawal in future revisions of this International Standard. They are retained because + of their widespread use, but their use in new implementations (for implementation + features) or new programs (for language [6.11] or library features [7.30]) is discouraged. +
+ This International Standard is divided into four major subdivisions: +
+ Examples are provided to illustrate possible forms of the constructions described. + Footnotes are provided to emphasize consequences of the rules described in that + subclause or elsewhere in this International Standard. References are used to refer to + other related subclauses. Recommendations are provided to give advice or guidance to + implementors. Annexes provide additional information and summarize the information + contained in this International Standard. A bibliography lists documents that were + referred to during the preparation of the standard. +
+ The language clause (clause 6) is derived from ''The C Reference Manual''. +
+ The library clause (clause 7) is based on the 1984 /usr/group Standard. + + + +
+ This International Standard specifies the form and establishes the interpretation of + programs written in the C programming language.1) It specifies +
+ This International Standard does not specify +
1) This International Standard is designed to promote the portability of C programs among a variety of + data-processing systems. It is intended for use by implementors and programmers. + + +
+ The following referenced documents are indispensable for the application of this + document. For dated references, only the edition cited applies. For undated references, + the latest edition of the referenced document (including any amendments) applies. +
+ ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for + use in the physical sciences and technology. +
+ ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information + interchange. +
+ ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental + terms. +
+ ISO 4217, Codes for the representation of currencies and funds. +
+ ISO 8601, Data elements and interchange formats -- Information interchange -- + Representation of dates and times. +
+ ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded + Character Set (UCS). +
+ IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously + designated IEC 559:1989). + + +
+ For the purposes of this International Standard, the following definitions apply. Other + terms are defined where they appear in italic type or on the left side of a syntax rule. + Terms explicitly defined in this International Standard are not to be presumed to refer + implicitly to similar terms defined elsewhere. Terms not defined in this International + Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not + defined in this International Standard are to be interpreted according to ISO 31-11. + +
+ access
+ <execution-time action> to read or modify the value of an object
+
+ NOTE 1 Where only one of these two actions is meant, ''read'' or ''modify'' is used. + +
+ NOTE 2 ''Modify'' includes the case where the new value being stored is the same as the previous value. + +
+ NOTE 3 Expressions that are not evaluated do not access objects. + + +
+ alignment
+ requirement that objects of a particular type be located on storage boundaries with
+ addresses that are particular multiples of a byte address
+
+
+ argument
+ actual argument
+ actual parameter (deprecated)
+ expression in the comma-separated list bounded by the parentheses in a function call
+ expression, or a sequence of preprocessing tokens in the comma-separated list bounded
+ by the parentheses in a function-like macro invocation
+
+
+ behavior
+ external appearance or action
+
+
+ implementation-defined behavior
+ unspecified behavior where each implementation documents how the choice is made
+
+ EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit + when a signed integer is shifted right. + + +
+ locale-specific behavior
+ behavior that depends on local conventions of nationality, culture, and language that each
+ implementation documents
+
+
+ EXAMPLE An example of locale-specific behavior is whether the islower function returns true for + characters other than the 26 lowercase Latin letters. + + +
+ undefined behavior
+ behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
+ for which this International Standard imposes no requirements
+
+ NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable + results, to behaving during translation or program execution in a documented manner characteristic of the + environment (with or without the issuance of a diagnostic message), to terminating a translation or + execution (with the issuance of a diagnostic message). + +
+ EXAMPLE An example of undefined behavior is the behavior on integer overflow. + + +
+ unspecified behavior
+ use of an unspecified value, or other behavior where this International Standard provides
+ two or more possibilities and imposes no further requirements on which is chosen in any
+ instance
+
+ EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are + evaluated. + + +
+ bit
+ unit of data storage in the execution environment large enough to hold an object that may
+ have one of two values
+
+ NOTE It need not be possible to express the address of each individual bit of an object. + + +
+ byte
+ addressable unit of data storage large enough to hold any member of the basic character
+ set of the execution environment
+
+ NOTE 1 It is possible to express the address of each individual byte of an object uniquely. + +
+ NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation- + defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order + bit. + + +
+ character
+ <abstract> member of a set of elements used for the organization, control, or
+ representation of data
+
+
+ character
+ single-byte character
+ <C> bit representation that fits in a byte
+
+
+
+ multibyte character
+ sequence of one or more bytes representing a member of the extended character set of
+ either the source or the execution environment
+
+ NOTE The extended character set is a superset of the basic character set. + + +
+ wide character
+ bit representation that fits in an object of type wchar_t, capable of representing any
+ character in the current locale
+
+
+ constraint
+ restriction, either syntactic or semantic, by which the exposition of language elements is
+ to be interpreted
+
+
+ correctly rounded result
+ representation in the result format that is nearest in value, subject to the current rounding
+ mode, to what the result would be given unlimited range and precision
+
+
+ diagnostic message
+ message belonging to an implementation-defined subset of the implementation's message
+ output
+
+
+ forward reference
+ reference to a later subclause of this International Standard that contains additional
+ information relevant to this subclause
+
+
+ implementation
+ particular set of software, running in a particular translation environment under particular
+ control options, that performs translation of programs for, and supports execution of
+ functions in, a particular execution environment
+
+
+ implementation limit
+ restriction imposed upon programs by the implementation
+
+
+ memory location
+ either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
+ nonzero width
+
+
+ NOTE 1 Two threads of execution can update and access separate memory locations without interfering + with each other. + +
+ NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same + applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the + two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member + declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all + members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those + intervening bit-fields happen to be. + +
+ EXAMPLE A structure declared as +
+ struct {
+ char a;
+ int b:5, c:11, :0, d:8;
+ struct { int ee:8; } e;
+ }
+
+ contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
+ memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
+ and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
+ modified, but b and a, for example, can be.
+
+
+
+ object
+ region of data storage in the execution environment, the contents of which can represent
+ values
+
+ NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1. + + +
+ parameter
+ formal parameter
+ formal argument (deprecated)
+ object declared as part of a function declaration or definition that acquires a value on
+ entry to the function, or an identifier from the comma-separated list bounded by the
+ parentheses immediately following the macro name in a function-like macro definition
+
+
+ recommended practice
+ specification that is strongly recommended as being in keeping with the intent of the
+ standard, but that may be impractical for some implementations
+
+
+ runtime-constraint
+ requirement on a program when calling a library function
+
+ NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and + need not be diagnosed at translation time. + +
+ NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime- + constraints for a library function are not violated by the program; see K.3.1.4. + + +
+ value
+ precise meaning of the contents of an object when interpreted as having a specific type
+
+
+ implementation-defined value
+ unspecified value where each implementation documents how the choice is made
+
+
+ indeterminate value
+ either an unspecified value or a trap representation
+
+
+ unspecified value
+ valid value of the relevant type where this International Standard imposes no
+ requirements on which value is chosen in any instance
+
+ NOTE An unspecified value cannot be a trap representation. + + +
+ trap representation
+ an object representation that need not represent a value of the object type
+
+
+ perform a trap
+ interrupt execution of the program such that no further operations are performed
+
+ NOTE In this International Standard, when the word ''trap'' is not immediately followed by + ''representation'', this is the intended usage.2) + + +
2) For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap + representation might perform a trap but is not required to (see 6.2.6.1). + + +
+ [^ x^]
+ ceiling of x: the least integer greater than or equal to x
+
+ EXAMPLE [^2.4^] is 3, [^-2.4^] is -2. + + +
+ [_ x_]
+ floor of x: the greatest integer less than or equal to x
+
+ EXAMPLE [_2.4_] is 2, [_-2.4_] is -3. + + + + + + +
+ In this International Standard, ''shall'' is to be interpreted as a requirement on an + implementation or on a program; conversely, ''shall not'' is to be interpreted as a + prohibition. +
+ If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime- + constraint is violated, the behavior is undefined. Undefined behavior is otherwise + indicated in this International Standard by the words ''undefined behavior'' or by the + omission of any explicit definition of behavior. There is no difference in emphasis among + these three; they all describe ''behavior that is undefined''. +
+ A program that is correct in all other aspects, operating on correct data, containing + unspecified behavior shall be a correct program and act in accordance with 5.1.2.3. +
+ The implementation shall not successfully translate a preprocessing translation unit + containing a #error preprocessing directive unless it is part of a group skipped by + conditional inclusion. +
+ A strictly conforming program shall use only those features of the language and library + specified in this International Standard.3) It shall not produce output dependent on any + unspecified, undefined, or implementation-defined behavior, and shall not exceed any + minimum implementation limit. +
+ The two forms of conforming implementation are hosted and freestanding. A conforming + hosted implementation shall accept any strictly conforming program. A conforming + freestanding implementation shall accept any strictly conforming program that does not + use complex types and in which the use of the features specified in the library clause + (clause 7) is confined to the contents of the standard headers <float.h>, + <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>, + <stddef.h>, and <stdint.h>. A conforming implementation may have extensions + (including additional library functions), provided they do not alter the behavior of any + strictly conforming program.4) + + + + +
+ A conforming program is one that is acceptable to a conforming implementation.5) +
+ An implementation shall be accompanied by a document that defines all implementation- + defined and locale-specific characteristics and all extensions. +
Forward references: conditional inclusion (6.10.1), error directive (6.10.5), + characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h> + (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15), + variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h> + (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20). + + + + + + +
3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
+ by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
+
+
+ #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
/* ... */
- if ((c = f()) == -1)
- /* ... */
- the int value returned by the function may be truncated when stored in the char, and then converted back
- to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of
- values as unsigned char (and char is narrower than int), the result of the conversion cannot be
- negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
- variable c should be declared as int.
-
-5 EXAMPLE 2 In the fragment:
- char c;
- int i;
- long l;
- l = (c = i);
- the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
- of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
- that is, long int type.
-
-6 EXAMPLE 3 Consider the fragment:
- const char **cpp;
- char *p;
- const char c = 'A';
- cpp = &p; // constraint violation
- *cpp = &c; // valid
- *p = 0; // valid
- The first assignment is unsafe because it would allow the following valid code to attempt to change the
- value of the const object c.
-
- 6.5.16.2 Compound assignment
- Constraints
-1 For the operators += and -= only, either the left operand shall be an atomic, qualified, or
- unqualified pointer to a complete object type, and the right shall have integer type; or the
- left operand shall have atomic, qualified, or unqualified arithmetic type, and the right
- shall have arithmetic type.
-2 For the other operators, the left operand shall have atomic, qualified, or unqualified
- arithmetic type, and (considering the type the left operand would have after lvalue
- conversion) each operand shall have arithmetic type consistent with those allowed by the
- corresponding binary operator.
- Semantics
-3 A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
- expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
- respect to an indeterminately-sequenced function call, the operation of a compound
-[page 103] (Contents)
-
- assignment is a single evaluation. If E1 has an atomic type, compound assignment is a
- read-modify-write operation with memory_order_seq_cst memory order
- semantics.113)
- 6.5.17 Comma operator
- Syntax
-1 expression:
- assignment-expression
- expression , assignment-expression
- Semantics
-2 The left operand of a comma operator is evaluated as a void expression; there is a
- sequence point between its evaluation and that of the right operand. Then the right
- operand is evaluated; the result has its type and value.114) *
-3 EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
- appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
- of initializers). On the other hand, it can be used within a parenthesized expression or within the second
- expression of a conditional operator in such contexts. In the function call
- f(a, (t=3, t+2), c)
- the function has three arguments, the second of which has the value 5.
-
- Forward references: initialization (6.7.9).
-
-
-
-
- 113) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
- where T is the type of E1:
- T tmp = E1;
- T result;
- do {
- result = tmp op (E2);
- } while (!atomic_compare_exchange_strong(&E1, &tmp, result));
- with result being the result of the operation.
- 114) A comma operator does not yield an lvalue.
-
-[page 104] (Contents)
-
- 6.6 Constant expressions
- Syntax
-1 constant-expression:
- conditional-expression
- Description
-2 A constant expression can be evaluated during translation rather than runtime, and
- accordingly may be used in any place that a constant may be.
- Constraints
-3 Constant expressions shall not contain assignment, increment, decrement, function-call,
- or comma operators, except when they are contained within a subexpression that is not
- evaluated.115)
-4 Each constant expression shall evaluate to a constant that is in the range of representable
- values for its type.
- Semantics
-5 An expression that evaluates to a constant is required in several contexts. If a floating
- expression is evaluated in the translation environment, the arithmetic precision and range
- shall be at least as great as if the expression were being evaluated in the execution
- environment.116)
-6 An integer constant expression117) shall have integer type and shall only have operands
- that are integer constants, enumeration constants, character constants, sizeof
- expressions whose results are integer constants, and floating constants that are the
- immediate operands of casts. Cast operators in an integer constant expression shall only
- convert arithmetic types to integer types, except as part of an operand to the sizeof
- operator.
-7 More latitude is permitted for constant expressions in initializers. Such a constant
- expression shall be, or evaluate to, one of the following:
- -- an arithmetic constant expression,
-
-
-
- 115) The operand of a sizeof operator is usually not evaluated (6.5.3.4).
- 116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
- the translation environment.
- 117) An integer constant expression is required in a number of contexts such as the size of a bit-field
- member of a structure, the value of an enumeration constant, and the size of a non-variable length
- array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
- preprocessing directives are discussed in 6.10.1.
-
-[page 105] (Contents)
-
- -- a null pointer constant,
- -- an address constant, or
- -- an address constant for a complete object type plus or minus an integer constant
- expression.
-8 An arithmetic constant expression shall have arithmetic type and shall only have
- operands that are integer constants, floating constants, enumeration constants, character
- constants, and sizeof expressions. Cast operators in an arithmetic constant expression
- shall only convert arithmetic types to arithmetic types, except as part of an operand to a
- sizeof operator whose result is an integer constant.
-9 An address constant is a null pointer, a pointer to an lvalue designating an object of static
- storage duration, or a pointer to a function designator; it shall be created explicitly using
- the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
- an expression of array or function type. The array-subscript [] and member-access .
- and -> operators, the address & and indirection * unary operators, and pointer casts may
- be used in the creation of an address constant, but the value of an object shall not be
- accessed by use of these operators.
-10 An implementation may accept other forms of constant expressions.
-11 The semantic rules for the evaluation of a constant expression are the same as for
- nonconstant expressions.118)
- Forward references: array declarators (6.7.6.2), initialization (6.7.9).
-
-
-
-
- 118) Thus, in the following initialization,
- static int i = 2 || 1 / 0;
- the expression is a valid integer constant expression with value one.
-
-[page 106] (Contents)
-
- 6.7 Declarations
- Syntax
-1 declaration:
- declaration-specifiers init-declarator-listopt ;
- static_assert-declaration
- declaration-specifiers:
- storage-class-specifier declaration-specifiersopt
- type-specifier declaration-specifiersopt
- type-qualifier declaration-specifiersopt
- function-specifier declaration-specifiersopt
- alignment-specifier declaration-specifiersopt
- init-declarator-list:
- init-declarator
- init-declarator-list , init-declarator
- init-declarator:
- declarator
- declarator = initializer
- Constraints
-2 A declaration other than a static_assert declaration shall declare at least a declarator
- (other than the parameters of a function or the members of a structure or union), a tag, or
- the members of an enumeration.
-3 If an identifier has no linkage, there shall be no more than one declaration of the identifier
- (in a declarator or type specifier) with the same scope and in the same name space, except
- that a typedef name can be redefined to denote the same type as it currently does and tags
- may be redeclared as specified in 6.7.2.3.
-4 All declarations in the same scope that refer to the same object or function shall specify
- compatible types.
- Semantics
-5 A declaration specifies the interpretation and attributes of a set of identifiers. A definition
- of an identifier is a declaration for that identifier that:
- -- for an object, causes storage to be reserved for that object;
- -- for a function, includes the function body;119)
-
-
-
- 119) Function definitions have a different syntax, described in 6.9.1.
-
-[page 107] (Contents)
-
- -- for an enumeration constant or typedef name, is the (only) declaration of the
- identifier.
-6 The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
- storage duration, and part of the type of the entities that the declarators denote. The init-
- declarator-list is a comma-separated sequence of declarators, each of which may have
- additional type information, or an initializer, or both. The declarators contain the
- identifiers (if any) being declared.
-7 If an identifier for an object is declared with no linkage, the type for the object shall be
- complete by the end of its declarator, or by the end of its init-declarator if it has an
- initializer; in the case of function parameters (including in prototypes), it is the adjusted
- type (see 6.7.6.3) that is required to be complete.
- Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
- (6.7.9), type names (6.7.7), type qualifiers (6.7.3).
- 6.7.1 Storage-class specifiers
- Syntax
-1 storage-class-specifier:
- typedef
- extern
- static
- _Thread_local
- auto
- register
- Constraints
-2 At most, one storage-class specifier may be given in the declaration specifiers in a
- declaration, except that _Thread_local may appear with static or extern.120)
-3 In the declaration of an object with block scope, if the declaration specifiers include
- _Thread_local, they shall also include either static or extern. If
- _Thread_local appears in any declaration of an object, it shall be present in every
- declaration of that object.
- Semantics
-4 The typedef specifier is called a ''storage-class specifier'' for syntactic convenience
- only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations
- were discussed in 6.2.2 and 6.2.4.
-
-
-
- 120) See ''future language directions'' (6.11.5).
-
-[page 108] (Contents)
-
-5 A declaration of an identifier for an object with storage-class specifier register
- suggests that access to the object be as fast as possible. The extent to which such
- suggestions are effective is implementation-defined.121)
-6 The declaration of an identifier for a function that has block scope shall have no explicit
- storage-class specifier other than extern.
-7 If an aggregate or union object is declared with a storage-class specifier other than
- typedef, the properties resulting from the storage-class specifier, except with respect to
- linkage, also apply to the members of the object, and so on recursively for any aggregate
- or union member objects.
- Forward references: type definitions (6.7.8).
- 6.7.2 Type specifiers
- Syntax
-1 type-specifier:
- void
- char
- short
- int
- long
- float
- double
- signed
- unsigned
- _Bool
- _Complex
- atomic-type-specifier
- struct-or-union-specifier
- enum-specifier
- typedef-name
- Constraints
-2 At least one type specifier shall be given in the declaration specifiers in each declaration,
- and in the specifier-qualifier list in each struct declaration and type name. Each list of
-
-
- 121) The implementation may treat any register declaration simply as an auto declaration. However,
- whether or not addressable storage is actually used, the address of any part of an object declared with
- storage-class specifier register cannot be computed, either explicitly (by use of the unary &
- operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
- 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier
- register is sizeof.
-
-[page 109] (Contents)
-
- type specifiers shall be one of the following multisets (delimited by commas, when there
- is more than one multiset per item); the type specifiers may occur in any order, possibly
- intermixed with the other declaration specifiers.
- -- void
- -- char
- -- signed char
- -- unsigned char
- -- short, signed short, short int, or signed short int
- -- unsigned short, or unsigned short int
- -- int, signed, or signed int
- -- unsigned, or unsigned int
- -- long, signed long, long int, or signed long int
- -- unsigned long, or unsigned long int
- -- long long, signed long long, long long int, or
- signed long long int
- -- unsigned long long, or unsigned long long int
- -- float
- -- double
- -- long double
- -- _Bool
- -- float _Complex
- -- double _Complex
- -- long double _Complex
- -- atomic type specifier
- -- struct or union specifier
- -- enum specifier
- -- typedef name
-3 The type specifier _Complex shall not be used if the implementation does not support
- complex types (see 6.10.8.3).
-
-
-
-
-[page 110] (Contents)
-
- Semantics
-4 Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1
- through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The
- characteristics of the other types are discussed in 6.2.5.
-5 Each of the comma-separated multisets designates the same type, except that for bit-
- fields, it is implementation-defined whether the specifier int designates the same type as
- signed int or the same type as unsigned int.
- Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2),
- structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).
- 6.7.2.1 Structure and union specifiers
- Syntax
-1 struct-or-union-specifier:
- struct-or-union identifieropt { struct-declaration-list }
- struct-or-union identifier
- struct-or-union:
- struct
- union
- struct-declaration-list:
- struct-declaration
- struct-declaration-list struct-declaration
- struct-declaration:
- specifier-qualifier-list struct-declarator-listopt ;
- static_assert-declaration
- specifier-qualifier-list:
- type-specifier specifier-qualifier-listopt
- type-qualifier specifier-qualifier-listopt
- struct-declarator-list:
- struct-declarator
- struct-declarator-list , struct-declarator
- struct-declarator:
- declarator
- declaratoropt : constant-expression
- Constraints
-2 A struct-declaration that does not declare an anonymous structure or anonymous union
- shall contain a struct-declarator-list.
-
-
-[page 111] (Contents)
-
-3 A structure or union shall not contain a member with incomplete or function type (hence,
- a structure shall not contain an instance of itself, but may contain a pointer to an instance
- of itself), except that the last member of a structure with more than one named member
- may have incomplete array type; such a structure (and any union containing, possibly
- recursively, a member that is such a structure) shall not be a member of a structure or an
- element of an array.
-4 The expression that specifies the width of a bit-field shall be an integer constant
- expression with a nonnegative value that does not exceed the width of an object of the
- type that would be specified were the colon and expression omitted.122) If the value is
- zero, the declaration shall have no declarator.
-5 A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
- int, unsigned int, or some other implementation-defined type. It is
- implementation-defined whether atomic types are permitted.
- Semantics
-6 As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
- storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
- of members whose storage overlap.
-7 Structure and union specifiers have the same form. The keywords struct and union
- indicate that the type being specified is, respectively, a structure type or a union type.
-8 The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
- within a translation unit. The struct-declaration-list is a sequence of declarations for the
- members of the structure or union. If the struct-declaration-list contains no named
- members, no anonymous structures, and no anonymous unions, the behavior is undefined.
- The type is incomplete until immediately after the } that terminates the list, and complete
- thereafter.
-9 A member of a structure or union may have any complete object type other than a
- variably modified type.123) In addition, a member may be declared to consist of a
- specified number of bits (including a sign bit, if any). Such a member is called a
- bit-field;124) its width is preceded by a colon.
-10 A bit-field is interpreted as having a signed or unsigned integer type consisting of the
- specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of
-
- 122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and
- value bits) of a _Bool may be just 1 bit.
- 123) A structure or union cannot contain a member with a variably modified type because member names
- are not ordinary identifiers as defined in 6.2.3.
- 124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to
- or arrays of bit-field objects.
-
-[page 112] (Contents)
-
- type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool
- bit-field has the semantics of a _Bool.
-11 An implementation may allocate any addressable storage unit large enough to hold a bit-
- field. If enough space remains, a bit-field that immediately follows another bit-field in a
- structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
- whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
- implementation-defined. The order of allocation of bit-fields within a unit (high-order to
- low-order or low-order to high-order) is implementation-defined. The alignment of the
- addressable storage unit is unspecified.
-12 A bit-field declaration with no declarator, but only a colon and a width, indicates an
- unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0
- indicates that no further bit-field is to be packed into the unit in which the previous bit-
- field, if any, was placed.
-13 An unnamed member of structure type with no tag is called an anonymous structure; an
- unnamed member of union type with no tag is called an anonymous union. The members
- of an anonymous structure or union are considered to be members of the containing
- structure or union. This applies recursively if the containing structure or union is also
- anonymous.
-14 Each non-bit-field member of a structure or union object is aligned in an implementation-
- defined manner appropriate to its type.
-15 Within a structure object, the non-bit-field members and the units in which bit-fields
- reside have addresses that increase in the order in which they are declared. A pointer to a
- structure object, suitably converted, points to its initial member (or if that member is a
- bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
- padding within a structure object, but not at its beginning.
-16 The size of a union is sufficient to contain the largest of its members. The value of at
- most one of the members can be stored in a union object at any time. A pointer to a
- union object, suitably converted, points to each of its members (or if a member is a bit-
- field, then to the unit in which it resides), and vice versa.
-17 There may be unnamed padding at the end of a structure or union.
-18 As a special case, the last element of a structure with more than one named member may
- have an incomplete array type; this is called a flexible array member. In most situations,
-
-
- 125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
- then it is implementation-defined whether the bit-field is signed or unsigned.
- 126) An unnamed bit-field structure member is useful for padding to conform to externally imposed
- layouts.
-
-[page 113] (Contents)
-
- the flexible array member is ignored. In particular, the size of the structure is as if the
- flexible array member were omitted except that it may have more trailing padding than
- the omission would imply. However, when a . (or ->) operator has a left operand that is
- (a pointer to) a structure with a flexible array member and the right operand names that
- member, it behaves as if that member were replaced with the longest array (with the same
- element type) that would not make the structure larger than the object being accessed; the
- offset of the array shall remain that of the flexible array member, even if this would differ
- from that of the replacement array. If this array would have no elements, it behaves as if
- it had one element but the behavior is undefined if any attempt is made to access that
- element or to generate a pointer one past it.
-19 EXAMPLE 1 The following illustrates anonymous structures and unions:
- struct v {
- union { // anonymous union
- struct { int i, j; }; // anonymous structure
- struct { long k, l; } w;
- };
- int m;
- } v1;
- v1.i = 2; // valid
- v1.k = 3; // invalid: inner structure is not anonymous
- v1.w.k = 5; // valid
-
-20 EXAMPLE 2 After the declaration:
- struct s { int n; double d[]; };
- the structure struct s has a flexible array member d. A typical way to use this is:
- int m = /* some value */;
- struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
- and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
- p had been declared as:
- struct { int n; double d[m]; } *p;
- (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
- not be the same).
-21 Following the above declaration:
- struct s t1 = { 0 }; // valid
- struct s t2 = { 1, { 4.2 }}; // invalid
- t1.n = 4; // valid
- t1.d[0] = 4.2; // might be undefined behavior
- The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
- contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
- sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
- in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
- code.
-
-[page 114] (Contents)
-
-22 After the further declaration:
- struct ss { int n; };
- the expressions:
- sizeof (struct s) >= sizeof (struct ss)
- sizeof (struct s) >= offsetof(struct s, d)
- are always equal to 1.
-23 If sizeof (double) is 8, then after the following code is executed:
- struct s *s1;
- struct s *s2;
- s1 = malloc(sizeof (struct s) + 64);
- s2 = malloc(sizeof (struct s) + 46);
- and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
- purposes, as if the identifiers had been declared as:
- struct { int n; double d[8]; } *s1;
- struct { int n; double d[5]; } *s2;
-24 Following the further successful assignments:
- s1 = malloc(sizeof (struct s) + 10);
- s2 = malloc(sizeof (struct s) + 6);
- they then behave as if the declarations were:
- struct { int n; double d[1]; } *s1, *s2;
- and:
- double *dp;
- dp = &(s1->d[0]); // valid
- *dp = 42; // valid
- dp = &(s2->d[0]); // valid
- *dp = 42; // undefined behavior
-25 The assignment:
- *s1 = *s2;
- only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
- of the structure, they might be copied or simply overwritten with indeterminate values.
-
- Forward references: declarators (6.7.6), tags (6.7.2.3).
-
-
-
-
-[page 115] (Contents)
-
- 6.7.2.2 Enumeration specifiers
- Syntax
-1 enum-specifier:
- enum identifieropt { enumerator-list }
- enum identifieropt { enumerator-list , }
- enum identifier
- enumerator-list:
- enumerator
- enumerator-list , enumerator
- enumerator:
- enumeration-constant
- enumeration-constant = constant-expression
- Constraints
-2 The expression that defines the value of an enumeration constant shall be an integer
- constant expression that has a value representable as an int.
- Semantics
-3 The identifiers in an enumerator list are declared as constants that have type int and
- may appear wherever such are permitted.127) An enumerator with = defines its
- enumeration constant as the value of the constant expression. If the first enumerator has
- no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
- defines its enumeration constant as the value of the constant expression obtained by
- adding 1 to the value of the previous enumeration constant. (The use of enumerators with
- = may produce enumeration constants with values that duplicate other values in the same
- enumeration.) The enumerators of an enumeration are also known as its members.
-4 Each enumerated type shall be compatible with char, a signed integer type, or an
- unsigned integer type. The choice of type is implementation-defined,128) but shall be
- capable of representing the values of all the members of the enumeration. The
- enumerated type is incomplete until immediately after the } that terminates the list of
- enumerator declarations, and complete thereafter.
-
-
-
-
- 127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
- each other and from other identifiers declared in ordinary declarators.
- 128) An implementation may delay the choice of which integer type until all enumeration constants have
- been seen.
-
-[page 116] (Contents)
-
-5 EXAMPLE The following fragment:
- enum hue { chartreuse, burgundy, claret=20, winedark };
- enum hue col, *cp;
- col = claret;
- cp = &col;
- if (*cp != burgundy)
- /* ... */
- makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
- pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.
-
- Forward references: tags (6.7.2.3).
- 6.7.2.3 Tags
- Constraints
-1 A specific type shall have its content defined at most once.
-2 Where two declarations that use the same tag declare the same type, they shall both use
- the same choice of struct, union, or enum.
-3 A type specifier of the form
- enum identifier
- without an enumerator list shall only appear after the type it specifies is complete.
- Semantics
-4 All declarations of structure, union, or enumerated types that have the same scope and
- use the same tag declare the same type. Irrespective of whether there is a tag or what
- other declarations of the type are in the same translation unit, the type is incomplete129)
- until immediately after the closing brace of the list defining the content, and complete
- thereafter.
-5 Two declarations of structure, union, or enumerated types which are in different scopes or
- use different tags declare distinct types. Each declaration of a structure, union, or
- enumerated type which does not include a tag declares a distinct type.
-6 A type specifier of the form
-
-
-
-
- 129) An incomplete type may only by used when the size of an object of that type is not needed. It is not
- needed, for example, when a typedef name is declared to be a specifier for a structure or union, or
- when a pointer to or a function returning a structure or union is being declared. (See incomplete types
- in 6.2.5.) The specification has to be complete before such a function is called or defined.
-
-[page 117] (Contents)
-
- struct-or-union identifieropt { struct-declaration-list }
- or
- enum identifieropt { enumerator-list }
- or
- enum identifieropt { enumerator-list , }
- declares a structure, union, or enumerated type. The list defines the structure content,
- union content, or enumeration content. If an identifier is provided,130) the type specifier
- also declares the identifier to be the tag of that type.
-7 A declaration of the form
- struct-or-union identifier ;
- specifies a structure or union type and declares the identifier as a tag of that type.131)
-8 If a type specifier of the form
- struct-or-union identifier
- occurs other than as part of one of the above forms, and no other declaration of the
- identifier as a tag is visible, then it declares an incomplete structure or union type, and
- declares the identifier as the tag of that type.131)
-9 If a type specifier of the form
- struct-or-union identifier
- or
- enum identifier
- occurs other than as part of one of the above forms, and a declaration of the identifier as a
- tag is visible, then it specifies the same type as that other declaration, and does not
- redeclare the tag.
-10 EXAMPLE 1 This mechanism allows declaration of a self-referential structure.
- struct tnode {
- int count;
- struct tnode *left, *right;
- };
- specifies a structure that contains an integer and two pointers to objects of the same type. Once this
- declaration has been given, the declaration
-
-
-
-
- 130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration
- of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
- can make use of that typedef name to declare objects having the specified structure, union, or
- enumerated type.
- 131) A similar construction with enum does not exist.
-
-[page 118] (Contents)
-
- struct tnode s, *sp;
- declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
- these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
- which sp points; the expression s.right->count designates the count member of the right struct
- tnode pointed to from s.
-11 The following alternative formulation uses the typedef mechanism:
- typedef struct tnode TNODE;
- struct tnode {
- int count;
- TNODE *left, *right;
- };
- TNODE s, *sp;
-
-12 EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
- structures, the declarations
- struct s1 { struct s2 *s2p; /* ... */ }; // D1
- struct s2 { struct s1 *s1p; /* ... */ }; // D2
- specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
- declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
- D2. To eliminate this context sensitivity, the declaration
- struct s2;
- may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
- completes the specification of the new type.
-
- Forward references: declarators (6.7.6), type definitions (6.7.8).
- 6.7.2.4 Atomic type specifiers
- Syntax
-1 atomic-type-specifier:
- _Atomic ( type-name )
- Constraints
-2 Atomic type specifiers shall not be used if the implementation does not support atomic
- types (see 6.10.8.3).
-3 The type name in an atomic type specifier shall not refer to an array type, a function type,
- an atomic type, or a qualified type.
- Semantics
-4 The properties associated with atomic types are meaningful only for expressions that are
- lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is
- interpreted as a type specifier (with a type name), not as a type qualifier.
-
-
-
-
-[page 119] (Contents)
-
- 6.7.3 Type qualifiers
- Syntax
-1 type-qualifier:
- const
- restrict
- volatile
- _Atomic
- Constraints
-2 Types other than pointer types whose referenced type is an object type shall not be
- restrict-qualified.
-3 The type modified by the _Atomic qualifier shall not be an array type or a function
- type.
- Semantics
-4 The properties associated with qualified types are meaningful only for expressions that
- are lvalues.132)
-5 If the same qualifier appears more than once in the same specifier-qualifier-list, either
- directly or via one or more typedefs, the behavior is the same as if it appeared only
- once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier-
- list, the resulting type is the so-qualified atomic type.
-6 If an attempt is made to modify an object defined with a const-qualified type through use
- of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
- made to refer to an object defined with a volatile-qualified type through use of an lvalue
- with non-volatile-qualified type, the behavior is undefined.133)
-7 An object that has volatile-qualified type may be modified in ways unknown to the
- implementation or have other unknown side effects. Therefore any expression referring
- to such an object shall be evaluated strictly according to the rules of the abstract machine,
- as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
- object shall agree with that prescribed by the abstract machine, except as modified by the
-
-
-
-
- 132) The implementation may place a const object that is not volatile in a read-only region of
- storage. Moreover, the implementation need not allocate storage for such an object if its address is
- never used.
- 133) This applies to those objects that behave as if they were defined with qualified types, even if they are
- never actually defined as objects in the program (such as an object at a memory-mapped input/output
- address).
-
-[page 120] (Contents)
-
- unknown factors mentioned previously.134) What constitutes an access to an object that
- has volatile-qualified type is implementation-defined.
-8 An object that is accessed through a restrict-qualified pointer has a special association
- with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
- that object use, directly or indirectly, the value of that particular pointer.135) The intended
- use of the restrict qualifier (like the register storage class) is to promote
- optimization, and deleting all instances of the qualifier from all preprocessing translation
- units composing a conforming program does not change its meaning (i.e., observable
- behavior).
-9 If the specification of an array type includes any type qualifiers, the element type is so-
- qualified, not the array type. If the specification of a function type includes any type
- qualifiers, the behavior is undefined.136)
-10 For two qualified types to be compatible, both shall have the identically qualified version
- of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
- does not affect the specified type.
-11 EXAMPLE 1 An object declared
- extern const volatile int real_time_clock;
- may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.
-
-12 EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
- modify an aggregate type:
- const struct s { int mem; } cs = { 1 };
- struct s ncs; // the object ncs is modifiable
- typedef int A[2][3];
- const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
- int *pi;
- const int *pci;
- ncs = cs; // valid
- cs = ncs; // violates modifiable lvalue constraint for =
- pi = &ncs.mem; // valid
- pi = &cs.mem; // violates type constraints for =
- pci = &cs.mem; // valid
- pi = a[0]; // invalid: a[0] has type ''const int *''
-
-
-
- 134) A volatile declaration may be used to describe an object corresponding to a memory-mapped
- input/output port or an object accessed by an asynchronously interrupting function. Actions on
- objects so declared shall not be ''optimized out'' by an implementation or reordered except as
- permitted by the rules for evaluating expressions.
- 135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this
- association between the allocated object and the pointer.
- 136) Both of these can occur through the use of typedefs.
-
-[page 121] (Contents)
-
-13 EXAMPLE 3 The declaration
- _Atomic volatile int *p;
- specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type.
-
- 6.7.3.1 Formal definition of restrict
-1 Let D be a declaration of an ordinary identifier that provides a means of designating an
- object P as a restrict-qualified pointer to type T.
-2 If D appears inside a block and does not have storage class extern, let B denote the
- block. If D appears in the list of parameter declarations of a function definition, let B
- denote the associated block. Otherwise, let B denote the block of main (or the block of
- whatever function is called at program startup in a freestanding environment).
-3 In what follows, a pointer expression E is said to be based on object P if (at some
- sequence point in the execution of B prior to the evaluation of E) modifying P to point to
- a copy of the array object into which it formerly pointed would change the value of E.137)
- Note that ''based'' is defined only for expressions with pointer types.
-4 During each execution of B, let L be any lvalue that has &L based on P. If L is used to
- access the value of the object X that it designates, and X is also modified (by any means),
- then the following requirements apply: T shall not be const-qualified. Every other lvalue
- used to access the value of X shall also have its address based on P. Every access that
- modifies X shall be considered also to modify P, for the purposes of this subclause. If P
- is assigned the value of a pointer expression E that is based on another restricted pointer
- object P2, associated with block B2, then either the execution of B2 shall begin before
- the execution of B, or the execution of B2 shall end prior to the assignment. If these
- requirements are not met, then the behavior is undefined.
-5 Here an execution of B means that portion of the execution of the program that would
- correspond to the lifetime of an object with scalar type and automatic storage duration
- associated with B.
-6 A translator is free to ignore any or all aliasing implications of uses of restrict.
-7 EXAMPLE 1 The file scope declarations
- int * restrict a;
- int * restrict b;
- extern int c[];
- assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
- program, then it is never accessed using either of the other two.
-
-
- 137) In other words, E depends on the value of P itself rather than on the value of an object referenced
- indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
- expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
- expressions *p and p[1] are not.
-
-[page 122] (Contents)
-
-8 EXAMPLE 2 The function parameter declarations in the following example
- void f(int n, int * restrict p, int * restrict q)
- {
- while (n-- > 0)
- *p++ = *q++;
- }
- assert that, during each execution of the function, if an object is accessed through one of the pointer
- parameters, then it is not also accessed through the other.
-9 The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
- analysis of function f without examining any of the calls of f in the program. The cost is that the
- programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
- second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
- both p and q.
- void g(void)
- {
- extern int d[100];
- f(50, d + 50, d); // valid
- f(50, d + 1, d); // undefined behavior
- }
-
-10 EXAMPLE 3 The function parameter declarations
- void h(int n, int * restrict p, int * restrict q, int * restrict r)
- {
- int i;
- for (i = 0; i < n; i++)
- p[i] = q[i] + r[i];
- }
- illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
- are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
- modified within function h.
-
-11 EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
- function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments
- between restricted pointers declared in nested blocks have defined behavior.
- {
- int * restrict p1;
- int * restrict q1;
- p1 = q1; // undefined behavior
- {
- int * restrict p2 = p1; // valid
- int * restrict q2 = q1; // valid
- p1 = q2; // undefined behavior
- p2 = q2; // undefined behavior
- }
- }
-
-
-
-
-[page 123] (Contents)
-
-12 The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
- precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
- example, this permits new_vector to return a vector.
- typedef struct { int n; float * restrict v; } vector;
- vector new_vector(int n)
- {
- vector t;
- t.n = n;
- t.v = malloc(n * sizeof (float));
- return t;
- }
-
- 6.7.4 Function specifiers
- Syntax
-1 function-specifier:
- inline
- _Noreturn
- Constraints
-2 Function specifiers shall be used only in the declaration of an identifier for a function.
-3 An inline definition of a function with external linkage shall not contain a definition of a
- modifiable object with static or thread storage duration, and shall not contain a reference
- to an identifier with internal linkage.
-4 In a hosted environment, no function specifier(s) shall appear in a declaration of main.
- Semantics
-5 A function specifier may appear more than once; the behavior is the same as if it
- appeared only once.
-6 A function declared with an inline function specifier is an inline function. Making a *
- function an inline function suggests that calls to the function be as fast as possible.138)
- The extent to which such suggestions are effective is implementation-defined.139)
-
-
-
-
- 138) By using, for example, an alternative to the usual function call mechanism, such as ''inline
- substitution''. Inline substitution is not textual substitution, nor does it create a new function.
- Therefore, for example, the expansion of a macro used within the body of the function uses the
- definition it had at the point the function body appears, and not where the function is called; and
- identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a
- single address, regardless of the number of inline definitions that occur in addition to the external
- definition.
- 139) For example, an implementation might never perform inline substitution, or might only perform inline
- substitutions to calls in the scope of an inline declaration.
-
-[page 124] (Contents)
-
-7 Any function with internal linkage can be an inline function. For a function with external
- linkage, the following restrictions apply: If a function is declared with an inline
- function specifier, then it shall also be defined in the same translation unit. If all of the
- file scope declarations for a function in a translation unit include the inline function
- specifier without extern, then the definition in that translation unit is an inline
- definition. An inline definition does not provide an external definition for the function,
- and does not forbid an external definition in another translation unit. An inline definition
- provides an alternative to an external definition, which a translator may use to implement
- any call to the function in the same translation unit. It is unspecified whether a call to the
- function uses the inline definition or the external definition.140)
-8 A function declared with a _Noreturn function specifier shall not return to its caller.
- Recommended practice
-9 The implementation should produce a diagnostic message for a function declared with a
- _Noreturn function specifier that appears to be capable of returning to its caller.
-10 EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
- definition, or a definition available for use only within the translation unit. A file scope declaration with
- extern creates an external definition. The following example shows an entire translation unit.
- inline double fahr(double t)
- {
- return (9.0 * t) / 5.0 + 32.0;
- }
- inline double cels(double t)
- {
- return (5.0 * (t - 32.0)) / 9.0;
- }
- extern double fahr(double); // creates an external definition
- double convert(int is_fahr, double temp)
- {
- /* A translator may perform inline substitutions */
- return is_fahr ? cels(temp) : fahr(temp);
- }
-11 Note that the definition of fahr is an external definition because fahr is also declared with extern, but
- the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
- external definition has to appear in another translation unit (see 6.9); the inline definition and the external
- definition are distinct and either may be used for the call.
-
-12 EXAMPLE 2
-
-
-
-
- 140) Since an inline definition is distinct from the corresponding external definition and from any other
- corresponding inline definitions in other translation units, all corresponding objects with static storage
- duration are also distinct in each of the definitions.
-
-[page 125] (Contents)
-
- _Noreturn void f () {
- abort(); // ok
- }
- _Noreturn void g (int i) { // causes undefined behavior if i <= 0
- if (i > 0) abort();
- }
-
- Forward references: function definitions (6.9.1).
- 6.7.5 Alignment specifier
- Syntax
-1 alignment-specifier:
- _Alignas ( type-name )
- _Alignas ( constant-expression )
- Constraints
-2 An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
- a function, or a parameter, or an object declared with the register storage-class
- specifier.
-3 The constant expression shall be an integer constant expression. It shall evaluate to a
- valid fundamental alignment, or to a valid extended alignment supported by the
- implementation in the context in which it appears, or to zero.
-4 The combined effect of all alignment attributes in a declaration shall not specify an
- alignment that is less strict than the alignment that would otherwise be required for the
- type of the object or member being declared.
- Semantics
-5 The first form is equivalent to _Alignas(alignof(type-name)).
-6 The alignment requirement of the declared object or member is taken to be the specified
- alignment. An alignment specification of zero has no effect.141) When multiple
- alignment specifiers occur in a declaration, the effective alignment requirement is the
- strictest specified alignment.
-7 If the definition of an object has an alignment specifier, any other declaration of that
- object shall either specify equivalent alignment or have no alignment specifier. If the
- definition of an object does not have an alignment specifier, any other declaration of that
- object shall also have no alignment specifier. If declarations of an object in different
- translation units have different alignment specifiers, the behavior is undefined.
-
-
-
- 141) An alignment specification of zero also does not affect other alignment specifications in the same
- declaration.
-
-[page 126] (Contents)
-
- 6.7.6 Declarators
- Syntax
-1 declarator:
- pointeropt direct-declarator
- direct-declarator:
- identifier
- ( declarator )
- direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
- direct-declarator [ static type-qualifier-listopt assignment-expression ]
- direct-declarator [ type-qualifier-list static assignment-expression ]
- direct-declarator [ type-qualifier-listopt * ]
- direct-declarator ( parameter-type-list )
- direct-declarator ( identifier-listopt )
- pointer:
- * type-qualifier-listopt
- * type-qualifier-listopt pointer
- type-qualifier-list:
- type-qualifier
- type-qualifier-list type-qualifier
- parameter-type-list:
- parameter-list
- parameter-list , ...
- parameter-list:
- parameter-declaration
- parameter-list , parameter-declaration
- parameter-declaration:
- declaration-specifiers declarator
- declaration-specifiers abstract-declaratoropt
- identifier-list:
- identifier
- identifier-list , identifier
- Semantics
-2 Each declarator declares one identifier, and asserts that when an operand of the same
- form as the declarator appears in an expression, it designates a function or object with the
- scope, storage duration, and type indicated by the declaration specifiers.
-3 A full declarator is a declarator that is not part of another declarator. The end of a full
- declarator is a sequence point. If, in the nested sequence of declarators in a full
-[page 127] (Contents)
-
- declarator, there is a declarator specifying a variable length array type, the type specified
- by the full declarator is said to be variably modified. Furthermore, any type derived by
- declarator type derivation from a variably modified type is itself variably modified.
-4 In the following subclauses, consider a declaration
- T D1
- where T contains the declaration specifiers that specify a type T (such as int) and D1 is
- a declarator that contains an identifier ident. The type specified for the identifier ident in
- the various forms of declarator is described inductively using this notation.
-5 If, in the declaration ''T D1'', D1 has the form
- identifier
- then the type specified for ident is T .
-6 If, in the declaration ''T D1'', D1 has the form
- ( D )
- then ident has the type specified by the declaration ''T D''. Thus, a declarator in
- parentheses is identical to the unparenthesized declarator, but the binding of complicated
- declarators may be altered by parentheses.
- Implementation limits
-7 As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
- function declarators that modify an arithmetic, structure, union, or void type, either
- directly or via one or more typedefs.
- Forward references: array declarators (6.7.6.2), type definitions (6.7.8).
- 6.7.6.1 Pointer declarators
- Semantics
-1 If, in the declaration ''T D1'', D1 has the form
- * type-qualifier-listopt D
- and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
- T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list
- pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer.
-2 For two pointer types to be compatible, both shall be identically qualified and both shall
- be pointers to compatible types.
-3 EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer
- to a constant value'' and a ''constant pointer to a variable value''.
-
-
-
-
-[page 128] (Contents)
-
- const int *ptr_to_constant;
- int *const constant_ptr;
- The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
- but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
- int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
- same location.
-4 The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
- type ''pointer to int''.
- typedef int *int_ptr;
- const int_ptr constant_ptr;
- declares constant_ptr as an object that has type ''const-qualified pointer to int''.
-
- 6.7.6.2 Array declarators
- Constraints
-1 In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
- an expression or *. If they delimit an expression (which specifies the size of an array), the
- expression shall have an integer type. If the expression is a constant expression, it shall
- have a value greater than zero. The element type shall not be an incomplete or function
- type. The optional type qualifiers and the keyword static shall appear only in a
- declaration of a function parameter with an array type, and then only in the outermost
- array type derivation.
-2 If an identifier is declared as having a variably modified type, it shall be an ordinary
- identifier (as defined in 6.2.3), have no linkage, and have either block scope or function
- prototype scope. If an identifier is declared to be an object with static or thread storage
- duration, it shall not have a variable length array type.
- Semantics
-3 If, in the declaration ''T D1'', D1 has one of the forms:
- D[ type-qualifier-listopt assignment-expressionopt ]
- D[ static type-qualifier-listopt assignment-expression ]
- D[ type-qualifier-list static assignment-expression ]
- D[ type-qualifier-listopt * ]
- and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
- T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142)
- (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)
-4 If the size is not present, the array type is an incomplete type. If the size is * instead of
- being an expression, the array type is a variable length array type of unspecified size,
- which can only be used in declarations or type names with function prototype scope;143)
-
- 142) When several ''array of'' specifications are adjacent, a multidimensional array is declared.
-
-[page 129] (Contents)
-
- such arrays are nonetheless complete types. If the size is an integer constant expression
- and the element type has a known constant size, the array type is not a variable length
- array type; otherwise, the array type is a variable length array type. (Variable length
- arrays are a conditional feature that implementations need not support; see 6.10.8.3.)
-5 If the size is an expression that is not an integer constant expression: if it occurs in a
- declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
- each time it is evaluated it shall have a value greater than zero. The size of each instance
- of a variable length array type does not change during its lifetime. Where a size
- expression is part of the operand of a sizeof operator and changing the value of the
- size expression would not affect the result of the operator, it is unspecified whether or not
- the size expression is evaluated.
-6 For two array types to be compatible, both shall have compatible element types, and if
- both size specifiers are present, and are integer constant expressions, then both size
- specifiers shall have the same constant value. If the two array types are used in a context
- which requires them to be compatible, it is undefined behavior if the two size specifiers
- evaluate to unequal values.
-7 EXAMPLE 1
- float fa[11], *afp[17];
- declares an array of float numbers and an array of pointers to float numbers.
-
-8 EXAMPLE 2 Note the distinction between the declarations
- extern int *x;
- extern int y[];
- The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
- (an incomplete type), the storage for which is defined elsewhere.
-
-9 EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types.
- extern int n;
- extern int m;
- void fcompat(void)
- {
- int a[n][6][m];
- int (*p)[4][n+1];
- int c[n][n][6][m];
- int (*r)[n][n][n+1];
- p = a; // invalid: not compatible because 4 != 6
- r = c; // compatible, but defined behavior only if
- // n == 6 and m == n+1
- }
-
-
-
-
- 143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3).
-
-[page 130] (Contents)
-
-10 EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
- function prototype scope. Array objects declared with the _Thread_local, static, or extern
- storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
- the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
- identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
- structures or unions.
- extern int n;
- int A[n]; // invalid: file scope VLA
- extern int (*p2)[n]; // invalid: file scope VM
- int B[100]; // valid: file scope but not VM
- void fvla(int m, int C[m][m]); // valid: VLA with prototype scope
- void fvla(int m, int C[m][m]) // valid: adjusted to auto pointer to VLA
- {
- typedef int VLA[m][m]; // valid: block scope typedef VLA
- struct tag {
- int (*y)[n]; // invalid: y not ordinary identifier
- int z[n]; // invalid: z not ordinary identifier
- };
- int D[m]; // valid: auto VLA
- static int E[m]; // invalid: static block scope VLA
- extern int F[m]; // invalid: F has linkage and is VLA
- int (*s)[m]; // valid: auto pointer to VLA
- extern int (*r)[m]; // invalid: r has linkage and points to VLA
- static int (*q)[m] = &B; // valid: q is a static block pointer to VLA
- }
-
- Forward references: function declarators (6.7.6.3), function definitions (6.9.1),
- initialization (6.7.9).
- 6.7.6.3 Function declarators (including prototypes)
- Constraints
-1 A function declarator shall not specify a return type that is a function type or an array
- type.
-2 The only storage-class specifier that shall occur in a parameter declaration is register.
-3 An identifier list in a function declarator that is not part of a definition of that function
- shall be empty.
-4 After adjustment, the parameters in a parameter type list in a function declarator that is
- part of a definition of that function shall not have incomplete type.
- Semantics
-5 If, in the declaration ''T D1'', D1 has the form
-
-
-
-
-[page 131] (Contents)
-
- D( parameter-type-list )
- or
- D( identifier-listopt )
- and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
- T '', then the type specified for ident is ''derived-declarator-type-list function returning
- T ''.
-6 A parameter type list specifies the types of, and may declare identifiers for, the
- parameters of the function.
-7 A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to
- type'', where the type qualifiers (if any) are those specified within the [ and ] of the
- array type derivation. If the keyword static also appears within the [ and ] of the
- array type derivation, then for each call to the function, the value of the corresponding
- actual argument shall provide access to the first element of an array with at least as many
- elements as specified by the size expression.
-8 A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to
- function returning type'', as in 6.3.2.1.
-9 If the list terminates with an ellipsis (, ...), no information about the number or types
- of the parameters after the comma is supplied.144)
-10 The special case of an unnamed parameter of type void as the only item in the list
- specifies that the function has no parameters.
-11 If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
- parameter name, it shall be taken as a typedef name.
-12 If the function declarator is not part of a definition of that function, parameters may have
- incomplete type and may use the [*] notation in their sequences of declarator specifiers
- to specify variable length array types.
-13 The storage-class specifier in the declaration specifiers for a parameter declaration, if
- present, is ignored unless the declared parameter is one of the members of the parameter
- type list for a function definition.
-14 An identifier list declares only the identifiers of the parameters of the function. An empty
- list in a function declarator that is part of a definition of that function specifies that the
- function has no parameters. The empty list in a function declarator that is not part of a
- definition of that function specifies that no information about the number or types of the
- parameters is supplied.145)
-
-
-
- 144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
- correspond to the ellipsis.
-
-[page 132] (Contents)
-
-15 For two function types to be compatible, both shall specify compatible return types.146)
- Moreover, the parameter type lists, if both are present, shall agree in the number of
- parameters and in use of the ellipsis terminator; corresponding parameters shall have
- compatible types. If one type has a parameter type list and the other type is specified by a
- function declarator that is not part of a function definition and that contains an empty
- identifier list, the parameter list shall not have an ellipsis terminator and the type of each
- parameter shall be compatible with the type that results from the application of the
- default argument promotions. If one type has a parameter type list and the other type is
- specified by a function definition that contains a (possibly empty) identifier list, both shall
- agree in the number of parameters, and the type of each prototype parameter shall be
- compatible with the type that results from the application of the default argument
- promotions to the type of the corresponding identifier. (In the determination of type
- compatibility and of a composite type, each parameter declared with function or array
- type is taken as having the adjusted type and each parameter declared with qualified type
- is taken as having the unqualified version of its declared type.)
-16 EXAMPLE 1 The declaration
- int f(void), *fip(), (*pfi)();
- declares a function f with no parameters returning an int, a function fip with no parameter specification
- returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
- int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
- declaration suggests, and the same construction in an expression requires, the calling of a function fip,
- and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
- extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
- designator, which is then used to call the function; it returns an int.
-17 If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
- declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
- internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
- the identifier of the pointer pfi has block scope and no linkage.
-
-18 EXAMPLE 2 The declaration
- int (*apfi[3])(int *x, int *y);
- declares an array apfi of three pointers to functions returning int. Each of these functions has two
- parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
- go out of scope at the end of the declaration of apfi.
-
-19 EXAMPLE 3 The declaration
- int (*fpfi(int (*)(long), int))(int, ...);
- declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
- parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
- The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
-
-
- 145) See ''future language directions'' (6.11.6).
- 146) If both function types are ''old style'', parameter types are not compared.
-
-[page 133] (Contents)
-
- additional arguments of any type.
-
-20 EXAMPLE 4 The following prototype has a variably modified parameter.
- void addscalar(int n, int m,
- double a[n][n*m+300], double x);
- int main()
- {
- double b[4][308];
- addscalar(4, 2, b, 2.17);
- return 0;
- }
- void addscalar(int n, int m,
- double a[n][n*m+300], double x)
- {
- for (int i = 0; i < n; i++)
- for (int j = 0, k = n*m+300; j < k; j++)
- // a is a pointer to a VLA with n*m+300 elements
- a[i][j] += x;
- }
-
-21 EXAMPLE 5 The following are all compatible function prototype declarators.
- double maximum(int n, int m, double a[n][m]);
- double maximum(int n, int m, double a[*][*]);
- double maximum(int n, int m, double a[ ][*]);
- double maximum(int n, int m, double a[ ][m]);
- as are:
- void f(double (* restrict a)[5]);
- void f(double a[restrict][5]);
- void f(double a[restrict 3][5]);
- void f(double a[restrict static 3][5]);
- (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
- non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)
-
- Forward references: function definitions (6.9.1), type names (6.7.7).
-
-
-
-
-[page 134] (Contents)
-
- 6.7.7 Type names
- Syntax
-1 type-name:
- specifier-qualifier-list abstract-declaratoropt
- abstract-declarator:
- pointer
- pointeropt direct-abstract-declarator
- direct-abstract-declarator:
- ( abstract-declarator )
- direct-abstract-declaratoropt [ type-qualifier-listopt
- assignment-expressionopt ]
- direct-abstract-declaratoropt [ static type-qualifier-listopt
- assignment-expression ]
- direct-abstract-declaratoropt [ type-qualifier-list static
- assignment-expression ]
- direct-abstract-declaratoropt [ * ]
- direct-abstract-declaratoropt ( parameter-type-listopt )
- Semantics
-2 In several contexts, it is necessary to specify a type. This is accomplished using a type
- name, which is syntactically a declaration for a function or an object of that type that
- omits the identifier.147)
-3 EXAMPLE The constructions
- (a) int
- (b) int *
- (c) int *[3]
- (d) int (*)[3]
- (e) int (*)[*]
- (f) int *()
- (g) int (*)(void)
- (h) int (*const [])(unsigned int, ...)
- name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
- array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
- with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
- returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
- parameter that has type unsigned int and an unspecified number of other parameters, returning an
- int.
-
-
-
-
- 147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no
- parameter specification'', rather than redundant parentheses around the omitted identifier.
-
-[page 135] (Contents)
-
- 6.7.8 Type definitions
- Syntax
-1 typedef-name:
- identifier
- Constraints
-2 If a typedef name specifies a variably modified type then it shall have block scope.
- Semantics
-3 In a declaration whose storage-class specifier is typedef, each declarator defines an
- identifier to be a typedef name that denotes the type specified for the identifier in the way
- described in 6.7.6. Any array size expressions associated with variable length array
- declarators are evaluated each time the declaration of the typedef name is reached in the
- order of execution. A typedef declaration does not introduce a new type, only a
- synonym for the type so specified. That is, in the following declarations:
- typedef T type_ident;
- type_ident D;
- type_ident is defined as a typedef name with the type specified by the declaration
- specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator-
- type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A
- typedef name shares the same name space as other identifiers declared in ordinary
- declarators.
-4 EXAMPLE 1 After
- typedef int MILES, KLICKSP();
- typedef struct { double hi, lo; } range;
- the constructions
- MILES distance;
- extern KLICKSP *metricp;
- range x;
- range z, *zp;
- are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no
- parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to
- such a structure. The object distance has a type compatible with any other int object.
-
-5 EXAMPLE 2 After the declarations
- typedef struct s1 { int x; } t1, *tp1;
- typedef struct s2 { int x; } t2, *tp2;
- type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
- s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.
-
-
-
-
-[page 136] (Contents)
-
-6 EXAMPLE 3 The following obscure constructions
- typedef signed int t;
- typedef int plain;
- struct tag {
- unsigned t:4;
- const t:5;
- plain r:5;
- };
- declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
- with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
- qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
- [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
- (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
- unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
- type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
- in an inner scope by
- t f(t (t));
- long t;
- then a function f is declared with type ''function returning signed int with one unnamed parameter
- with type pointer to function returning signed int with one unnamed parameter with type signed
- int'', and an identifier t with type long int.
-
-7 EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
- following declarations of the signal function specify exactly the same type, the first without making use
- of any typedef names.
- typedef void fv(int), (*pfv)(int);
- void (*signal(int, void (*)(int)))(int);
- fv *signal(int, fv *);
- pfv signal(int, pfv);
-
-8 EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
- time the typedef name is defined, not each time it is used:
- void copyt(int n)
- {
- typedef int B[n]; // B is n ints, n evaluated now
- n += 1;
- B a; // a is n ints, n without += 1
- int b[n]; // a and b are different sizes
- for (int i = 1; i < n; i++)
- a[i-1] = b[i];
- }
-
-
-
-
-[page 137] (Contents)
-
- 6.7.9 Initialization
- Syntax
-1 initializer:
- assignment-expression
- { initializer-list }
- { initializer-list , }
- initializer-list:
- designationopt initializer
- initializer-list , designationopt initializer
- designation:
- designator-list =
- designator-list:
- designator
- designator-list designator
- designator:
- [ constant-expression ]
- . identifier
- Constraints
-2 No initializer shall attempt to provide a value for an object not contained within the entity
- being initialized.
-3 The type of the entity to be initialized shall be an array of unknown size or a complete
- object type that is not a variable length array type.
-4 All the expressions in an initializer for an object that has static or thread storage duration
- shall be constant expressions or string literals.
-5 If the declaration of an identifier has block scope, and the identifier has external or
- internal linkage, the declaration shall have no initializer for the identifier.
-6 If a designator has the form
- [ constant-expression ]
- then the current object (defined below) shall have array type and the expression shall be
- an integer constant expression. If the array is of unknown size, any nonnegative value is
- valid.
-7 If a designator has the form
- . identifier
- then the current object (defined below) shall have structure or union type and the
- identifier shall be the name of a member of that type.
-[page 138] (Contents)
-
- Semantics
-8 An initializer specifies the initial value stored in an object.
-9 Except where explicitly stated otherwise, for the purposes of this subclause unnamed
- members of objects of structure and union type do not participate in initialization.
- Unnamed members of structure objects have indeterminate value even after initialization.
-10 If an object that has automatic storage duration is not initialized explicitly, its value is
- indeterminate. If an object that has static or thread storage duration is not initialized
- explicitly, then:
- -- if it has pointer type, it is initialized to a null pointer;
- -- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
- -- if it is an aggregate, every member is initialized (recursively) according to these rules,
- and any padding is initialized to zero bits;
- -- if it is a union, the first named member is initialized (recursively) according to these
- rules, and any padding is initialized to zero bits;
-11 The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
- initial value of the object is that of the expression (after conversion); the same type
- constraints and conversions as for simple assignment apply, taking the type of the scalar
- to be the unqualified version of its declared type.
-12 The rest of this subclause deals with initializers for objects that have aggregate or union
- type.
-13 The initializer for a structure or union object that has automatic storage duration shall be
- either an initializer list as described below, or a single expression that has compatible
- structure or union type. In the latter case, the initial value of the object, including
- unnamed members, is that of the expression.
-14 An array of character type may be initialized by a character string literal or UTF-8 string
- literal, optionally enclosed in braces. Successive bytes of the string literal (including the
- terminating null character if there is room or if the array is of unknown size) initialize the
- elements of the array.
-15 An array with element type compatible with a qualified or unqualified version of
- wchar_t may be initialized by a wide string literal, optionally enclosed in braces.
- Successive wide characters of the wide string literal (including the terminating null wide
- character if there is room or if the array is of unknown size) initialize the elements of the
- array.
-16 Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
- enclosed list of initializers for the elements or named members.
-
-
-[page 139] (Contents)
-
-17 Each brace-enclosed initializer list has an associated current object. When no
- designations are present, subobjects of the current object are initialized in order according
- to the type of the current object: array elements in increasing subscript order, structure
- members in declaration order, and the first named member of a union.148) In contrast, a
- designation causes the following initializer to begin initialization of the subobject
- described by the designator. Initialization then continues forward in order, beginning
- with the next subobject after that described by the designator.149)
-18 Each designator list begins its description with the current object associated with the
- closest surrounding brace pair. Each item in the designator list (in order) specifies a
- particular member of its current object and changes the current object for the next
- designator (if any) to be that member.150) The current object that results at the end of the
- designator list is the subobject to be initialized by the following initializer.
-19 The initialization shall occur in initializer list order, each initializer provided for a
- particular subobject overriding any previously listed initializer for the same subobject;151)
- all subobjects that are not initialized explicitly shall be initialized implicitly the same as
- objects that have static storage duration.
-20 If the aggregate or union contains elements or members that are aggregates or unions,
- these rules apply recursively to the subaggregates or contained unions. If the initializer of
- a subaggregate or contained union begins with a left brace, the initializers enclosed by
- that brace and its matching right brace initialize the elements or members of the
- subaggregate or the contained union. Otherwise, only enough initializers from the list are
- taken to account for the elements or members of the subaggregate or the first member of
- the contained union; any remaining initializers are left to initialize the next element or
- member of the aggregate of which the current subaggregate or contained union is a part.
-21 If there are fewer initializers in a brace-enclosed list than there are elements or members
- of an aggregate, or fewer characters in a string literal used to initialize an array of known
- size than there are elements in the array, the remainder of the aggregate shall be
- initialized implicitly the same as objects that have static storage duration.
-
-
-
- 148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
- subobjects are initialized as usual, but the subaggregate or contained union does not become the
- current object: current objects are associated only with brace-enclosed initializer lists.
- 149) After a union member is initialized, the next object is not the next member of the union; instead, it is
- the next subobject of an object containing the union.
- 150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
- the surrounding brace pair. Note, too, that each separate designator list is independent.
- 151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
- not be evaluated at all.
-
-[page 140] (Contents)
-
-22 If an array of unknown size is initialized, its size is determined by the largest indexed
- element with an explicit initializer. The array type is completed at the end of its
- initializer list.
-23 The evaluations of the initialization list expressions are indeterminately sequenced with
- respect to one another and thus the order in which any side effects occur is
- unspecified.152)
-24 EXAMPLE 1 Provided that <complex.h> has been #included, the declarations
- int i = 3.5;
- double complex c = 5 + 3 * I;
- define and initialize i with the value 3 and c with the value 5.0 + i3.0.
-
-25 EXAMPLE 2 The declaration
- int x[] = { 1, 3, 5 };
- defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
- and there are three initializers.
-
-26 EXAMPLE 3 The declaration
- int y[4][3] = {
- { 1, 3, 5 },
- { 2, 4, 6 },
- { 3, 5, 7 },
- };
- is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
- y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
- y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
- been achieved by
- int y[4][3] = {
- 1, 3, 5, 2, 4, 6, 3, 5, 7
- };
- The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
- next three are taken successively for y[1] and y[2].
-
-27 EXAMPLE 4 The declaration
- int z[4][3] = {
- { 1 }, { 2 }, { 3 }, { 4 }
- };
- initializes the first column of z as specified and initializes the rest with zeros.
-
-28 EXAMPLE 5 The declaration
- struct { int a[3], b; } w[] = { { 1 }, 2 };
- is a definition with an inconsistently bracketed initialization. It defines an array with two element
-
-
-
- 152) In particular, the evaluation order need not be the same as the order of subobject initialization.
-
-[page 141] (Contents)
-
- structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
-
-29 EXAMPLE 6 The declaration
- short q[4][3][2] = {
- { 1 },
- { 2, 3 },
- { 4, 5, 6 }
- };
- contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
- object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
- q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
- q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
- only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
- for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
- respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
- diagnostic message would have been issued. The same initialization result could have been achieved by:
- short q[4][3][2] = {
- 1, 0, 0, 0, 0, 0,
- 2, 3, 0, 0, 0, 0,
- 4, 5, 6
- };
- or by:
- short q[4][3][2] = {
- {
- { 1 },
- },
- {
- { 2, 3 },
- },
- {
- { 4, 5 },
- { 6 },
- }
- };
- in a fully bracketed form.
-30 Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
- cause confusion.
-
-31 EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the
- declaration
- typedef int A[]; // OK - declared with block scope
- the declaration
- A a = { 1, 2 }, b = { 3, 4, 5 };
- is identical to
- int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
- due to the rules for incomplete types.
-
-[page 142] (Contents)
-
-32 EXAMPLE 8 The declaration
- char s[] = "abc", t[3] = "abc";
- defines ''plain'' char array objects s and t whose elements are initialized with character string literals.
- This declaration is identical to
- char s[] = { 'a', 'b', 'c', '\0' },
- t[] = { 'a', 'b', 'c' };
- The contents of the arrays are modifiable. On the other hand, the declaration
- char *p = "abc";
- defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char''
- with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
- modify the contents of the array, the behavior is undefined.
-
-33 EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using
- designators:
- enum { member_one, member_two };
- const char *nm[] = {
- [member_two] = "member two",
- [member_one] = "member one",
- };
-
-34 EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order:
- div_t answer = { .quot = 2, .rem = -1 };
-
-35 EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
- might be misunderstood:
- struct { int a[3], b; } w[] =
- { [0].a = {1}, [1].a[0] = 2 };
-
-36 EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator:
- int a[MAX] = {
- 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
- };
-37 In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
- than ten, some of the values provided by the first five initializers will be overridden by the second five.
-
-38 EXAMPLE 13 Any member of a union can be initialized:
- union { /* ... */ } u = { .any_member = 42 };
-
- Forward references: common definitions <stddef.h> (7.19).
-
-
-
-
-[page 143] (Contents)
-
- 6.7.10 Static assertions
- Syntax
-1 static_assert-declaration:
- _Static_assert ( constant-expression , string-literal ) ;
- Constraints
-2 The constant expression shall compare unequal to 0.
- Semantics
-3 The constant expression shall be an integer constant expression. If the value of the
- constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
- constraint is violated and the implementation shall produce a diagnostic message that
- includes the text of the string literal, except that characters not in the basic source
- character set are not required to appear in the message.
- Forward references: diagnostics (7.2).
-
-
-
-
-[page 144] (Contents)
-
- 6.8 Statements and blocks
- Syntax
-1 statement:
- labeled-statement
- compound-statement
- expression-statement
- selection-statement
- iteration-statement
- jump-statement
- Semantics
-2 A statement specifies an action to be performed. Except as indicated, statements are
- executed in sequence.
-3 A block allows a set of declarations and statements to be grouped into one syntactic unit.
- The initializers of objects that have automatic storage duration, and the variable length
- array declarators of ordinary identifiers with block scope, are evaluated and the values are
- stored in the objects (including storing an indeterminate value in objects without an
- initializer) each time the declaration is reached in the order of execution, as if it were a
- statement, and within each declaration in the order that declarators appear.
-4 A full expression is an expression that is not part of another expression or of a declarator.
- Each of the following is a full expression: an initializer that is not part of a compound
- literal; the expression in an expression statement; the controlling expression of a selection
- statement (if or switch); the controlling expression of a while or do statement; each
- of the (optional) expressions of a for statement; the (optional) expression in a return
- statement. There is a sequence point between the evaluation of a full expression and the
- evaluation of the next full expression to be evaluated.
- Forward references: expression and null statements (6.8.3), selection statements
- (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
- 6.8.1 Labeled statements
- Syntax
-1 labeled-statement:
- identifier : statement
- case constant-expression : statement
- default : statement
- Constraints
-2 A case or default label shall appear only in a switch statement. Further
- constraints on such labels are discussed under the switch statement.
-
-[page 145] (Contents)
-
-3 Label names shall be unique within a function.
- Semantics
-4 Any statement may be preceded by a prefix that declares an identifier as a label name.
- Labels in themselves do not alter the flow of control, which continues unimpeded across
- them.
- Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).
- 6.8.2 Compound statement
- Syntax
-1 compound-statement:
- { block-item-listopt }
- block-item-list:
- block-item
- block-item-list block-item
- block-item:
- declaration
- statement
- Semantics
-2 A compound statement is a block.
- 6.8.3 Expression and null statements
- Syntax
-1 expression-statement:
- expressionopt ;
- Semantics
-2 The expression in an expression statement is evaluated as a void expression for its side
- effects.153)
-3 A null statement (consisting of just a semicolon) performs no operations.
-4 EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
- discarding of its value may be made explicit by converting the expression to a void expression by means of
- a cast:
- int p(int);
- /* ... */
- (void)p(0);
-
-
-
- 153) Such as assignments, and function calls which have side effects.
-
-[page 146] (Contents)
-
-5 EXAMPLE 2 In the program fragment
- char *s;
- /* ... */
- while (*s++ != '\0')
- ;
- a null statement is used to supply an empty loop body to the iteration statement.
-
-6 EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound
- statement.
- while (loop1) {
- /* ... */
- while (loop2) {
- /* ... */
- if (want_out)
- goto end_loop1;
- /* ... */
- }
- /* ... */
- end_loop1: ;
- }
-
- Forward references: iteration statements (6.8.5).
- 6.8.4 Selection statements
- Syntax
-1 selection-statement:
- if ( expression ) statement
- if ( expression ) statement else statement
- switch ( expression ) statement
- Semantics
-2 A selection statement selects among a set of statements depending on the value of a
- controlling expression.
-3 A selection statement is a block whose scope is a strict subset of the scope of its
- enclosing block. Each associated substatement is also a block whose scope is a strict
- subset of the scope of the selection statement.
- 6.8.4.1 The if statement
- Constraints
-1 The controlling expression of an if statement shall have scalar type.
- Semantics
-2 In both forms, the first substatement is executed if the expression compares unequal to 0.
- In the else form, the second substatement is executed if the expression compares equal
-
-
-[page 147] (Contents)
-
- to 0. If the first substatement is reached via a label, the second substatement is not
- executed.
-3 An else is associated with the lexically nearest preceding if that is allowed by the
- syntax.
- 6.8.4.2 The switch statement
- Constraints
-1 The controlling expression of a switch statement shall have integer type.
-2 If a switch statement has an associated case or default label within the scope of an
- identifier with a variably modified type, the entire switch statement shall be within the
- scope of that identifier.154)
-3 The expression of each case label shall be an integer constant expression and no two of
- the case constant expressions in the same switch statement shall have the same value
- after conversion. There may be at most one default label in a switch statement.
- (Any enclosed switch statement may have a default label or case constant
- expressions with values that duplicate case constant expressions in the enclosing
- switch statement.)
- Semantics
-4 A switch statement causes control to jump to, into, or past the statement that is the
- switch body, depending on the value of a controlling expression, and on the presence of a
- default label and the values of any case labels on or in the switch body. A case or
- default label is accessible only within the closest enclosing switch statement.
-5 The integer promotions are performed on the controlling expression. The constant
- expression in each case label is converted to the promoted type of the controlling
- expression. If a converted value matches that of the promoted controlling expression,
- control jumps to the statement following the matched case label. Otherwise, if there is
- a default label, control jumps to the labeled statement. If no converted case constant
- expression matches and there is no default label, no part of the switch body is
- executed.
- Implementation limits
-6 As discussed in 5.2.4.1, the implementation may limit the number of case values in a
- switch statement.
-
-
-
-
- 154) That is, the declaration either precedes the switch statement, or it follows the last case or
- default label associated with the switch that is in the block containing the declaration.
-
-[page 148] (Contents)
-
-7 EXAMPLE In the artificial program fragment
- switch (expr)
- {
- int i = 4;
- f(i);
- case 0:
- i = 17;
- /* falls through into default code */
- default:
- printf("%d\n", i);
- }
- the object whose identifier is i exists with automatic storage duration (within the block) but is never
- initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
- access an indeterminate value. Similarly, the call to the function f cannot be reached.
-
- 6.8.5 Iteration statements
- Syntax
-1 iteration-statement:
- while ( expression ) statement
- do statement while ( expression ) ;
- for ( expressionopt ; expressionopt ; expressionopt ) statement
- for ( declaration expressionopt ; expressionopt ) statement
- Constraints
-2 The controlling expression of an iteration statement shall have scalar type.
-3 The declaration part of a for statement shall only declare identifiers for objects having
- storage class auto or register.
- Semantics
-4 An iteration statement causes a statement called the loop body to be executed repeatedly
- until the controlling expression compares equal to 0. The repetition occurs regardless of
- whether the loop body is entered from the iteration statement or by a jump.155)
-5 An iteration statement is a block whose scope is a strict subset of the scope of its
- enclosing block. The loop body is also a block whose scope is a strict subset of the scope
- of the iteration statement.
-6 An iteration statement whose controlling expression is not a constant expression,156) that
- performs no input/output operations, does not access volatile objects, and performs no
- synchronization or atomic operations in its body, controlling expression, or (in the case of
-
- 155) Code jumped over is not executed. In particular, the controlling expression of a for or while
- statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.
- 156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression.
-
-[page 149] (Contents)
-
- a for statement) its expression-3, may be assumed by the implementation to
- terminate.157)
- 6.8.5.1 The while statement
-1 The evaluation of the controlling expression takes place before each execution of the loop
- body.
- 6.8.5.2 The do statement
-1 The evaluation of the controlling expression takes place after each execution of the loop
- body.
- 6.8.5.3 The for statement
-1 The statement
- for ( clause-1 ; expression-2 ; expression-3 ) statement
- behaves as follows: The expression expression-2 is the controlling expression that is
- evaluated before each execution of the loop body. The expression expression-3 is
- evaluated as a void expression after each execution of the loop body. If clause-1 is a
- declaration, the scope of any identifiers it declares is the remainder of the declaration and
- the entire loop, including the other two expressions; it is reached in the order of execution
- before the first evaluation of the controlling expression. If clause-1 is an expression, it is
- evaluated as a void expression before the first evaluation of the controlling expression.158)
-2 Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
- nonzero constant.
- 6.8.6 Jump statements
- Syntax
-1 jump-statement:
- goto identifier ;
- continue ;
- break ;
- return expressionopt ;
-
-
-
-
- 157) This is intended to allow compiler transformations such as removal of empty loops even when
- termination cannot be proven.
- 158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
- the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
- such that execution of the loop continues until the expression compares equal to 0; and expression-3
- specifies an operation (such as incrementing) that is performed after each iteration.
-
-[page 150] (Contents)
-
- Semantics
-2 A jump statement causes an unconditional jump to another place.
- 6.8.6.1 The goto statement
- Constraints
-1 The identifier in a goto statement shall name a label located somewhere in the enclosing
- function. A goto statement shall not jump from outside the scope of an identifier having
- a variably modified type to inside the scope of that identifier.
- Semantics
-2 A goto statement causes an unconditional jump to the statement prefixed by the named
- label in the enclosing function.
-3 EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
- following outline presents one possible approach to a problem based on these three assumptions:
- 1. The general initialization code accesses objects only visible to the current function.
- 2. The general initialization code is too large to warrant duplication.
- 3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
- continue statements, for example.)
+ fesetround(FE_UPWARD);
/* ... */
- goto first_time;
- for (;;) {
- // determine next operation
- /* ... */
- if (need to reinitialize) {
- // reinitialize-only code
- /* ... */
- first_time:
- // general initialization code
- /* ... */
- continue;
- }
- // handle other operations
- /* ... */
- }
-
-
-
-
-[page 151] (Contents)
-
-4 EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
- modified types. A jump within the scope, however, is permitted.
- goto lab3; // invalid: going INTO scope of VLA.
- {
- double a[n];
- a[j] = 4.4;
- lab3:
- a[j] = 3.3;
- goto lab4; // valid: going WITHIN scope of VLA.
- a[j] = 5.5;
- lab4:
- a[j] = 6.6;
- }
- goto lab4; // invalid: going INTO scope of VLA.
-
- 6.8.6.2 The continue statement
- Constraints
-1 A continue statement shall appear only in or as a loop body.
- Semantics
-2 A continue statement causes a jump to the loop-continuation portion of the smallest
- enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
- of the statements
- while (/* ... */) { do { for (/* ... */) {
- /* ... */ /* ... */ /* ... */
- continue; continue; continue;
- /* ... */ /* ... */ /* ... */
- contin: ; contin: ; contin: ;
- } } while (/* ... */); }
- unless the continue statement shown is in an enclosed iteration statement (in which
- case it is interpreted within that statement), it is equivalent to goto contin;.159)
- 6.8.6.3 The break statement
- Constraints
-1 A break statement shall appear only in or as a switch body or loop body.
- Semantics
-2 A break statement terminates execution of the smallest enclosing switch or iteration
- statement.
-
-
-
- 159) Following the contin: label is a null statement.
-
-[page 152] (Contents)
-
- 6.8.6.4 The return statement
- Constraints
-1 A return statement with an expression shall not appear in a function whose return type
- is void. A return statement without an expression shall only appear in a function
- whose return type is void.
- Semantics
-2 A return statement terminates execution of the current function and returns control to
- its caller. A function may have any number of return statements.
-3 If a return statement with an expression is executed, the value of the expression is
- returned to the caller as the value of the function call expression. If the expression has a
- type different from the return type of the function in which it appears, the value is
- converted as if by assignment to an object having the return type of the function.160)
-4 EXAMPLE In:
- struct s { double i; } f(void);
- union {
+ #endif
+
+
+
+
4) This implies that a conforming implementation reserves no identifiers other than those explicitly + reserved in this International Standard. + +
5) Strictly conforming programs are intended to be maximally portable among conforming + implementations. Conforming programs may depend upon nonportable features of a conforming + implementation. + + +
+ An implementation translates C source files and executes C programs in two data- + processing-system environments, which will be called the translation environment and + the execution environment in this International Standard. Their characteristics define and + constrain the results of executing conforming C programs constructed according to the + syntactic and semantic rules for conforming implementations. +
Forward references: In this clause, only a few of many possible forward references + have been noted. + +
+ A C program need not all be translated at the same time. The text of the program is kept + in units called source files, (or preprocessing files) in this International Standard. A + source file together with all the headers and source files included via the preprocessing + directive #include is known as a preprocessing translation unit. After preprocessing, a + preprocessing translation unit is called a translation unit. Previously translated translation + units may be preserved individually or in libraries. The separate translation units of a + program communicate by (for example) calls to functions whose identifiers have external + linkage, manipulation of objects whose identifiers have external linkage, or manipulation + of data files. Translation units may be separately translated and then later linked to + produce an executable program. +
Forward references: linkages of identifiers (6.2.2), external definitions (6.9), + preprocessing directives (6.10). + +
+ The precedence among the syntax rules of translation is specified by the following + phases.6) +
Forward references: universal character names (6.4.3), lexical elements (6.4), + preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9). + + + + + +
6) Implementations shall behave as if these separate phases occur, even though many are typically folded + together in practice. Source files, translation units, and translated translation units need not + necessarily be stored as files, nor need there be any one-to-one correspondence between these entities + and any external representation. The description is conceptual only, and does not specify any + particular implementation. + +
7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is + context-dependent. For example, see the handling of < within a #include preprocessing directive. + +
8) An implementation need not convert all non-corresponding source characters to the same execution + character. + + +
+ A conforming implementation shall produce at least one diagnostic message (identified in + an implementation-defined manner) if a preprocessing translation unit or translation unit + contains a violation of any syntax rule or constraint, even if the behavior is also explicitly + specified as undefined or implementation-defined. Diagnostic messages need not be + produced in other circumstances.9) +
+ EXAMPLE An implementation shall issue a diagnostic for the translation unit: +
+ char i; + int i; ++ because in those cases where wording in this International Standard describes the behavior for a construct + as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed. + + +
9) The intent is that an implementation should identify the nature of, and where possible localize, each + violation. Of course, an implementation is free to produce any number of diagnostics as long as a + valid program is still correctly translated. It may also successfully translate an invalid program. + + +
+ Two execution environments are defined: freestanding and hosted. In both cases, + program startup occurs when a designated C function is called by the execution + environment. All objects with static storage duration shall be initialized (set to their + initial values) before program startup. The manner and timing of such initialization are + otherwise unspecified. Program termination returns control to the execution + environment. +
Forward references: storage durations of objects (6.2.4), initialization (6.7.9). + +
+ In a freestanding environment (in which C program execution may take place without any + benefit of an operating system), the name and type of the function called at program + startup are implementation-defined. Any library facilities available to a freestanding + program, other than the minimal set required by clause 4, are implementation-defined. +
+ The effect of program termination in a freestanding environment is implementation- + defined. + +
+ A hosted environment need not be provided, but shall conform to the following + specifications if present. + + + + + + +
+ The function called at program startup is named main. The implementation declares no + prototype for this function. It shall be defined with a return type of int and with no + parameters: +
+ int main(void) { /* ... */ }
+
+ or with two parameters (referred to here as argc and argv, though any names may be
+ used, as they are local to the function in which they are declared):
+
+ int main(int argc, char *argv[]) { /* ... */ }
+
+ or equivalent;10) or in some other implementation-defined manner.
++ If they are declared, the parameters to the main function shall obey the following + constraints: +
10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as + char ** argv, and so on. + + +
+ In a hosted environment, a program may use all the functions, macros, type definitions, + and objects described in the library clause (clause 7). + + + + + + +
+ If the return type of the main function is a type compatible with int, a return from the + initial call to the main function is equivalent to calling the exit function with the value + returned by the main function as its argument;11) reaching the } that terminates the + main function returns a value of 0. If the return type is not compatible with int, the + termination status returned to the host environment is unspecified. +
Forward references: definition of terms (7.1.1), the exit function (7.22.4.4). + +
11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main + will have ended in the former case, even where they would not have in the latter. + + +
+ The semantic descriptions in this International Standard describe the behavior of an + abstract machine in which issues of optimization are irrelevant. +
+ Accessing a volatile object, modifying an object, modifying a file, or calling a function + that does any of those operations are all side effects,12) which are changes in the state of + the execution environment. Evaluation of an expression in general includes both value + computations and initiation of side effects. Value computation for an lvalue expression + includes determining the identity of the designated object. +
+ Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations + executed by a single thread, which induces a partial order among those evaluations. + Given any two evaluations A and B, if A is sequenced before B, then the execution of A + shall precede the execution of B. (Conversely, if A is sequenced before B, then B is + sequenced after A.) If A is not sequenced before or after B, then A and B are + unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced + either before or after B, but it is unspecified which.13) The presence of a sequence point + between the evaluation of expressions A and B implies that every value computation and + side effect associated with A is sequenced before every value computation and side effect + associated with B. (A summary of the sequence points is given in annex C.) +
+ In the abstract machine, all expressions are evaluated as specified by the semantics. An + actual implementation need not evaluate part of an expression if it can deduce that its + value is not used and that no needed side effects are produced (including any caused by + + + calling a function or accessing a volatile object). +
+ When the processing of the abstract machine is interrupted by receipt of a signal, the + values of objects that are neither lock-free atomic objects nor of type volatile + sig_atomic_t are unspecified, and the value of any object that is modified by the + handler that is neither a lock-free atomic object nor of type volatile + sig_atomic_t becomes undefined. +
+ The least requirements on a conforming implementation are: +
+ What constitutes an interactive device is implementation-defined. +
+ More stringent correspondences between abstract and actual semantics may be defined by + each implementation. +
+ EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual + semantics: at every sequence point, the values of the actual objects would agree with those specified by the + abstract semantics. The keyword volatile would then be redundant. +
+ Alternatively, an implementation might perform various optimizations within each translation unit, such + that the actual semantics would agree with the abstract semantics only when making function calls across + translation unit boundaries. In such an implementation, at the time of each function entry and function + return where the calling function and the called function are in different translation units, the values of all + externally linked objects and of all objects accessible via pointers therein would agree with the abstract + semantics. Furthermore, at the time of each such function entry the values of the parameters of the called + function and of all objects accessible via pointers therein would agree with the abstract semantics. In this + type of implementation, objects referred to by interrupt service routines activated by the signal function + would require explicit specification of volatile storage, as well as other implementation-defined + restrictions. + +
+ EXAMPLE 2 In executing the fragment +
+ char c1, c2; + /* ... */ + c1 = c1 + c2; ++ the ''integer promotions'' require that the abstract machine promote the value of each variable to int size + and then add the two ints and truncate the sum. Provided the addition of two chars can be done without + overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only + produce the same result, possibly omitting the promotions. + +
+ EXAMPLE 3 Similarly, in the fragment +
+ float f1, f2; + double d; + /* ... */ + f1 = f2 * d; ++ the multiplication may be executed using single-precision arithmetic if the implementation can ascertain + that the result would be the same as if it were executed using double-precision arithmetic (for example, if d + were replaced by the constant 2.0, which has type double). + +
+ EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate + semantics. Values are independent of whether they are represented in a register or in memory. For + example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load + is required to round to the precision of the storage type. In particular, casts and assignments are required to + perform their specified conversion. For the fragment +
+ double d1, d2; + float f; + d1 = f = expression; + d2 = (float) expression; ++ the values assigned to d1 and d2 are required to have been converted to float. + +
+ EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in + precision as well as range. The implementation cannot generally apply the mathematical associative rules + for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of + overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to + rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real + numbers are often not valid (see F.9). +
+ double x, y, z; + /* ... */ + x = (x * y) * z; // not equivalent to x *= y * z; + z = (x - y) + y ; // not equivalent to z = x; + z = x + x * y; // not equivalent to z = x * (1.0 + y); + y = x / 5.0; // not equivalent to y = x * 0.2; ++ +
+ EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment +
+ int a, b; + /* ... */ + a = a + 32760 + b + 5; ++ the expression statement behaves exactly the same as +
+ a = (((a + 32760) + b) + 5); ++ due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is + next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in + which overflows produce an explicit trap and in which the range of values representable by an int is + [-32768, +32767], the implementation cannot rewrite this expression as +
+ a = ((a + b) + 32765); ++ since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap + while the original expression would not; nor can the expression be rewritten either as + +
+ a = ((a + 32765) + b); ++ or +
+ a = (a + (b + 32765)); ++ since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine + in which overflow silently generates some value and where positive and negative overflows cancel, the + above expression statement can be rewritten by the implementation in any of the above ways because the + same result will occur. + +
+ EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the + following fragment +
+ #include <stdio.h> + int sum; + char *p; + /* ... */ + sum = sum * 10 - '0' + (*p++ = getchar()); ++ the expression statement is grouped as if it were written as +
+ sum = (((sum * 10) - '0') + ((*(p++)) = (getchar()))); ++ but the actual increment of p can occur at any time between the previous sequence point and the next + sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned + value. + +
Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the + signal function (7.14), files (7.21.3). + +
12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status + flags and control modes. Floating-point operations implicitly set the status flags; modes affect result + values of floating-point operations. Implementations that support such floating-point state are + required to regard changes to it as side effects -- see annex F for details. The floating-point + environment library <fenv.h> provides a programming facility for indicating when these side + effects matter, freeing the implementations in other cases. + +
13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations + cannot interleave, but can be executed in any order. + + +
+ Under a hosted implementation, a program can have more than one thread of execution + (or thread) running concurrently. The execution of each thread proceeds as defined by + the remainder of this standard. The execution of the entire program consists of an + execution of all of its threads.14) Under a freestanding implementation, it is + implementation-defined whether a program can have more than one thread of execution. +
+ The value of an object visible to a thread T at a particular point is the initial value of the + object, a value stored in the object by T , or a value stored in the object by another thread, + according to the rules below. +
+ NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by + the desire to support atomic operations with explicit and detailed visibility constraints. However, it also + implicitly supports a simpler view for more restricted programs. + +
+ Two expression evaluations conflict if one of them modifies a memory location and the + other one reads or modifies the same memory location. + + + + + +
+ The library defines a number of atomic operations (7.17) and operations on mutexes + (7.25.4) that are specially identified as synchronization operations. These operations play + a special role in making assignments in one thread visible to another. A synchronization + operation on one or more memory locations is either an acquire operation, a release + operation, both an acquire and release operation, or a consume operation. A + synchronization operation without an associated memory location is a fence and can be + either an acquire fence, a release fence, or both an acquire and release fence. In addition, + there are relaxed atomic operations, which are not synchronization operations, and + atomic read-modify-write operations, which have special characteristics. +
+ NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations + composing the mutex. Correspondingly, a call that releases the same mutex will perform a release + operation on those same locations. Informally, performing a release operation on A forces prior side effects + on other memory locations to become visible to other threads that later perform an acquire or consume + operation on A. We do not include relaxed atomic operations as synchronization operations although, like + synchronization operations, they cannot contribute to data races. + +
+ All modifications to a particular atomic object M occur in some particular total order, + called the modification order of M. If A and B are modifications of an atomic object M, + and A happens before B, then A shall precede B in the modification order of M, which is + defined below. +
+ NOTE 3 This states that the modification orders must respect the ''happens before'' relation. + +
+ NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be + combined into a single total order for all objects. In general this will be impossible since different threads + may observe modifications to different variables in inconsistent orders. + +
+ A release sequence on an atomic object M is a maximal contiguous sub-sequence of side + effects in the modification order of M, where the first operation is a release and every + subsequent operation either is performed by the same thread that performed the release or + is an atomic read-modify-write operation. +
+ Certain library calls synchronize with other library calls performed by another thread. In + particular, an atomic operation A that performs a release operation on an object M + synchronizes with an atomic operation B that performs an acquire operation on M and + reads a value written by any side effect in the release sequence headed by A. +
+ NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as + described below. Such a requirement would sometimes interfere with efficient implementation. + +
+ NOTE 6 The specifications of the synchronization operations define when one reads the value written by + another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total + order. Each mutex acquisition ''reads the value written'' by the last mutex release. + +
+ An evaluation A carries a dependency 15) to an evaluation B if: + + + +
+ An evaluation A is dependency-ordered before16) an evaluation B if: +
+ An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A + is dependency-ordered before B, or, for some evaluation X: +
+ NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced + before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The + first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed + by ''sequenced before''. The reason for this limitation is that a consume operation participating in a + ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this + consume operation actually carries a dependency. The reason that this limitation applies only to the end of + such a concatenation is that any subsequent release operation will provide the required ordering for a prior + consume operation. The second exception is that a concatenation is not permitted to consist entirely of + ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be + transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships + consisting entirely of ''sequenced before''. + +
+ An evaluation A happens before an evaluation B if A is sequenced before B or A inter- + thread happens before B. + + + + +
+ A visible side effect A on an object M with respect to a value computation B of M + satisfies the conditions: +
+ NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data + race and the behavior is undefined. + +
+ NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually + detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable + restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent) + execution. + +
+ The visible sequence of side effects on an atomic object M, with respect to a value + computation B of M, is a maximal contiguous sub-sequence of side effects in the + modification order of M, where the first side effect is visible with respect to B, and for + every subsequent side effect, it is not the case that B happens before it. The value of an + atomic object M, as determined by evaluation B, shall be the value stored by some + operation in the visible sequence of M with respect to B. Furthermore, if a value + computation A of an atomic object M happens before a value computation B of M, and + the value computed by A corresponds to the value stored by side effect X, then the value + computed by B shall either equal the value computed by A, or be the value stored by side + effect Y , where Y follows X in the modification order of M. +
+ NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if + both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee + provided by most hardware available to C atomic operations. + +
+ NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the + values observed by loads of atomics, which we are restricting here. The intended reading is that there must + exist an association of atomic loads with modifications they observe that, together with suitably chosen + modification orders and the ''happens before'' relation derived as described above, satisfy the resulting + constraints as imposed here. + +
+ The execution of a program contains a data race if it contains two conflicting actions in + different threads, at least one of which is not atomic, and neither happens before the + other. Any such data race results in undefined behavior. +
+ NOTE 12 It can be shown that programs that correctly use simple mutexes and + memory_order_seq_cst operations to prevent all data races, and use no other synchronization + operations, behave as though the operations executed by their constituent threads were simply interleaved, + with each value computation of an object being the last value stored in that interleaving. This is normally + referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data- + race-free programs cannot observe most program transformations that do not change single-threaded + program semantics. In fact, most single-threaded program transformations continue to be allowed, since + any program that behaves differently as a result must contain undefined behavior. + +
+ NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location + that would not be modified by the abstract machine are generally precluded by this standard, since such an + assignment might overwrite another assignment by a different thread in cases in which an abstract machine + execution would not have encountered a data race. This includes implementations of data member + assignment that overwrite adjacent members in separate memory locations. We also generally preclude + reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the + "visible sequence" rules. + +
+ NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may + not preserve the semantics of the program as defined in this standard, since they potentially introduce a data + race. However, they are typically valid in the context of an optimizing compiler that targets a specific + machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that + is not tolerant of races or provides hardware race detection. + + +
14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of + atomic operations, for example, allow executions inconsistent with a simple interleaving as described + below. + +
15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly + strictly intra-thread. + +
16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses + release/consume in place of release/acquire. + + +
+ Two sets of characters and their associated collating sequences shall be defined: the set in + which source files are written (the source character set), and the set interpreted in the + execution environment (the execution character set). Each set is further divided into a + basic character set, whose contents are given by this subclause, and a set of zero or more + locale-specific members (which are not members of the basic character set) called + extended characters. The combined set is also called the extended character set. The + values of the members of the execution character set are implementation-defined. +
+ In a character constant or string literal, members of the execution character set shall be + represented by corresponding members of the source character set or by escape + sequences consisting of the backslash \ followed by one or more characters. A byte with + all bits set to 0, called the null character, shall exist in the basic execution character set; it + is used to terminate a character string. +
+ Both the basic source and basic execution character sets shall have the following + members: the 26 uppercase letters of the Latin alphabet +
+ A B C D E F G H I J K L M + N O P Q R S T U V W X Y Z ++ the 26 lowercase letters of the Latin alphabet +
+ a b c d e f g h i j k l m + n o p q r s t u v w x y z ++ the 10 decimal digits +
+ 0 1 2 3 4 5 6 7 8 9 ++ the following 29 graphic characters +
+ ! " # % & ' ( ) * + , - . / :
+ ; < = > ? [ \ ] ^ _ { | } ~
+
+ the space character, and control characters representing horizontal tab, vertical tab, and
+ form feed. The representation of each member of the source and execution basic
+ character sets shall fit in a byte. In both the source and execution basic character sets, the
+ value of each character after 0 in the above list of decimal digits shall be one greater than
+ the value of the previous. In source files, there shall be some way of indicating the end of
+ each line of text; this International Standard treats such an end-of-line indicator as if it
+ were a single new-line character. In the basic execution character set, there shall be
+ control characters representing alert, backspace, carriage return, and new line. If any
+ other characters are encountered in a source file (except in an identifier, a character
+ constant, a string literal, a header name, a comment, or a preprocessing token that is never
+
+ converted to a token), the behavior is undefined.
++ A letter is an uppercase letter or a lowercase letter as defined above; in this International + Standard the term does not include other characters that are letters in other alphabets. +
+ The universal character name construct provides a way to name other characters. +
Forward references: universal character names (6.4.3), character constants (6.4.4.4), + preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1). + +
+ Before any other processing takes place, each occurrence of one of the following + sequences of three characters (called trigraph sequences17)) is replaced with the + corresponding single character. +
+ ??= # ??) ] ??! |
+ ??( [ ??' ^ ??> }
+ ??/ \ ??< { ??- ~
+
+ No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
+ above is not changed.
++ EXAMPLE 1 +
+ ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??) ++ becomes +
+ #define arraycheck(a, b) a[b] || b[a] ++ +
+ EXAMPLE 2 The following source line +
+ printf("Eh???/n");
+
+ becomes (after replacement of the trigraph sequence ??/)
+
+ printf("Eh?\n");
+
+
+
+17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as + described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set. + + +
+ The source character set may contain multibyte characters, used to represent members of + the extended character set. The execution character set may also contain multibyte + characters, which need not have the same encoding as for the source character set. For + both character sets, the following shall hold: +
+ For source files, the following shall hold: +
+ The active position is that location on a display device where the next character output by + the fputc function would appear. The intent of writing a printing character (as defined + by the isprint function) to a display device is to display a graphic representation of + that character at the active position and then advance the active position to the next + position on the current line. The direction of writing is locale-specific. If the active + position is at the final position of a line (if there is one), the behavior of the display device + is unspecified. +
+ Alphabetic escape sequences representing nongraphic characters in the execution + character set are intended to produce actions on display devices as follows: + \a (alert) Produces an audible or visible alert without changing the active position. + \b (backspace) Moves the active position to the previous position on the current line. If +
+ the active position is at the initial position of a line, the behavior of the display + device is unspecified. ++ \f ( form feed) Moves the active position to the initial position at the start of the next +
+ logical page. ++ \n (new line) Moves the active position to the initial position of the next line. + \r (carriage return) Moves the active position to the initial position of the current line. + \t (horizontal tab) Moves the active position to the next horizontal tabulation position +
+ on the current line. If the active position is at or past the last defined horizontal + tabulation position, the behavior of the display device is unspecified. ++ \v (vertical tab) Moves the active position to the initial position of the next vertical + +
+ tabulation position. If the active position is at or past the last defined vertical + tabulation position, the behavior of the display device is unspecified. ++
+ Each of these escape sequences shall produce a unique implementation-defined value + which can be stored in a single char object. The external representations in a text file + need not be identical to the internal representations, and are outside the scope of this + International Standard. +
Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3). + +
+ Functions shall be implemented such that they may be interrupted at any time by a signal, + or may be called by a signal handler, or both, with no alteration to earlier, but still active, + invocations' control flow (after the interruption), function return values, or objects with + automatic storage duration. All such objects shall be maintained outside the function + image (the instructions that compose the executable representation of a function) on a + per-invocation basis. + +
+ Both the translation and execution environments constrain the implementation of + language translators and libraries. The following summarizes the language-related + environmental limits on a conforming implementation; the library-related limits are + discussed in clause 7. + +
+ The implementation shall be able to translate and execute at least one program that + contains at least one instance of every one of the following limits:18) +
+ universal character name specifying a short identifier of 00010000 or more is + considered 10 characters, and each extended source character is considered the same + number of characters as the corresponding universal character name, if any)19) ++
18) Implementations should avoid imposing fixed translation limits whenever possible. + +
19) See ''future language directions'' (6.11.3). + + +
+ An implementation is required to document all the limits specified in this subclause, + which are specified in the headers <limits.h> and <float.h>. Additional limits are + specified in <stdint.h>. +
Forward references: integer types <stdint.h> (7.20). + +
+ The values given below shall be replaced by constant expressions suitable for use in #if + preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the + following shall be replaced by expressions that have the same type as would an + expression that is an object of the corresponding type converted according to the integer + promotions. Their implementation-defined values shall be equal or greater in magnitude + + + + (absolute value) to those shown, with the same sign. +
+ If the value of an object of type char is treated as a signed integer when used in an + expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the + value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of + CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of + UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1. +
Forward references: representations of types (6.2.6), conditional inclusion (6.10.1). + +
+ The characteristics of floating types are defined in terms of a model that describes a + representation of floating-point numbers and values that provide information about an + implementation's floating-point arithmetic.21) The following parameters are used to + define the model for each floating-point type: +
+ s sign ((+-)1) + b base or radix of exponent representation (an integer > 1) + e exponent (an integer between a minimum emin and a maximum emax ) + p precision (the number of base-b digits in the significand) + fk nonnegative integers less than b (the significand digits) ++
+ A floating-point number (x) is defined by the following model: +
+ p + x = sb e (Sum) f k b-k , + k=1 + emin <= e <= emax ++ +
+ In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be + able to contain other kinds of floating-point numbers, such as subnormal floating-point + numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0, + e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and + NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates + through almost every arithmetic operation without raising a floating-point exception; a + signaling NaN generally raises a floating-point exception when occurring as an + + + + arithmetic operand.22) +
+ An implementation may give zero and values that are not floating-point numbers (such as + infinities and NaNs) a sign or may leave them unsigned. Wherever such values are + unsigned, any requirement in this International Standard to retrieve the sign shall produce + an unspecified sign, and any requirement to set the sign shall be ignored. +
+ The minimum range of representable values for a floating type is the most negative finite + floating-point number representable in that type through the most positive finite floating- + point number representable in that type. In addition, if negative infinity is representable + in a type, the range of that type is extended to all negative real numbers; likewise, if + positive infinity is representable in a type, the range of that type is extended to all positive + real numbers. +
+ The accuracy of the floating-point operations (+, -, *, /) and of the library functions in + <math.h> and <complex.h> that return floating-point results is implementation- + defined, as is the accuracy of the conversion between floating-point internal + representations and string representations performed by the library functions in + <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the + accuracy is unknown. +
+ All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant + expressions suitable for use in #if preprocessing directives; all floating values shall be + constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX, + and FLT_ROUNDS have separate names for all three floating-point types. The floating- + point model representation is provided for all values except FLT_EVAL_METHOD and + FLT_ROUNDS. +
+ The rounding mode for floating-point addition is characterized by the implementation- + defined value of FLT_ROUNDS:23) +
+ -1 indeterminable + 0 toward zero + 1 to nearest + 2 toward positive infinity + 3 toward negative infinity ++ All other values for FLT_ROUNDS characterize implementation-defined rounding + behavior. + + + +
+ Except for assignment and cast (which remove all extra range and precision), the values + yielded by operators with floating operands and values subject to the usual arithmetic + conversions and of floating constants are evaluated to a format whose range and precision + may be greater than required by the type. The use of evaluation formats is characterized + by the implementation-defined value of FLT_EVAL_METHOD:24) +
+ -1 indeterminable; + 0 evaluate all operations and constants just to the range and precision of the + type; + 1 evaluate operations and constants of type float and double to the + range and precision of the double type, evaluate long double + operations and constants to the range and precision of the long double + type; + 2 evaluate all operations and constants to the range and precision of the + long double type. ++ All other negative values for FLT_EVAL_METHOD characterize implementation-defined + behavior. +
+ The presence or absence of subnormal numbers is characterized by the implementation- + defined values of FLT_HAS_SUBNORM, DBL_HAS_SUBNORM, and + LDBL_HAS_SUBNORM: +
+ -1 indeterminable25) + 0 absent26) (type does not support subnormal numbers) + 1 present (type does support subnormal numbers) ++
+ The values given in the following list shall be replaced by constant expressions with + implementation-defined values that are greater or equal in magnitude (absolute value) to + those shown, with the same sign: +
+ { p log10 b if b is a power of 10
+ {
+ { [^1 + p log10 b^] otherwise
+
+ FLT_DECIMAL_DIG 6
+ DBL_DECIMAL_DIG 10
+ LDBL_DECIMAL_DIG 10
+
+ { pmax log10 b if b is a power of 10
+ {
+ { [^1 + pmax log10 b^] otherwise
+
+ DECIMAL_DIG 10
+
+ { p log10 b if b is a power of 10
+ {
+ { [_( p - 1) log10 b_] otherwise
+
+ FLT_DIG 6
+ DBL_DIG 10
+ LDBL_DIG 10
++ [ ] ++ FLT_MIN_10_EXP -37 + DBL_MIN_10_EXP -37 + LDBL_MIN_10_EXP -37 +
+ FLT_MAX_EXP + DBL_MAX_EXP + LDBL_MAX_EXP ++
+ FLT_MAX_10_EXP +37 + DBL_MAX_10_EXP +37 + LDBL_MAX_10_EXP +37 ++
+ The values given in the following list shall be replaced by constant expressions with + implementation-defined values that are greater than or equal to those shown: +
+ FLT_MAX 1E+37 + DBL_MAX 1E+37 + LDBL_MAX 1E+37 ++
+ The values given in the following list shall be replaced by constant expressions with + implementation-defined (positive) values that are less than or equal to those shown: +
+ FLT_EPSILON 1E-5 + DBL_EPSILON 1E-9 + LDBL_EPSILON 1E-9 ++
+ FLT_MIN 1E-37 + DBL_MIN 1E-37 + LDBL_MIN 1E-37 ++
+ Conversion from (at least) double to decimal with DECIMAL_DIG digits and back + should be the identity function. +
+ EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum + requirements of this International Standard, and the appropriate values in a <float.h> header for type + float: +
+ 6 + x = s16e (Sum) f k 16-k , + k=1 + -31 <= e <= +32 ++ +
+ FLT_RADIX 16 + FLT_MANT_DIG 6 + FLT_EPSILON 9.53674316E-07F + FLT_DECIMAL_DIG 9 + FLT_DIG 6 + FLT_MIN_EXP -31 + FLT_MIN 2.93873588E-39F + FLT_MIN_10_EXP -38 + FLT_MAX_EXP +32 + FLT_MAX 3.40282347E+38F + FLT_MAX_10_EXP +38 ++ +
+ EXAMPLE 2 The following describes floating-point representations that also meet the requirements for + single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a + <float.h> header for types float and double: +
+ 24 + x f = s2e (Sum) f k 2-k , + k=1 + -125 <= e <= +128 ++ +
+ 53 + x d = s2e (Sum) f k 2-k , + k=1 + -1021 <= e <= +1024 ++ +
+ FLT_RADIX 2 + DECIMAL_DIG 17 + FLT_MANT_DIG 24 + FLT_EPSILON 1.19209290E-07F // decimal constant + FLT_EPSILON 0X1P-23F // hex constant + FLT_DECIMAL_DIG 9 ++ + + +
+ FLT_DIG 6 + FLT_MIN_EXP -125 + FLT_MIN 1.17549435E-38F // decimal constant + FLT_MIN 0X1P-126F // hex constant + FLT_TRUE_MIN 1.40129846E-45F // decimal constant + FLT_TRUE_MIN 0X1P-149F // hex constant + FLT_HAS_SUBNORM 1 + FLT_MIN_10_EXP -37 + FLT_MAX_EXP +128 + FLT_MAX 3.40282347E+38F // decimal constant + FLT_MAX 0X1.fffffeP127F // hex constant + FLT_MAX_10_EXP +38 + DBL_MANT_DIG 53 + DBL_EPSILON 2.2204460492503131E-16 // decimal constant + DBL_EPSILON 0X1P-52 // hex constant + DBL_DECIMAL_DIG 17 + DBL_DIG 15 + DBL_MIN_EXP -1021 + DBL_MIN 2.2250738585072014E-308 // decimal constant + DBL_MIN 0X1P-1022 // hex constant + DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant + DBL_TRUE_MIN 0X1P-1074 // hex constant + DBL_HAS_SUBNORM 1 + DBL_MIN_10_EXP -307 + DBL_MAX_EXP +1024 + DBL_MAX 1.7976931348623157E+308 // decimal constant + DBL_MAX 0X1.fffffffffffffP1023 // hex constant + DBL_MAX_10_EXP +308 ++ If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For + example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of + precision), then DECIMAL_DIG would be 21. + +
Forward references: conditional inclusion (6.10.1), complex arithmetic + <complex.h> (7.3), extended multibyte and wide character utilities <wchar.h> + (7.28), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h> + (7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12). + + +
21) The floating-point model is intended to clarify the description of each floating-point characteristic and + does not require the floating-point arithmetic of the implementation to be identical. + +
22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support + IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with + similar behavior. + +
23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through + the function fesetround in <fenv.h>. + +
24) The evaluation method determines evaluation formats of expressions involving all floating types, not + just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float + _Complex operands is represented in the double _Complex format, and its parts are evaluated to + double. + +
25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret + subnormal representations as zero, nor as nonzero. + +
26) Characterization as absent is intended if no floating-point operations produce subnormal results from + non-subnormal inputs, even if the type format includes representations of subnormal numbers. + +
27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a + positive number no greater than the minimum normalized positive number for the type. + +
28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent + limits are one less than shown here. + + +
+ In the syntax notation used in this clause, syntactic categories (nonterminals) are + indicated by italic type, and literal words and character set members (terminals) by bold + type. A colon (:) following a nonterminal introduces its definition. Alternative + definitions are listed on separate lines, except when prefaced by the words ''one of''. An + optional symbol is indicated by the subscript ''opt'', so that +
+ { expressionopt }
+
+ indicates an optional expression enclosed in braces.
++ When syntactic categories are referred to in the main text, they are not italicized and + words are separated by spaces instead of hyphens. +
+ A summary of the language syntax is given in annex A. + +
+ An identifier can denote an object; a function; a tag or a member of a structure, union, or + enumeration; a typedef name; a label name; a macro name; or a macro parameter. The + same identifier can denote different entities at different points in the program. A member + of an enumeration is called an enumeration constant. Macro names and macro + parameters are not considered further here, because prior to the semantic phase of + program translation any occurrences of macro names in the source file are replaced by the + preprocessing token sequences that constitute their macro definitions. +
+ For each different entity that an identifier designates, the identifier is visible (i.e., can be + used) only within a region of program text called its scope. Different entities designated + by the same identifier either have different scopes, or are in different name spaces. There + are four kinds of scopes: function, file, block, and function prototype. (A function + prototype is a declaration of a function that declares the types of its parameters.) +
+ A label name is the only kind of identifier that has function scope. It can be used (in a + goto statement) anywhere in the function in which it appears, and is declared implicitly + by its syntactic appearance (followed by a : and a statement). +
+ Every other identifier has scope determined by the placement of its declaration (in a + declarator or type specifier). If the declarator or type specifier that declares the identifier + appears outside of any block or list of parameters, the identifier has file scope, which + terminates at the end of the translation unit. If the declarator or type specifier that + declares the identifier appears inside a block or within the list of parameter declarations in + a function definition, the identifier has block scope, which terminates at the end of the + associated block. If the declarator or type specifier that declares the identifier appears + + within the list of parameter declarations in a function prototype (not part of a function + definition), the identifier has function prototype scope, which terminates at the end of the + function declarator. If an identifier designates two different entities in the same name + space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end + strictly before the scope of the other entity (the outer scope). Within the inner scope, the + identifier designates the entity declared in the inner scope; the entity declared in the outer + scope is hidden (and not visible) within the inner scope. +
+ Unless explicitly stated otherwise, where this International Standard uses the term + ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the + entity in the relevant name space whose declaration is visible at the point the identifier + occurs. +
+ Two identifiers have the same scope if and only if their scopes terminate at the same + point. +
+ Structure, union, and enumeration tags have scope that begins just after the appearance of + the tag in a type specifier that declares the tag. Each enumeration constant has scope that + begins just after the appearance of its defining enumerator in an enumerator list. Any + other identifier has scope that begins just after the completion of its declarator. +
+ As a special case, a type name (which is not a declaration of an identifier) is considered to + have a scope that begins just after the place within the type name where the omitted + identifier would appear were it not omitted. +
Forward references: declarations (6.7), function calls (6.5.2.2), function definitions + (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3), + source file inclusion (6.10.2), statements (6.8). + +
+ An identifier declared in different scopes or in the same scope more than once can be + made to refer to the same object or function by a process called linkage.29) There are + three kinds of linkage: external, internal, and none. +
+ In the set of translation units and libraries that constitutes an entire program, each + declaration of a particular identifier with external linkage denotes the same object or + function. Within one translation unit, each declaration of an identifier with internal + linkage denotes the same object or function. Each declaration of an identifier with no + linkage denotes a unique entity. +
+ If the declaration of a file scope identifier for an object or a function contains the storage- + class specifier static, the identifier has internal linkage.30) + + + + +
+ For an identifier declared with the storage-class specifier extern in a scope in which a + prior declaration of that identifier is visible,31) if the prior declaration specifies internal or + external linkage, the linkage of the identifier at the later declaration is the same as the + linkage specified at the prior declaration. If no prior declaration is visible, or if the prior + declaration specifies no linkage, then the identifier has external linkage. +
+ If the declaration of an identifier for a function has no storage-class specifier, its linkage + is determined exactly as if it were declared with the storage-class specifier extern. If + the declaration of an identifier for an object has file scope and no storage-class specifier, + its linkage is external. +
+ The following identifiers have no linkage: an identifier declared to be anything other than + an object or a function; an identifier declared to be a function parameter; a block scope + identifier for an object declared without the storage-class specifier extern. +
+ If, within a translation unit, the same identifier appears with both internal and external + linkage, the behavior is undefined. +
Forward references: declarations (6.7), expressions (6.5), external definitions (6.9), + statements (6.8). + +
29) There is no linkage between different identifiers. + +
30) A function declaration can contain the storage-class specifier static only if it is at file scope; see + 6.7.1. + +
31) As specified in 6.2.1, the later declaration might hide the prior declaration. + + +
+ If more than one declaration of a particular identifier is visible at any point in a + translation unit, the syntactic context disambiguates uses that refer to different entities. + Thus, there are separate name spaces for various categories of identifiers, as follows: +
Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1), + structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags + (6.7.2.3), the goto statement (6.8.6.1). + + + +
32) There is only one name space for tags even though three are possible. + + +
+ An object has a storage duration that determines its lifetime. There are four storage + durations: static, thread, automatic, and allocated. Allocated storage is described in + 7.22.3. +
+ The lifetime of an object is the portion of program execution during which storage is + guaranteed to be reserved for it. An object exists, has a constant address,33) and retains + its last-stored value throughout its lifetime.34) If an object is referred to outside of its + lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when + the object it points to (or just past) reaches the end of its lifetime. +
+ An object whose identifier is declared without the storage-class specifier + _Thread_local, and either with external or internal linkage or with the storage-class + specifier static, has static storage duration. Its lifetime is the entire execution of the + program and its stored value is initialized only once, prior to program startup. +
+ An object whose identifier is declared with the storage-class specifier _Thread_local + has thread storage duration. Its lifetime is the entire execution of the thread for which it + is created, and its stored value is initialized when the thread is started. There is a distinct + object per thread, and use of the declared name in an expression refers to the object + associated with the thread evaluating the expression. The result of attempting to + indirectly access an object with thread storage duration from a thread other than the one + with which the object is associated is implementation-defined. +
+ An object whose identifier is declared with no linkage and without the storage-class + specifier static has automatic storage duration, as do some compound literals. The + result of attempting to indirectly access an object with automatic storage duration from a + thread other than the one with which the object is associated is implementation-defined. +
+ For such an object that does not have a variable length array type, its lifetime extends + from entry into the block with which it is associated until execution of that block ends in + any way. (Entering an enclosed block or calling a function suspends, but does not end, + execution of the current block.) If the block is entered recursively, a new instance of the + object is created each time. The initial value of the object is indeterminate. If an + initialization is specified for the object, it is performed each time the declaration or + compound literal is reached in the execution of the block; otherwise, the value becomes + indeterminate each time the declaration is reached. + + + + +
+ For such an object that does have a variable length array type, its lifetime extends from + the declaration of the object until execution of the program leaves the scope of the + declaration.35) If the scope is entered recursively, a new instance of the object is created + each time. The initial value of the object is indeterminate. +
+ A non-lvalue expression with structure or union type, where the structure or union + contains a member with array type (including, recursively, members of all contained + structures and unions) refers to an object with automatic storage duration and temporary + lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the + value of the expression. Its lifetime ends when the evaluation of the containing full + expression or full declarator ends. Any attempt to modify an object with temporary + lifetime results in undefined behavior. +
Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators + (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8). + +
33) The term ''constant address'' means that two pointers to the object constructed at possibly different + times will compare equal. The address may be different during two different executions of the same + program. + +
34) In the case of a volatile object, the last store need not be explicit in the program. + +
35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an + embedded block prior to the declaration, leaves the scope of the declaration. + +
36) The address of such an object is taken implicitly when an array member is accessed. + + +
+ The meaning of a value stored in an object or returned by a function is determined by the + type of the expression used to access it. (An identifier declared to be an object is the + simplest such expression; the type is specified in the declaration of the identifier.) Types + are partitioned into object types (types that describe objects) and function types (types + that describe functions). At various points within a translation unit an object type may be + incomplete (lacking sufficient information to determine the size of objects of that type) or + complete (having sufficient information).37) +
+ An object declared as type _Bool is large enough to store the values 0 and 1. +
+ An object declared as type char is large enough to store any member of the basic + execution character set. If a member of the basic execution character set is stored in a + char object, its value is guaranteed to be nonnegative. If any other character is stored in + a char object, the resulting value is implementation-defined but shall be within the range + of values that can be represented in that type. +
+ There are five standard signed integer types, designated as signed char, short + int, int, long int, and long long int. (These and other types may be + designated in several additional ways, as described in 6.7.2.) There may also be + implementation-defined extended signed integer types.38) The standard and extended + signed integer types are collectively called signed integer types.39) + + +
+ An object declared as type signed char occupies the same amount of storage as a + ''plain'' char object. A ''plain'' int object has the natural size suggested by the + architecture of the execution environment (large enough to contain any value in the range + INT_MIN to INT_MAX as defined in the header <limits.h>). +
+ For each of the signed integer types, there is a corresponding (but different) unsigned + integer type (designated with the keyword unsigned) that uses the same amount of + storage (including sign information) and has the same alignment requirements. The type + _Bool and the unsigned integer types that correspond to the standard signed integer + types are the standard unsigned integer types. The unsigned integer types that + correspond to the extended signed integer types are the extended unsigned integer types. + The standard and extended unsigned integer types are collectively called unsigned integer + types.40) +
+ The standard signed integer types and standard unsigned integer types are collectively + called the standard integer types, the extended signed integer types and extended + unsigned integer types are collectively called the extended integer types. +
+ For any two integer types with the same signedness and different integer conversion rank + (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a + subrange of the values of the other type. +
+ The range of nonnegative values of a signed integer type is a subrange of the + corresponding unsigned integer type, and the representation of the same value in each + type is the same.41) A computation involving unsigned operands can never overflow, + because a result that cannot be represented by the resulting unsigned integer type is + reduced modulo the number that is one greater than the largest value that can be + represented by the resulting type. +
+ There are three real floating types, designated as float, double, and long + double.42) The set of values of the type float is a subset of the set of values of the + type double; the set of values of the type double is a subset of the set of values of the + type long double. + + + +
+ There are three complex types, designated as float _Complex, double + _Complex, and long double _Complex.43) (Complex types are a conditional + feature that implementations need not support; see 6.10.8.3.) The real floating and + complex types are collectively called the floating types. +
+ For each floating type there is a corresponding real type, which is always a real floating + type. For real floating types, it is the same type. For complex types, it is the type given + by deleting the keyword _Complex from the type name. +
+ Each complex type has the same representation and alignment requirements as an array + type containing exactly two elements of the corresponding real type; the first element is + equal to the real part, and the second element to the imaginary part, of the complex + number. +
+ The type char, the signed and unsigned integer types, and the floating types are + collectively called the basic types. The basic types are complete object types. Even if the + implementation defines two or more basic types to have the same representation, they are + nevertheless different types.44) +
+ The three types char, signed char, and unsigned char are collectively called + the character types. The implementation shall define char to have the same range, + representation, and behavior as either signed char or unsigned char.45) +
+ An enumeration comprises a set of named integer constant values. Each distinct + enumeration constitutes a different enumerated type. +
+ The type char, the signed and unsigned integer types, and the enumerated types are + collectively called integer types. The integer and real floating types are collectively called + real types. +
+ Integer and floating types are collectively called arithmetic types. Each arithmetic type + belongs to one type domain: the real type domain comprises the real types, the complex + type domain comprises the complex types. +
+ The void type comprises an empty set of values; it is an incomplete object type that + cannot be completed. + + + + +
+ Any number of derived types can be constructed from the object and function types, as + follows: +
+ Arithmetic types and pointer types are collectively called scalar types. Array and + structure types are collectively called aggregate types.46) +
+ An array type of unknown size is an incomplete type. It is completed, for an identifier of + that type, by specifying the size in a later declaration (with internal or external linkage). + A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete + + + + type. It is completed, for all declarations of that type, by declaring the same structure or + union tag with its defining content later in the same scope. +
+ A type has known constant size if the type is not incomplete and is not a variable length + array type. +
+ Array, function, and pointer types are collectively called derived declarator types. A + declarator type derivation from a type T is the construction of a derived declarator type + from T by the application of an array-type, a function-type, or a pointer-type derivation to + T. +
+ A type is characterized by its type category, which is either the outermost derivation of a + derived type (as noted above in the construction of derived types), or the type itself if the + type consists of no derived types. +
+ Any type so far mentioned is an unqualified type. Each unqualified type has several + qualified versions of its type,47) corresponding to the combinations of one, two, or all + three of the const, volatile, and restrict qualifiers. The qualified or unqualified + versions of a type are distinct types that belong to the same type category and have the + same representation and alignment requirements.48) A derived type is not qualified by the + qualifiers (if any) of the type from which it is derived. +
+ Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier + designates an atomic type. The size, representation, and alignment of an atomic type + need not be the same as those of the corresponding unqualified type. Therefore, this + Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the + atomic version of a type is permitted along with the other qualified versions of a type. + The phrase ''qualified or unqualified type'', without specific mention of atomic, does not + include the atomic types. +
+ A pointer to void shall have the same representation and alignment requirements as a + pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of + compatible types shall have the same representation and alignment requirements. All + pointers to structure types shall have the same representation and alignment requirements + as each other. All pointers to union types shall have the same representation and + alignment requirements as each other. Pointers to other types need not have the same + representation or alignment requirements. +
+ EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is + pointer, not a floating type. The const-qualified version of this type is designated as ''float * const'' + whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const- + + + + qualified float'' and is a pointer to a qualified type. + +
+ EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to + function returning struct tag''. The array has length five and the function has a single parameter of type + float. Its type category is array. + +
Forward references: compatible type and composite type (6.2.7), declarations (6.7). + +
37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at + different points within a translation unit. + +
38) Implementation-defined keywords shall have the form of an identifier reserved for any use as + described in 7.1.3. + +
39) Therefore, any statement in this Standard about signed integer types also applies to the extended + signed integer types. + +
40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended + unsigned integer types. + +
41) The same representation and alignment requirements are meant to imply interchangeability as + arguments to functions, return values from functions, and members of unions. + +
42) See ''future language directions'' (6.11.1). + +
43) A specification for imaginary types is in annex G. + +
44) An implementation may define new keywords that provide alternative ways to designate a basic (or + any other) type; this does not violate the requirement that all basic types be different. + Implementation-defined keywords shall have the form of an identifier reserved for any use as + described in 7.1.3. + +
45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be + used to distinguish the two options. Irrespective of the choice made, char is a separate type from the + other two and is not compatible with either. + +
46) Note that aggregate type does not include union type because an object with union type can only + contain one member at a time. + +
47) See 6.7.3 regarding qualified array and function types. + +
48) The same representation and alignment requirements are meant to imply interchangeability as + arguments to functions, return values from functions, and members of unions. + + +
+ The representations of all types are unspecified except as stated in this subclause. +
+ Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, + the number, order, and encoding of which are either explicitly specified or + implementation-defined. +
+ Values stored in unsigned bit-fields and objects of type unsigned char shall be + represented using a pure binary notation.49) +
+ Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT + bits, where n is the size of an object of that type, in bytes. The value may be copied into + an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is + called the object representation of the value. Values stored in bit-fields consist of m bits, + where m is the size specified for the bit-field. The object representation is the set of m + bits the bit-field comprises in the addressable storage unit holding it. Two values (other + than NaNs) with the same object representation compare equal, but values that compare + equal may have different object representations. +
+ Certain object representations need not represent a value of the object type. If the stored + value of an object has such a representation and is read by an lvalue expression that does + not have character type, the behavior is undefined. If such a representation is produced + by a side effect that modifies all or any part of the object by an lvalue expression that + does not have character type, the behavior is undefined.50) Such a representation is called + a trap representation. +
+ When a value is stored in an object of structure or union type, including in a member + object, the bytes of the object representation that correspond to any padding bytes take + unspecified values.51) The value of a structure or union object is never a trap + + + + representation, even though the value of a member of the structure or union object may be + a trap representation. +
+ When a value is stored in a member of an object of union type, the bytes of the object + representation that do not correspond to that member but do correspond to other members + take unspecified values. +
+ Where an operator is applied to a value that has more than one object representation, + which object representation is used shall not affect the value of the result.52) Where a + value is stored in an object using a type that has more than one object representation for + that value, it is unspecified which representation is used, but a trap representation shall + not be generated. +
+ Loads and stores of objects with atomic types are done with + memory_order_seq_cst semantics. +
Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function + designators (6.3.2.1), order and consistency (7.17.3). + +
49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
+ represented by successive bits are additive, begin with 1, and are multiplied by successive integral
+ powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
+ Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
+ type unsigned char range from 0 to 2
+
+
+ CHAR_BIT
+ - 1.
+
+
+
50) Thus, an automatic variable can be initialized to a trap representation without causing undefined + behavior, but the value of the variable cannot be used until a proper value is stored in it. + +
51) Thus, for example, structure assignment need not copy any padding bits. + +
52) It is possible for objects x and y with the same effective type T to have the same value when they are + accessed as objects of type T, but to have different values in other contexts. In particular, if == is + defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0. + Furthermore, x == y does not necessarily imply that x and y have the same value; other operations + on values of type T may distinguish between them. + + +
+ For unsigned integer types other than unsigned char, the bits of the object + representation shall be divided into two groups: value bits and padding bits (there need + not be any of the latter). If there are N value bits, each bit shall represent a different + power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of + representing values from 0 to 2 N - 1 using a pure binary representation; this shall be + known as the value representation. The values of any padding bits are unspecified.53) +
+ For signed integer types, the bits of the object representation shall be divided into three + groups: value bits, padding bits, and the sign bit. There need not be any padding bits; + signed char shall not have any padding bits. There shall be exactly one sign bit. + Each bit that is a value bit shall have the same value as the same bit in the object + representation of the corresponding unsigned type (if there are M value bits in the signed + type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect + + + the resulting value. If the sign bit is one, the value shall be modified in one of the + following ways: +
+ If the implementation supports negative zeros, they shall be generated only by: +
+ If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<, + and >> operators with operands that would produce such a value is undefined. +
+ The values of any padding bits are unspecified.54) A valid (non-trap) object representation + of a signed integer type where the sign bit is zero is a valid object representation of the + corresponding unsigned type, and shall represent the same value. For any integer type, + the object representation where all the bits are zero shall be a representation of the value + zero in that type. +
+ The precision of an integer type is the number of bits it uses to represent values, + excluding any sign and padding bits. The width of an integer type is the same but + including any sign bit; thus for unsigned integer types the two values are the same, while + for signed integer types the width is one greater than the precision. + + + + + + +
53) Some combinations of padding bits might generate trap representations, for example, if one padding + bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap + representation other than as part of an exceptional condition such as an overflow, and this cannot occur + with unsigned types. All other combinations of padding bits are alternative object representations of + the value specified by the value bits. + +
54) Some combinations of padding bits might generate trap representations, for example, if one padding + bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap + representation other than as part of an exceptional condition such as an overflow. All other + combinations of padding bits are alternative object representations of the value specified by the value + bits. + + +
+ Two types have compatible type if their types are the same. Additional rules for + determining whether two types are compatible are described in 6.7.2 for type specifiers, + in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure, + union, or enumerated types declared in separate translation units are compatible if their + tags and members satisfy the following requirements: If one is declared with a tag, the + other shall be declared with the same tag. If both are completed anywhere within their + respective translation units, then the following additional requirements apply: there shall + be a one-to-one correspondence between their members such that each pair of + corresponding members are declared with compatible types; if one member of the pair is + declared with an alignment specifier, the other is declared with an equivalent alignment + specifier; and if one member of the pair is declared with a name, the other is declared + with the same name. For two structures, corresponding members shall be declared in the + same order. For two structures or unions, corresponding bit-fields shall have the same + widths. For two enumerations, corresponding members shall have the same values. +
+ All declarations that refer to the same object or function shall have compatible type; + otherwise, the behavior is undefined. +
+ A composite type can be constructed from two types that are compatible; it is a type that + is compatible with both of the two types and satisfies the following conditions: +
+ For an identifier with internal or external linkage declared in a scope in which a prior + declaration of that identifier is visible,56) if the prior declaration specifies internal or + external linkage, the type of the identifier at the later declaration becomes the composite + type. +
Forward references: array declarators (6.7.6.2). +
+ EXAMPLE Given the following two file scope declarations: +
+ int f(int (*)(), double (*)[3]); + int f(int (*)(char *), double (*)[]); ++ The resulting composite type for the function is: +
+ int f(int (*)(char *), double (*)[3]); ++ + +
55) Two types need not be identical to be compatible. + +
56) As specified in 6.2.1, the later declaration might hide the prior declaration. + + +
+ Complete object types have alignment requirements which place restrictions on the + addresses at which objects of that type may be allocated. An alignment is an + implementation-defined integer value representing the number of bytes between + successive addresses at which a given object can be allocated. An object type imposes an + alignment requirement on every object of that type: stricter alignment can be requested + using the _Alignas keyword. +
+ A fundamental alignment is represented by an alignment less than or equal to the greatest + alignment supported by the implementation in all contexts, which is equal to + alignof(max_align_t). +
+ An extended alignment is represented by an alignment greater than + alignof(max_align_t). It is implementation-defined whether any extended + alignments are supported and the contexts in which they are supported. A type having an + extended alignment requirement is an over-aligned type.57) +
+ Alignments are represented as values of the type size_t. Valid alignments include only + those values returned by an alignof expression for fundamental types, plus an + additional implementation-defined set of values, which may be empty. Every valid + alignment value shall be a nonnegative integral power of two. + + + +
+ Alignments have an order from weaker to stronger or stricter alignments. Stricter + alignments have larger alignment values. An address that satisfies an alignment + requirement also satisfies any weaker valid alignment requirement. +
+ The alignment requirement of a complete type can be queried using an alignof + expression. The types char, signed char, and unsigned char shall have the + weakest alignment requirement. +
+ Comparing alignments is meaningful and provides the obvious results: +
57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended + alignment has been applied. + + +
+ Several operators convert operand values from one type to another automatically. This + subclause specifies the result required from such an implicit conversion, as well as those + that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes + the conversions performed by most ordinary operators; it is supplemented as required by + the discussion of each operator in 6.5. +
+ Conversion of an operand value to a compatible type causes no change to the value or the + representation. +
Forward references: cast operators (6.5.4). + +
+ Every integer type has an integer conversion rank defined as follows: +
+ The following may be used in an expression wherever an int or unsigned int may + be used: + +
+ The integer promotions preserve value including sign. As discussed earlier, whether a + ''plain'' char is treated as signed is implementation-defined. +
Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers + (6.7.2.1). + +
58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain + argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the + shift operators, as specified by their respective subclauses. + + +
+ When any scalar value is converted to _Bool, the result is 0 if the value compares equal + to 0; otherwise, the result is 1.59) + +
59) NaNs do not compare equal to 0 and thus convert to 1. + + +
+ When a value with integer type is converted to another integer type other than _Bool, if + the value can be represented by the new type, it is unchanged. +
+ Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or + subtracting one more than the maximum value that can be represented in the new type + until the value is in the range of the new type.60) +
+ Otherwise, the new type is signed and the value cannot be represented in it; either the + result is implementation-defined or an implementation-defined signal is raised. + +
60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression. + + +
+ When a finite value of real floating type is converted to an integer type other than _Bool, + the fractional part is discarded (i.e., the value is truncated toward zero). If the value of + the integral part cannot be represented by the integer type, the behavior is undefined.61) + + + +
+ When a value of integer type is converted to a real floating type, if the value being + converted can be represented exactly in the new type, it is unchanged. If the value being + converted is in the range of values that can be represented but cannot be represented + exactly, the result is either the nearest higher or nearest lower representable value, chosen + in an implementation-defined manner. If the value being converted is outside the range of + values that can be represented, the behavior is undefined. Results of some implicit + conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that + required by the new type. + +
61) The remaindering operation performed when a value of integer type is converted to unsigned type + need not be performed when a value of real floating type is converted to unsigned type. Thus, the + range of portable real floating values is (-1, Utype_MAX+1). + + +
+ When a value of real floating type is converted to a real floating type, if the value being + converted can be represented exactly in the new type, it is unchanged. If the value being + converted is in the range of values that can be represented but cannot be represented + exactly, the result is either the nearest higher or nearest lower representable value, chosen + in an implementation-defined manner. If the value being converted is outside the range of + values that can be represented, the behavior is undefined. Results of some implicit + conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that + required by the new type. + +
+ When a value of complex type is converted to another complex type, both the real and + imaginary parts follow the conversion rules for the corresponding real types. + +
+ When a value of real type is converted to a complex type, the real part of the complex + result value is determined by the rules of conversion to the corresponding real type and + the imaginary part of the complex result value is a positive zero or an unsigned zero. +
+ When a value of complex type is converted to a real type, the imaginary part of the + complex value is discarded and the value of the real part is converted according to the + conversion rules for the corresponding real type. + +
+ Many operators that expect operands of arithmetic type cause conversions and yield result + types in a similar way. The purpose is to determine a common real type for the operands + and result. For the specified operands, each operand is converted, without change of type + domain, to a type whose corresponding real type is the common real type. Unless + explicitly stated otherwise, the common real type is also the corresponding real type of + the result, whose type domain is the type domain of the operands if they are the same, + and complex otherwise. This pattern is called the usual arithmetic conversions: + +
+ First, if the corresponding real type of either operand is long double, the other + operand is converted, without change of type domain, to a type whose + corresponding real type is long double. + Otherwise, if the corresponding real type of either operand is double, the other + operand is converted, without change of type domain, to a type whose + corresponding real type is double. + Otherwise, if the corresponding real type of either operand is float, the other + operand is converted, without change of type domain, to a type whose + corresponding real type is float.62) + Otherwise, the integer promotions are performed on both operands. Then the + following rules are applied to the promoted operands: + If both operands have the same type, then no further conversion is needed. + Otherwise, if both operands have signed integer types or both have unsigned + integer types, the operand with the type of lesser integer conversion rank is + converted to the type of the operand with greater rank. + Otherwise, if the operand that has unsigned integer type has rank greater or + equal to the rank of the type of the other operand, then the operand with + signed integer type is converted to the type of the operand with unsigned + integer type. + Otherwise, if the type of the operand with signed integer type can represent + all of the values of the type of the operand with unsigned integer type, then + the operand with unsigned integer type is converted to the type of the + operand with signed integer type. + Otherwise, both operands are converted to the unsigned integer type + corresponding to the type of the operand with signed integer type. ++
+ The values of floating operands and of the results of floating expressions may be + represented in greater precision and range than that required by the type; the types are not + changed thereby.63) + + + + + + +
62) For example, addition of a double _Complex and a float entails just the conversion of the + float operand to double (and yields a double _Complex result). + +
63) The cast and assignment operators are still required to remove extra range and precision. + + +
+ An lvalue is an expression (with an object type other than void) that potentially + designates an object;64) if an lvalue does not designate an object when it is evaluated, the + behavior is undefined. When an object is said to have a particular type, the type is + specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that + does not have array type, does not have an incomplete type, does not have a const- + qualified type, and if it is a structure or union, does not have any member (including, + recursively, any member or element of all contained aggregates or unions) with a const- + qualified type. +
+ Except when it is the operand of the sizeof operator, the unary & operator, the ++ + operator, the -- operator, or the left operand of the . operator or an assignment operator, + an lvalue that does not have array type is converted to the value stored in the designated + object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has + qualified type, the value has the unqualified version of the type of the lvalue; additionally, + if the lvalue has atomic type, the value has the non-atomic version of the type of the + lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete + type and does not have array type, the behavior is undefined. If the lvalue designates an + object of automatic storage duration that could have been declared with the register + storage class (never had its address taken), and that object is uninitialized (not declared + with an initializer and no assignment to it has been performed prior to use), the behavior + is undefined. +
+ Except when it is the operand of the sizeof operator or the unary & operator, or is a + string literal used to initialize an array, an expression that has type ''array of type'' is + converted to an expression with type ''pointer to type'' that points to the initial element of + the array object and is not an lvalue. If the array object has register storage class, the + behavior is undefined. +
+ A function designator is an expression that has function type. Except when it is the + operand of the sizeof operator65) or the unary & operator, a function designator with + type ''function returning type'' is converted to an expression that has type ''pointer to + + + + function returning type''. +
Forward references: address and indirection operators (6.5.3.2), assignment operators + (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix + increment and decrement operators (6.5.2.4), prefix increment and decrement operators + (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3). + +
64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left + operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an + object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described + as the ''value of an expression''. + An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary + expression that is a pointer to an object, *E is an lvalue that designates the object to which E points. + +
65) Because this conversion does not occur, the operand of the sizeof operator remains a function + designator and violates the constraint in 6.5.3.4. + + +
+ The (nonexistent) value of a void expression (an expression that has type void) shall not + be used in any way, and implicit or explicit conversions (except to void) shall not be + applied to such an expression. If an expression of any other type is evaluated as a void + expression, its value or designator is discarded. (A void expression is evaluated for its + side effects.) + +
+ A pointer to void may be converted to or from a pointer to any object type. A pointer to + any object type may be converted to a pointer to void and back again; the result shall + compare equal to the original pointer. +
+ For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to + the q-qualified version of the type; the values stored in the original and converted pointers + shall compare equal. +
+ An integer constant expression with the value 0, or such an expression cast to type + void *, is called a null pointer constant.66) If a null pointer constant is converted to a + pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal + to a pointer to any object or function. +
+ Conversion of a null pointer to another pointer type yields a null pointer of that type. + Any two null pointers shall compare equal. +
+ An integer may be converted to any pointer type. Except as previously specified, the + result is implementation-defined, might not be correctly aligned, might not point to an + entity of the referenced type, and might be a trap representation.67) +
+ Any pointer type may be converted to an integer type. Except as previously specified, the + result is implementation-defined. If the result cannot be represented in the integer type, + the behavior is undefined. The result need not be in the range of values of any integer + type. + + + + + +
+ A pointer to an object type may be converted to a pointer to a different object type. If the + resulting pointer is not correctly aligned68) for the referenced type, the behavior is + undefined. Otherwise, when converted back again, the result shall compare equal to the + original pointer. When a pointer to an object is converted to a pointer to a character type, + the result points to the lowest addressed byte of the object. Successive increments of the + result, up to the size of the object, yield pointers to the remaining bytes of the object. +
+ A pointer to a function of one type may be converted to a pointer to a function of another + type and back again; the result shall compare equal to the original pointer. If a converted + pointer is used to call a function whose type is not compatible with the referenced type, + the behavior is undefined. +
Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types + capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1). + + + + + + +
66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19. + +
67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to + be consistent with the addressing structure of the execution environment. + +
68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a + pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is + correctly aligned for a pointer to type C. + + +
+
+ token: + keyword + identifier + constant + string-literal + punctuator + preprocessing-token: + header-name + identifier + pp-number + character-constant + string-literal + punctuator + each non-white-space character that cannot be one of the above ++
+ Each preprocessing token that is converted to a token shall have the lexical form of a + keyword, an identifier, a constant, a string literal, or a punctuator. +
+ A token is the minimal lexical element of the language in translation phases 7 and 8. The + categories of tokens are: keywords, identifiers, constants, string literals, and punctuators. + A preprocessing token is the minimal lexical element of the language in translation + phases 3 through 6. The categories of preprocessing tokens are: header names, + identifiers, preprocessing numbers, character constants, string literals, punctuators, and + single non-white-space characters that do not lexically match the other preprocessing + token categories.69) If a ' or a " character matches the last category, the behavior is + undefined. Preprocessing tokens can be separated by white space; this consists of + comments (described later), or white-space characters (space, horizontal tab, new-line, + vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances + during translation phase 4, white space (or the absence thereof) serves as more than + preprocessing token separation. White space may appear within a preprocessing token + only as part of a header name or between the quotation characters in a character constant + or string literal. + + + + +
+ If the input stream has been parsed into preprocessing tokens up to a given character, the + next preprocessing token is the longest sequence of characters that could constitute a + preprocessing token. There is one exception to this rule: header name preprocessing + tokens are recognized only within #include preprocessing directives and in + implementation-defined locations within #pragma directives. In such contexts, a + sequence of characters that could be either a header name or a string literal is recognized + as the former. +
+ EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a + valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex + might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program + fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or + not E is a macro name. + +
+ EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on + increment operators, even though the parse x ++ + ++ y might yield a correct expression. + +
Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5), + floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix + increment and decrement operators (6.5.2.4), prefix increment and decrement operators + (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals + (6.4.5). + +
69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot + occur in source files. + + +
+
+ keyword: one of + alignof goto union + auto if unsigned + break inline void + case int volatile + char long while + const register _Alignas + continue restrict _Atomic + default return _Bool + do short _Complex + double signed _Generic + else sizeof _Imaginary + enum static _Noreturn + extern struct _Static_assert + float switch _Thread_local + for typedef ++
+ The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as + keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for + + specifying imaginary types.70) + +
70) One possible specification for imaginary types appears in annex G. + + +
+
+ identifier: + identifier-nondigit + identifier identifier-nondigit + identifier digit + identifier-nondigit: + nondigit + universal-character-name + other implementation-defined characters + nondigit: one of + _ a b c d e f g h i j k l m + n o p q r s t u v w x y z + A B C D E F G H I J K L M + N O P Q R S T U V W X Y Z + digit: one of + 0 1 2 3 4 5 6 7 8 9 ++
+ An identifier is a sequence of nondigit characters (including the underscore _, the + lowercase and uppercase Latin letters, and other characters) and digits, which designates + one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct. + There is no specific limit on the maximum length of an identifier. +
+ Each universal character name in an identifier shall designate a character whose encoding + in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character + shall not be a universal character name designating a character whose encoding falls into + one of the ranges specified in D.2. An implementation may allow multibyte characters + that are not part of the basic source character set to appear in identifiers; which characters + and their correspondence to universal character names is implementation-defined. + + + + +
+ When preprocessing tokens are converted to tokens during translation phase 7, if a + preprocessing token could be converted to either a keyword or an identifier, it is converted + to a keyword. +
+ As discussed in 5.2.4.1, an implementation may limit the number of significant initial + characters in an identifier; the limit for an external name (an identifier that has external + linkage) may be more restrictive than that for an internal name (a macro name or an + identifier that does not have external linkage). The number of significant characters in an + identifier is implementation-defined. +
+ Any identifiers that differ in a significant character are different identifiers. If two + identifiers differ only in nonsignificant characters, the behavior is undefined. +
Forward references: universal character names (6.4.3), macro replacement (6.10.3). + +
71) On systems in which linkers cannot accept extended characters, an encoding of the universal character + name may be used in forming valid external identifiers. For example, some otherwise unused + character or sequence of characters may be used to encode the \u in a universal character name. + Extended characters may produce a long external identifier. + + +
+ The identifier __func__ shall be implicitly declared by the translator as if, + immediately following the opening brace of each function definition, the declaration +
+ static const char __func__[] = "function-name"; ++ appeared, where function-name is the name of the lexically-enclosing function.72) +
+ This name is encoded as if the implicit declaration had been written in the source + character set and then translated into the execution character set as indicated in translation + phase 5. +
+ EXAMPLE Consider the code fragment: +
+ #include <stdio.h> + void myfunc(void) + { + printf("%s\n", __func__); + /* ... */ + } ++ Each time the function is called, it will print to the standard output stream: +
+ myfunc ++ +
Forward references: function definitions (6.9.1). + + + + + + +
72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other + identifier is explicitly declared using the name __func__, the behavior is undefined. + + +
+
+ universal-character-name: + \u hex-quad + \U hex-quad hex-quad + hex-quad: + hexadecimal-digit hexadecimal-digit + hexadecimal-digit hexadecimal-digit ++
+ A universal character name shall not specify a character whose short identifier is less than + 00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through + DFFF inclusive.73) +
+ Universal character names may be used in identifiers, character constants, and string + literals to designate characters that are not in the basic character set. +
+ The universal character name \Unnnnnnnn designates the character whose eight-digit + short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal + character name \unnnn designates the character whose four-digit short identifier is nnnn + (and whose eight-digit short identifier is 0000nnnn). + + + + + + +
73) The disallowed characters are the characters in the basic character set and the code positions reserved + by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by + UTF-16). + + +
74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997. + + +
+
+ constant: + integer-constant + floating-constant + enumeration-constant + character-constant ++
+ Each constant shall have a type and the value of a constant shall be in the range of + representable values for its type. +
+ Each constant has a type, determined by its form and value, as detailed later. + +
+ +
+ integer-constant: + decimal-constant integer-suffixopt + octal-constant integer-suffixopt + hexadecimal-constant integer-suffixopt + decimal-constant: + nonzero-digit + decimal-constant digit + octal-constant: + 0 + octal-constant octal-digit + hexadecimal-constant: + hexadecimal-prefix hexadecimal-digit + hexadecimal-constant hexadecimal-digit + hexadecimal-prefix: one of + 0x 0X + nonzero-digit: one of + 1 2 3 4 5 6 7 8 9 + octal-digit: one of + 0 1 2 3 4 5 6 7 + hexadecimal-digit: one of + 0 1 2 3 4 5 6 7 8 9 + a b c d e f + A B C D E F + integer-suffix: + unsigned-suffix long-suffixopt + unsigned-suffix long-long-suffix + long-suffix unsigned-suffixopt + long-long-suffix unsigned-suffixopt + unsigned-suffix: one of + u U + long-suffix: one of + l L + long-long-suffix: one of + ll LL ++
+ An integer constant begins with a digit, but has no period or exponent part. It may have a + prefix that specifies its base and a suffix that specifies its type. +
+ A decimal constant begins with a nonzero digit and consists of a sequence of decimal + digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the + digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed + by a sequence of the decimal digits and the letters a (or A) through f (or F) with values + 10 through 15 respectively. +
+ The value of a decimal constant is computed base 10; that of an octal constant, base 8; + that of a hexadecimal constant, base 16. The lexically first digit is the most significant. +
+ The type of an integer constant is the first of the corresponding list in which its value can + be represented. + +
+ Octal or Hexadecimal ++ Suffix Decimal Constant Constant + + none int int +
+ long int unsigned int + long long int long int + unsigned long int + long long int + unsigned long long int ++ + u or U unsigned int unsigned int +
+ unsigned long int unsigned long int + unsigned long long int unsigned long long int ++ + l or L long int long int +
+ long long int unsigned long int + long long int + unsigned long long int ++ + Both u or U unsigned long int unsigned long int + and l or L unsigned long long int unsigned long long int + + ll or LL long long int long long int +
+ unsigned long long int ++ + Both u or U unsigned long long int unsigned long long int + and ll or LL +
+ If an integer constant cannot be represented by any type in its list, it may have an + extended integer type, if the extended integer type can represent its value. If all of the + types in the list for the constant are signed, the extended integer type shall be signed. If + all of the types in the list for the constant are unsigned, the extended integer type shall be + unsigned. If the list contains both signed and unsigned types, the extended integer type + may be signed or unsigned. If an integer constant cannot be represented by any type in + its list and has no extended integer type, then the integer constant has no type. + + +
+ +
+ floating-constant: + decimal-floating-constant + hexadecimal-floating-constant + decimal-floating-constant: + fractional-constant exponent-partopt floating-suffixopt + digit-sequence exponent-part floating-suffixopt + hexadecimal-floating-constant: + hexadecimal-prefix hexadecimal-fractional-constant + binary-exponent-part floating-suffixopt + hexadecimal-prefix hexadecimal-digit-sequence + binary-exponent-part floating-suffixopt + fractional-constant: + digit-sequenceopt . digit-sequence + digit-sequence . + exponent-part: + e signopt digit-sequence + E signopt digit-sequence + sign: one of + + - + digit-sequence: + digit + digit-sequence digit + hexadecimal-fractional-constant: + hexadecimal-digit-sequenceopt . + hexadecimal-digit-sequence + hexadecimal-digit-sequence . + binary-exponent-part: + p signopt digit-sequence + P signopt digit-sequence + hexadecimal-digit-sequence: + hexadecimal-digit + hexadecimal-digit-sequence hexadecimal-digit + floating-suffix: one of + f l F L ++
+ A floating constant has a significand part that may be followed by an exponent part and a + suffix that specifies its type. The components of the significand part may include a digit + sequence representing the whole-number part, followed by a period (.), followed by a + digit sequence representing the fraction part. The components of the exponent part are an + e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence. + Either the whole-number part or the fraction part has to be present; for decimal floating + constants, either the period or the exponent part has to be present. +
+ The significand part is interpreted as a (decimal or hexadecimal) rational number; the + digit sequence in the exponent part is interpreted as a decimal integer. For decimal + floating constants, the exponent indicates the power of 10 by which the significand part is + to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2 + by which the significand part is to be scaled. For decimal floating constants, and also for + hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either + the nearest representable value, or the larger or smaller representable value immediately + adjacent to the nearest representable value, chosen in an implementation-defined manner. + For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is + correctly rounded. +
+ An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has + type float. If suffixed by the letter l or L, it has type long double. +
+ Floating constants are converted to internal format as if at translation-time. The + conversion of a floating constant shall not raise an exceptional condition or a floating- + point exception at execution time. All floating constants of the same source form75) shall + convert to the same internal format with the same value. +
+ The implementation should produce a diagnostic message if a hexadecimal constant + cannot be represented exactly in its evaluation format; the implementation should then + proceed with the translation of the program. +
+ The translation-time conversion of floating constants should match the execution-time + conversion of character strings by library functions, such as strtod, given matching + inputs suitable for both conversions, the same result format, and default execution-time + rounding.76) + + + +
75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not + convert to the same internal format and value. + +
76) The specification for the library functions recommends more accurate conversion than required for + floating constants (see 7.22.1.3). + + +
+
+ enumeration-constant: + identifier ++
+ An identifier declared as an enumeration constant has type int. +
Forward references: enumeration specifiers (6.7.2.2). + +
+ +
+ character-constant: + ' c-char-sequence ' + L' c-char-sequence ' + u' c-char-sequence ' + U' c-char-sequence ' + c-char-sequence: + c-char + c-char-sequence c-char + c-char: + any member of the source character set except + the single-quote ', backslash \, or new-line character + escape-sequence + escape-sequence: + simple-escape-sequence + octal-escape-sequence + hexadecimal-escape-sequence + universal-character-name + simple-escape-sequence: one of + \' \" \? \\ + \a \b \f \n \r \t \v + octal-escape-sequence: + \ octal-digit + \ octal-digit octal-digit + \ octal-digit octal-digit octal-digit + hexadecimal-escape-sequence: + \x hexadecimal-digit + hexadecimal-escape-sequence hexadecimal-digit ++
+ An integer character constant is a sequence of one or more multibyte characters enclosed + in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the + letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are + any members of the source character set; they are mapped in an implementation-defined + manner to members of the execution character set. +
+ The single-quote ', the double-quote ", the question-mark ?, the backslash \, and + arbitrary integer values are representable according to the following table of escape + sequences: +
+ single quote ' \' + double quote " \" + question mark ? \? + backslash \ \\ + octal character \octal digits + hexadecimal character \x hexadecimal digits ++
+ The double-quote " and question-mark ? are representable either by themselves or by the + escape sequences \" and \?, respectively, but the single-quote ' and the backslash \ + shall be represented, respectively, by the escape sequences \' and \\. +
+ The octal digits that follow the backslash in an octal escape sequence are taken to be part + of the construction of a single character for an integer character constant or of a single + wide character for a wide character constant. The numerical value of the octal integer so + formed specifies the value of the desired character or wide character. +
+ The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape + sequence are taken to be part of the construction of a single character for an integer + character constant or of a single wide character for a wide character constant. The + numerical value of the hexadecimal integer so formed specifies the value of the desired + character or wide character. +
+ Each octal or hexadecimal escape sequence is the longest sequence of characters that can + constitute the escape sequence. +
+ In addition, characters not in the basic character set are representable by universal + character names and certain nongraphic characters are representable by escape sequences + consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t, + and \v.77) + +
+ The value of an octal or hexadecimal escape sequence shall be in the range of + representable values for the corresponding type: +
+ Prefix Corresponding Type + none unsigned char + L the unsigned type corresponding to wchar_t + u char16_t + U char32_t ++
+ An integer character constant has type int. The value of an integer character constant + containing a single character that maps to a single-byte execution character is the + numerical value of the representation of the mapped character interpreted as an integer. + The value of an integer character constant containing more than one character (e.g., + 'ab'), or containing a character or escape sequence that does not map to a single-byte + execution character, is implementation-defined. If an integer character constant contains + a single character or escape sequence, its value is the one that results when an object with + type char whose value is that of the single character or escape sequence is converted to + type int. +
+ A wide character constant prefixed by the letter L has type wchar_t, an integer type + defined in the <stddef.h> header; a wide character constant prefixed by the letter u or + U has type char16_t or char32_t, respectively, unsigned integer types defined in the + <uchar.h> header. The value of a wide character constant containing a single + multibyte character that maps to a single member of the extended execution character set + is the wide character corresponding to that multibyte character, as defined by the + mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an + implementation-defined current locale. The value of a wide character constant containing + more than one multibyte character or a single multibyte character that maps to multiple + members of the extended execution character set, or containing a multibyte character or + escape sequence not represented in the extended execution character set, is + implementation-defined. +
+ EXAMPLE 1 The construction '\0' is commonly used to represent the null character. + +
+ EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight + bits for objects that have type char. In an implementation in which type char has the same range of + values as signed char, the integer character constant '\xFF' has the value -1; if type char has the + same range of values as unsigned char, the character constant '\xFF' has the value +255. + + + + + +
+ EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123' + specifies an integer character constant containing only one character, since a hexadecimal escape sequence + is terminated only by a non-hexadecimal character. To specify an integer character constant containing the + two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal + escape sequence is terminated after three octal digits. (The value of this two-character integer character + constant is implementation-defined.) + +
+ EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction + L'\1234' specifies the implementation-defined value that results from the combination of the values + 0123 and '4'. + +
Forward references: common definitions <stddef.h> (7.19), the mbtowc function + (7.22.7.2), Unicode utilities <uchar.h> (7.27). + +
77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash, + the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4). + + +
+
+ string-literal: + encoding-prefixopt " s-char-sequenceopt " + encoding-prefix: + u8 + u + U + L + s-char-sequence: + s-char + s-char-sequence s-char + s-char: + any member of the source character set except + the double-quote ", backslash \, or new-line character + escape-sequence ++
+ A sequence of adjacent string literal tokens shall not include both a wide string literal and + a UTF-8 string literal. +
+ A character string literal is a sequence of zero or more multibyte characters enclosed in + double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8. + A wide string literal is the same, except prefixed by the letter L, u, or U. +
+ The same considerations apply to each element of the sequence in a string literal as if it + were in an integer character constant (for a character or UTF-8 string literal) or a wide + character constant (for a wide string literal), except that the single-quote ' is + representable either by itself or by the escape sequence \', but the double-quote " shall + + be represented by the escape sequence \". +
+ In translation phase 6, the multibyte character sequences specified by any sequence of + adjacent character and identically-prefixed string literal tokens are concatenated into a + single multibyte character sequence. If any of the tokens has an encoding prefix, the + resulting multibyte character sequence is treated as having the same prefix; otherwise, it + is treated as a character string literal. Whether differently-prefixed wide string literal + tokens can be concatenated and, if so, the treatment of the resulting multibyte character + sequence are implementation-defined. +
+ In translation phase 7, a byte or code of value zero is appended to each multibyte + character sequence that results from a string literal or literals.78) The multibyte character + sequence is then used to initialize an array of static storage duration and length just + sufficient to contain the sequence. For character string literals, the array elements have + type char, and are initialized with the individual bytes of the multibyte character + sequence. For UTF-8 string literals, the array elements have type char, and are + initialized with the characters of the multibyte character sequence, as encoded in UTF-8. + For wide string literals prefixed by the letter L, the array elements have type wchar_t + and are initialized with the sequence of wide characters corresponding to the multibyte + character sequence, as defined by the mbstowcs function with an implementation- + defined current locale. For wide string literals prefixed by the letter u or U, the array + elements have type char16_t or char32_t, respectively, and are initialized with the + sequence of wide characters corresponding to the multibyte character sequence, as + defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for + its type, with an implementation-defined current locale. The value of a string literal + containing a multibyte character or escape sequence not represented in the execution + character set is implementation-defined. +
+ It is unspecified whether these arrays are distinct provided their elements have the + appropriate values. If the program attempts to modify such an array, the behavior is + undefined. +
+ EXAMPLE 1 This pair of adjacent character string literals +
+ "\x12" "3" ++ produces a single character string literal containing the two characters whose values are '\x12' and '3', + because escape sequences are converted into single members of the execution character set just prior to + adjacent string literal concatenation. + +
+ EXAMPLE 2 Each of the sequences of adjacent string literal tokens + + + + +
+ "a" "b" L"c" + "a" L"b" "c" + L"a" "b" L"c" + L"a" L"b" L"c" ++ is equivalent to the string literal +
+ L"abc" ++ Likewise, each of the sequences +
+ "a" "b" u"c" + "a" u"b" "c" + u"a" "b" u"c" + u"a" u"b" u"c" ++ is equivalent to +
+ u"abc" ++ +
Forward references: common definitions <stddef.h> (7.19), the mbstowcs + function (7.22.8.1), Unicode utilities <uchar.h> (7.27). + +
78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a + \0 escape sequence. + + +
+
+ punctuator: one of
+ [ ] ( ) { } . ->
+ ++ -- & * + - ~ !
+ / % << >> < > <= >= == != ^ | && ||
+ ? : ; ...
+ = *= /= %= += -= <<= >>= &= ^= |=
+ , # ##
+ <: :> <% %> %: %:%:
+
++ A punctuator is a symbol that has independent syntactic and semantic significance. + Depending on context, it may specify an operation to be performed (which in turn may + yield a value or a function designator, produce a side effect, or some combination thereof) + in which case it is known as an operator (other forms of operator also exist in some + contexts). An operand is an entity on which an operator acts. + +
+ In all aspects of the language, the six tokens79) +
+ <: :> <% %> %: %:%: ++ behave, respectively, the same as the six tokens +
+ [ ] { } # ##
+
+ except for their spelling.80)
+Forward references: expressions (6.5), declarations (6.7), preprocessing directives + (6.10), statements (6.8). + +
79) These tokens are sometimes called ''digraphs''. + +
80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely + interchanged. + + +
+
+ header-name: + < h-char-sequence > + " q-char-sequence " + h-char-sequence: + h-char + h-char-sequence h-char + h-char: + any member of the source character set except + the new-line character and > + q-char-sequence: + q-char + q-char-sequence q-char + q-char: + any member of the source character set except + the new-line character and " ++
+ The sequences in both forms of header names are mapped in an implementation-defined + manner to headers or external source file names as specified in 6.10.2. +
+ If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters, + the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the + + + + + + sequence between the " delimiters, the behavior is undefined.81) Header name + preprocessing tokens are recognized only within #include preprocessing directives and + in implementation-defined locations within #pragma directives.82) +
+ EXAMPLE The following sequence of characters: +
+ 0x3<1/a.h>1e2 + #include <1/a.h> + #define const.member@$ ++ forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited + by a { on the left and a } on the right). +
+ {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
+ {#}{include} {<1/a.h>}
+ {#}{define} {const}{.}{member}{@}{$}
+
+
+Forward references: source file inclusion (6.10.2). + +
81) Thus, sequences of characters that resemble escape sequences cause undefined behavior. + +
82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9. + + +
+
+ pp-number: + digit + . digit + pp-number digit + pp-number identifier-nondigit + pp-number e sign + pp-number E sign + pp-number p sign + pp-number P sign + pp-number . ++
+ A preprocessing number begins with a digit optionally preceded by a period (.) and may + be followed by valid identifier characters and the character sequences e+, e-, E+, E-, + p+, p-, P+, or P-. +
+ Preprocessing number tokens lexically include all floating and integer constant tokens. +
+ A preprocessing number does not have type or a value; it acquires both after a successful + conversion (as part of translation phase 7) to a floating constant token or an integer + constant token. + + + + +
+ Except within a character constant, a string literal, or a comment, the characters /* + introduce a comment. The contents of such a comment are examined only to identify + multibyte characters and to find the characters */ that terminate it.83) +
+ Except within a character constant, a string literal, or a comment, the characters // + introduce a comment that includes all multibyte characters up to, but not including, the + next new-line character. The contents of such a comment are examined only to identify + multibyte characters and to find the terminating new-line character. +
+ EXAMPLE +
+ "a//b" // four-character string literal + #include "//e" // undefined behavior + // */ // comment, not syntax error + f = g/**//h; // equivalent to f = g / h; + //\ + i(); // part of a two-line comment + /\ + / j(); // part of a two-line comment + #define glue(x,y) x##y + glue(/,/) k(); // syntax error, not comment + /*//*/ l(); // equivalent to l(); + m = n//**/o + + p; // equivalent to m = n + p; ++ + + + + + +
83) Thus, /* ... */ comments do not nest. + + +
+ An expression is a sequence of operators and operands that specifies computation of a + value, or that designates an object or a function, or that generates side effects, or that + performs a combination thereof. The value computations of the operands of an operator + are sequenced before the value computation of the result of the operator. +
+ If a side effect on a scalar object is unsequenced relative to either a different side effect + on the same scalar object or a value computation using the value of the same scalar + object, the behavior is undefined. If there are multiple allowable orderings of the + subexpressions of an expression, the behavior is undefined if such an unsequenced side + effect occurs in any of the orderings.84) +
+ The grouping of operators and operands is indicated by the syntax.85) Except as specified + later, side effects and value computations of subexpressions are unsequenced.86) * +
+ Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, + collectively described as bitwise operators) are required to have operands that have + integer type. These operators yield values that depend on the internal representations of + integers, and have implementation-defined and undefined aspects for signed types. +
+ If an exceptional condition occurs during the evaluation of an expression (that is, if the + result is not mathematically defined or not in the range of representable values for its + type), the behavior is undefined. + + + + +
+ The effective type of an object for an access to its stored value is the declared type of the + object, if any.87) If a value is stored into an object having no declared type through an + lvalue having a type that is not a character type, then the type of the lvalue becomes the + effective type of the object for that access and for subsequent accesses that do not modify + the stored value. If a value is copied into an object having no declared type using + memcpy or memmove, or is copied as an array of character type, then the effective type + of the modified object for that access and for subsequent accesses that do not modify the + value is the effective type of the object from which the value is copied, if it has one. For + all other accesses to an object having no declared type, the effective type of the object is + simply the type of the lvalue used for the access. +
+ An object shall have its stored value accessed only by an lvalue expression that has one of + the following types:88) +
+ A floating expression may be contracted, that is, evaluated as though it were a single + operation, thereby omitting rounding errors implied by the source code and the + expression evaluation method.89) The FP_CONTRACT pragma in <math.h> provides a + way to disallow contracted expressions. Otherwise, whether and how expressions are + contracted is implementation-defined.90) +
Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2). + + + + +
84) This paragraph renders undefined statement expressions such as
+
+
+ i = ++i + 1;
+ a[i++] = i;
+
+ while allowing
+
+
+ i = i + 1;
+ a[i] = i;
+
+
+
+
85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same + as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the + expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in + 6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators + (6.5.3), and an operand contained between any of the following pairs of operators: grouping + parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and + the conditional operator ? : (6.5.15). + Within each major subclause, the operators have the same precedence. Left- or right-associativity is + indicated in each subclause by the syntax for the expressions discussed therein. + +
86) In an expression that is evaluated more than once during the execution of a program, unsequenced and + indeterminately sequenced evaluations of its subexpressions need not be performed consistently in + different evaluations. + +
87) Allocated objects have no declared type. + +
88) The intent of this list is to specify those circumstances in which an object may or may not be aliased. + +
89) The intermediate operations in the contracted expression are evaluated as if to infinite precision and + range, while the final operation is rounded to the format determined by the expression evaluation + method. A contracted expression might also omit the raising of floating-point exceptions. + +
90) This license is specifically intended to allow implementations to exploit fast machine instructions that + combine multiple C operators. As contractions potentially undermine predictability, and can even + decrease accuracy for containing expressions, their use needs to be well-defined and clearly + documented. + + +
+
+ primary-expression: + identifier + constant + string-literal + ( expression ) + generic-selection ++
+ An identifier is a primary expression, provided it has been declared as designating an + object (in which case it is an lvalue) or a function (in which case it is a function + designator).91) +
+ A constant is a primary expression. Its type depends on its form and value, as detailed in + 6.4.4. +
+ A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5. +
+ A parenthesized expression is a primary expression. Its type and value are identical to + those of the unparenthesized expression. It is an lvalue, a function designator, or a void + expression if the unparenthesized expression is, respectively, an lvalue, a function + designator, or a void expression. +
Forward references: declarations (6.7). + +
91) Thus, an undeclared identifier is a violation of the syntax. + + +
+
+ generic-selection: + _Generic ( assignment-expression , generic-assoc-list ) + generic-assoc-list: + generic-association + generic-assoc-list , generic-association + generic-association: + type-name : assignment-expression + default : assignment-expression ++
+ A generic selection shall have no more than one default generic association. The type + name in a generic association shall specify a complete object type other than a variably + + + modified type. No two generic associations in the same generic selection shall specify + compatible types. The controlling expression of a generic selection shall have type + compatible with at most one of the types named in its generic association list. If a + generic selection has no default generic association, its controlling expression shall + have type compatible with exactly one of the types named in its generic association list. +
+ The controlling expression of a generic selection is not evaluated. If a generic selection + has a generic association with a type name that is compatible with the type of the + controlling expression, then the result expression of the generic selection is the + expression in that generic association. Otherwise, the result expression of the generic + selection is the expression in the default generic association. None of the expressions + from any other generic association of the generic selection is evaluated. +
+ The type and value of a generic selection are identical to those of its result expression. It + is an lvalue, a function designator, or a void expression if its result expression is, + respectively, an lvalue, a function designator, or a void expression. +
+ EXAMPLE The cbrt type-generic macro could be implemented as follows: +
+ #define cbrt(X) _Generic((X), \ + long double: cbrtl, \ + default: cbrt, \ + float: cbrtf \ + )(X) ++ + +
+ +
+ postfix-expression:
+ primary-expression
+ postfix-expression [ expression ]
+ postfix-expression ( argument-expression-listopt )
+ postfix-expression . identifier
+ postfix-expression -> identifier
+ postfix-expression ++
+ postfix-expression --
+ ( type-name ) { initializer-list }
+ ( type-name ) { initializer-list , }
+ argument-expression-list:
+ assignment-expression
+ argument-expression-list , assignment-expression
+
+
++ One of the expressions shall have type ''pointer to complete object type'', the other + expression shall have integer type, and the result has type ''type''. +
+ A postfix expression followed by an expression in square brackets [] is a subscripted + designation of an element of an array object. The definition of the subscript operator [] + is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that + apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the + initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th + element of E1 (counting from zero). +
+ Successive subscript operators designate an element of a multidimensional array object. + If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as + other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with + dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or + implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional + array, which itself is converted into a pointer if used as other than an lvalue. It follows + from this that arrays are stored in row-major order (last subscript varies fastest). +
+ EXAMPLE Consider the array object defined by the declaration +
+ int x[3][5]; ++ Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an + array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to + a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually + entails multiplying i by the size of the object to which the pointer points, namely an array of five int + objects. The results are added and indirection is applied to yield an array of five ints. When used in the + expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j] + yields an int. + +
Forward references: additive operators (6.5.6), address and indirection operators + (6.5.3.2), array declarators (6.7.6.2). + +
+ The expression that denotes the called function92) shall have type pointer to function + returning void or returning a complete object type other than an array type. +
+ If the expression that denotes the called function has a type that includes a prototype, the + number of arguments shall agree with the number of parameters. Each argument shall + + + + have a type such that its value may be assigned to an object with the unqualified version + of the type of its corresponding parameter. +
+ A postfix expression followed by parentheses () containing a possibly empty, comma- + separated list of expressions is a function call. The postfix expression denotes the called + function. The list of expressions specifies the arguments to the function. +
+ An argument may be an expression of any complete object type. In preparing for the call + to a function, the arguments are evaluated, and each parameter is assigned the value of the + corresponding argument.93) +
+ If the expression that denotes the called function has type pointer to function returning an + object type, the function call expression has the same type as that object type, and has the + value determined as specified in 6.8.6.4. Otherwise, the function call has type void. * +
+ If the expression that denotes the called function has a type that does not include a + prototype, the integer promotions are performed on each argument, and arguments that + have type float are promoted to double. These are called the default argument + promotions. If the number of arguments does not equal the number of parameters, the + behavior is undefined. If the function is defined with a type that includes a prototype, and + either the prototype ends with an ellipsis (, ...) or the types of the arguments after + promotion are not compatible with the types of the parameters, the behavior is undefined. + If the function is defined with a type that does not include a prototype, and the types of + the arguments after promotion are not compatible with those of the parameters after + promotion, the behavior is undefined, except for the following cases: +
+ If the expression that denotes the called function has a type that does include a prototype, + the arguments are implicitly converted, as if by assignment, to the types of the + corresponding parameters, taking the type of each parameter to be the unqualified version + of its declared type. The ellipsis notation in a function prototype declarator causes + argument type conversion to stop after the last declared parameter. The default argument + promotions are performed on trailing arguments. + + + + +
+ No other conversions are performed implicitly; in particular, the number and types of + arguments are not compared with those of the parameters in a function definition that + does not include a function prototype declarator. +
+ If the function is defined with a type that is not compatible with the type (of the + expression) pointed to by the expression that denotes the called function, the behavior is + undefined. +
+ There is a sequence point after the evaluations of the function designator and the actual + arguments but before the actual call. Every evaluation in the calling function (including + other function calls) that is not otherwise specifically sequenced before or after the + execution of the body of the called function is indeterminately sequenced with respect to + the execution of the called function.94) +
+ Recursive function calls shall be permitted, both directly and indirectly through any chain + of other functions. +
+ EXAMPLE In the function call +
+ (*pf[f1()]) (f2(), f3() + f4()) ++ the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before + the function pointed to by pf[f1()] is called. + +
Forward references: function declarators (including prototypes) (6.7.6.3), function + definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1). + +
92) Most often, this is the result of converting an identifier that is a function designator. + +
93) A function may change the values of its parameters, but these changes cannot affect the values of the + arguments. On the other hand, it is possible to pass a pointer to an object, and the function may + change the value of the object pointed to. A parameter declared to have array or function type is + adjusted to have a pointer type as described in 6.9.1. + +
94) In other words, function executions do not ''interleave'' with each other. + + +
+ The first operand of the . operator shall have an atomic, qualified, or unqualified + structure or union type, and the second operand shall name a member of that type. +
+ The first operand of the -> operator shall have type ''pointer to atomic, qualified, or + unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the + second operand shall name a member of the type pointed to. +
+ A postfix expression followed by the . operator and an identifier designates a member of + a structure or union object. The value is that of the named member,95) and is an lvalue if + the first expression is an lvalue. If the first expression has qualified type, the result has + the so-qualified version of the type of the designated member. + + +
+ A postfix expression followed by the -> operator and an identifier designates a member + of a structure or union object. The value is that of the named member of the object to + which the first expression points, and is an lvalue.96) If the first expression is a pointer to + a qualified type, the result has the so-qualified version of the type of the designated + member. +
+ Accessing a member of an atomic structure or union object results in undefined + behavior.97) +
+ One special guarantee is made in order to simplify the use of unions: if a union contains + several structures that share a common initial sequence (see below), and if the union + object currently contains one of these structures, it is permitted to inspect the common + initial part of any of them anywhere that a declaration of the completed type of the union + is visible. Two structures share a common initial sequence if corresponding members + have compatible types (and, for bit-fields, the same widths) for a sequence of one or more + initial members. +
+ EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or + union, f().x is a valid postfix expression but is not an lvalue. + +
+ EXAMPLE 2 In: +
+ struct s { int i; const int ci; };
+ struct s s;
+ const struct s cs;
+ volatile struct s vs;
+
+ the various members have the types:
++ s.i int + s.ci const int + cs.i const int + cs.ci const int + vs.i volatile int + vs.ci volatile const int ++ + + + + +
+ EXAMPLE 3 The following is a valid fragment: +
+ union {
struct {
- int f1;
- struct s f2;
- } u1;
+ int alltypes;
+ } n;
struct {
- struct s f3;
- int f4;
- } u2;
- } g;
- struct s f(void)
- {
- return g.u1.f2;
- }
- /* ... */
- g.u2.f3 = f();
- there is no undefined behavior, although there would be if the assignment were done directly (without using
- a function call to fetch the value).
-
-
-
-
- 160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
- apply to the case of function return. The representation of floating-point values may have wider range
- or precision than implied by the type; a cast may be used to remove this extra range and precision.
-
-[page 153] (Contents)
-
- 6.9 External definitions
- Syntax
-1 translation-unit:
- external-declaration
- translation-unit external-declaration
- external-declaration:
- function-definition
- declaration
- Constraints
-2 The storage-class specifiers auto and register shall not appear in the declaration
- specifiers in an external declaration.
-3 There shall be no more than one external definition for each identifier declared with
- internal linkage in a translation unit. Moreover, if an identifier declared with internal
- linkage is used in an expression (other than as a part of the operand of a sizeof
- operator whose result is an integer constant), there shall be exactly one external definition
- for the identifier in the translation unit.
- Semantics
-4 As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
- which consists of a sequence of external declarations. These are described as ''external''
- because they appear outside any function (and hence have file scope). As discussed in
- 6.7, a declaration that also causes storage to be reserved for an object or a function named
- by the identifier is a definition.
-5 An external definition is an external declaration that is also a definition of a function
- (other than an inline definition) or an object. If an identifier declared with external
- linkage is used in an expression (other than as part of the operand of a sizeof operator
- whose result is an integer constant), somewhere in the entire program there shall be
- exactly one external definition for the identifier; otherwise, there shall be no more than
- one.161)
-
-
-
-
- 161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
- external definition for it.
-
-[page 154] (Contents)
-
- 6.9.1 Function definitions
- Syntax
-1 function-definition:
- declaration-specifiers declarator declaration-listopt compound-statement
- declaration-list:
- declaration
- declaration-list declaration
- Constraints
-2 The identifier declared in a function definition (which is the name of the function) shall
- have a function type, as specified by the declarator portion of the function definition.162)
-3 The return type of a function shall be void or a complete object type other than array
- type.
-4 The storage-class specifier, if any, in the declaration specifiers shall be either extern or
- static.
-5 If the declarator includes a parameter type list, the declaration of each parameter shall
- include an identifier, except for the special case of a parameter list consisting of a single
- parameter of type void, in which case there shall not be an identifier. No declaration list
- shall follow.
-6 If the declarator includes an identifier list, each declaration in the declaration list shall
- have at least one declarator, those declarators shall declare only identifiers from the
- identifier list, and every identifier in the identifier list shall be declared. An identifier
- declared as a typedef name shall not be redeclared as a parameter. The declarations in the
- declaration list shall contain no storage-class specifier other than register and no
- initializations.
-
-
-
- 162) The intent is that the type category in a function definition cannot be inherited from a typedef:
- typedef int F(void); // type F is ''function with no parameters
- // returning int''
- F f, g; // f and g both have type compatible with F
- F f { /* ... */ } // WRONG: syntax/constraint error
- F g() { /* ... */ } // WRONG: declares that g returns a function
- int f(void) { /* ... */ } // RIGHT: f has type compatible with F
- int g() { /* ... */ } // RIGHT: g has type compatible with F
- F *e(void) { /* ... */ } // e returns a pointer to a function
- F *((e))(void) { /* ... */ } // same: parentheses irrelevant
- int (*fp)(void); // fp points to a function that has type F
- F *Fp; // Fp points to a function that has type F
-
-
-[page 155] (Contents)
-
- Semantics
-7 The declarator in a function definition specifies the name of the function being defined
- and the identifiers of its parameters. If the declarator includes a parameter type list, the
- list also specifies the types of all the parameters; such a declarator also serves as a
- function prototype for later calls to the same function in the same translation unit. If the
- declarator includes an identifier list,163) the types of the parameters shall be declared in a
- following declaration list. In either case, the type of each parameter is adjusted as
- described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
- type.
-8 If a function that accepts a variable number of arguments is defined without a parameter
- type list that ends with the ellipsis notation, the behavior is undefined.
-9 Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout
- of the storage for parameters is unspecified.
-10 On entry to the function, the size expressions of each variably modified parameter are
- evaluated and the value of each argument expression is converted to the type of the
- corresponding parameter as if by assignment. (Array expressions and function
- designators as arguments were converted to pointers before the call.)
-11 After all parameters have been assigned, the compound statement that constitutes the
- body of the function definition is executed.
-12 If the } that terminates a function is reached, and the value of the function call is used by
- the caller, the behavior is undefined.
-13 EXAMPLE 1 In the following:
- extern int max(int a, int b)
- {
- return a > b ? a : b;
- }
- extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
- function declarator; and
- { return a > b ? a : b; }
- is the function body. The following similar definition uses the identifier-list form for the parameter
- declarations:
-
-
-
-
- 163) See ''future language directions'' (6.11.7).
- 164) A parameter identifier cannot be redeclared in the function body except in an enclosed block.
-
-[page 156] (Contents)
-
- extern int max(a, b)
- int a, b;
- {
- return a > b ? a : b;
- }
- Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
- that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
- to the function, whereas the second form does not.
-
-14 EXAMPLE 2 To pass one function to another, one might say
- int f(void);
- /* ... */
- g(f);
- Then the definition of g might read
- void g(int (*funcp)(void))
- {
- /* ... */
- (*funcp)(); /* or funcp(); ... */
- }
- or, equivalently,
- void g(int func(void))
- {
- /* ... */
- func(); /* or (*func)(); ... */
- }
-
- 6.9.2 External object definitions
- Semantics
-1 If the declaration of an identifier for an object has file scope and an initializer, the
- declaration is an external definition for the identifier.
-2 A declaration of an identifier for an object that has file scope without an initializer, and
- without a storage-class specifier or with the storage-class specifier static, constitutes a
- tentative definition. If a translation unit contains one or more tentative definitions for an
- identifier, and the translation unit contains no external definition for that identifier, then
- the behavior is exactly as if the translation unit contains a file scope declaration of that
- identifier, with the composite type as of the end of the translation unit, with an initializer
- equal to 0.
-3 If the declaration of an identifier for an object is a tentative definition and has internal
- linkage, the declared type shall not be an incomplete type.
-
-
-
-
-[page 157] (Contents)
-
-4 EXAMPLE 1
- int i1 = 1; // definition, external linkage
- static int i2 = 2; // definition, internal linkage
- extern int i3 = 3; // definition, external linkage
- int i4; // tentative definition, external linkage
- static int i5; // tentative definition, internal linkage
- int i1; // valid tentative definition, refers to previous
- int i2; // 6.2.2 renders undefined, linkage disagreement
- int i3; // valid tentative definition, refers to previous
- int i4; // valid tentative definition, refers to previous
- int i5; // 6.2.2 renders undefined, linkage disagreement
- extern int i1; // refers to previous, whose linkage is external
- extern int i2; // refers to previous, whose linkage is internal
- extern int i3; // refers to previous, whose linkage is external
- extern int i4; // refers to previous, whose linkage is external
- extern int i5; // refers to previous, whose linkage is internal
-
-5 EXAMPLE 2 If at the end of the translation unit containing
- int i[];
- the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
- zero on program startup.
-
-
-
-
-[page 158] (Contents)
-
- 6.10 Preprocessing directives
- Syntax
-1 preprocessing-file:
- groupopt
- group:
- group-part
- group group-part
- group-part:
- if-section
- control-line
- text-line
- # non-directive
- if-section:
- if-group elif-groupsopt else-groupopt endif-line
- if-group:
- # if constant-expression new-line groupopt
- # ifdef identifier new-line groupopt
- # ifndef identifier new-line groupopt
- elif-groups:
- elif-group
- elif-groups elif-group
- elif-group:
- # elif constant-expression new-line groupopt
- else-group:
- # else new-line groupopt
- endif-line:
- # endif new-line
-
-
-
-
-[page 159] (Contents)
-
- control-line:
- # include pp-tokens new-line
- # define identifier replacement-list new-line
- # define identifier lparen identifier-listopt )
- replacement-list new-line
- # define identifier lparen ... ) replacement-list new-line
- # define identifier lparen identifier-list , ... )
- replacement-list new-line
- # undef identifier new-line
- # line pp-tokens new-line
- # error pp-tokensopt new-line
- # pragma pp-tokensopt new-line
- # new-line
- text-line:
- pp-tokensopt new-line
- non-directive:
- pp-tokens new-line
- lparen:
- a ( character not immediately preceded by white-space
- replacement-list:
- pp-tokensopt
- pp-tokens:
- preprocessing-token
- pp-tokens preprocessing-token
- new-line:
- the new-line character
- Description
-2 A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
- following constraints: The first token in the sequence is a # preprocessing token that (at
- the start of translation phase 4) is either the first character in the source file (optionally
- after white space containing no new-line characters) or that follows white space
- containing at least one new-line character. The last token in the sequence is the first new-
- line character that follows the first token in the sequence.165) A new-line character ends
- the preprocessing directive even if it occurs within what would otherwise be an
-
- 165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic
- significance, as all white space is equivalent except in certain situations during preprocessing (see the
- # character string literal creation operator in 6.10.3.2, for example).
-
-[page 160] (Contents)
-
- invocation of a function-like macro.
-3 A text line shall not begin with a # preprocessing token. A non-directive shall not begin
- with any of the directive names appearing in the syntax.
-4 When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
- sequence of preprocessing tokens to occur between the directive name and the following
- new-line character.
- Constraints
-5 The only white-space characters that shall appear between preprocessing tokens within a
- preprocessing directive (from just after the introducing # preprocessing token through
- just before the terminating new-line character) are space and horizontal-tab (including
- spaces that have replaced comments or possibly other white-space characters in
- translation phase 3).
- Semantics
-6 The implementation can process and skip sections of source files conditionally, include
- other source files, and replace macros. These capabilities are called preprocessing,
- because conceptually they occur before translation of the resulting translation unit.
-7 The preprocessing tokens within a preprocessing directive are not subject to macro
- expansion unless otherwise stated.
-8 EXAMPLE In:
- #define EMPTY
- EMPTY # include <file.h>
- the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
- begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
- replaced.
-
- 6.10.1 Conditional inclusion
- Constraints
-1 The expression that controls conditional inclusion shall be an integer constant expression
- except that: identifiers (including those lexically identical to keywords) are interpreted as *
- described below;166) and it may contain unary operator expressions of the form
- defined identifier
- or
- defined ( identifier )
- which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is
-
-
- 166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
- either are or are not macro names -- there simply are no keywords, enumeration constants, etc.
-
-[page 161] (Contents)
-
- predefined or if it has been the subject of a #define preprocessing directive without an
- intervening #undef directive with the same subject identifier), 0 if it is not.
-2 Each preprocessing token that remains (in the list of preprocessing tokens that will
- become the controlling expression) after all macro replacements have occurred shall be in
- the lexical form of a token (6.4).
- Semantics
-3 Preprocessing directives of the forms
- # if constant-expression new-line groupopt
- # elif constant-expression new-line groupopt
- check whether the controlling constant expression evaluates to nonzero.
-4 Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
- the controlling constant expression are replaced (except for those macro names modified
- by the defined unary operator), just as in normal text. If the token defined is
- generated as a result of this replacement process or use of the defined unary operator
- does not match one of the two specified forms prior to macro replacement, the behavior is
- undefined. After all replacements due to macro expansion and the defined unary
- operator have been performed, all remaining identifiers (including those lexically
- identical to keywords) are replaced with the pp-number 0, and then each preprocessing
- token is converted into a token. The resulting tokens compose the controlling constant
- expression which is evaluated according to the rules of 6.6. For the purposes of this
- token conversion and evaluation, all signed integer types and all unsigned integer types
- act as if they have the same representation as, respectively, the types intmax_t and
- uintmax_t defined in the header <stdint.h>.167) This includes interpreting
- character constants, which may involve converting escape sequences into execution
- character set members. Whether the numeric value for these character constants matches
- the value obtained when an identical character constant occurs in an expression (other
- than within a #if or #elif directive) is implementation-defined.168) Also, whether a
- single-character character constant may have a negative value is implementation-defined.
-
-
-
-
- 167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
- 0x8000 is signed and positive within a #if expression even though it would be unsigned in
- translation phase 7.
- 168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
- evaluate to the same value in these two contexts.
- #if 'z' - 'a' == 25
- if ('z' - 'a' == 25)
-
-
-[page 162] (Contents)
-
-5 Preprocessing directives of the forms
- # ifdef identifier new-line groupopt
- # ifndef identifier new-line groupopt
- check whether the identifier is or is not currently defined as a macro name. Their
- conditions are equivalent to #if defined identifier and #if !defined identifier
- respectively.
-6 Each directive's condition is checked in order. If it evaluates to false (zero), the group
- that it controls is skipped: directives are processed only through the name that determines
- the directive in order to keep track of the level of nested conditionals; the rest of the
- directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the
- group. Only the first group whose control condition evaluates to true (nonzero) is
- processed. If none of the conditions evaluates to true, and there is a #else directive, the
- group controlled by the #else is processed; lacking a #else directive, all the groups
- until the #endif are skipped.169)
- Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
- integer types (7.20.1.5).
- 6.10.2 Source file inclusion
- Constraints
-1 A #include directive shall identify a header or source file that can be processed by the
- implementation.
- Semantics
-2 A preprocessing directive of the form
- # include <h-char-sequence> new-line
- searches a sequence of implementation-defined places for a header identified uniquely by
- the specified sequence between the < and > delimiters, and causes the replacement of that
- directive by the entire contents of the header. How the places are specified or the header
- identified is implementation-defined.
-3 A preprocessing directive of the form
- # include "q-char-sequence" new-line
- causes the replacement of that directive by the entire contents of the source file identified
- by the specified sequence between the " delimiters. The named source file is searched
-
-
- 169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
- before the terminating new-line character. However, comments may appear anywhere in a source file,
- including within a preprocessing directive.
-
-[page 163] (Contents)
-
- for in an implementation-defined manner. If this search is not supported, or if the search
- fails, the directive is reprocessed as if it read
- # include <h-char-sequence> new-line
- with the identical contained sequence (including > characters, if any) from the original
- directive.
-4 A preprocessing directive of the form
- # include pp-tokens new-line
- (that does not match one of the two previous forms) is permitted. The preprocessing
- tokens after include in the directive are processed just as in normal text. (Each
- identifier currently defined as a macro name is replaced by its replacement list of
- preprocessing tokens.) The directive resulting after all replacements shall match one of
- the two previous forms.170) The method by which a sequence of preprocessing tokens
- between a < and a > preprocessing token pair or a pair of " characters is combined into a
- single header name preprocessing token is implementation-defined.
-5 The implementation shall provide unique mappings for sequences consisting of one or
- more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
- first character shall not be a digit. The implementation may ignore distinctions of
- alphabetical case and restrict the mapping to eight significant characters before the
- period.
-6 A #include preprocessing directive may appear in a source file that has been read
- because of a #include directive in another file, up to an implementation-defined
- nesting limit (see 5.2.4.1).
-7 EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following:
- #include <stdio.h>
- #include "myprog.h"
-
-
-
-
- 170) Note that adjacent string literals are not concatenated into a single string literal (see the translation
- phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.
-
-[page 164] (Contents)
-
-8 EXAMPLE 2 This illustrates macro-replaced #include directives:
- #if VERSION == 1
- #define INCFILE "vers1.h"
- #elif VERSION == 2
- #define INCFILE "vers2.h" // and so on
- #else
- #define INCFILE "versN.h"
- #endif
- #include INCFILE
-
- Forward references: macro replacement (6.10.3).
- 6.10.3 Macro replacement
- Constraints
-1 Two replacement lists are identical if and only if the preprocessing tokens in both have
- the same number, ordering, spelling, and white-space separation, where all white-space
- separations are considered identical.
-2 An identifier currently defined as an object-like macro shall not be redefined by another
- #define preprocessing directive unless the second definition is an object-like macro
- definition and the two replacement lists are identical. Likewise, an identifier currently
- defined as a function-like macro shall not be redefined by another #define
- preprocessing directive unless the second definition is a function-like macro definition
- that has the same number and spelling of parameters, and the two replacement lists are
- identical.
-3 There shall be white-space between the identifier and the replacement list in the definition
- of an object-like macro.
-4 If the identifier-list in the macro definition does not end with an ellipsis, the number of
- arguments (including those arguments consisting of no preprocessing tokens) in an
- invocation of a function-like macro shall equal the number of parameters in the macro
- definition. Otherwise, there shall be more arguments in the invocation than there are
- parameters in the macro definition (excluding the ...). There shall exist a )
- preprocessing token that terminates the invocation.
-5 The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like
- macro that uses the ellipsis notation in the parameters.
-6 A parameter identifier in a function-like macro shall be uniquely declared within its
- scope.
- Semantics
-7 The identifier immediately following the define is called the macro name. There is one
- name space for macro names. Any white-space characters preceding or following the
- replacement list of preprocessing tokens are not considered part of the replacement list
-
-[page 165] (Contents)
-
- for either form of macro.
-8 If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
- a preprocessing directive could begin, the identifier is not subject to macro replacement.
-9 A preprocessing directive of the form
- # define identifier replacement-list new-line
- defines an object-like macro that causes each subsequent instance of the macro name171)
- to be replaced by the replacement list of preprocessing tokens that constitute the
- remainder of the directive. The replacement list is then rescanned for more macro names
- as specified below.
-10 A preprocessing directive of the form
- # define identifier lparen identifier-listopt ) replacement-list new-line
- # define identifier lparen ... ) replacement-list new-line
- # define identifier lparen identifier-list , ... ) replacement-list new-line
- defines a function-like macro with parameters, whose use is similar syntactically to a
- function call. The parameters are specified by the optional list of identifiers, whose scope
- extends from their declaration in the identifier list until the new-line character that
- terminates the #define preprocessing directive. Each subsequent instance of the
- function-like macro name followed by a ( as the next preprocessing token introduces the
- sequence of preprocessing tokens that is replaced by the replacement list in the definition
- (an invocation of the macro). The replaced sequence of preprocessing tokens is
- terminated by the matching ) preprocessing token, skipping intervening matched pairs of
- left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
- tokens making up an invocation of a function-like macro, new-line is considered a normal
- white-space character.
-11 The sequence of preprocessing tokens bounded by the outside-most matching parentheses
- forms the list of arguments for the function-like macro. The individual arguments within
- the list are separated by comma preprocessing tokens, but comma preprocessing tokens
- between matching inner parentheses do not separate arguments. If there are sequences of
- preprocessing tokens within the list of arguments that would otherwise act as
- preprocessing directives,172) the behavior is undefined.
-12 If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
- including any separating comma preprocessing tokens, are merged to form a single item:
-
-
- 171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
- not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
- are never scanned for macro names or parameters.
- 172) Despite the name, a non-directive is a preprocessing directive.
-
-[page 166] (Contents)
-
- the variable arguments. The number of arguments so combined is such that, following
- merger, the number of arguments is one more than the number of parameters in the macro
- definition (excluding the ...).
- 6.10.3.1 Argument substitution
-1 After the arguments for the invocation of a function-like macro have been identified,
- argument substitution takes place. A parameter in the replacement list, unless preceded
- by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
- replaced by the corresponding argument after all macros contained therein have been
- expanded. Before being substituted, each argument's preprocessing tokens are
- completely macro replaced as if they formed the rest of the preprocessing file; no other
- preprocessing tokens are available.
-2 An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it
- were a parameter, and the variable arguments shall form the preprocessing tokens used to
- replace it.
- 6.10.3.2 The # operator
- Constraints
-1 Each # preprocessing token in the replacement list for a function-like macro shall be
- followed by a parameter as the next preprocessing token in the replacement list.
- Semantics
-2 If, in the replacement list, a parameter is immediately preceded by a # preprocessing
- token, both are replaced by a single character string literal preprocessing token that
- contains the spelling of the preprocessing token sequence for the corresponding
- argument. Each occurrence of white space between the argument's preprocessing tokens
- becomes a single space character in the character string literal. White space before the
- first preprocessing token and after the last preprocessing token composing the argument
- is deleted. Otherwise, the original spelling of each preprocessing token in the argument
- is retained in the character string literal, except for special handling for producing the
- spelling of string literals and character constants: a \ character is inserted before each "
- and \ character of a character constant or string literal (including the delimiting "
- characters), except that it is implementation-defined whether a \ character is inserted
- before the \ character beginning a universal character name. If the replacement that
- results is not a valid character string literal, the behavior is undefined. The character
- string literal corresponding to an empty argument is "". The order of evaluation of # and
- ## operators is unspecified.
-
-
-
-
-[page 167] (Contents)
-
- 6.10.3.3 The ## operator
- Constraints
-1 A ## preprocessing token shall not occur at the beginning or at the end of a replacement
- list for either form of macro definition.
- Semantics
-2 If, in the replacement list of a function-like macro, a parameter is immediately preceded
- or followed by a ## preprocessing token, the parameter is replaced by the corresponding
- argument's preprocessing token sequence; however, if an argument consists of no
- preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
- instead.173)
-3 For both object-like and function-like macro invocations, before the replacement list is
- reexamined for more macro names to replace, each instance of a ## preprocessing token
- in the replacement list (not from an argument) is deleted and the preceding preprocessing
- token is concatenated with the following preprocessing token. Placemarker
- preprocessing tokens are handled specially: concatenation of two placemarkers results in
- a single placemarker preprocessing token, and concatenation of a placemarker with a
- non-placemarker preprocessing token results in the non-placemarker preprocessing token.
- If the result is not a valid preprocessing token, the behavior is undefined. The resulting
- token is available for further macro replacement. The order of evaluation of ## operators
- is unspecified.
-4 EXAMPLE In the following fragment:
- #define hash_hash # ## #
- #define mkstr(a) # a
- #define in_between(a) mkstr(a)
- #define join(c, d) in_between(c hash_hash d)
- char p[] = join(x, y); // equivalent to
- // char p[] = "x ## y";
- The expansion produces, at various stages:
- join(x, y)
- in_between(x hash_hash y)
- in_between(x ## y)
- mkstr(x ## y)
- "x ## y"
- In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
- this new token is not the ## operator.
-
-
- 173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
- exist only within translation phase 4.
-
-[page 168] (Contents)
-
- 6.10.3.4 Rescanning and further replacement
-1 After all parameters in the replacement list have been substituted and # and ##
- processing has taken place, all placemarker preprocessing tokens are removed. The
- resulting preprocessing token sequence is then rescanned, along with all subsequent
- preprocessing tokens of the source file, for more macro names to replace.
-2 If the name of the macro being replaced is found during this scan of the replacement list
- (not including the rest of the source file's preprocessing tokens), it is not replaced.
- Furthermore, if any nested replacements encounter the name of the macro being replaced,
- it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
- available for further replacement even if they are later (re)examined in contexts in which
- that macro name preprocessing token would otherwise have been replaced.
-3 The resulting completely macro-replaced preprocessing token sequence is not processed
- as a preprocessing directive even if it resembles one, but all pragma unary operator
- expressions within it are then processed as specified in 6.10.9 below.
- 6.10.3.5 Scope of macro definitions
-1 A macro definition lasts (independent of block structure) until a corresponding #undef
- directive is encountered or (if none is encountered) until the end of the preprocessing
- translation unit. Macro definitions have no significance after translation phase 4.
-2 A preprocessing directive of the form
- # undef identifier new-line
- causes the specified identifier no longer to be defined as a macro name. It is ignored if
- the specified identifier is not currently defined as a macro name.
-3 EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in
- #define TABSIZE 100
- int table[TABSIZE];
-
-4 EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
- It has the advantages of working for any compatible types of the arguments and of generating in-line code
- without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
- arguments a second time (including side effects) and generating more code than a function if invoked
- several times. It also cannot have its address taken, as it has none.
- #define max(a, b) ((a) > (b) ? (a) : (b))
- The parentheses ensure that the arguments and the resulting expression are bound properly.
-
-
-
-
-[page 169] (Contents)
-
-5 EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence
- #define x 3
- #define f(a) f(x * (a))
- #undef x
- #define x 2
- #define g f
- #define z z[0]
- #define h g(~
- #define m(a) a(w)
- #define w 0,1
- #define t(a) a
- #define p() int
- #define q(x) x
- #define r(x,y) x ## y
- #define str(x) # x
- f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
- g(x+(3,4)-w) | h 5) & m
- (f)^m(m);
- p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
- char c[2][6] = { str(hello), str() };
- results in
- f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
- f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
- int i[] = { 1, 23, 4, 5, };
- char c[2][6] = { "hello", "" };
-
-6 EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the
- sequence
- #define str(s) # s
- #define xstr(s) str(s)
- #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
- x ## s, x ## t)
- #define INCFILE(n) vers ## n
- #define glue(a, b) a ## b
- #define xglue(a, b) glue(a, b)
- #define HIGHLOW "hello"
- #define LOW LOW ", world"
- debug(1, 2);
- fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
- == 0) str(: @\n), s);
- #include xstr(INCFILE(2).h)
- glue(HIGH, LOW);
- xglue(HIGH, LOW)
- results in
-
-
-
-
-[page 170] (Contents)
-
- printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
- fputs(
- "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
- s);
- #include "vers2.h" (after macro replacement, before file access)
- "hello";
- "hello" ", world"
- or, after concatenation of the character string literals,
- printf("x1= %d, x2= %s", x1, x2);
- fputs(
- "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
- s);
- #include "vers2.h" (after macro replacement, before file access)
- "hello";
- "hello, world"
- Space around the # and ## tokens in the macro definition is optional.
-
-7 EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence
- #define t(x,y,z) x ## y ## z
- int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
- t(10,,), t(,11,), t(,,12), t(,,) };
- results in
- int j[] = { 123, 45, 67, 89,
- 10, 11, 12, };
-
-8 EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid.
- #define OBJ_LIKE (1-1)
- #define OBJ_LIKE /* white space */ (1-1) /* other */
- #define FUNC_LIKE(a) ( a )
- #define FUNC_LIKE( a )( /* note the white space */ \
- a /* other stuff on this line
- */ )
- But the following redefinitions are invalid:
- #define OBJ_LIKE (0) // different token sequence
- #define OBJ_LIKE (1 - 1) // different white space
- #define FUNC_LIKE(b) ( a ) // different parameter usage
- #define FUNC_LIKE(b) ( b ) // different parameter spelling
-
-9 EXAMPLE 7 Finally, to show the variable argument list macro facilities:
- #define debug(...) fprintf(stderr, __VA_ARGS__)
- #define showlist(...) puts(#__VA_ARGS__)
- #define report(test, ...) ((test)?puts(#test):\
- printf(__VA_ARGS__))
- debug("Flag");
- debug("X = %d\n", x);
- showlist(The first, second, and third items.);
- report(x>y, "x is %d but y is %d", x, y);
-
-
-[page 171] (Contents)
-
- results in
- fprintf(stderr, "Flag" );
- fprintf(stderr, "X = %d\n", x );
- puts( "The first, second, and third items." );
- ((x>y)?puts("x>y"):
- printf("x is %d but y is %d", x, y));
-
- 6.10.4 Line control
- Constraints
-1 The string literal of a #line directive, if present, shall be a character string literal.
- Semantics
-2 The line number of the current source line is one greater than the number of new-line
- characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
- file to the current token.
-3 A preprocessing directive of the form
- # line digit-sequence new-line
- causes the implementation to behave as if the following sequence of source lines begins
- with a source line that has a line number as specified by the digit sequence (interpreted as
- a decimal integer). The digit sequence shall not specify zero, nor a number greater than
- 2147483647.
-4 A preprocessing directive of the form
- # line digit-sequence "s-char-sequenceopt" new-line
- sets the presumed line number similarly and changes the presumed name of the source
- file to be the contents of the character string literal.
-5 A preprocessing directive of the form
- # line pp-tokens new-line
- (that does not match one of the two previous forms) is permitted. The preprocessing
- tokens after line on the directive are processed just as in normal text (each identifier
- currently defined as a macro name is replaced by its replacement list of preprocessing
- tokens). The directive resulting after all replacements shall match one of the two
- previous forms and is then processed as appropriate.
-
-
-
-
-[page 172] (Contents)
-
- 6.10.5 Error directive
- Semantics
-1 A preprocessing directive of the form
- # error pp-tokensopt new-line
- causes the implementation to produce a diagnostic message that includes the specified
- sequence of preprocessing tokens.
- 6.10.6 Pragma directive
- Semantics
-1 A preprocessing directive of the form
- # pragma pp-tokensopt new-line
- where the preprocessing token STDC does not immediately follow pragma in the
- directive (prior to any macro replacement)174) causes the implementation to behave in an
- implementation-defined manner. The behavior might cause translation to fail or cause the
- translator or the resulting program to behave in a non-conforming manner. Any such
- pragma that is not recognized by the implementation is ignored.
-2 If the preprocessing token STDC does immediately follow pragma in the directive (prior
- to any macro replacement), then no macro replacement is performed on the directive, and
- the directive shall have one of the following forms175) whose meanings are described
- elsewhere:
- #pragma STDC FP_CONTRACT on-off-switch
- #pragma STDC FENV_ACCESS on-off-switch
- #pragma STDC CX_LIMITED_RANGE on-off-switch
- on-off-switch: one of
- ON OFF DEFAULT
- Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
- (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).
-
-
-
-
- 174) An implementation is not required to perform macro replacement in pragmas, but it is permitted
- except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
- replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
- implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
- but is not required to.
- 175) See ''future language directions'' (6.11.8).
-
-[page 173] (Contents)
-
- 6.10.7 Null directive
- Semantics
-1 A preprocessing directive of the form
- # new-line
- has no effect.
- 6.10.8 Predefined macro names
-1 The values of the predefined macros listed in the following subclauses176) (except for
- __FILE__ and __LINE__) remain constant throughout the translation unit.
-2 None of these macro names, nor the identifier defined, shall be the subject of a
- #define or a #undef preprocessing directive. Any other predefined macro names
- shall begin with a leading underscore followed by an uppercase letter or a second
- underscore.
-3 The implementation shall not predefine the macro __cplusplus, nor shall it define it
- in any standard header.
- Forward references: standard headers (7.1.2).
- 6.10.8.1 Mandatory macros
-1 The following macro names shall be defined by the implementation:
- __DATE__ The date of translation of the preprocessing translation unit: a character
- string literal of the form "Mmm dd yyyy", where the names of the
- months are the same as those generated by the asctime function, and the
- first character of dd is a space character if the value is less than 10. If the
- date of translation is not available, an implementation-defined valid date
- shall be supplied.
- __FILE__ The presumed name of the current source file (a character string literal).177)
- __LINE__ The presumed line number (within the current source file) of the current
- source line (an integer constant).177)
- __STDC__ The integer constant 1, intended to indicate a conforming implementation.
- __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted
- implementation or the integer constant 0 if it is not.
-
-
-
-
- 176) See ''future language directions'' (6.11.9).
- 177) The presumed source file name and line number can be changed by the #line directive.
-
-[page 174] (Contents)
-
- __STDC_VERSION__ The integer constant 201ymmL.178)
- __TIME__ The time of translation of the preprocessing translation unit: a character
- string literal of the form "hh:mm:ss" as in the time generated by the
- asctime function. If the time of translation is not available, an
- implementation-defined valid time shall be supplied.
- Forward references: the asctime function (7.26.3.1).
- 6.10.8.2 Environment macros
-1 The following macro names are conditionally defined by the implementation:
- __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example,
- 199712L). If this symbol is defined, then every character in the Unicode
- required set, when stored in an object of type wchar_t, has the same
- value as the short identifier of that character. The Unicode required set
- consists of all the characters that are defined by ISO/IEC 10646, along with
- all amendments and technical corrigenda, as of the specified year and
- month. If some other encoding is used, the macro shall not be defined and
- the actual encoding used is implementation-defined.
- __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in
- the encoding for wchar_t, a member of the basic character set need not
- have a code value equal to its value when used as the lone character in an
- integer character constant.
- __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type
- char16_t are UTF-16 encoded. If some other encoding is used, the
- macro shall not be defined and the actual encoding used is implementation-
- defined.
- __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type
- char32_t are UTF-32 encoded. If some other encoding is used, the
- macro shall not be defined and the actual encoding used is implementation-
- defined.
- Forward references: common definitions (7.19), unicode utilities (7.27).
-
-
-
-
- 178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
- ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
- remain an integer constant of type long int that is increased with each revision of this International
- Standard.
-
-[page 175] (Contents)
-
- 6.10.8.3 Conditional feature macros
-1 The following macro names are conditionally defined by the implementation:
- __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to
- the specifications in annex L (Analyzability).
- __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the
- specifications in annex F (IEC 60559 floating-point arithmetic).
- __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate
- adherence to the specifications in annex G (IEC 60559 compatible complex
- arithmetic).
- __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support
- for the extensions defined in annex K (Bounds-checking interfaces).179)
- __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the
- implementation does not support complex types or the <complex.h>
- header.
- __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the
- implementation does not support atomic types (including the _Atomic
- type qualifier and the <stdatomic.h> header) or the <threads.h>
- header.
- __STDC_NO_VLA__ The integer constant 1, intended to indicate that the
- implementation does not support variable length arrays or variably
- modified types.
-2 An implementation that defines __STDC_NO_COMPLEX__ shall not define
- __STDC_IEC_559_COMPLEX__.
- 6.10.9 Pragma operator
- Semantics
-1 A unary operator expression of the form:
- _Pragma ( string-literal )
- is processed as follows: The string literal is destringized by deleting the L prefix, if
- present, deleting the leading and trailing double-quotes, replacing each escape sequence
- \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The
- resulting sequence of characters is processed through translation phase 3 to produce
- preprocessing tokens that are executed as if they were the pp-tokens in a pragma
-
-
- 179) The intention is that this will remain an integer constant of type long int that is increased with
- each revision of this International Standard.
-
-[page 176] (Contents)
-
- directive. The original four preprocessing tokens in the unary operator expression are
- removed.
-2 EXAMPLE A directive of the form:
- #pragma listing on "..\listing.dir"
- can also be expressed as:
- _Pragma ( "listing on \"..\\listing.dir\"" )
- The latter form is processed in the same way whether it appears literally as shown, or results from macro
- replacement, as in:
- #define LISTING(x) PRAGMA(listing on #x)
- #define PRAGMA(x) _Pragma(#x)
- LISTING ( ..\listing.dir )
-
-
-
-
-[page 177] (Contents)
-
- 6.11 Future language directions
- 6.11.1 Floating types
-1 Future standardization may include additional floating-point types, including those with
- greater range, precision, or both than long double.
- 6.11.2 Linkages of identifiers
-1 Declaring an identifier with internal linkage at file scope without the static storage-
- class specifier is an obsolescent feature.
- 6.11.3 External names
-1 Restriction of the significance of an external name to fewer than 255 characters
- (considering each universal character name or extended source character as a single
- character) is an obsolescent feature that is a concession to existing implementations.
- 6.11.4 Character escape sequences
-1 Lowercase letters as escape sequences are reserved for future standardization. Other
- characters may be used in extensions.
- 6.11.5 Storage-class specifiers
-1 The placement of a storage-class specifier other than at the beginning of the declaration
- specifiers in a declaration is an obsolescent feature.
- 6.11.6 Function declarators
-1 The use of function declarators with empty parentheses (not prototype-format parameter
- type declarators) is an obsolescent feature.
- 6.11.7 Function definitions
-1 The use of function definitions with separate parameter identifier and declaration lists
- (not prototype-format parameter type and identifier declarators) is an obsolescent feature.
- 6.11.8 Pragma directives
-1 Pragmas whose first preprocessing token is STDC are reserved for future standardization.
- 6.11.9 Predefined macro names
-1 Macro names beginning with __STDC_ are reserved for future standardization.
-
-
-
-
-[page 178] (Contents)
-
-
- 7. Library
- 7.1 Introduction
- 7.1.1 Definitions of terms
-1 A string is a contiguous sequence of characters terminated by and including the first null
- character. The term multibyte string is sometimes used instead to emphasize special
- processing given to multibyte characters contained in the string or to avoid confusion
- with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
- character. The length of a string is the number of bytes preceding the null character and
- the value of a string is the sequence of the values of the contained characters, in order.
-2 The decimal-point character is the character used by functions that convert floating-point
- numbers to or from character sequences to denote the beginning of the fractional part of
- such character sequences.180) It is represented in the text and examples by a period, but
- may be changed by the setlocale function.
-3 A null wide character is a wide character with code value zero.
-4 A wide string is a contiguous sequence of wide characters terminated by and including
- the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
- addressed) wide character. The length of a wide string is the number of wide characters
- preceding the null wide character and the value of a wide string is the sequence of code
- values of the contained wide characters, in order.
-5 A shift sequence is a contiguous sequence of bytes within a multibyte string that
- (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
- corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
- character.181)
- Forward references: character handling (7.4), the setlocale function (7.11.1.1).
-
-
-
-
- 180) The functions that make use of the decimal-point character are the numeric conversion functions
- (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2).
- 181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
- enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
- sequence of maximum length. Whether these counts provide for more than one shift sequence is the
- implementation's choice.
-
-[page 179] (Contents)
-
- 7.1.2 Standard headers
-1 Each library function is declared, with a type that includes a prototype, in a header,182)
- whose contents are made available by the #include preprocessing directive. The
- header declares a set of related functions, plus any necessary types and additional macros
- needed to facilitate their use. Declarations of types described in this clause shall not
- include type qualifiers, unless explicitly stated otherwise.
-2 The standard headers are183)
- <assert.h> <iso646.h> <stdarg.h> <string.h>
- <complex.h> <limits.h> <stdatomic.h> <tgmath.h>
- <ctype.h> <locale.h> <stdbool.h> <threads.h>
- <errno.h> <math.h> <stddef.h> <time.h>
- <fenv.h> <setjmp.h> <stdint.h> <uchar.h>
- <float.h> <signal.h> <stdio.h> <wchar.h>
- <inttypes.h> <stdalign.h> <stdlib.h> <wctype.h>
-3 If a file with the same name as one of the above < and > delimited sequences, not
- provided as part of the implementation, is placed in any of the standard places that are
- searched for included source files, the behavior is undefined.
-4 Standard headers may be included in any order; each may be included more than once in
- a given scope, with no effect different from being included only once, except that the
- effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
- used, a header shall be included outside of any external declaration or definition, and it
- shall first be included before the first reference to any of the functions or objects it
- declares, or to any of the types or macros it defines. However, if an identifier is declared
- or defined in more than one header, the second and subsequent associated headers may be
- included after the initial reference to the identifier. The program shall not have any
- macros with names lexically identical to keywords currently defined prior to the
- inclusion.
-5 Any definition of an object-like macro described in this clause shall expand to code that is
- fully protected by parentheses where necessary, so that it groups in an arbitrary
- expression as if it were a single identifier.
-6 Any declaration of a library function shall have external linkage.
-
-
-
-
- 182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
- necessarily valid source file names.
- 183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that
- implementations need not support; see 6.10.8.3.
-
-[page 180] (Contents)
-
-7 A summary of the contents of the standard headers is given in annex B.
- Forward references: diagnostics (7.2).
- 7.1.3 Reserved identifiers
-1 Each header declares or defines all identifiers listed in its associated subclause, and
- optionally declares or defines identifiers listed in its associated future library directions
- subclause and identifiers which are always reserved either for any use or for use as file
- scope identifiers.
- -- All identifiers that begin with an underscore and either an uppercase letter or another
- underscore are always reserved for any use.
- -- All identifiers that begin with an underscore are always reserved for use as identifiers
- with file scope in both the ordinary and tag name spaces.
- -- Each macro name in any of the following subclauses (including the future library
- directions) is reserved for use as specified if any of its associated headers is included;
- unless explicitly stated otherwise (see 7.1.4).
- -- All identifiers with external linkage in any of the following subclauses (including the
- future library directions) and errno are always reserved for use as identifiers with
- external linkage.184)
- -- Each identifier with file scope listed in any of the following subclauses (including the
- future library directions) is reserved for use as a macro name and as an identifier with
- file scope in the same name space if any of its associated headers is included.
-2 No other identifiers are reserved. If the program declares or defines an identifier in a
- context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
- identifier as a macro name, the behavior is undefined.
-3 If the program removes (with #undef) any macro definition of an identifier in the first
- group listed above, the behavior is undefined.
-
-
-
-
- 184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
- va_copy, and va_end.
-
-[page 181] (Contents)
-
- 7.1.4 Use of library functions
-1 Each of the following statements applies unless explicitly stated otherwise in the detailed
- descriptions that follow: If an argument to a function has an invalid value (such as a value
- outside the domain of the function, or a pointer outside the address space of the program,
- or a null pointer, or a pointer to non-modifiable storage when the corresponding
- parameter is not const-qualified) or a type (after promotion) not expected by a function
- with variable number of arguments, the behavior is undefined. If a function argument is
- described as being an array, the pointer actually passed to the function shall have a value
- such that all address computations and accesses to objects (that would be valid if the
- pointer did point to the first element of such an array) are in fact valid. Any function
- declared in a header may be additionally implemented as a function-like macro defined in
- the header, so if a library function is declared explicitly when its header is included, one
- of the techniques shown below can be used to ensure the declaration is not affected by
- such a macro. Any macro definition of a function can be suppressed locally by enclosing
- the name of the function in parentheses, because the name is then not followed by the left
- parenthesis that indicates expansion of a macro function name. For the same syntactic
- reason, it is permitted to take the address of a library function even if it is also defined as
- a macro.185) The use of #undef to remove any macro definition will also ensure that an
- actual function is referred to. Any invocation of a library function that is implemented as
- a macro shall expand to code that evaluates each of its arguments exactly once, fully
- protected by parentheses where necessary, so it is generally safe to use arbitrary
- expressions as arguments.186) Likewise, those function-like macros described in the
- following subclauses may be invoked in an expression anywhere a function with a
- compatible return type could be called.187) All object-like macros listed as expanding to
-
-
- 185) This means that an implementation shall provide an actual function for each library function, even if it
- also provides a macro for that function.
- 186) Such macros might not contain the sequence points that the corresponding function calls do.
- 187) Because external identifiers and some macro names beginning with an underscore are reserved,
- implementations may provide special semantics for such names. For example, the identifier
- _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
- appropriate header could specify
- #define abs(x) _BUILTIN_abs(x)
- for a compiler whose code generator will accept it.
- In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
- function may write
- #undef abs
- whether the implementation's header provides a macro implementation of abs or a built-in
- implementation. The prototype for the function, which precedes and is hidden by any macro
- definition, is thereby revealed also.
-
-[page 182] (Contents)
-
- integer constant expressions shall additionally be suitable for use in #if preprocessing
- directives.
-2 Provided that a library function can be declared without reference to any type defined in a
- header, it is also permissible to declare the function and use it without including its
- associated header.
-3 There is a sequence point immediately before a library function returns.
-4 The functions in the standard library are not guaranteed to be reentrant and may modify
- objects with static or thread storage duration.188)
-5 Unless explicitly stated otherwise in the detailed descriptions that follow, library
- functions shall prevent data races as follows: A library function shall not directly or
- indirectly access objects accessible by threads other than the current thread unless the
- objects are accessed directly or indirectly via the function's arguments. A library
- function shall not directly or indirectly modify objects accessible by threads other than
- the current thread unless the objects are accessed directly or indirectly via the function's
- non-const arguments.189) Implementations may share their own internal objects between
- threads if the objects are not visible to users and are protected against data races.
-6 Unless otherwise specified, library functions shall perform all operations solely within the
- current thread if those operations have effects that are visible to users.190)
-7 EXAMPLE The function atoi may be used in any of several ways:
- -- by use of its associated header (possibly generating a macro expansion)
- #include <stdlib.h>
- const char *str;
+ int type;
+ int intnode;
+ } ni;
+ struct {
+ int type;
+ double doublenode;
+ } nf;
+ } u;
+ u.nf.type = 1;
+ u.nf.doublenode = 3.14;
+ /* ... */
+ if (u.n.alltypes == 1)
+ if (sin(u.nf.doublenode) == 0.0)
+ /* ... */
+
+ The following is not a valid fragment (because the union type is not visible within function f):
+
+ struct t1 { int m; };
+ struct t2 { int m; };
+ int f(struct t1 *p1, struct t2 *p2)
+ {
+ if (p1->m < 0)
+ p2->m = -p2->m;
+ return p1->m;
+ }
+ int g()
+ {
+ union {
+ struct t1 s1;
+ struct t2 s2;
+ } u;
+ /* ... */
+ return f(&u.s1, &u.s2);
+ }
+
+
+Forward references: address and indirection operators (6.5.3.2), structure and union + specifiers (6.7.2.1). + + +
95) If the member used to read the contents of a union object is not the same as the member last used to + store a value in the object, the appropriate part of the object representation of the value is reinterpreted + as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type + punning''). This might be a trap representation. + +
96) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to + its operand), the expression (&E)->MOS is the same as E.MOS. + +
97) For example, a data race would occur if access to the entire structure or union in one thread conflicts + with access to a member from another thread, where at least one access is a modification. Members + can be safely accessed using a non-atomic object which is assigned to or from the atomic object. + + +
+ The operand of the postfix increment or decrement operator shall have atomic, qualified, + or unqualified real or pointer type, and shall be a modifiable lvalue. +
+ The result of the postfix ++ operator is the value of the operand. As a side effect, the + value of the operand object is incremented (that is, the value 1 of the appropriate type is + added to it). See the discussions of additive operators and compound assignment for + information on constraints, types, and conversions and the effects of operations on + pointers. The value computation of the result is sequenced before the side effect of + updating the stored value of the operand. With respect to an indeterminately-sequenced + function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object + with atomic type is a read-modify-write operation with memory_order_seq_cst + memory order semantics.98) +
+ The postfix -- operator is analogous to the postfix ++ operator, except that the value of + the operand is decremented (that is, the value 1 of the appropriate type is subtracted from + it). +
Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). + +
98) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
+ where T is the type of E:
+
+
+ T tmp;
+ T result = E;
+ do {
+ tmp = result + 1;
+ } while (!atomic_compare_exchange_strong(&E, &result, tmp));
+
+ with result being the result of the operation.
+
+
+
+ The type name shall specify a complete object type or an array of unknown size, but not a + variable length array type. +
+ All the constraints for initializer lists in 6.7.9 also apply to compound literals. +
+ A postfix expression that consists of a parenthesized type name followed by a brace- + enclosed list of initializers is a compound literal. It provides an unnamed object whose + value is given by the initializer list.99) + + + +
+ If the type name specifies an array of unknown size, the size is determined by the + initializer list as specified in 6.7.9, and the type of the compound literal is that of the + completed array type. Otherwise (when the type name specifies an object type), the type + of the compound literal is that specified by the type name. In either case, the result is an + lvalue. +
+ The value of the compound literal is that of an unnamed object initialized by the + initializer list. If the compound literal occurs outside the body of a function, the object + has static storage duration; otherwise, it has automatic storage duration associated with + the enclosing block. +
+ All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100) +
+ String literals, and compound literals with const-qualified types, need not designate + distinct objects.101) +
+ EXAMPLE 1 The file scope definition +
+ int *p = (int []){2, 4};
+
+ initializes p to point to the first element of an array of two ints, the first having the value two and the
+ second, four. The expressions in this compound literal are required to be constant. The unnamed object
+ has static storage duration.
+
++ EXAMPLE 2 In contrast, in +
+ void f(void)
+ {
+ int *p;
+ /*...*/
+ p = (int [2]){*p};
+ /*...*/
+ }
+
+ p is assigned the address of the first element of an array of two ints, the first having the value previously
+ pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
+ unnamed object has automatic storage duration.
+
++ EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects + created using compound literals can be passed to functions without depending on member order: +
+ drawline((struct point){.x=1, .y=1},
+ (struct point){.x=3, .y=4});
+
+ Or, if drawline instead expected pointers to struct point:
+
+
+
+
+
+ drawline(&(struct point){.x=1, .y=1},
+ &(struct point){.x=3, .y=4});
+
+
++ EXAMPLE 4 A read-only compound literal can be specified through constructions like: +
+ (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
+
+
++ EXAMPLE 5 The following three expressions have different meanings: +
+ "/tmp/fileXXXXXX"
+ (char []){"/tmp/fileXXXXXX"}
+ (const char []){"/tmp/fileXXXXXX"}
+
+ The first always has static storage duration and has type array of char, but need not be modifiable; the last
+ two have automatic storage duration when they occur within the body of a function, and the first of these
+ two is modifiable.
+
++ EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory + and can even be shared. For example, +
+ (const char []){"abc"} == "abc"
+
+ might yield 1 if the literals' storage is shared.
+
++ EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly + linked object. For example, there is no way to write a self-referential compound literal that could be used + as the function argument in place of the named object endless_zeros below: +
+ struct int_list { int car; struct int_list *cdr; };
+ struct int_list endless_zeros = {0, &endless_zeros};
+ eval(endless_zeros);
+
+
++ EXAMPLE 8 Each compound literal creates only a single object in a given scope: +
+ struct s { int i; };
+ int f (void)
+ {
+ struct s *p = 0, *q;
+ int j = 0;
+ again:
+ q = p, p = &((struct s){ j++ });
+ if (j < 2) goto again;
+ return p == q && q->i == 1;
+ }
+
+ The function f() always returns the value 1.
++ Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the + lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would + have an indeterminate value, which would result in undefined behavior. + +
Forward references: type names (6.7.7), initialization (6.7.9). + + +
99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types + or void only, and the result of a cast expression is not an lvalue. + +
100) For example, subobjects without explicit initializers are initialized to zero. + +
101) This allows implementations to share storage for string literals and constant compound literals with + the same or overlapping representations. + + +
+
+ unary-expression: + postfix-expression + ++ unary-expression + -- unary-expression + unary-operator cast-expression + sizeof unary-expression + sizeof ( type-name ) + alignof ( type-name ) + unary-operator: one of + & * + - ~ ! ++ +
+ The operand of the prefix increment or decrement operator shall have atomic, qualified, + or unqualified real or pointer type, and shall be a modifiable lvalue. +
+ The value of the operand of the prefix ++ operator is incremented. The result is the new + value of the operand after incrementation. The expression ++E is equivalent to (E+=1). + See the discussions of additive operators and compound assignment for information on + constraints, types, side effects, and conversions and the effects of operations on pointers. +
+ The prefix -- operator is analogous to the prefix ++ operator, except that the value of the + operand is decremented. +
Forward references: additive operators (6.5.6), compound assignment (6.5.16.2). + +
+ The operand of the unary & operator shall be either a function designator, the result of a + [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is + not declared with the register storage-class specifier. +
+ The operand of the unary * operator shall have pointer type. +
+ The unary & operator yields the address of its operand. If the operand has type ''type'', + the result has type ''pointer to type''. If the operand is the result of a unary * operator, + neither that operator nor the & operator is evaluated and the result is as if both were + omitted, except that the constraints on the operators still apply and the result is not an + + lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor + the unary * that is implied by the [] is evaluated and the result is as if the & operator + were removed and the [] operator were changed to a + operator. Otherwise, the result is + a pointer to the object or function designated by its operand. +
+ The unary * operator denotes indirection. If the operand points to a function, the result is + a function designator; if it points to an object, the result is an lvalue designating the + object. If the operand has type ''pointer to type'', the result has type ''type''. If an + invalid value has been assigned to the pointer, the behavior of the unary * operator is + undefined.102) +
Forward references: storage-class specifiers (6.7.1), structure and union specifiers + (6.7.2.1). + +
102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is + always true that if E is a function designator or an lvalue that is a valid operand of the unary & + operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of + an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. + Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an + address inappropriately aligned for the type of object pointed to, and the address of an object after the + end of its lifetime. + + +
+ The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, + integer type; of the ! operator, scalar type. +
+ The result of the unary + operator is the value of its (promoted) operand. The integer + promotions are performed on the operand, and the result has the promoted type. +
+ The result of the unary - operator is the negative of its (promoted) operand. The integer + promotions are performed on the operand, and the result has the promoted type. +
+ The result of the ~ operator is the bitwise complement of its (promoted) operand (that is, + each bit in the result is set if and only if the corresponding bit in the converted operand is + not set). The integer promotions are performed on the operand, and the result has the + promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent + to the maximum value representable in that type minus E. +
+ The result of the logical negation operator ! is 0 if the value of its operand compares + unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. + The expression !E is equivalent to (0==E). + + + + + +
+ The sizeof operator shall not be applied to an expression that has function type or an + incomplete type, to the parenthesized name of such a type, or to an expression that + designates a bit-field member. The alignof operator shall not be applied to a function + type or an incomplete type. +
+ The sizeof operator yields the size (in bytes) of its operand, which may be an + expression or the parenthesized name of a type. The size is determined from the type of + the operand. The result is an integer. If the type of the operand is a variable length array + type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an + integer constant. +
+ The alignof operator yields the alignment requirement of its operand type. The result + is an integer constant. When applied to an array type, the result is the alignment + requirement of the element type. +
+ When sizeof is applied to an operand that has type char, unsigned char, or + signed char, (or a qualified version thereof) the result is 1. When applied to an + operand that has array type, the result is the total number of bytes in the array.103) When + applied to an operand that has structure or union type, the result is the total number of + bytes in such an object, including internal and trailing padding. +
+ The value of the result of both operators is implementation-defined, and its type (an + unsigned integer type) is size_t, defined in <stddef.h> (and other headers). +
+ EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage + allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to + allocate and return a pointer to void. For example: +
+ extern void *alloc(size_t); + double *dp = alloc(sizeof *dp); ++ The implementation of the alloc function should ensure that its return value is aligned suitably for + conversion to a pointer to double. + +
+ EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array: +
+ sizeof array / sizeof array[0] ++ +
+ EXAMPLE 3 In this example, the size of a variable length array is computed and returned from a + function: +
+ #include <stddef.h> ++ + + + +
+ size_t fsize3(int n)
+ {
+ char b[n+3]; // variable length array
+ return sizeof b; // execution time sizeof
+ }
+ int main()
+ {
+ size_t size;
+ size = fsize3(10); // fsize3 returns 13
+ return 0;
+ }
+
+
+Forward references: common definitions <stddef.h> (7.19), declarations (6.7), + structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2). + +
103) When applied to a parameter declared to have array or function type, the sizeof operator yields the + size of the adjusted (pointer) type (see 6.9.1). + + +
+
+ cast-expression: + unary-expression + ( type-name ) cast-expression ++
+ Unless the type name specifies a void type, the type name shall specify atomic, qualified, + or unqualified scalar type, and the operand shall have scalar type. +
+ Conversions that involve pointers, other than where permitted by the constraints of + 6.5.16.1, shall be specified by means of an explicit cast. +
+ A pointer type shall not be converted to any floating type. A floating type shall not be + converted to any pointer type. +
+ Preceding an expression by a parenthesized type name converts the value of the + expression to the named type. This construction is called a cast.104) A cast that specifies + no conversion has no effect on the type or value of an expression. +
+ If the value of the expression is represented with greater precision or range than required + by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the + type of the expression is the same as the named type and removes any extra range and + precision. +
Forward references: equality operators (6.5.9), function declarators (including + prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7). + + + +
104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the + unqualified version of the type. + + +
+
+ multiplicative-expression: + cast-expression + multiplicative-expression * cast-expression + multiplicative-expression / cast-expression + multiplicative-expression % cast-expression ++
+ Each of the operands shall have arithmetic type. The operands of the % operator shall + have integer type. +
+ The usual arithmetic conversions are performed on the operands. +
+ The result of the binary * operator is the product of the operands. +
+ The result of the / operator is the quotient from the division of the first operand by the + second; the result of the % operator is the remainder. In both operations, if the value of + the second operand is zero, the behavior is undefined. +
+ When integers are divided, the result of the / operator is the algebraic quotient with any + fractional part discarded.105) If the quotient a/b is representable, the expression + (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is + undefined. + +
105) This is often called ''truncation toward zero''. + + +
+
+ additive-expression: + multiplicative-expression + additive-expression + multiplicative-expression + additive-expression - multiplicative-expression ++
+ For addition, either both operands shall have arithmetic type, or one operand shall be a + pointer to a complete object type and the other shall have integer type. (Incrementing is + equivalent to adding 1.) +
+ For subtraction, one of the following shall hold: + + + + + +
+ If both operands have arithmetic type, the usual arithmetic conversions are performed on + them. +
+ The result of the binary + operator is the sum of the operands. +
+ The result of the binary - operator is the difference resulting from the subtraction of the + second operand from the first. +
+ For the purposes of these operators, a pointer to an object that is not an element of an + array behaves the same as a pointer to the first element of an array of length one with the + type of the object as its element type. +
+ When an expression that has integer type is added to or subtracted from a pointer, the + result has the type of the pointer operand. If the pointer operand points to an element of + an array object, and the array is large enough, the result points to an element offset from + the original element such that the difference of the subscripts of the resulting and original + array elements equals the integer expression. In other words, if the expression P points to + the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and + (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of + the array object, provided they exist. Moreover, if the expression P points to the last + element of an array object, the expression (P)+1 points one past the last element of the + array object, and if the expression Q points one past the last element of an array object, + the expression (Q)-1 points to the last element of the array object. If both the pointer + operand and the result point to elements of the same array object, or one past the last + element of the array object, the evaluation shall not produce an overflow; otherwise, the + behavior is undefined. If the result points one past the last element of the array object, it + shall not be used as the operand of a unary * operator that is evaluated. +
+ When two pointers are subtracted, both shall point to elements of the same array object, + or one past the last element of the array object; the result is the difference of the + subscripts of the two array elements. The size of the result is implementation-defined, + and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. + If the result is not representable in an object of that type, the behavior is undefined. In + other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of + an array object, the expression (P)-(Q) has the value i-j provided the value fits in an + + object of type ptrdiff_t. Moreover, if the expression P points either to an element of + an array object or one past the last element of an array object, and the expression Q points + to the last element of the same array object, the expression ((Q)+1)-(P) has the same + value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the + expression P points one past the last element of the array object, even though the + expression (Q)+1 does not point to an element of the array object.106) +
+ EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types. +
+ {
+ int n = 4, m = 3;
+ int a[n][m];
+ int (*p)[m] = a; // p == &a[0]
+ p += 1; // p == &a[1]
+ (*p)[2] = 99; // a[1][2] == 99
+ n = p - a; // n == 1
+ }
+
++ If array a in the above example were declared to be an array of known constant size, and pointer p were + declared to be a pointer to an array of the same known constant size (pointing to a), the results would be + the same. + +
Forward references: array declarators (6.7.6.2), common definitions <stddef.h> + (7.19). + +
106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In + this scheme the integer expression added to or subtracted from the converted pointer is first multiplied + by the size of the object originally pointed to, and the resulting pointer is converted back to the + original type. For pointer subtraction, the result of the difference between the character pointers is + similarly divided by the size of the object originally pointed to. + When viewed in this way, an implementation need only provide one extra byte (which may overlap + another object in the program) just after the end of the object in order to satisfy the ''one past the last + element'' requirements. + + +
+
+ shift-expression: + additive-expression + shift-expression << additive-expression + shift-expression >> additive-expression ++
+ Each of the operands shall have integer type. +
+ The integer promotions are performed on each of the operands. The type of the result is + that of the promoted left operand. If the value of the right operand is negative or is + + + greater than or equal to the width of the promoted left operand, the behavior is undefined. +
+ The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with + zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo + one more than the maximum value representable in the result type. If E1 has a signed + type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is + the resulting value; otherwise, the behavior is undefined. +
+ The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type + or if E1 has a signed type and a nonnegative value, the value of the result is the integral + part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the + resulting value is implementation-defined. + +
+
+ relational-expression: + shift-expression + relational-expression < shift-expression + relational-expression > shift-expression + relational-expression <= shift-expression + relational-expression >= shift-expression ++
+ One of the following shall hold: +
+ If both of the operands have arithmetic type, the usual arithmetic conversions are + performed. +
+ For the purposes of these operators, a pointer to an object that is not an element of an + array behaves the same as a pointer to the first element of an array of length one with the + type of the object as its element type. +
+ When two pointers are compared, the result depends on the relative locations in the + address space of the objects pointed to. If two pointers to object types both point to the + same object, or both point one past the last element of the same array object, they + compare equal. If the objects pointed to are members of the same aggregate object, + pointers to structure members declared later compare greater than pointers to members + declared earlier in the structure, and pointers to array elements with larger subscript + values compare greater than pointers to elements of the same array with lower subscript + + values. All pointers to members of the same union object compare equal. If the + expression P points to an element of an array object and the expression Q points to the + last element of the same array object, the pointer expression Q+1 compares greater than + P. In all other cases, the behavior is undefined. +
+ Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= + (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is + false.107) The result has type int. + +
107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it + means (a<b)<c; in other words, ''if a is less than b, compare 1 to c; otherwise, compare 0 to c''. + + +
+
+ equality-expression: + relational-expression + equality-expression == relational-expression + equality-expression != relational-expression ++
+ One of the following shall hold: +
+ The == (equal to) and != (not equal to) operators are analogous to the relational + operators except for their lower precedence.108) Each of the operators yields 1 if the + specified relation is true and 0 if it is false. The result has type int. For any pair of + operands, exactly one of the relations is true. +
+ If both of the operands have arithmetic type, the usual arithmetic conversions are + performed. Values of complex types are equal if and only if both their real parts are equal + and also their imaginary parts are equal. Any two values of arithmetic types from + different type domains are equal if and only if the results of their conversions to the + (complex) result type determined by the usual arithmetic conversions are equal. + + + + +
+ Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a + null pointer constant, the null pointer constant is converted to the type of the pointer. If + one operand is a pointer to an object type and the other is a pointer to a qualified or + unqualified version of void, the former is converted to the type of the latter. +
+ Two pointers compare equal if and only if both are null pointers, both are pointers to the + same object (including a pointer to an object and a subobject at its beginning) or function, + both are pointers to one past the last element of the same array object, or one is a pointer + to one past the end of one array object and the other is a pointer to the start of a different + array object that happens to immediately follow the first array object in the address + space.109) +
+ For the purposes of these operators, a pointer to an object that is not an element of an + array behaves the same as a pointer to the first element of an array of length one with the + type of the object as its element type. + +
108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value. + +
109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or + adjacent members of a structure with no padding between them, or because the implementation chose + to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses + outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined + behavior. + + +
+
+ AND-expression: + equality-expression + AND-expression & equality-expression ++
+ Each of the operands shall have integer type. +
+ The usual arithmetic conversions are performed on the operands. +
+ The result of the binary & operator is the bitwise AND of the operands (that is, each bit in + the result is set if and only if each of the corresponding bits in the converted operands is + set). + + + + + + +
+
+ exclusive-OR-expression: + AND-expression + exclusive-OR-expression ^ AND-expression ++
+ Each of the operands shall have integer type. +
+ The usual arithmetic conversions are performed on the operands. +
+ The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit + in the result is set if and only if exactly one of the corresponding bits in the converted + operands is set). + +
+
+ inclusive-OR-expression: + exclusive-OR-expression + inclusive-OR-expression | exclusive-OR-expression ++
+ Each of the operands shall have integer type. +
+ The usual arithmetic conversions are performed on the operands. +
+ The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in + the result is set if and only if at least one of the corresponding bits in the converted + operands is set). + + +
+
+ logical-AND-expression: + inclusive-OR-expression + logical-AND-expression && inclusive-OR-expression ++
+ Each of the operands shall have scalar type. +
+ The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it + yields 0. The result has type int. +
+ Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation; + if the second operand is evaluated, there is a sequence point between the evaluations of + the first and second operands. If the first operand compares equal to 0, the second + operand is not evaluated. + +
+
+ logical-OR-expression: + logical-AND-expression + logical-OR-expression || logical-AND-expression ++
+ Each of the operands shall have scalar type. +
+ The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it + yields 0. The result has type int. +
+ Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the + second operand is evaluated, there is a sequence point between the evaluations of the first + and second operands. If the first operand compares unequal to 0, the second operand is + not evaluated. + + +
+
+ conditional-expression: + logical-OR-expression + logical-OR-expression ? expression : conditional-expression ++
+ The first operand shall have scalar type. +
+ One of the following shall hold for the second and third operands: +
+ The first operand is evaluated; there is a sequence point between its evaluation and the + evaluation of the second or third operand (whichever is evaluated). The second operand + is evaluated only if the first compares unequal to 0; the third operand is evaluated only if + the first compares equal to 0; the result is the value of the second or third operand + (whichever is evaluated), converted to the type described below.110) * +
+ If both the second and third operands have arithmetic type, the result type that would be + determined by the usual arithmetic conversions, were they applied to those two operands, + is the type of the result. If both the operands have structure or union type, the result has + that type. If both operands have void type, the result has void type. +
+ If both the second and third operands are pointers or one is a null pointer constant and the + other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers + of the types referenced by both operands. Furthermore, if both operands are pointers to + compatible types or to differently qualified versions of compatible types, the result type is + a pointer to an appropriately qualified version of the composite type; if one operand is a + null pointer constant, the result has the type of the other operand; otherwise, one operand + is a pointer to void or a qualified version of void, in which case the result type is a + pointer to an appropriately qualified version of void. + + +
+ EXAMPLE The common type that results when the second and third operands are pointers is determined + in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two + pointers have compatible types. +
+ Given the declarations +
+ const void *c_vp; + void *vp; + const int *c_ip; + volatile int *v_ip; + int *ip; + const char *c_cp; ++ the third column in the following table is the common type that is the result of a conditional expression in + which the first two columns are the second and third operands (in either order): +
+ c_vp c_ip const void * + v_ip 0 volatile int * + c_ip v_ip const volatile int * + vp c_cp const void * + ip c_ip const int * + vp ip void * ++ + +
110) A conditional expression does not yield an lvalue. + + +
+
+ assignment-expression: + conditional-expression + unary-expression assignment-operator assignment-expression + assignment-operator: one of + = *= /= %= += -= <<= >>= &= ^= |= ++
+ An assignment operator shall have a modifiable lvalue as its left operand. +
+ An assignment operator stores a value in the object designated by the left operand. An + assignment expression has the value of the left operand after the assignment,111) but is not + an lvalue. The type of an assignment expression is the type the left operand would have + after lvalue conversion. The side effect of updating the stored value of the left operand is + sequenced after the value computations of the left and right operands. The evaluations of + the operands are unsequenced. + + + + + + +
111) The implementation is permitted to read the object to determine the value but is not required to, even + when the object has volatile-qualified type. + + +
+ One of the following shall hold:112) +
+ In simple assignment (=), the value of the right operand is converted to the type of the + assignment expression and replaces the value stored in the object designated by the left + operand. +
+ If the value being stored in an object is read from another object that overlaps in any way + the storage of the first object, then the overlap shall be exact and the two objects shall + have qualified or unqualified versions of a compatible type; otherwise, the behavior is + undefined. +
+ EXAMPLE 1 In the program fragment + + + + + +
+ int f(void);
+ char c;
+ /* ... */
+ if ((c = f()) == -1)
/* ... */
- i = atoi(str);
- -- by use of its associated header (assuredly generating a true function reference)
-
-
-
-
- 188) Thus, a signal handler cannot, in general, call standard library functions.
- 189) This means, for example, that an implementation is not permitted to use a static object for internal
- purposes without synchronization because it could cause a data race even in programs that do not
- explicitly share objects between threads.
- 190) This allows implementations to parallelize operations if there are no visible side effects.
-
-[page 183] (Contents)
-
- #include <stdlib.h>
- #undef atoi
- const char *str;
- /* ... */
- i = atoi(str);
- or
- #include <stdlib.h>
- const char *str;
- /* ... */
- i = (atoi)(str);
--- by explicit declaration
- extern int atoi(const char *);
- const char *str;
- /* ... */
- i = atoi(str);
-
-
-
-
-[page 184] (Contents)
-
- 7.2 Diagnostics <assert.h>
-1 The header <assert.h> defines the assert and static_assert macros and
- refers to another macro,
- NDEBUG
- which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
- point in the source file where <assert.h> is included, the assert macro is defined
- simply as
- #define assert(ignore) ((void)0)
- The assert macro is redefined according to the current state of NDEBUG each time that
- <assert.h> is included.
-2 The assert macro shall be implemented as a macro, not as an actual function. If the
- macro definition is suppressed in order to access an actual function, the behavior is
- undefined.
-3 The macro
- static_assert
- expands to _Static_assert.
- 7.2.1 Program diagnostics
- 7.2.1.1 The assert macro
- Synopsis
-1 #include <assert.h>
- void assert(scalar expression);
- Description
-2 The assert macro puts diagnostic tests into programs; it expands to a void expression.
- When it is executed, if expression (which shall have a scalar type) is false (that is,
- compares equal to 0), the assert macro writes information about the particular call that
- failed (including the text of the argument, the name of the source file, the source line
- number, and the name of the enclosing function -- the latter are respectively the values of
- the preprocessing macros __FILE__ and __LINE__ and of the identifier
- __func__) on the standard error stream in an implementation-defined format.191) It
- then calls the abort function.
-
-
-
- 191) The message written might be of the form:
- Assertion failed: expression, function abc, file xyz, line nnn.
-
-
-[page 185] (Contents)
-
- Returns
-3 The assert macro returns no value.
- Forward references: the abort function (7.22.4.1).
-
-
-
-
-[page 186] (Contents)
-
- 7.3 Complex arithmetic <complex.h>
- 7.3.1 Introduction
-1 The header <complex.h> defines macros and declares functions that support complex
- arithmetic.192)
-2 Implementations that define the macro __STDC_NO_COMPLEX__ need not provide
- this header nor support any of its facilities.
-3 Each synopsis specifies a family of functions consisting of a principal function with one
- or more double complex parameters and a double complex or double return
- value; and other functions with the same name but with f and l suffixes which are
- corresponding functions with float and long double parameters and return values.
-4 The macro
- complex
- expands to _Complex; the macro
- _Complex_I
- expands to a constant expression of type const float _Complex, with the value of
- the imaginary unit.193)
-5 The macros
- imaginary
- and
- _Imaginary_I
- are defined if and only if the implementation supports imaginary types;194) if defined,
- they expand to _Imaginary and a constant expression of type const float
- _Imaginary with the value of the imaginary unit.
-6 The macro
- I
- expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
- defined, I shall expand to _Complex_I.
-7 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
- redefine the macros complex, imaginary, and I.
-
- 192) See ''future library directions'' (7.30.1).
- 193) The imaginary unit is a number i such that i 2 = -1.
- 194) A specification for imaginary types is in informative annex G.
-
-[page 187] (Contents)
-
- Forward references: IEC 60559-compatible complex arithmetic (annex G).
- 7.3.2 Conventions
-1 Values are interpreted as radians, not degrees. An implementation may set errno but is
- not required to.
- 7.3.3 Branch cuts
-1 Some of the functions below have branch cuts, across which the function is
- discontinuous. For implementations with a signed zero (including all IEC 60559
- implementations) that follow the specifications of annex G, the sign of zero distinguishes
- one side of a cut from another so the function is continuous (except for format
- limitations) as the cut is approached from either side. For example, for the square root
- function, which has a branch cut along the negative real axis, the top of the cut, with
- imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
- imaginary part -0, maps to the negative imaginary axis.
-2 Implementations that do not support a signed zero (see annex F) cannot distinguish the
- sides of branch cuts. These implementations shall map a cut so the function is continuous
- as the cut is approached coming around the finite endpoint of the cut in a counter
- clockwise direction. (Branch cuts for the functions specified here have just one finite
- endpoint.) For example, for the square root function, coming counter clockwise around
- the finite endpoint of the cut along the negative real axis approaches the cut from above,
- so the cut maps to the positive imaginary axis.
- 7.3.4 The CX_LIMITED_RANGE pragma
- Synopsis
-1 #include <complex.h>
- #pragma STDC CX_LIMITED_RANGE on-off-switch
- Description
-2 The usual mathematical formulas for complex multiply, divide, and absolute value are
- problematic because of their treatment of infinities and because of undue overflow and
- underflow. The CX_LIMITED_RANGE pragma can be used to inform the
- implementation that (where the state is ''on'') the usual mathematical formulas are
- acceptable.195) The pragma can occur either outside external declarations or preceding all
- explicit declarations and statements inside a compound statement. When outside external
- declarations, the pragma takes effect from its occurrence until another
- CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
- When inside a compound statement, the pragma takes effect from its occurrence until
- another CX_LIMITED_RANGE pragma is encountered (including within a nested
- compound statement), or until the end of the compound statement; at the end of a
- compound statement the state for the pragma is restored to its condition just before the
-
-[page 188] (Contents)
-
- compound statement. If this pragma is used in any other context, the behavior is
- undefined. The default state for the pragma is ''off''.
- 7.3.5 Trigonometric functions
- 7.3.5.1 The cacos functions
- Synopsis
-1 #include <complex.h>
- double complex cacos(double complex z);
- float complex cacosf(float complex z);
- long double complex cacosl(long double complex z);
- Description
-2 The cacos functions compute the complex arc cosine of z, with branch cuts outside the
- interval [-1, +1] along the real axis.
- Returns
-3 The cacos functions return the complex arc cosine value, in the range of a strip
- mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the
- real axis.
- 7.3.5.2 The casin functions
- Synopsis
-1 #include <complex.h>
- double complex casin(double complex z);
- float complex casinf(float complex z);
- long double complex casinl(long double complex z);
- Description
-2 The casin functions compute the complex arc sine of z, with branch cuts outside the
- interval [-1, +1] along the real axis.
- Returns
-3 The casin functions return the complex arc sine value, in the range of a strip
- mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
-
- 195) The purpose of the pragma is to allow the implementation to use the formulas:
- (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
- (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
- | x + iy | = sqrt: x 2 + y 2
- -----
- where the programmer can determine they are safe.
-
-[page 189] (Contents)
-
- along the real axis.
- 7.3.5.3 The catan functions
- Synopsis
-1 #include <complex.h>
- double complex catan(double complex z);
- float complex catanf(float complex z);
- long double complex catanl(long double complex z);
- Description
-2 The catan functions compute the complex arc tangent of z, with branch cuts outside the
- interval [-i, +i] along the imaginary axis.
- Returns
-3 The catan functions return the complex arc tangent value, in the range of a strip
- mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
- along the real axis.
- 7.3.5.4 The ccos functions
- Synopsis
-1 #include <complex.h>
- double complex ccos(double complex z);
- float complex ccosf(float complex z);
- long double complex ccosl(long double complex z);
- Description
-2 The ccos functions compute the complex cosine of z.
- Returns
-3 The ccos functions return the complex cosine value.
- 7.3.5.5 The csin functions
- Synopsis
-1 #include <complex.h>
- double complex csin(double complex z);
- float complex csinf(float complex z);
- long double complex csinl(long double complex z);
- Description
-2 The csin functions compute the complex sine of z.
-
-
-
-[page 190] (Contents)
-
- Returns
-3 The csin functions return the complex sine value.
- 7.3.5.6 The ctan functions
- Synopsis
-1 #include <complex.h>
- double complex ctan(double complex z);
- float complex ctanf(float complex z);
- long double complex ctanl(long double complex z);
- Description
-2 The ctan functions compute the complex tangent of z.
- Returns
-3 The ctan functions return the complex tangent value.
- 7.3.6 Hyperbolic functions
- 7.3.6.1 The cacosh functions
- Synopsis
-1 #include <complex.h>
- double complex cacosh(double complex z);
- float complex cacoshf(float complex z);
- long double complex cacoshl(long double complex z);
- Description
-2 The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
- cut at values less than 1 along the real axis.
- Returns
-3 The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
- half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the
- imaginary axis.
- 7.3.6.2 The casinh functions
- Synopsis
-1 #include <complex.h>
- double complex casinh(double complex z);
- float complex casinhf(float complex z);
- long double complex casinhl(long double complex z);
-
-
-
-[page 191] (Contents)
-
- Description
-2 The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
- outside the interval [-i, +i] along the imaginary axis.
- Returns
-3 The casinh functions return the complex arc hyperbolic sine value, in the range of a
- strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
- along the imaginary axis.
- 7.3.6.3 The catanh functions
- Synopsis
-1 #include <complex.h>
- double complex catanh(double complex z);
- float complex catanhf(float complex z);
- long double complex catanhl(long double complex z);
- Description
-2 The catanh functions compute the complex arc hyperbolic tangent of z, with branch
- cuts outside the interval [-1, +1] along the real axis.
- Returns
-3 The catanh functions return the complex arc hyperbolic tangent value, in the range of a
- strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
- along the imaginary axis.
- 7.3.6.4 The ccosh functions
- Synopsis
-1 #include <complex.h>
- double complex ccosh(double complex z);
- float complex ccoshf(float complex z);
- long double complex ccoshl(long double complex z);
- Description
-2 The ccosh functions compute the complex hyperbolic cosine of z.
- Returns
-3 The ccosh functions return the complex hyperbolic cosine value.
-
-
-
-
-[page 192] (Contents)
-
- 7.3.6.5 The csinh functions
- Synopsis
-1 #include <complex.h>
- double complex csinh(double complex z);
- float complex csinhf(float complex z);
- long double complex csinhl(long double complex z);
- Description
-2 The csinh functions compute the complex hyperbolic sine of z.
- Returns
-3 The csinh functions return the complex hyperbolic sine value.
- 7.3.6.6 The ctanh functions
- Synopsis
-1 #include <complex.h>
- double complex ctanh(double complex z);
- float complex ctanhf(float complex z);
- long double complex ctanhl(long double complex z);
- Description
-2 The ctanh functions compute the complex hyperbolic tangent of z.
- Returns
-3 The ctanh functions return the complex hyperbolic tangent value.
- 7.3.7 Exponential and logarithmic functions
- 7.3.7.1 The cexp functions
- Synopsis
-1 #include <complex.h>
- double complex cexp(double complex z);
- float complex cexpf(float complex z);
- long double complex cexpl(long double complex z);
- Description
-2 The cexp functions compute the complex base-e exponential of z.
- Returns
-3 The cexp functions return the complex base-e exponential value.
-
-
-
-[page 193] (Contents)
-
- 7.3.7.2 The clog functions
- Synopsis
-1 #include <complex.h>
- double complex clog(double complex z);
- float complex clogf(float complex z);
- long double complex clogl(long double complex z);
- Description
-2 The clog functions compute the complex natural (base-e) logarithm of z, with a branch
- cut along the negative real axis.
- Returns
-3 The clog functions return the complex natural logarithm value, in the range of a strip
- mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the
- imaginary axis.
- 7.3.8 Power and absolute-value functions
- 7.3.8.1 The cabs functions
- Synopsis
-1 #include <complex.h>
- double cabs(double complex z);
- float cabsf(float complex z);
- long double cabsl(long double complex z);
- Description
-2 The cabs functions compute the complex absolute value (also called norm, modulus, or
- magnitude) of z.
- Returns
-3 The cabs functions return the complex absolute value.
- 7.3.8.2 The cpow functions
- Synopsis
-1 #include <complex.h>
- double complex cpow(double complex x, double complex y);
- float complex cpowf(float complex x, float complex y);
- long double complex cpowl(long double complex x,
- long double complex y);
-
-
-
-
-[page 194] (Contents)
-
- Description
-2 The cpow functions compute the complex power function xy , with a branch cut for the
- first parameter along the negative real axis.
- Returns
-3 The cpow functions return the complex power function value.
- 7.3.8.3 The csqrt functions
- Synopsis
-1 #include <complex.h>
- double complex csqrt(double complex z);
- float complex csqrtf(float complex z);
- long double complex csqrtl(long double complex z);
- Description
-2 The csqrt functions compute the complex square root of z, with a branch cut along the
- negative real axis.
- Returns
-3 The csqrt functions return the complex square root value, in the range of the right half-
- plane (including the imaginary axis).
- 7.3.9 Manipulation functions
- 7.3.9.1 The carg functions
- Synopsis
-1 #include <complex.h>
- double carg(double complex z);
- float cargf(float complex z);
- long double cargl(long double complex z);
- Description
-2 The carg functions compute the argument (also called phase angle) of z, with a branch
- cut along the negative real axis.
- Returns
-3 The carg functions return the value of the argument in the interval [-pi , +pi ].
-
-
-
-
-[page 195] (Contents)
-
- 7.3.9.2 The cimag functions
- Synopsis
-1 #include <complex.h>
- double cimag(double complex z);
- float cimagf(float complex z);
- long double cimagl(long double complex z);
- Description
-2 The cimag functions compute the imaginary part of z.196)
- Returns
-3 The cimag functions return the imaginary part value (as a real).
- 7.3.9.3 The CMPLX macros
- Synopsis
-1 #include <complex.h>
- double complex CMPLX(double x, double y);
- float complex CMPLXF(float x, float y);
- long double complex CMPLXL(long double x, long double y);
- Description
-2 The CMPLX macros expand to an expression of the specified complex type, with the real
- part having the (converted) value of x and the imaginary part having the (converted)
- value of y.
- Recommended practice
-3 The resulting expression should be suitable for use as an initializer for an object with
- static or thread storage duration, provided both arguments are likewise suitable.
- Returns
-4 The CMPLX macros return the complex value x + i y.
-5 NOTE These macros act as if the implementation supported imaginary types and the definitions were:
- #define CMPLX(x, y) ((double complex)((double)(x) + \
- _Imaginary_I * (double)(y)))
- #define CMPLXF(x, y) ((float complex)((float)(x) + \
- _Imaginary_I * (float)(y)))
- #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
- _Imaginary_I * (long double)(y)))
-
-
-
-
- 196) For a variable z of complex type, z == creal(z) + cimag(z)*I.
-
-[page 196] (Contents)
-
- 7.3.9.4 The conj functions
- Synopsis
-1 #include <complex.h>
- double complex conj(double complex z);
- float complex conjf(float complex z);
- long double complex conjl(long double complex z);
- Description
-2 The conj functions compute the complex conjugate of z, by reversing the sign of its
- imaginary part.
- Returns
-3 The conj functions return the complex conjugate value.
- 7.3.9.5 The cproj functions
- Synopsis
-1 #include <complex.h>
- double complex cproj(double complex z);
- float complex cprojf(float complex z);
- long double complex cprojl(long double complex z);
- Description
-2 The cproj functions compute a projection of z onto the Riemann sphere: z projects to
- z except that all complex infinities (even those with one infinite part and one NaN part)
- project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
- equivalent to
- INFINITY + I * copysign(0.0, cimag(z))
- Returns
-3 The cproj functions return the value of the projection onto the Riemann sphere.
- 7.3.9.6 The creal functions
- Synopsis
-1 #include <complex.h>
- double creal(double complex z);
- float crealf(float complex z);
- long double creall(long double complex z);
- Description
-2 The creal functions compute the real part of z.197)
-
-
-[page 197] (Contents)
-
- Returns
-3 The creal functions return the real part value.
-
-
-
-
- 197) For a variable z of complex type, z == creal(z) + cimag(z)*I.
-
-[page 198] (Contents)
-
- 7.4 Character handling <ctype.h>
-1 The header <ctype.h> declares several functions useful for classifying and mapping
- characters.198) In all cases the argument is an int, the value of which shall be
- representable as an unsigned char or shall equal the value of the macro EOF. If the
- argument has any other value, the behavior is undefined.
-2 The behavior of these functions is affected by the current locale. Those functions that
- have locale-specific aspects only when not in the "C" locale are noted below.
-3 The term printing character refers to a member of a locale-specific set of characters, each
- of which occupies one printing position on a display device; the term control character
- refers to a member of a locale-specific set of characters that are not printing
- characters.199) All letters and digits are printing characters.
- Forward references: EOF (7.21.1), localization (7.11).
- 7.4.1 Character classification functions
-1 The functions in this subclause return nonzero (true) if and only if the value of the
- argument c conforms to that in the description of the function.
- 7.4.1.1 The isalnum function
- Synopsis
-1 #include <ctype.h>
- int isalnum(int c);
- Description
-2 The isalnum function tests for any character for which isalpha or isdigit is true.
- 7.4.1.2 The isalpha function
- Synopsis
-1 #include <ctype.h>
- int isalpha(int c);
- Description
-2 The isalpha function tests for any character for which isupper or islower is true,
- or any character that is one of a locale-specific set of alphabetic characters for which
-
-
-
- 198) See ''future library directions'' (7.30.2).
- 199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
- whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
- values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).
-
-[page 199] (Contents)
-
- none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale,
- isalpha returns true only for the characters for which isupper or islower is true.
- 7.4.1.3 The isblank function
- Synopsis
-1 #include <ctype.h>
- int isblank(int c);
- Description
-2 The isblank function tests for any character that is a standard blank character or is one
- of a locale-specific set of characters for which isspace is true and that is used to
- separate words within a line of text. The standard blank characters are the following:
- space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
- for the standard blank characters.
- 7.4.1.4 The iscntrl function
- Synopsis
-1 #include <ctype.h>
- int iscntrl(int c);
- Description
-2 The iscntrl function tests for any control character.
- 7.4.1.5 The isdigit function
- Synopsis
-1 #include <ctype.h>
- int isdigit(int c);
- Description
-2 The isdigit function tests for any decimal-digit character (as defined in 5.2.1).
- 7.4.1.6 The isgraph function
- Synopsis
-1 #include <ctype.h>
- int isgraph(int c);
-
-
-
-
- 200) The functions islower and isupper test true or false separately for each of these additional
- characters; all four combinations are possible.
-
-[page 200] (Contents)
-
- Description
-2 The isgraph function tests for any printing character except space (' ').
- 7.4.1.7 The islower function
- Synopsis
-1 #include <ctype.h>
- int islower(int c);
- Description
-2 The islower function tests for any character that is a lowercase letter or is one of a
- locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
- isspace is true. In the "C" locale, islower returns true only for the lowercase
- letters (as defined in 5.2.1).
- 7.4.1.8 The isprint function
- Synopsis
-1 #include <ctype.h>
- int isprint(int c);
- Description
-2 The isprint function tests for any printing character including space (' ').
- 7.4.1.9 The ispunct function
- Synopsis
-1 #include <ctype.h>
- int ispunct(int c);
- Description
-2 The ispunct function tests for any printing character that is one of a locale-specific set
- of punctuation characters for which neither isspace nor isalnum is true. In the "C"
- locale, ispunct returns true for every printing character for which neither isspace
- nor isalnum is true.
- 7.4.1.10 The isspace function
- Synopsis
-1 #include <ctype.h>
- int isspace(int c);
- Description
-2 The isspace function tests for any character that is a standard white-space character or
- is one of a locale-specific set of characters for which isalnum is false. The standard
-
-[page 201] (Contents)
-
- white-space characters are the following: space (' '), form feed ('\f'), new-line
- ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
- "C" locale, isspace returns true only for the standard white-space characters.
- 7.4.1.11 The isupper function
- Synopsis
-1 #include <ctype.h>
- int isupper(int c);
- Description
-2 The isupper function tests for any character that is an uppercase letter or is one of a
- locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
- isspace is true. In the "C" locale, isupper returns true only for the uppercase
- letters (as defined in 5.2.1).
- 7.4.1.12 The isxdigit function
- Synopsis
-1 #include <ctype.h>
- int isxdigit(int c);
- Description
-2 The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).
- 7.4.2 Character case mapping functions
- 7.4.2.1 The tolower function
- Synopsis
-1 #include <ctype.h>
- int tolower(int c);
- Description
-2 The tolower function converts an uppercase letter to a corresponding lowercase letter.
- Returns
-3 If the argument is a character for which isupper is true and there are one or more
- corresponding characters, as specified by the current locale, for which islower is true,
- the tolower function returns one of the corresponding characters (always the same one
- for any given locale); otherwise, the argument is returned unchanged.
-
-
-
-
-[page 202] (Contents)
-
- 7.4.2.2 The toupper function
- Synopsis
-1 #include <ctype.h>
- int toupper(int c);
- Description
-2 The toupper function converts a lowercase letter to a corresponding uppercase letter.
- Returns
-3 If the argument is a character for which islower is true and there are one or more
- corresponding characters, as specified by the current locale, for which isupper is true,
- the toupper function returns one of the corresponding characters (always the same one
- for any given locale); otherwise, the argument is returned unchanged.
-
-
-
-
-[page 203] (Contents)
-
- 7.5 Errors <errno.h>
-1 The header <errno.h> defines several macros, all relating to the reporting of error
- conditions.
-2 The macros are
- EDOM
- EILSEQ
- ERANGE
- which expand to integer constant expressions with type int, distinct positive values, and
- which are suitable for use in #if preprocessing directives; and
- errno
- which expands to a modifiable lvalue201) that has type int and thread local storage
- duration, the value of which is set to a positive error number by several library functions.
- If a macro definition is suppressed in order to access an actual object, or a program
- defines an identifier with the name errno, the behavior is undefined.
-3 The value of errno in the initial thread is zero at program startup (the initial value of
- errno in other threads is an indeterminate value), but is never set to zero by any library
- function.202) The value of errno may be set to nonzero by a library function call
- whether or not there is an error, provided the use of errno is not documented in the
- description of the function in this International Standard.
-4 Additional macro definitions, beginning with E and a digit or E and an uppercase
- letter,203) may also be specified by the implementation.
-
-
-
-
- 201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
- resulting from a function call (for example, *errno()).
- 202) Thus, a program that uses errno for error checking should set it to zero before a library function call,
- then inspect it before a subsequent library function call. Of course, a library function can save the
- value of errno on entry and then set it to zero, as long as the original value is restored if errno's
- value is still zero just before the return.
- 203) See ''future library directions'' (7.30.3).
-
-[page 204] (Contents)
-
- 7.6 Floating-point environment <fenv.h>
-1 The header <fenv.h> defines several macros, and declares types and functions that
- provide access to the floating-point environment. The floating-point environment refers
- collectively to any floating-point status flags and control modes supported by the
- implementation.204) A floating-point status flag is a system variable whose value is set
- (but never cleared) when a floating-point exception is raised, which occurs as a side effect
- of exceptional floating-point arithmetic to provide auxiliary information.205) A floating-
- point control mode is a system variable whose value may be set by the user to affect the
- subsequent behavior of floating-point arithmetic.
-2 The floating-point environment has thread storage duration. The initial state for a
- thread's floating-point environment is the current state of the floating-point environment
- of the thread that creates it at the time of creation.
-3 Certain programming conventions support the intended model of use for the floating-
- point environment:206)
- -- a function call does not alter its caller's floating-point control modes, clear its caller's
- floating-point status flags, nor depend on the state of its caller's floating-point status
- flags unless the function is so documented;
- -- a function call is assumed to require default floating-point control modes, unless its
- documentation promises otherwise;
- -- a function call is assumed to have the potential for raising floating-point exceptions,
- unless its documentation promises otherwise.
-4 The type
- fenv_t
- represents the entire floating-point environment.
-5 The type
- fexcept_t
- represents the floating-point status flags collectively, including any status the
- implementation associates with the flags.
-
-
- 204) This header is designed to support the floating-point exception status flags and directed-rounding
- control modes required by IEC 60559, and other similar floating-point state information. It is also
- designed to facilitate code portability among all systems.
- 205) A floating-point status flag is not an object and can be set more than once within an expression.
- 206) With these conventions, a programmer can safely assume default floating-point control modes (or be
- unaware of them). The responsibilities associated with accessing the floating-point environment fall
- on the programmer or program that does so explicitly.
-
-[page 205] (Contents)
-
-6 Each of the macros
- FE_DIVBYZERO
- FE_INEXACT
- FE_INVALID
- FE_OVERFLOW
- FE_UNDERFLOW
- is defined if and only if the implementation supports the floating-point exception by
- means of the functions in 7.6.2.207) Additional implementation-defined floating-point
- exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also
- be specified by the implementation. The defined macros expand to integer constant
- expressions with values such that bitwise ORs of all combinations of the macros result in
- distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in
- zero.208)
-7 The macro
- FE_ALL_EXCEPT
- is simply the bitwise OR of all floating-point exception macros defined by the
- implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.
-8 Each of the macros
- FE_DOWNWARD
- FE_TONEAREST
- FE_TOWARDZERO
- FE_UPWARD
- is defined if and only if the implementation supports getting and setting the represented
- rounding direction by means of the fegetround and fesetround functions.
- Additional implementation-defined rounding directions, with macro definitions beginning
- with FE_ and an uppercase letter, may also be specified by the implementation. The
- defined macros expand to integer constant expressions whose values are distinct
- nonnegative values.209)
-9 The macro
-
-
-
- 207) The implementation supports a floating-point exception if there are circumstances where a call to at
- least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not
- necessary for all the functions to succeed all the time.
- 208) The macros should be distinct powers of two.
- 209) Even though the rounding direction macros may expand to constants corresponding to the values of
- FLT_ROUNDS, they are not required to do so.
-
-[page 206] (Contents)
-
- FE_DFL_ENV
- represents the default floating-point environment -- the one installed at program startup
- -- and has type ''pointer to const-qualified fenv_t''. It can be used as an argument to
- <fenv.h> functions that manage the floating-point environment.
-10 Additional implementation-defined environments, with macro definitions beginning with
- FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may
- also be specified by the implementation.
- 7.6.1 The FENV_ACCESS pragma
- Synopsis
-1 #include <fenv.h>
- #pragma STDC FENV_ACCESS on-off-switch
- Description
-2 The FENV_ACCESS pragma provides a means to inform the implementation when a
- program might access the floating-point environment to test floating-point status flags or
- run under non-default floating-point control modes.210) The pragma shall occur either
- outside external declarations or preceding all explicit declarations and statements inside a
- compound statement. When outside external declarations, the pragma takes effect from
- its occurrence until another FENV_ACCESS pragma is encountered, or until the end of
- the translation unit. When inside a compound statement, the pragma takes effect from its
- occurrence until another FENV_ACCESS pragma is encountered (including within a
- nested compound statement), or until the end of the compound statement; at the end of a
- compound statement the state for the pragma is restored to its condition just before the
- compound statement. If this pragma is used in any other context, the behavior is
- undefined. If part of a program tests floating-point status flags, sets floating-point control
- modes, or runs under non-default mode settings, but was translated with the state for the
- FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or
- ''off'') for the pragma is implementation-defined. (When execution passes from a part of
- the program translated with FENV_ACCESS ''off'' to a part translated with
- FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the
- floating-point control modes have their default settings.)
-
-
-
-
- 210) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
- tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
- folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default
- modes are in effect and the flags are not tested.
-
-[page 207] (Contents)
-
-3 EXAMPLE
- #include <fenv.h>
- void f(double x)
- {
- #pragma STDC FENV_ACCESS ON
- void g(double);
- void h(double);
- /* ... */
- g(x + 1);
- h(x + 1);
- /* ... */
- }
-4 If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
- x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
- contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.211)
-
- 7.6.2 Floating-point exceptions
-1 The following functions provide access to the floating-point status flags.212) The int
- input argument for the functions represents a subset of floating-point exceptions, and can
- be zero or the bitwise OR of one or more floating-point exception macros, for example
- FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
- functions is undefined.
- 7.6.2.1 The feclearexcept function
- Synopsis
-1 #include <fenv.h>
- int feclearexcept(int excepts);
- Description
-2 The feclearexcept function attempts to clear the supported floating-point exceptions
- represented by its argument.
- Returns
-3 The feclearexcept function returns zero if the excepts argument is zero or if all
- the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.
-
-
- 211) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
- hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is
- ''off'', just one evaluation of x + 1 would suffice.
- 212) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
- abstraction of flags that are either set or clear. An implementation may endow floating-point status
- flags with more information -- for example, the address of the code which first raised the floating-
- point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
- content of flags.
-
-[page 208] (Contents)
-
- 7.6.2.2 The fegetexceptflag function
- Synopsis
-1 #include <fenv.h>
- int fegetexceptflag(fexcept_t *flagp,
- int excepts);
- Description
-2 The fegetexceptflag function attempts to store an implementation-defined
- representation of the states of the floating-point status flags indicated by the argument
- excepts in the object pointed to by the argument flagp.
- Returns
-3 The fegetexceptflag function returns zero if the representation was successfully
- stored. Otherwise, it returns a nonzero value.
- 7.6.2.3 The feraiseexcept function
- Synopsis
-1 #include <fenv.h>
- int feraiseexcept(int excepts);
- Description
-2 The feraiseexcept function attempts to raise the supported floating-point exceptions
- represented by its argument.213) The order in which these floating-point exceptions are
- raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
- additionally raises the ''inexact'' floating-point exception whenever it raises the
- ''overflow'' or ''underflow'' floating-point exception is implementation-defined.
- Returns
-3 The feraiseexcept function returns zero if the excepts argument is zero or if all
- the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.
-
-
-
-
- 213) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
- Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
- in F.8.6 is in the same spirit.
-
-[page 209] (Contents)
-
- 7.6.2.4 The fesetexceptflag function
- Synopsis
-1 #include <fenv.h>
- int fesetexceptflag(const fexcept_t *flagp,
- int excepts);
- Description
-2 The fesetexceptflag function attempts to set the floating-point status flags
- indicated by the argument excepts to the states stored in the object pointed to by
- flagp. The value of *flagp shall have been set by a previous call to
- fegetexceptflag whose second argument represented at least those floating-point
- exceptions represented by the argument excepts. This function does not raise floating-
- point exceptions, but only sets the state of the flags.
- Returns
-3 The fesetexceptflag function returns zero if the excepts argument is zero or if
- all the specified flags were successfully set to the appropriate state. Otherwise, it returns
- a nonzero value.
- 7.6.2.5 The fetestexcept function
- Synopsis
-1 #include <fenv.h>
- int fetestexcept(int excepts);
- Description
-2 The fetestexcept function determines which of a specified subset of the floating-
- point exception flags are currently set. The excepts argument specifies the floating-
- point status flags to be queried.214)
- Returns
-3 The fetestexcept function returns the value of the bitwise OR of the floating-point
- exception macros corresponding to the currently set floating-point exceptions included in
- excepts.
-4 EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set:
-
-
-
-
- 214) This mechanism allows testing several floating-point exceptions with just one function call.
-
-[page 210] (Contents)
-
- #include <fenv.h>
- /* ... */
- {
- #pragma STDC FENV_ACCESS ON
- int set_excepts;
- feclearexcept(FE_INVALID | FE_OVERFLOW);
- // maybe raise exceptions
- set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
- if (set_excepts & FE_INVALID) f();
- if (set_excepts & FE_OVERFLOW) g();
- /* ... */
- }
-
- 7.6.3 Rounding
-1 The fegetround and fesetround functions provide control of rounding direction
- modes.
- 7.6.3.1 The fegetround function
- Synopsis
-1 #include <fenv.h>
- int fegetround(void);
- Description
-2 The fegetround function gets the current rounding direction.
- Returns
-3 The fegetround function returns the value of the rounding direction macro
- representing the current rounding direction or a negative value if there is no such
- rounding direction macro or the current rounding direction is not determinable.
- 7.6.3.2 The fesetround function
- Synopsis
-1 #include <fenv.h>
- int fesetround(int round);
- Description
-2 The fesetround function establishes the rounding direction represented by its
- argument round. If the argument is not equal to the value of a rounding direction macro,
- the rounding direction is not changed.
- Returns
-3 The fesetround function returns zero if and only if the requested rounding direction
- was established.
-
-
-[page 211] (Contents)
-
-4 EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the
- rounding direction fails.
- #include <fenv.h>
- #include <assert.h>
- void f(int round_dir)
+
+ the int value returned by the function may be truncated when stored in the char, and then converted back
+ to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of
+ values as unsigned char (and char is narrower than int), the result of the conversion cannot be
+ negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
+ variable c should be declared as int.
+
++ EXAMPLE 2 In the fragment: +
+ char c; + int i; + long l; + l = (c = i); ++ the value of i is converted to the type of the assignment expression c = i, that is, char type. The value + of the expression enclosed in parentheses is then converted to the type of the outer assignment expression, + that is, long int type. + +
+ EXAMPLE 3 Consider the fragment: +
+ const char **cpp; + char *p; + const char c = 'A'; + cpp = &p; // constraint violation + *cpp = &c; // valid + *p = 0; // valid ++ The first assignment is unsafe because it would allow the following valid code to attempt to change the + value of the const object c. + + +
112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion + (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type + qualifiers that were applied to the type category of the expression (for example, it removes const but + not volatile from the type int volatile * const). + + +
+ For the operators += and -= only, either the left operand shall be an atomic, qualified, or + unqualified pointer to a complete object type, and the right shall have integer type; or the + left operand shall have atomic, qualified, or unqualified arithmetic type, and the right + shall have arithmetic type. +
+ For the other operators, the left operand shall have atomic, qualified, or unqualified + arithmetic type, and (considering the type the left operand would have after lvalue + conversion) each operand shall have arithmetic type consistent with those allowed by the + corresponding binary operator. +
+ A compound assignment of the form E1 op = E2 is equivalent to the simple assignment + expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with + respect to an indeterminately-sequenced function call, the operation of a compound + + assignment is a single evaluation. If E1 has an atomic type, compound assignment is a + read-modify-write operation with memory_order_seq_cst memory order + semantics.113) + +
113) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
+ where T is the type of E1:
+
+
+ T tmp = E1;
+ T result;
+ do {
+ result = tmp op (E2);
+ } while (!atomic_compare_exchange_strong(&E1, &tmp, result));
+
+ with result being the result of the operation.
+
+
+
+
+ expression: + assignment-expression + expression , assignment-expression ++
+ The left operand of a comma operator is evaluated as a void expression; there is a + sequence point between its evaluation and that of the right operand. Then the right + operand is evaluated; the result has its type and value.114) * +
+ EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot + appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists + of initializers). On the other hand, it can be used within a parenthesized expression or within the second + expression of a conditional operator in such contexts. In the function call +
+ f(a, (t=3, t+2), c) ++ the function has three arguments, the second of which has the value 5. + +
Forward references: initialization (6.7.9). + + + + + + +
114) A comma operator does not yield an lvalue. + + +
+
+ constant-expression: + conditional-expression ++
+ A constant expression can be evaluated during translation rather than runtime, and + accordingly may be used in any place that a constant may be. +
+ Constant expressions shall not contain assignment, increment, decrement, function-call, + or comma operators, except when they are contained within a subexpression that is not + evaluated.115) +
+ Each constant expression shall evaluate to a constant that is in the range of representable + values for its type. +
+ An expression that evaluates to a constant is required in several contexts. If a floating + expression is evaluated in the translation environment, the arithmetic precision and range + shall be at least as great as if the expression were being evaluated in the execution + environment.116) +
+ An integer constant expression117) shall have integer type and shall only have operands + that are integer constants, enumeration constants, character constants, sizeof + expressions whose results are integer constants, and floating constants that are the + immediate operands of casts. Cast operators in an integer constant expression shall only + convert arithmetic types to integer types, except as part of an operand to the sizeof + operator. +
+ More latitude is permitted for constant expressions in initializers. Such a constant + expression shall be, or evaluate to, one of the following: +
+ An arithmetic constant expression shall have arithmetic type and shall only have + operands that are integer constants, floating constants, enumeration constants, character + constants, and sizeof expressions. Cast operators in an arithmetic constant expression + shall only convert arithmetic types to arithmetic types, except as part of an operand to a + sizeof operator whose result is an integer constant. +
+ An address constant is a null pointer, a pointer to an lvalue designating an object of static + storage duration, or a pointer to a function designator; it shall be created explicitly using + the unary & operator or an integer constant cast to pointer type, or implicitly by the use of + an expression of array or function type. The array-subscript [] and member-access . + and -> operators, the address & and indirection * unary operators, and pointer casts may + be used in the creation of an address constant, but the value of an object shall not be + accessed by use of these operators. +
+ An implementation may accept other forms of constant expressions. +
+ The semantic rules for the evaluation of a constant expression are the same as for + nonconstant expressions.118) +
Forward references: array declarators (6.7.6.2), initialization (6.7.9). + + + + + + +
115) The operand of a sizeof operator is usually not evaluated (6.5.3.4). + +
116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in + the translation environment. + +
117) An integer constant expression is required in a number of contexts such as the size of a bit-field + member of a structure, the value of an enumeration constant, and the size of a non-variable length + array. Further constraints that apply to the integer constant expressions used in conditional-inclusion + preprocessing directives are discussed in 6.10.1. + +
118) Thus, in the following initialization,
+
+
+ static int i = 2 || 1 / 0;
+
+ the expression is a valid integer constant expression with value one.
+
+
+
+
+ declaration: + declaration-specifiers init-declarator-listopt ; + static_assert-declaration + declaration-specifiers: + storage-class-specifier declaration-specifiersopt + type-specifier declaration-specifiersopt + type-qualifier declaration-specifiersopt + function-specifier declaration-specifiersopt + alignment-specifier declaration-specifiersopt + init-declarator-list: + init-declarator + init-declarator-list , init-declarator + init-declarator: + declarator + declarator = initializer ++
+ A declaration other than a static_assert declaration shall declare at least a declarator + (other than the parameters of a function or the members of a structure or union), a tag, or + the members of an enumeration. +
+ If an identifier has no linkage, there shall be no more than one declaration of the identifier + (in a declarator or type specifier) with the same scope and in the same name space, except + that a typedef name can be redefined to denote the same type as it currently does and tags + may be redeclared as specified in 6.7.2.3. +
+ All declarations in the same scope that refer to the same object or function shall specify + compatible types. +
+ A declaration specifies the interpretation and attributes of a set of identifiers. A definition + of an identifier is a declaration for that identifier that: +
+ The declaration specifiers consist of a sequence of specifiers that indicate the linkage, + storage duration, and part of the type of the entities that the declarators denote. The init- + declarator-list is a comma-separated sequence of declarators, each of which may have + additional type information, or an initializer, or both. The declarators contain the + identifiers (if any) being declared. +
+ If an identifier for an object is declared with no linkage, the type for the object shall be + complete by the end of its declarator, or by the end of its init-declarator if it has an + initializer; in the case of function parameters (including in prototypes), it is the adjusted + type (see 6.7.6.3) that is required to be complete. +
Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization + (6.7.9), type names (6.7.7), type qualifiers (6.7.3). + +
119) Function definitions have a different syntax, described in 6.9.1. + + +
+
+ storage-class-specifier: + typedef + extern + static + _Thread_local + auto + register ++
+ At most, one storage-class specifier may be given in the declaration specifiers in a + declaration, except that _Thread_local may appear with static or extern.120) +
+ In the declaration of an object with block scope, if the declaration specifiers include + _Thread_local, they shall also include either static or extern. If + _Thread_local appears in any declaration of an object, it shall be present in every + declaration of that object. +
+ The typedef specifier is called a ''storage-class specifier'' for syntactic convenience + only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations + were discussed in 6.2.2 and 6.2.4. + + + + +
+ A declaration of an identifier for an object with storage-class specifier register + suggests that access to the object be as fast as possible. The extent to which such + suggestions are effective is implementation-defined.121) +
+ The declaration of an identifier for a function that has block scope shall have no explicit + storage-class specifier other than extern. +
+ If an aggregate or union object is declared with a storage-class specifier other than + typedef, the properties resulting from the storage-class specifier, except with respect to + linkage, also apply to the members of the object, and so on recursively for any aggregate + or union member objects. +
Forward references: type definitions (6.7.8). + +
120) See ''future language directions'' (6.11.5). + +
121) The implementation may treat any register declaration simply as an auto declaration. However, + whether or not addressable storage is actually used, the address of any part of an object declared with + storage-class specifier register cannot be computed, either explicitly (by use of the unary & + operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in + 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier + register is sizeof. + + +
+
+ type-specifier: + void + char + short + int + long + float + double + signed + unsigned + _Bool + _Complex + atomic-type-specifier + struct-or-union-specifier + enum-specifier + typedef-name ++
+ At least one type specifier shall be given in the declaration specifiers in each declaration, + and in the specifier-qualifier list in each struct declaration and type name. Each list of + + + + type specifiers shall be one of the following multisets (delimited by commas, when there + is more than one multiset per item); the type specifiers may occur in any order, possibly + intermixed with the other declaration specifiers. +
+ The type specifier _Complex shall not be used if the implementation does not support + complex types (see 6.10.8.3). + +
+ Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1 + through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The + characteristics of the other types are discussed in 6.2.5. +
+ Each of the comma-separated multisets designates the same type, except that for bit- + fields, it is implementation-defined whether the specifier int designates the same type as + signed int or the same type as unsigned int. +
Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2), + structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8). + +
+
+ struct-or-union-specifier:
+ struct-or-union identifieropt { struct-declaration-list }
+ struct-or-union identifier
+ struct-or-union:
+ struct
+ union
+ struct-declaration-list:
+ struct-declaration
+ struct-declaration-list struct-declaration
+ struct-declaration:
+ specifier-qualifier-list struct-declarator-listopt ;
+ static_assert-declaration
+ specifier-qualifier-list:
+ type-specifier specifier-qualifier-listopt
+ type-qualifier specifier-qualifier-listopt
+ struct-declarator-list:
+ struct-declarator
+ struct-declarator-list , struct-declarator
+ struct-declarator:
+ declarator
+ declaratoropt : constant-expression
+
++ A struct-declaration that does not declare an anonymous structure or anonymous union + shall contain a struct-declarator-list. + +
+ A structure or union shall not contain a member with incomplete or function type (hence, + a structure shall not contain an instance of itself, but may contain a pointer to an instance + of itself), except that the last member of a structure with more than one named member + may have incomplete array type; such a structure (and any union containing, possibly + recursively, a member that is such a structure) shall not be a member of a structure or an + element of an array. +
+ The expression that specifies the width of a bit-field shall be an integer constant + expression with a nonnegative value that does not exceed the width of an object of the + type that would be specified were the colon and expression omitted.122) If the value is + zero, the declaration shall have no declarator. +
+ A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed + int, unsigned int, or some other implementation-defined type. It is + implementation-defined whether atomic types are permitted. +
+ As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose + storage is allocated in an ordered sequence, and a union is a type consisting of a sequence + of members whose storage overlap. +
+ Structure and union specifiers have the same form. The keywords struct and union + indicate that the type being specified is, respectively, a structure type or a union type. +
+ The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type, + within a translation unit. The struct-declaration-list is a sequence of declarations for the + members of the structure or union. If the struct-declaration-list contains no named + members, no anonymous structures, and no anonymous unions, the behavior is undefined. + The type is incomplete until immediately after the } that terminates the list, and complete + thereafter. +
+ A member of a structure or union may have any complete object type other than a + variably modified type.123) In addition, a member may be declared to consist of a + specified number of bits (including a sign bit, if any). Such a member is called a + bit-field;124) its width is preceded by a colon. +
+ A bit-field is interpreted as having a signed or unsigned integer type consisting of the + specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of + + + type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool + bit-field has the semantics of a _Bool. +
+ An implementation may allocate any addressable storage unit large enough to hold a bit- + field. If enough space remains, a bit-field that immediately follows another bit-field in a + structure shall be packed into adjacent bits of the same unit. If insufficient space remains, + whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is + implementation-defined. The order of allocation of bit-fields within a unit (high-order to + low-order or low-order to high-order) is implementation-defined. The alignment of the + addressable storage unit is unspecified. +
+ A bit-field declaration with no declarator, but only a colon and a width, indicates an + unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0 + indicates that no further bit-field is to be packed into the unit in which the previous bit- + field, if any, was placed. +
+ An unnamed member of structure type with no tag is called an anonymous structure; an + unnamed member of union type with no tag is called an anonymous union. The members + of an anonymous structure or union are considered to be members of the containing + structure or union. This applies recursively if the containing structure or union is also + anonymous. +
+ Each non-bit-field member of a structure or union object is aligned in an implementation- + defined manner appropriate to its type. +
+ Within a structure object, the non-bit-field members and the units in which bit-fields + reside have addresses that increase in the order in which they are declared. A pointer to a + structure object, suitably converted, points to its initial member (or if that member is a + bit-field, then to the unit in which it resides), and vice versa. There may be unnamed + padding within a structure object, but not at its beginning. +
+ The size of a union is sufficient to contain the largest of its members. The value of at + most one of the members can be stored in a union object at any time. A pointer to a + union object, suitably converted, points to each of its members (or if a member is a bit- + field, then to the unit in which it resides), and vice versa. +
+ There may be unnamed padding at the end of a structure or union. +
+ As a special case, the last element of a structure with more than one named member may + have an incomplete array type; this is called a flexible array member. In most situations, + + + + the flexible array member is ignored. In particular, the size of the structure is as if the + flexible array member were omitted except that it may have more trailing padding than + the omission would imply. However, when a . (or ->) operator has a left operand that is + (a pointer to) a structure with a flexible array member and the right operand names that + member, it behaves as if that member were replaced with the longest array (with the same + element type) that would not make the structure larger than the object being accessed; the + offset of the array shall remain that of the flexible array member, even if this would differ + from that of the replacement array. If this array would have no elements, it behaves as if + it had one element but the behavior is undefined if any attempt is made to access that + element or to generate a pointer one past it. +
+ EXAMPLE 1 The following illustrates anonymous structures and unions: +
+ struct v {
+ union { // anonymous union
+ struct { int i, j; }; // anonymous structure
+ struct { long k, l; } w;
+ };
+ int m;
+ } v1;
+ v1.i = 2; // valid
+ v1.k = 3; // invalid: inner structure is not anonymous
+ v1.w.k = 5; // valid
+
+
++ EXAMPLE 2 After the declaration: +
+ struct s { int n; double d[]; };
+
+ the structure struct s has a flexible array member d. A typical way to use this is:
++ int m = /* some value */; + struct s *p = malloc(sizeof (struct s) + sizeof (double [m])); ++ and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if + p had been declared as: +
+ struct { int n; double d[m]; } *p;
+
+ (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
+ not be the same).
++ Following the above declaration: +
+ struct s t1 = { 0 }; // valid
+ struct s t2 = { 1, { 4.2 }}; // invalid
+ t1.n = 4; // valid
+ t1.d[0] = 4.2; // might be undefined behavior
+
+ The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
+ contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
++ sizeof (struct s) >= offsetof(struct s, d) + sizeof (double) ++ in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming + code. + +
+ After the further declaration: +
+ struct ss { int n; };
+
+ the expressions:
++ sizeof (struct s) >= sizeof (struct ss) + sizeof (struct s) >= offsetof(struct s, d) ++ are always equal to 1. +
+ If sizeof (double) is 8, then after the following code is executed: +
+ struct s *s1; + struct s *s2; + s1 = malloc(sizeof (struct s) + 64); + s2 = malloc(sizeof (struct s) + 46); ++ and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most + purposes, as if the identifiers had been declared as: +
+ struct { int n; double d[8]; } *s1;
+ struct { int n; double d[5]; } *s2;
+
++ Following the further successful assignments: +
+ s1 = malloc(sizeof (struct s) + 10); + s2 = malloc(sizeof (struct s) + 6); ++ they then behave as if the declarations were: +
+ struct { int n; double d[1]; } *s1, *s2;
+
+ and:
++ double *dp; + dp = &(s1->d[0]); // valid + *dp = 42; // valid + dp = &(s2->d[0]); // valid + *dp = 42; // undefined behavior ++
+ The assignment: +
+ *s1 = *s2; ++ only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes + of the structure, they might be copied or simply overwritten with indeterminate values. + +
Forward references: declarators (6.7.6), tags (6.7.2.3). + + +
122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and + value bits) of a _Bool may be just 1 bit. + +
123) A structure or union cannot contain a member with a variably modified type because member names + are not ordinary identifiers as defined in 6.2.3. + +
124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to + or arrays of bit-field objects. + +
125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int, + then it is implementation-defined whether the bit-field is signed or unsigned. + +
126) An unnamed bit-field structure member is useful for padding to conform to externally imposed + layouts. + + +
+
+ enum-specifier:
+ enum identifieropt { enumerator-list }
+ enum identifieropt { enumerator-list , }
+ enum identifier
+ enumerator-list:
+ enumerator
+ enumerator-list , enumerator
+ enumerator:
+ enumeration-constant
+ enumeration-constant = constant-expression
+
++ The expression that defines the value of an enumeration constant shall be an integer + constant expression that has a value representable as an int. +
+ The identifiers in an enumerator list are declared as constants that have type int and + may appear wherever such are permitted.127) An enumerator with = defines its + enumeration constant as the value of the constant expression. If the first enumerator has + no =, the value of its enumeration constant is 0. Each subsequent enumerator with no = + defines its enumeration constant as the value of the constant expression obtained by + adding 1 to the value of the previous enumeration constant. (The use of enumerators with + = may produce enumeration constants with values that duplicate other values in the same + enumeration.) The enumerators of an enumeration are also known as its members. +
+ Each enumerated type shall be compatible with char, a signed integer type, or an + unsigned integer type. The choice of type is implementation-defined,128) but shall be + capable of representing the values of all the members of the enumeration. The + enumerated type is incomplete until immediately after the } that terminates the list of + enumerator declarations, and complete thereafter. + + + + + +
+ EXAMPLE The following fragment: +
+ enum hue { chartreuse, burgundy, claret=20, winedark };
+ enum hue col, *cp;
+ col = claret;
+ cp = &col;
+ if (*cp != burgundy)
+ /* ... */
+
+ makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
+ pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.
+
+Forward references: tags (6.7.2.3). + +
127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from + each other and from other identifiers declared in ordinary declarators. + +
128) An implementation may delay the choice of which integer type until all enumeration constants have + been seen. + + +
+ A specific type shall have its content defined at most once. +
+ Where two declarations that use the same tag declare the same type, they shall both use + the same choice of struct, union, or enum. +
+ A type specifier of the form +
+ enum identifier ++ without an enumerator list shall only appear after the type it specifies is complete. +
+ All declarations of structure, union, or enumerated types that have the same scope and + use the same tag declare the same type. Irrespective of whether there is a tag or what + other declarations of the type are in the same translation unit, the type is incomplete129) + until immediately after the closing brace of the list defining the content, and complete + thereafter. +
+ Two declarations of structure, union, or enumerated types which are in different scopes or + use different tags declare distinct types. Each declaration of a structure, union, or + enumerated type which does not include a tag declares a distinct type. +
+ A type specifier of the form + + + + + +
+ struct-or-union identifieropt { struct-declaration-list }
+
+ or
+
+ enum identifieropt { enumerator-list }
+
+ or
+
+ enum identifieropt { enumerator-list , }
+
+ declares a structure, union, or enumerated type. The list defines the structure content,
+ union content, or enumeration content. If an identifier is provided,130) the type specifier
+ also declares the identifier to be the tag of that type.
++ A declaration of the form +
+ struct-or-union identifier ; ++ specifies a structure or union type and declares the identifier as a tag of that type.131) +
+ If a type specifier of the form +
+ struct-or-union identifier ++ occurs other than as part of one of the above forms, and no other declaration of the + identifier as a tag is visible, then it declares an incomplete structure or union type, and + declares the identifier as the tag of that type.131) +
+ If a type specifier of the form +
+ struct-or-union identifier ++ or +
+ enum identifier ++ occurs other than as part of one of the above forms, and a declaration of the identifier as a + tag is visible, then it specifies the same type as that other declaration, and does not + redeclare the tag. +
+ EXAMPLE 1 This mechanism allows declaration of a self-referential structure. +
+ struct tnode {
+ int count;
+ struct tnode *left, *right;
+ };
+
+ specifies a structure that contains an integer and two pointers to objects of the same type. Once this
+ declaration has been given, the declaration
+
+
+
+
+
++ struct tnode s, *sp; ++ declares s to be an object of the given type and sp to be a pointer to an object of the given type. With + these declarations, the expression sp->left refers to the left struct tnode pointer of the object to + which sp points; the expression s.right->count designates the count member of the right struct + tnode pointed to from s. +
+ The following alternative formulation uses the typedef mechanism: +
+ typedef struct tnode TNODE;
+ struct tnode {
+ int count;
+ TNODE *left, *right;
+ };
+ TNODE s, *sp;
+
+
++ EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential + structures, the declarations +
+ struct s1 { struct s2 *s2p; /* ... */ }; // D1
+ struct s2 { struct s1 *s1p; /* ... */ }; // D2
+
+ specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
+ declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
+ D2. To eliminate this context sensitivity, the declaration
++ struct s2; ++ may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then + completes the specification of the new type. + +
Forward references: declarators (6.7.6), type definitions (6.7.8). + +
129) An incomplete type may only by used when the size of an object of that type is not needed. It is not + needed, for example, when a typedef name is declared to be a specifier for a structure or union, or + when a pointer to or a function returning a structure or union is being declared. (See incomplete types + in 6.2.5.) The specification has to be complete before such a function is called or defined. + +
130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration + of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations + can make use of that typedef name to declare objects having the specified structure, union, or + enumerated type. + +
131) A similar construction with enum does not exist. + + +
+
+ atomic-type-specifier: + _Atomic ( type-name ) ++
+ Atomic type specifiers shall not be used if the implementation does not support atomic + types (see 6.10.8.3). +
+ The type name in an atomic type specifier shall not refer to an array type, a function type, + an atomic type, or a qualified type. +
+ The properties associated with atomic types are meaningful only for expressions that are + lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is + interpreted as a type specifier (with a type name), not as a type qualifier. + + +
+
+ type-qualifier: + const + restrict + volatile + _Atomic ++
+ Types other than pointer types whose referenced type is an object type shall not be + restrict-qualified. +
+ The type modified by the _Atomic qualifier shall not be an array type or a function + type. +
+ The properties associated with qualified types are meaningful only for expressions that + are lvalues.132) +
+ If the same qualifier appears more than once in the same specifier-qualifier-list, either + directly or via one or more typedefs, the behavior is the same as if it appeared only + once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier- + list, the resulting type is the so-qualified atomic type. +
+ If an attempt is made to modify an object defined with a const-qualified type through use + of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is + made to refer to an object defined with a volatile-qualified type through use of an lvalue + with non-volatile-qualified type, the behavior is undefined.133) +
+ An object that has volatile-qualified type may be modified in ways unknown to the + implementation or have other unknown side effects. Therefore any expression referring + to such an object shall be evaluated strictly according to the rules of the abstract machine, + as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the + object shall agree with that prescribed by the abstract machine, except as modified by the + + + + + + unknown factors mentioned previously.134) What constitutes an access to an object that + has volatile-qualified type is implementation-defined. +
+ An object that is accessed through a restrict-qualified pointer has a special association + with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to + that object use, directly or indirectly, the value of that particular pointer.135) The intended + use of the restrict qualifier (like the register storage class) is to promote + optimization, and deleting all instances of the qualifier from all preprocessing translation + units composing a conforming program does not change its meaning (i.e., observable + behavior). +
+ If the specification of an array type includes any type qualifiers, the element type is so- + qualified, not the array type. If the specification of a function type includes any type + qualifiers, the behavior is undefined.136) +
+ For two qualified types to be compatible, both shall have the identically qualified version + of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers + does not affect the specified type. +
+ EXAMPLE 1 An object declared +
+ extern const volatile int real_time_clock; ++ may be modifiable by hardware, but cannot be assigned to, incremented, or decremented. + +
+ EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers + modify an aggregate type: +
+ const struct s { int mem; } cs = { 1 };
+ struct s ncs; // the object ncs is modifiable
+ typedef int A[2][3];
+ const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
+ int *pi;
+ const int *pci;
+ ncs = cs; // valid
+ cs = ncs; // violates modifiable lvalue constraint for =
+ pi = &ncs.mem; // valid
+ pi = &cs.mem; // violates type constraints for =
+ pci = &cs.mem; // valid
+ pi = a[0]; // invalid: a[0] has type ''const int *''
+
+
+
+
+
++ EXAMPLE 3 The declaration +
+ _Atomic volatile int *p; ++ specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type. + + +
132) The implementation may place a const object that is not volatile in a read-only region of + storage. Moreover, the implementation need not allocate storage for such an object if its address is + never used. + +
133) This applies to those objects that behave as if they were defined with qualified types, even if they are + never actually defined as objects in the program (such as an object at a memory-mapped input/output + address). + +
134) A volatile declaration may be used to describe an object corresponding to a memory-mapped + input/output port or an object accessed by an asynchronously interrupting function. Actions on + objects so declared shall not be ''optimized out'' by an implementation or reordered except as + permitted by the rules for evaluating expressions. + +
135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this + association between the allocated object and the pointer. + +
136) Both of these can occur through the use of typedefs. + + +
+ Let D be a declaration of an ordinary identifier that provides a means of designating an + object P as a restrict-qualified pointer to type T. +
+ If D appears inside a block and does not have storage class extern, let B denote the + block. If D appears in the list of parameter declarations of a function definition, let B + denote the associated block. Otherwise, let B denote the block of main (or the block of + whatever function is called at program startup in a freestanding environment). +
+ In what follows, a pointer expression E is said to be based on object P if (at some + sequence point in the execution of B prior to the evaluation of E) modifying P to point to + a copy of the array object into which it formerly pointed would change the value of E.137) + Note that ''based'' is defined only for expressions with pointer types. +
+ During each execution of B, let L be any lvalue that has &L based on P. If L is used to + access the value of the object X that it designates, and X is also modified (by any means), + then the following requirements apply: T shall not be const-qualified. Every other lvalue + used to access the value of X shall also have its address based on P. Every access that + modifies X shall be considered also to modify P, for the purposes of this subclause. If P + is assigned the value of a pointer expression E that is based on another restricted pointer + object P2, associated with block B2, then either the execution of B2 shall begin before + the execution of B, or the execution of B2 shall end prior to the assignment. If these + requirements are not met, then the behavior is undefined. +
+ Here an execution of B means that portion of the execution of the program that would + correspond to the lifetime of an object with scalar type and automatic storage duration + associated with B. +
+ A translator is free to ignore any or all aliasing implications of uses of restrict. +
+ EXAMPLE 1 The file scope declarations +
+ int * restrict a; + int * restrict b; + extern int c[]; ++ assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the + program, then it is never accessed using either of the other two. + + + +
+ EXAMPLE 2 The function parameter declarations in the following example +
+ void f(int n, int * restrict p, int * restrict q)
+ {
+ while (n-- > 0)
+ *p++ = *q++;
+ }
+
+ assert that, during each execution of the function, if an object is accessed through one of the pointer
+ parameters, then it is not also accessed through the other.
++ The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence + analysis of function f without examining any of the calls of f in the program. The cost is that the + programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the + second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through + both p and q. +
+ void g(void)
+ {
+ extern int d[100];
+ f(50, d + 50, d); // valid
+ f(50, d + 1, d); // undefined behavior
+ }
+
+
++ EXAMPLE 3 The function parameter declarations +
+ void h(int n, int * restrict p, int * restrict q, int * restrict r)
+ {
+ int i;
+ for (i = 0; i < n; i++)
+ p[i] = q[i] + r[i];
+ }
+
+ illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
+ are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
+ modified within function h.
+
++ EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a + function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments + between restricted pointers declared in nested blocks have defined behavior. + +
+ {
+ int * restrict p1;
+ int * restrict q1;
+ p1 = q1; // undefined behavior
+ {
+ int * restrict p2 = p1; // valid
+ int * restrict q2 = q1; // valid
+ p1 = q2; // undefined behavior
+ p2 = q2; // undefined behavior
+ }
+ }
+
++ The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more + precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For + example, this permits new_vector to return a vector. +
+ typedef struct { int n; float * restrict v; } vector;
+ vector new_vector(int n)
+ {
+ vector t;
+ t.n = n;
+ t.v = malloc(n * sizeof (float));
+ return t;
+ }
+
+
+
+137) In other words, E depends on the value of P itself rather than on the value of an object referenced + indirectly through P. For example, if identifier p has type (int **restrict), then the pointer + expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer + expressions *p and p[1] are not. + + +
+
+ function-specifier: + inline + _Noreturn ++
+ Function specifiers shall be used only in the declaration of an identifier for a function. +
+ An inline definition of a function with external linkage shall not contain a definition of a + modifiable object with static or thread storage duration, and shall not contain a reference + to an identifier with internal linkage. +
+ In a hosted environment, no function specifier(s) shall appear in a declaration of main. +
+ A function specifier may appear more than once; the behavior is the same as if it + appeared only once. +
+ A function declared with an inline function specifier is an inline function. Making a * + function an inline function suggests that calls to the function be as fast as possible.138) + The extent to which such suggestions are effective is implementation-defined.139) + + + + + +
+ Any function with internal linkage can be an inline function. For a function with external + linkage, the following restrictions apply: If a function is declared with an inline + function specifier, then it shall also be defined in the same translation unit. If all of the + file scope declarations for a function in a translation unit include the inline function + specifier without extern, then the definition in that translation unit is an inline + definition. An inline definition does not provide an external definition for the function, + and does not forbid an external definition in another translation unit. An inline definition + provides an alternative to an external definition, which a translator may use to implement + any call to the function in the same translation unit. It is unspecified whether a call to the + function uses the inline definition or the external definition.140) +
+ A function declared with a _Noreturn function specifier shall not return to its caller. +
+ The implementation should produce a diagnostic message for a function declared with a + _Noreturn function specifier that appears to be capable of returning to its caller. +
+ EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external + definition, or a definition available for use only within the translation unit. A file scope declaration with + extern creates an external definition. The following example shows an entire translation unit. +
+ inline double fahr(double t)
+ {
+ return (9.0 * t) / 5.0 + 32.0;
+ }
+ inline double cels(double t)
+ {
+ return (5.0 * (t - 32.0)) / 9.0;
+ }
+ extern double fahr(double); // creates an external definition
+ double convert(int is_fahr, double temp)
+ {
+ /* A translator may perform inline substitutions */
+ return is_fahr ? cels(temp) : fahr(temp);
+ }
+
++ Note that the definition of fahr is an external definition because fahr is also declared with extern, but + the definition of cels is an inline definition. Because cels has external linkage and is referenced, an + external definition has to appear in another translation unit (see 6.9); the inline definition and the external + definition are distinct and either may be used for the call. + +
+ EXAMPLE 2 + + + + + +
+ _Noreturn void f () {
+ abort(); // ok
+ }
+ _Noreturn void g (int i) { // causes undefined behavior if i <= 0
+ if (i > 0) abort();
+ }
+
+
+Forward references: function definitions (6.9.1). + +
138) By using, for example, an alternative to the usual function call mechanism, such as ''inline + substitution''. Inline substitution is not textual substitution, nor does it create a new function. + Therefore, for example, the expansion of a macro used within the body of the function uses the + definition it had at the point the function body appears, and not where the function is called; and + identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a + single address, regardless of the number of inline definitions that occur in addition to the external + definition. + +
139) For example, an implementation might never perform inline substitution, or might only perform inline + substitutions to calls in the scope of an inline declaration. + +
140) Since an inline definition is distinct from the corresponding external definition and from any other + corresponding inline definitions in other translation units, all corresponding objects with static storage + duration are also distinct in each of the definitions. + + +
+
+ alignment-specifier: + _Alignas ( type-name ) + _Alignas ( constant-expression ) ++
+ An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or + a function, or a parameter, or an object declared with the register storage-class + specifier. +
+ The constant expression shall be an integer constant expression. It shall evaluate to a + valid fundamental alignment, or to a valid extended alignment supported by the + implementation in the context in which it appears, or to zero. +
+ The combined effect of all alignment attributes in a declaration shall not specify an + alignment that is less strict than the alignment that would otherwise be required for the + type of the object or member being declared. +
+ The first form is equivalent to _Alignas(alignof(type-name)). +
+ The alignment requirement of the declared object or member is taken to be the specified + alignment. An alignment specification of zero has no effect.141) When multiple + alignment specifiers occur in a declaration, the effective alignment requirement is the + strictest specified alignment. +
+ If the definition of an object has an alignment specifier, any other declaration of that + object shall either specify equivalent alignment or have no alignment specifier. If the + definition of an object does not have an alignment specifier, any other declaration of that + object shall also have no alignment specifier. If declarations of an object in different + translation units have different alignment specifiers, the behavior is undefined. + + + + + +
141) An alignment specification of zero also does not affect other alignment specifications in the same + declaration. + + +
+
+ declarator: + pointeropt direct-declarator + direct-declarator: + identifier + ( declarator ) + direct-declarator [ type-qualifier-listopt assignment-expressionopt ] + direct-declarator [ static type-qualifier-listopt assignment-expression ] + direct-declarator [ type-qualifier-list static assignment-expression ] + direct-declarator [ type-qualifier-listopt * ] + direct-declarator ( parameter-type-list ) + direct-declarator ( identifier-listopt ) + pointer: + * type-qualifier-listopt + * type-qualifier-listopt pointer + type-qualifier-list: + type-qualifier + type-qualifier-list type-qualifier + parameter-type-list: + parameter-list + parameter-list , ... + parameter-list: + parameter-declaration + parameter-list , parameter-declaration + parameter-declaration: + declaration-specifiers declarator + declaration-specifiers abstract-declaratoropt + identifier-list: + identifier + identifier-list , identifier ++
+ Each declarator declares one identifier, and asserts that when an operand of the same + form as the declarator appears in an expression, it designates a function or object with the + scope, storage duration, and type indicated by the declaration specifiers. +
+ A full declarator is a declarator that is not part of another declarator. The end of a full + declarator is a sequence point. If, in the nested sequence of declarators in a full + + declarator, there is a declarator specifying a variable length array type, the type specified + by the full declarator is said to be variably modified. Furthermore, any type derived by + declarator type derivation from a variably modified type is itself variably modified. +
+ In the following subclauses, consider a declaration +
+ T D1 ++ where T contains the declaration specifiers that specify a type T (such as int) and D1 is + a declarator that contains an identifier ident. The type specified for the identifier ident in + the various forms of declarator is described inductively using this notation. +
+ If, in the declaration ''T D1'', D1 has the form +
+ identifier ++ then the type specified for ident is T . +
+ If, in the declaration ''T D1'', D1 has the form +
+ ( D ) ++ then ident has the type specified by the declaration ''T D''. Thus, a declarator in + parentheses is identical to the unparenthesized declarator, but the binding of complicated + declarators may be altered by parentheses. +
+ As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and + function declarators that modify an arithmetic, structure, union, or void type, either + directly or via one or more typedefs. +
Forward references: array declarators (6.7.6.2), type definitions (6.7.8). + +
+ If, in the declaration ''T D1'', D1 has the form +
+ * type-qualifier-listopt D ++ and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list + T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list + pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer. +
+ For two pointer types to be compatible, both shall be identically qualified and both shall + be pointers to compatible types. +
+ EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer + to a constant value'' and a ''constant pointer to a variable value''. + +
+ const int *ptr_to_constant; + int *const constant_ptr; ++ The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer, + but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the + int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the + same location. +
+ The declaration of the constant pointer constant_ptr may be clarified by including a definition for the + type ''pointer to int''. +
+ typedef int *int_ptr; + const int_ptr constant_ptr; ++ declares constant_ptr as an object that has type ''const-qualified pointer to int''. + + +
+ In addition to optional type qualifiers and the keyword static, the [ and ] may delimit + an expression or *. If they delimit an expression (which specifies the size of an array), the + expression shall have an integer type. If the expression is a constant expression, it shall + have a value greater than zero. The element type shall not be an incomplete or function + type. The optional type qualifiers and the keyword static shall appear only in a + declaration of a function parameter with an array type, and then only in the outermost + array type derivation. +
+ If an identifier is declared as having a variably modified type, it shall be an ordinary + identifier (as defined in 6.2.3), have no linkage, and have either block scope or function + prototype scope. If an identifier is declared to be an object with static or thread storage + duration, it shall not have a variable length array type. +
+ If, in the declaration ''T D1'', D1 has one of the forms: +
+ D[ type-qualifier-listopt assignment-expressionopt ] + D[ static type-qualifier-listopt assignment-expression ] + D[ type-qualifier-list static assignment-expression ] + D[ type-qualifier-listopt * ] ++ and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list + T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142) + (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.) +
+ If the size is not present, the array type is an incomplete type. If the size is * instead of + being an expression, the array type is a variable length array type of unspecified size, + which can only be used in declarations or type names with function prototype scope;143) + + + such arrays are nonetheless complete types. If the size is an integer constant expression + and the element type has a known constant size, the array type is not a variable length + array type; otherwise, the array type is a variable length array type. (Variable length + arrays are a conditional feature that implementations need not support; see 6.10.8.3.) +
+ If the size is an expression that is not an integer constant expression: if it occurs in a + declaration at function prototype scope, it is treated as if it were replaced by *; otherwise, + each time it is evaluated it shall have a value greater than zero. The size of each instance + of a variable length array type does not change during its lifetime. Where a size + expression is part of the operand of a sizeof operator and changing the value of the + size expression would not affect the result of the operator, it is unspecified whether or not + the size expression is evaluated. +
+ For two array types to be compatible, both shall have compatible element types, and if + both size specifiers are present, and are integer constant expressions, then both size + specifiers shall have the same constant value. If the two array types are used in a context + which requires them to be compatible, it is undefined behavior if the two size specifiers + evaluate to unequal values. +
+ EXAMPLE 1 +
+ float fa[11], *afp[17]; ++ declares an array of float numbers and an array of pointers to float numbers. + +
+ EXAMPLE 2 Note the distinction between the declarations +
+ extern int *x; + extern int y[]; ++ The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size + (an incomplete type), the storage for which is defined elsewhere. + +
+ EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types. +
+ extern int n;
+ extern int m;
+ void fcompat(void)
+ {
+ int a[n][6][m];
+ int (*p)[4][n+1];
+ int c[n][n][6][m];
+ int (*r)[n][n][n+1];
+ p = a; // invalid: not compatible because 4 != 6
+ r = c; // compatible, but defined behavior only if
+ // n == 6 and m == n+1
+ }
+
+
+
+
+
+
++ EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or + function prototype scope. Array objects declared with the _Thread_local, static, or extern + storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with + the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all + identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of + structures or unions. +
+ extern int n;
+ int A[n]; // invalid: file scope VLA
+ extern int (*p2)[n]; // invalid: file scope VM
+ int B[100]; // valid: file scope but not VM
+ void fvla(int m, int C[m][m]); // valid: VLA with prototype scope
+ void fvla(int m, int C[m][m]) // valid: adjusted to auto pointer to VLA
+ {
+ typedef int VLA[m][m]; // valid: block scope typedef VLA
+ struct tag {
+ int (*y)[n]; // invalid: y not ordinary identifier
+ int z[n]; // invalid: z not ordinary identifier
+ };
+ int D[m]; // valid: auto VLA
+ static int E[m]; // invalid: static block scope VLA
+ extern int F[m]; // invalid: F has linkage and is VLA
+ int (*s)[m]; // valid: auto pointer to VLA
+ extern int (*r)[m]; // invalid: r has linkage and points to VLA
+ static int (*q)[m] = &B; // valid: q is a static block pointer to VLA
+ }
+
+
+Forward references: function declarators (6.7.6.3), function definitions (6.9.1), + initialization (6.7.9). + +
142) When several ''array of'' specifications are adjacent, a multidimensional array is declared. + +
143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3). + + +
+ A function declarator shall not specify a return type that is a function type or an array + type. +
+ The only storage-class specifier that shall occur in a parameter declaration is register. +
+ An identifier list in a function declarator that is not part of a definition of that function + shall be empty. +
+ After adjustment, the parameters in a parameter type list in a function declarator that is + part of a definition of that function shall not have incomplete type. +
+ If, in the declaration ''T D1'', D1 has the form + +
+ D( parameter-type-list ) ++ or +
+ D( identifier-listopt ) ++ and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list + T '', then the type specified for ident is ''derived-declarator-type-list function returning + T ''. +
+ A parameter type list specifies the types of, and may declare identifiers for, the + parameters of the function. +
+ A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to + type'', where the type qualifiers (if any) are those specified within the [ and ] of the + array type derivation. If the keyword static also appears within the [ and ] of the + array type derivation, then for each call to the function, the value of the corresponding + actual argument shall provide access to the first element of an array with at least as many + elements as specified by the size expression. +
+ A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to + function returning type'', as in 6.3.2.1. +
+ If the list terminates with an ellipsis (, ...), no information about the number or types + of the parameters after the comma is supplied.144) +
+ The special case of an unnamed parameter of type void as the only item in the list + specifies that the function has no parameters. +
+ If, in a parameter declaration, an identifier can be treated either as a typedef name or as a + parameter name, it shall be taken as a typedef name. +
+ If the function declarator is not part of a definition of that function, parameters may have + incomplete type and may use the [*] notation in their sequences of declarator specifiers + to specify variable length array types. +
+ The storage-class specifier in the declaration specifiers for a parameter declaration, if + present, is ignored unless the declared parameter is one of the members of the parameter + type list for a function definition. +
+ An identifier list declares only the identifiers of the parameters of the function. An empty + list in a function declarator that is part of a definition of that function specifies that the + function has no parameters. The empty list in a function declarator that is not part of a + definition of that function specifies that no information about the number or types of the + parameters is supplied.145) + + + + +
+ For two function types to be compatible, both shall specify compatible return types.146) + Moreover, the parameter type lists, if both are present, shall agree in the number of + parameters and in use of the ellipsis terminator; corresponding parameters shall have + compatible types. If one type has a parameter type list and the other type is specified by a + function declarator that is not part of a function definition and that contains an empty + identifier list, the parameter list shall not have an ellipsis terminator and the type of each + parameter shall be compatible with the type that results from the application of the + default argument promotions. If one type has a parameter type list and the other type is + specified by a function definition that contains a (possibly empty) identifier list, both shall + agree in the number of parameters, and the type of each prototype parameter shall be + compatible with the type that results from the application of the default argument + promotions to the type of the corresponding identifier. (In the determination of type + compatibility and of a composite type, each parameter declared with function or array + type is taken as having the adjusted type and each parameter declared with qualified type + is taken as having the unqualified version of its declared type.) +
+ EXAMPLE 1 The declaration +
+ int f(void), *fip(), (*pfi)(); ++ declares a function f with no parameters returning an int, a function fip with no parameter specification + returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an + int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the + declaration suggests, and the same construction in an expression requires, the calling of a function fip, + and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the + extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function + designator, which is then used to call the function; it returns an int. +
+ If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the + declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either + internal or external linkage (depending on what file scope declarations for these identifiers are visible), and + the identifier of the pointer pfi has block scope and no linkage. + +
+ EXAMPLE 2 The declaration +
+ int (*apfi[3])(int *x, int *y); ++ declares an array apfi of three pointers to functions returning int. Each of these functions has two + parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and + go out of scope at the end of the declaration of apfi. + +
+ EXAMPLE 3 The declaration +
+ int (*fpfi(int (*)(long), int))(int, ...); ++ declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two + parameters: a pointer to a function returning an int (with one parameter of type long int), and an int. + The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more + + + + additional arguments of any type. + +
+ EXAMPLE 4 The following prototype has a variably modified parameter. +
+ void addscalar(int n, int m,
+ double a[n][n*m+300], double x);
+ int main()
{
- #pragma STDC FENV_ACCESS ON
- int save_round;
- int setround_ok;
- save_round = fegetround();
- setround_ok = fesetround(round_dir);
- assert(setround_ok == 0);
- /* ... */
- fesetround(save_round);
- /* ... */
+ double b[4][308];
+ addscalar(4, 2, b, 2.17);
+ return 0;
}
-
- 7.6.4 Environment
-1 The functions in this section manage the floating-point environment -- status flags and
- control modes -- as one entity.
- 7.6.4.1 The fegetenv function
- Synopsis
-1 #include <fenv.h>
- int fegetenv(fenv_t *envp);
- Description
-2 The fegetenv function attempts to store the current floating-point environment in the
- object pointed to by envp.
- Returns
-3 The fegetenv function returns zero if the environment was successfully stored.
- Otherwise, it returns a nonzero value.
- 7.6.4.2 The feholdexcept function
- Synopsis
-1 #include <fenv.h>
- int feholdexcept(fenv_t *envp);
- Description
-2 The feholdexcept function saves the current floating-point environment in the object
- pointed to by envp, clears the floating-point status flags, and then installs a non-stop
- (continue on floating-point exceptions) mode, if available, for all floating-point
- exceptions.215)
-
-[page 212] (Contents)
-
- Returns
-3 The feholdexcept function returns zero if and only if non-stop floating-point
- exception handling was successfully installed.
- 7.6.4.3 The fesetenv function
- Synopsis
-1 #include <fenv.h>
- int fesetenv(const fenv_t *envp);
- Description
-2 The fesetenv function attempts to establish the floating-point environment represented
- by the object pointed to by envp. The argument envp shall point to an object set by a
- call to fegetenv or feholdexcept, or equal a floating-point environment macro.
- Note that fesetenv merely installs the state of the floating-point status flags
- represented through its argument, and does not raise these floating-point exceptions.
- Returns
-3 The fesetenv function returns zero if the environment was successfully established.
- Otherwise, it returns a nonzero value.
- 7.6.4.4 The feupdateenv function
- Synopsis
-1 #include <fenv.h>
- int feupdateenv(const fenv_t *envp);
- Description
-2 The feupdateenv function attempts to save the currently raised floating-point
- exceptions in its automatic storage, install the floating-point environment represented by
- the object pointed to by envp, and then raise the saved floating-point exceptions. The
- argument envp shall point to an object set by a call to feholdexcept or fegetenv,
- or equal a floating-point environment macro.
- Returns
-3 The feupdateenv function returns zero if all the actions were successfully carried out.
- Otherwise, it returns a nonzero value.
-
-
-
-
- 215) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
- handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
- such systems, the feholdexcept function can be used in conjunction with the feupdateenv
- function to write routines that hide spurious floating-point exceptions from their callers.
-
-[page 213] (Contents)
-
-4 EXAMPLE Hide spurious underflow floating-point exceptions:
- #include <fenv.h>
- double f(double x)
+ void addscalar(int n, int m,
+ double a[n][n*m+300], double x)
+ {
+ for (int i = 0; i < n; i++)
+ for (int j = 0, k = n*m+300; j < k; j++)
+ // a is a pointer to a VLA with n*m+300 elements
+ a[i][j] += x;
+ }
+
+
++ EXAMPLE 5 The following are all compatible function prototype declarators. +
+ double maximum(int n, int m, double a[n][m]); + double maximum(int n, int m, double a[*][*]); + double maximum(int n, int m, double a[ ][*]); + double maximum(int n, int m, double a[ ][m]); ++ as are: +
+ void f(double (* restrict a)[5]); + void f(double a[restrict][5]); + void f(double a[restrict 3][5]); + void f(double a[restrict static 3][5]); ++ (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a + non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.) + +
Forward references: function definitions (6.9.1), type names (6.7.7). + + +
144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that + correspond to the ellipsis. + +
145) See ''future language directions'' (6.11.6). + +
146) If both function types are ''old style'', parameter types are not compared. + + +
+
+ type-name: + specifier-qualifier-list abstract-declaratoropt + abstract-declarator: + pointer + pointeropt direct-abstract-declarator + direct-abstract-declarator: + ( abstract-declarator ) + direct-abstract-declaratoropt [ type-qualifier-listopt + assignment-expressionopt ] + direct-abstract-declaratoropt [ static type-qualifier-listopt + assignment-expression ] + direct-abstract-declaratoropt [ type-qualifier-list static + assignment-expression ] + direct-abstract-declaratoropt [ * ] + direct-abstract-declaratoropt ( parameter-type-listopt ) ++
+ In several contexts, it is necessary to specify a type. This is accomplished using a type + name, which is syntactically a declaration for a function or an object of that type that + omits the identifier.147) +
+ EXAMPLE The constructions +
+ (a) int + (b) int * + (c) int *[3] + (d) int (*)[3] + (e) int (*)[*] + (f) int *() + (g) int (*)(void) + (h) int (*const [])(unsigned int, ...) ++ name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an + array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function + with no parameter specification returning a pointer to int, (g) pointer to function with no parameters + returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one + parameter that has type unsigned int and an unspecified number of other parameters, returning an + int. + + + + + + +
147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no + parameter specification'', rather than redundant parentheses around the omitted identifier. + + +
+
+ typedef-name: + identifier ++
+ If a typedef name specifies a variably modified type then it shall have block scope. +
+ In a declaration whose storage-class specifier is typedef, each declarator defines an + identifier to be a typedef name that denotes the type specified for the identifier in the way + described in 6.7.6. Any array size expressions associated with variable length array + declarators are evaluated each time the declaration of the typedef name is reached in the + order of execution. A typedef declaration does not introduce a new type, only a + synonym for the type so specified. That is, in the following declarations: +
+ typedef T type_ident; + type_ident D; ++ type_ident is defined as a typedef name with the type specified by the declaration + specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator- + type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A + typedef name shares the same name space as other identifiers declared in ordinary + declarators. +
+ EXAMPLE 1 After +
+ typedef int MILES, KLICKSP();
+ typedef struct { double hi, lo; } range;
+
+ the constructions
++ MILES distance; + extern KLICKSP *metricp; + range x; + range z, *zp; ++ are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no + parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to + such a structure. The object distance has a type compatible with any other int object. + +
+ EXAMPLE 2 After the declarations +
+ typedef struct s1 { int x; } t1, *tp1;
+ typedef struct s2 { int x; } t2, *tp2;
+
+ type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
+ s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.
+
++ EXAMPLE 3 The following obscure constructions +
+ typedef signed int t;
+ typedef int plain;
+ struct tag {
+ unsigned t:4;
+ const t:5;
+ plain r:5;
+ };
+
+ declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
+ with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
+ qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
+ [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
+ (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
+ unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
+ type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
+ in an inner scope by
++ t f(t (t)); + long t; ++ then a function f is declared with type ''function returning signed int with one unnamed parameter + with type pointer to function returning signed int with one unnamed parameter with type signed + int'', and an identifier t with type long int. + +
+ EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the + following declarations of the signal function specify exactly the same type, the first without making use + of any typedef names. +
+ typedef void fv(int), (*pfv)(int); + void (*signal(int, void (*)(int)))(int); + fv *signal(int, fv *); + pfv signal(int, pfv); ++ +
+ EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the + time the typedef name is defined, not each time it is used: + +
+ void copyt(int n)
{
- #pragma STDC FENV_ACCESS ON
- double result;
- fenv_t save_env;
- if (feholdexcept(&save_env))
- return /* indication of an environmental problem */;
- // compute result
- if (/* test spurious underflow */)
- if (feclearexcept(FE_UNDERFLOW))
- return /* indication of an environmental problem */;
- if (feupdateenv(&save_env))
- return /* indication of an environmental problem */;
- return result;
+ typedef int B[n]; // B is n ints, n evaluated now
+ n += 1;
+ B a; // a is n ints, n without += 1
+ int b[n]; // a and b are different sizes
+ for (int i = 1; i < n; i++)
+ a[i-1] = b[i];
}
+
-
-
-
-[page 214] (Contents)
-
- 7.7 Characteristics of floating types <float.h>
-1 The header <float.h> defines several macros that expand to various limits and
- parameters of the standard floating-point types.
-2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
- in 5.2.4.2.2.
-
-
-
-
-[page 215] (Contents)
-
- 7.8 Format conversion of integer types <inttypes.h>
-1 The header <inttypes.h> includes the header <stdint.h> and extends it with
- additional facilities provided by hosted implementations.
-2 It declares functions for manipulating greatest-width integers and converting numeric
- character strings to greatest-width integers, and it declares the type
- imaxdiv_t
- which is a structure type that is the type of the value returned by the imaxdiv function.
- For each type declared in <stdint.h>, it defines corresponding macros for conversion
- specifiers for use with the formatted input/output functions.216)
- Forward references: integer types <stdint.h> (7.20), formatted input/output
- functions (7.21.6), formatted wide character input/output functions (7.28.2).
- 7.8.1 Macros for format specifiers
-1 Each of the following object-like macros expands to a character string literal containing a *
- conversion specifier, possibly modified by a length modifier, suitable for use within the
- format argument of a formatted input/output function when converting the corresponding
- integer type. These macro names have the general form of PRI (character string literals
- for the fprintf and fwprintf family) or SCN (character string literals for the
- fscanf and fwscanf family),217) followed by the conversion specifier, followed by a
- name corresponding to a similar type name in 7.20.1. In these names, N represents the
- width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
- format string to print the value of an integer of type int_fast32_t.
-2 The fprintf macros for signed integers are:
- PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR
- PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR
-3 The fprintf macros for unsigned integers are:
- PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR
- PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR
- PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR
- PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR
-4 The fscanf macros for signed integers are:
-
-
-
- 216) See ''future library directions'' (7.30.4).
- 217) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
- different format specifiers may be required for fprintf and fscanf, even when the type is the
- same.
-
-[page 216] (Contents)
-
- SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR
- SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR
-5 The fscanf macros for unsigned integers are:
- SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR
- SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR
- SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR
-6 For each type that the implementation provides in <stdint.h>, the corresponding
- fprintf macros shall be defined and the corresponding fscanf macros shall be
- defined unless the implementation does not have a suitable fscanf length modifier for
- the type.
-7 EXAMPLE
- #include <inttypes.h>
- #include <wchar.h>
- int main(void)
- {
- uintmax_t i = UINTMAX_MAX; // this type always exists
- wprintf(L"The largest integer value is %020"
- PRIxMAX "\n", i);
- return 0;
- }
-
- 7.8.2 Functions for greatest-width integer types
- 7.8.2.1 The imaxabs function
- Synopsis
-1 #include <inttypes.h>
- intmax_t imaxabs(intmax_t j);
- Description
-2 The imaxabs function computes the absolute value of an integer j. If the result cannot
- be represented, the behavior is undefined.218)
- Returns
-3 The imaxabs function returns the absolute value.
-
-
-
-
- 218) The absolute value of the most negative number cannot be represented in two's complement.
-
-[page 217] (Contents)
-
- 7.8.2.2 The imaxdiv function
- Synopsis
-1 #include <inttypes.h>
- imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
- Description
-2 The imaxdiv function computes numer / denom and numer % denom in a single
- operation.
- Returns
-3 The imaxdiv function returns a structure of type imaxdiv_t comprising both the
- quotient and the remainder. The structure shall contain (in either order) the members
- quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
- either part of the result cannot be represented, the behavior is undefined.
- 7.8.2.3 The strtoimax and strtoumax functions
- Synopsis
-1 #include <inttypes.h>
- intmax_t strtoimax(const char * restrict nptr,
- char ** restrict endptr, int base);
- uintmax_t strtoumax(const char * restrict nptr,
- char ** restrict endptr, int base);
- Description
-2 The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
- strtoul, and strtoull functions, except that the initial portion of the string is
- converted to intmax_t and uintmax_t representation, respectively.
- Returns
-3 The strtoimax and strtoumax functions return the converted value, if any. If no
- conversion could be performed, zero is returned. If the correct value is outside the range
- of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
- (according to the return type and sign of the value, if any), and the value of the macro
- ERANGE is stored in errno.
- Forward references: the strtol, strtoll, strtoul, and strtoull functions
- (7.22.1.4).
-
-
-
-
-[page 218] (Contents)
-
- 7.8.2.4 The wcstoimax and wcstoumax functions
- Synopsis
-1 #include <stddef.h> // for wchar_t
- #include <inttypes.h>
- intmax_t wcstoimax(const wchar_t * restrict nptr,
- wchar_t ** restrict endptr, int base);
- uintmax_t wcstoumax(const wchar_t * restrict nptr,
- wchar_t ** restrict endptr, int base);
- Description
-2 The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
- wcstoul, and wcstoull functions except that the initial portion of the wide string is
- converted to intmax_t and uintmax_t representation, respectively.
- Returns
-3 The wcstoimax function returns the converted value, if any. If no conversion could be
- performed, zero is returned. If the correct value is outside the range of representable
- values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
- return type and sign of the value, if any), and the value of the macro ERANGE is stored in
- errno.
- Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
- (7.28.4.1.2).
-
-
-
-
-[page 219] (Contents)
-
- 7.9 Alternative spellings <iso646.h>
-1 The header <iso646.h> defines the following eleven macros (on the left) that expand
- to the corresponding tokens (on the right):
- and &&
- and_eq &=
- bitand &
- bitor |
- compl ~
- not !
- not_eq !=
- or ||
- or_eq |=
- xor ^
- xor_eq ^=
-
-
-
-
-[page 220] (Contents)
-
- 7.10 Sizes of integer types <limits.h>
-1 The header <limits.h> defines several macros that expand to various limits and
- parameters of the standard integer types.
-2 The macros, their meanings, and the constraints (or restrictions) on their values are listed
- in 5.2.4.2.1.
-
-
-
-
-[page 221] (Contents)
-
- 7.11 Localization <locale.h>
-1 The header <locale.h> declares two functions, one type, and defines several macros.
-2 The type is
- struct lconv
- which contains members related to the formatting of numeric values. The structure shall
- contain at least the following members, in any order. The semantics of the members and
- their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
- the values specified in the comments.
- char *decimal_point; // "."
- char *thousands_sep; // ""
- char *grouping; // ""
- char *mon_decimal_point; // ""
- char *mon_thousands_sep; // ""
- char *mon_grouping; // ""
- char *positive_sign; // ""
- char *negative_sign; // ""
- char *currency_symbol; // ""
- char frac_digits; // CHAR_MAX
- char p_cs_precedes; // CHAR_MAX
- char n_cs_precedes; // CHAR_MAX
- char p_sep_by_space; // CHAR_MAX
- char n_sep_by_space; // CHAR_MAX
- char p_sign_posn; // CHAR_MAX
- char n_sign_posn; // CHAR_MAX
- char *int_curr_symbol; // ""
- char int_frac_digits; // CHAR_MAX
- char int_p_cs_precedes; // CHAR_MAX
- char int_n_cs_precedes; // CHAR_MAX
- char int_p_sep_by_space; // CHAR_MAX
- char int_n_sep_by_space; // CHAR_MAX
- char int_p_sign_posn; // CHAR_MAX
- char int_n_sign_posn; // CHAR_MAX
-
-
-
-
-[page 222] (Contents)
-
-3 The macros defined are NULL (described in 7.19); and
- LC_ALL
- LC_COLLATE
- LC_CTYPE
- LC_MONETARY
- LC_NUMERIC
- LC_TIME
- which expand to integer constant expressions with distinct values, suitable for use as the
- first argument to the setlocale function.219) Additional macro definitions, beginning
- with the characters LC_ and an uppercase letter,220) may also be specified by the
- implementation.
- 7.11.1 Locale control
- 7.11.1.1 The setlocale function
- Synopsis
-1 #include <locale.h>
- char *setlocale(int category, const char *locale);
- Description
-2 The setlocale function selects the appropriate portion of the program's locale as
- specified by the category and locale arguments. The setlocale function may be
- used to change or query the program's entire current locale or portions thereof. The value
- LC_ALL for category names the program's entire locale; the other values for
- category name only a portion of the program's locale. LC_COLLATE affects the
- behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
- the character handling functions221) and the multibyte and wide character functions.
- LC_MONETARY affects the monetary formatting information returned by the
- localeconv function. LC_NUMERIC affects the decimal-point character for the
- formatted input/output functions and the string conversion functions, as well as the
- nonmonetary formatting information returned by the localeconv function. LC_TIME
- affects the behavior of the strftime and wcsftime functions.
-3 A value of "C" for locale specifies the minimal environment for C translation; a value
- of "" for locale specifies the locale-specific native environment. Other
- implementation-defined strings may be passed as the second argument to setlocale.
-
- 219) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C.
- 220) See ''future library directions'' (7.30.5).
- 221) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
- isxdigit.
-
-[page 223] (Contents)
-
-4 At program startup, the equivalent of
- setlocale(LC_ALL, "C");
- is executed.
-5 A call to the setlocale function may introduce a data race with other calls to the
- setlocale function or with calls to functions that are affected by the current locale.
- The implementation shall behave as if no library function calls the setlocale function.
- Returns
-6 If a pointer to a string is given for locale and the selection can be honored, the
- setlocale function returns a pointer to the string associated with the specified
- category for the new locale. If the selection cannot be honored, the setlocale
- function returns a null pointer and the program's locale is not changed.
-7 A null pointer for locale causes the setlocale function to return a pointer to the
- string associated with the category for the program's current locale; the program's
- locale is not changed.222)
-8 The pointer to string returned by the setlocale function is such that a subsequent call
- with that string value and its associated category will restore that part of the program's
- locale. The string pointed to shall not be modified by the program, but may be
- overwritten by a subsequent call to the setlocale function.
- Forward references: formatted input/output functions (7.21.6), multibyte/wide
- character conversion functions (7.22.7), multibyte/wide string conversion functions
- (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the
- strftime function (7.26.3.5), the strxfrm function (7.23.4.5).
- 7.11.2 Numeric formatting convention inquiry
- 7.11.2.1 The localeconv function
- Synopsis
-1 #include <locale.h>
- struct lconv *localeconv(void);
- Description
-2 The localeconv function sets the components of an object with type struct lconv
- with values appropriate for the formatting of numeric quantities (monetary and otherwise)
- according to the rules of the current locale.
-
-
-
- 222) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
- locale when category has the value LC_ALL.
-
-[page 224] (Contents)
-
-3 The members of the structure with type char * are pointers to strings, any of which
- (except decimal_point) can point to "", to indicate that the value is not available in
- the current locale or is of zero length. Apart from grouping and mon_grouping, the
- strings shall start and end in the initial shift state. The members with type char are
- nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
- available in the current locale. The members include the following:
- char *decimal_point
- The decimal-point character used to format nonmonetary quantities.
- char *thousands_sep
- The character used to separate groups of digits before the decimal-point
- character in formatted nonmonetary quantities.
- char *grouping
- A string whose elements indicate the size of each group of digits in
- formatted nonmonetary quantities.
- char *mon_decimal_point
- The decimal-point used to format monetary quantities.
- char *mon_thousands_sep
- The separator for groups of digits before the decimal-point in formatted
- monetary quantities.
- char *mon_grouping
- A string whose elements indicate the size of each group of digits in
- formatted monetary quantities.
- char *positive_sign
- The string used to indicate a nonnegative-valued formatted monetary
- quantity.
- char *negative_sign
- The string used to indicate a negative-valued formatted monetary quantity.
- char *currency_symbol
- The local currency symbol applicable to the current locale.
- char frac_digits
- The number of fractional digits (those after the decimal-point) to be
- displayed in a locally formatted monetary quantity.
- char p_cs_precedes
- Set to 1 or 0 if the currency_symbol respectively precedes or
- succeeds the value for a nonnegative locally formatted monetary quantity.
-
-
-
-[page 225] (Contents)
-
-char n_cs_precedes
- Set to 1 or 0 if the currency_symbol respectively precedes or
- succeeds the value for a negative locally formatted monetary quantity.
-char p_sep_by_space
- Set to a value indicating the separation of the currency_symbol, the
- sign string, and the value for a nonnegative locally formatted monetary
- quantity.
-char n_sep_by_space
- Set to a value indicating the separation of the currency_symbol, the
- sign string, and the value for a negative locally formatted monetary
- quantity.
-char p_sign_posn
- Set to a value indicating the positioning of the positive_sign for a
- nonnegative locally formatted monetary quantity.
-char n_sign_posn
- Set to a value indicating the positioning of the negative_sign for a
- negative locally formatted monetary quantity.
-char *int_curr_symbol
- The international currency symbol applicable to the current locale. The
- first three characters contain the alphabetic international currency symbol
- in accordance with those specified in ISO 4217. The fourth character
- (immediately preceding the null character) is the character used to separate
- the international currency symbol from the monetary quantity.
-char int_frac_digits
- The number of fractional digits (those after the decimal-point) to be
- displayed in an internationally formatted monetary quantity.
-char int_p_cs_precedes
- Set to 1 or 0 if the int_curr_symbol respectively precedes or
- succeeds the value for a nonnegative internationally formatted monetary
- quantity.
-char int_n_cs_precedes
- Set to 1 or 0 if the int_curr_symbol respectively precedes or
- succeeds the value for a negative internationally formatted monetary
- quantity.
-char int_p_sep_by_space
- Set to a value indicating the separation of the int_curr_symbol, the
- sign string, and the value for a nonnegative internationally formatted
- monetary quantity.
-[page 226] (Contents)
-
- char int_n_sep_by_space
- Set to a value indicating the separation of the int_curr_symbol, the
- sign string, and the value for a negative internationally formatted monetary
- quantity.
- char int_p_sign_posn
- Set to a value indicating the positioning of the positive_sign for a
- nonnegative internationally formatted monetary quantity.
- char int_n_sign_posn
- Set to a value indicating the positioning of the negative_sign for a
- negative internationally formatted monetary quantity.
-4 The elements of grouping and mon_grouping are interpreted according to the
- following:
- CHAR_MAX No further grouping is to be performed.
- 0 The previous element is to be repeatedly used for the remainder of the
- digits.
- other The integer value is the number of digits that compose the current group.
- The next element is examined to determine the size of the next group of
- digits before the current group.
-5 The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
- and int_n_sep_by_space are interpreted according to the following:
- 0 No space separates the currency symbol and value.
- 1 If the currency symbol and sign string are adjacent, a space separates them from the
- value; otherwise, a space separates the currency symbol from the value.
- 2 If the currency symbol and sign string are adjacent, a space separates them;
- otherwise, a space separates the sign string from the value.
- For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
- int_curr_symbol is used instead of a space.
-6 The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and
- int_n_sign_posn are interpreted according to the following:
- 0 Parentheses surround the quantity and currency symbol.
- 1 The sign string precedes the quantity and currency symbol.
- 2 The sign string succeeds the quantity and currency symbol.
- 3 The sign string immediately precedes the currency symbol.
- 4 The sign string immediately succeeds the currency symbol.
-
-
-[page 227] (Contents)
-
-7 The implementation shall behave as if no library function calls the localeconv
- function.
- Returns
-8 The localeconv function returns a pointer to the filled-in object. The structure
- pointed to by the return value shall not be modified by the program, but may be
- overwritten by a subsequent call to the localeconv function. In addition, calls to the
- setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
- overwrite the contents of the structure.
-9 EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
- monetary quantities.
- Local format International format
-
- Country Positive Negative Positive Negative
-
- Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56
- Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234
- Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56
- Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C
-10 For these four countries, the respective values for the monetary members of the structure returned by
- localeconv could be:
- Country1 Country2 Country3 Country4
-
- mon_decimal_point "," "" "," "."
- mon_thousands_sep "." "." "." ","
- mon_grouping "\3" "\3" "\3" "\3"
- positive_sign "" "" "" ""
- negative_sign "-" "-" "-" "C"
- currency_symbol "mk" "L." "\u0192" "SFrs."
- frac_digits 2 0 2 2
- p_cs_precedes 0 1 1 1
- n_cs_precedes 0 1 1 1
- p_sep_by_space 1 0 1 0
- n_sep_by_space 1 0 2 0
- p_sign_posn 1 1 1 1
- n_sign_posn 1 1 4 2
- int_curr_symbol "FIM " "ITL " "NLG " "CHF "
- int_frac_digits 2 0 2 2
- int_p_cs_precedes 1 1 1 1
- int_n_cs_precedes 1 1 1 1
- int_p_sep_by_space 1 1 1 1
- int_n_sep_by_space 2 1 2 1
- int_p_sign_posn 1 1 1 1
- int_n_sign_posn 4 1 4 2
-
-
-
-
-[page 228] (Contents)
-
-11 EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
- affect the formatted value.
- p_sep_by_space
-
- p_cs_precedes p_sign_posn 0 1 2
-
- 0 0 (1.25$) (1.25 $) (1.25$)
- 1 +1.25$ +1.25 $ + 1.25$
- 2 1.25$+ 1.25 $+ 1.25$ +
- 3 1.25+$ 1.25 +$ 1.25+ $
- 4 1.25$+ 1.25 $+ 1.25$ +
-
- 1 0 ($1.25) ($ 1.25) ($1.25)
- 1 +$1.25 +$ 1.25 + $1.25
- 2 $1.25+ $ 1.25+ $1.25 +
- 3 +$1.25 +$ 1.25 + $1.25
- 4 $+1.25 $+ 1.25 $ +1.25
-
-
-
-
-[page 229] (Contents)
-
- 7.12 Mathematics <math.h>
-1 The header <math.h> declares two types and many mathematical functions and defines
- several macros. Most synopses specify a family of functions consisting of a principal
- function with one or more double parameters, a double return value, or both; and
- other functions with the same name but with f and l suffixes, which are corresponding
- functions with float and long double parameters, return values, or both.223)
- Integer arithmetic functions and conversion functions are discussed later.
-2 The types
- float_t
- double_t
- are floating types at least as wide as float and double, respectively, and such that
- double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
- float_t and double_t are float and double, respectively; if
- FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
- 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
- otherwise implementation-defined.224)
-3 The macro
- HUGE_VAL
- expands to a positive double constant expression, not necessarily representable as a
- float. The macros
- HUGE_VALF
- HUGE_VALL
- are respectively float and long double analogs of HUGE_VAL.225)
-4 The macro
- INFINITY
- expands to a constant expression of type float representing positive or unsigned
- infinity, if available; else to a positive constant of type float that overflows at
-
-
-
- 223) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
- and return values in wider format than the synopsis prototype indicates.
- 224) The types float_t and double_t are intended to be the implementation's most efficient types at
- least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the
- type float_t is the narrowest type used by the implementation to evaluate floating expressions.
- 225) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
- supports infinities.
-
-[page 230] (Contents)
-
- translation time.226)
-5 The macro
- NAN
- is defined if and only if the implementation supports quiet NaNs for the float type. It
- expands to a constant expression of type float representing a quiet NaN.
-6 The number classification macros
- FP_INFINITE
- FP_NAN
- FP_NORMAL
- FP_SUBNORMAL
- FP_ZERO
- represent the mutually exclusive kinds of floating-point values. They expand to integer
- constant expressions with distinct values. Additional implementation-defined floating-
- point classifications, with macro definitions beginning with FP_ and an uppercase letter,
- may also be specified by the implementation.
-7 The macro
- FP_FAST_FMA
- is optionally defined. If defined, it indicates that the fma function generally executes
- about as fast as, or faster than, a multiply and an add of double operands.227) The
- macros
- FP_FAST_FMAF
- FP_FAST_FMAL
- are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
- these macros expand to the integer constant 1.
-8 The macros
- FP_ILOGB0
- FP_ILOGBNAN
- expand to integer constant expressions whose values are returned by ilogb(x) if x is
- zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
- -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.
-
-
- 226) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
- 227) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
- directly with a hardware multiply-add instruction. Software implementations are expected to be
- substantially slower.
-
-[page 231] (Contents)
-
-9 The macros
- MATH_ERRNO
- MATH_ERREXCEPT
- expand to the integer constants 1 and 2, respectively; the macro
- math_errhandling
- expands to an expression that has type int and the value MATH_ERRNO,
- MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
- constant for the duration of the program. It is unspecified whether
- math_errhandling is a macro or an identifier with external linkage. If a macro
- definition is suppressed or a program defines an identifier with the name
- math_errhandling, the behavior is undefined. If the expression
- math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
- shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
- <fenv.h>.
- 7.12.1 Treatment of error conditions
-1 The behavior of each of the functions in <math.h> is specified for all representable
- values of its input arguments, except where stated otherwise. Each function shall execute
- as if it were a single operation without raising SIGFPE and without generating any of the
- floating-point exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect
- the result of the function.
-2 For all functions, a domain error occurs if an input argument is outside the domain over
- which the mathematical function is defined. The description of each function lists any
- required domain errors; an implementation may define additional domain errors, provided
- that such errors are consistent with the mathematical definition of the function.228) On a
- domain error, the function returns an implementation-defined value; if the integer
- expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
- errno acquires the value EDOM; if the integer expression math_errhandling &
- MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised.
-3 Similarly, a pole error (also known as a singularity or infinitary) occurs if the
- mathematical function has an exact infinite result as the finite input argument(s) are
- approached in the limit (for example, log(0.0)). The description of each function lists
- any required pole errors; an implementation may define additional pole errors, provided
- that such errors are consistent with the mathematical definition of the function. On a pole
- error, the function returns an implementation-defined value; if the integer expression
-
-
- 228) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
- error if the mathematical domain of the function does not include the infinity.
-
-[page 232] (Contents)
-
- math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
- acquires the value ERANGE; if the integer expression math_errhandling &
- MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised.
-4 Likewise, a range error occurs if the mathematical result of the function cannot be
- represented in an object of the specified type, due to extreme magnitude.
-5 A floating result overflows if the magnitude of the mathematical result is finite but so
- large that the mathematical result cannot be represented without extraordinary roundoff
- error in an object of the specified type. If a floating result overflows and default rounding
- is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or *
- HUGE_VALL according to the return type, with the same sign as the correct value of the
- function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
- the integer expression errno acquires the value ERANGE; if the integer expression
- math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating-
- point exception is raised.
-6 The result underflows if the magnitude of the mathematical result is so small that the
- mathematical result cannot be represented, without extraordinary roundoff error, in an
- object of the specified type.229) If the result underflows, the function returns an
- implementation-defined value whose magnitude is no greater than the smallest
- normalized positive number in the specified type; if the integer expression
- math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
- value ERANGE is implementation-defined; if the integer expression
- math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow''
- floating-point exception is raised is implementation-defined.
-7 If a domain, pole, or range error occurs and the integer expression
- math_errhandling & MATH_ERRNO is zero,230) then errno shall either be set to
- the value corresponding to the error or left unmodified. If no such error occurs, errno
- shall be left unmodified regardless of the setting of math_errhandling.
-
-
-
-
- 229) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and
- also ''flush-to-zero'' underflow.
- 230) Math errors are being indicated by the floating-point exception flags rather than by errno.
-
-[page 233] (Contents)
-
- 7.12.2 The FP_CONTRACT pragma
- Synopsis
-1 #include <math.h>
- #pragma STDC FP_CONTRACT on-off-switch
- Description
-2 The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the
- state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur
- either outside external declarations or preceding all explicit declarations and statements
- inside a compound statement. When outside external declarations, the pragma takes
- effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
- the end of the translation unit. When inside a compound statement, the pragma takes
- effect from its occurrence until another FP_CONTRACT pragma is encountered
- (including within a nested compound statement), or until the end of the compound
- statement; at the end of a compound statement the state for the pragma is restored to its
- condition just before the compound statement. If this pragma is used in any other
- context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is
- implementation-defined.
- 7.12.3 Classification macros
-1 In the synopses in this subclause, real-floating indicates that the argument shall be an
- expression of real floating type.
- 7.12.3.1 The fpclassify macro
- Synopsis
-1 #include <math.h>
- int fpclassify(real-floating x);
- Description
-2 The fpclassify macro classifies its argument value as NaN, infinite, normal,
- subnormal, zero, or into another implementation-defined category. First, an argument
- represented in a format wider than its semantic type is converted to its semantic type.
- Then classification is based on the type of the argument.231)
- Returns
-3 The fpclassify macro returns the value of the number classification macro
- appropriate to the value of its argument. *
-
-
- 231) Since an expression can be evaluated with more range and precision than its type has, it is important to
- know the type that classification is based on. For example, a normal long double value might
- become subnormal when converted to double, and zero when converted to float.
-
-[page 234] (Contents)
-
- 7.12.3.2 The isfinite macro
- Synopsis
-1 #include <math.h>
- int isfinite(real-floating x);
- Description
-2 The isfinite macro determines whether its argument has a finite value (zero,
- subnormal, or normal, and not infinite or NaN). First, an argument represented in a
- format wider than its semantic type is converted to its semantic type. Then determination
- is based on the type of the argument.
- Returns
-3 The isfinite macro returns a nonzero value if and only if its argument has a finite
- value.
- 7.12.3.3 The isinf macro
- Synopsis
-1 #include <math.h>
- int isinf(real-floating x);
- Description
-2 The isinf macro determines whether its argument value is an infinity (positive or
- negative). First, an argument represented in a format wider than its semantic type is
- converted to its semantic type. Then determination is based on the type of the argument.
- Returns
-3 The isinf macro returns a nonzero value if and only if its argument has an infinite
- value.
- 7.12.3.4 The isnan macro
- Synopsis
-1 #include <math.h>
- int isnan(real-floating x);
- Description
-2 The isnan macro determines whether its argument value is a NaN. First, an argument
- represented in a format wider than its semantic type is converted to its semantic type.
- Then determination is based on the type of the argument.232)
-
-
- 232) For the isnan macro, the type for determination does not matter unless the implementation supports
- NaNs in the evaluation type but not in the semantic type.
-
-[page 235] (Contents)
-
- Returns
-3 The isnan macro returns a nonzero value if and only if its argument has a NaN value.
- 7.12.3.5 The isnormal macro
- Synopsis
-1 #include <math.h>
- int isnormal(real-floating x);
- Description
-2 The isnormal macro determines whether its argument value is normal (neither zero,
- subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
- semantic type is converted to its semantic type. Then determination is based on the type
- of the argument.
- Returns
-3 The isnormal macro returns a nonzero value if and only if its argument has a normal
- value.
- 7.12.3.6 The signbit macro
- Synopsis
-1 #include <math.h>
- int signbit(real-floating x);
- Description
-2 The signbit macro determines whether the sign of its argument value is negative.233)
- Returns
-3 The signbit macro returns a nonzero value if and only if the sign of its argument value
- is negative.
-
-
-
-
- 233) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
- unsigned, it is treated as positive.
-
-[page 236] (Contents)
-
- 7.12.4 Trigonometric functions
- 7.12.4.1 The acos functions
- Synopsis
-1 #include <math.h>
- double acos(double x);
- float acosf(float x);
- long double acosl(long double x);
- Description
-2 The acos functions compute the principal value of the arc cosine of x. A domain error
- occurs for arguments not in the interval [-1, +1].
- Returns
-3 The acos functions return arccos x in the interval [0, pi ] radians.
- 7.12.4.2 The asin functions
- Synopsis
-1 #include <math.h>
- double asin(double x);
- float asinf(float x);
- long double asinl(long double x);
- Description
-2 The asin functions compute the principal value of the arc sine of x. A domain error
- occurs for arguments not in the interval [-1, +1].
- Returns
-3 The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians.
- 7.12.4.3 The atan functions
- Synopsis
-1 #include <math.h>
- double atan(double x);
- float atanf(float x);
- long double atanl(long double x);
- Description
-2 The atan functions compute the principal value of the arc tangent of x.
-
-
-
-
-[page 237] (Contents)
-
- Returns
-3 The atan functions return arctan x in the interval [-pi /2, +pi /2] radians.
- 7.12.4.4 The atan2 functions
- Synopsis
-1 #include <math.h>
- double atan2(double y, double x);
- float atan2f(float y, float x);
- long double atan2l(long double y, long double x);
- Description
-2 The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
- arguments to determine the quadrant of the return value. A domain error may occur if
- both arguments are zero.
- Returns
-3 The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians.
- 7.12.4.5 The cos functions
- Synopsis
-1 #include <math.h>
- double cos(double x);
- float cosf(float x);
- long double cosl(long double x);
- Description
-2 The cos functions compute the cosine of x (measured in radians).
- Returns
-3 The cos functions return cos x.
- 7.12.4.6 The sin functions
- Synopsis
-1 #include <math.h>
- double sin(double x);
- float sinf(float x);
- long double sinl(long double x);
- Description
-2 The sin functions compute the sine of x (measured in radians).
-
-
-
-[page 238] (Contents)
-
- Returns
-3 The sin functions return sin x.
- 7.12.4.7 The tan functions
- Synopsis
-1 #include <math.h>
- double tan(double x);
- float tanf(float x);
- long double tanl(long double x);
- Description
-2 The tan functions return the tangent of x (measured in radians).
- Returns
-3 The tan functions return tan x.
- 7.12.5 Hyperbolic functions
- 7.12.5.1 The acosh functions
- Synopsis
-1 #include <math.h>
- double acosh(double x);
- float acoshf(float x);
- long double acoshl(long double x);
- Description
-2 The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
- error occurs for arguments less than 1.
- Returns
-3 The acosh functions return arcosh x in the interval [0, +(inf)].
- 7.12.5.2 The asinh functions
- Synopsis
-1 #include <math.h>
- double asinh(double x);
- float asinhf(float x);
- long double asinhl(long double x);
- Description
-2 The asinh functions compute the arc hyperbolic sine of x.
-
-
-[page 239] (Contents)
-
- Returns
-3 The asinh functions return arsinh x.
- 7.12.5.3 The atanh functions
- Synopsis
-1 #include <math.h>
- double atanh(double x);
- float atanhf(float x);
- long double atanhl(long double x);
- Description
-2 The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
- for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals
- -1 or +1.
- Returns
-3 The atanh functions return artanh x.
- 7.12.5.4 The cosh functions
- Synopsis
-1 #include <math.h>
- double cosh(double x);
- float coshf(float x);
- long double coshl(long double x);
- Description
-2 The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
- magnitude of x is too large.
- Returns
-3 The cosh functions return cosh x.
- 7.12.5.5 The sinh functions
- Synopsis
-1 #include <math.h>
- double sinh(double x);
- float sinhf(float x);
- long double sinhl(long double x);
- Description
-2 The sinh functions compute the hyperbolic sine of x. A range error occurs if the
- magnitude of x is too large.
-[page 240] (Contents)
-
- Returns
-3 The sinh functions return sinh x.
- 7.12.5.6 The tanh functions
- Synopsis
-1 #include <math.h>
- double tanh(double x);
- float tanhf(float x);
- long double tanhl(long double x);
- Description
-2 The tanh functions compute the hyperbolic tangent of x.
- Returns
-3 The tanh functions return tanh x.
- 7.12.6 Exponential and logarithmic functions
- 7.12.6.1 The exp functions
- Synopsis
-1 #include <math.h>
- double exp(double x);
- float expf(float x);
- long double expl(long double x);
- Description
-2 The exp functions compute the base-e exponential of x. A range error occurs if the
- magnitude of x is too large.
- Returns
-3 The exp functions return ex .
- 7.12.6.2 The exp2 functions
- Synopsis
-1 #include <math.h>
- double exp2(double x);
- float exp2f(float x);
- long double exp2l(long double x);
- Description
-2 The exp2 functions compute the base-2 exponential of x. A range error occurs if the
- magnitude of x is too large.
-
-[page 241] (Contents)
-
- Returns
-3 The exp2 functions return 2x .
- 7.12.6.3 The expm1 functions
- Synopsis
-1 #include <math.h>
- double expm1(double x);
- float expm1f(float x);
- long double expm1l(long double x);
- Description
-2 The expm1 functions compute the base-e exponential of the argument, minus 1. A range
- error occurs if x is too large.234)
- Returns
-3 The expm1 functions return ex - 1.
- 7.12.6.4 The frexp functions
- Synopsis
-1 #include <math.h>
- double frexp(double value, int *exp);
- float frexpf(float value, int *exp);
- long double frexpl(long double value, int *exp);
- Description
-2 The frexp functions break a floating-point number into a normalized fraction and an
- integral power of 2. They store the integer in the int object pointed to by exp.
- Returns
-3 If value is not a floating-point number or if the integral power of 2 is outside the range
- of int, the results are unspecified. Otherwise, the frexp functions return the value x,
- such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp .
- If value is zero, both parts of the result are zero.
-
-
-
-
- 234) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.
-
-[page 242] (Contents)
-
- 7.12.6.5 The ilogb functions
- Synopsis
-1 #include <math.h>
- int ilogb(double x);
- int ilogbf(float x);
- int ilogbl(long double x);
- Description
-2 The ilogb functions extract the exponent of x as a signed int value. If x is zero they
- compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
- a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
- the corresponding logb function and casting the returned value to type int. A domain
- error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
- the range of the return type, the numeric result is unspecified.
- Returns
-3 The ilogb functions return the exponent of x as a signed int value.
- Forward references: the logb functions (7.12.6.11).
- 7.12.6.6 The ldexp functions
- Synopsis
-1 #include <math.h>
- double ldexp(double x, int exp);
- float ldexpf(float x, int exp);
- long double ldexpl(long double x, int exp);
- Description
-2 The ldexp functions multiply a floating-point number by an integral power of 2. A
- range error may occur.
- Returns
-3 The ldexp functions return x x 2exp .
- 7.12.6.7 The log functions
- Synopsis
-1 #include <math.h>
- double log(double x);
- float logf(float x);
- long double logl(long double x);
-
-
-
-[page 243] (Contents)
-
- Description
-2 The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
- the argument is negative. A pole error may occur if the argument is zero.
- Returns
-3 The log functions return loge x.
- 7.12.6.8 The log10 functions
- Synopsis
-1 #include <math.h>
- double log10(double x);
- float log10f(float x);
- long double log10l(long double x);
- Description
-2 The log10 functions compute the base-10 (common) logarithm of x. A domain error
- occurs if the argument is negative. A pole error may occur if the argument is zero.
- Returns
-3 The log10 functions return log10 x.
- 7.12.6.9 The log1p functions
- Synopsis
-1 #include <math.h>
- double log1p(double x);
- float log1pf(float x);
- long double log1pl(long double x);
- Description
-2 The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.235)
- A domain error occurs if the argument is less than -1. A pole error may occur if the
- argument equals -1.
- Returns
-3 The log1p functions return loge (1 + x).
-
-
-
-
- 235) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).
-
-[page 244] (Contents)
-
- 7.12.6.10 The log2 functions
- Synopsis
-1 #include <math.h>
- double log2(double x);
- float log2f(float x);
- long double log2l(long double x);
- Description
-2 The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
- argument is less than zero. A pole error may occur if the argument is zero.
- Returns
-3 The log2 functions return log2 x.
- 7.12.6.11 The logb functions
- Synopsis
-1 #include <math.h>
- double logb(double x);
- float logbf(float x);
- long double logbl(long double x);
- Description
-2 The logb functions extract the exponent of x, as a signed integer value in floating-point
- format. If x is subnormal it is treated as though it were normalized; thus, for positive
- finite x,
- 1 <= x x FLT_RADIX-logb(x) < FLT_RADIX
- A domain error or pole error may occur if the argument is zero.
- Returns
-3 The logb functions return the signed exponent of x.
- 7.12.6.12 The modf functions
- Synopsis
-1 #include <math.h>
- double modf(double value, double *iptr);
- float modff(float value, float *iptr);
- long double modfl(long double value, long double *iptr);
- Description
-2 The modf functions break the argument value into integral and fractional parts, each of
- which has the same type and sign as the argument. They store the integral part (in
-[page 245] (Contents)
-
- floating-point format) in the object pointed to by iptr.
- Returns
-3 The modf functions return the signed fractional part of value.
- 7.12.6.13 The scalbn and scalbln functions
- Synopsis
-1 #include <math.h>
- double scalbn(double x, int n);
- float scalbnf(float x, int n);
- long double scalbnl(long double x, int n);
- double scalbln(double x, long int n);
- float scalblnf(float x, long int n);
- long double scalblnl(long double x, long int n);
- Description
-2 The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not
- normally by computing FLT_RADIXn explicitly. A range error may occur.
- Returns
-3 The scalbn and scalbln functions return x x FLT_RADIXn .
- 7.12.7 Power and absolute-value functions
- 7.12.7.1 The cbrt functions
- Synopsis
-1 #include <math.h>
- double cbrt(double x);
- float cbrtf(float x);
- long double cbrtl(long double x);
- Description
-2 The cbrt functions compute the real cube root of x.
- Returns
-3 The cbrt functions return x1/3 .
-
-
-
-
-[page 246] (Contents)
-
- 7.12.7.2 The fabs functions
- Synopsis
-1 #include <math.h>
- double fabs(double x);
- float fabsf(float x);
- long double fabsl(long double x);
- Description
-2 The fabs functions compute the absolute value of a floating-point number x.
- Returns
-3 The fabs functions return | x |.
- 7.12.7.3 The hypot functions
- Synopsis
-1 #include <math.h>
- double hypot(double x, double y);
- float hypotf(float x, float y);
- long double hypotl(long double x, long double y);
- Description
-2 The hypot functions compute the square root of the sum of the squares of x and y,
- without undue overflow or underflow. A range error may occur.
-3 Returns
-4 The hypot functions return sqrt:x2 + y2 .
- -
- -----
- 7.12.7.4 The pow functions
- Synopsis
-1 #include <math.h>
- double pow(double x, double y);
- float powf(float x, float y);
- long double powl(long double x, long double y);
- Description
-2 The pow functions compute x raised to the power y. A domain error occurs if x is finite
- and negative and y is finite and not an integer value. A range error may occur. A domain
- error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
- zero and y is less than zero.
-
-
-
-
-[page 247] (Contents)
-
- Returns
-3 The pow functions return xy .
- 7.12.7.5 The sqrt functions
- Synopsis
-1 #include <math.h>
- double sqrt(double x);
- float sqrtf(float x);
- long double sqrtl(long double x);
- Description
-2 The sqrt functions compute the nonnegative square root of x. A domain error occurs if
- the argument is less than zero.
- Returns
-3 The sqrt functions return sqrt:x.
- -
- -
- 7.12.8 Error and gamma functions
- 7.12.8.1 The erf functions
- Synopsis
-1 #include <math.h>
- double erf(double x);
- float erff(float x);
- long double erfl(long double x);
- Description
-2 The erf functions compute the error function of x.
- Returns
-3 2 x
- (integral) e-t dt.
- 2
- The erf functions return erf x =
- sqrt:pi
- -
- - 0
-
- 7.12.8.2 The erfc functions
- Synopsis
-1 #include <math.h>
- double erfc(double x);
- float erfcf(float x);
- long double erfcl(long double x);
- Description
-2 The erfc functions compute the complementary error function of x. A range error
- occurs if x is too large.
-[page 248] (Contents)
-
- Returns
-3 2 (inf)
- (integral) e-t dt.
- 2
- The erfc functions return erfc x = 1 - erf x =
- sqrt:pi
- -
- - x
-
- 7.12.8.3 The lgamma functions
- Synopsis
-1 #include <math.h>
- double lgamma(double x);
- float lgammaf(float x);
- long double lgammal(long double x);
- Description
-2 The lgamma functions compute the natural logarithm of the absolute value of gamma of
- x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
- or zero.
- Returns
-3 The lgamma functions return loge | (Gamma)(x) |.
- 7.12.8.4 The tgamma functions
- Synopsis
-1 #include <math.h>
- double tgamma(double x);
- float tgammaf(float x);
- long double tgammal(long double x);
- Description
-2 The tgamma functions compute the gamma function of x. A domain error or pole error
- may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
- too large and may occur if the magnitude of x is too small.
- Returns
-3 The tgamma functions return (Gamma)(x).
-
-
-
-
-[page 249] (Contents)
-
- 7.12.9 Nearest integer functions
- 7.12.9.1 The ceil functions
- Synopsis
-1 #include <math.h>
- double ceil(double x);
- float ceilf(float x);
- long double ceill(long double x);
- Description
-2 The ceil functions compute the smallest integer value not less than x.
- Returns
-3 The ceil functions return [^x^], expressed as a floating-point number.
- 7.12.9.2 The floor functions
- Synopsis
-1 #include <math.h>
- double floor(double x);
- float floorf(float x);
- long double floorl(long double x);
- Description
-2 The floor functions compute the largest integer value not greater than x.
- Returns
-3 The floor functions return [_x_], expressed as a floating-point number.
- 7.12.9.3 The nearbyint functions
- Synopsis
-1 #include <math.h>
- double nearbyint(double x);
- float nearbyintf(float x);
- long double nearbyintl(long double x);
- Description
-2 The nearbyint functions round their argument to an integer value in floating-point
- format, using the current rounding direction and without raising the ''inexact'' floating-
- point exception.
-
-
-
-
-[page 250] (Contents)
-
- Returns
-3 The nearbyint functions return the rounded integer value.
- 7.12.9.4 The rint functions
- Synopsis
-1 #include <math.h>
- double rint(double x);
- float rintf(float x);
- long double rintl(long double x);
- Description
-2 The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
- rint functions may raise the ''inexact'' floating-point exception if the result differs in
- value from the argument.
- Returns
-3 The rint functions return the rounded integer value.
- 7.12.9.5 The lrint and llrint functions
- Synopsis
-1 #include <math.h>
- long int lrint(double x);
- long int lrintf(float x);
- long int lrintl(long double x);
- long long int llrint(double x);
- long long int llrintf(float x);
- long long int llrintl(long double x);
- Description
-2 The lrint and llrint functions round their argument to the nearest integer value,
- rounding according to the current rounding direction. If the rounded value is outside the
- range of the return type, the numeric result is unspecified and a domain error or range
- error may occur.
- Returns
-3 The lrint and llrint functions return the rounded integer value.
-
-
-
-
-[page 251] (Contents)
-
- 7.12.9.6 The round functions
- Synopsis
-1 #include <math.h>
- double round(double x);
- float roundf(float x);
- long double roundl(long double x);
- Description
-2 The round functions round their argument to the nearest integer value in floating-point
- format, rounding halfway cases away from zero, regardless of the current rounding
- direction.
- Returns
-3 The round functions return the rounded integer value.
- 7.12.9.7 The lround and llround functions
- Synopsis
-1 #include <math.h>
- long int lround(double x);
- long int lroundf(float x);
- long int lroundl(long double x);
- long long int llround(double x);
- long long int llroundf(float x);
- long long int llroundl(long double x);
- Description
-2 The lround and llround functions round their argument to the nearest integer value,
- rounding halfway cases away from zero, regardless of the current rounding direction. If
- the rounded value is outside the range of the return type, the numeric result is unspecified
- and a domain error or range error may occur.
- Returns
-3 The lround and llround functions return the rounded integer value.
- 7.12.9.8 The trunc functions
- Synopsis
-1 #include <math.h>
- double trunc(double x);
- float truncf(float x);
- long double truncl(long double x);
-
-
-[page 252] (Contents)
-
- Description
-2 The trunc functions round their argument to the integer value, in floating format,
- nearest to but no larger in magnitude than the argument.
- Returns
-3 The trunc functions return the truncated integer value.
- 7.12.10 Remainder functions
- 7.12.10.1 The fmod functions
- Synopsis
-1 #include <math.h>
- double fmod(double x, double y);
- float fmodf(float x, float y);
- long double fmodl(long double x, long double y);
- Description
-2 The fmod functions compute the floating-point remainder of x/y.
- Returns
-3 The fmod functions return the value x - ny, for some integer n such that, if y is nonzero,
- the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
- whether a domain error occurs or the fmod functions return zero is implementation-
- defined.
- 7.12.10.2 The remainder functions
- Synopsis
-1 #include <math.h>
- double remainder(double x, double y);
- float remainderf(float x, float y);
- long double remainderl(long double x, long double y);
- Description
-2 The remainder functions compute the remainder x REM y required by IEC 60559.236)
-
-
-
-
- 236) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the
- mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever
- | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for *
- all implementations.
-
-[page 253] (Contents)
-
- Returns
-3 The remainder functions return x REM y. If y is zero, whether a domain error occurs
- or the functions return zero is implementation defined.
- 7.12.10.3 The remquo functions
- Synopsis
-1 #include <math.h>
- double remquo(double x, double y, int *quo);
- float remquof(float x, float y, int *quo);
- long double remquol(long double x, long double y,
- int *quo);
- Description
-2 The remquo functions compute the same remainder as the remainder functions. In
- the object pointed to by quo they store a value whose sign is the sign of x/y and whose
- magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
- n is an implementation-defined integer greater than or equal to 3.
- Returns
-3 The remquo functions return x REM y. If y is zero, the value stored in the object
- pointed to by quo is unspecified and whether a domain error occurs or the functions
- return zero is implementation defined.
- 7.12.11 Manipulation functions
- 7.12.11.1 The copysign functions
- Synopsis
-1 #include <math.h>
- double copysign(double x, double y);
- float copysignf(float x, float y);
- long double copysignl(long double x, long double y);
- Description
-2 The copysign functions produce a value with the magnitude of x and the sign of y.
- They produce a NaN (with the sign of y) if x is a NaN. On implementations that
- represent a signed zero but do not treat negative zero consistently in arithmetic
- operations, the copysign functions regard the sign of zero as positive.
- Returns
-3 The copysign functions return a value with the magnitude of x and the sign of y.
-
-
-
-[page 254] (Contents)
-
- 7.12.11.2 The nan functions
- Synopsis
-1 #include <math.h>
- double nan(const char *tagp);
- float nanf(const char *tagp);
- long double nanl(const char *tagp);
- Description
-2 The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
- sequence)", (char**) NULL); the call nan("") is equivalent to
- strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
- sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
- NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
- and strtold.
- Returns
-3 The nan functions return a quiet NaN, if available, with content indicated through tagp.
- If the implementation does not support quiet NaNs, the functions return zero.
- Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
- 7.12.11.3 The nextafter functions
- Synopsis
-1 #include <math.h>
- double nextafter(double x, double y);
- float nextafterf(float x, float y);
- long double nextafterl(long double x, long double y);
- Description
-2 The nextafter functions determine the next representable value, in the type of the
- function, after x in the direction of y, where x and y are first converted to the type of the
- function.237) The nextafter functions return y if x equals y. A range error may occur
- if the magnitude of x is the largest finite value representable in the type and the result is
- infinite or not representable in the type.
- Returns
-3 The nextafter functions return the next representable value in the specified format
- after x in the direction of y.
-
-
- 237) The argument values are converted to the type of the function, even by a macro implementation of the
- function.
-
-[page 255] (Contents)
-
- 7.12.11.4 The nexttoward functions
- Synopsis
-1 #include <math.h>
- double nexttoward(double x, long double y);
- float nexttowardf(float x, long double y);
- long double nexttowardl(long double x, long double y);
- Description
-2 The nexttoward functions are equivalent to the nextafter functions except that the
- second parameter has type long double and the functions return y converted to the
- type of the function if x equals y.238)
- 7.12.12 Maximum, minimum, and positive difference functions
- 7.12.12.1 The fdim functions
- Synopsis
-1 #include <math.h>
- double fdim(double x, double y);
- float fdimf(float x, float y);
- long double fdiml(long double x, long double y);
- Description
-2 The fdim functions determine the positive difference between their arguments:
- {x - y if x > y
++
+ initializer:
+ assignment-expression
+ { initializer-list }
+ { initializer-list , }
+ initializer-list:
+ designationopt initializer
+ initializer-list , designationopt initializer
+ designation:
+ designator-list =
+ designator-list:
+ designator
+ designator-list designator
+ designator:
+ [ constant-expression ]
+ . identifier
+
++ No initializer shall attempt to provide a value for an object not contained within the entity + being initialized. +
+ The type of the entity to be initialized shall be an array of unknown size or a complete + object type that is not a variable length array type. +
+ All the expressions in an initializer for an object that has static or thread storage duration + shall be constant expressions or string literals. +
+ If the declaration of an identifier has block scope, and the identifier has external or + internal linkage, the declaration shall have no initializer for the identifier. +
+ If a designator has the form +
+ [ constant-expression ] ++ then the current object (defined below) shall have array type and the expression shall be + an integer constant expression. If the array is of unknown size, any nonnegative value is + valid. +
+ If a designator has the form +
+ . identifier ++ then the current object (defined below) shall have structure or union type and the + identifier shall be the name of a member of that type. + +
+ An initializer specifies the initial value stored in an object. +
+ Except where explicitly stated otherwise, for the purposes of this subclause unnamed + members of objects of structure and union type do not participate in initialization. + Unnamed members of structure objects have indeterminate value even after initialization. +
+ If an object that has automatic storage duration is not initialized explicitly, its value is + indeterminate. If an object that has static or thread storage duration is not initialized + explicitly, then: +
+ The initializer for a scalar shall be a single expression, optionally enclosed in braces. The + initial value of the object is that of the expression (after conversion); the same type + constraints and conversions as for simple assignment apply, taking the type of the scalar + to be the unqualified version of its declared type. +
+ The rest of this subclause deals with initializers for objects that have aggregate or union + type. +
+ The initializer for a structure or union object that has automatic storage duration shall be + either an initializer list as described below, or a single expression that has compatible + structure or union type. In the latter case, the initial value of the object, including + unnamed members, is that of the expression. +
+ An array of character type may be initialized by a character string literal or UTF-8 string + literal, optionally enclosed in braces. Successive bytes of the string literal (including the + terminating null character if there is room or if the array is of unknown size) initialize the + elements of the array. +
+ An array with element type compatible with a qualified or unqualified version of + wchar_t may be initialized by a wide string literal, optionally enclosed in braces. + Successive wide characters of the wide string literal (including the terminating null wide + character if there is room or if the array is of unknown size) initialize the elements of the + array. +
+ Otherwise, the initializer for an object that has aggregate or union type shall be a brace- + enclosed list of initializers for the elements or named members. + +
+ Each brace-enclosed initializer list has an associated current object. When no + designations are present, subobjects of the current object are initialized in order according + to the type of the current object: array elements in increasing subscript order, structure + members in declaration order, and the first named member of a union.148) In contrast, a + designation causes the following initializer to begin initialization of the subobject + described by the designator. Initialization then continues forward in order, beginning + with the next subobject after that described by the designator.149) +
+ Each designator list begins its description with the current object associated with the + closest surrounding brace pair. Each item in the designator list (in order) specifies a + particular member of its current object and changes the current object for the next + designator (if any) to be that member.150) The current object that results at the end of the + designator list is the subobject to be initialized by the following initializer. +
+ The initialization shall occur in initializer list order, each initializer provided for a + particular subobject overriding any previously listed initializer for the same subobject;151) + all subobjects that are not initialized explicitly shall be initialized implicitly the same as + objects that have static storage duration. +
+ If the aggregate or union contains elements or members that are aggregates or unions, + these rules apply recursively to the subaggregates or contained unions. If the initializer of + a subaggregate or contained union begins with a left brace, the initializers enclosed by + that brace and its matching right brace initialize the elements or members of the + subaggregate or the contained union. Otherwise, only enough initializers from the list are + taken to account for the elements or members of the subaggregate or the first member of + the contained union; any remaining initializers are left to initialize the next element or + member of the aggregate of which the current subaggregate or contained union is a part. +
+ If there are fewer initializers in a brace-enclosed list than there are elements or members + of an aggregate, or fewer characters in a string literal used to initialize an array of known + size than there are elements in the array, the remainder of the aggregate shall be + initialized implicitly the same as objects that have static storage duration. + + + + +
+ If an array of unknown size is initialized, its size is determined by the largest indexed + element with an explicit initializer. The array type is completed at the end of its + initializer list. +
+ The evaluations of the initialization list expressions are indeterminately sequenced with + respect to one another and thus the order in which any side effects occur is + unspecified.152) +
+ EXAMPLE 1 Provided that <complex.h> has been #included, the declarations +
+ int i = 3.5; + double complex c = 5 + 3 * I; ++ define and initialize i with the value 3 and c with the value 5.0 + i3.0. + +
+ EXAMPLE 2 The declaration +
+ int x[] = { 1, 3, 5 };
+
+ defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
+ and there are three initializers.
+
++ EXAMPLE 3 The declaration +
+ int y[4][3] = {
+ { 1, 3, 5 },
+ { 2, 4, 6 },
+ { 3, 5, 7 },
+ };
+
+ is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
+ y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
+ y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
+ been achieved by
+
+ int y[4][3] = {
+ 1, 3, 5, 2, 4, 6, 3, 5, 7
+ };
+
+ The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
+ next three are taken successively for y[1] and y[2].
+
++ EXAMPLE 4 The declaration +
+ int z[4][3] = {
+ { 1 }, { 2 }, { 3 }, { 4 }
+ };
+
+ initializes the first column of z as specified and initializes the rest with zeros.
+
++ EXAMPLE 5 The declaration +
+ struct { int a[3], b; } w[] = { { 1 }, 2 };
+
+ is a definition with an inconsistently bracketed initialization. It defines an array with two element
+
+
+
+
+ structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
+
++ EXAMPLE 6 The declaration +
+ short q[4][3][2] = {
+ { 1 },
+ { 2, 3 },
+ { 4, 5, 6 }
+ };
+
+ contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
+ object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
+ q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
+ q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
+ only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
+ for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
+ respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
+ diagnostic message would have been issued. The same initialization result could have been achieved by:
+
+ short q[4][3][2] = {
+ 1, 0, 0, 0, 0, 0,
+ 2, 3, 0, 0, 0, 0,
+ 4, 5, 6
+ };
+
+ or by:
+
+ short q[4][3][2] = {
+ {
+ { 1 },
+ },
+ {
+ { 2, 3 },
+ },
+ {
+ { 4, 5 },
+ { 6 },
+ }
+ };
+
+ in a fully bracketed form.
++ Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to + cause confusion. + +
+ EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the + declaration +
+ typedef int A[]; // OK - declared with block scope ++ the declaration +
+ A a = { 1, 2 }, b = { 3, 4, 5 };
+
+ is identical to
+
+ int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
+
+ due to the rules for incomplete types.
+
++ EXAMPLE 8 The declaration +
+ char s[] = "abc", t[3] = "abc"; ++ defines ''plain'' char array objects s and t whose elements are initialized with character string literals. + This declaration is identical to +
+ char s[] = { 'a', 'b', 'c', '\0' },
+ t[] = { 'a', 'b', 'c' };
+
+ The contents of the arrays are modifiable. On the other hand, the declaration
++ char *p = "abc"; ++ defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char'' + with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to + modify the contents of the array, the behavior is undefined. + +
+ EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using + designators: +
+ enum { member_one, member_two };
+ const char *nm[] = {
+ [member_two] = "member two",
+ [member_one] = "member one",
+ };
+
+
++ EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order: +
+ div_t answer = { .quot = 2, .rem = -1 };
+
+
++ EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists + might be misunderstood: +
+ struct { int a[3], b; } w[] =
+ { [0].a = {1}, [1].a[0] = 2 };
+
+
++ EXAMPLE 12 Space can be ''allocated'' from both ends of an array by using a single designator: +
+ int a[MAX] = {
+ 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
+ };
+
++ In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less + than ten, some of the values provided by the first five initializers will be overridden by the second five. + +
+ EXAMPLE 13 Any member of a union can be initialized: +
+ union { /* ... */ } u = { .any_member = 42 };
+
+
+Forward references: common definitions <stddef.h> (7.19). + + +
148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its + subobjects are initialized as usual, but the subaggregate or contained union does not become the + current object: current objects are associated only with brace-enclosed initializer lists. + +
149) After a union member is initialized, the next object is not the next member of the union; instead, it is + the next subobject of an object containing the union. + +
150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with + the surrounding brace pair. Note, too, that each separate designator list is independent. + +
151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might + not be evaluated at all. + +
152) In particular, the evaluation order need not be the same as the order of subobject initialization. + + +
+
+ static_assert-declaration: + _Static_assert ( constant-expression , string-literal ) ; ++
+ The constant expression shall compare unequal to 0. +
+ The constant expression shall be an integer constant expression. If the value of the + constant expression compares unequal to 0, the declaration has no effect. Otherwise, the + constraint is violated and the implementation shall produce a diagnostic message that + includes the text of the string literal, except that characters not in the basic source + character set are not required to appear in the message. +
Forward references: diagnostics (7.2). + + +
+
+ statement: + labeled-statement + compound-statement + expression-statement + selection-statement + iteration-statement + jump-statement ++
+ A statement specifies an action to be performed. Except as indicated, statements are + executed in sequence. +
+ A block allows a set of declarations and statements to be grouped into one syntactic unit. + The initializers of objects that have automatic storage duration, and the variable length + array declarators of ordinary identifiers with block scope, are evaluated and the values are + stored in the objects (including storing an indeterminate value in objects without an + initializer) each time the declaration is reached in the order of execution, as if it were a + statement, and within each declaration in the order that declarators appear. +
+ A full expression is an expression that is not part of another expression or of a declarator. + Each of the following is a full expression: an initializer that is not part of a compound + literal; the expression in an expression statement; the controlling expression of a selection + statement (if or switch); the controlling expression of a while or do statement; each + of the (optional) expressions of a for statement; the (optional) expression in a return + statement. There is a sequence point between the evaluation of a full expression and the + evaluation of the next full expression to be evaluated. +
Forward references: expression and null statements (6.8.3), selection statements + (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4). + +
+
+ labeled-statement: + identifier : statement + case constant-expression : statement + default : statement ++
+ A case or default label shall appear only in a switch statement. Further + constraints on such labels are discussed under the switch statement. + +
+ Label names shall be unique within a function. +
+ Any statement may be preceded by a prefix that declares an identifier as a label name. + Labels in themselves do not alter the flow of control, which continues unimpeded across + them. +
Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2). + +
+
+ compound-statement:
+ { block-item-listopt }
+ block-item-list:
+ block-item
+ block-item-list block-item
+ block-item:
+ declaration
+ statement
+
++ A compound statement is a block. + +
+
+ expression-statement: + expressionopt ; ++
+ The expression in an expression statement is evaluated as a void expression for its side + effects.153) +
+ A null statement (consisting of just a semicolon) performs no operations. +
+ EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the + discarding of its value may be made explicit by converting the expression to a void expression by means of + a cast: +
+ int p(int); + /* ... */ + (void)p(0); ++ + + + +
+ EXAMPLE 2 In the program fragment +
+ char *s; + /* ... */ + while (*s++ != '\0') + ; ++ a null statement is used to supply an empty loop body to the iteration statement. + +
+ EXAMPLE 3 A null statement may also be used to carry a label just before the closing } of a compound + statement. +
+ while (loop1) {
+ /* ... */
+ while (loop2) {
+ /* ... */
+ if (want_out)
+ goto end_loop1;
+ /* ... */
+ }
+ /* ... */
+ end_loop1: ;
+ }
+
+
+Forward references: iteration statements (6.8.5). + +
153) Such as assignments, and function calls which have side effects. + + +
+
+ selection-statement: + if ( expression ) statement + if ( expression ) statement else statement + switch ( expression ) statement ++
+ A selection statement selects among a set of statements depending on the value of a + controlling expression. +
+ A selection statement is a block whose scope is a strict subset of the scope of its + enclosing block. Each associated substatement is also a block whose scope is a strict + subset of the scope of the selection statement. + +
+ The controlling expression of an if statement shall have scalar type. +
+ In both forms, the first substatement is executed if the expression compares unequal to 0. + In the else form, the second substatement is executed if the expression compares equal + + to 0. If the first substatement is reached via a label, the second substatement is not + executed. +
+ An else is associated with the lexically nearest preceding if that is allowed by the + syntax. + +
+ The controlling expression of a switch statement shall have integer type. +
+ If a switch statement has an associated case or default label within the scope of an + identifier with a variably modified type, the entire switch statement shall be within the + scope of that identifier.154) +
+ The expression of each case label shall be an integer constant expression and no two of + the case constant expressions in the same switch statement shall have the same value + after conversion. There may be at most one default label in a switch statement. + (Any enclosed switch statement may have a default label or case constant + expressions with values that duplicate case constant expressions in the enclosing + switch statement.) +
+ A switch statement causes control to jump to, into, or past the statement that is the + switch body, depending on the value of a controlling expression, and on the presence of a + default label and the values of any case labels on or in the switch body. A case or + default label is accessible only within the closest enclosing switch statement. +
+ The integer promotions are performed on the controlling expression. The constant + expression in each case label is converted to the promoted type of the controlling + expression. If a converted value matches that of the promoted controlling expression, + control jumps to the statement following the matched case label. Otherwise, if there is + a default label, control jumps to the labeled statement. If no converted case constant + expression matches and there is no default label, no part of the switch body is + executed. +
+ As discussed in 5.2.4.1, the implementation may limit the number of case values in a + switch statement. + + + + + +
+ EXAMPLE In the artificial program fragment +
+ switch (expr)
{
- {+0 if x <= y
- A range error may occur.
- Returns
-3 The fdim functions return the positive difference value.
- 7.12.12.2 The fmax functions
- Synopsis
-1 #include <math.h>
- double fmax(double x, double y);
- float fmaxf(float x, float y);
- long double fmaxl(long double x, long double y);
-
-
-
- 238) The result of the nexttoward functions is determined in the type of the function, without loss of
- range or precision in a floating second argument.
-
-[page 256] (Contents)
-
- Description
-2 The fmax functions determine the maximum numeric value of their arguments.239)
- Returns
-3 The fmax functions return the maximum numeric value of their arguments.
- 7.12.12.3 The fmin functions
- Synopsis
-1 #include <math.h>
- double fmin(double x, double y);
- float fminf(float x, float y);
- long double fminl(long double x, long double y);
- Description
-2 The fmin functions determine the minimum numeric value of their arguments.240)
- Returns
-3 The fmin functions return the minimum numeric value of their arguments.
- 7.12.13 Floating multiply-add
- 7.12.13.1 The fma functions
- Synopsis
-1 #include <math.h>
- double fma(double x, double y, double z);
- float fmaf(float x, float y, float z);
- long double fmal(long double x, long double y,
- long double z);
- Description
-2 The fma functions compute (x x y) + z, rounded as one ternary operation: they compute
- the value (as if) to infinite precision and round once to the result format, according to the
- current rounding mode. A range error may occur.
- Returns
-3 The fma functions return (x x y) + z, rounded as one ternary operation.
-
-
-
-
- 239) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the
- fmax functions choose the numeric value. See F.10.9.2.
- 240) The fmin functions are analogous to the fmax functions in their treatment of NaNs.
-
-[page 257] (Contents)
-
- 7.12.14 Comparison macros
-1 The relational and equality operators support the usual mathematical relationships
- between numeric values. For any ordered pair of numeric values exactly one of the
- relationships -- less, greater, and equal -- is true. Relational operators may raise the
- ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a
- numeric value, or for two NaNs, just the unordered relationship is true.241) The following
- subclauses provide macros that are quiet (non floating-point exception raising) versions
- of the relational operators, and other comparison macros that facilitate writing efficient
- code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In
- the synopses in this subclause, real-floating indicates that the argument shall be an
- expression of real floating type242) (both arguments need not have the same type).243)
- 7.12.14.1 The isgreater macro
- Synopsis
-1 #include <math.h>
- int isgreater(real-floating x, real-floating y);
- Description
-2 The isgreater macro determines whether its first argument is greater than its second
- argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
- unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point
- exception when x and y are unordered.
- Returns
-3 The isgreater macro returns the value of (x) > (y).
- 7.12.14.2 The isgreaterequal macro
- Synopsis
-1 #include <math.h>
- int isgreaterequal(real-floating x, real-floating y);
-
-
-
-
- 241) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if
- the operands compare unordered, as an error indicator for programs written without consideration of
- NaNs; the result in these cases is false.
- 242) If any argument is of integer type, or any other type that is not a real floating type, the behavior is
- undefined.
- 243) Whether an argument represented in a format wider than its semantic type is converted to the semantic
- type is unspecified.
-
-[page 258] (Contents)
-
- Description
-2 The isgreaterequal macro determines whether its first argument is greater than or
- equal to its second argument. The value of isgreaterequal(x, y) is always equal
- to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
- not raise the ''invalid'' floating-point exception when x and y are unordered.
- Returns
-3 The isgreaterequal macro returns the value of (x) >= (y).
- 7.12.14.3 The isless macro
- Synopsis
-1 #include <math.h>
- int isless(real-floating x, real-floating y);
- Description
-2 The isless macro determines whether its first argument is less than its second
- argument. The value of isless(x, y) is always equal to (x) < (y); however,
- unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point
- exception when x and y are unordered.
- Returns
-3 The isless macro returns the value of (x) < (y).
- 7.12.14.4 The islessequal macro
- Synopsis
-1 #include <math.h>
- int islessequal(real-floating x, real-floating y);
- Description
-2 The islessequal macro determines whether its first argument is less than or equal to
- its second argument. The value of islessequal(x, y) is always equal to
- (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
- the ''invalid'' floating-point exception when x and y are unordered.
- Returns
-3 The islessequal macro returns the value of (x) <= (y).
-
-
-
-
-[page 259] (Contents)
-
- 7.12.14.5 The islessgreater macro
- Synopsis
-1 #include <math.h>
- int islessgreater(real-floating x, real-floating y);
- Description
-2 The islessgreater macro determines whether its first argument is less than or
- greater than its second argument. The islessgreater(x, y) macro is similar to
- (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
- the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x
- and y twice).
- Returns
-3 The islessgreater macro returns the value of (x) < (y) || (x) > (y).
- 7.12.14.6 The isunordered macro
- Synopsis
-1 #include <math.h>
- int isunordered(real-floating x, real-floating y);
- Description
-2 The isunordered macro determines whether its arguments are unordered.
- Returns
-3 The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.
-
-
-
-
-[page 260] (Contents)
-
- 7.13 Nonlocal jumps <setjmp.h>
-1 The header <setjmp.h> defines the macro setjmp, and declares one function and
- one type, for bypassing the normal function call and return discipline.244)
-2 The type declared is
- jmp_buf
- which is an array type suitable for holding the information needed to restore a calling
- environment. The environment of a call to the setjmp macro consists of information
- sufficient for a call to the longjmp function to return execution to the correct block and
- invocation of that block, were it called recursively. It does not include the state of the
- floating-point status flags, of open files, or of any other component of the abstract
- machine.
-3 It is unspecified whether setjmp is a macro or an identifier declared with external
- linkage. If a macro definition is suppressed in order to access an actual function, or a
- program defines an external identifier with the name setjmp, the behavior is undefined.
- 7.13.1 Save calling environment
- 7.13.1.1 The setjmp macro
- Synopsis
-1 #include <setjmp.h>
- int setjmp(jmp_buf env);
- Description
-2 The setjmp macro saves its calling environment in its jmp_buf argument for later use
- by the longjmp function.
- Returns
-3 If the return is from a direct invocation, the setjmp macro returns the value zero. If the
- return is from a call to the longjmp function, the setjmp macro returns a nonzero
- value.
- Environmental limits
-4 An invocation of the setjmp macro shall appear only in one of the following contexts:
- -- the entire controlling expression of a selection or iteration statement;
- -- one operand of a relational or equality operator with the other operand an integer
- constant expression, with the resulting expression being the entire controlling
-
-
- 244) These functions are useful for dealing with unusual conditions encountered in a low-level function of
- a program.
-
-[page 261] (Contents)
-
- expression of a selection or iteration statement;
- -- the operand of a unary ! operator with the resulting expression being the entire
- controlling expression of a selection or iteration statement; or
- -- the entire expression of an expression statement (possibly cast to void).
-5 If the invocation appears in any other context, the behavior is undefined.
- 7.13.2 Restore calling environment
- 7.13.2.1 The longjmp function
- Synopsis
-1 #include <setjmp.h>
- _Noreturn void longjmp(jmp_buf env, int val);
- Description
-2 The longjmp function restores the environment saved by the most recent invocation of
- the setjmp macro in the same invocation of the program with the corresponding
- jmp_buf argument. If there has been no such invocation, or if the function containing
- the invocation of the setjmp macro has terminated execution245) in the interim, or if the
- invocation of the setjmp macro was within the scope of an identifier with variably
- modified type and execution has left that scope in the interim, the behavior is undefined.
-3 All accessible objects have values, and all other components of the abstract machine246)
- have state, as of the time the longjmp function was called, except that the values of
- objects of automatic storage duration that are local to the function containing the
- invocation of the corresponding setjmp macro that do not have volatile-qualified type
- and have been changed between the setjmp invocation and longjmp call are
- indeterminate.
- Returns
-4 After longjmp is completed, program execution continues as if the corresponding
- invocation of the setjmp macro had just returned the value specified by val. The
- longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
- the setjmp macro returns the value 1.
-5 EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
- might cause memory associated with a variable length array object to be squandered.
-
-
-
-
- 245) For example, by executing a return statement or because another longjmp call has caused a
- transfer to a setjmp invocation in a function earlier in the set of nested calls.
- 246) This includes, but is not limited to, the floating-point status flags and the state of open files.
-
-[page 262] (Contents)
-
- #include <setjmp.h>
- jmp_buf buf;
- void g(int n);
- void h(int n);
- int n = 6;
- void f(void)
- {
- int x[n]; // valid: f is not terminated
- setjmp(buf);
- g(n);
- }
- void g(int n)
- {
- int a[n]; // a may remain allocated
- h(n);
- }
- void h(int n)
- {
- int b[n]; // b may remain allocated
- longjmp(buf, 2); // might cause memory loss
- }
-
-
-
-
-[page 263] (Contents)
-
- 7.14 Signal handling <signal.h>
-1 The header <signal.h> declares a type and two functions and defines several macros,
- for handling various signals (conditions that may be reported during program execution).
-2 The type defined is
- sig_atomic_t
- which is the (possibly volatile-qualified) integer type of an object that can be accessed as
- an atomic entity, even in the presence of asynchronous interrupts.
-3 The macros defined are
- SIG_DFL
- SIG_ERR
- SIG_IGN
- which expand to constant expressions with distinct values that have type compatible with
- the second argument to, and the return value of, the signal function, and whose values
- compare unequal to the address of any declarable function; and the following, which
- expand to positive integer constant expressions with type int and distinct values that are
- the signal numbers, each corresponding to the specified condition:
- SIGABRT abnormal termination, such as is initiated by the abort function
- SIGFPE an erroneous arithmetic operation, such as zero divide or an operation
- resulting in overflow
- SIGILL detection of an invalid function image, such as an invalid instruction
- SIGINT receipt of an interactive attention signal
- SIGSEGV an invalid access to storage
- SIGTERM a termination request sent to the program
-4 An implementation need not generate any of these signals, except as a result of explicit
- calls to the raise function. Additional signals and pointers to undeclarable functions,
- with macro definitions beginning, respectively, with the letters SIG and an uppercase
- letter or with SIG_ and an uppercase letter,247) may also be specified by the
- implementation. The complete set of signals, their semantics, and their default handling
- is implementation-defined; all signal numbers shall be positive.
-
-
-
-
- 247) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms
- (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
- and termination.
-
-[page 264] (Contents)
-
- 7.14.1 Specify signal handling
- 7.14.1.1 The signal function
- Synopsis
-1 #include <signal.h>
- void (*signal(int sig, void (*func)(int)))(int);
- Description
-2 The signal function chooses one of three ways in which receipt of the signal number
- sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
- for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
- Otherwise, func shall point to a function to be called when that signal occurs. An
- invocation of such a function because of a signal, or (recursively) of any further functions
- called by that invocation (other than functions in the standard library),248) is called a
- signal handler.
-3 When a signal occurs and func points to a function, it is implementation-defined
- whether the equivalent of signal(sig, SIG_DFL); is executed or the
- implementation prevents some implementation-defined set of signals (at least including
- sig) from occurring until the current signal handling has completed; in the case of
- SIGILL, the implementation may alternatively define that no action is taken. Then the
- equivalent of (*func)(sig); is executed. If and when the function returns, if the
- value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
- value corresponding to a computational exception, the behavior is undefined; otherwise
- the program will resume execution at the point it was interrupted.
-4 If the signal occurs as the result of calling the abort or raise function, the signal
- handler shall not call the raise function.
-5 If the signal occurs other than as the result of calling the abort or raise function, the
- behavior is undefined if the signal handler refers to any object with static or thread
- storage duration that is not a lock-free atomic object other than by assigning a value to an
- object declared as volatile sig_atomic_t, or the signal handler calls any function
- in the standard library other than the abort function, the _Exit function, the
- quick_exit function, or the signal function with the first argument equal to the
- signal number corresponding to the signal that caused the invocation of the handler.
- Furthermore, if such a call to the signal function results in a SIG_ERR return, the
- value of errno is indeterminate.249)
-
-
- 248) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler
- called via the abort function).
- 249) If any signal is generated by an asynchronous signal handler, the behavior is undefined.
-
-[page 265] (Contents)
-
-6 At program startup, the equivalent of
- signal(sig, SIG_IGN);
- may be executed for some signals selected in an implementation-defined manner; the
- equivalent of
- signal(sig, SIG_DFL);
- is executed for all other signals defined by the implementation.
-7 The implementation shall behave as if no library function calls the signal function.
- Returns
-8 If the request can be honored, the signal function returns the value of func for the
- most recent successful call to signal for the specified signal sig. Otherwise, a value of
- SIG_ERR is returned and a positive value is stored in errno.
- Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
- _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).
- 7.14.2 Send signal
- 7.14.2.1 The raise function
- Synopsis
-1 #include <signal.h>
- int raise(int sig);
- Description
-2 The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
- signal handler is called, the raise function shall not return until after the signal handler
- does.
- Returns
-3 The raise function returns zero if successful, nonzero if unsuccessful.
-
-
-
-
-[page 266] (Contents)
-
- 7.15 Alignment <stdalign.h>
-1 The header <stdalign.h> defines two macros.
-2 The macro
- alignas
- expands to _Alignas.
-3 The remaining macro is suitable for use in #if preprocessing directives. It is
- __alignas_is_defined
- which expands to the integer constant 1.
-
-
-
-
-[page 267] (Contents)
-
- 7.16 Variable arguments <stdarg.h>
-1 The header <stdarg.h> declares a type and defines four macros, for advancing
- through a list of arguments whose number and types are not known to the called function
- when it is translated.
-2 A function may be called with a variable number of arguments of varying types. As
- described in 6.9.1, its parameter list contains one or more parameters. The rightmost
- parameter plays a special role in the access mechanism, and will be designated parmN in
- this description.
-3 The type declared is
- va_list
- which is a complete object type suitable for holding information needed by the macros
- va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
- desired, the called function shall declare an object (generally referred to as ap in this
- subclause) having type va_list. The object ap may be passed as an argument to
- another function; if that function invokes the va_arg macro with parameter ap, the
- value of ap in the calling function is indeterminate and shall be passed to the va_end
- macro prior to any further reference to ap.250)
- 7.16.1 Variable argument list access macros
-1 The va_start and va_arg macros described in this subclause shall be implemented
- as macros, not functions. It is unspecified whether va_copy and va_end are macros or
- identifiers declared with external linkage. If a macro definition is suppressed in order to
- access an actual function, or a program defines an external identifier with the same name,
- the behavior is undefined. Each invocation of the va_start and va_copy macros
- shall be matched by a corresponding invocation of the va_end macro in the same
- function.
- 7.16.1.1 The va_arg macro
- Synopsis
-1 #include <stdarg.h>
- type va_arg(va_list ap, type);
- Description
-2 The va_arg macro expands to an expression that has the specified type and the value of
- the next argument in the call. The parameter ap shall have been initialized by the
- va_start or va_copy macro (without an intervening invocation of the va_end
-
- 250) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
- case the original function may make further use of the original list after the other function returns.
-
-[page 268] (Contents)
-
- macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
- values of successive arguments are returned in turn. The parameter type shall be a type
- name specified such that the type of a pointer to an object that has the specified type can
- be obtained simply by postfixing a * to type. If there is no actual next argument, or if
- type is not compatible with the type of the actual next argument (as promoted according
- to the default argument promotions), the behavior is undefined, except for the following
- cases:
- -- one type is a signed integer type, the other type is the corresponding unsigned integer
- type, and the value is representable in both types;
- -- one type is pointer to void and the other is a pointer to a character type.
- Returns
-3 The first invocation of the va_arg macro after that of the va_start macro returns the
- value of the argument after that specified by parmN . Successive invocations return the
- values of the remaining arguments in succession.
- 7.16.1.2 The va_copy macro
- Synopsis
-1 #include <stdarg.h>
- void va_copy(va_list dest, va_list src);
- Description
-2 The va_copy macro initializes dest as a copy of src, as if the va_start macro had
- been applied to dest followed by the same sequence of uses of the va_arg macro as
- had previously been used to reach the present state of src. Neither the va_copy nor
- va_start macro shall be invoked to reinitialize dest without an intervening
- invocation of the va_end macro for the same dest.
- Returns
-3 The va_copy macro returns no value.
- 7.16.1.3 The va_end macro
- Synopsis
-1 #include <stdarg.h>
- void va_end(va_list ap);
- Description
-2 The va_end macro facilitates a normal return from the function whose variable
- argument list was referred to by the expansion of the va_start macro, or the function
- containing the expansion of the va_copy macro, that initialized the va_list ap. The
- va_end macro may modify ap so that it is no longer usable (without being reinitialized
-
-[page 269] (Contents)
-
- by the va_start or va_copy macro). If there is no corresponding invocation of the
- va_start or va_copy macro, or if the va_end macro is not invoked before the
- return, the behavior is undefined.
- Returns
-3 The va_end macro returns no value.
- 7.16.1.4 The va_start macro
- Synopsis
-1 #include <stdarg.h>
- void va_start(va_list ap, parmN);
- Description
-2 The va_start macro shall be invoked before any access to the unnamed arguments.
-3 The va_start macro initializes ap for subsequent use by the va_arg and va_end
- macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
- without an intervening invocation of the va_end macro for the same ap.
-4 The parameter parmN is the identifier of the rightmost parameter in the variable
- parameter list in the function definition (the one just before the , ...). If the parameter
- parmN is declared with the register storage class, with a function or array type, or
- with a type that is not compatible with the type that results after application of the default
- argument promotions, the behavior is undefined.
- Returns
-5 The va_start macro returns no value.
-6 EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
- more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
- pointers is specified by the first argument to f1.
- #include <stdarg.h>
- #define MAXARGS 31
- void f1(int n_ptrs, ...)
- {
- va_list ap;
- char *array[MAXARGS];
- int ptr_no = 0;
-
-
-
-
-[page 270] (Contents)
-
- if (n_ptrs > MAXARGS)
- n_ptrs = MAXARGS;
- va_start(ap, n_ptrs);
- while (ptr_no < n_ptrs)
- array[ptr_no++] = va_arg(ap, char *);
- va_end(ap);
- f2(n_ptrs, array);
- }
- Each call to f1 is required to have visible the definition of the function or a declaration such as
- void f1(int, ...);
-
-7 EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
- indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
- is gathered again and passed to function f4.
- #include <stdarg.h>
- #define MAXARGS 31
- void f3(int n_ptrs, int f4_after, ...)
- {
- va_list ap, ap_save;
- char *array[MAXARGS];
- int ptr_no = 0;
- if (n_ptrs > MAXARGS)
- n_ptrs = MAXARGS;
- va_start(ap, f4_after);
- while (ptr_no < n_ptrs) {
- array[ptr_no++] = va_arg(ap, char *);
- if (ptr_no == f4_after)
- va_copy(ap_save, ap);
- }
- va_end(ap);
- f2(n_ptrs, array);
- // Now process the saved copy.
- n_ptrs -= f4_after;
- ptr_no = 0;
- while (ptr_no < n_ptrs)
- array[ptr_no++] = va_arg(ap_save, char *);
- va_end(ap_save);
- f4(n_ptrs, array);
- }
-
-
-
-
-[page 271] (Contents)
-
- 7.17 Atomics <stdatomic.h>
- 7.17.1 Introduction
-1 The header <stdatomic.h> defines several macros and declares several types and
- functions for performing atomic operations on data shared between threads.
-2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
- this header nor support any of its facilities.
-3 The macros defined are the atomic lock-free macros
- ATOMIC_CHAR_LOCK_FREE
- ATOMIC_CHAR16_T_LOCK_FREE
- ATOMIC_CHAR32_T_LOCK_FREE
- ATOMIC_WCHAR_T_LOCK_FREE
- ATOMIC_SHORT_LOCK_FREE
- ATOMIC_INT_LOCK_FREE
- ATOMIC_LONG_LOCK_FREE
- ATOMIC_LLONG_LOCK_FREE
- ATOMIC_ADDRESS_LOCK_FREE
- which indicate the lock-free property of the corresponding atomic types (both signed and
- unsigned); and
- ATOMIC_FLAG_INIT
- which expands to an initializer for an object of type atomic_flag.
-4 The types include
- memory_order
- which is an enumerated type whose enumerators identify memory ordering constraints;
- atomic_flag
- which is a structure type representing a lock-free, primitive atomic flag;
- atomic_bool
- which is a structure type representing the atomic analog of the type _Bool;
- atomic_address
- which is a structure type representing the atomic analog of a pointer type; and several
- atomic analogs of integer types.
-5 In the following operation definitions:
- -- An A refers to one of the atomic types.
-
-
-[page 272] (Contents)
-
- -- A C refers to its corresponding non-atomic type. The atomic_address atomic
- type corresponds to the void * non-atomic type.
- -- An M refers to the type of the other argument for arithmetic operations. For atomic
- integer types, M is C. For atomic address types, M is ptrdiff_t.
- -- The functions not ending in _explicit have the same semantics as the
- corresponding _explicit function with memory_order_seq_cst for the
- memory_order argument.
-6 NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not
- changed in the standard. This qualification means that volatility is preserved when applying these
- operations to volatile objects.
-
- 7.17.2 Initialization
- 7.17.2.1 The ATOMIC_VAR_INIT macro
- Synopsis
-1 #include <stdatomic.h>
- #define ATOMIC_VAR_INIT(C value)
- Description
-2 The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
- atomic object of a type that is initialization-compatible with value. An atomic object
- with automatic storage duration that is not explicitly initialized using
- ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
- initialization for objects with static or thread-local storage duration is guaranteed to
- produce a valid state.
-3 Concurrent access to the variable being initialized, even via an atomic operation,
- constitutes a data race.
-4 EXAMPLE
- atomic_int guide = ATOMIC_VAR_INIT(42);
-
- 7.17.2.2 The atomic_init generic function
- Synopsis
-1 #include <stdatomic.h>
- void atomic_init(volatile A *obj, C value);
- Description
-2 The atomic_init generic function initializes the atomic object pointed to by obj to
- the value value, while also initializing any additional state that the implementation
- might need to carry for the atomic object.
-
-
-
-[page 273] (Contents)
-
-3 Although this function initializes an atomic object, it does not avoid data races;
- concurrent access to the variable being initialized, even via an atomic operation,
- constitutes a data race.
- Returns
-4 The atomic_init generic function returns no value.
-5 EXAMPLE
- atomic_int guide;
- atomic_init(&guide, 42);
-
- 7.17.3 Order and consistency
-1 The enumerated type memory_order specifies the detailed regular (non-atomic)
- memory synchronization operations as defined in 5.1.2.4 and may provide for operation
- ordering. Its enumeration constants are as follows:
- memory_order_relaxed
- memory_order_consume
- memory_order_acquire
- memory_order_release
- memory_order_acq_rel
- memory_order_seq_cst
-2 For memory_order_relaxed, no operation orders memory.
-3 For memory_order_release, memory_order_acq_rel, and
- memory_order_seq_cst, a store operation performs a release operation on the
- affected memory location.
-4 For memory_order_acquire, memory_order_acq_rel, and
- memory_order_seq_cst, a load operation performs an acquire operation on the
- affected memory location.
-5 For memory_order_consume, a load operation performs a consume operation on the
- affected memory location.
-6 For memory_order_seq_cst, there shall be a single total order S on all operations,
- consistent with the ''happens before'' order and modification orders for all affected
- locations, such that each memory_order_seq_cst operation that loads a value
- observes either the last preceding modification according to this order S, or the result of
- an operation that is not memory_order_seq_cst.
-7 NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
- an order that does include lock and unlock operations, since the ordering between those is already included
- in the ''happens before'' ordering.
-
-8 NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
- memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic
-
-[page 274] (Contents)
-
- object be indivisible with respect to all other atomic accesses to that object.
-
-9 For an atomic operation B that reads the value of an atomic object M, if there is a
- memory_order_seq_cst fence X sequenced before B, then B observes either the
- last memory_order_seq_cst modification of M preceding X in the total order S or
- a later modification of M in its modification order.
-10 For atomic operations A and B on an atomic object M, where A modifies M and B takes
- its value, if there is a memory_order_seq_cst fence X such that A is sequenced
- before X and B follows X in S, then B observes either the effects of A or a later
- modification of M in its modification order.
-11 For atomic operations A and B on an atomic object M, where A modifies M and B takes
- its value, if there are memory_order_seq_cst fences X and Y such that A is
- sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes
- either the effects of A or a later modification of M in its modification order.
-12 Atomic read-modify-write operations shall always read the last value (in the modification
- order) stored before the write associated with the read-modify-write operation.
-13 An atomic store shall only store a value that has been computed from constants and
- program input values by a finite sequence of program evaluations, such that each
- evaluation observes the values of variables as computed by the last prior assignment in
- the sequence.251) The ordering of evaluations in this sequence shall be such that
- -- If an evaluation B observes a value computed by A in a different thread, then B does
- not happen before A.
- -- If an evaluation A is included in the sequence, then all evaluations that assign to the
- same variable and happen before A are also included.
-14 NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when
- relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
- sequence out of thread order. For example, with x and y initially zero,
- // Thread 1:
- r1 = atomic_load_explicit(&y, memory_order_relaxed);
- atomic_store_explicit(&x, r1, memory_order_relaxed);
-
- // Thread 2:
- r2 = atomic_load_explicit(&x, memory_order_relaxed);
- atomic_store_explicit(&y, 42, memory_order_relaxed);
- is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:
-
-
-
-
- 251) Among other implications, atomic variables shall not decay.
-
-[page 275] (Contents)
-
- atomic_store_explicit(&y, 42, memory_order_relaxed);
- r1 = atomic_load_explicit(&y, memory_order_relaxed);
- atomic_store_explicit(&x, r1, memory_order_relaxed);
- r2 = atomic_load_explicit(&x, memory_order_relaxed);
- On the other hand,
- // Thread 1:
- r1 = atomic_load_explicit(&y, memory_order_relaxed);
- atomic_store_explicit(&x, r1, memory_order_relaxed);
-
- // Thread 2:
- r2 = atomic_load_explicit(&x, memory_order_relaxed);
- atomic_store_explicit(&y, r2, memory_order_relaxed);
- is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results
- in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with
- weaker than memory_order_acq_rel ordering, the second requirement has no impact.
-
- Recommended practice
-15 The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
- with x and y initially zero:
- // Thread 1:
- r1 = atomic_load_explicit(&x, memory_order_relaxed);
- if (r1 == 42)
- atomic_store_explicit(&y, r1, memory_order_relaxed);
-
- // Thread 2:
- r2 = atomic_load_explicit(&y, memory_order_relaxed);
- if (r2 == 42)
- atomic_store_explicit(&x, 42, memory_order_relaxed);
- However, this is not useful behavior, and implementations should not allow it.
-16 Implementations should make atomic stores visible to atomic loads within a reasonable
- amount of time.
- 7.17.3.1 The kill_dependency macro
- Synopsis
-1 #include <stdatomic.h>
- type kill_dependency(type y);
- Description
-2 The kill_dependency macro terminates a dependency chain; the argument does not
- carry a dependency to the return value.
-
-
-
-[page 276] (Contents)
-
- Returns
-3 The kill_dependency macro returns the value of y.
- 7.17.4 Fences
-1 This subclause introduces synchronization primitives called fences. Fences can have
- acquire semantics, release semantics, or both. A fence with acquire semantics is called
- an acquire fence; a fence with release semantics is called a release fence.
-2 A release fence A synchronizes with an acquire fence B if there exist atomic operations
- X and Y , both operating on some atomic object M, such that A is sequenced before X, X
- modifies M, Y is sequenced before B, and Y reads the value written by X or a value
- written by any side effect in the hypothetical release sequence X would head if it were a
- release operation.
-3 A release fence A synchronizes with an atomic operation B that performs an acquire
- operation on an atomic object M if there exists an atomic operation X such that A is
- sequenced before X, X modifies M, and B reads the value written by X or a value written
- by any side effect in the hypothetical release sequence X would head if it were a release
- operation.
-4 An atomic operation A that is a release operation on an atomic object M synchronizes
- with an acquire fence B if there exists some atomic operation X on M such that X is
- sequenced before B and reads the value written by A or a value written by any side effect
- in the release sequence headed by A.
- 7.17.4.1 The atomic_thread_fence function
- Synopsis
-1 #include <stdatomic.h>
- void atomic_thread_fence(memory_order order);
- Description
-2 Depending on the value of order, this operation:
- -- has no effects, if order == memory_order_relaxed;
- -- is an acquire fence, if order == memory_order_acquire or order ==
- memory_order_consume;
- -- is a release fence, if order == memory_order_release;
- -- is both an acquire fence and a release fence, if order ==
- memory_order_acq_rel;
- -- is a sequentially consistent acquire and release fence, if order ==
- memory_order_seq_cst.
-
-
-[page 277] (Contents)
-
- Returns
-3 The atomic_thread_fence function returns no value.
- 7.17.4.2 The atomic_signal_fence function
- Synopsis
-1 #include <stdatomic.h>
- void atomic_signal_fence(memory_order order);
- Description
-2 Equivalent to atomic_thread_fence(order), except that ''synchronizes with''
- relationships are established only between a thread and a signal handler executed in the
- same thread.
-3 NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
- performed by the thread become visible to the signal handler.
-
-4 NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
- atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
- have inserted are not emitted.
-
- Returns
-5 The atomic_signal_fence function returns no value.
- 7.17.5 Lock-free property
-1 The atomic lock-free macros indicate the lock-free property of integer and address atomic
- types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
- the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.
-2 NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
- memory location via two different addresses will communicate atomically. The implementation should not
- depend on any per-process state. This restriction enables communication via memory mapped into a
- process more than once and memory shared between two processes.
-
- 7.17.5.1 The atomic_is_lock_free generic function
- Synopsis
-1 #include <stdatomic.h>
- _Bool atomic_is_lock_free(atomic_type const volatile *obj);
- Description
-2 The atomic_is_lock_free generic function indicates whether or not the object
- pointed to by obj is lock-free. atomic_type can be any atomic type.
- Returns
-3 The atomic_is_lock_free generic function returns nonzero (true) if and only if the
- object's operations are lock-free. The result of a lock-free query on one object cannot be
-
-[page 278] (Contents)
-
- inferred from the result of a lock-free query on another object.
- 7.17.6 Atomic integer and address types
-1 For each line in the following table, the atomic type name is declared as the
- corresponding direct type.
-
-
-
-
-[page 279] (Contents)
-
- Atomic type name Direct type
- atomic_char _Atomic char
- atomic_schar _Atomic signed char
- atomic_uchar _Atomic unsigned char
- atomic_short _Atomic short
- atomic_ushort _Atomic unsigned short
- atomic_int _Atomic int
- atomic_uint _Atomic unsigned int
- atomic_long _Atomic long
- atomic_ulong _Atomic unsigned long
- atomic_llong _Atomic long long
- atomic_ullong _Atomic unsigned long long
- atomic_char16_t _Atomic char16_t
- atomic_char32_t _Atomic char32_t
- atomic_wchar_t _Atomic wchar_t
- atomic_int_least8_t _Atomic int_least8_t
- atomic_uint_least8_t _Atomic uint_least8_t
- atomic_int_least16_t _Atomic int_least16_t
- atomic_uint_least16_t _Atomic uint_least16_t
- atomic_int_least32_t _Atomic int_least32_t
- atomic_uint_least32_t _Atomic uint_least32_t
- atomic_int_least64_t _Atomic int_least64_t
- atomic_uint_least64_t _Atomic uint_least64_t
- atomic_int_fast8_t _Atomic int_fast8_t
- atomic_uint_fast8_t _Atomic uint_fast8_t
- atomic_int_fast16_t _Atomic int_fast16_t
- atomic_uint_fast16_t _Atomic uint_fast16_t
- atomic_int_fast32_t _Atomic int_fast32_t
- atomic_uint_fast32_t _Atomic uint_fast32_t
- atomic_int_fast64_t _Atomic int_fast64_t
- atomic_uint_fast64_t _Atomic uint_fast64_t
- atomic_intptr_t _Atomic intptr_t
- atomic_uintptr_t _Atomic uintptr_t
- atomic_size_t _Atomic size_t
- atomic_ptrdiff_t _Atomic ptrdiff_t
- atomic_intmax_t _Atomic intmax_t
- atomic_uintmax_t _Atomic uintmax_t
-2 The semantics of the operations on these types are defined in 7.17.7.
-3 The atomic_bool type provides an atomic boolean.
-
-
-[page 280] (Contents)
-
-4 The atomic_address type provides atomic void * operations. The unit of
- addition/subtraction shall be one byte.
-5 NOTE The representation of atomic integer and address types need not have the same size as their
- corresponding regular types. They should have the same size whenever possible, as it eases effort required
- to port existing code.
-
- 7.17.7 Operations on atomic types
-1 There are only a few kinds of operations on atomic types, though there are many
- instances of those kinds. This subclause specifies each general kind.
- 7.17.7.1 The atomic_store generic functions
- Synopsis
-1 #include <stdatomic.h>
- void atomic_store(volatile A *object, C desired);
- void atomic_store_explicit(volatile A *object,
- C desired, memory_order order);
- Description
-2 The order argument shall not be memory_order_acquire,
- memory_order_consume, nor memory_order_acq_rel. Atomically replace the
- value pointed to by object with the value of desired. Memory is affected according
- to the value of order.
- Returns
-3 The atomic_store generic functions return no value.
- 7.17.7.2 The atomic_load generic functions
- Synopsis
-1 #include <stdatomic.h>
- C atomic_load(volatile A *object);
- C atomic_load_explicit(volatile A *object,
- memory_order order);
- Description
-2 The order argument shall not be memory_order_release nor
- memory_order_acq_rel. Memory is affected according to the value of order.
- Returns
- Atomically returns the value pointed to by object.
-
-
-
-
-[page 281] (Contents)
-
- 7.17.7.3 The atomic_exchange generic functions
- Synopsis
-1 #include <stdatomic.h>
- C atomic_exchange(volatile A *object, C desired);
- C atomic_exchange_explicit(volatile A *object,
- C desired, memory_order order);
- Description
-2 Atomically replace the value pointed to by object with desired. Memory is affected
- according to the value of order. These operations are read-modify-write operations
- (5.1.2.4).
- Returns
-3 Atomically returns the value pointed to by object immediately before the effects.
- 7.17.7.4 The atomic_compare_exchange generic functions
- Synopsis
-1 #include <stdatomic.h>
- _Bool atomic_compare_exchange_strong(volatile A *object,
- C *expected, C desired);
- _Bool atomic_compare_exchange_strong_explicit(
- volatile A *object, C *expected, C desired,
- memory_order success, memory_order failure);
- _Bool atomic_compare_exchange_weak(volatile A *object,
- C *expected, C desired);
- _Bool atomic_compare_exchange_weak_explicit(
- volatile A *object, C *expected, C desired,
- memory_order success, memory_order failure);
- Description
-2 The failure argument shall not be memory_order_release nor
- memory_order_acq_rel. The failure argument shall be no stronger than the
- success argument. Atomically, compares the value pointed to by object for equality
- with that in expected, and if true, replaces the value pointed to by object with
- desired, and if false, updates the value in expected with the value pointed to by
- object. Further, if the comparison is true, memory is affected according to the value of
- success, and if the comparison is false, memory is affected according to the value of
- failure. These operations are atomic read-modify-write operations (5.1.2.4).
-3 NOTE 1 The effect of the compare-and-exchange operations is
-
-
-
-
-[page 282] (Contents)
-
- if (*object == *expected)
- *object = desired;
- else
- *expected = *object;
-
-4 The weak compare-and-exchange operations may fail spuriously, that is, return zero
- while leaving the value pointed to by expected unchanged.
-5 NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
- machines, e.g. load-locked store-conditional machines.
-
-6 EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
- be in a loop.
- exp = atomic_load(&cur);
- do {
- des = function(exp);
- } while (!atomic_compare_exchange_weak(&cur, &exp, des));
- When a compare-and-exchange is in a loop, the weak version will yield better performance on some
- platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
- strong one is preferable.
-
- Returns
-7 The result of the comparison.
- 7.17.7.5 The atomic_fetch and modify generic functions
-1 The following operations perform arithmetic and bitwise computations. All of these
- operations are applicable to an object of any atomic integer type. Only addition and
- subtraction are applicable to atomic_address. None of these operations is applicable
- to atomic_bool. The key, operator, and computation correspondence is:
- key op computation
- add + addition
- sub - subtraction
- or | bitwise inclusive or
- xor ^ bitwise exclusive or
- and & bitwise and
- Synopsis
-2 #include <stdatomic.h>
- C atomic_fetch_key(volatile A *object, M operand);
- C atomic_fetch_key_explicit(volatile A *object,
- M operand, memory_order order);
- Description
-3 Atomically replaces the value pointed to by object with the result of the computation
- applied to the value pointed to by object and the given operand. Memory is affected
- according to the value of order. These operations are atomic read-modify-write
-[page 283] (Contents)
-
- operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's
- complement representation with silent wrap-around on overflow; there are no undefined
- results. For address types, the result may be an undefined address, but the operations
- otherwise have no undefined behavior.
- Returns
-4 Atomically, the value pointed to by object immediately before the effects.
-5 NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
- operation of the corresponding op= compound assignment operators. The only differences are that the
- compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
- compound assignment operator is the updated value of the object, whereas the value returned by the
- atomic_fetch and modify generic functions is the previous value of the atomic object.
-
- 7.17.8 Atomic flag type and operations
-1 The atomic_flag type provides the classic test-and-set functionality. It has two
- states, set and clear.
-2 Operations on an object of type atomic_flag shall be lock free.
-3 NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
- the atomic_flag type is the minimum hardware-implemented type needed to conform to this
- International standard. The remaining types can be emulated with atomic_flag, though with less than
- ideal properties.
-
-4 The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
- clear state. An atomic_flag that is not explicitly initialized with
- ATOMIC_FLAG_INIT is initially in an indeterminate state.
-5 EXAMPLE
- atomic_flag guard = ATOMIC_FLAG_INIT;
-
- 7.17.8.1 The atomic_flag_test_and_set functions
- Synopsis
-1 #include <stdatomic.h>
- bool atomic_flag_test_and_set(
- volatile atomic_flag *object);
- bool atomic_flag_test_and_set_explicit(
- volatile atomic_flag *object, memory_order order);
- Description
-2 Atomically sets the value pointed to by object to true. Memory is affected according
- to the value of order. These operations are atomic read-modify-write operations
- (5.1.2.4).
-
-
-
-
-[page 284] (Contents)
-
- Returns
-3 Atomically, the value of the object immediately before the effects.
- 7.17.8.2 The atomic_flag_clear functions
- Synopsis
-1 #include <stdatomic.h>
- void atomic_flag_clear(volatile atomic_flag *object);
- void atomic_flag_clear_explicit(
- volatile atomic_flag *object, memory_order order);
- Description
-2 The order argument shall not be memory_order_acquire nor
- memory_order_acq_rel. Atomically sets the value pointed to by object to false.
- Memory is affected according to the value of order.
- Returns
-3 The atomic_flag_clear functions return no value.
-
-
-
-
-[page 285] (Contents)
-
- 7.18 Boolean type and values <stdbool.h>
-1 The header <stdbool.h> defines four macros.
-2 The macro
- bool
- expands to _Bool.
-3 The remaining three macros are suitable for use in #if preprocessing directives. They
- are
- true
- which expands to the integer constant 1,
- false
- which expands to the integer constant 0, and
- __bool_true_false_are_defined
- which expands to the integer constant 1.
-4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
- redefine the macros bool, true, and false.252)
-
-
-
-
- 252) See ''future library directions'' (7.30.7).
-
-[page 286] (Contents)
-
- 7.19 Common definitions <stddef.h>
-1 The header <stddef.h> defines the following macros and declares the following types.
- Some are also defined in other headers, as noted in their respective subclauses.
-2 The types are
- ptrdiff_t
- which is the signed integer type of the result of subtracting two pointers;
- size_t
- which is the unsigned integer type of the result of the sizeof operator;
- max_align_t
- which is an object type whose alignment is as great as is supported by the implementation
- in all contexts; and
- wchar_t
- which is an integer type whose range of values can represent distinct codes for all
- members of the largest extended character set specified among the supported locales; the
- null character shall have the code value zero. Each member of the basic character set
- shall have a code value equal to its value when used as the lone character in an integer
- character constant if an implementation does not define
- __STDC_MB_MIGHT_NEQ_WC__.
-3 The macros are
- NULL
- which expands to an implementation-defined null pointer constant; and
- offsetof(type, member-designator)
- which expands to an integer constant expression that has type size_t, the value of
- which is the offset in bytes, to the structure member (designated by member-designator),
- from the beginning of its structure (designated by type). The type and member designator
- shall be such that given
- static type t;
- then the expression &(t.member-designator) evaluates to an address constant. (If the
- specified member is a bit-field, the behavior is undefined.)
- Recommended practice
-4 The types used for size_t and ptrdiff_t should not have an integer conversion rank
- greater than that of signed long int unless the implementation supports objects
- large enough to make this necessary.
-
-[page 287] (Contents)
-
-Forward references: localization (7.11).
-
-
-
-
-[page 288] (Contents)
-
- 7.20 Integer types <stdint.h>
-1 The header <stdint.h> declares sets of integer types having specified widths, and
- defines corresponding sets of macros.253) It also defines macros that specify limits of
- integer types corresponding to types defined in other standard headers.
-2 Types are defined in the following categories:
- -- integer types having certain exact widths;
- -- integer types having at least certain specified widths;
- -- fastest integer types having at least certain specified widths;
- -- integer types wide enough to hold pointers to objects;
- -- integer types having greatest width.
- (Some of these types may denote the same type.)
-3 Corresponding macros specify limits of the declared types and construct suitable
- constants.
-4 For each type described herein that the implementation provides,254) <stdint.h> shall
- declare that typedef name and define the associated macros. Conversely, for each type
- described herein that the implementation does not provide, <stdint.h> shall not
- declare that typedef name nor shall it define the associated macros. An implementation
- shall provide those types described as ''required'', but need not provide any of the others
- (described as ''optional'').
- 7.20.1 Integer types
-1 When typedef names differing only in the absence or presence of the initial u are defined,
- they shall denote corresponding signed and unsigned types as described in 6.2.5; an
- implementation providing one of these corresponding types shall also provide the other.
-2 In the following descriptions, the symbol N represents an unsigned decimal integer with
- no leading zeros (e.g., 8 or 24, but not 04 or 048).
-
-
-
-
- 253) See ''future library directions'' (7.30.8).
- 254) Some of these types may denote implementation-defined extended integer types.
-
-[page 289] (Contents)
-
- 7.20.1.1 Exact-width integer types
-1 The typedef name intN_t designates a signed integer type with width N , no padding
- bits, and a two's complement representation. Thus, int8_t denotes such a signed
- integer type with a width of exactly 8 bits.
-2 The typedef name uintN_t designates an unsigned integer type with width N and no
- padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
- exactly 24 bits.
-3 These types are optional. However, if an implementation provides integer types with
- widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
- two's complement representation, it shall define the corresponding typedef names.
- 7.20.1.2 Minimum-width integer types
-1 The typedef name int_leastN_t designates a signed integer type with a width of at
- least N , such that no signed integer type with lesser size has at least the specified width.
- Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
-2 The typedef name uint_leastN_t designates an unsigned integer type with a width
- of at least N , such that no unsigned integer type with lesser size has at least the specified
- width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
- least 16 bits.
-3 The following types are required:
- int_least8_t uint_least8_t
- int_least16_t uint_least16_t
- int_least32_t uint_least32_t
- int_least64_t uint_least64_t
- All other types of this form are optional.
- 7.20.1.3 Fastest minimum-width integer types
-1 Each of the following types designates an integer type that is usually fastest255) to operate
- with among all integer types that have at least the specified width.
-2 The typedef name int_fastN_t designates the fastest signed integer type with a width
- of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
- type with a width of at least N .
-
-
-
-
- 255) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
- grounds for choosing one type over another, it will simply pick some integer type satisfying the
- signedness and width requirements.
-
-[page 290] (Contents)
-
-3 The following types are required:
- int_fast8_t uint_fast8_t
- int_fast16_t uint_fast16_t
- int_fast32_t uint_fast32_t
- int_fast64_t uint_fast64_t
- All other types of this form are optional.
- 7.20.1.4 Integer types capable of holding object pointers
-1 The following type designates a signed integer type with the property that any valid
- pointer to void can be converted to this type, then converted back to pointer to void,
- and the result will compare equal to the original pointer:
- intptr_t
- The following type designates an unsigned integer type with the property that any valid
- pointer to void can be converted to this type, then converted back to pointer to void,
- and the result will compare equal to the original pointer:
- uintptr_t
- These types are optional.
- 7.20.1.5 Greatest-width integer types
-1 The following type designates a signed integer type capable of representing any value of
- any signed integer type:
- intmax_t
- The following type designates an unsigned integer type capable of representing any value
- of any unsigned integer type:
- uintmax_t
- These types are required.
- 7.20.2 Limits of specified-width integer types
-1 The following object-like macros specify the minimum and maximum limits of the types *
- declared in <stdint.h>. Each macro name corresponds to a similar type name in
- 7.20.1.
-2 Each instance of any defined macro shall be replaced by a constant expression suitable
- for use in #if preprocessing directives, and this expression shall have the same type as
- would an expression that is an object of the corresponding type converted according to
- the integer promotions. Its implementation-defined value shall be equal to or greater in
- magnitude (absolute value) than the corresponding value given below, with the same sign,
- except where stated to be exactly the given value.
-
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-
- 7.20.2.1 Limits of exact-width integer types
-1 -- minimum values of exact-width signed integer types
- INTN_MIN exactly -(2 N -1 )
- -- maximum values of exact-width signed integer types
- INTN_MAX exactly 2 N -1 - 1
- -- maximum values of exact-width unsigned integer types
- UINTN_MAX exactly 2 N - 1
- 7.20.2.2 Limits of minimum-width integer types
-1 -- minimum values of minimum-width signed integer types
- INT_LEASTN_MIN -(2 N -1 - 1)
- -- maximum values of minimum-width signed integer types
- INT_LEASTN_MAX 2 N -1 - 1
- -- maximum values of minimum-width unsigned integer types
- UINT_LEASTN_MAX 2N - 1
- 7.20.2.3 Limits of fastest minimum-width integer types
-1 -- minimum values of fastest minimum-width signed integer types
- INT_FASTN_MIN -(2 N -1 - 1)
- -- maximum values of fastest minimum-width signed integer types
- INT_FASTN_MAX 2 N -1 - 1
- -- maximum values of fastest minimum-width unsigned integer types
- UINT_FASTN_MAX 2N - 1
- 7.20.2.4 Limits of integer types capable of holding object pointers
-1 -- minimum value of pointer-holding signed integer type
- INTPTR_MIN -(215 - 1)
- -- maximum value of pointer-holding signed integer type
- INTPTR_MAX 215 - 1
- -- maximum value of pointer-holding unsigned integer type
- UINTPTR_MAX 216 - 1
-
-
-
-[page 292] (Contents)
-
- 7.20.2.5 Limits of greatest-width integer types
-1 -- minimum value of greatest-width signed integer type
- INTMAX_MIN -(263 - 1)
- -- maximum value of greatest-width signed integer type
- INTMAX_MAX 263 - 1
- -- maximum value of greatest-width unsigned integer type
- UINTMAX_MAX 264 - 1
- 7.20.3 Limits of other integer types
-1 The following object-like macros specify the minimum and maximum limits of integer *
- types corresponding to types defined in other standard headers.
-2 Each instance of these macros shall be replaced by a constant expression suitable for use
- in #if preprocessing directives, and this expression shall have the same type as would an
- expression that is an object of the corresponding type converted according to the integer
- promotions. Its implementation-defined value shall be equal to or greater in magnitude
- (absolute value) than the corresponding value given below, with the same sign. An
- implementation shall define only the macros corresponding to those typedef names it
- actually provides.256)
- -- limits of ptrdiff_t
- PTRDIFF_MIN -65535
- PTRDIFF_MAX +65535
- -- limits of sig_atomic_t
- SIG_ATOMIC_MIN see below
- SIG_ATOMIC_MAX see below
- -- limit of size_t
- SIZE_MAX 65535
- -- limits of wchar_t
- WCHAR_MIN see below
- WCHAR_MAX see below
- -- limits of wint_t
-
-
-
-
- 256) A freestanding implementation need not provide all of these types.
-
-[page 293] (Contents)
-
- WINT_MIN see below
- WINT_MAX see below
-3 If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
- SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX
- shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
- type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
- SIG_ATOMIC_MAX shall be no less than 255.
-4 If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
- shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127;
- otherwise, wchar_t is defined as an unsigned integer type, and the value of
- WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.257)
-5 If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall
- be no greater than -32767 and the value of WINT_MAX shall be no less than 32767;
- otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
- shall be 0 and the value of WINT_MAX shall be no less than 65535.
- 7.20.4 Macros for integer constants
-1 The following function-like macros expand to integer constants suitable for initializing *
- objects that have integer types corresponding to types defined in <stdint.h>. Each
- macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.
-2 The argument in any instance of these macros shall be an unsuffixed integer constant (as
- defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
-3 Each invocation of one of these macros shall expand to an integer constant expression
- suitable for use in #if preprocessing directives. The type of the expression shall have
- the same type as would an expression of the corresponding type converted according to
- the integer promotions. The value of the expression shall be that of the argument.
- 7.20.4.1 Macros for minimum-width integer constants
-1 The macro INTN_C(value) shall expand to an integer constant expression
- corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
- to an integer constant expression corresponding to the type uint_leastN_t. For
- example, if uint_least64_t is a name for the type unsigned long long int,
- then UINT64_C(0x123) might expand to the integer constant 0x123ULL.
-
-
-
-
- 257) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
- character set.
-
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-
- 7.20.4.2 Macros for greatest-width integer constants
-1 The following macro expands to an integer constant expression having the value specified
- by its argument and the type intmax_t:
- INTMAX_C(value)
- The following macro expands to an integer constant expression having the value specified
- by its argument and the type uintmax_t:
- UINTMAX_C(value)
-
-
-
-
-[page 295] (Contents)
-
- 7.21 Input/output <stdio.h>
- 7.21.1 Introduction
-1 The header <stdio.h> defines several macros, and declares three types and many
- functions for performing input and output.
-2 The types declared are size_t (described in 7.19);
- FILE
- which is an object type capable of recording all the information needed to control a
- stream, including its file position indicator, a pointer to its associated buffer (if any), an
- error indicator that records whether a read/write error has occurred, and an end-of-file
- indicator that records whether the end of the file has been reached; and
- fpos_t
- which is a complete object type other than an array type capable of recording all the
- information needed to specify uniquely every position within a file.
-3 The macros are NULL (described in 7.19);
- _IOFBF
- _IOLBF
- _IONBF
- which expand to integer constant expressions with distinct values, suitable for use as the
- third argument to the setvbuf function;
- BUFSIZ
- which expands to an integer constant expression that is the size of the buffer used by the
- setbuf function;
- EOF
- which expands to an integer constant expression, with type int and a negative value, that
- is returned by several functions to indicate end-of-file, that is, no more input from a
- stream;
- FOPEN_MAX
- which expands to an integer constant expression that is the minimum number of files that
- the implementation guarantees can be open simultaneously;
- FILENAME_MAX
- which expands to an integer constant expression that is the size needed for an array of
- char large enough to hold the longest file name string that the implementation
-
-
-
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-
- guarantees can be opened;258)
- L_tmpnam
- which expands to an integer constant expression that is the size needed for an array of
- char large enough to hold a temporary file name string generated by the tmpnam
- function;
- SEEK_CUR
- SEEK_END
- SEEK_SET
- which expand to integer constant expressions with distinct values, suitable for use as the
- third argument to the fseek function;
- TMP_MAX
- which expands to an integer constant expression that is the minimum number of unique
- file names that can be generated by the tmpnam function;
- stderr
- stdin
- stdout
- which are expressions of type ''pointer to FILE'' that point to the FILE objects
- associated, respectively, with the standard error, input, and output streams.
-4 The header <wchar.h> declares a number of functions useful for wide character input
- and output. The wide character input/output functions described in that subclause
- provide operations analogous to most of those described here, except that the
- fundamental units internal to the program are wide characters. The external
- representation (in the file) is a sequence of ''generalized'' multibyte characters, as
- described further in 7.21.3.
-5 The input/output functions are given the following collective terms:
- -- The wide character input functions -- those functions described in 7.28 that perform
- input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
- fwscanf, wscanf, vfwscanf, and vwscanf.
- -- The wide character output functions -- those functions described in 7.28 that perform
- output from wide characters and wide strings: fputwc, fputws, putwc,
- putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.
-
-
- 258) If the implementation imposes no practical limit on the length of file name strings, the value of
- FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
- string. Of course, file name string contents are subject to other system-specific constraints; therefore
- all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.
-
-[page 297] (Contents)
-
- -- The wide character input/output functions -- the union of the ungetwc function, the
- wide character input functions, and the wide character output functions.
- -- The byte input/output functions -- those functions described in this subclause that
- perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
- fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf, *
- ungetc, vfprintf, vfscanf, vprintf, and vscanf.
- Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
- tmpnam function (7.21.4.4), <wchar.h> (7.28).
- 7.21.2 Streams
-1 Input and output, whether to or from physical devices such as terminals and tape drives,
- or whether to or from files supported on structured storage devices, are mapped into
- logical data streams, whose properties are more uniform than their various inputs and
- outputs. Two forms of mapping are supported, for text streams and for binary
- streams.259)
-2 A text stream is an ordered sequence of characters composed into lines, each line
- consisting of zero or more characters plus a terminating new-line character. Whether the
- last line requires a terminating new-line character is implementation-defined. Characters
- may have to be added, altered, or deleted on input and output to conform to differing
- conventions for representing text in the host environment. Thus, there need not be a one-
- to-one correspondence between the characters in a stream and those in the external
- representation. Data read in from a text stream will necessarily compare equal to the data
- that were earlier written out to that stream only if: the data consist only of printing
- characters and the control characters horizontal tab and new-line; no new-line character is
- immediately preceded by space characters; and the last character is a new-line character.
- Whether space characters that are written out immediately before a new-line character
- appear when read in is implementation-defined.
-3 A binary stream is an ordered sequence of characters that can transparently record
- internal data. Data read in from a binary stream shall compare equal to the data that were
- earlier written out to that stream, under the same implementation. Such a stream may,
- however, have an implementation-defined number of null characters appended to the end
- of the stream.
-4 Each stream has an orientation. After a stream is associated with an external file, but
- before any operations are performed on it, the stream is without orientation. Once a wide
- character input/output function has been applied to a stream without orientation, the
-
-
- 259) An implementation need not distinguish between text streams and binary streams. In such an
- implementation, there need be no new-line characters in a text stream nor any limit to the length of a
- line.
-
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-
- stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
- been applied to a stream without orientation, the stream becomes a byte-oriented stream.
- Only a call to the freopen function or the fwide function can otherwise alter the
- orientation of a stream. (A successful call to freopen removes any orientation.)260)
-5 Byte input/output functions shall not be applied to a wide-oriented stream and wide
- character input/output functions shall not be applied to a byte-oriented stream. The
- remaining stream operations do not affect, and are not affected by, a stream's orientation,
- except for the following additional restrictions:
- -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both
- text and binary streams.
- -- For wide-oriented streams, after a successful call to a file-positioning function that
- leaves the file position indicator prior to the end-of-file, a wide character output
- function can overwrite a partial multibyte character; any file contents beyond the
- byte(s) written are henceforth indeterminate.
-6 Each wide-oriented stream has an associated mbstate_t object that stores the current
- parse state of the stream. A successful call to fgetpos stores a representation of the
- value of this mbstate_t object as part of the value of the fpos_t object. A later
- successful call to fsetpos using the same stored fpos_t value restores the value of
- the associated mbstate_t object as well as the position within the controlled stream.
- Environmental limits
-7 An implementation shall support text files with lines containing at least 254 characters,
- including the terminating new-line character. The value of the macro BUFSIZ shall be at
- least 256.
- Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5),
- mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function
- (7.21.9.3).
-
-
-
-
- 260) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.
-
-[page 299] (Contents)
-
- 7.21.3 Files
-1 A stream is associated with an external file (which may be a physical device) by opening
- a file, which may involve creating a new file. Creating an existing file causes its former
- contents to be discarded, if necessary. If a file can support positioning requests (such as a
- disk file, as opposed to a terminal), then a file position indicator associated with the
- stream is positioned at the start (character number zero) of the file, unless the file is
- opened with append mode in which case it is implementation-defined whether the file
- position indicator is initially positioned at the beginning or the end of the file. The file
- position indicator is maintained by subsequent reads, writes, and positioning requests, to
- facilitate an orderly progression through the file.
-2 Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
- stream causes the associated file to be truncated beyond that point is implementation-
- defined.
-3 When a stream is unbuffered, characters are intended to appear from the source or at the
- destination as soon as possible. Otherwise characters may be accumulated and
- transmitted to or from the host environment as a block. When a stream is fully buffered,
- characters are intended to be transmitted to or from the host environment as a block when
- a buffer is filled. When a stream is line buffered, characters are intended to be
- transmitted to or from the host environment as a block when a new-line character is
- encountered. Furthermore, characters are intended to be transmitted as a block to the host
- environment when a buffer is filled, when input is requested on an unbuffered stream, or
- when input is requested on a line buffered stream that requires the transmission of
- characters from the host environment. Support for these characteristics is
- implementation-defined, and may be affected via the setbuf and setvbuf functions.
-4 A file may be disassociated from a controlling stream by closing the file. Output streams
- are flushed (any unwritten buffer contents are transmitted to the host environment) before
- the stream is disassociated from the file. The value of a pointer to a FILE object is
- indeterminate after the associated file is closed (including the standard text streams).
- Whether a file of zero length (on which no characters have been written by an output
- stream) actually exists is implementation-defined.
-5 The file may be subsequently reopened, by the same or another program execution, and
- its contents reclaimed or modified (if it can be repositioned at its start). If the main
- function returns to its original caller, or if the exit function is called, all open files are
- closed (hence all output streams are flushed) before program termination. Other paths to
- program termination, such as calling the abort function, need not close all files
- properly.
-6 The address of the FILE object used to control a stream may be significant; a copy of a
- FILE object need not serve in place of the original.
-
-[page 300] (Contents)
-
-7 At program startup, three text streams are predefined and need not be opened explicitly
- -- standard input (for reading conventional input), standard output (for writing
- conventional output), and standard error (for writing diagnostic output). As initially
- opened, the standard error stream is not fully buffered; the standard input and standard
- output streams are fully buffered if and only if the stream can be determined not to refer
- to an interactive device.
-8 Functions that open additional (nontemporary) files require a file name, which is a string.
- The rules for composing valid file names are implementation-defined. Whether the same
- file can be simultaneously open multiple times is also implementation-defined.
-9 Although both text and binary wide-oriented streams are conceptually sequences of wide
- characters, the external file associated with a wide-oriented stream is a sequence of
- multibyte characters, generalized as follows:
- -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte
- encodings valid for use internal to the program).
- -- A file need not begin nor end in the initial shift state.261)
-10 Moreover, the encodings used for multibyte characters may differ among files. Both the
- nature and choice of such encodings are implementation-defined.
-11 The wide character input functions read multibyte characters from the stream and convert
- them to wide characters as if they were read by successive calls to the fgetwc function.
- Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
- described by the stream's own mbstate_t object. The byte input functions read
- characters from the stream as if by successive calls to the fgetc function.
-12 The wide character output functions convert wide characters to multibyte characters and
- write them to the stream as if they were written by successive calls to the fputwc
- function. Each conversion occurs as if by a call to the wcrtomb function, with the
- conversion state described by the stream's own mbstate_t object. The byte output
- functions write characters to the stream as if by successive calls to the fputc function.
-13 In some cases, some of the byte input/output functions also perform conversions between
- multibyte characters and wide characters. These conversions also occur as if by calls to
- the mbrtowc and wcrtomb functions.
-14 An encoding error occurs if the character sequence presented to the underlying
- mbrtowc function does not form a valid (generalized) multibyte character, or if the code
- value passed to the underlying wcrtomb does not correspond to a valid (generalized)
-
-
- 261) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
- undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
- with state-dependent encoding that does not assuredly end in the initial shift state.
-
-[page 301] (Contents)
-
- multibyte character. The wide character input/output functions and the byte input/output
- functions store the value of the macro EILSEQ in errno if and only if an encoding error
- occurs.
- Environmental limits
-15 The value of FOPEN_MAX shall be at least eight, including the three standard text
- streams.
- Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
- fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
- (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the
- fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function
- (7.28.6.3.2), the wcrtomb function (7.28.6.3.3).
- 7.21.4 Operations on files
- 7.21.4.1 The remove function
- Synopsis
-1 #include <stdio.h>
- int remove(const char *filename);
- Description
-2 The remove function causes the file whose name is the string pointed to by filename
- to be no longer accessible by that name. A subsequent attempt to open that file using that
- name will fail, unless it is created anew. If the file is open, the behavior of the remove
- function is implementation-defined.
- Returns
-3 The remove function returns zero if the operation succeeds, nonzero if it fails.
- 7.21.4.2 The rename function
- Synopsis
-1 #include <stdio.h>
- int rename(const char *old, const char *new);
- Description
-2 The rename function causes the file whose name is the string pointed to by old to be
- henceforth known by the name given by the string pointed to by new. The file named
- old is no longer accessible by that name. If a file named by the string pointed to by new
- exists prior to the call to the rename function, the behavior is implementation-defined.
-
-
-
-
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-
- Returns
-3 The rename function returns zero if the operation succeeds, nonzero if it fails,262) in
- which case if the file existed previously it is still known by its original name.
- 7.21.4.3 The tmpfile function
- Synopsis
-1 #include <stdio.h>
- FILE *tmpfile(void);
- Description
-2 The tmpfile function creates a temporary binary file that is different from any other
- existing file and that will automatically be removed when it is closed or at program
- termination. If the program terminates abnormally, whether an open temporary file is
- removed is implementation-defined. The file is opened for update with "wb+" mode.
- Recommended practice
-3 It should be possible to open at least TMP_MAX temporary files during the lifetime of the
- program (this limit may be shared with tmpnam) and there should be no limit on the
- number simultaneously open other than this limit and any limit on the number of open
- files (FOPEN_MAX).
- Returns
-4 The tmpfile function returns a pointer to the stream of the file that it created. If the file
- cannot be created, the tmpfile function returns a null pointer.
- Forward references: the fopen function (7.21.5.3).
- 7.21.4.4 The tmpnam function
- Synopsis
-1 #include <stdio.h>
- char *tmpnam(char *s);
- Description
-2 The tmpnam function generates a string that is a valid file name and that is not the same
- as the name of an existing file.263) The function is potentially capable of generating at
-
-
- 262) Among the reasons the implementation may cause the rename function to fail are that the file is open
- or that it is necessary to copy its contents to effectuate its renaming.
- 263) Files created using strings generated by the tmpnam function are temporary only in the sense that
- their names should not collide with those generated by conventional naming rules for the
- implementation. It is still necessary to use the remove function to remove such files when their use
- is ended, and before program termination.
-
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-
- least TMP_MAX different strings, but any or all of them may already be in use by existing
- files and thus not be suitable return values.
-3 The tmpnam function generates a different string each time it is called.
-4 Calls to the tmpnam function with a null pointer argument may introduce data races with
- each other. The implementation shall behave as if no library function calls the tmpnam
- function.
- Returns
-5 If no suitable string can be generated, the tmpnam function returns a null pointer.
- Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
- internal static object and returns a pointer to that object (subsequent calls to the tmpnam
- function may modify the same object). If the argument is not a null pointer, it is assumed
- to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
- in that array and returns the argument as its value.
- Environmental limits
-6 The value of the macro TMP_MAX shall be at least 25.
- 7.21.5 File access functions
- 7.21.5.1 The fclose function
- Synopsis
-1 #include <stdio.h>
- int fclose(FILE *stream);
- Description
-2 A successful call to the fclose function causes the stream pointed to by stream to be
- flushed and the associated file to be closed. Any unwritten buffered data for the stream
- are delivered to the host environment to be written to the file; any unread buffered data
- are discarded. Whether or not the call succeeds, the stream is disassociated from the file
- and any buffer set by the setbuf or setvbuf function is disassociated from the stream
- (and deallocated if it was automatically allocated).
- Returns
-3 The fclose function returns zero if the stream was successfully closed, or EOF if any
- errors were detected.
-
-
-
-
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-
- 7.21.5.2 The fflush function
- Synopsis
-1 #include <stdio.h>
- int fflush(FILE *stream);
- Description
-2 If stream points to an output stream or an update stream in which the most recent
- operation was not input, the fflush function causes any unwritten data for that stream
- to be delivered to the host environment to be written to the file; otherwise, the behavior is
- undefined.
-3 If stream is a null pointer, the fflush function performs this flushing action on all
- streams for which the behavior is defined above.
- Returns
-4 The fflush function sets the error indicator for the stream and returns EOF if a write
- error occurs, otherwise it returns zero.
- Forward references: the fopen function (7.21.5.3).
- 7.21.5.3 The fopen function
- Synopsis
-1 #include <stdio.h>
- FILE *fopen(const char * restrict filename,
- const char * restrict mode);
- Description
-2 The fopen function opens the file whose name is the string pointed to by filename,
- and associates a stream with it.
-3 The argument mode points to a string. If the string is one of the following, the file is
- open in the indicated mode. Otherwise, the behavior is undefined.264)
- r open text file for reading
- w truncate to zero length or create text file for writing
- wx create text file for writing
- a append; open or create text file for writing at end-of-file
- rb open binary file for reading
- wb truncate to zero length or create binary file for writing
-
-
- 264) If the string begins with one of the above sequences, the implementation might choose to ignore the
- remaining characters, or it might use them to select different kinds of a file (some of which might not
- conform to the properties in 7.21.2).
-
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-
- wbx create binary file for writing
- ab append; open or create binary file for writing at end-of-file
- r+ open text file for update (reading and writing)
- w+ truncate to zero length or create text file for update
- w+x create text file for update
- a+ append; open or create text file for update, writing at end-of-file
- r+b or rb+ open binary file for update (reading and writing)
- w+b or wb+ truncate to zero length or create binary file for update
- w+bx or wb+x create binary file for update
- a+b or ab+ append; open or create binary file for update, writing at end-of-file
-4 Opening a file with read mode ('r' as the first character in the mode argument) fails if
- the file does not exist or cannot be read.
-5 Opening a file with exclusive mode ('x' as the last character in the mode argument)
- fails if the file already exists or cannot be created. Otherwise, the file is created with
- exclusive (also known as non-shared) access to the extent that the underlying system
- supports exclusive access.
-6 Opening a file with append mode ('a' as the first character in the mode argument)
- causes all subsequent writes to the file to be forced to the then current end-of-file,
- regardless of intervening calls to the fseek function. In some implementations, opening
- a binary file with append mode ('b' as the second or third character in the above list of
- mode argument values) may initially position the file position indicator for the stream
- beyond the last data written, because of null character padding.
-7 When a file is opened with update mode ('+' as the second or third character in the
- above list of mode argument values), both input and output may be performed on the
- associated stream. However, output shall not be directly followed by input without an
- intervening call to the fflush function or to a file positioning function (fseek,
- fsetpos, or rewind), and input shall not be directly followed by output without an
- intervening call to a file positioning function, unless the input operation encounters end-
- of-file. Opening (or creating) a text file with update mode may instead open (or create) a
- binary stream in some implementations.
-8 When opened, a stream is fully buffered if and only if it can be determined not to refer to
- an interactive device. The error and end-of-file indicators for the stream are cleared.
- Returns
-9 The fopen function returns a pointer to the object controlling the stream. If the open
- operation fails, fopen returns a null pointer.
- Forward references: file positioning functions (7.21.9).
-
-
-
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-
- 7.21.5.4 The freopen function
- Synopsis
-1 #include <stdio.h>
- FILE *freopen(const char * restrict filename,
- const char * restrict mode,
- FILE * restrict stream);
- Description
-2 The freopen function opens the file whose name is the string pointed to by filename
- and associates the stream pointed to by stream with it. The mode argument is used just
- as in the fopen function.265)
-3 If filename is a null pointer, the freopen function attempts to change the mode of
- the stream to that specified by mode, as if the name of the file currently associated with
- the stream had been used. It is implementation-defined which changes of mode are
- permitted (if any), and under what circumstances.
-4 The freopen function first attempts to close any file that is associated with the specified
- stream. Failure to close the file is ignored. The error and end-of-file indicators for the
- stream are cleared.
- Returns
-5 The freopen function returns a null pointer if the open operation fails. Otherwise,
- freopen returns the value of stream.
- 7.21.5.5 The setbuf function
- Synopsis
-1 #include <stdio.h>
- void setbuf(FILE * restrict stream,
- char * restrict buf);
- Description
-2 Except that it returns no value, the setbuf function is equivalent to the setvbuf
- function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
- is a null pointer), with the value _IONBF for mode.
-
-
-
-
- 265) The primary use of the freopen function is to change the file associated with a standard text stream
- (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
- returned by the fopen function may be assigned.
-
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-
- Returns
-3 The setbuf function returns no value.
- Forward references: the setvbuf function (7.21.5.6).
- 7.21.5.6 The setvbuf function
- Synopsis
-1 #include <stdio.h>
- int setvbuf(FILE * restrict stream,
- char * restrict buf,
- int mode, size_t size);
- Description
-2 The setvbuf function may be used only after the stream pointed to by stream has
- been associated with an open file and before any other operation (other than an
- unsuccessful call to setvbuf) is performed on the stream. The argument mode
- determines how stream will be buffered, as follows: _IOFBF causes input/output to be
- fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
- input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
- used instead of a buffer allocated by the setvbuf function266) and the argument size
- specifies the size of the array; otherwise, size may determine the size of a buffer
- allocated by the setvbuf function. The contents of the array at any time are
- indeterminate.
- Returns
-3 The setvbuf function returns zero on success, or nonzero if an invalid value is given
- for mode or if the request cannot be honored.
-
-
-
-
- 266) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
- before a buffer that has automatic storage duration is deallocated upon block exit.
-
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-
- 7.21.6 Formatted input/output functions
-1 The formatted input/output functions shall behave as if there is a sequence point after the
- actions associated with each specifier.267)
- 7.21.6.1 The fprintf function
- Synopsis
-1 #include <stdio.h>
- int fprintf(FILE * restrict stream,
- const char * restrict format, ...);
- Description
-2 The fprintf function writes output to the stream pointed to by stream, under control
- of the string pointed to by format that specifies how subsequent arguments are
- converted for output. If there are insufficient arguments for the format, the behavior is
- undefined. If the format is exhausted while arguments remain, the excess arguments are
- evaluated (as always) but are otherwise ignored. The fprintf function returns when
- the end of the format string is encountered.
-3 The format shall be a multibyte character sequence, beginning and ending in its initial
- shift state. The format is composed of zero or more directives: ordinary multibyte
- characters (not %), which are copied unchanged to the output stream; and conversion
- specifications, each of which results in fetching zero or more subsequent arguments,
- converting them, if applicable, according to the corresponding conversion specifier, and
- then writing the result to the output stream.
-4 Each conversion specification is introduced by the character %. After the %, the following
- appear in sequence:
- -- Zero or more flags (in any order) that modify the meaning of the conversion
- specification.
- -- An optional minimum field width. If the converted value has fewer characters than the
- field width, it is padded with spaces (by default) on the left (or right, if the left
- adjustment flag, described later, has been given) to the field width. The field width
- takes the form of an asterisk * (described later) or a nonnegative decimal integer.268)
- -- An optional precision that gives the minimum number of digits to appear for the d, i,
- o, u, x, and X conversions, the number of digits to appear after the decimal-point
- character for a, A, e, E, f, and F conversions, the maximum number of significant
- digits for the g and G conversions, or the maximum number of bytes to be written for
-
-
- 267) The fprintf functions perform writes to memory for the %n specifier.
- 268) Note that 0 is taken as a flag, not as the beginning of a field width.
-
-[page 309] (Contents)
-
- s conversions. The precision takes the form of a period (.) followed either by an
- asterisk * (described later) or by an optional decimal integer; if only the period is
- specified, the precision is taken as zero. If a precision appears with any other
- conversion specifier, the behavior is undefined.
- -- An optional length modifier that specifies the size of the argument.
- -- A conversion specifier character that specifies the type of conversion to be applied.
-5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
- this case, an int argument supplies the field width or precision. The arguments
- specifying field width, or precision, or both, shall appear (in that order) before the
- argument (if any) to be converted. A negative field width argument is taken as a - flag
- followed by a positive field width. A negative precision argument is taken as if the
- precision were omitted.
-6 The flag characters and their meanings are:
- - The result of the conversion is left-justified within the field. (It is right-justified if
- this flag is not specified.)
- + The result of a signed conversion always begins with a plus or minus sign. (It
- begins with a sign only when a negative value is converted if this flag is not
- specified.)269)
- space If the first character of a signed conversion is not a sign, or if a signed conversion
- results in no characters, a space is prefixed to the result. If the space and + flags
- both appear, the space flag is ignored.
- # The result is converted to an ''alternative form''. For o conversion, it increases
- the precision, if and only if necessary, to force the first digit of the result to be a
- zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
- conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
- and G conversions, the result of converting a floating-point number always
- contains a decimal-point character, even if no digits follow it. (Normally, a
- decimal-point character appears in the result of these conversions only if a digit
- follows it.) For g and G conversions, trailing zeros are not removed from the
- result. For other conversions, the behavior is undefined.
- 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
- (following any indication of sign or base) are used to pad to the field width rather
- than performing space padding, except when converting an infinity or NaN. If the
- 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
-
-
- 269) The results of all floating conversions of a negative zero, and of negative values that round to zero,
- include a minus sign.
-
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-
- conversions, if a precision is specified, the 0 flag is ignored. For other
- conversions, the behavior is undefined.
-7 The length modifiers and their meanings are:
- hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- signed char or unsigned char argument (the argument will have
- been promoted according to the integer promotions, but its value shall be
- converted to signed char or unsigned char before printing); or that
- a following n conversion specifier applies to a pointer to a signed char
- argument.
- h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- short int or unsigned short int argument (the argument will
- have been promoted according to the integer promotions, but its value shall
- be converted to short int or unsigned short int before printing);
- or that a following n conversion specifier applies to a pointer to a short
- int argument.
- l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- long int or unsigned long int argument; that a following n
- conversion specifier applies to a pointer to a long int argument; that a
- following c conversion specifier applies to a wint_t argument; that a
- following s conversion specifier applies to a pointer to a wchar_t
- argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
- specifier.
- ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- long long int or unsigned long long int argument; or that a
- following n conversion specifier applies to a pointer to a long long int
- argument.
- j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
- an intmax_t or uintmax_t argument; or that a following n conversion
- specifier applies to a pointer to an intmax_t argument.
- z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- size_t or the corresponding signed integer type argument; or that a
- following n conversion specifier applies to a pointer to a signed integer type
- corresponding to size_t argument.
- t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- ptrdiff_t or the corresponding unsigned integer type argument; or that a
- following n conversion specifier applies to a pointer to a ptrdiff_t
- argument.
-
-
-[page 311] (Contents)
-
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
- applies to a long double argument.
- If a length modifier appears with any conversion specifier other than as specified above,
- the behavior is undefined.
-8 The conversion specifiers and their meanings are:
- d,i The int argument is converted to signed decimal in the style [-]dddd. The
- precision specifies the minimum number of digits to appear; if the value
- being converted can be represented in fewer digits, it is expanded with
- leading zeros. The default precision is 1. The result of converting a zero
- value with a precision of zero is no characters.
- o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
- decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
- letters abcdef are used for x conversion and the letters ABCDEF for X
- conversion. The precision specifies the minimum number of digits to appear;
- if the value being converted can be represented in fewer digits, it is expanded
- with leading zeros. The default precision is 1. The result of converting a
- zero value with a precision of zero is no characters.
- f,F A double argument representing a floating-point number is converted to
- decimal notation in the style [-]ddd.ddd, where the number of digits after
- the decimal-point character is equal to the precision specification. If the
- precision is missing, it is taken as 6; if the precision is zero and the # flag is
- not specified, no decimal-point character appears. If a decimal-point
- character appears, at least one digit appears before it. The value is rounded to
- the appropriate number of digits.
- A double argument representing an infinity is converted in one of the styles
- [-]inf or [-]infinity -- which style is implementation-defined. A
- double argument representing a NaN is converted in one of the styles
- [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
- any n-char-sequence, is implementation-defined. The F conversion specifier
- produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
- respectively.270)
- e,E A double argument representing a floating-point number is converted in the
- style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
- argument is nonzero) before the decimal-point character and the number of
- digits after it is equal to the precision; if the precision is missing, it is taken as
-
-
- 270) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
- the # and 0 flag characters have no effect.
-
-[page 312] (Contents)
-
- 6; if the precision is zero and the # flag is not specified, no decimal-point
- character appears. The value is rounded to the appropriate number of digits.
- The E conversion specifier produces a number with E instead of e
- introducing the exponent. The exponent always contains at least two digits,
- and only as many more digits as necessary to represent the exponent. If the
- value is zero, the exponent is zero.
- A double argument representing an infinity or NaN is converted in the style
- of an f or F conversion specifier.
-g,G A double argument representing a floating-point number is converted in
- style f or e (or in style F or E in the case of a G conversion specifier),
- depending on the value converted and the precision. Let P equal the
- precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
- Then, if a conversion with style E would have an exponent of X:
- -- if P > X >= -4, the conversion is with style f (or F) and precision
- P - (X + 1).
- -- otherwise, the conversion is with style e (or E) and precision P - 1.
- Finally, unless the # flag is used, any trailing zeros are removed from the
- fractional portion of the result and the decimal-point character is removed if
- there is no fractional portion remaining.
- A double argument representing an infinity or NaN is converted in the style
- of an f or F conversion specifier.
-a,A A double argument representing a floating-point number is converted in the
- style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
- nonzero if the argument is a normalized floating-point number and is
- otherwise unspecified) before the decimal-point character271) and the number
- of hexadecimal digits after it is equal to the precision; if the precision is
- missing and FLT_RADIX is a power of 2, then the precision is sufficient for
- an exact representation of the value; if the precision is missing and
- FLT_RADIX is not a power of 2, then the precision is sufficient to
-
-
-
-
-271) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
- that subsequent digits align to nibble (4-bit) boundaries.
-
-[page 313] (Contents)
-
- distinguish272) values of type double, except that trailing zeros may be
- omitted; if the precision is zero and the # flag is not specified, no decimal-
- point character appears. The letters abcdef are used for a conversion and
- the letters ABCDEF for A conversion. The A conversion specifier produces a
- number with X and P instead of x and p. The exponent always contains at
- least one digit, and only as many more digits as necessary to represent the
- decimal exponent of 2. If the value is zero, the exponent is zero.
- A double argument representing an infinity or NaN is converted in the style
- of an f or F conversion specifier.
-c If no l length modifier is present, the int argument is converted to an
- unsigned char, and the resulting character is written.
- If an l length modifier is present, the wint_t argument is converted as if by
- an ls conversion specification with no precision and an argument that points
- to the initial element of a two-element array of wchar_t, the first element
- containing the wint_t argument to the lc conversion specification and the
- second a null wide character.
-s If no l length modifier is present, the argument shall be a pointer to the initial
- element of an array of character type.273) Characters from the array are
- written up to (but not including) the terminating null character. If the
- precision is specified, no more than that many bytes are written. If the
- precision is not specified or is greater than the size of the array, the array shall
- contain a null character.
- If an l length modifier is present, the argument shall be a pointer to the initial
- element of an array of wchar_t type. Wide characters from the array are
- converted to multibyte characters (each as if by a call to the wcrtomb
- function, with the conversion state described by an mbstate_t object
- initialized to zero before the first wide character is converted) up to and
- including a terminating null wide character. The resulting multibyte
- characters are written up to (but not including) the terminating null character
- (byte). If no precision is specified, the array shall contain a null wide
- character. If a precision is specified, no more than that many bytes are
- written (including shift sequences, if any), and the array shall contain a null
- wide character if, to equal the multibyte character sequence length given by
-
-272) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
- FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
- might suffice depending on the implementation's scheme for determining the digit to the left of the
- decimal-point character.
-273) No special provisions are made for multibyte characters.
-
-[page 314] (Contents)
-
- the precision, the function would need to access a wide character one past the
- end of the array. In no case is a partial multibyte character written.274)
- p The argument shall be a pointer to void. The value of the pointer is
- converted to a sequence of printing characters, in an implementation-defined
- manner.
- n The argument shall be a pointer to signed integer into which is written the
- number of characters written to the output stream so far by this call to
- fprintf. No argument is converted, but one is consumed. If the conversion
- specification includes any flags, a field width, or a precision, the behavior is
- undefined.
- % A % character is written. No argument is converted. The complete
- conversion specification shall be %%.
-9 If a conversion specification is invalid, the behavior is undefined.275) If any argument is
- not the correct type for the corresponding conversion specification, the behavior is
- undefined.
-10 In no case does a nonexistent or small field width cause truncation of a field; if the result
- of a conversion is wider than the field width, the field is expanded to contain the
- conversion result.
-11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
- to a hexadecimal floating number with the given precision.
- Recommended practice
-12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
- representable in the given precision, the result should be one of the two adjacent numbers
- in hexadecimal floating style with the given precision, with the extra stipulation that the
- error should have a correct sign for the current rounding direction.
-13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
- DECIMAL_DIG, then the result should be correctly rounded.276) If the number of
- significant decimal digits is more than DECIMAL_DIG but the source value is exactly
- representable with DECIMAL_DIG digits, then the result should be an exact
- representation with trailing zeros. Otherwise, the source value is bounded by two
- adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
-
-
- 274) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
- 275) See ''future library directions'' (7.30.9).
- 276) For binary-to-decimal conversion, the result format's values are the numbers representable with the
- given format specifier. The number of significant digits is determined by the format specifier, and in
- the case of fixed-point conversion by the source value as well.
-
-[page 315] (Contents)
-
- of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
- the error should have a correct sign for the current rounding direction.
- Returns
-14 The fprintf function returns the number of characters transmitted, or a negative value
- if an output or encoding error occurred.
- Environmental limits
-15 The number of characters that can be produced by any single conversion shall be at least
- 4095.
-16 EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
- places:
- #include <math.h>
- #include <stdio.h>
- /* ... */
- char *weekday, *month; // pointers to strings
- int day, hour, min;
- fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
- weekday, month, day, hour, min);
- fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
-
-17 EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
- members of the extended character set that consist of more than one byte each consist of exactly two bytes,
- the first of which is denoted here by a and the second by an uppercase letter.
-18 Given the following wide string with length seven,
- static wchar_t wstr[] = L" X Yabc Z W";
- the seven calls
- fprintf(stdout, "|1234567890123|\n");
- fprintf(stdout, "|%13ls|\n", wstr);
- fprintf(stdout, "|%-13.9ls|\n", wstr);
- fprintf(stdout, "|%13.10ls|\n", wstr);
- fprintf(stdout, "|%13.11ls|\n", wstr);
- fprintf(stdout, "|%13.15ls|\n", &wstr[2]);
- fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);
- will print the following seven lines:
- |1234567890123|
- | X Yabc Z W|
- | X Yabc Z |
- | X Yabc Z|
- | X Yabc Z W|
- | abc Z W|
- | Z|
-
- Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3).
-
-
-
-[page 316] (Contents)
-
- 7.21.6.2 The fscanf function
- Synopsis
-1 #include <stdio.h>
- int fscanf(FILE * restrict stream,
- const char * restrict format, ...);
- Description
-2 The fscanf function reads input from the stream pointed to by stream, under control
- of the string pointed to by format that specifies the admissible input sequences and how
- they are to be converted for assignment, using subsequent arguments as pointers to the
- objects to receive the converted input. If there are insufficient arguments for the format,
- the behavior is undefined. If the format is exhausted while arguments remain, the excess
- arguments are evaluated (as always) but are otherwise ignored.
-3 The format shall be a multibyte character sequence, beginning and ending in its initial
- shift state. The format is composed of zero or more directives: one or more white-space
- characters, an ordinary multibyte character (neither % nor a white-space character), or a
- conversion specification. Each conversion specification is introduced by the character %.
- After the %, the following appear in sequence:
- -- An optional assignment-suppressing character *.
- -- An optional decimal integer greater than zero that specifies the maximum field width
- (in characters).
- -- An optional length modifier that specifies the size of the receiving object.
- -- A conversion specifier character that specifies the type of conversion to be applied.
-4 The fscanf function executes each directive of the format in turn. When all directives
- have been executed, or if a directive fails (as detailed below), the function returns.
- Failures are described as input failures (due to the occurrence of an encoding error or the
- unavailability of input characters), or matching failures (due to inappropriate input).
-5 A directive composed of white-space character(s) is executed by reading input up to the
- first non-white-space character (which remains unread), or until no more characters can
- be read.
-6 A directive that is an ordinary multibyte character is executed by reading the next
- characters of the stream. If any of those characters differ from the ones composing the
- directive, the directive fails and the differing and subsequent characters remain unread.
- Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
- read, the directive fails.
-7 A directive that is a conversion specification defines a set of matching input sequences, as
- described below for each specifier. A conversion specification is executed in the
-
-[page 317] (Contents)
-
- following steps:
-8 Input white-space characters (as specified by the isspace function) are skipped, unless
- the specification includes a [, c, or n specifier.277)
-9 An input item is read from the stream, unless the specification includes an n specifier. An
- input item is defined as the longest sequence of input characters which does not exceed
- any specified field width and which is, or is a prefix of, a matching input sequence.278)
- The first character, if any, after the input item remains unread. If the length of the input
- item is zero, the execution of the directive fails; this condition is a matching failure unless
- end-of-file, an encoding error, or a read error prevented input from the stream, in which
- case it is an input failure.
-10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
- count of input characters) is converted to a type appropriate to the conversion specifier. If
- the input item is not a matching sequence, the execution of the directive fails: this
- condition is a matching failure. Unless assignment suppression was indicated by a *, the
- result of the conversion is placed in the object pointed to by the first argument following
- the format argument that has not already received a conversion result. If this object
- does not have an appropriate type, or if the result of the conversion cannot be represented
- in the object, the behavior is undefined.
-11 The length modifiers and their meanings are:
- hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to signed char or unsigned char.
- h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to short int or unsigned short
- int.
- l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to long int or unsigned long
- int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
- an argument with type pointer to double; or that a following c, s, or [
- conversion specifier applies to an argument with type pointer to wchar_t.
- ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to long long int or unsigned
- long long int.
-
-
-
- 277) These white-space characters are not counted against a specified field width.
- 278) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
- that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.
-
-[page 318] (Contents)
-
- j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to intmax_t or uintmax_t.
- z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to size_t or the corresponding signed
- integer type.
- t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to ptrdiff_t or the corresponding
- unsigned integer type.
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
- applies to an argument with type pointer to long double.
- If a length modifier appears with any conversion specifier other than as specified above,
- the behavior is undefined.
-12 The conversion specifiers and their meanings are:
- d Matches an optionally signed decimal integer, whose format is the same as
- expected for the subject sequence of the strtol function with the value 10
- for the base argument. The corresponding argument shall be a pointer to
- signed integer.
- i Matches an optionally signed integer, whose format is the same as expected
- for the subject sequence of the strtol function with the value 0 for the
- base argument. The corresponding argument shall be a pointer to signed
- integer.
- o Matches an optionally signed octal integer, whose format is the same as
- expected for the subject sequence of the strtoul function with the value 8
- for the base argument. The corresponding argument shall be a pointer to
- unsigned integer.
- u Matches an optionally signed decimal integer, whose format is the same as
- expected for the subject sequence of the strtoul function with the value 10
- for the base argument. The corresponding argument shall be a pointer to
- unsigned integer.
- x Matches an optionally signed hexadecimal integer, whose format is the same
- as expected for the subject sequence of the strtoul function with the value
- 16 for the base argument. The corresponding argument shall be a pointer to
- unsigned integer.
- a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
- format is the same as expected for the subject sequence of the strtod
- function. The corresponding argument shall be a pointer to floating.
-
-
-[page 319] (Contents)
-
-c Matches a sequence of characters of exactly the number specified by the field
- width (1 if no field width is present in the directive).279)
- If no l length modifier is present, the corresponding argument shall be a
- pointer to the initial element of a character array large enough to accept the
- sequence. No null character is added.
- If an l length modifier is present, the input shall be a sequence of multibyte
- characters that begins in the initial shift state. Each multibyte character in the
- sequence is converted to a wide character as if by a call to the mbrtowc
- function, with the conversion state described by an mbstate_t object
- initialized to zero before the first multibyte character is converted. The
- corresponding argument shall be a pointer to the initial element of an array of
- wchar_t large enough to accept the resulting sequence of wide characters.
- No null wide character is added.
-s Matches a sequence of non-white-space characters.279)
- If no l length modifier is present, the corresponding argument shall be a
- pointer to the initial element of a character array large enough to accept the
- sequence and a terminating null character, which will be added automatically.
- If an l length modifier is present, the input shall be a sequence of multibyte
- characters that begins in the initial shift state. Each multibyte character is
- converted to a wide character as if by a call to the mbrtowc function, with
- the conversion state described by an mbstate_t object initialized to zero
- before the first multibyte character is converted. The corresponding argument
- shall be a pointer to the initial element of an array of wchar_t large enough
- to accept the sequence and the terminating null wide character, which will be
- added automatically.
-[ Matches a nonempty sequence of characters from a set of expected characters
- (the scanset).279)
- If no l length modifier is present, the corresponding argument shall be a
- pointer to the initial element of a character array large enough to accept the
- sequence and a terminating null character, which will be added automatically.
- If an l length modifier is present, the input shall be a sequence of multibyte
- characters that begins in the initial shift state. Each multibyte character is
- converted to a wide character as if by a call to the mbrtowc function, with
- the conversion state described by an mbstate_t object initialized to zero
-
-279) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
- conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
- resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
-
-[page 320] (Contents)
-
- before the first multibyte character is converted. The corresponding argument
- shall be a pointer to the initial element of an array of wchar_t large enough
- to accept the sequence and the terminating null wide character, which will be
- added automatically.
- The conversion specifier includes all subsequent characters in the format
- string, up to and including the matching right bracket (]). The characters
- between the brackets (the scanlist) compose the scanset, unless the character
- after the left bracket is a circumflex (^), in which case the scanset contains all
- characters that do not appear in the scanlist between the circumflex and the
- right bracket. If the conversion specifier begins with [] or [^], the right
- bracket character is in the scanlist and the next following right bracket
- character is the matching right bracket that ends the specification; otherwise
- the first following right bracket character is the one that ends the
- specification. If a - character is in the scanlist and is not the first, nor the
- second where the first character is a ^, nor the last character, the behavior is
- implementation-defined.
- p Matches an implementation-defined set of sequences, which should be the
- same as the set of sequences that may be produced by the %p conversion of
- the fprintf function. The corresponding argument shall be a pointer to a
- pointer to void. The input item is converted to a pointer value in an
- implementation-defined manner. If the input item is a value converted earlier
- during the same program execution, the pointer that results shall compare
- equal to that value; otherwise the behavior of the %p conversion is undefined.
- n No input is consumed. The corresponding argument shall be a pointer to
- signed integer into which is to be written the number of characters read from
- the input stream so far by this call to the fscanf function. Execution of a
- %n directive does not increment the assignment count returned at the
- completion of execution of the fscanf function. No argument is converted,
- but one is consumed. If the conversion specification includes an assignment-
- suppressing character or a field width, the behavior is undefined.
- % Matches a single % character; no conversion or assignment occurs. The
- complete conversion specification shall be %%.
-13 If a conversion specification is invalid, the behavior is undefined.280)
-14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
- respectively, a, e, f, g, and x.
-
-
-
- 280) See ''future library directions'' (7.30.9).
-
-[page 321] (Contents)
-
-15 Trailing white space (including new-line characters) is left unread unless matched by a
- directive. The success of literal matches and suppressed assignments is not directly
- determinable other than via the %n directive.
- Returns
-16 The fscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the function returns the
- number of input items assigned, which can be fewer than provided for, or even zero, in
- the event of an early matching failure.
-17 EXAMPLE 1 The call:
- #include <stdio.h>
- /* ... */
- int n, i; float x; char name[50];
- n = fscanf(stdin, "%d%f%s", &i, &x, name);
- with the input line:
- 25 54.32E-1 thompson
- will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
- thompson\0.
-
-18 EXAMPLE 2 The call:
- #include <stdio.h>
- /* ... */
- int i; float x; char name[50];
- fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
- with input:
- 56789 0123 56a72
- will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the
- sequence 56\0. The next character read from the input stream will be a.
-
-19 EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name:
- #include <stdio.h>
- /* ... */
- int count; float quant; char units[21], item[21];
- do {
- count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
- fscanf(stdin,"%*[^\n]");
- } while (!feof(stdin) && !ferror(stdin));
-20 If the stdin stream contains the following lines:
- 2 quarts of oil
- -12.8degrees Celsius
- lots of luck
- 10.0LBS of
- dirt
- 100ergs of energy
-
-[page 322] (Contents)
-
- the execution of the above example will be analogous to the following assignments:
- quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
- count = 3;
- quant = -12.8; strcpy(units, "degrees");
- count = 2; // "C" fails to match "o"
- count = 0; // "l" fails to match "%f"
- quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
- count = 3;
- count = 0; // "100e" fails to match "%f"
- count = EOF;
-
-21 EXAMPLE 4 In:
- #include <stdio.h>
- /* ... */
- int d1, d2, n1, n2, i;
- i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
- the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value
- of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.
-
-22 EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the
- members of the extended character set that consist of more than one byte each consist of exactly two bytes,
- the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as
- such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes
- entry into the alternate shift state.
-23 After the call:
- #include <stdio.h>
- /* ... */
- char str[50];
- fscanf(stdin, "a%s", str);
- with the input line:
- a(uparrow) X Y(downarrow) bc
- str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte
- characters, in the more general case) appears to be a single-byte white-space character.
-24 In contrast, after the call:
- #include <stdio.h>
- #include <stddef.h>
- /* ... */
- wchar_t wstr[50];
- fscanf(stdin, "a%ls", wstr);
- with the same input line, wstr will contain the two wide characters that correspond to X and Y and a
- terminating null wide character.
-25 However, the call:
-
-
-
-
-[page 323] (Contents)
-
- #include <stdio.h>
- #include <stddef.h>
- /* ... */
- wchar_t wstr[50];
- fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr);
- with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format
- string.
-26 Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
- character Y, after the call:
- #include <stdio.h>
- #include <stddef.h>
- /* ... */
- wchar_t wstr[50];
- fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr);
- with the same input line, zero will again be returned, but stdin will be left with a partially consumed
- multibyte character.
-
- Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the
- strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state
- (7.28.6), the wcrtomb function (7.28.6.3.3).
- 7.21.6.3 The printf function
- Synopsis
-1 #include <stdio.h>
- int printf(const char * restrict format, ...);
- Description
-2 The printf function is equivalent to fprintf with the argument stdout interposed
- before the arguments to printf.
- Returns
-3 The printf function returns the number of characters transmitted, or a negative value if
- an output or encoding error occurred.
- 7.21.6.4 The scanf function
- Synopsis
-1 #include <stdio.h>
- int scanf(const char * restrict format, ...);
- Description
-2 The scanf function is equivalent to fscanf with the argument stdin interposed
- before the arguments to scanf.
-
-
-
-[page 324] (Contents)
-
- Returns
-3 The scanf function returns the value of the macro EOF if an input failure occurs before
- the first conversion (if any) has completed. Otherwise, the scanf function returns the
- number of input items assigned, which can be fewer than provided for, or even zero, in
- the event of an early matching failure.
- 7.21.6.5 The snprintf function
- Synopsis
-1 #include <stdio.h>
- int snprintf(char * restrict s, size_t n,
- const char * restrict format, ...);
- Description
-2 The snprintf function is equivalent to fprintf, except that the output is written into
- an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
- and s may be a null pointer. Otherwise, output characters beyond the n-1st are
- discarded rather than being written to the array, and a null character is written at the end
- of the characters actually written into the array. If copying takes place between objects
- that overlap, the behavior is undefined.
- Returns
-3 The snprintf function returns the number of characters that would have been written
- had n been sufficiently large, not counting the terminating null character, or a negative
- value if an encoding error occurred. Thus, the null-terminated output has been
- completely written if and only if the returned value is nonnegative and less than n.
- 7.21.6.6 The sprintf function
- Synopsis
-1 #include <stdio.h>
- int sprintf(char * restrict s,
- const char * restrict format, ...);
- Description
-2 The sprintf function is equivalent to fprintf, except that the output is written into
- an array (specified by the argument s) rather than to a stream. A null character is written
- at the end of the characters written; it is not counted as part of the returned value. If
- copying takes place between objects that overlap, the behavior is undefined.
- Returns
-3 The sprintf function returns the number of characters written in the array, not
- counting the terminating null character, or a negative value if an encoding error occurred.
-
-[page 325] (Contents)
-
- 7.21.6.7 The sscanf function
- Synopsis
-1 #include <stdio.h>
- int sscanf(const char * restrict s,
- const char * restrict format, ...);
- Description
-2 The sscanf function is equivalent to fscanf, except that input is obtained from a
- string (specified by the argument s) rather than from a stream. Reaching the end of the
- string is equivalent to encountering end-of-file for the fscanf function. If copying
- takes place between objects that overlap, the behavior is undefined.
- Returns
-3 The sscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the sscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.21.6.8 The vfprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vfprintf(FILE * restrict stream,
- const char * restrict format,
- va_list arg);
- Description
-2 The vfprintf function is equivalent to fprintf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vfprintf function does not invoke the
- va_end macro.281)
- Returns
-3 The vfprintf function returns the number of characters transmitted, or a negative
- value if an output or encoding error occurred.
-4 EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine.
-
-
-
-
- 281) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
- vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
-
-[page 326] (Contents)
-
- #include <stdarg.h>
- #include <stdio.h>
- void error(char *function_name, char *format, ...)
- {
- va_list args;
- va_start(args, format);
- // print out name of function causing error
- fprintf(stderr, "ERROR in %s: ", function_name);
- // print out remainder of message
- vfprintf(stderr, format, args);
- va_end(args);
- }
-
- 7.21.6.9 The vfscanf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vfscanf(FILE * restrict stream,
- const char * restrict format,
- va_list arg);
- Description
-2 The vfscanf function is equivalent to fscanf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vfscanf function does not invoke the
- va_end macro.281)
- Returns
-3 The vfscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the vfscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.21.6.10 The vprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vprintf(const char * restrict format,
- va_list arg);
- Description
-2 The vprintf function is equivalent to printf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
-
-[page 327] (Contents)
-
- possibly subsequent va_arg calls). The vprintf function does not invoke the
- va_end macro.281)
- Returns
-3 The vprintf function returns the number of characters transmitted, or a negative value
- if an output or encoding error occurred.
- 7.21.6.11 The vscanf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vscanf(const char * restrict format,
- va_list arg);
- Description
-2 The vscanf function is equivalent to scanf, with the variable argument list replaced
- by arg, which shall have been initialized by the va_start macro (and possibly
- subsequent va_arg calls). The vscanf function does not invoke the va_end
- macro.281)
- Returns
-3 The vscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the vscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.21.6.12 The vsnprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vsnprintf(char * restrict s, size_t n,
- const char * restrict format,
- va_list arg);
- Description
-2 The vsnprintf function is equivalent to snprintf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vsnprintf function does not invoke the
- va_end macro.281) If copying takes place between objects that overlap, the behavior is
- undefined.
-
-
-
-[page 328] (Contents)
-
- Returns
-3 The vsnprintf function returns the number of characters that would have been written
- had n been sufficiently large, not counting the terminating null character, or a negative
- value if an encoding error occurred. Thus, the null-terminated output has been
- completely written if and only if the returned value is nonnegative and less than n.
- 7.21.6.13 The vsprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vsprintf(char * restrict s,
- const char * restrict format,
- va_list arg);
- Description
-2 The vsprintf function is equivalent to sprintf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vsprintf function does not invoke the
- va_end macro.281) If copying takes place between objects that overlap, the behavior is
- undefined.
- Returns
-3 The vsprintf function returns the number of characters written in the array, not
- counting the terminating null character, or a negative value if an encoding error occurred.
- 7.21.6.14 The vsscanf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- int vsscanf(const char * restrict s,
- const char * restrict format,
- va_list arg);
- Description
-2 The vsscanf function is equivalent to sscanf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vsscanf function does not invoke the
- va_end macro.281)
- Returns
-3 The vsscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the vsscanf function
-[page 329] (Contents)
-
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.21.7 Character input/output functions
- 7.21.7.1 The fgetc function
- Synopsis
-1 #include <stdio.h>
- int fgetc(FILE *stream);
- Description
-2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
- next character is present, the fgetc function obtains that character as an unsigned
- char converted to an int and advances the associated file position indicator for the
- stream (if defined).
- Returns
-3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
- of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
- fgetc function returns the next character from the input stream pointed to by stream.
- If a read error occurs, the error indicator for the stream is set and the fgetc function
- returns EOF.282)
- 7.21.7.2 The fgets function
- Synopsis
-1 #include <stdio.h>
- char *fgets(char * restrict s, int n,
- FILE * restrict stream);
- Description
-2 The fgets function reads at most one less than the number of characters specified by n
- from the stream pointed to by stream into the array pointed to by s. No additional
- characters are read after a new-line character (which is retained) or after end-of-file. A
- null character is written immediately after the last character read into the array.
- Returns
-3 The fgets function returns s if successful. If end-of-file is encountered and no
- characters have been read into the array, the contents of the array remain unchanged and a
- null pointer is returned. If a read error occurs during the operation, the array contents are
- indeterminate and a null pointer is returned.
-
- 282) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
-
-[page 330] (Contents)
-
- 7.21.7.3 The fputc function
- Synopsis
-1 #include <stdio.h>
- int fputc(int c, FILE *stream);
- Description
-2 The fputc function writes the character specified by c (converted to an unsigned
- char) to the output stream pointed to by stream, at the position indicated by the
- associated file position indicator for the stream (if defined), and advances the indicator
- appropriately. If the file cannot support positioning requests, or if the stream was opened
- with append mode, the character is appended to the output stream.
- Returns
-3 The fputc function returns the character written. If a write error occurs, the error
- indicator for the stream is set and fputc returns EOF.
- 7.21.7.4 The fputs function
- Synopsis
-1 #include <stdio.h>
- int fputs(const char * restrict s,
- FILE * restrict stream);
- Description
-2 The fputs function writes the string pointed to by s to the stream pointed to by
- stream. The terminating null character is not written.
- Returns
-3 The fputs function returns EOF if a write error occurs; otherwise it returns a
- nonnegative value.
- 7.21.7.5 The getc function
- Synopsis
-1 #include <stdio.h>
- int getc(FILE *stream);
- Description
-2 The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
- may evaluate stream more than once, so the argument should never be an expression
- with side effects.
-
-
-
-
-[page 331] (Contents)
-
- Returns
-3 The getc function returns the next character from the input stream pointed to by
- stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
- getc returns EOF. If a read error occurs, the error indicator for the stream is set and
- getc returns EOF.
- 7.21.7.6 The getchar function
- Synopsis
-1 #include <stdio.h>
- int getchar(void);
- Description
-2 The getchar function is equivalent to getc with the argument stdin.
- Returns
-3 The getchar function returns the next character from the input stream pointed to by
- stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
- getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
- getchar returns EOF. *
- 7.21.7.7 The putc function
- Synopsis
-1 #include <stdio.h>
- int putc(int c, FILE *stream);
- Description
-2 The putc function is equivalent to fputc, except that if it is implemented as a macro, it
- may evaluate stream more than once, so that argument should never be an expression
- with side effects.
- Returns
-3 The putc function returns the character written. If a write error occurs, the error
- indicator for the stream is set and putc returns EOF.
- 7.21.7.8 The putchar function
- Synopsis
-1 #include <stdio.h>
- int putchar(int c);
- Description
-2 The putchar function is equivalent to putc with the second argument stdout.
-
-
-[page 332] (Contents)
-
- Returns
-3 The putchar function returns the character written. If a write error occurs, the error
- indicator for the stream is set and putchar returns EOF.
- 7.21.7.9 The puts function
- Synopsis
-1 #include <stdio.h>
- int puts(const char *s);
- Description
-2 The puts function writes the string pointed to by s to the stream pointed to by stdout,
- and appends a new-line character to the output. The terminating null character is not
- written.
- Returns
-3 The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
- value.
- 7.21.7.10 The ungetc function
- Synopsis
-1 #include <stdio.h>
- int ungetc(int c, FILE *stream);
- Description
-2 The ungetc function pushes the character specified by c (converted to an unsigned
- char) back onto the input stream pointed to by stream. Pushed-back characters will be
- returned by subsequent reads on that stream in the reverse order of their pushing. A
- successful intervening call (with the stream pointed to by stream) to a file positioning
- function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
- stream. The external storage corresponding to the stream is unchanged.
-3 One character of pushback is guaranteed. If the ungetc function is called too many
- times on the same stream without an intervening read or file positioning operation on that
- stream, the operation may fail.
-4 If the value of c equals that of the macro EOF, the operation fails and the input stream is
- unchanged.
-5 A successful call to the ungetc function clears the end-of-file indicator for the stream.
- The value of the file position indicator for the stream after reading or discarding all
- pushed-back characters shall be the same as it was before the characters were pushed
- back. For a text stream, the value of its file position indicator after a successful call to the
- ungetc function is unspecified until all pushed-back characters are read or discarded.
-
-[page 333] (Contents)
-
- For a binary stream, its file position indicator is decremented by each successful call to
- the ungetc function; if its value was zero before a call, it is indeterminate after the
- call.283)
- Returns
-6 The ungetc function returns the character pushed back after conversion, or EOF if the
- operation fails.
- Forward references: file positioning functions (7.21.9).
- 7.21.8 Direct input/output functions
- 7.21.8.1 The fread function
- Synopsis
-1 #include <stdio.h>
- size_t fread(void * restrict ptr,
- size_t size, size_t nmemb,
- FILE * restrict stream);
- Description
-2 The fread function reads, into the array pointed to by ptr, up to nmemb elements
- whose size is specified by size, from the stream pointed to by stream. For each
- object, size calls are made to the fgetc function and the results stored, in the order
- read, in an array of unsigned char exactly overlaying the object. The file position
- indicator for the stream (if defined) is advanced by the number of characters successfully
- read. If an error occurs, the resulting value of the file position indicator for the stream is
- indeterminate. If a partial element is read, its value is indeterminate.
- Returns
-3 The fread function returns the number of elements successfully read, which may be
- less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
- fread returns zero and the contents of the array and the state of the stream remain
- unchanged.
-
-
-
-
- 283) See ''future library directions'' (7.30.9).
-
-[page 334] (Contents)
-
- 7.21.8.2 The fwrite function
- Synopsis
-1 #include <stdio.h>
- size_t fwrite(const void * restrict ptr,
- size_t size, size_t nmemb,
- FILE * restrict stream);
- Description
-2 The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
- whose size is specified by size, to the stream pointed to by stream. For each object,
- size calls are made to the fputc function, taking the values (in order) from an array of
- unsigned char exactly overlaying the object. The file position indicator for the
- stream (if defined) is advanced by the number of characters successfully written. If an
- error occurs, the resulting value of the file position indicator for the stream is
- indeterminate.
- Returns
-3 The fwrite function returns the number of elements successfully written, which will be
- less than nmemb only if a write error is encountered. If size or nmemb is zero,
- fwrite returns zero and the state of the stream remains unchanged.
- 7.21.9 File positioning functions
- 7.21.9.1 The fgetpos function
- Synopsis
-1 #include <stdio.h>
- int fgetpos(FILE * restrict stream,
- fpos_t * restrict pos);
- Description
-2 The fgetpos function stores the current values of the parse state (if any) and file
- position indicator for the stream pointed to by stream in the object pointed to by pos.
- The values stored contain unspecified information usable by the fsetpos function for
- repositioning the stream to its position at the time of the call to the fgetpos function.
- Returns
-3 If successful, the fgetpos function returns zero; on failure, the fgetpos function
- returns nonzero and stores an implementation-defined positive value in errno.
- Forward references: the fsetpos function (7.21.9.3).
-
-
-
-
-[page 335] (Contents)
-
- 7.21.9.2 The fseek function
- Synopsis
-1 #include <stdio.h>
- int fseek(FILE *stream, long int offset, int whence);
- Description
-2 The fseek function sets the file position indicator for the stream pointed to by stream.
- If a read or write error occurs, the error indicator for the stream is set and fseek fails.
-3 For a binary stream, the new position, measured in characters from the beginning of the
- file, is obtained by adding offset to the position specified by whence. The specified
- position is the beginning of the file if whence is SEEK_SET, the current value of the file
- position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
- meaningfully support fseek calls with a whence value of SEEK_END.
-4 For a text stream, either offset shall be zero, or offset shall be a value returned by
- an earlier successful call to the ftell function on a stream associated with the same file
- and whence shall be SEEK_SET.
-5 After determining the new position, a successful call to the fseek function undoes any
- effects of the ungetc function on the stream, clears the end-of-file indicator for the
- stream, and then establishes the new position. After a successful fseek call, the next
- operation on an update stream may be either input or output.
- Returns
-6 The fseek function returns nonzero only for a request that cannot be satisfied.
- Forward references: the ftell function (7.21.9.4).
- 7.21.9.3 The fsetpos function
- Synopsis
-1 #include <stdio.h>
- int fsetpos(FILE *stream, const fpos_t *pos);
- Description
-2 The fsetpos function sets the mbstate_t object (if any) and file position indicator
- for the stream pointed to by stream according to the value of the object pointed to by
- pos, which shall be a value obtained from an earlier successful call to the fgetpos
- function on a stream associated with the same file. If a read or write error occurs, the
- error indicator for the stream is set and fsetpos fails.
-3 A successful call to the fsetpos function undoes any effects of the ungetc function
- on the stream, clears the end-of-file indicator for the stream, and then establishes the new
- parse state and position. After a successful fsetpos call, the next operation on an
-
-[page 336] (Contents)
-
- update stream may be either input or output.
- Returns
-4 If successful, the fsetpos function returns zero; on failure, the fsetpos function
- returns nonzero and stores an implementation-defined positive value in errno.
- 7.21.9.4 The ftell function
- Synopsis
-1 #include <stdio.h>
- long int ftell(FILE *stream);
- Description
-2 The ftell function obtains the current value of the file position indicator for the stream
- pointed to by stream. For a binary stream, the value is the number of characters from
- the beginning of the file. For a text stream, its file position indicator contains unspecified
- information, usable by the fseek function for returning the file position indicator for the
- stream to its position at the time of the ftell call; the difference between two such
- return values is not necessarily a meaningful measure of the number of characters written
- or read.
- Returns
-3 If successful, the ftell function returns the current value of the file position indicator
- for the stream. On failure, the ftell function returns -1L and stores an
- implementation-defined positive value in errno.
- 7.21.9.5 The rewind function
- Synopsis
-1 #include <stdio.h>
- void rewind(FILE *stream);
- Description
-2 The rewind function sets the file position indicator for the stream pointed to by
- stream to the beginning of the file. It is equivalent to
- (void)fseek(stream, 0L, SEEK_SET)
- except that the error indicator for the stream is also cleared.
- Returns
-3 The rewind function returns no value.
-
-
-
-
-[page 337] (Contents)
-
- 7.21.10 Error-handling functions
- 7.21.10.1 The clearerr function
- Synopsis
-1 #include <stdio.h>
- void clearerr(FILE *stream);
- Description
-2 The clearerr function clears the end-of-file and error indicators for the stream pointed
- to by stream.
- Returns
-3 The clearerr function returns no value.
- 7.21.10.2 The feof function
- Synopsis
-1 #include <stdio.h>
- int feof(FILE *stream);
- Description
-2 The feof function tests the end-of-file indicator for the stream pointed to by stream.
- Returns
-3 The feof function returns nonzero if and only if the end-of-file indicator is set for
- stream.
- 7.21.10.3 The ferror function
- Synopsis
-1 #include <stdio.h>
- int ferror(FILE *stream);
- Description
-2 The ferror function tests the error indicator for the stream pointed to by stream.
- Returns
-3 The ferror function returns nonzero if and only if the error indicator is set for
- stream.
-
-
-
-
-[page 338] (Contents)
-
- 7.21.10.4 The perror function
- Synopsis
-1 #include <stdio.h>
- void perror(const char *s);
- Description
-2 The perror function maps the error number in the integer expression errno to an
- error message. It writes a sequence of characters to the standard error stream thus: first
- (if s is not a null pointer and the character pointed to by s is not the null character), the
- string pointed to by s followed by a colon (:) and a space; then an appropriate error
- message string followed by a new-line character. The contents of the error message
- strings are the same as those returned by the strerror function with argument errno.
- Returns
-3 The perror function returns no value.
- Forward references: the strerror function (7.23.6.2).
-
-
-
-
-[page 339] (Contents)
-
- 7.22 General utilities <stdlib.h>
-1 The header <stdlib.h> declares five types and several functions of general utility, and
- defines several macros.284)
-2 The types declared are size_t and wchar_t (both described in 7.19),
- div_t
- which is a structure type that is the type of the value returned by the div function,
- ldiv_t
- which is a structure type that is the type of the value returned by the ldiv function, and
- lldiv_t
- which is a structure type that is the type of the value returned by the lldiv function.
-3 The macros defined are NULL (described in 7.19);
- EXIT_FAILURE
- and
- EXIT_SUCCESS
- which expand to integer constant expressions that can be used as the argument to the
- exit function to return unsuccessful or successful termination status, respectively, to the
- host environment;
- RAND_MAX
- which expands to an integer constant expression that is the maximum value returned by
- the rand function; and
- MB_CUR_MAX
- which expands to a positive integer expression with type size_t that is the maximum
- number of bytes in a multibyte character for the extended character set specified by the
- current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.
-
-
-
-
- 284) See ''future library directions'' (7.30.10).
-
-[page 340] (Contents)
-
- 7.22.1 Numeric conversion functions
-1 The functions atof, atoi, atol, and atoll need not affect the value of the integer
- expression errno on an error. If the value of the result cannot be represented, the
- behavior is undefined.
- 7.22.1.1 The atof function
- Synopsis
-1 #include <stdlib.h>
- double atof(const char *nptr);
- Description
-2 The atof function converts the initial portion of the string pointed to by nptr to
- double representation. Except for the behavior on error, it is equivalent to
- strtod(nptr, (char **)NULL)
- Returns
-3 The atof function returns the converted value.
- Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
- 7.22.1.2 The atoi, atol, and atoll functions
- Synopsis
-1 #include <stdlib.h>
- int atoi(const char *nptr);
- long int atol(const char *nptr);
- long long int atoll(const char *nptr);
- Description
-2 The atoi, atol, and atoll functions convert the initial portion of the string pointed
- to by nptr to int, long int, and long long int representation, respectively.
- Except for the behavior on error, they are equivalent to
- atoi: (int)strtol(nptr, (char **)NULL, 10)
- atol: strtol(nptr, (char **)NULL, 10)
- atoll: strtoll(nptr, (char **)NULL, 10)
- Returns
-3 The atoi, atol, and atoll functions return the converted value.
- Forward references: the strtol, strtoll, strtoul, and strtoull functions
- (7.22.1.4).
-
-
-
-[page 341] (Contents)
-
- 7.22.1.3 The strtod, strtof, and strtold functions
- Synopsis
-1 #include <stdlib.h>
- double strtod(const char * restrict nptr,
- char ** restrict endptr);
- float strtof(const char * restrict nptr,
- char ** restrict endptr);
- long double strtold(const char * restrict nptr,
- char ** restrict endptr);
- Description
-2 The strtod, strtof, and strtold functions convert the initial portion of the string
- pointed to by nptr to double, float, and long double representation,
- respectively. First, they decompose the input string into three parts: an initial, possibly
- empty, sequence of white-space characters (as specified by the isspace function), a
- subject sequence resembling a floating-point constant or representing an infinity or NaN;
- and a final string of one or more unrecognized characters, including the terminating null
- character of the input string. Then, they attempt to convert the subject sequence to a
- floating-point number, and return the result.
-3 The expected form of the subject sequence is an optional plus or minus sign, then one of
- the following:
- -- a nonempty sequence of decimal digits optionally containing a decimal-point
- character, then an optional exponent part as defined in 6.4.4.2;
- -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
- decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
- -- INF or INFINITY, ignoring case
- -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
- n-char-sequence:
- digit
- nondigit
- n-char-sequence digit
- n-char-sequence nondigit
- The subject sequence is defined as the longest initial subsequence of the input string,
- starting with the first non-white-space character, that is of the expected form. The subject
- sequence contains no characters if the input string is not of the expected form.
-4 If the subject sequence has the expected form for a floating-point number, the sequence of
- characters starting with the first digit or the decimal-point character (whichever occurs
- first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
-[page 342] (Contents)
-
- decimal-point character is used in place of a period, and that if neither an exponent part
- nor a decimal-point character appears in a decimal floating point number, or if a binary
- exponent part does not appear in a hexadecimal floating point number, an exponent part
- of the appropriate type with value zero is assumed to follow the last digit in the string. If
- the subject sequence begins with a minus sign, the sequence is interpreted as negated.285)
- A character sequence INF or INFINITY is interpreted as an infinity, if representable in
- the return type, else like a floating constant that is too large for the range of the return
- type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet
- NaN, if supported in the return type, else like a subject sequence part that does not have
- the expected form; the meaning of the n-char sequences is implementation-defined.286) A
- pointer to the final string is stored in the object pointed to by endptr, provided that
- endptr is not a null pointer.
-5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
- value resulting from the conversion is correctly rounded.
-6 In other than the "C" locale, additional locale-specific subject sequence forms may be
- accepted.
-7 If the subject sequence is empty or does not have the expected form, no conversion is
- performed; the value of nptr is stored in the object pointed to by endptr, provided
- that endptr is not a null pointer.
- Recommended practice
-8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
- the result is not exactly representable, the result should be one of the two numbers in the
- appropriate internal format that are adjacent to the hexadecimal floating source value,
- with the extra stipulation that the error should have a correct sign for the current rounding
- direction.
-9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
- <float.h>) significant digits, the result should be correctly rounded. If the subject
- sequence D has the decimal form and more than DECIMAL_DIG significant digits,
- consider the two bounding, adjacent decimal strings L and U, both having
- DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
- The result should be one of the (equal or adjacent) values that would be obtained by
- correctly rounding L and U according to the current rounding direction, with the extra
-
- 285) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
- negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
- methods may yield different results if rounding is toward positive or negative infinity. In either case,
- the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
- 286) An implementation may use the n-char sequence to determine extra information to be represented in
- the NaN's significand.
-
-[page 343] (Contents)
-
- stipulation that the error with respect to D should have a correct sign for the current
- rounding direction.287)
- Returns
-10 The functions return the converted value, if any. If no conversion could be performed,
- zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
- plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
- return type and sign of the value), and the value of the macro ERANGE is stored in
- errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
- no greater than the smallest normalized positive number in the return type; whether
- errno acquires the value ERANGE is implementation-defined.
- 7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions
- Synopsis
-1 #include <stdlib.h>
- long int strtol(
- const char * restrict nptr,
- char ** restrict endptr,
- int base);
- long long int strtoll(
- const char * restrict nptr,
- char ** restrict endptr,
- int base);
- unsigned long int strtoul(
- const char * restrict nptr,
- char ** restrict endptr,
- int base);
- unsigned long long int strtoull(
- const char * restrict nptr,
- char ** restrict endptr,
- int base);
- Description
-2 The strtol, strtoll, strtoul, and strtoull functions convert the initial
- portion of the string pointed to by nptr to long int, long long int, unsigned
- long int, and unsigned long long int representation, respectively. First,
- they decompose the input string into three parts: an initial, possibly empty, sequence of
- white-space characters (as specified by the isspace function), a subject sequence
-
-
- 287) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
- to the same internal floating value, but if not will round to adjacent values.
-
-[page 344] (Contents)
-
- resembling an integer represented in some radix determined by the value of base, and a
- final string of one or more unrecognized characters, including the terminating null
- character of the input string. Then, they attempt to convert the subject sequence to an
- integer, and return the result.
-3 If the value of base is zero, the expected form of the subject sequence is that of an
- integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
- not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
- expected form of the subject sequence is a sequence of letters and digits representing an
- integer with the radix specified by base, optionally preceded by a plus or minus sign,
- but not including an integer suffix. The letters from a (or A) through z (or Z) are
- ascribed the values 10 through 35; only letters and digits whose ascribed values are less
- than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
- optionally precede the sequence of letters and digits, following the sign if present.
-4 The subject sequence is defined as the longest initial subsequence of the input string,
- starting with the first non-white-space character, that is of the expected form. The subject
- sequence contains no characters if the input string is empty or consists entirely of white
- space, or if the first non-white-space character is other than a sign or a permissible letter
- or digit.
-5 If the subject sequence has the expected form and the value of base is zero, the sequence
- of characters starting with the first digit is interpreted as an integer constant according to
- the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
- is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
- as given above. If the subject sequence begins with a minus sign, the value resulting from
- the conversion is negated (in the return type). A pointer to the final string is stored in the
- object pointed to by endptr, provided that endptr is not a null pointer.
-6 In other than the "C" locale, additional locale-specific subject sequence forms may be
- accepted.
-7 If the subject sequence is empty or does not have the expected form, no conversion is
- performed; the value of nptr is stored in the object pointed to by endptr, provided
- that endptr is not a null pointer.
- Returns
-8 The strtol, strtoll, strtoul, and strtoull functions return the converted
- value, if any. If no conversion could be performed, zero is returned. If the correct value
- is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
- LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
- and sign of the value, if any), and the value of the macro ERANGE is stored in errno.
-
-
-
-
-[page 345] (Contents)
-
- 7.22.2 Pseudo-random sequence generation functions
- 7.22.2.1 The rand function
- Synopsis
-1 #include <stdlib.h>
- int rand(void);
- Description
-2 The rand function computes a sequence of pseudo-random integers in the range 0 to
- RAND_MAX.288)
-3 The rand function is not required to avoid data races. The implementation shall behave
- as if no library function calls the rand function.
- Returns
-4 The rand function returns a pseudo-random integer.
- Environmental limits
-5 The value of the RAND_MAX macro shall be at least 32767.
- 7.22.2.2 The srand function
- Synopsis
-1 #include <stdlib.h>
- void srand(unsigned int seed);
- Description
-2 The srand function uses the argument as a seed for a new sequence of pseudo-random
- numbers to be returned by subsequent calls to rand. If srand is then called with the
- same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
- called before any calls to srand have been made, the same sequence shall be generated
- as when srand is first called with a seed value of 1.
-3 The implementation shall behave as if no library function calls the srand function.
- Returns
-4 The srand function returns no value.
-
-
-
-
- 288) There are no guarantees as to the quality of the random sequence produced and some implementations
- are known to produce sequences with distressingly non-random low-order bits. Applications with
- particular requirements should use a generator that is known to be sufficient for their needs.
-
-[page 346] (Contents)
-
-5 EXAMPLE The following functions define a portable implementation of rand and srand.
- static unsigned long int next = 1;
- int rand(void) // RAND_MAX assumed to be 32767
- {
- next = next * 1103515245 + 12345;
- return (unsigned int)(next/65536) % 32768;
- }
- void srand(unsigned int seed)
- {
- next = seed;
+ int i = 4;
+ f(i);
+ case 0:
+ i = 17;
+ /* falls through into default code */
+ default:
+ printf("%d\n", i);
+ }
+
+ the object whose identifier is i exists with automatic storage duration (within the block) but is never
+ initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
+ access an indeterminate value. Similarly, the call to the function f cannot be reached.
+
+
+154) That is, the declaration either precedes the switch statement, or it follows the last case or + default label associated with the switch that is in the block containing the declaration. + + +
+
+ iteration-statement: + while ( expression ) statement + do statement while ( expression ) ; + for ( expressionopt ; expressionopt ; expressionopt ) statement + for ( declaration expressionopt ; expressionopt ) statement ++
+ The controlling expression of an iteration statement shall have scalar type. +
+ The declaration part of a for statement shall only declare identifiers for objects having + storage class auto or register. +
+ An iteration statement causes a statement called the loop body to be executed repeatedly + until the controlling expression compares equal to 0. The repetition occurs regardless of + whether the loop body is entered from the iteration statement or by a jump.155) +
+ An iteration statement is a block whose scope is a strict subset of the scope of its + enclosing block. The loop body is also a block whose scope is a strict subset of the scope + of the iteration statement. +
+ An iteration statement whose controlling expression is not a constant expression,156) that + performs no input/output operations, does not access volatile objects, and performs no + synchronization or atomic operations in its body, controlling expression, or (in the case of + + + a for statement) its expression-3, may be assumed by the implementation to + terminate.157) + +
155) Code jumped over is not executed. In particular, the controlling expression of a for or while + statement is not evaluated before entering the loop body, nor is clause-1 of a for statement. + +
156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression. + +
157) This is intended to allow compiler transformations such as removal of empty loops even when + termination cannot be proven. + + +
+ The evaluation of the controlling expression takes place before each execution of the loop + body. + +
+ The evaluation of the controlling expression takes place after each execution of the loop + body. + +
+ The statement +
+ for ( clause-1 ; expression-2 ; expression-3 ) statement ++ behaves as follows: The expression expression-2 is the controlling expression that is + evaluated before each execution of the loop body. The expression expression-3 is + evaluated as a void expression after each execution of the loop body. If clause-1 is a + declaration, the scope of any identifiers it declares is the remainder of the declaration and + the entire loop, including the other two expressions; it is reached in the order of execution + before the first evaluation of the controlling expression. If clause-1 is an expression, it is + evaluated as a void expression before the first evaluation of the controlling expression.158) +
+ Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a + nonzero constant. + +
158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in + the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration, + such that execution of the loop continues until the expression compares equal to 0; and expression-3 + specifies an operation (such as incrementing) that is performed after each iteration. + + +
+
+ jump-statement: + goto identifier ; + continue ; + break ; + return expressionopt ; ++ + + + + +
+ A jump statement causes an unconditional jump to another place. + +
+ The identifier in a goto statement shall name a label located somewhere in the enclosing + function. A goto statement shall not jump from outside the scope of an identifier having + a variably modified type to inside the scope of that identifier. +
+ A goto statement causes an unconditional jump to the statement prefixed by the named + label in the enclosing function. +
+ EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The + following outline presents one possible approach to a problem based on these three assumptions: +
+ /* ... */
+ goto first_time;
+ for (;;) {
+ // determine next operation
+ /* ... */
+ if (need to reinitialize) {
+ // reinitialize-only code
+ /* ... */
+ first_time:
+ // general initialization code
+ /* ... */
+ continue;
}
-
- 7.22.3 Memory management functions
-1 The order and contiguity of storage allocated by successive calls to the
- aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
- pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
- a pointer to any type of object with a fundamental alignment requirement and then used
- to access such an object or an array of such objects in the space allocated (until the space
- is explicitly deallocated). The lifetime of an allocated object extends from the allocation
- until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
- any other object. The pointer returned points to the start (lowest byte address) of the
- allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
- the space requested is zero, the behavior is implementation-defined: either a null pointer
- is returned, or the behavior is as if the size were some nonzero value, except that the
- returned pointer shall not be used to access an object.
- 7.22.3.1 The aligned_alloc function
- Synopsis
-1 #include <stdlib.h>
- void *aligned_alloc(size_t alignment, size_t size);
- Description
-2 The aligned_alloc function allocates space for an object whose alignment is
- specified by alignment, whose size is specified by size, and whose value is
- indeterminate. The value of alignment shall be a valid alignment supported by the
- implementation and the value of size shall be an integral multiple of alignment.
- Returns
-3 The aligned_alloc function returns either a null pointer or a pointer to the allocated
- space.
-
-
-
-
-[page 347] (Contents)
-
- 7.22.3.2 The calloc function
- Synopsis
-1 #include <stdlib.h>
- void *calloc(size_t nmemb, size_t size);
- Description
-2 The calloc function allocates space for an array of nmemb objects, each of whose size
- is size. The space is initialized to all bits zero.289)
- Returns
-3 The calloc function returns either a null pointer or a pointer to the allocated space.
- 7.22.3.3 The free function
- Synopsis
-1 #include <stdlib.h>
- void free(void *ptr);
- Description
-2 The free function causes the space pointed to by ptr to be deallocated, that is, made
- available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
- the argument does not match a pointer earlier returned by a memory management
- function, or if the space has been deallocated by a call to free or realloc, the
- behavior is undefined.
- Returns
-3 The free function returns no value.
- 7.22.3.4 The malloc function
- Synopsis
-1 #include <stdlib.h>
- void *malloc(size_t size);
- Description
-2 The malloc function allocates space for an object whose size is specified by size and
- whose value is indeterminate.
-
-
-
-
- 289) Note that this need not be the same as the representation of floating-point zero or a null pointer
- constant.
-
-[page 348] (Contents)
-
- Returns
-3 The malloc function returns either a null pointer or a pointer to the allocated space.
- 7.22.3.5 The realloc function
- Synopsis
-1 #include <stdlib.h>
- void *realloc(void *ptr, size_t size);
- Description
-2 The realloc function deallocates the old object pointed to by ptr and returns a
- pointer to a new object that has the size specified by size. The contents of the new
- object shall be the same as that of the old object prior to deallocation, up to the lesser of
- the new and old sizes. Any bytes in the new object beyond the size of the old object have
- indeterminate values.
-3 If ptr is a null pointer, the realloc function behaves like the malloc function for the
- specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
- management function, or if the space has been deallocated by a call to the free or
- realloc function, the behavior is undefined. If memory for the new object cannot be
- allocated, the old object is not deallocated and its value is unchanged.
- Returns
-4 The realloc function returns a pointer to the new object (which may have the same
- value as a pointer to the old object), or a null pointer if the new object could not be
- allocated.
- 7.22.4 Communication with the environment
- 7.22.4.1 The abort function
- Synopsis
-1 #include <stdlib.h>
- _Noreturn void abort(void);
- Description
-2 The abort function causes abnormal program termination to occur, unless the signal
- SIGABRT is being caught and the signal handler does not return. Whether open streams
- with unwritten buffered data are flushed, open streams are closed, or temporary files are
- removed is implementation-defined. An implementation-defined form of the status
- unsuccessful termination is returned to the host environment by means of the function
- call raise(SIGABRT).
-
-
-
-
-[page 349] (Contents)
-
- Returns
-3 The abort function does not return to its caller.
- 7.22.4.2 The atexit function
- Synopsis
-1 #include <stdlib.h>
- int atexit(void (*func)(void));
- Description
-2 The atexit function registers the function pointed to by func, to be called without
- arguments at normal program termination.290)
- Environmental limits
-3 The implementation shall support the registration of at least 32 functions.
- Returns
-4 The atexit function returns zero if the registration succeeds, nonzero if it fails.
- Forward references: the at_quick_exit function (7.22.4.3), the exit function
- (7.22.4.4).
- 7.22.4.3 The at_quick_exit function
- Synopsis
-1 #include <stdlib.h>
- int at_quick_exit(void (*func)(void));
- Description
-2 The at_quick_exit function registers the function pointed to by func, to be called
- without arguments should quick_exit be called.291)
- Environmental limits
-3 The implementation shall support the registration of at least 32 functions.
- Returns
-4 The at_quick_exit function returns zero if the registration succeeds, nonzero if it
- fails.
- Forward references: the quick_exit function (7.22.4.7).
-
-
- 290) The atexit function registrations are distinct from the at_quick_exit registrations, so
- applications may need to call both registration functions with the same argument.
- 291) The at_quick_exit function registrations are distinct from the atexit registrations, so
- applications may need to call both registration functions with the same argument.
-
-[page 350] (Contents)
-
- 7.22.4.4 The exit function
- Synopsis
-1 #include <stdlib.h>
- _Noreturn void exit(int status);
- Description
-2 The exit function causes normal program termination to occur. No functions registered
- by the at_quick_exit function are called. If a program calls the exit function
- more than once, or calls the quick_exit function in addition to the exit function, the
- behavior is undefined.
-3 First, all functions registered by the atexit function are called, in the reverse order of
- their registration,292) except that a function is called after any previously registered
- functions that had already been called at the time it was registered. If, during the call to
- any such function, a call to the longjmp function is made that would terminate the call
- to the registered function, the behavior is undefined.
-4 Next, all open streams with unwritten buffered data are flushed, all open streams are
- closed, and all files created by the tmpfile function are removed.
-5 Finally, control is returned to the host environment. If the value of status is zero or
- EXIT_SUCCESS, an implementation-defined form of the status successful termination is
- returned. If the value of status is EXIT_FAILURE, an implementation-defined form
- of the status unsuccessful termination is returned. Otherwise the status returned is
- implementation-defined.
- Returns
-6 The exit function cannot return to its caller.
- 7.22.4.5 The _Exit function
- Synopsis
-1 #include <stdlib.h>
- _Noreturn void _Exit(int status);
- Description
-2 The _Exit function causes normal program termination to occur and control to be
- returned to the host environment. No functions registered by the atexit function, the
- at_quick_exit function, or signal handlers registered by the signal function are
- called. The status returned to the host environment is determined in the same way as for
-
-
- 292) Each function is called as many times as it was registered, and in the correct order with respect to
- other registered functions.
-
-[page 351] (Contents)
-
- the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
- flushed, open streams are closed, or temporary files are removed is implementation-
- defined.
- Returns
-3 The _Exit function cannot return to its caller.
- 7.22.4.6 The getenv function
- Synopsis
-1 #include <stdlib.h>
- char *getenv(const char *name);
- Description
-2 The getenv function searches an environment list, provided by the host environment,
- for a string that matches the string pointed to by name. The set of environment names
- and the method for altering the environment list are implementation-defined. The
- getenv function need not avoid data races with other threads of execution that modify
- the environment list.293)
-3 The implementation shall behave as if no library function calls the getenv function.
- Returns
-4 The getenv function returns a pointer to a string associated with the matched list
- member. The string pointed to shall not be modified by the program, but may be
- overwritten by a subsequent call to the getenv function. If the specified name cannot
- be found, a null pointer is returned.
- 7.22.4.7 The quick_exit function
- Synopsis
-1 #include <stdlib.h>
- _Noreturn void quick_exit(int status);
- Description
-2 The quick_exit function causes normal program termination to occur. No functions
- registered by the atexit function or signal handlers registered by the signal function
- are called. If a program calls the quick_exit function more than once, or calls the
- exit function in addition to the quick_exit function, the behavior is undefined.
-3 The quick_exit function first calls all functions registered by the at_quick_exit
- function, in the reverse order of their registration,294) except that a function is called after
-
-
- 293) Many implementations provide non-standard functions that modify the environment list.
-
-[page 352] (Contents)
-
- any previously registered functions that had already been called at the time it was
- registered. If, during the call to any such function, a call to the longjmp function is
- made that would terminate the call to the registered function, the behavior is undefined.
-4 Then control is returned to the host environment by means of the function call
- _Exit(status).
- Returns
-5 The quick_exit function cannot return to its caller.
- 7.22.4.8 The system function
- Synopsis
-1 #include <stdlib.h>
- int system(const char *string);
- Description
-2 If string is a null pointer, the system function determines whether the host
- environment has a command processor. If string is not a null pointer, the system
- function passes the string pointed to by string to that command processor to be
- executed in a manner which the implementation shall document; this might then cause the
- program calling system to behave in a non-conforming manner or to terminate.
- Returns
-3 If the argument is a null pointer, the system function returns nonzero only if a
- command processor is available. If the argument is not a null pointer, and the system
- function does return, it returns an implementation-defined value.
- 7.22.5 Searching and sorting utilities
-1 These utilities make use of a comparison function to search or sort arrays of unspecified
- type. Where an argument declared as size_t nmemb specifies the length of the array
- for a function, nmemb can have the value zero on a call to that function; the comparison
- function is not called, a search finds no matching element, and sorting performs no
- rearrangement. Pointer arguments on such a call shall still have valid values, as described
- in 7.1.4.
-2 The implementation shall ensure that the second argument of the comparison function
- (when called from bsearch), or both arguments (when called from qsort), are
- pointers to elements of the array.295) The first argument when called from bsearch
- shall equal key.
-
-
-
- 294) Each function is called as many times as it was registered, and in the correct order with respect to
- other registered functions.
-
-[page 353] (Contents)
-
-3 The comparison function shall not alter the contents of the array. The implementation
- may reorder elements of the array between calls to the comparison function, but shall not
- alter the contents of any individual element.
-4 When the same objects (consisting of size bytes, irrespective of their current positions
- in the array) are passed more than once to the comparison function, the results shall be
- consistent with one another. That is, for qsort they shall define a total ordering on the
- array, and for bsearch the same object shall always compare the same way with the
- key.
-5 A sequence point occurs immediately before and immediately after each call to the
- comparison function, and also between any call to the comparison function and any
- movement of the objects passed as arguments to that call.
- 7.22.5.1 The bsearch function
- Synopsis
-1 #include <stdlib.h>
- void *bsearch(const void *key, const void *base,
- size_t nmemb, size_t size,
- int (*compar)(const void *, const void *));
- Description
-2 The bsearch function searches an array of nmemb objects, the initial element of which
- is pointed to by base, for an element that matches the object pointed to by key. The
- size of each element of the array is specified by size.
-3 The comparison function pointed to by compar is called with two arguments that point
- to the key object and to an array element, in that order. The function shall return an
- integer less than, equal to, or greater than zero if the key object is considered,
- respectively, to be less than, to match, or to be greater than the array element. The array
- shall consist of: all the elements that compare less than, all the elements that compare
- equal to, and all the elements that compare greater than the key object, in that order.296)
- Returns
-4 The bsearch function returns a pointer to a matching element of the array, or a null
- pointer if no match is found. If two elements compare as equal, which element is
-
-
- 295) That is, if the value passed is p, then the following expressions are always nonzero:
- ((char *)p - (char *)base) % size == 0
- (char *)p >= (char *)base
- (char *)p < (char *)base + nmemb * size
-
- 296) In practice, the entire array is sorted according to the comparison function.
-
-[page 354] (Contents)
-
- matched is unspecified.
- 7.22.5.2 The qsort function
- Synopsis
-1 #include <stdlib.h>
- void qsort(void *base, size_t nmemb, size_t size,
- int (*compar)(const void *, const void *));
- Description
-2 The qsort function sorts an array of nmemb objects, the initial element of which is
- pointed to by base. The size of each object is specified by size.
-3 The contents of the array are sorted into ascending order according to a comparison
- function pointed to by compar, which is called with two arguments that point to the
- objects being compared. The function shall return an integer less than, equal to, or
- greater than zero if the first argument is considered to be respectively less than, equal to,
- or greater than the second.
-4 If two elements compare as equal, their order in the resulting sorted array is unspecified.
- Returns
-5 The qsort function returns no value.
- 7.22.6 Integer arithmetic functions
- 7.22.6.1 The abs, labs and llabs functions
- Synopsis
-1 #include <stdlib.h>
- int abs(int j);
- long int labs(long int j);
- long long int llabs(long long int j);
- Description
-2 The abs, labs, and llabs functions compute the absolute value of an integer j. If the
- result cannot be represented, the behavior is undefined.297)
- Returns
-3 The abs, labs, and llabs, functions return the absolute value.
-
-
-
-
- 297) The absolute value of the most negative number cannot be represented in two's complement.
-
-[page 355] (Contents)
-
- 7.22.6.2 The div, ldiv, and lldiv functions
- Synopsis
-1 #include <stdlib.h>
- div_t div(int numer, int denom);
- ldiv_t ldiv(long int numer, long int denom);
- lldiv_t lldiv(long long int numer, long long int denom);
- Description
-2 The div, ldiv, and lldiv, functions compute numer / denom and numer %
- denom in a single operation.
- Returns
-3 The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
- lldiv_t, respectively, comprising both the quotient and the remainder. The structures
- shall contain (in either order) the members quot (the quotient) and rem (the remainder),
- each of which has the same type as the arguments numer and denom. If either part of
- the result cannot be represented, the behavior is undefined.
- 7.22.7 Multibyte/wide character conversion functions
-1 The behavior of the multibyte character functions is affected by the LC_CTYPE category
- of the current locale. For a state-dependent encoding, each function is placed into its
- initial conversion state at program startup and can be returned to that state by a call for
- which its character pointer argument, s, is a null pointer. Subsequent calls with s as
- other than a null pointer cause the internal conversion state of the function to be altered as
- necessary. A call with s as a null pointer causes these functions to return a nonzero value
- if encodings have state dependency, and zero otherwise.298) Changing the LC_CTYPE
- category causes the conversion state of these functions to be indeterminate.
- 7.22.7.1 The mblen function
- Synopsis
-1 #include <stdlib.h>
- int mblen(const char *s, size_t n);
- Description
-2 If s is not a null pointer, the mblen function determines the number of bytes contained
- in the multibyte character pointed to by s. Except that the conversion state of the
- mbtowc function is not affected, it is equivalent to
-
-
-
- 298) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
- character codes, but are grouped with an adjacent multibyte character.
-
-[page 356] (Contents)
-
- mbtowc((wchar_t *)0, (const char *)0, 0);
- mbtowc((wchar_t *)0, s, n);
-3 The implementation shall behave as if no library function calls the mblen function.
- Returns
-4 If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
- character encodings, respectively, do or do not have state-dependent encodings. If s is
- not a null pointer, the mblen function either returns 0 (if s points to the null character),
- or returns the number of bytes that are contained in the multibyte character (if the next n
- or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid
- multibyte character).
- Forward references: the mbtowc function (7.22.7.2).
- 7.22.7.2 The mbtowc function
- Synopsis
-1 #include <stdlib.h>
- int mbtowc(wchar_t * restrict pwc,
- const char * restrict s,
- size_t n);
- Description
-2 If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
- the byte pointed to by s to determine the number of bytes needed to complete the next
- multibyte character (including any shift sequences). If the function determines that the
- next multibyte character is complete and valid, it determines the value of the
- corresponding wide character and then, if pwc is not a null pointer, stores that value in
- the object pointed to by pwc. If the corresponding wide character is the null wide
- character, the function is left in the initial conversion state.
-3 The implementation shall behave as if no library function calls the mbtowc function.
- Returns
-4 If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
- character encodings, respectively, do or do not have state-dependent encodings. If s is
- not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
- or returns the number of bytes that are contained in the converted multibyte character (if
- the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not
- form a valid multibyte character).
-5 In no case will the value returned be greater than n or the value of the MB_CUR_MAX
- macro.
-
-
-[page 357] (Contents)
-
- 7.22.7.3 The wctomb function
- Synopsis
-1 #include <stdlib.h>
- int wctomb(char *s, wchar_t wc);
- Description
-2 The wctomb function determines the number of bytes needed to represent the multibyte
- character corresponding to the wide character given by wc (including any shift
- sequences), and stores the multibyte character representation in the array whose first
- element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
- are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
- sequence needed to restore the initial shift state, and the function is left in the initial
- conversion state.
-3 The implementation shall behave as if no library function calls the wctomb function.
- Returns
-4 If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
- character encodings, respectively, do or do not have state-dependent encodings. If s is
- not a null pointer, the wctomb function returns -1 if the value of wc does not correspond
- to a valid multibyte character, or returns the number of bytes that are contained in the
- multibyte character corresponding to the value of wc.
-5 In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
- 7.22.8 Multibyte/wide string conversion functions
-1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of
- the current locale.
- 7.22.8.1 The mbstowcs function
- Synopsis
-1 #include <stdlib.h>
- size_t mbstowcs(wchar_t * restrict pwcs,
- const char * restrict s,
- size_t n);
- Description
-2 The mbstowcs function converts a sequence of multibyte characters that begins in the
- initial shift state from the array pointed to by s into a sequence of corresponding wide
- characters and stores not more than n wide characters into the array pointed to by pwcs.
- No multibyte characters that follow a null character (which is converted into a null wide
- character) will be examined or converted. Each multibyte character is converted as if by
- a call to the mbtowc function, except that the conversion state of the mbtowc function is
-[page 358] (Contents)
-
- not affected.
-3 No more than n elements will be modified in the array pointed to by pwcs. If copying
- takes place between objects that overlap, the behavior is undefined.
- Returns
-4 If an invalid multibyte character is encountered, the mbstowcs function returns
- (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
- elements modified, not including a terminating null wide character, if any.299)
- 7.22.8.2 The wcstombs function
- Synopsis
-1 #include <stdlib.h>
- size_t wcstombs(char * restrict s,
- const wchar_t * restrict pwcs,
- size_t n);
- Description
-2 The wcstombs function converts a sequence of wide characters from the array pointed
- to by pwcs into a sequence of corresponding multibyte characters that begins in the
- initial shift state, and stores these multibyte characters into the array pointed to by s,
- stopping if a multibyte character would exceed the limit of n total bytes or if a null
- character is stored. Each wide character is converted as if by a call to the wctomb
- function, except that the conversion state of the wctomb function is not affected.
-3 No more than n bytes will be modified in the array pointed to by s. If copying takes place
- between objects that overlap, the behavior is undefined.
- Returns
-4 If a wide character is encountered that does not correspond to a valid multibyte character,
- the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
- returns the number of bytes modified, not including a terminating null character, if
- any.299)
-
-
-
-
- 299) The array will not be null-terminated if the value returned is n.
-
-[page 359] (Contents)
-
- 7.23 String handling <string.h>
- 7.23.1 String function conventions
-1 The header <string.h> declares one type and several functions, and defines one
- macro useful for manipulating arrays of character type and other objects treated as arrays
- of character type.300) The type is size_t and the macro is NULL (both described in
- 7.19). Various methods are used for determining the lengths of the arrays, but in all cases
- a char * or void * argument points to the initial (lowest addressed) character of the
- array. If an array is accessed beyond the end of an object, the behavior is undefined.
-2 Where an argument declared as size_t n specifies the length of the array for a
- function, n can have the value zero on a call to that function. Unless explicitly stated
- otherwise in the description of a particular function in this subclause, pointer arguments
- on such a call shall still have valid values, as described in 7.1.4. On such a call, a
- function that locates a character finds no occurrence, a function that compares two
- character sequences returns zero, and a function that copies characters copies zero
- characters.
-3 For all functions in this subclause, each character shall be interpreted as if it had the type
- unsigned char (and therefore every possible object representation is valid and has a
- different value).
- 7.23.2 Copying functions
- 7.23.2.1 The memcpy function
- Synopsis
-1 #include <string.h>
- void *memcpy(void * restrict s1,
- const void * restrict s2,
- size_t n);
- Description
-2 The memcpy function copies n characters from the object pointed to by s2 into the
- object pointed to by s1. If copying takes place between objects that overlap, the behavior
- is undefined.
- Returns
-3 The memcpy function returns the value of s1.
-
-
-
-
- 300) See ''future library directions'' (7.30.11).
-
-[page 360] (Contents)
-
- 7.23.2.2 The memmove function
- Synopsis
-1 #include <string.h>
- void *memmove(void *s1, const void *s2, size_t n);
- Description
-2 The memmove function copies n characters from the object pointed to by s2 into the
- object pointed to by s1. Copying takes place as if the n characters from the object
- pointed to by s2 are first copied into a temporary array of n characters that does not
- overlap the objects pointed to by s1 and s2, and then the n characters from the
- temporary array are copied into the object pointed to by s1.
- Returns
-3 The memmove function returns the value of s1.
- 7.23.2.3 The strcpy function
- Synopsis
-1 #include <string.h>
- char *strcpy(char * restrict s1,
- const char * restrict s2);
- Description
-2 The strcpy function copies the string pointed to by s2 (including the terminating null
- character) into the array pointed to by s1. If copying takes place between objects that
- overlap, the behavior is undefined.
- Returns
-3 The strcpy function returns the value of s1.
- 7.23.2.4 The strncpy function
- Synopsis
-1 #include <string.h>
- char *strncpy(char * restrict s1,
- const char * restrict s2,
- size_t n);
- Description
-2 The strncpy function copies not more than n characters (characters that follow a null
- character are not copied) from the array pointed to by s2 to the array pointed to by
-
-
-
-
-[page 361] (Contents)
-
- s1.301) If copying takes place between objects that overlap, the behavior is undefined.
-3 If the array pointed to by s2 is a string that is shorter than n characters, null characters
- are appended to the copy in the array pointed to by s1, until n characters in all have been
- written.
- Returns
-4 The strncpy function returns the value of s1.
- 7.23.3 Concatenation functions
- 7.23.3.1 The strcat function
- Synopsis
-1 #include <string.h>
- char *strcat(char * restrict s1,
- const char * restrict s2);
- Description
-2 The strcat function appends a copy of the string pointed to by s2 (including the
- terminating null character) to the end of the string pointed to by s1. The initial character
- of s2 overwrites the null character at the end of s1. If copying takes place between
- objects that overlap, the behavior is undefined.
- Returns
-3 The strcat function returns the value of s1.
- 7.23.3.2 The strncat function
- Synopsis
-1 #include <string.h>
- char *strncat(char * restrict s1,
- const char * restrict s2,
- size_t n);
- Description
-2 The strncat function appends not more than n characters (a null character and
- characters that follow it are not appended) from the array pointed to by s2 to the end of
- the string pointed to by s1. The initial character of s2 overwrites the null character at the
- end of s1. A terminating null character is always appended to the result.302) If copying
-
- 301) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
- not be null-terminated.
- 302) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
- strlen(s1)+n+1.
-
-[page 362] (Contents)
-
- takes place between objects that overlap, the behavior is undefined.
- Returns
-3 The strncat function returns the value of s1.
- Forward references: the strlen function (7.23.6.3).
- 7.23.4 Comparison functions
-1 The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
- and strncmp is determined by the sign of the difference between the values of the first
- pair of characters (both interpreted as unsigned char) that differ in the objects being
- compared.
- 7.23.4.1 The memcmp function
- Synopsis
-1 #include <string.h>
- int memcmp(const void *s1, const void *s2, size_t n);
- Description
-2 The memcmp function compares the first n characters of the object pointed to by s1 to
- the first n characters of the object pointed to by s2.303)
- Returns
-3 The memcmp function returns an integer greater than, equal to, or less than zero,
- accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
- pointed to by s2.
- 7.23.4.2 The strcmp function
- Synopsis
-1 #include <string.h>
- int strcmp(const char *s1, const char *s2);
- Description
-2 The strcmp function compares the string pointed to by s1 to the string pointed to by
- s2.
- Returns
-3 The strcmp function returns an integer greater than, equal to, or less than zero,
- accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
-
- 303) The contents of ''holes'' used as padding for purposes of alignment within structure objects are
- indeterminate. Strings shorter than their allocated space and unions may also cause problems in
- comparison.
-
-[page 363] (Contents)
-
- pointed to by s2.
- 7.23.4.3 The strcoll function
- Synopsis
-1 #include <string.h>
- int strcoll(const char *s1, const char *s2);
- Description
-2 The strcoll function compares the string pointed to by s1 to the string pointed to by
- s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
- Returns
-3 The strcoll function returns an integer greater than, equal to, or less than zero,
- accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
- pointed to by s2 when both are interpreted as appropriate to the current locale.
- 7.23.4.4 The strncmp function
- Synopsis
-1 #include <string.h>
- int strncmp(const char *s1, const char *s2, size_t n);
- Description
-2 The strncmp function compares not more than n characters (characters that follow a
- null character are not compared) from the array pointed to by s1 to the array pointed to
- by s2.
- Returns
-3 The strncmp function returns an integer greater than, equal to, or less than zero,
- accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
- to, or less than the possibly null-terminated array pointed to by s2.
- 7.23.4.5 The strxfrm function
- Synopsis
-1 #include <string.h>
- size_t strxfrm(char * restrict s1,
- const char * restrict s2,
- size_t n);
- Description
-2 The strxfrm function transforms the string pointed to by s2 and places the resulting
- string into the array pointed to by s1. The transformation is such that if the strcmp
- function is applied to two transformed strings, it returns a value greater than, equal to, or
-
-[page 364] (Contents)
-
- less than zero, corresponding to the result of the strcoll function applied to the same
- two original strings. No more than n characters are placed into the resulting array
- pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
- be a null pointer. If copying takes place between objects that overlap, the behavior is
- undefined.
- Returns
-3 The strxfrm function returns the length of the transformed string (not including the
- terminating null character). If the value returned is n or more, the contents of the array
- pointed to by s1 are indeterminate.
-4 EXAMPLE The value of the following expression is the size of the array needed to hold the
- transformation of the string pointed to by s.
- 1 + strxfrm(NULL, s, 0)
-
- 7.23.5 Search functions
- 7.23.5.1 The memchr function
- Synopsis
-1 #include <string.h>
- void *memchr(const void *s, int c, size_t n);
- Description
-2 The memchr function locates the first occurrence of c (converted to an unsigned
- char) in the initial n characters (each interpreted as unsigned char) of the object
- pointed to by s. The implementation shall behave as if it reads the characters sequentially
- and stops as soon as a matching character is found.
- Returns
-3 The memchr function returns a pointer to the located character, or a null pointer if the
- character does not occur in the object.
- 7.23.5.2 The strchr function
- Synopsis
-1 #include <string.h>
- char *strchr(const char *s, int c);
- Description
-2 The strchr function locates the first occurrence of c (converted to a char) in the
- string pointed to by s. The terminating null character is considered to be part of the
- string.
-
-
-
-[page 365] (Contents)
-
- Returns
-3 The strchr function returns a pointer to the located character, or a null pointer if the
- character does not occur in the string.
- 7.23.5.3 The strcspn function
- Synopsis
-1 #include <string.h>
- size_t strcspn(const char *s1, const char *s2);
- Description
-2 The strcspn function computes the length of the maximum initial segment of the string
- pointed to by s1 which consists entirely of characters not from the string pointed to by
- s2.
- Returns
-3 The strcspn function returns the length of the segment.
- 7.23.5.4 The strpbrk function
- Synopsis
-1 #include <string.h>
- char *strpbrk(const char *s1, const char *s2);
- Description
-2 The strpbrk function locates the first occurrence in the string pointed to by s1 of any
- character from the string pointed to by s2.
- Returns
-3 The strpbrk function returns a pointer to the character, or a null pointer if no character
- from s2 occurs in s1.
- 7.23.5.5 The strrchr function
- Synopsis
-1 #include <string.h>
- char *strrchr(const char *s, int c);
- Description
-2 The strrchr function locates the last occurrence of c (converted to a char) in the
- string pointed to by s. The terminating null character is considered to be part of the
- string.
-
-
-
-
-[page 366] (Contents)
-
- Returns
-3 The strrchr function returns a pointer to the character, or a null pointer if c does not
- occur in the string.
- 7.23.5.6 The strspn function
- Synopsis
-1 #include <string.h>
- size_t strspn(const char *s1, const char *s2);
- Description
-2 The strspn function computes the length of the maximum initial segment of the string
- pointed to by s1 which consists entirely of characters from the string pointed to by s2.
- Returns
-3 The strspn function returns the length of the segment.
- 7.23.5.7 The strstr function
- Synopsis
-1 #include <string.h>
- char *strstr(const char *s1, const char *s2);
- Description
-2 The strstr function locates the first occurrence in the string pointed to by s1 of the
- sequence of characters (excluding the terminating null character) in the string pointed to
- by s2.
- Returns
-3 The strstr function returns a pointer to the located string, or a null pointer if the string
- is not found. If s2 points to a string with zero length, the function returns s1.
- 7.23.5.8 The strtok function
- Synopsis
-1 #include <string.h>
- char *strtok(char * restrict s1,
- const char * restrict s2);
- Description
-2 A sequence of calls to the strtok function breaks the string pointed to by s1 into a
- sequence of tokens, each of which is delimited by a character from the string pointed to
- by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
- sequence have a null first argument. The separator string pointed to by s2 may be
- different from call to call.
-[page 367] (Contents)
-
-3 The first call in the sequence searches the string pointed to by s1 for the first character
- that is not contained in the current separator string pointed to by s2. If no such character
- is found, then there are no tokens in the string pointed to by s1 and the strtok function
- returns a null pointer. If such a character is found, it is the start of the first token.
-4 The strtok function then searches from there for a character that is contained in the
- current separator string. If no such character is found, the current token extends to the
- end of the string pointed to by s1, and subsequent searches for a token will return a null
- pointer. If such a character is found, it is overwritten by a null character, which
- terminates the current token. The strtok function saves a pointer to the following
- character, from which the next search for a token will start.
-5 Each subsequent call, with a null pointer as the value of the first argument, starts
- searching from the saved pointer and behaves as described above.
-6 The strtok function is not required to avoid data races. The implementation shall
- behave as if no library function calls the strtok function.
- Returns
-7 The strtok function returns a pointer to the first character of a token, or a null pointer
- if there is no token.
-8 EXAMPLE
- #include <string.h>
- static char str[] = "?a???b,,,#c";
- char *t;
- t = strtok(str, "?"); // t points to the token "a"
- t = strtok(NULL, ","); // t points to the token "??b"
- t = strtok(NULL, "#,"); // t points to the token "c"
- t = strtok(NULL, "?"); // t is a null pointer
-
- 7.23.6 Miscellaneous functions
- 7.23.6.1 The memset function
- Synopsis
-1 #include <string.h>
- void *memset(void *s, int c, size_t n);
- Description
-2 The memset function copies the value of c (converted to an unsigned char) into
- each of the first n characters of the object pointed to by s.
- Returns
-3 The memset function returns the value of s.
-
-
-
-[page 368] (Contents)
-
- 7.23.6.2 The strerror function
- Synopsis
-1 #include <string.h>
- char *strerror(int errnum);
- Description
-2 The strerror function maps the number in errnum to a message string. Typically,
- the values for errnum come from errno, but strerror shall map any value of type
- int to a message.
-3 The strerror function is not required to avoid data races. The implementation shall
- behave as if no library function calls the strerror function.
- Returns
-4 The strerror function returns a pointer to the string, the contents of which are locale-
- specific. The array pointed to shall not be modified by the program, but may be
- overwritten by a subsequent call to the strerror function.
- 7.23.6.3 The strlen function
- Synopsis
-1 #include <string.h>
- size_t strlen(const char *s);
- Description
-2 The strlen function computes the length of the string pointed to by s.
- Returns
-3 The strlen function returns the number of characters that precede the terminating null
- character.
-
-
-
-
-[page 369] (Contents)
-
- 7.24 Type-generic math <tgmath.h>
-1 The header <tgmath.h> includes the headers <math.h> and <complex.h> and
- defines several type-generic macros.
-2 Of the <math.h> and <complex.h> functions without an f (float) or l (long
- double) suffix, several have one or more parameters whose corresponding real type is
- double. For each such function, except modf, there is a corresponding type-generic
- macro.304) The parameters whose corresponding real type is double in the function
- synopsis are generic parameters. Use of the macro invokes a function whose
- corresponding real type and type domain are determined by the arguments for the generic
- parameters.305)
-3 Use of the macro invokes a function whose generic parameters have the corresponding
- real type determined as follows:
- -- First, if any argument for generic parameters has type long double, the type
- determined is long double.
- -- Otherwise, if any argument for generic parameters has type double or is of integer
- type, the type determined is double.
- -- Otherwise, the type determined is float.
-4 For each unsuffixed function in <math.h> for which there is a function in
- <complex.h> with the same name except for a c prefix, the corresponding type-
- generic macro (for both functions) has the same name as the function in <math.h>. The
- corresponding type-generic macro for fabs and cabs is fabs.
-
-
-
-
- 304) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
- make available the corresponding ordinary function.
- 305) If the type of the argument is not compatible with the type of the parameter for the selected function,
- the behavior is undefined.
-
-[page 370] (Contents)
-
- <math.h> <complex.h> type-generic
- function function macro
- acos cacos acos
- asin casin asin
- atan catan atan
- acosh cacosh acosh
- asinh casinh asinh
- atanh catanh atanh
- cos ccos cos
- sin csin sin
- tan ctan tan
- cosh ccosh cosh
- sinh csinh sinh
- tanh ctanh tanh
- exp cexp exp
- log clog log
- pow cpow pow
- sqrt csqrt sqrt
- fabs cabs fabs
- If at least one argument for a generic parameter is complex, then use of the macro invokes
- a complex function; otherwise, use of the macro invokes a real function.
-5 For each unsuffixed function in <math.h> without a c-prefixed counterpart in
- <complex.h> (except modf), the corresponding type-generic macro has the same
- name as the function. These type-generic macros are:
- atan2 fma llround remainder
- cbrt fmax log10 remquo
- ceil fmin log1p rint
- copysign fmod log2 round
- erf frexp logb scalbn
- erfc hypot lrint scalbln
- exp2 ilogb lround tgamma
- expm1 ldexp nearbyint trunc
- fdim lgamma nextafter
- floor llrint nexttoward
- If all arguments for generic parameters are real, then use of the macro invokes a real
- function; otherwise, use of the macro results in undefined behavior.
-
-
-
-
-[page 371] (Contents)
-
-6 For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a
- function in <math.h>, the corresponding type-generic macro has the same name as the
- function. These type-generic macros are:
- carg conj creal
- cimag cproj
- Use of the macro with any real or complex argument invokes a complex function.
-7 EXAMPLE With the declarations
- #include <tgmath.h>
- int n;
- float f;
- double d;
- long double ld;
- float complex fc;
- double complex dc;
- long double complex ldc;
- functions invoked by use of type-generic macros are shown in the following table:
- macro use invokes
- exp(n) exp(n), the function
- acosh(f) acoshf(f)
- sin(d) sin(d), the function
- atan(ld) atanl(ld)
- log(fc) clogf(fc)
- sqrt(dc) csqrt(dc)
- pow(ldc, f) cpowl(ldc, f)
- remainder(n, n) remainder(n, n), the function
- nextafter(d, f) nextafter(d, f), the function
- nexttoward(f, ld) nexttowardf(f, ld)
- copysign(n, ld) copysignl(n, ld)
- ceil(fc) undefined behavior
- rint(dc) undefined behavior
- fmax(ldc, ld) undefined behavior
- carg(n) carg(n), the function
- cproj(f) cprojf(f)
- creal(d) creal(d), the function
- cimag(ld) cimagl(ld)
- fabs(fc) cabsf(fc)
- carg(dc) carg(dc), the function
- cproj(ldc) cprojl(ldc)
-
-
-
-
-[page 372] (Contents)
-
- 7.25 Threads <threads.h>
- 7.25.1 Introduction
-1 The header <threads.h> defines macros, and declares types, enumeration constants,
- and functions that support multiple threads of execution.
-2 Implementations that define the macro __STDC_NO_THREADS__ need not provide
- this header nor support any of its facilities.
-3 The macros are
- ONCE_FLAG_INIT
- which expands to a value that can be used to initialize an object of type once_flag;
- and
- TSS_DTOR_ITERATIONS
- which expands to an integer constant expression representing the maximum number of
- times that destructors will be called when a thread terminates.
-4 The types are
- cnd_t
- which is a complete object type that holds an identifier for a condition variable;
- thrd_t
- which is a complete object type that holds an identifier for a thread;
- tss_t
- which is a complete object type that holds an identifier for a thread-specific storage
- pointer;
- mtx_t
- which is a complete object type that holds an identifier for a mutex;
- tss_dtor_t
- which is the function pointer type void (*)(void*), used for a destructor for a
- thread-specific storage pointer;
- thrd_start_t
- which is the function pointer type int (*)(void*) that is passed to thrd_create
- to create a new thread;
- once_flag
- which is a complete object type that holds a flag for use by call_once; and
-
-
-[page 373] (Contents)
-
- xtime
- which is a structure type that holds a time specified in seconds and nanoseconds. The
- structure shall contain at least the following members, in any order.
- time_t sec;
- long nsec;
-5 The enumeration constants are
- mtx_plain
- which is passed to mtx_init to create a mutex object that supports neither timeout nor
- test and return;
- mtx_recursive
- which is passed to mtx_init to create a mutex object that supports recursive locking;
- mtx_timed
- which is passed to mtx_init to create a mutex object that supports timeout;
- mtx_try
- which is passed to mtx_init to create a mutex object that supports test and return;
- thrd_timeout
- which is returned by a timed wait function to indicate that the time specified in the call
- was reached without acquiring the requested resource;
- thrd_success
- which is returned by a function to indicate that the requested operation succeeded;
- thrd_busy
- which is returned by a function to indicate that the requested operation failed because a
- resource requested by a test and return function is already in use;
- thrd_error
- which is returned by a function to indicate that the requested operation failed; and
- thrd_nomem
- which is returned by a function to indicate that the requested operation failed because it
- was unable to allocate memory.
-
-
-
-
-[page 374] (Contents)
-
- 7.25.2 Initialization functions
- 7.25.2.1 The call_once function
- Synopsis
-1 #include <threads.h>
- void call_once(once_flag *flag, void (*func)(void));
- Description
-2 The call_once function uses the once_flag pointed to by flag to ensure that
- func is called exactly once, the first time the call_once function is called with that
- value of flag. Completion of an effective call to the call_once function synchronizes
- with all subsequent calls to the call_once function with the same value of flag.
- Returns
-3 The call_once function returns no value.
- 7.25.3 Condition variable functions
- 7.25.3.1 The cnd_broadcast function
- Synopsis
-1 #include <threads.h>
- int cnd_broadcast(cnd_t *cond);
- Description
-2 The cnd_broadcast function unblocks all of the threads that are blocked on the
- condition variable pointed to by cond at the time of the call. If no threads are blocked
- on the condition variable pointed to by cond at the time of the call, the function does
- nothing.
- Returns
-3 The cnd_broadcast function returns thrd_success on success, or thrd_error
- if the request could not be honored.
- 7.25.3.2 The cnd_destroy function
- Synopsis
-1 #include <threads.h>
- void cnd_destroy(cnd_t *cond);
- Description
-2 The cnd_destroy function releases all resources used by the condition variable
- pointed to by cond. The cnd_destroy function requires that no threads be blocked
- waiting for the condition variable pointed to by cond.
-
-[page 375] (Contents)
-
- Returns
-3 The cnd_destroy function returns no value.
- 7.25.3.3 The cnd_init function
- Synopsis
-1 #include <threads.h>
- int cnd_init(cnd_t *cond);
- Description
-2 The cnd_init function creates a condition variable. If it succeeds it sets the variable
- pointed to by cond to a value that uniquely identifies the newly created condition
- variable. A thread that calls cnd_wait on a newly created condition variable will
- block.
- Returns
-3 The cnd_init function returns thrd_success on success, or thrd_nomem if no
- memory could be allocated for the newly created condition, or thrd_error if the
- request could not be honored.
- 7.25.3.4 The cnd_signal function
- Synopsis
-1 #include <threads.h>
- int cnd_signal(cnd_t *cond);
- Description
-2 The cnd_signal function unblocks one of the threads that are blocked on the
- condition variable pointed to by cond at the time of the call. If no threads are blocked
- on the condition variable at the time of the call, the function does nothing and return
- success.
- Returns
-3 The cnd_signal function returns thrd_success on success or thrd_error if
- the request could not be honored.
- 7.25.3.5 The cnd_timedwait function
- Synopsis
-1 #include <threads.h>
- int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
- const xtime *xt);
-
-
-
-
-[page 376] (Contents)
-
- Description
-2 The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
- endeavors to block until the condition variable pointed to by cond is signaled by a call to
- cnd_signal or to cnd_broadcast, or until after the time specified by the xtime
- object pointed to by xt. When the calling thread becomes unblocked it locks the variable
- pointed to by mtx before it returns. The cnd_timedwait function requires that the
- mutex pointed to by mtx be locked by the calling thread.
- Returns
-3 The cnd_timedwait function returns thrd_success upon success, or
- thrd_timeout if the time specified in the call was reached without acquiring the
- requested resource, or thrd_error if the request could not be honored.
- 7.25.3.6 The cnd_wait function
- Synopsis
-1 #include <threads.h>
- int cnd_wait(cnd_t *cond, mtx_t *mtx);
- Description
-2 The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
- to block until the condition variable pointed to by cond is signaled by a call to
- cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
- locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is
- not locked by the calling thread, the cnd_wait function will act as if the abort
- function is called.
- Returns
-3 The cnd_wait function returns thrd_success on success or thrd_error if the
- request could not be honored.
- 7.25.4 Mutex functions
- 7.25.4.1 The mtx_destroy function
- Synopsis
-1 #include <threads.h>
- void mtx_destroy(mtx_t *mtx);
- Description
-2 The mtx_destroy function releases any resources used by the mutex pointed to by
- mtx. No threads can be blocked waiting for the mutex pointed to by mtx.
-
-
-
-[page 377] (Contents)
-
- Returns
-3 The mtx_destroy function returns no value.
- 7.25.4.2 The mtx_init function
- Synopsis
-1 #include <threads.h>
- int mtx_init(mtx_t *mtx, int type);
- Description
-2 The mtx_init function creates a mutex object with properties indicated by type,
- which must have one of the six values:
- mtx_plain for a simple non-recursive mutex,
- mtx_timed for a non-recursive mutex that supports timeout,
- mtx_try for a non-recursive mutex that supports test and return,
- mtx_plain | mtx_recursive for a simple recursive mutex,
- mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or
- mtx_try | mtx_recursive for a recursive mutex that supports test and return.
-3 If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
- uniquely identifies the newly created mutex.
- Returns
-4 The mtx_init function returns thrd_success on success, or thrd_error if the
- request could not be honored.
- 7.25.4.3 The mtx_lock function
- Synopsis
-1 #include <threads.h>
- int mtx_lock(mtx_t *mtx);
- Description
-2 The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
- is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
- on the same mutex shall synchronize with this operation.
- Returns
-3 The mtx_lock function returns thrd_success on success, or thrd_busy if the
- resource requested is already in use, or thrd_error if the request could not be
- honored.
-
-
-
-
-[page 378] (Contents)
-
- 7.25.4.4 The mtx_timedlock function
- Synopsis
-1 #include <threads.h>
- int mtx_timedlock(mtx_t *mtx, const xtime *xt);
- Description
-2 The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
- mtx or until the time specified by the xtime object xt has passed. The specified mutex
- shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same
- mutex shall synchronize with this operation.
- Returns
-3 The mtx_timedlock function returns thrd_success on success, or thrd_busy
- if the resource requested is already in use, or thrd_timeout if the time specified was
- reached without acquiring the requested resource, or thrd_error if the request could
- not be honored.
- 7.25.4.5 The mtx_trylock function
- Synopsis
-1 #include <threads.h>
- int mtx_trylock(mtx_t *mtx);
- Description
-2 The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The
- specified mutex shall support either test and return or timeout. If the mutex is already
- locked, the function returns without blocking. If the operation succeeds, prior calls to
- mtx_unlock on the same mutex shall synchronize with this operation.
- Returns
-3 The mtx_trylock function returns thrd_success on success, or thrd_busy if
- the resource requested is already in use, or thrd_error if the request could not be
- honored.
- 7.25.4.6 The mtx_unlock function
- Synopsis
-1 #include <threads.h>
- int mtx_unlock(mtx_t *mtx);
- Description
-2 The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
- by mtx shall be locked by the calling thread.
-
-[page 379] (Contents)
-
- Returns
-3 The mtx_unlock function returns thrd_success on success or thrd_error if
- the request could not be honored.
- 7.25.5 Thread functions
- 7.25.5.1 The thrd_create function
- Synopsis
-1 #include <threads.h>
- int thrd_create(thrd_t *thr, thrd_start_t func,
- void *arg);
- Description
-2 The thrd_create function creates a new thread executing func(arg). If the
- thrd_create function succeeds, it sets the object pointed to by thr to the identifier of
- the newly created thread. (A thread's identifier may be reused for a different thread once
- the original thread has exited and either been detached or joined to another thread.) The
- completion of the thrd_create function synchronizes with the beginning of the
- execution of the new thread.
- Returns
-3 The thrd_create function returns thrd_success on success, or thrd_nomem if
- no memory could be allocated for the thread requested, or thrd_error if the request
- could not be honored.
- 7.25.5.2 The thrd_current function
- Synopsis
-1 #include <threads.h>
- thrd_t thrd_current(void);
- Description
-2 The thrd_current function identifies the thread that called it.
- Returns
-3 The thrd_current function returns the identifier of the thread that called it.
- 7.25.5.3 The thrd_detach function
- Synopsis
-1 #include <threads.h>
- int thrd_detach(thrd_t thr);
-
-
-
-[page 380] (Contents)
-
- Description
-2 The thrd_detach function tells the operating system to dispose of any resources
- allocated to the thread identified by thr when that thread terminates. The thread
- identified by thr shall not have been previously detached or joined with another thread.
- Returns
-3 The thrd_detach function returns thrd_success on success or thrd_error if
- the request could not be honored.
- 7.25.5.4 The thrd_equal function
- Synopsis
-1 #include <threads.h>
- int thrd_equal(thrd_t thr0, thrd_t thr1);
- Description
-2 The thrd_equal function will determine whether the thread identified by thr0 refers
- to the thread identified by thr1.
- Returns
-3 The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
- different threads. Otherwise the thrd_equal function returns a nonzero value.
- 7.25.5.5 The thrd_exit function
- Synopsis
-1 #include <threads.h>
- void thrd_exit(int res);
- Description
-2 The thrd_exit function terminates execution of the calling thread and sets its result
- code to res.
- Returns
-3 The thrd_exit function returns no value.
- 7.25.5.6 The thrd_join function
- Synopsis
-1 #include <threads.h>
- int thrd_join(thrd_t thr, int *res);
- Description
-2 The thrd_join function joins the thread identified by thr with the current thread by
- blocking until the other thread has terminated. If the parameter res is not a null pointer,
-
-[page 381] (Contents)
-
- it stores the thread's result code in the integer pointed to by res. The termination of the
- other thread synchronizes with the completion of the thrd_join function. The thread
- identified by thr shall not have been previously detached or joined with another thread.
- Returns
-3 The thrd_join function returns thrd_success on success or thrd_error if the
- request could not be honored.
- 7.25.5.7 The thrd_sleep function
- Synopsis
-1 #include <threads.h>
- void thrd_sleep(const xtime *xt);
- Description
-2 The thrd_sleep function suspends execution of the calling thread until after the time
- specified by the xtime object pointed to by xt.
- Returns
-3 The thrd_sleep function returns no value.
- 7.25.5.8 The thrd_yield function
- Synopsis
-1 #include <threads.h>
- void thrd_yield(void);
- Description
-2 The thrd_yield function endeavors to permit other threads to run, even if the current
- thread would ordinarily continue to run.
- Returns
-3 The thrd_yield function returns no value.
- 7.25.6 Thread-specific storage functions
- 7.25.6.1 The tss_create function
- Synopsis
-1 #include <threads.h>
- int tss_create(tss_t *key, tss_dtor_t dtor);
- Description
-2 The tss_create function creates a thread-specific storage pointer with destructor
- dtor, which may be null.
-
-
-[page 382] (Contents)
-
- Returns
-3 If the tss_create function is successful, it sets the thread-specific storage pointed to
- by key to a value that uniquely identifies the newly created pointer and returns
- thrd_success; otherwise, thrd_error is returned and the thread-specific storage
- pointed to by key is set to an undefined value.
- 7.25.6.2 The tss_delete function
- Synopsis
-1 #include <threads.h>
- void tss_delete(tss_t key);
- Description
-2 The tss_delete function releases any resources used by the thread-specific storage
- identified by key.
- Returns
-3 The tss_delete function returns no value.
- 7.25.6.3 The tss_get function
- Synopsis
-1 #include <threads.h>
- void *tss_get(tss_t key);
- Description
-2 The tss_get function returns the value for the current thread held in the thread-specific
- storage identified by key.
- Returns
-3 The tss_get function returns the value for the current thread if successful, or zero if
- unsuccessful.
- 7.25.6.4 The tss_set function
- Synopsis
-1 #include <threads.h>
- int tss_set(tss_t key, void *val);
- Description
-2 The tss_set function sets the value for the current thread held in the thread-specific
- storage identified by key to val.
-
-
-
-
-[page 383] (Contents)
-
- Returns
-3 The tss_set function returns thrd_success on success or thrd_error if the
- request could not be honored.
- 7.25.7 Time functions
- 7.25.7.1 The xtime_get function
- Synopsis
-1 #include <threads.h>
- int xtime_get(xtime *xt, int base);
- Description
-2 The xtime_get function sets the xtime object pointed to by xt to hold the current
- time based on the time base base.
- Returns
-3 If the xtime_get function is successful it returns the nonzero value base, which must
- be TIME_UTC; otherwise, it returns zero.306)
-
-
-
-
- 306) Although an xtime object describes times with nanosecond resolution, the actual resolution in an
- xtime object is system dependent.
-
-[page 384] (Contents)
-
- 7.26 Date and time <time.h>
- 7.26.1 Components of time
-1 The header <time.h> defines two macros, and declares several types and functions for
- manipulating time. Many functions deal with a calendar time that represents the current
- date (according to the Gregorian calendar) and time. Some functions deal with local
- time, which is the calendar time expressed for some specific time zone, and with Daylight
- Saving Time, which is a temporary change in the algorithm for determining local time.
- The local time zone and Daylight Saving Time are implementation-defined.
-2 The macros defined are NULL (described in 7.19); and
- CLOCKS_PER_SEC
- which expands to an expression with type clock_t (described below) that is the
- number per second of the value returned by the clock function.
-3 The types declared are size_t (described in 7.19);
- clock_t
- and
- time_t
- which are arithmetic types capable of representing times; and
- struct tm
- which holds the components of a calendar time, called the broken-down time.
-4 The range and precision of times representable in clock_t and time_t are
- implementation-defined. The tm structure shall contain at least the following members,
- in any order. The semantics of the members and their normal ranges are expressed in the
- comments.307)
- int tm_sec; // seconds after the minute -- [0, 60]
- int tm_min; // minutes after the hour -- [0, 59]
- int tm_hour; // hours since midnight -- [0, 23]
- int tm_mday; // day of the month -- [1, 31]
- int tm_mon; // months since January -- [0, 11]
- int tm_year; // years since 1900
- int tm_wday; // days since Sunday -- [0, 6]
- int tm_yday; // days since January 1 -- [0, 365]
- int tm_isdst; // Daylight Saving Time flag
-
-
-
- 307) The range [0, 60] for tm_sec allows for a positive leap second.
-
-[page 385] (Contents)
-
- The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
- Saving Time is not in effect, and negative if the information is not available.
- 7.26.2 Time manipulation functions
- 7.26.2.1 The clock function
- Synopsis
-1 #include <time.h>
- clock_t clock(void);
- Description
-2 The clock function determines the processor time used.
- Returns
-3 The clock function returns the implementation's best approximation to the processor
- time used by the program since the beginning of an implementation-defined era related
- only to the program invocation. To determine the time in seconds, the value returned by
- the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
- the processor time used is not available or its value cannot be represented, the function
- returns the value (clock_t)(-1).308)
- 7.26.2.2 The difftime function
- Synopsis
-1 #include <time.h>
- double difftime(time_t time1, time_t time0);
- Description
-2 The difftime function computes the difference between two calendar times: time1 -
- time0.
- Returns
-3 The difftime function returns the difference expressed in seconds as a double.
-
-
-
-
- 308) In order to measure the time spent in a program, the clock function should be called at the start of
- the program and its return value subtracted from the value returned by subsequent calls.
-
-[page 386] (Contents)
-
- 7.26.2.3 The mktime function
- Synopsis
-1 #include <time.h>
- time_t mktime(struct tm *timeptr);
- Description
-2 The mktime function converts the broken-down time, expressed as local time, in the
- structure pointed to by timeptr into a calendar time value with the same encoding as
- that of the values returned by the time function. The original values of the tm_wday
- and tm_yday components of the structure are ignored, and the original values of the
- other components are not restricted to the ranges indicated above.309) On successful
- completion, the values of the tm_wday and tm_yday components of the structure are
- set appropriately, and the other components are set to represent the specified calendar
- time, but with their values forced to the ranges indicated above; the final value of
- tm_mday is not set until tm_mon and tm_year are determined.
- Returns
-3 The mktime function returns the specified calendar time encoded as a value of type
- time_t. If the calendar time cannot be represented, the function returns the value
- (time_t)(-1).
-4 EXAMPLE What day of the week is July 4, 2001?
- #include <stdio.h>
- #include <time.h>
- static const char *const wday[] = {
- "Sunday", "Monday", "Tuesday", "Wednesday",
- "Thursday", "Friday", "Saturday", "-unknown-"
- };
- struct tm time_str;
+ // handle other operations
/* ... */
-
-
-
-
- 309) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
- Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
- causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.
-
-[page 387] (Contents)
-
- time_str.tm_year = 2001 - 1900;
- time_str.tm_mon = 7 - 1;
- time_str.tm_mday = 4;
- time_str.tm_hour = 0;
- time_str.tm_min = 0;
- time_str.tm_sec = 1;
- time_str.tm_isdst = -1;
- if (mktime(&time_str) == (time_t)(-1))
- time_str.tm_wday = 7;
- printf("%s\n", wday[time_str.tm_wday]);
-
- 7.26.2.4 The time function
- Synopsis
-1 #include <time.h>
- time_t time(time_t *timer);
- Description
-2 The time function determines the current calendar time. The encoding of the value is
- unspecified.
- Returns
-3 The time function returns the implementation's best approximation to the current
- calendar time. The value (time_t)(-1) is returned if the calendar time is not
- available. If timer is not a null pointer, the return value is also assigned to the object it
- points to.
- 7.26.3 Time conversion functions
-1 Except for the strftime function, these functions each return a pointer to one of two
- types of static objects: a broken-down time structure or an array of char. Execution of
- any of the functions that return a pointer to one of these object types may overwrite the
- information in any object of the same type pointed to by the value returned from any
- previous call to any of them and the functions are not required to avoid data races. The
- implementation shall behave as if no other library functions call these functions.
- 7.26.3.1 The asctime function
- Synopsis
-1 #include <time.h>
- char *asctime(const struct tm *timeptr);
- Description
-2 The asctime function converts the broken-down time in the structure pointed to by
- timeptr into a string in the form
- Sun Sep 16 01:03:52 1973\n\0
-
-[page 388] (Contents)
-
- using the equivalent of the following algorithm.
- char *asctime(const struct tm *timeptr)
- {
- static const char wday_name[7][3] = {
- "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
- };
- static const char mon_name[12][3] = {
- "Jan", "Feb", "Mar", "Apr", "May", "Jun",
- "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
- };
- static char result[26];
- sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
- wday_name[timeptr->tm_wday],
- mon_name[timeptr->tm_mon],
- timeptr->tm_mday, timeptr->tm_hour,
- timeptr->tm_min, timeptr->tm_sec,
- 1900 + timeptr->tm_year);
- return result;
}
-3 If any of the fields of the broken-down time contain values that are outside their normal
- ranges,310) the behavior of the asctime function is undefined. Likewise, if the
- calculated year exceeds four digits or is less than the year 1000, the behavior is
- undefined.
- Returns
-4 The asctime function returns a pointer to the string.
- 7.26.3.2 The ctime function
- Synopsis
-1 #include <time.h>
- char *ctime(const time_t *timer);
- Description
-2 The ctime function converts the calendar time pointed to by timer to local time in the
- form of a string. It is equivalent to
- asctime(localtime(timer))
-
-
-
- 310) See 7.26.1.
-
-[page 389] (Contents)
-
- Returns
-3 The ctime function returns the pointer returned by the asctime function with that
- broken-down time as argument.
- Forward references: the localtime function (7.26.3.4).
- 7.26.3.3 The gmtime function
- Synopsis
-1 #include <time.h>
- struct tm *gmtime(const time_t *timer);
- Description
-2 The gmtime function converts the calendar time pointed to by timer into a broken-
- down time, expressed as UTC.
- Returns
-3 The gmtime function returns a pointer to the broken-down time, or a null pointer if the
- specified time cannot be converted to UTC.
- 7.26.3.4 The localtime function
- Synopsis
-1 #include <time.h>
- struct tm *localtime(const time_t *timer);
- Description
-2 The localtime function converts the calendar time pointed to by timer into a
- broken-down time, expressed as local time.
- Returns
-3 The localtime function returns a pointer to the broken-down time, or a null pointer if
- the specified time cannot be converted to local time.
- 7.26.3.5 The strftime function
- Synopsis
-1 #include <time.h>
- size_t strftime(char * restrict s,
- size_t maxsize,
- const char * restrict format,
- const struct tm * restrict timeptr);
-
-
-
-
-[page 390] (Contents)
-
- Description
-2 The strftime function places characters into the array pointed to by s as controlled by
- the string pointed to by format. The format shall be a multibyte character sequence,
- beginning and ending in its initial shift state. The format string consists of zero or
- more conversion specifiers and ordinary multibyte characters. A conversion specifier
- consists of a % character, possibly followed by an E or O modifier character (described
- below), followed by a character that determines the behavior of the conversion specifier.
- All ordinary multibyte characters (including the terminating null character) are copied
- unchanged into the array. If copying takes place between objects that overlap, the
- behavior is undefined. No more than maxsize characters are placed into the array.
-3 Each conversion specifier is replaced by appropriate characters as described in the
- following list. The appropriate characters are determined using the LC_TIME category
- of the current locale and by the values of zero or more members of the broken-down time
- structure pointed to by timeptr, as specified in brackets in the description. If any of
- the specified values is outside the normal range, the characters stored are unspecified.
- %a is replaced by the locale's abbreviated weekday name. [tm_wday]
- %A is replaced by the locale's full weekday name. [tm_wday]
- %b is replaced by the locale's abbreviated month name. [tm_mon]
- %B is replaced by the locale's full month name. [tm_mon]
- %c is replaced by the locale's appropriate date and time representation. [all specified
- in 7.26.1]
- %C is replaced by the year divided by 100 and truncated to an integer, as a decimal
- number (00-99). [tm_year]
- %d is replaced by the day of the month as a decimal number (01-31). [tm_mday]
- %D is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year]
- %e is replaced by the day of the month as a decimal number (1-31); a single digit is
- preceded by a space. [tm_mday]
- %F is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon,
- tm_mday]
- %g is replaced by the last 2 digits of the week-based year (see below) as a decimal
- number (00-99). [tm_year, tm_wday, tm_yday]
- %G is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
- [tm_year, tm_wday, tm_yday]
- %h is equivalent to ''%b''. [tm_mon]
- %H is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour]
- %I is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour]
- %j is replaced by the day of the year as a decimal number (001-366). [tm_yday]
- %m is replaced by the month as a decimal number (01-12). [tm_mon]
- %M is replaced by the minute as a decimal number (00-59). [tm_min]
- %n is replaced by a new-line character.
-
-[page 391] (Contents)
-
- %p is replaced by the locale's equivalent of the AM/PM designations associated with a
- 12-hour clock. [tm_hour]
- %r is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec]
- %R is equivalent to ''%H:%M''. [tm_hour, tm_min]
- %S is replaced by the second as a decimal number (00-60). [tm_sec]
- %t is replaced by a horizontal-tab character.
- %T is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min,
- tm_sec]
- %u is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday
- is 1. [tm_wday]
- %U is replaced by the week number of the year (the first Sunday as the first day of week
- 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
- %V is replaced by the ISO 8601 week number (see below) as a decimal number
- (01-53). [tm_year, tm_wday, tm_yday]
- %w is replaced by the weekday as a decimal number (0-6), where Sunday is 0.
- [tm_wday]
- %W is replaced by the week number of the year (the first Monday as the first day of
- week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
- %x is replaced by the locale's appropriate date representation. [all specified in 7.26.1]
- %X is replaced by the locale's appropriate time representation. [all specified in 7.26.1]
- %y is replaced by the last 2 digits of the year as a decimal number (00-99).
- [tm_year]
- %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year]
- %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4
- hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
- zone is determinable. [tm_isdst]
- %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no
- time zone is determinable. [tm_isdst]
- %% is replaced by %.
-4 Some conversion specifiers can be modified by the inclusion of an E or O modifier
- character to indicate an alternative format or specification. If the alternative format or
- specification does not exist for the current locale, the modifier is ignored.
- %Ec is replaced by the locale's alternative date and time representation.
- %EC is replaced by the name of the base year (period) in the locale's alternative
- representation.
- %Ex is replaced by the locale's alternative date representation.
- %EX is replaced by the locale's alternative time representation.
- %Ey is replaced by the offset from %EC (year only) in the locale's alternative
- representation.
- %EY is replaced by the locale's full alternative year representation.
-
-[page 392] (Contents)
-
- %Od is replaced by the day of the month, using the locale's alternative numeric symbols
- (filled as needed with leading zeros, or with leading spaces if there is no alternative
- symbol for zero).
- %Oe is replaced by the day of the month, using the locale's alternative numeric symbols
- (filled as needed with leading spaces).
- %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric
- symbols.
- %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric
- symbols.
- %Om is replaced by the month, using the locale's alternative numeric symbols.
- %OM is replaced by the minutes, using the locale's alternative numeric symbols.
- %OS is replaced by the seconds, using the locale's alternative numeric symbols.
- %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative
- representation, where Monday is 1.
- %OU is replaced by the week number, using the locale's alternative numeric symbols.
- %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric
- symbols.
- %Ow is replaced by the weekday as a number, using the locale's alternative numeric
- symbols.
- %OW is replaced by the week number of the year, using the locale's alternative numeric
- symbols.
- %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric
- symbols.
-5 %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
- weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
- which is also the week that includes the first Thursday of the year, and is also the first
- week that contains at least four days in the year. If the first Monday of January is the
- 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
- for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
- December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
- the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
- %V is replaced by 01.
-6 If a conversion specifier is not one of the above, the behavior is undefined.
-7 In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
- following specifiers are:
- %a the first three characters of %A.
- %A one of ''Sunday'', ''Monday'', ... , ''Saturday''.
- %b the first three characters of %B.
- %B one of ''January'', ''February'', ... , ''December''.
- %c equivalent to ''%a %b %e %T %Y''.
-[page 393] (Contents)
-
- %p one of ''AM'' or ''PM''.
- %r equivalent to ''%I:%M:%S %p''.
- %x equivalent to ''%m/%d/%y''.
- %X equivalent to %T.
- %Z implementation-defined.
- Returns
-8 If the total number of resulting characters including the terminating null character is not
- more than maxsize, the strftime function returns the number of characters placed
- into the array pointed to by s not including the terminating null character. Otherwise,
- zero is returned and the contents of the array are indeterminate.
-
-
-
-
-[page 394] (Contents)
-
- 7.27 Unicode utilities <uchar.h>
-1 The header <uchar.h> declares types and functions for manipulating Unicode
- characters.
-2 The types declared are mbstate_t (described in 7.29.1) and size_t (described in
- 7.19);
- char16_t
- which is an unsigned integer type used for 16-bit characters and is the same type as
- uint_least16_t (described in 7.20.1.2); and
- char32_t
- which is an unsigned integer type used for 32-bit characters and is the same type as
- uint_least32_t (also described in 7.20.1.2).
- 7.27.1 Restartable multibyte/wide character conversion functions
-1 These functions have a parameter, ps, of type pointer to mbstate_t that points to an
- object that can completely describe the current conversion state of the associated
- multibyte character sequence, which the functions alter as necessary. If ps is a null
- pointer, each function uses its own internal mbstate_t object instead, which is
- initialized at program startup to the initial conversion state; the functions are not required
- to avoid data races in this case. The implementation behaves as if no library function
- calls these functions with a null pointer for ps.
- 7.27.1.1 The mbrtoc16 function
- Synopsis
-1 #include <uchar.h>
- size_t mbrtoc16(char16_t * restrict pc16,
- const char * restrict s, size_t n,
- mbstate_t * restrict ps);
- Description
-2 If s is a null pointer, the mbrtoc16 function is equivalent to the call:
- mbrtoc16(NULL, "", 1, ps)
- In this case, the values of the parameters pc16 and n are ignored.
-3 If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
- the byte pointed to by s to determine the number of bytes needed to complete the next
- multibyte character (including any shift sequences). If the function determines that the
- next multibyte character is complete and valid, it determines the values of the
- corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
- the first (or only) such character in the object pointed to by pc16. Subsequent calls will
-[page 395] (Contents)
-
- store successive wide characters without consuming any additional input until all the
- characters have been stored. If the corresponding wide character is the null wide
- character, the resulting state described is the initial conversion state.
- Returns
-4 The mbrtoc16 function returns the first of the following that applies (given the current
- conversion state):
- 0 if the next n or fewer bytes complete the multibyte character that
- corresponds to the null wide character (which is the value stored).
- between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
- character (which is the value stored); the value returned is the number
- of bytes that complete the multibyte character.
- (size_t)(-3) if the next character resulting from a previous call has been stored (no
- bytes from the input have been consumed by this call).
- (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
- multibyte character, and all n bytes have been processed (no value is
- stored).311)
- (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
- do not contribute to a complete and valid multibyte character (no
- value is stored); the value of the macro EILSEQ is stored in errno,
- and the conversion state is unspecified.
- 7.27.1.2 The c16rtomb function
- Synopsis
-1 #include <uchar.h>
- size_t c16rtomb(char * restrict s, char16_t c16,
- mbstate_t * restrict ps);
- Description
-2 If s is a null pointer, the c16rtomb function is equivalent to the call
- c16rtomb(buf, L'\0', ps)
- where buf is an internal buffer.
-3 If s is not a null pointer, the c16rtomb function determines the number of bytes needed
- to represent the multibyte character that corresponds to the wide character given by c16
- (including any shift sequences), and stores the multibyte character representation in the
-
-
- 311) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
- sequence of redundant shift sequences (for implementations with state-dependent encodings).
-
-[page 396] (Contents)
-
- array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
- c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
- to restore the initial shift state; the resulting state described is the initial conversion state.
- Returns
-4 The c16rtomb function returns the number of bytes stored in the array object (including
- any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
- the function stores the value of the macro EILSEQ in errno and returns
- (size_t)(-1); the conversion state is unspecified.
- 7.27.1.3 The mbrtoc32 function
- Synopsis
-1 #include <uchar.h>
- size_t mbrtoc32(char32_t * restrict pc32,
- const char * restrict s, size_t n,
- mbstate_t * restrict ps);
- Description
-2 If s is a null pointer, the mbrtoc32 function is equivalent to the call:
- mbrtoc32(NULL, "", 1, ps)
- In this case, the values of the parameters pc32 and n are ignored.
-3 If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
- the byte pointed to by s to determine the number of bytes needed to complete the next
- multibyte character (including any shift sequences). If the function determines that the
- next multibyte character is complete and valid, it determines the values of the
- corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
- the first (or only) such character in the object pointed to by pc32. Subsequent calls will
- store successive wide characters without consuming any additional input until all the
- characters have been stored. If the corresponding wide character is the null wide
- character, the resulting state described is the initial conversion state.
- Returns
-4 The mbrtoc32 function returns the first of the following that applies (given the current
- conversion state):
- 0 if the next n or fewer bytes complete the multibyte character that
- corresponds to the null wide character (which is the value stored).
- between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
- character (which is the value stored); the value returned is the number
- of bytes that complete the multibyte character.
-
-
-[page 397] (Contents)
-
- (size_t)(-3) if the next character resulting from a previous call has been stored (no
- bytes from the input have been consumed by this call).
- (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
- multibyte character, and all n bytes have been processed (no value is
- stored).312)
- (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
- do not contribute to a complete and valid multibyte character (no
- value is stored); the value of the macro EILSEQ is stored in errno,
- and the conversion state is unspecified.
- 7.27.1.4 The c32rtomb function
- Synopsis
-1 #include <uchar.h>
- size_t c32rtomb(char * restrict s, char32_t c32,
- mbstate_t * restrict ps);
- Description
-2 If s is a null pointer, the c32rtomb function is equivalent to the call
- c32rtomb(buf, L'\0', ps)
- where buf is an internal buffer.
-3 If s is not a null pointer, the c32rtomb function determines the number of bytes needed
- to represent the multibyte character that corresponds to the wide character given by c32
- (including any shift sequences), and stores the multibyte character representation in the
- array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
- c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
- to restore the initial shift state; the resulting state described is the initial conversion state.
- Returns
-4 The c32rtomb function returns the number of bytes stored in the array object (including
- any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
- the function stores the value of the macro EILSEQ in errno and returns
- (size_t)(-1); the conversion state is unspecified.
-
-
-
-
- 312) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
- sequence of redundant shift sequences (for implementations with state-dependent encodings).
-
-[page 398] (Contents)
-
- 7.28 Extended multibyte and wide character utilities <wchar.h>
- 7.28.1 Introduction
-1 The header <wchar.h> defines four macros, and declares four data types, one tag, and
- many functions.313)
-2 The types declared are wchar_t and size_t (both described in 7.19);
- mbstate_t
- which is a complete object type other than an array type that can hold the conversion state
- information necessary to convert between sequences of multibyte characters and wide
- characters;
- wint_t
- which is an integer type unchanged by default argument promotions that can hold any
- value corresponding to members of the extended character set, as well as at least one
- value that does not correspond to any member of the extended character set (see WEOF
- below);314) and
- struct tm
- which is declared as an incomplete structure type (the contents are described in 7.26.1).
-3 The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
- (described in 7.20.3); and
- WEOF
- which expands to a constant expression of type wint_t whose value does not
- correspond to any member of the extended character set.315) It is accepted (and returned)
- by several functions in this subclause to indicate end-of-file, that is, no more input from a
- stream. It is also used as a wide character value that does not correspond to any member
- of the extended character set.
-4 The functions declared are grouped as follows:
- -- Functions that perform input and output of wide characters, or multibyte characters,
- or both;
- -- Functions that provide wide string numeric conversion;
- -- Functions that perform general wide string manipulation;
-
-
- 313) See ''future library directions'' (7.30.12).
- 314) wchar_t and wint_t can be the same integer type.
- 315) The value of the macro WEOF may differ from that of EOF and need not be negative.
-
-[page 399] (Contents)
-
- -- Functions for wide string date and time conversion; and
- -- Functions that provide extended capabilities for conversion between multibyte and
- wide character sequences.
-5 Unless explicitly stated otherwise, if the execution of a function described in this
- subclause causes copying to take place between objects that overlap, the behavior is
- undefined.
- 7.28.2 Formatted wide character input/output functions
-1 The formatted wide character input/output functions shall behave as if there is a sequence
- point after the actions associated with each specifier.316)
- 7.28.2.1 The fwprintf function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- int fwprintf(FILE * restrict stream,
- const wchar_t * restrict format, ...);
- Description
-2 The fwprintf function writes output to the stream pointed to by stream, under
- control of the wide string pointed to by format that specifies how subsequent arguments
- are converted for output. If there are insufficient arguments for the format, the behavior
- is undefined. If the format is exhausted while arguments remain, the excess arguments
- are evaluated (as always) but are otherwise ignored. The fwprintf function returns
- when the end of the format string is encountered.
-3 The format is composed of zero or more directives: ordinary wide characters (not %),
- which are copied unchanged to the output stream; and conversion specifications, each of
- which results in fetching zero or more subsequent arguments, converting them, if
- applicable, according to the corresponding conversion specifier, and then writing the
- result to the output stream.
-4 Each conversion specification is introduced by the wide character %. After the %, the
- following appear in sequence:
- -- Zero or more flags (in any order) that modify the meaning of the conversion
- specification.
- -- An optional minimum field width. If the converted value has fewer wide characters
- than the field width, it is padded with spaces (by default) on the left (or right, if the
-
-
- 316) The fwprintf functions perform writes to memory for the %n specifier.
-
-[page 400] (Contents)
-
- left adjustment flag, described later, has been given) to the field width. The field
- width takes the form of an asterisk * (described later) or a nonnegative decimal
- integer.317)
- -- An optional precision that gives the minimum number of digits to appear for the d, i,
- o, u, x, and X conversions, the number of digits to appear after the decimal-point
- wide character for a, A, e, E, f, and F conversions, the maximum number of
- significant digits for the g and G conversions, or the maximum number of wide
- characters to be written for s conversions. The precision takes the form of a period
- (.) followed either by an asterisk * (described later) or by an optional decimal
- integer; if only the period is specified, the precision is taken as zero. If a precision
- appears with any other conversion specifier, the behavior is undefined.
- -- An optional length modifier that specifies the size of the argument.
- -- A conversion specifier wide character that specifies the type of conversion to be
- applied.
-5 As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
- this case, an int argument supplies the field width or precision. The arguments
- specifying field width, or precision, or both, shall appear (in that order) before the
- argument (if any) to be converted. A negative field width argument is taken as a - flag
- followed by a positive field width. A negative precision argument is taken as if the
- precision were omitted.
-6 The flag wide characters and their meanings are:
- - The result of the conversion is left-justified within the field. (It is right-justified if
- this flag is not specified.)
- + The result of a signed conversion always begins with a plus or minus sign. (It
- begins with a sign only when a negative value is converted if this flag is not
- specified.)318)
- space If the first wide character of a signed conversion is not a sign, or if a signed
- conversion results in no wide characters, a space is prefixed to the result. If the
- space and + flags both appear, the space flag is ignored.
- # The result is converted to an ''alternative form''. For o conversion, it increases
- the precision, if and only if necessary, to force the first digit of the result to be a
- zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
- conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
-
-
- 317) Note that 0 is taken as a flag, not as the beginning of a field width.
- 318) The results of all floating conversions of a negative zero, and of negative values that round to zero,
- include a minus sign.
-
-[page 401] (Contents)
-
- and G conversions, the result of converting a floating-point number always
- contains a decimal-point wide character, even if no digits follow it. (Normally, a
- decimal-point wide character appears in the result of these conversions only if a
- digit follows it.) For g and G conversions, trailing zeros are not removed from the
- result. For other conversions, the behavior is undefined.
- 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
- (following any indication of sign or base) are used to pad to the field width rather
- than performing space padding, except when converting an infinity or NaN. If the
- 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
- conversions, if a precision is specified, the 0 flag is ignored. For other
- conversions, the behavior is undefined.
-7 The length modifiers and their meanings are:
- hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- signed char or unsigned char argument (the argument will have
- been promoted according to the integer promotions, but its value shall be
- converted to signed char or unsigned char before printing); or that
- a following n conversion specifier applies to a pointer to a signed char
- argument.
- h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- short int or unsigned short int argument (the argument will
- have been promoted according to the integer promotions, but its value shall
- be converted to short int or unsigned short int before printing);
- or that a following n conversion specifier applies to a pointer to a short
- int argument.
- l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- long int or unsigned long int argument; that a following n
- conversion specifier applies to a pointer to a long int argument; that a
- following c conversion specifier applies to a wint_t argument; that a
- following s conversion specifier applies to a pointer to a wchar_t
- argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
- specifier.
- ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- long long int or unsigned long long int argument; or that a
- following n conversion specifier applies to a pointer to a long long int
- argument.
- j Specifies that a following d, i, o, u, x, or X conversion specifier applies to
- an intmax_t or uintmax_t argument; or that a following n conversion
- specifier applies to a pointer to an intmax_t argument.
-
-[page 402] (Contents)
-
- z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- size_t or the corresponding signed integer type argument; or that a
- following n conversion specifier applies to a pointer to a signed integer type
- corresponding to size_t argument.
- t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
- ptrdiff_t or the corresponding unsigned integer type argument; or that a
- following n conversion specifier applies to a pointer to a ptrdiff_t
- argument.
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
- applies to a long double argument.
- If a length modifier appears with any conversion specifier other than as specified above,
- the behavior is undefined.
-8 The conversion specifiers and their meanings are:
- d,i The int argument is converted to signed decimal in the style [-]dddd. The
- precision specifies the minimum number of digits to appear; if the value
- being converted can be represented in fewer digits, it is expanded with
- leading zeros. The default precision is 1. The result of converting a zero
- value with a precision of zero is no wide characters.
- o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
- decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
- letters abcdef are used for x conversion and the letters ABCDEF for X
- conversion. The precision specifies the minimum number of digits to appear;
- if the value being converted can be represented in fewer digits, it is expanded
- with leading zeros. The default precision is 1. The result of converting a
- zero value with a precision of zero is no wide characters.
- f,F A double argument representing a floating-point number is converted to
- decimal notation in the style [-]ddd.ddd, where the number of digits after
- the decimal-point wide character is equal to the precision specification. If the
- precision is missing, it is taken as 6; if the precision is zero and the # flag is
- not specified, no decimal-point wide character appears. If a decimal-point
- wide character appears, at least one digit appears before it. The value is
- rounded to the appropriate number of digits.
- A double argument representing an infinity is converted in one of the styles
- [-]inf or [-]infinity -- which style is implementation-defined. A
- double argument representing a NaN is converted in one of the styles
- [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of
- any n-wchar-sequence, is implementation-defined. The F conversion
- specifier produces INF, INFINITY, or NAN instead of inf, infinity, or
-
-[page 403] (Contents)
-
- nan, respectively.319)
-e,E A double argument representing a floating-point number is converted in the
- style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
- argument is nonzero) before the decimal-point wide character and the number
- of digits after it is equal to the precision; if the precision is missing, it is taken
- as 6; if the precision is zero and the # flag is not specified, no decimal-point
- wide character appears. The value is rounded to the appropriate number of
- digits. The E conversion specifier produces a number with E instead of e
- introducing the exponent. The exponent always contains at least two digits,
- and only as many more digits as necessary to represent the exponent. If the
- value is zero, the exponent is zero.
- A double argument representing an infinity or NaN is converted in the style
- of an f or F conversion specifier.
-g,G A double argument representing a floating-point number is converted in
- style f or e (or in style F or E in the case of a G conversion specifier),
- depending on the value converted and the precision. Let P equal the
- precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
- Then, if a conversion with style E would have an exponent of X:
- -- if P > X >= -4, the conversion is with style f (or F) and precision
- P - (X + 1).
- -- otherwise, the conversion is with style e (or E) and precision P - 1.
- Finally, unless the # flag is used, any trailing zeros are removed from the
- fractional portion of the result and the decimal-point wide character is
- removed if there is no fractional portion remaining.
- A double argument representing an infinity or NaN is converted in the style
- of an f or F conversion specifier.
-a,A A double argument representing a floating-point number is converted in the
- style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
- nonzero if the argument is a normalized floating-point number and is
- otherwise unspecified) before the decimal-point wide character320) and the
- number of hexadecimal digits after it is equal to the precision; if the precision
- is missing and FLT_RADIX is a power of 2, then the precision is sufficient
-
-
-319) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
- meaning; the # and 0 flag wide characters have no effect.
-320) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
- character so that subsequent digits align to nibble (4-bit) boundaries.
-
-[page 404] (Contents)
-
- for an exact representation of the value; if the precision is missing and
- FLT_RADIX is not a power of 2, then the precision is sufficient to
- distinguish321) values of type double, except that trailing zeros may be
- omitted; if the precision is zero and the # flag is not specified, no decimal-
- point wide character appears. The letters abcdef are used for a conversion
- and the letters ABCDEF for A conversion. The A conversion specifier
- produces a number with X and P instead of x and p. The exponent always
- contains at least one digit, and only as many more digits as necessary to
- represent the decimal exponent of 2. If the value is zero, the exponent is
- zero.
- A double argument representing an infinity or NaN is converted in the style
- of an f or F conversion specifier.
-c If no l length modifier is present, the int argument is converted to a wide
- character as if by calling btowc and the resulting wide character is written.
- If an l length modifier is present, the wint_t argument is converted to
- wchar_t and written.
-s If no l length modifier is present, the argument shall be a pointer to the initial
- element of a character array containing a multibyte character sequence
- beginning in the initial shift state. Characters from the array are converted as
- if by repeated calls to the mbrtowc function, with the conversion state
- described by an mbstate_t object initialized to zero before the first
- multibyte character is converted, and written up to (but not including) the
- terminating null wide character. If the precision is specified, no more than
- that many wide characters are written. If the precision is not specified or is
- greater than the size of the converted array, the converted array shall contain a
- null wide character.
- If an l length modifier is present, the argument shall be a pointer to the initial
- element of an array of wchar_t type. Wide characters from the array are
- written up to (but not including) a terminating null wide character. If the
- precision is specified, no more than that many wide characters are written. If
- the precision is not specified or is greater than the size of the array, the array
- shall contain a null wide character.
-p The argument shall be a pointer to void. The value of the pointer is
- converted to a sequence of printing wide characters, in an implementation-
-
-321) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
- FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
- might suffice depending on the implementation's scheme for determining the digit to the left of the
- decimal-point wide character.
-
-[page 405] (Contents)
-
- defined manner.
- n The argument shall be a pointer to signed integer into which is written the
- number of wide characters written to the output stream so far by this call to
- fwprintf. No argument is converted, but one is consumed. If the
- conversion specification includes any flags, a field width, or a precision, the
- behavior is undefined.
- % A % wide character is written. No argument is converted. The complete
- conversion specification shall be %%.
-9 If a conversion specification is invalid, the behavior is undefined.322) If any argument is
- not the correct type for the corresponding conversion specification, the behavior is
- undefined.
-10 In no case does a nonexistent or small field width cause truncation of a field; if the result
- of a conversion is wider than the field width, the field is expanded to contain the
- conversion result.
-11 For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
- to a hexadecimal floating number with the given precision.
- Recommended practice
-12 For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
- representable in the given precision, the result should be one of the two adjacent numbers
- in hexadecimal floating style with the given precision, with the extra stipulation that the
- error should have a correct sign for the current rounding direction.
-13 For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
- DECIMAL_DIG, then the result should be correctly rounded.323) If the number of
- significant decimal digits is more than DECIMAL_DIG but the source value is exactly
- representable with DECIMAL_DIG digits, then the result should be an exact
- representation with trailing zeros. Otherwise, the source value is bounded by two
- adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
- of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
- the error should have a correct sign for the current rounding direction.
- Returns
-14 The fwprintf function returns the number of wide characters transmitted, or a negative
- value if an output or encoding error occurred.
-
- 322) See ''future library directions'' (7.30.12).
- 323) For binary-to-decimal conversion, the result format's values are the numbers representable with the
- given format specifier. The number of significant digits is determined by the format specifier, and in
- the case of fixed-point conversion by the source value as well.
-
-[page 406] (Contents)
-
- Environmental limits
-15 The number of wide characters that can be produced by any single conversion shall be at
- least 4095.
-16 EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
- places:
- #include <math.h>
- #include <stdio.h>
- #include <wchar.h>
- /* ... */
- wchar_t *weekday, *month; // pointers to wide strings
- int day, hour, min;
- fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
- weekday, month, day, hour, min);
- fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
-
- Forward references: the btowc function (7.28.6.1.1), the mbrtowc function
- (7.28.6.3.2).
- 7.28.2.2 The fwscanf function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- int fwscanf(FILE * restrict stream,
- const wchar_t * restrict format, ...);
- Description
-2 The fwscanf function reads input from the stream pointed to by stream, under
- control of the wide string pointed to by format that specifies the admissible input
- sequences and how they are to be converted for assignment, using subsequent arguments
- as pointers to the objects to receive the converted input. If there are insufficient
- arguments for the format, the behavior is undefined. If the format is exhausted while
- arguments remain, the excess arguments are evaluated (as always) but are otherwise
- ignored.
-3 The format is composed of zero or more directives: one or more white-space wide
- characters, an ordinary wide character (neither % nor a white-space wide character), or a
- conversion specification. Each conversion specification is introduced by the wide
- character %. After the %, the following appear in sequence:
- -- An optional assignment-suppressing wide character *.
- -- An optional decimal integer greater than zero that specifies the maximum field width
- (in wide characters).
-
-
-
-[page 407] (Contents)
-
- -- An optional length modifier that specifies the size of the receiving object.
- -- A conversion specifier wide character that specifies the type of conversion to be
- applied.
-4 The fwscanf function executes each directive of the format in turn. When all directives
- have been executed, or if a directive fails (as detailed below), the function returns.
- Failures are described as input failures (due to the occurrence of an encoding error or the
- unavailability of input characters), or matching failures (due to inappropriate input).
-5 A directive composed of white-space wide character(s) is executed by reading input up to
- the first non-white-space wide character (which remains unread), or until no more wide
- characters can be read.
-6 A directive that is an ordinary wide character is executed by reading the next wide
- character of the stream. If that wide character differs from the directive, the directive
- fails and the differing and subsequent wide characters remain unread. Similarly, if end-
- of-file, an encoding error, or a read error prevents a wide character from being read, the
- directive fails.
-7 A directive that is a conversion specification defines a set of matching input sequences, as
- described below for each specifier. A conversion specification is executed in the
- following steps:
-8 Input white-space wide characters (as specified by the iswspace function) are skipped,
- unless the specification includes a [, c, or n specifier.324)
-9 An input item is read from the stream, unless the specification includes an n specifier. An
- input item is defined as the longest sequence of input wide characters which does not
- exceed any specified field width and which is, or is a prefix of, a matching input
- sequence.325) The first wide character, if any, after the input item remains unread. If the
- length of the input item is zero, the execution of the directive fails; this condition is a
- matching failure unless end-of-file, an encoding error, or a read error prevented input
- from the stream, in which case it is an input failure.
-10 Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
- count of input wide characters) is converted to a type appropriate to the conversion
- specifier. If the input item is not a matching sequence, the execution of the directive fails:
- this condition is a matching failure. Unless assignment suppression was indicated by a *,
- the result of the conversion is placed in the object pointed to by the first argument
- following the format argument that has not already received a conversion result. If this
-
-
- 324) These white-space wide characters are not counted against a specified field width.
- 325) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
- sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.
-
-[page 408] (Contents)
-
- object does not have an appropriate type, or if the result of the conversion cannot be
- represented in the object, the behavior is undefined.
-11 The length modifiers and their meanings are:
- hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to signed char or unsigned char.
- h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to short int or unsigned short
- int.
- l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to long int or unsigned long
- int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
- an argument with type pointer to double; or that a following c, s, or [
- conversion specifier applies to an argument with type pointer to wchar_t.
- ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to long long int or unsigned
- long long int.
- j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to intmax_t or uintmax_t.
- z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to size_t or the corresponding signed
- integer type.
- t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
- to an argument with type pointer to ptrdiff_t or the corresponding
- unsigned integer type.
- L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
- applies to an argument with type pointer to long double.
- If a length modifier appears with any conversion specifier other than as specified above,
- the behavior is undefined.
-12 The conversion specifiers and their meanings are:
- d Matches an optionally signed decimal integer, whose format is the same as
- expected for the subject sequence of the wcstol function with the value 10
- for the base argument. The corresponding argument shall be a pointer to
- signed integer.
- i Matches an optionally signed integer, whose format is the same as expected
- for the subject sequence of the wcstol function with the value 0 for the
- base argument. The corresponding argument shall be a pointer to signed
-
-[page 409] (Contents)
-
- integer.
-o Matches an optionally signed octal integer, whose format is the same as
- expected for the subject sequence of the wcstoul function with the value 8
- for the base argument. The corresponding argument shall be a pointer to
- unsigned integer.
-u Matches an optionally signed decimal integer, whose format is the same as
- expected for the subject sequence of the wcstoul function with the value 10
- for the base argument. The corresponding argument shall be a pointer to
- unsigned integer.
-x Matches an optionally signed hexadecimal integer, whose format is the same
- as expected for the subject sequence of the wcstoul function with the value
- 16 for the base argument. The corresponding argument shall be a pointer to
- unsigned integer.
-a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
- format is the same as expected for the subject sequence of the wcstod
- function. The corresponding argument shall be a pointer to floating.
-c Matches a sequence of wide characters of exactly the number specified by the
- field width (1 if no field width is present in the directive).
- If no l length modifier is present, characters from the input field are
- converted as if by repeated calls to the wcrtomb function, with the
- conversion state described by an mbstate_t object initialized to zero
- before the first wide character is converted. The corresponding argument
- shall be a pointer to the initial element of a character array large enough to
- accept the sequence. No null character is added.
- If an l length modifier is present, the corresponding argument shall be a
- pointer to the initial element of an array of wchar_t large enough to accept
- the sequence. No null wide character is added.
-s Matches a sequence of non-white-space wide characters.
- If no l length modifier is present, characters from the input field are
- converted as if by repeated calls to the wcrtomb function, with the
- conversion state described by an mbstate_t object initialized to zero
- before the first wide character is converted. The corresponding argument
- shall be a pointer to the initial element of a character array large enough to
- accept the sequence and a terminating null character, which will be added
- automatically.
- If an l length modifier is present, the corresponding argument shall be a
- pointer to the initial element of an array of wchar_t large enough to accept
-
-[page 410] (Contents)
-
- the sequence and the terminating null wide character, which will be added
- automatically.
-[ Matches a nonempty sequence of wide characters from a set of expected
- characters (the scanset).
- If no l length modifier is present, characters from the input field are
- converted as if by repeated calls to the wcrtomb function, with the
- conversion state described by an mbstate_t object initialized to zero
- before the first wide character is converted. The corresponding argument
- shall be a pointer to the initial element of a character array large enough to
- accept the sequence and a terminating null character, which will be added
- automatically.
- If an l length modifier is present, the corresponding argument shall be a
- pointer to the initial element of an array of wchar_t large enough to accept
- the sequence and the terminating null wide character, which will be added
- automatically.
- The conversion specifier includes all subsequent wide characters in the
- format string, up to and including the matching right bracket (]). The wide
- characters between the brackets (the scanlist) compose the scanset, unless the
- wide character after the left bracket is a circumflex (^), in which case the
- scanset contains all wide characters that do not appear in the scanlist between
- the circumflex and the right bracket. If the conversion specifier begins with
- [] or [^], the right bracket wide character is in the scanlist and the next
- following right bracket wide character is the matching right bracket that ends
- the specification; otherwise the first following right bracket wide character is
- the one that ends the specification. If a - wide character is in the scanlist and
- is not the first, nor the second where the first wide character is a ^, nor the
- last character, the behavior is implementation-defined.
-p Matches an implementation-defined set of sequences, which should be the
- same as the set of sequences that may be produced by the %p conversion of
- the fwprintf function. The corresponding argument shall be a pointer to a
- pointer to void. The input item is converted to a pointer value in an
- implementation-defined manner. If the input item is a value converted earlier
- during the same program execution, the pointer that results shall compare
- equal to that value; otherwise the behavior of the %p conversion is undefined.
-n No input is consumed. The corresponding argument shall be a pointer to
- signed integer into which is to be written the number of wide characters read
- from the input stream so far by this call to the fwscanf function. Execution
- of a %n directive does not increment the assignment count returned at the
- completion of execution of the fwscanf function. No argument is
-[page 411] (Contents)
-
- converted, but one is consumed. If the conversion specification includes an
- assignment-suppressing wide character or a field width, the behavior is
- undefined.
- % Matches a single % wide character; no conversion or assignment occurs. The
- complete conversion specification shall be %%.
-13 If a conversion specification is invalid, the behavior is undefined.326)
-14 The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
- respectively, a, e, f, g, and x.
-15 Trailing white space (including new-line wide characters) is left unread unless matched
- by a directive. The success of literal matches and suppressed assignments is not directly
- determinable other than via the %n directive.
- Returns
-16 The fwscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the function returns the
- number of input items assigned, which can be fewer than provided for, or even zero, in
- the event of an early matching failure.
-17 EXAMPLE 1 The call:
- #include <stdio.h>
- #include <wchar.h>
- /* ... */
- int n, i; float x; wchar_t name[50];
- n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
- with the input line:
- 25 54.32E-1 thompson
- will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
- thompson\0.
-
-18 EXAMPLE 2 The call:
- #include <stdio.h>
- #include <wchar.h>
- /* ... */
- int i; float x; double y;
- fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
- with input:
- 56789 0123 56a72
- will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value
- 56.0. The next wide character read from the input stream will be a.
-
-
- 326) See ''future library directions'' (7.30.12).
-
-[page 412] (Contents)
-
- Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the
- wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb
- function (7.28.6.3.3).
- 7.28.2.3 The swprintf function
- Synopsis
-1 #include <wchar.h>
- int swprintf(wchar_t * restrict s,
- size_t n,
- const wchar_t * restrict format, ...);
- Description
-2 The swprintf function is equivalent to fwprintf, except that the argument s
- specifies an array of wide characters into which the generated output is to be written,
- rather than written to a stream. No more than n wide characters are written, including a
- terminating null wide character, which is always added (unless n is zero).
- Returns
-3 The swprintf function returns the number of wide characters written in the array, not
- counting the terminating null wide character, or a negative value if an encoding error
- occurred or if n or more wide characters were requested to be written.
- 7.28.2.4 The swscanf function
- Synopsis
-1 #include <wchar.h>
- int swscanf(const wchar_t * restrict s,
- const wchar_t * restrict format, ...);
- Description
-2 The swscanf function is equivalent to fwscanf, except that the argument s specifies a
- wide string from which the input is to be obtained, rather than from a stream. Reaching
- the end of the wide string is equivalent to encountering end-of-file for the fwscanf
- function.
- Returns
-3 The swscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the swscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
-
-
-
-
-[page 413] (Contents)
-
- 7.28.2.5 The vfwprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- #include <wchar.h>
- int vfwprintf(FILE * restrict stream,
- const wchar_t * restrict format,
- va_list arg);
- Description
-2 The vfwprintf function is equivalent to fwprintf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vfwprintf function does not invoke the
- va_end macro.327)
- Returns
-3 The vfwprintf function returns the number of wide characters transmitted, or a
- negative value if an output or encoding error occurred.
-4 EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting
- routine.
- #include <stdarg.h>
- #include <stdio.h>
- #include <wchar.h>
- void error(char *function_name, wchar_t *format, ...)
- {
- va_list args;
- va_start(args, format);
- // print out name of function causing error
- fwprintf(stderr, L"ERROR in %s: ", function_name);
- // print out remainder of message
- vfwprintf(stderr, format, args);
- va_end(args);
- }
-
-
-
-
- 327) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
- invoke the va_arg macro, the value of arg after the return is indeterminate.
-
-[page 414] (Contents)
-
- 7.28.2.6 The vfwscanf function
- Synopsis
-1 #include <stdarg.h>
- #include <stdio.h>
- #include <wchar.h>
- int vfwscanf(FILE * restrict stream,
- const wchar_t * restrict format,
- va_list arg);
- Description
-2 The vfwscanf function is equivalent to fwscanf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vfwscanf function does not invoke the
- va_end macro.327)
- Returns
-3 The vfwscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the vfwscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.28.2.7 The vswprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <wchar.h>
- int vswprintf(wchar_t * restrict s,
- size_t n,
- const wchar_t * restrict format,
- va_list arg);
- Description
-2 The vswprintf function is equivalent to swprintf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vswprintf function does not invoke the
- va_end macro.327)
- Returns
-3 The vswprintf function returns the number of wide characters written in the array, not
- counting the terminating null wide character, or a negative value if an encoding error
- occurred or if n or more wide characters were requested to be generated.
-
-
-[page 415] (Contents)
-
- 7.28.2.8 The vswscanf function
- Synopsis
-1 #include <stdarg.h>
- #include <wchar.h>
- int vswscanf(const wchar_t * restrict s,
- const wchar_t * restrict format,
- va_list arg);
- Description
-2 The vswscanf function is equivalent to swscanf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vswscanf function does not invoke the
- va_end macro.327)
- Returns
-3 The vswscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the vswscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.28.2.9 The vwprintf function
- Synopsis
-1 #include <stdarg.h>
- #include <wchar.h>
- int vwprintf(const wchar_t * restrict format,
- va_list arg);
- Description
-2 The vwprintf function is equivalent to wprintf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vwprintf function does not invoke the
- va_end macro.327)
- Returns
-3 The vwprintf function returns the number of wide characters transmitted, or a negative
- value if an output or encoding error occurred.
-
-
-
-
-[page 416] (Contents)
-
- 7.28.2.10 The vwscanf function
- Synopsis
-1 #include <stdarg.h>
- #include <wchar.h>
- int vwscanf(const wchar_t * restrict format,
- va_list arg);
- Description
-2 The vwscanf function is equivalent to wscanf, with the variable argument list
- replaced by arg, which shall have been initialized by the va_start macro (and
- possibly subsequent va_arg calls). The vwscanf function does not invoke the
- va_end macro.327)
- Returns
-3 The vwscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the vwscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.28.2.11 The wprintf function
- Synopsis
-1 #include <wchar.h>
- int wprintf(const wchar_t * restrict format, ...);
- Description
-2 The wprintf function is equivalent to fwprintf with the argument stdout
- interposed before the arguments to wprintf.
- Returns
-3 The wprintf function returns the number of wide characters transmitted, or a negative
- value if an output or encoding error occurred.
- 7.28.2.12 The wscanf function
- Synopsis
-1 #include <wchar.h>
- int wscanf(const wchar_t * restrict format, ...);
- Description
-2 The wscanf function is equivalent to fwscanf with the argument stdin interposed
- before the arguments to wscanf.
-
-
-[page 417] (Contents)
-
- Returns
-3 The wscanf function returns the value of the macro EOF if an input failure occurs
- before the first conversion (if any) has completed. Otherwise, the wscanf function
- returns the number of input items assigned, which can be fewer than provided for, or even
- zero, in the event of an early matching failure.
- 7.28.3 Wide character input/output functions
- 7.28.3.1 The fgetwc function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- wint_t fgetwc(FILE *stream);
- Description
-2 If the end-of-file indicator for the input stream pointed to by stream is not set and a
- next wide character is present, the fgetwc function obtains that wide character as a
- wchar_t converted to a wint_t and advances the associated file position indicator for
- the stream (if defined).
- Returns
-3 If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
- of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
- the fgetwc function returns the next wide character from the input stream pointed to by
- stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
- function returns WEOF. If an encoding error occurs (including too few bytes), the value of
- the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.328)
- 7.28.3.2 The fgetws function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- wchar_t *fgetws(wchar_t * restrict s,
- int n, FILE * restrict stream);
- Description
-2 The fgetws function reads at most one less than the number of wide characters
- specified by n from the stream pointed to by stream into the array pointed to by s. No
-
-
- 328) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
- Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.
-
-[page 418] (Contents)
-
- additional wide characters are read after a new-line wide character (which is retained) or
- after end-of-file. A null wide character is written immediately after the last wide
- character read into the array.
- Returns
-3 The fgetws function returns s if successful. If end-of-file is encountered and no
- characters have been read into the array, the contents of the array remain unchanged and a
- null pointer is returned. If a read or encoding error occurs during the operation, the array
- contents are indeterminate and a null pointer is returned.
- 7.28.3.3 The fputwc function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- wint_t fputwc(wchar_t c, FILE *stream);
- Description
-2 The fputwc function writes the wide character specified by c to the output stream
- pointed to by stream, at the position indicated by the associated file position indicator
- for the stream (if defined), and advances the indicator appropriately. If the file cannot
- support positioning requests, or if the stream was opened with append mode, the
- character is appended to the output stream.
- Returns
-3 The fputwc function returns the wide character written. If a write error occurs, the
- error indicator for the stream is set and fputwc returns WEOF. If an encoding error
- occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.
- 7.28.3.4 The fputws function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- int fputws(const wchar_t * restrict s,
- FILE * restrict stream);
- Description
-2 The fputws function writes the wide string pointed to by s to the stream pointed to by
- stream. The terminating null wide character is not written.
- Returns
-3 The fputws function returns EOF if a write or encoding error occurs; otherwise, it
- returns a nonnegative value.
-
-[page 419] (Contents)
-
- 7.28.3.5 The fwide function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- int fwide(FILE *stream, int mode);
- Description
-2 The fwide function determines the orientation of the stream pointed to by stream. If
- mode is greater than zero, the function first attempts to make the stream wide oriented. If
- mode is less than zero, the function first attempts to make the stream byte oriented.329)
- Otherwise, mode is zero and the function does not alter the orientation of the stream.
- Returns
-3 The fwide function returns a value greater than zero if, after the call, the stream has
- wide orientation, a value less than zero if the stream has byte orientation, or zero if the
- stream has no orientation.
- 7.28.3.6 The getwc function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- wint_t getwc(FILE *stream);
- Description
-2 The getwc function is equivalent to fgetwc, except that if it is implemented as a
- macro, it may evaluate stream more than once, so the argument should never be an
- expression with side effects.
- Returns
-3 The getwc function returns the next wide character from the input stream pointed to by
- stream, or WEOF.
- 7.28.3.7 The getwchar function
- Synopsis
-1 #include <wchar.h>
- wint_t getwchar(void);
-
-
-
-
- 329) If the orientation of the stream has already been determined, fwide does not change it.
-
-[page 420] (Contents)
-
- Description
-2 The getwchar function is equivalent to getwc with the argument stdin.
- Returns
-3 The getwchar function returns the next wide character from the input stream pointed to
- by stdin, or WEOF.
- 7.28.3.8 The putwc function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- wint_t putwc(wchar_t c, FILE *stream);
- Description
-2 The putwc function is equivalent to fputwc, except that if it is implemented as a
- macro, it may evaluate stream more than once, so that argument should never be an
- expression with side effects.
- Returns
-3 The putwc function returns the wide character written, or WEOF.
- 7.28.3.9 The putwchar function
- Synopsis
-1 #include <wchar.h>
- wint_t putwchar(wchar_t c);
- Description
-2 The putwchar function is equivalent to putwc with the second argument stdout.
- Returns
-3 The putwchar function returns the character written, or WEOF.
- 7.28.3.10 The ungetwc function
- Synopsis
-1 #include <stdio.h>
- #include <wchar.h>
- wint_t ungetwc(wint_t c, FILE *stream);
- Description
-2 The ungetwc function pushes the wide character specified by c back onto the input
- stream pointed to by stream. Pushed-back wide characters will be returned by
- subsequent reads on that stream in the reverse order of their pushing. A successful
-
-[page 421] (Contents)
-
- intervening call (with the stream pointed to by stream) to a file positioning function
- (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
- stream. The external storage corresponding to the stream is unchanged.
-3 One wide character of pushback is guaranteed, even if the call to the ungetwc function
- follows just after a call to a formatted wide character input function fwscanf,
- vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
- on the same stream without an intervening read or file positioning operation on that
- stream, the operation may fail.
-4 If the value of c equals that of the macro WEOF, the operation fails and the input stream is
- unchanged.
-5 A successful call to the ungetwc function clears the end-of-file indicator for the stream.
- The value of the file position indicator for the stream after reading or discarding all
- pushed-back wide characters is the same as it was before the wide characters were pushed
- back. For a text or binary stream, the value of its file position indicator after a successful
- call to the ungetwc function is unspecified until all pushed-back wide characters are
- read or discarded.
- Returns
-6 The ungetwc function returns the wide character pushed back, or WEOF if the operation
- fails.
- 7.28.4 General wide string utilities
-1 The header <wchar.h> declares a number of functions useful for wide string
- manipulation. Various methods are used for determining the lengths of the arrays, but in
- all cases a wchar_t * argument points to the initial (lowest addressed) element of the
- array. If an array is accessed beyond the end of an object, the behavior is undefined.
-2 Where an argument declared as size_t n determines the length of the array for a
- function, n can have the value zero on a call to that function. Unless explicitly stated
- otherwise in the description of a particular function in this subclause, pointer arguments
- on such a call shall still have valid values, as described in 7.1.4. On such a call, a
- function that locates a wide character finds no occurrence, a function that compares two
- wide character sequences returns zero, and a function that copies wide characters copies
- zero wide characters.
-
-
-
-
-[page 422] (Contents)
-
- 7.28.4.1 Wide string numeric conversion functions
- 7.28.4.1.1 The wcstod, wcstof, and wcstold functions
- Synopsis
-1 #include <wchar.h>
- double wcstod(const wchar_t * restrict nptr,
- wchar_t ** restrict endptr);
- float wcstof(const wchar_t * restrict nptr,
- wchar_t ** restrict endptr);
- long double wcstold(const wchar_t * restrict nptr,
- wchar_t ** restrict endptr);
- Description
-2 The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
- string pointed to by nptr to double, float, and long double representation,
- respectively. First, they decompose the input string into three parts: an initial, possibly
- empty, sequence of white-space wide characters (as specified by the iswspace
- function), a subject sequence resembling a floating-point constant or representing an
- infinity or NaN; and a final wide string of one or more unrecognized wide characters,
- including the terminating null wide character of the input wide string. Then, they attempt
- to convert the subject sequence to a floating-point number, and return the result.
-3 The expected form of the subject sequence is an optional plus or minus sign, then one of
- the following:
- -- a nonempty sequence of decimal digits optionally containing a decimal-point wide
- character, then an optional exponent part as defined for the corresponding single-byte
- characters in 6.4.4.2;
- -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
- decimal-point wide character, then an optional binary exponent part as defined in
- 6.4.4.2;
- -- INF or INFINITY, or any other wide string equivalent except for case
- -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
- case in the NAN part, where:
- n-wchar-sequence:
- digit
- nondigit
- n-wchar-sequence digit
- n-wchar-sequence nondigit
- The subject sequence is defined as the longest initial subsequence of the input wide
- string, starting with the first non-white-space wide character, that is of the expected form.
-[page 423] (Contents)
-
- The subject sequence contains no wide characters if the input wide string is not of the
- expected form.
-4 If the subject sequence has the expected form for a floating-point number, the sequence of
- wide characters starting with the first digit or the decimal-point wide character
- (whichever occurs first) is interpreted as a floating constant according to the rules of
- 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
- if neither an exponent part nor a decimal-point wide character appears in a decimal
- floating point number, or if a binary exponent part does not appear in a hexadecimal
- floating point number, an exponent part of the appropriate type with value zero is
- assumed to follow the last digit in the string. If the subject sequence begins with a minus
- sign, the sequence is interpreted as negated.330) A wide character sequence INF or
- INFINITY is interpreted as an infinity, if representable in the return type, else like a
- floating constant that is too large for the range of the return type. A wide character
- sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
- in the return type, else like a subject sequence part that does not have the expected form;
- the meaning of the n-wchar sequences is implementation-defined.331) A pointer to the
- final wide string is stored in the object pointed to by endptr, provided that endptr is
- not a null pointer.
-5 If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
- value resulting from the conversion is correctly rounded.
-6 In other than the "C" locale, additional locale-specific subject sequence forms may be
- accepted.
-7 If the subject sequence is empty or does not have the expected form, no conversion is
- performed; the value of nptr is stored in the object pointed to by endptr, provided
- that endptr is not a null pointer.
- Recommended practice
-8 If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
- the result is not exactly representable, the result should be one of the two numbers in the
- appropriate internal format that are adjacent to the hexadecimal floating source value,
- with the extra stipulation that the error should have a correct sign for the current rounding
- direction.
-
-
-
- 330) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
- negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
- methods may yield different results if rounding is toward positive or negative infinity. In either case,
- the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
- 331) An implementation may use the n-wchar sequence to determine extra information to be represented in
- the NaN's significand.
-
-[page 424] (Contents)
-
-9 If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
- <float.h>) significant digits, the result should be correctly rounded. If the subject
- sequence D has the decimal form and more than DECIMAL_DIG significant digits,
- consider the two bounding, adjacent decimal strings L and U, both having
- DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
- The result should be one of the (equal or adjacent) values that would be obtained by
- correctly rounding L and U according to the current rounding direction, with the extra
- stipulation that the error with respect to D should have a correct sign for the current
- rounding direction.332)
- Returns
-10 The functions return the converted value, if any. If no conversion could be performed,
- zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
- plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
- return type and sign of the value), and the value of the macro ERANGE is stored in
- errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
- no greater than the smallest normalized positive number in the return type; whether
- errno acquires the value ERANGE is implementation-defined.
-
-
-
-
- 332) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
- to the same internal floating value, but if not will round to adjacent values.
-
-[page 425] (Contents)
-
- 7.28.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
- Synopsis
-1 #include <wchar.h>
- long int wcstol(
- const wchar_t * restrict nptr,
- wchar_t ** restrict endptr,
- int base);
- long long int wcstoll(
- const wchar_t * restrict nptr,
- wchar_t ** restrict endptr,
- int base);
- unsigned long int wcstoul(
- const wchar_t * restrict nptr,
- wchar_t ** restrict endptr,
- int base);
- unsigned long long int wcstoull(
- const wchar_t * restrict nptr,
- wchar_t ** restrict endptr,
- int base);
- Description
-2 The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
- portion of the wide string pointed to by nptr to long int, long long int,
- unsigned long int, and unsigned long long int representation,
- respectively. First, they decompose the input string into three parts: an initial, possibly
- empty, sequence of white-space wide characters (as specified by the iswspace
- function), a subject sequence resembling an integer represented in some radix determined
- by the value of base, and a final wide string of one or more unrecognized wide
- characters, including the terminating null wide character of the input wide string. Then,
- they attempt to convert the subject sequence to an integer, and return the result.
-3 If the value of base is zero, the expected form of the subject sequence is that of an
- integer constant as described for the corresponding single-byte characters in 6.4.4.1,
- optionally preceded by a plus or minus sign, but not including an integer suffix. If the
- value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
- is a sequence of letters and digits representing an integer with the radix specified by
- base, optionally preceded by a plus or minus sign, but not including an integer suffix.
- The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
- letters and digits whose ascribed values are less than that of base are permitted. If the
- value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
- of letters and digits, following the sign if present.
-
-[page 426] (Contents)
-
-4 The subject sequence is defined as the longest initial subsequence of the input wide
- string, starting with the first non-white-space wide character, that is of the expected form.
- The subject sequence contains no wide characters if the input wide string is empty or
- consists entirely of white space, or if the first non-white-space wide character is other
- than a sign or a permissible letter or digit.
-5 If the subject sequence has the expected form and the value of base is zero, the sequence
- of wide characters starting with the first digit is interpreted as an integer constant
- according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
- value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
- letter its value as given above. If the subject sequence begins with a minus sign, the value
- resulting from the conversion is negated (in the return type). A pointer to the final wide
- string is stored in the object pointed to by endptr, provided that endptr is not a null
- pointer.
-6 In other than the "C" locale, additional locale-specific subject sequence forms may be
- accepted.
-7 If the subject sequence is empty or does not have the expected form, no conversion is
- performed; the value of nptr is stored in the object pointed to by endptr, provided
- that endptr is not a null pointer.
- Returns
-8 The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
- value, if any. If no conversion could be performed, zero is returned. If the correct value
- is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
- LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
- sign of the value, if any), and the value of the macro ERANGE is stored in errno.
- 7.28.4.2 Wide string copying functions
- 7.28.4.2.1 The wcscpy function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcscpy(wchar_t * restrict s1,
- const wchar_t * restrict s2);
- Description
-2 The wcscpy function copies the wide string pointed to by s2 (including the terminating
- null wide character) into the array pointed to by s1.
- Returns
-3 The wcscpy function returns the value of s1.
-
-
-[page 427] (Contents)
-
- 7.28.4.2.2 The wcsncpy function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcsncpy(wchar_t * restrict s1,
- const wchar_t * restrict s2,
- size_t n);
- Description
-2 The wcsncpy function copies not more than n wide characters (those that follow a null
- wide character are not copied) from the array pointed to by s2 to the array pointed to by
- s1.333)
-3 If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
- wide characters are appended to the copy in the array pointed to by s1, until n wide
- characters in all have been written.
- Returns
-4 The wcsncpy function returns the value of s1.
- 7.28.4.2.3 The wmemcpy function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wmemcpy(wchar_t * restrict s1,
- const wchar_t * restrict s2,
- size_t n);
- Description
-2 The wmemcpy function copies n wide characters from the object pointed to by s2 to the
- object pointed to by s1.
- Returns
-3 The wmemcpy function returns the value of s1.
-
-
-
-
- 333) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
- result will not be null-terminated.
-
-[page 428] (Contents)
-
- 7.28.4.2.4 The wmemmove function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
- size_t n);
- Description
-2 The wmemmove function copies n wide characters from the object pointed to by s2 to
- the object pointed to by s1. Copying takes place as if the n wide characters from the
- object pointed to by s2 are first copied into a temporary array of n wide characters that
- does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
- the temporary array are copied into the object pointed to by s1.
- Returns
-3 The wmemmove function returns the value of s1.
- 7.28.4.3 Wide string concatenation functions
- 7.28.4.3.1 The wcscat function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcscat(wchar_t * restrict s1,
- const wchar_t * restrict s2);
- Description
-2 The wcscat function appends a copy of the wide string pointed to by s2 (including the
- terminating null wide character) to the end of the wide string pointed to by s1. The initial
- wide character of s2 overwrites the null wide character at the end of s1.
- Returns
-3 The wcscat function returns the value of s1.
- 7.28.4.3.2 The wcsncat function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcsncat(wchar_t * restrict s1,
- const wchar_t * restrict s2,
- size_t n);
- Description
-2 The wcsncat function appends not more than n wide characters (a null wide character
- and those that follow it are not appended) from the array pointed to by s2 to the end of
-
-[page 429] (Contents)
-
- the wide string pointed to by s1. The initial wide character of s2 overwrites the null
- wide character at the end of s1. A terminating null wide character is always appended to
- the result.334)
- Returns
-3 The wcsncat function returns the value of s1.
- 7.28.4.4 Wide string comparison functions
-1 Unless explicitly stated otherwise, the functions described in this subclause order two
- wide characters the same way as two integers of the underlying integer type designated
- by wchar_t.
- 7.28.4.4.1 The wcscmp function
- Synopsis
-1 #include <wchar.h>
- int wcscmp(const wchar_t *s1, const wchar_t *s2);
- Description
-2 The wcscmp function compares the wide string pointed to by s1 to the wide string
- pointed to by s2.
- Returns
-3 The wcscmp function returns an integer greater than, equal to, or less than zero,
- accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
- wide string pointed to by s2.
- 7.28.4.4.2 The wcscoll function
- Synopsis
-1 #include <wchar.h>
- int wcscoll(const wchar_t *s1, const wchar_t *s2);
- Description
-2 The wcscoll function compares the wide string pointed to by s1 to the wide string
- pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
- current locale.
- Returns
-3 The wcscoll function returns an integer greater than, equal to, or less than zero,
- accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
-
-
- 334) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
- wcslen(s1)+n+1.
-
-[page 430] (Contents)
-
- wide string pointed to by s2 when both are interpreted as appropriate to the current
- locale.
- 7.28.4.4.3 The wcsncmp function
- Synopsis
-1 #include <wchar.h>
- int wcsncmp(const wchar_t *s1, const wchar_t *s2,
- size_t n);
- Description
-2 The wcsncmp function compares not more than n wide characters (those that follow a
- null wide character are not compared) from the array pointed to by s1 to the array
- pointed to by s2.
- Returns
-3 The wcsncmp function returns an integer greater than, equal to, or less than zero,
- accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
- to, or less than the possibly null-terminated array pointed to by s2.
- 7.28.4.4.4 The wcsxfrm function
- Synopsis
-1 #include <wchar.h>
- size_t wcsxfrm(wchar_t * restrict s1,
- const wchar_t * restrict s2,
- size_t n);
- Description
-2 The wcsxfrm function transforms the wide string pointed to by s2 and places the
- resulting wide string into the array pointed to by s1. The transformation is such that if
- the wcscmp function is applied to two transformed wide strings, it returns a value greater
- than, equal to, or less than zero, corresponding to the result of the wcscoll function
- applied to the same two original wide strings. No more than n wide characters are placed
- into the resulting array pointed to by s1, including the terminating null wide character. If
- n is zero, s1 is permitted to be a null pointer.
- Returns
-3 The wcsxfrm function returns the length of the transformed wide string (not including
- the terminating null wide character). If the value returned is n or greater, the contents of
- the array pointed to by s1 are indeterminate.
-4 EXAMPLE The value of the following expression is the length of the array needed to hold the
- transformation of the wide string pointed to by s:
-
-
-[page 431] (Contents)
-
- 1 + wcsxfrm(NULL, s, 0)
-
- 7.28.4.4.5 The wmemcmp function
- Synopsis
-1 #include <wchar.h>
- int wmemcmp(const wchar_t *s1, const wchar_t *s2,
- size_t n);
- Description
-2 The wmemcmp function compares the first n wide characters of the object pointed to by
- s1 to the first n wide characters of the object pointed to by s2.
- Returns
-3 The wmemcmp function returns an integer greater than, equal to, or less than zero,
- accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
- pointed to by s2.
- 7.28.4.5 Wide string search functions
- 7.28.4.5.1 The wcschr function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcschr(const wchar_t *s, wchar_t c);
- Description
-2 The wcschr function locates the first occurrence of c in the wide string pointed to by s.
- The terminating null wide character is considered to be part of the wide string.
- Returns
-3 The wcschr function returns a pointer to the located wide character, or a null pointer if
- the wide character does not occur in the wide string.
- 7.28.4.5.2 The wcscspn function
- Synopsis
-1 #include <wchar.h>
- size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
- Description
-2 The wcscspn function computes the length of the maximum initial segment of the wide
- string pointed to by s1 which consists entirely of wide characters not from the wide
- string pointed to by s2.
-
-
-
-[page 432] (Contents)
-
- Returns
-3 The wcscspn function returns the length of the segment.
- 7.28.4.5.3 The wcspbrk function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
- Description
-2 The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
- any wide character from the wide string pointed to by s2.
- Returns
-3 The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
- no wide character from s2 occurs in s1.
- 7.28.4.5.4 The wcsrchr function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
- Description
-2 The wcsrchr function locates the last occurrence of c in the wide string pointed to by
- s. The terminating null wide character is considered to be part of the wide string.
- Returns
-3 The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
- not occur in the wide string.
- 7.28.4.5.5 The wcsspn function
- Synopsis
-1 #include <wchar.h>
- size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
- Description
-2 The wcsspn function computes the length of the maximum initial segment of the wide
- string pointed to by s1 which consists entirely of wide characters from the wide string
- pointed to by s2.
- Returns
-3 The wcsspn function returns the length of the segment.
-
-
-[page 433] (Contents)
-
- 7.28.4.5.6 The wcsstr function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
- Description
-2 The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
- the sequence of wide characters (excluding the terminating null wide character) in the
- wide string pointed to by s2.
- Returns
-3 The wcsstr function returns a pointer to the located wide string, or a null pointer if the
- wide string is not found. If s2 points to a wide string with zero length, the function
- returns s1.
- 7.28.4.5.7 The wcstok function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wcstok(wchar_t * restrict s1,
- const wchar_t * restrict s2,
- wchar_t ** restrict ptr);
- Description
-2 A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
- a sequence of tokens, each of which is delimited by a wide character from the wide string
- pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
- which the wcstok function stores information necessary for it to continue scanning the
- same wide string.
-3 The first call in a sequence has a non-null first argument and stores an initial value in the
- object pointed to by ptr. Subsequent calls in the sequence have a null first argument and
- the object pointed to by ptr is required to have the value stored by the previous call in
- the sequence, which is then updated. The separator wide string pointed to by s2 may be
- different from call to call.
-4 The first call in the sequence searches the wide string pointed to by s1 for the first wide
- character that is not contained in the current separator wide string pointed to by s2. If no
- such wide character is found, then there are no tokens in the wide string pointed to by s1
- and the wcstok function returns a null pointer. If such a wide character is found, it is
- the start of the first token.
-5 The wcstok function then searches from there for a wide character that is contained in
- the current separator wide string. If no such wide character is found, the current token
-[page 434] (Contents)
-
- extends to the end of the wide string pointed to by s1, and subsequent searches in the
- same wide string for a token return a null pointer. If such a wide character is found, it is
- overwritten by a null wide character, which terminates the current token.
-6 In all cases, the wcstok function stores sufficient information in the pointer pointed to
- by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
- value for ptr, shall start searching just past the element overwritten by a null wide
- character (if any).
- Returns
-7 The wcstok function returns a pointer to the first wide character of a token, or a null
- pointer if there is no token.
-8 EXAMPLE
- #include <wchar.h>
- static wchar_t str1[] = L"?a???b,,,#c";
- static wchar_t str2[] = L"\t \t";
- wchar_t *t, *ptr1, *ptr2;
- t = wcstok(str1, L"?", &ptr1); // t points to the token L"a"
- t = wcstok(NULL, L",", &ptr1); // t points to the token L"??b"
- t = wcstok(str2, L" \t", &ptr2); // t is a null pointer
- t = wcstok(NULL, L"#,", &ptr1); // t points to the token L"c"
- t = wcstok(NULL, L"?", &ptr1); // t is a null pointer
-
- 7.28.4.5.8 The wmemchr function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wmemchr(const wchar_t *s, wchar_t c,
- size_t n);
- Description
-2 The wmemchr function locates the first occurrence of c in the initial n wide characters of
- the object pointed to by s.
- Returns
-3 The wmemchr function returns a pointer to the located wide character, or a null pointer if
- the wide character does not occur in the object.
-
-
-
-
-[page 435] (Contents)
-
- 7.28.4.6 Miscellaneous functions
- 7.28.4.6.1 The wcslen function
- Synopsis
-1 #include <wchar.h>
- size_t wcslen(const wchar_t *s);
- Description
-2 The wcslen function computes the length of the wide string pointed to by s.
- Returns
-3 The wcslen function returns the number of wide characters that precede the terminating
- null wide character.
- 7.28.4.6.2 The wmemset function
- Synopsis
-1 #include <wchar.h>
- wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
- Description
-2 The wmemset function copies the value of c into each of the first n wide characters of
- the object pointed to by s.
- Returns
-3 The wmemset function returns the value of s.
- 7.28.5 Wide character time conversion functions
- 7.28.5.1 The wcsftime function
- Synopsis
-1 #include <time.h>
- #include <wchar.h>
- size_t wcsftime(wchar_t * restrict s,
- size_t maxsize,
- const wchar_t * restrict format,
- const struct tm * restrict timeptr);
- Description
-2 The wcsftime function is equivalent to the strftime function, except that:
- -- The argument s points to the initial element of an array of wide characters into which
- the generated output is to be placed.
-
-
-[page 436] (Contents)
-
- -- The argument maxsize indicates the limiting number of wide characters.
- -- The argument format is a wide string and the conversion specifiers are replaced by
- corresponding sequences of wide characters.
- -- The return value indicates the number of wide characters.
- Returns
-3 If the total number of resulting wide characters including the terminating null wide
- character is not more than maxsize, the wcsftime function returns the number of
- wide characters placed into the array pointed to by s not including the terminating null
- wide character. Otherwise, zero is returned and the contents of the array are
- indeterminate.
- 7.28.6 Extended multibyte/wide character conversion utilities
-1 The header <wchar.h> declares an extended set of functions useful for conversion
- between multibyte characters and wide characters.
-2 Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and
- 7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used
- to describe the current conversion state from a particular multibyte character sequence to
- a wide character sequence (or the reverse) under the rules of a particular setting for the
- LC_CTYPE category of the current locale.
-3 The initial conversion state corresponds, for a conversion in either direction, to the
- beginning of a new multibyte character in the initial shift state. A zero-valued
- mbstate_t object is (at least) one way to describe an initial conversion state. A zero-
- valued mbstate_t object can be used to initiate conversion involving any multibyte
- character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
- been altered by any of the functions described in this subclause, and is then used with a
- different multibyte character sequence, or in the other conversion direction, or with a
- different LC_CTYPE category setting than on earlier function calls, the behavior is
- undefined.335)
-4 On entry, each function takes the described conversion state (either internal or pointed to
- by an argument) as current. The conversion state described by the referenced object is
- altered as needed to track the shift state, and the position within a multibyte character, for
- the associated multibyte character sequence.
-
-
-
-
- 335) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and
- mbsrtowcs functions as long as they are used to step sequentially through the same multibyte
- character string.
-
-[page 437] (Contents)
-
- 7.28.6.1 Single-byte/wide character conversion functions
- 7.28.6.1.1 The btowc function
- Synopsis
-1 #include <wchar.h> *
- wint_t btowc(int c);
- Description
-2 The btowc function determines whether c constitutes a valid single-byte character in the
- initial shift state.
- Returns
-3 The btowc function returns WEOF if c has the value EOF or if (unsigned char)c
- does not constitute a valid single-byte character in the initial shift state. Otherwise, it
- returns the wide character representation of that character.
- 7.28.6.1.2 The wctob function
- Synopsis
-1 #include <wchar.h> *
- int wctob(wint_t c);
- Description
-2 The wctob function determines whether c corresponds to a member of the extended
- character set whose multibyte character representation is a single byte when in the initial
- shift state.
- Returns
-3 The wctob function returns EOF if c does not correspond to a multibyte character with
- length one in the initial shift state. Otherwise, it returns the single-byte representation of
- that character as an unsigned char converted to an int.
- 7.28.6.2 Conversion state functions
- 7.28.6.2.1 The mbsinit function
- Synopsis
-1 #include <wchar.h>
- int mbsinit(const mbstate_t *ps);
- Description
-2 If ps is not a null pointer, the mbsinit function determines whether the referenced
- mbstate_t object describes an initial conversion state.
-
-
-
-[page 438] (Contents)
-
- Returns
-3 The mbsinit function returns nonzero if ps is a null pointer or if the referenced object
- describes an initial conversion state; otherwise, it returns zero.
- 7.28.6.3 Restartable multibyte/wide character conversion functions
-1 These functions differ from the corresponding multibyte character functions of 7.22.7
- (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type
- pointer to mbstate_t that points to an object that can completely describe the current
- conversion state of the associated multibyte character sequence. If ps is a null pointer,
- each function uses its own internal mbstate_t object instead, which is initialized at
- program startup to the initial conversion state; the functions are not required to avoid data
- races in this case. The implementation behaves as if no library function calls these
- functions with a null pointer for ps.
-2 Also unlike their corresponding functions, the return value does not represent whether the
- encoding is state-dependent.
- 7.28.6.3.1 The mbrlen function
- Synopsis
-1 #include <wchar.h>
- size_t mbrlen(const char * restrict s,
- size_t n,
- mbstate_t * restrict ps);
- Description
-2 The mbrlen function is equivalent to the call:
- mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
- where internal is the mbstate_t object for the mbrlen function, except that the
- expression designated by ps is evaluated only once.
- Returns
-3 The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
- or (size_t)(-1).
- Forward references: the mbrtowc function (7.28.6.3.2).
-
-
-
-
-[page 439] (Contents)
-
- 7.28.6.3.2 The mbrtowc function
- Synopsis
-1 #include <wchar.h>
- size_t mbrtowc(wchar_t * restrict pwc,
- const char * restrict s,
- size_t n,
- mbstate_t * restrict ps);
- Description
-2 If s is a null pointer, the mbrtowc function is equivalent to the call:
- mbrtowc(NULL, "", 1, ps)
- In this case, the values of the parameters pwc and n are ignored.
-3 If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with
- the byte pointed to by s to determine the number of bytes needed to complete the next
- multibyte character (including any shift sequences). If the function determines that the
- next multibyte character is complete and valid, it determines the value of the
- corresponding wide character and then, if pwc is not a null pointer, stores that value in
- the object pointed to by pwc. If the corresponding wide character is the null wide
- character, the resulting state described is the initial conversion state.
- Returns
-4 The mbrtowc function returns the first of the following that applies (given the current
- conversion state):
- 0 if the next n or fewer bytes complete the multibyte character that
- corresponds to the null wide character (which is the value stored).
- between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
- character (which is the value stored); the value returned is the number
- of bytes that complete the multibyte character.
- (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
- multibyte character, and all n bytes have been processed (no value is
- stored).336)
- (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
- do not contribute to a complete and valid multibyte character (no
- value is stored); the value of the macro EILSEQ is stored in errno,
- and the conversion state is unspecified.
-
- 336) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
- sequence of redundant shift sequences (for implementations with state-dependent encodings).
-
-[page 440] (Contents)
-
- 7.28.6.3.3 The wcrtomb function
- Synopsis
-1 #include <wchar.h>
- size_t wcrtomb(char * restrict s,
- wchar_t wc,
- mbstate_t * restrict ps);
- Description
-2 If s is a null pointer, the wcrtomb function is equivalent to the call
- wcrtomb(buf, L'\0', ps)
- where buf is an internal buffer.
-3 If s is not a null pointer, the wcrtomb function determines the number of bytes needed
- to represent the multibyte character that corresponds to the wide character given by wc
- (including any shift sequences), and stores the multibyte character representation in the
- array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
- wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
- to restore the initial shift state; the resulting state described is the initial conversion state.
- Returns
-4 The wcrtomb function returns the number of bytes stored in the array object (including
- any shift sequences). When wc is not a valid wide character, an encoding error occurs:
- the function stores the value of the macro EILSEQ in errno and returns
- (size_t)(-1); the conversion state is unspecified.
- 7.28.6.4 Restartable multibyte/wide string conversion functions
-1 These functions differ from the corresponding multibyte string functions of 7.22.8
- (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to
- mbstate_t that points to an object that can completely describe the current conversion
- state of the associated multibyte character sequence. If ps is a null pointer, each function
- uses its own internal mbstate_t object instead, which is initialized at program startup
- to the initial conversion state; the functions are not required to avoid data races in this
- case. The implementation behaves as if no library function calls these functions with a
- null pointer for ps.
-2 Also unlike their corresponding functions, the conversion source parameter, src, has a
- pointer-to-pointer type. When the function is storing the results of conversions (that is,
- when dst is not a null pointer), the pointer object pointed to by this parameter is updated
- to reflect the amount of the source processed by that invocation.
-
-
-
-
-[page 441] (Contents)
-
- 7.28.6.4.1 The mbsrtowcs function
- Synopsis
-1 #include <wchar.h>
- size_t mbsrtowcs(wchar_t * restrict dst,
- const char ** restrict src,
- size_t len,
- mbstate_t * restrict ps);
- Description
-2 The mbsrtowcs function converts a sequence of multibyte characters that begins in the
- conversion state described by the object pointed to by ps, from the array indirectly
- pointed to by src into a sequence of corresponding wide characters. If dst is not a null
- pointer, the converted characters are stored into the array pointed to by dst. Conversion
- continues up to and including a terminating null character, which is also stored.
- Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
- not form a valid multibyte character, or (if dst is not a null pointer) when len wide
- characters have been stored into the array pointed to by dst.337) Each conversion takes
- place as if by a call to the mbrtowc function.
-3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
- pointer (if conversion stopped due to reaching a terminating null character) or the address
- just past the last multibyte character converted (if any). If conversion stopped due to
- reaching a terminating null character and if dst is not a null pointer, the resulting state
- described is the initial conversion state.
- Returns
-4 If the input conversion encounters a sequence of bytes that do not form a valid multibyte
- character, an encoding error occurs: the mbsrtowcs function stores the value of the
- macro EILSEQ in errno and returns (size_t)(-1); the conversion state is
- unspecified. Otherwise, it returns the number of multibyte characters successfully
- converted, not including the terminating null character (if any).
-
-
-
-
- 337) Thus, the value of len is ignored if dst is a null pointer.
-
-[page 442] (Contents)
-
- 7.28.6.4.2 The wcsrtombs function
- Synopsis
-1 #include <wchar.h>
- size_t wcsrtombs(char * restrict dst,
- const wchar_t ** restrict src,
- size_t len,
- mbstate_t * restrict ps);
- Description
-2 The wcsrtombs function converts a sequence of wide characters from the array
- indirectly pointed to by src into a sequence of corresponding multibyte characters that
- begins in the conversion state described by the object pointed to by ps. If dst is not a
- null pointer, the converted characters are then stored into the array pointed to by dst.
- Conversion continues up to and including a terminating null wide character, which is also
- stored. Conversion stops earlier in two cases: when a wide character is reached that does
- not correspond to a valid multibyte character, or (if dst is not a null pointer) when the
- next multibyte character would exceed the limit of len total bytes to be stored into the
- array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
- function.338)
-3 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
- pointer (if conversion stopped due to reaching a terminating null wide character) or the
- address just past the last wide character converted (if any). If conversion stopped due to
- reaching a terminating null wide character, the resulting state described is the initial
- conversion state.
- Returns
-4 If conversion stops because a wide character is reached that does not correspond to a
- valid multibyte character, an encoding error occurs: the wcsrtombs function stores the
- value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
- state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
- character sequence, not including the terminating null character (if any).
-
-
-
-
- 338) If conversion stops because a terminating null wide character has been reached, the bytes stored
- include those necessary to reach the initial shift state immediately before the null byte.
-
-[page 443] (Contents)
-
- 7.29 Wide character classification and mapping utilities <wctype.h>
- 7.29.1 Introduction
-1 The header <wctype.h> defines one macro, and declares three data types and many
- functions.339)
-2 The types declared are
- wint_t
- described in 7.28.1;
- wctrans_t
- which is a scalar type that can hold values which represent locale-specific character
- mappings; and
- wctype_t
- which is a scalar type that can hold values which represent locale-specific character
- classifications.
-3 The macro defined is WEOF (described in 7.28.1).
-4 The functions declared are grouped as follows:
- -- Functions that provide wide character classification;
- -- Extensible functions that provide wide character classification;
- -- Functions that provide wide character case mapping;
- -- Extensible functions that provide wide character mapping.
-5 For all functions described in this subclause that accept an argument of type wint_t, the
- value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
- this argument has any other value, the behavior is undefined.
-6 The behavior of these functions is affected by the LC_CTYPE category of the current
- locale.
-
-
-
-
- 339) See ''future library directions'' (7.30.13).
-
-[page 444] (Contents)
-
- 7.29.2 Wide character classification utilities
-1 The header <wctype.h> declares several functions useful for classifying wide
- characters.
-2 The term printing wide character refers to a member of a locale-specific set of wide
- characters, each of which occupies at least one printing position on a display device. The
- term control wide character refers to a member of a locale-specific set of wide characters
- that are not printing wide characters.
- 7.29.2.1 Wide character classification functions
-1 The functions in this subclause return nonzero (true) if and only if the value of the
- argument wc conforms to that in the description of the function.
-2 Each of the following functions returns true for each wide character that corresponds (as
- if by a call to the wctob function) to a single-byte character for which the corresponding
- character classification function from 7.4.1 returns true, except that the iswgraph and
- iswpunct functions may differ with respect to wide characters other than L' ' that are
- both printing and white-space wide characters.340)
- Forward references: the wctob function (7.28.6.1.2).
- 7.29.2.1.1 The iswalnum function
- Synopsis
-1 #include <wctype.h>
- int iswalnum(wint_t wc);
- Description
-2 The iswalnum function tests for any wide character for which iswalpha or
- iswdigit is true.
- 7.29.2.1.2 The iswalpha function
- Synopsis
-1 #include <wctype.h>
- int iswalpha(wint_t wc);
- Description
-2 The iswalpha function tests for any wide character for which iswupper or
- iswlower is true, or any wide character that is one of a locale-specific set of alphabetic
-
- 340) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
- iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
- (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)
- && iswspace(wc) is true, but not both.
-
-[page 445] (Contents)
-
- wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace
- is true.341)
- 7.29.2.1.3 The iswblank function
- Synopsis
-1 #include <wctype.h>
- int iswblank(wint_t wc);
- Description
-2 The iswblank function tests for any wide character that is a standard blank wide
- character or is one of a locale-specific set of wide characters for which iswspace is true
- and that is used to separate words within a line of text. The standard blank wide
- characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
- locale, iswblank returns true only for the standard blank characters.
- 7.29.2.1.4 The iswcntrl function
- Synopsis
-1 #include <wctype.h>
- int iswcntrl(wint_t wc);
- Description
-2 The iswcntrl function tests for any control wide character.
- 7.29.2.1.5 The iswdigit function
- Synopsis
-1 #include <wctype.h>
- int iswdigit(wint_t wc);
- Description
-2 The iswdigit function tests for any wide character that corresponds to a decimal-digit
- character (as defined in 5.2.1).
- 7.29.2.1.6 The iswgraph function
- Synopsis
-1 #include <wctype.h>
- int iswgraph(wint_t wc);
-
-
-
-
- 341) The functions iswlower and iswupper test true or false separately for each of these additional
- wide characters; all four combinations are possible.
-
-[page 446] (Contents)
-
- Description
-2 The iswgraph function tests for any wide character for which iswprint is true and
- iswspace is false.342)
- 7.29.2.1.7 The iswlower function
- Synopsis
-1 #include <wctype.h>
- int iswlower(wint_t wc);
- Description
-2 The iswlower function tests for any wide character that corresponds to a lowercase
- letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
- iswdigit, iswpunct, or iswspace is true.
- 7.29.2.1.8 The iswprint function
- Synopsis
-1 #include <wctype.h>
- int iswprint(wint_t wc);
- Description
-2 The iswprint function tests for any printing wide character.
- 7.29.2.1.9 The iswpunct function
- Synopsis
-1 #include <wctype.h>
- int iswpunct(wint_t wc);
- Description
-2 The iswpunct function tests for any printing wide character that is one of a locale-
- specific set of punctuation wide characters for which neither iswspace nor iswalnum
- is true.342)
- 7.29.2.1.10 The iswspace function
- Synopsis
-1 #include <wctype.h>
- int iswspace(wint_t wc);
-
-
-
- 342) Note that the behavior of the iswgraph and iswpunct functions may differ from their
- corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
- characters other than ' '.
-
-[page 447] (Contents)
-
- Description
-2 The iswspace function tests for any wide character that corresponds to a locale-specific
- set of white-space wide characters for which none of iswalnum, iswgraph, or
- iswpunct is true.
- 7.29.2.1.11 The iswupper function
- Synopsis
-1 #include <wctype.h>
- int iswupper(wint_t wc);
- Description
-2 The iswupper function tests for any wide character that corresponds to an uppercase
- letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
- iswdigit, iswpunct, or iswspace is true.
- 7.29.2.1.12 The iswxdigit function
- Synopsis
-1 #include <wctype.h>
- int iswxdigit(wint_t wc);
- Description
-2 The iswxdigit function tests for any wide character that corresponds to a
- hexadecimal-digit character (as defined in 6.4.4.1).
- 7.29.2.2 Extensible wide character classification functions
-1 The functions wctype and iswctype provide extensible wide character classification
- as well as testing equivalent to that performed by the functions described in the previous
- subclause (7.29.2.1).
- 7.29.2.2.1 The iswctype function
- Synopsis
-1 #include <wctype.h>
- int iswctype(wint_t wc, wctype_t desc);
- Description
-2 The iswctype function determines whether the wide character wc has the property
- described by desc. The current setting of the LC_CTYPE category shall be the same as
- during the call to wctype that returned the value desc.
-3 Each of the following expressions has a truth-value equivalent to the call to the wide
- character classification function (7.29.2.1) in the comment that follows the expression:
-
-
-[page 448] (Contents)
-
- iswctype(wc, wctype("alnum")) // iswalnum(wc)
- iswctype(wc, wctype("alpha")) // iswalpha(wc)
- iswctype(wc, wctype("blank")) // iswblank(wc)
- iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
- iswctype(wc, wctype("digit")) // iswdigit(wc)
- iswctype(wc, wctype("graph")) // iswgraph(wc)
- iswctype(wc, wctype("lower")) // iswlower(wc)
- iswctype(wc, wctype("print")) // iswprint(wc)
- iswctype(wc, wctype("punct")) // iswpunct(wc)
- iswctype(wc, wctype("space")) // iswspace(wc)
- iswctype(wc, wctype("upper")) // iswupper(wc)
- iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
- Returns
-4 The iswctype function returns nonzero (true) if and only if the value of the wide
- character wc has the property described by desc. If desc is zero, the iswctype
- function returns zero (false).
- Forward references: the wctype function (7.29.2.2.2).
- 7.29.2.2.2 The wctype function
- Synopsis
-1 #include <wctype.h>
- wctype_t wctype(const char *property);
- Description
-2 The wctype function constructs a value with type wctype_t that describes a class of
- wide characters identified by the string argument property.
-3 The strings listed in the description of the iswctype function shall be valid in all
- locales as property arguments to the wctype function.
- Returns
-4 If property identifies a valid class of wide characters according to the LC_CTYPE
- category of the current locale, the wctype function returns a nonzero value that is valid
- as the second argument to the iswctype function; otherwise, it returns zero.
-
-
-
-
-[page 449] (Contents)
-
- 7.29.3 Wide character case mapping utilities
-1 The header <wctype.h> declares several functions useful for mapping wide characters.
- 7.29.3.1 Wide character case mapping functions
- 7.29.3.1.1 The towlower function
- Synopsis
-1 #include <wctype.h>
- wint_t towlower(wint_t wc);
- Description
-2 The towlower function converts an uppercase letter to a corresponding lowercase letter.
- Returns
-3 If the argument is a wide character for which iswupper is true and there are one or
- more corresponding wide characters, as specified by the current locale, for which
- iswlower is true, the towlower function returns one of the corresponding wide
- characters (always the same one for any given locale); otherwise, the argument is
- returned unchanged.
- 7.29.3.1.2 The towupper function
- Synopsis
-1 #include <wctype.h>
- wint_t towupper(wint_t wc);
- Description
-2 The towupper function converts a lowercase letter to a corresponding uppercase letter.
- Returns
-3 If the argument is a wide character for which iswlower is true and there are one or
- more corresponding wide characters, as specified by the current locale, for which
- iswupper is true, the towupper function returns one of the corresponding wide
- characters (always the same one for any given locale); otherwise, the argument is
- returned unchanged.
- 7.29.3.2 Extensible wide character case mapping functions
-1 The functions wctrans and towctrans provide extensible wide character mapping as
- well as case mapping equivalent to that performed by the functions described in the
- previous subclause (7.29.3.1).
-
-
-
-
-[page 450] (Contents)
-
- 7.29.3.2.1 The towctrans function
- Synopsis
-1 #include <wctype.h>
- wint_t towctrans(wint_t wc, wctrans_t desc);
- Description
-2 The towctrans function maps the wide character wc using the mapping described by
- desc. The current setting of the LC_CTYPE category shall be the same as during the call
- to wctrans that returned the value desc.
-3 Each of the following expressions behaves the same as the call to the wide character case
- mapping function (7.29.3.1) in the comment that follows the expression:
- towctrans(wc, wctrans("tolower")) // towlower(wc)
- towctrans(wc, wctrans("toupper")) // towupper(wc)
- Returns
-4 The towctrans function returns the mapped value of wc using the mapping described
- by desc. If desc is zero, the towctrans function returns the value of wc.
- 7.29.3.2.2 The wctrans function
- Synopsis
-1 #include <wctype.h>
- wctrans_t wctrans(const char *property);
- Description
-2 The wctrans function constructs a value with type wctrans_t that describes a
- mapping between wide characters identified by the string argument property.
-3 The strings listed in the description of the towctrans function shall be valid in all
- locales as property arguments to the wctrans function.
- Returns
-4 If property identifies a valid mapping of wide characters according to the LC_CTYPE
- category of the current locale, the wctrans function returns a nonzero value that is valid
- as the second argument to the towctrans function; otherwise, it returns zero.
-
-
-
-
-[page 451] (Contents)
-
- 7.30 Future library directions
-1 The following names are grouped under individual headers for convenience. All external
- names described below are reserved no matter what headers are included by the program.
- 7.30.1 Complex arithmetic <complex.h>
-1 The function names
- cerf cexpm1 clog2
- cerfc clog10 clgamma
- cexp2 clog1p ctgamma
- and the same names suffixed with f or l may be added to the declarations in the
- <complex.h> header.
- 7.30.2 Character handling <ctype.h>
-1 Function names that begin with either is or to, and a lowercase letter may be added to
- the declarations in the <ctype.h> header.
- 7.30.3 Errors <errno.h>
-1 Macros that begin with E and a digit or E and an uppercase letter may be added to the
- declarations in the <errno.h> header.
- 7.30.4 Format conversion of integer types <inttypes.h>
-1 Macro names beginning with PRI or SCN followed by any lowercase letter or X may be
- added to the macros defined in the <inttypes.h> header.
- 7.30.5 Localization <locale.h>
-1 Macros that begin with LC_ and an uppercase letter may be added to the definitions in
- the <locale.h> header.
- 7.30.6 Signal handling <signal.h>
-1 Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
- letter may be added to the definitions in the <signal.h> header.
- 7.30.7 Boolean type and values <stdbool.h>
-1 The ability to undefine and perhaps then redefine the macros bool, true, and false is
- an obsolescent feature.
- 7.30.8 Integer types <stdint.h>
-1 Typedef names beginning with int or uint and ending with _t may be added to the
- types defined in the <stdint.h> header. Macro names beginning with INT or UINT
- and ending with _MAX, _MIN, or _C may be added to the macros defined in the
- <stdint.h> header.
-
-[page 452] (Contents)
-
- 7.30.9 Input/output <stdio.h>
-1 Lowercase letters may be added to the conversion specifiers and length modifiers in
- fprintf and fscanf. Other characters may be used in extensions.
-2 The use of ungetc on a binary stream where the file position indicator is zero prior to *
- the call is an obsolescent feature.
- 7.30.10 General utilities <stdlib.h>
-1 Function names that begin with str and a lowercase letter may be added to the
- declarations in the <stdlib.h> header.
- 7.30.11 String handling <string.h>
-1 Function names that begin with str, mem, or wcs and a lowercase letter may be added
- to the declarations in the <string.h> header.
- 7.30.12 Extended multibyte and wide character utilities <wchar.h>
-1 Function names that begin with wcs and a lowercase letter may be added to the
- declarations in the <wchar.h> header.
-2 Lowercase letters may be added to the conversion specifiers and length modifiers in
- fwprintf and fwscanf. Other characters may be used in extensions.
- 7.30.13 Wide character classification and mapping utilities
- <wctype.h>
-1 Function names that begin with is or to and a lowercase letter may be added to the
- declarations in the <wctype.h> header.
-
-
-
-
-[page 453] (Contents)
-
- Annex A
- (informative)
- Language syntax summary
-1 NOTE The notation is described in 6.1.
-
- A.1 Lexical grammar
- A.1.1 Lexical elements
- (6.4) token:
- keyword
- identifier
- constant
- string-literal
- punctuator
- (6.4) preprocessing-token:
- header-name
- identifier
- pp-number
- character-constant
- string-literal
- punctuator
- each non-white-space character that cannot be one of the above
-
-
-
-
-[page 454] (Contents)
-
-A.1.2 Keywords
-(6.4.1) keyword: one of
- alignof goto union
- auto if unsigned
- break inline void
- case int volatile
- char long while
- const register _Alignas
- continue restrict _Atomic
- default return _Bool
- do short _Complex
- double signed _Generic
- else sizeof _Imaginary
- enum static _Noreturn
- extern struct _Static_assert
- float switch _Thread_local
- for typedef
-A.1.3 Identifiers
-(6.4.2.1) identifier:
- identifier-nondigit
- identifier identifier-nondigit
- identifier digit
-(6.4.2.1) identifier-nondigit:
- nondigit
- universal-character-name
- other implementation-defined characters
-(6.4.2.1) nondigit: one of
- _ a b c d e f g h i j k l m
- n o p q r s t u v w x y z
- A B C D E F G H I J K L M
- N O P Q R S T U V W X Y Z
-(6.4.2.1) digit: one of
- 0 1 2 3 4 5 6 7 8 9
-
-
-
-
-[page 455] (Contents)
-
-A.1.4 Universal character names
-(6.4.3) universal-character-name:
- \u hex-quad
- \U hex-quad hex-quad
-(6.4.3) hex-quad:
- hexadecimal-digit hexadecimal-digit
- hexadecimal-digit hexadecimal-digit
-A.1.5 Constants
-(6.4.4) constant:
- integer-constant
- floating-constant
- enumeration-constant
- character-constant
-(6.4.4.1) integer-constant:
- decimal-constant integer-suffixopt
- octal-constant integer-suffixopt
- hexadecimal-constant integer-suffixopt
-(6.4.4.1) decimal-constant:
- nonzero-digit
- decimal-constant digit
-(6.4.4.1) octal-constant:
- 0
- octal-constant octal-digit
-(6.4.4.1) hexadecimal-constant:
- hexadecimal-prefix hexadecimal-digit
- hexadecimal-constant hexadecimal-digit
-(6.4.4.1) hexadecimal-prefix: one of
- 0x 0X
-(6.4.4.1) nonzero-digit: one of
- 1 2 3 4 5 6 7 8 9
-(6.4.4.1) octal-digit: one of
- 0 1 2 3 4 5 6 7
-
-
-
-
-[page 456] (Contents)
-
-(6.4.4.1) hexadecimal-digit: one of
- 0 1 2 3 4 5 6 7 8 9
- a b c d e f
- A B C D E F
-(6.4.4.1) integer-suffix:
- unsigned-suffix long-suffixopt
- unsigned-suffix long-long-suffix
- long-suffix unsigned-suffixopt
- long-long-suffix unsigned-suffixopt
-(6.4.4.1) unsigned-suffix: one of
- u U
-(6.4.4.1) long-suffix: one of
- l L
-(6.4.4.1) long-long-suffix: one of
- ll LL
-(6.4.4.2) floating-constant:
- decimal-floating-constant
- hexadecimal-floating-constant
-(6.4.4.2) decimal-floating-constant:
- fractional-constant exponent-partopt floating-suffixopt
- digit-sequence exponent-part floating-suffixopt
-(6.4.4.2) hexadecimal-floating-constant:
- hexadecimal-prefix hexadecimal-fractional-constant
- binary-exponent-part floating-suffixopt
- hexadecimal-prefix hexadecimal-digit-sequence
- binary-exponent-part floating-suffixopt
-(6.4.4.2) fractional-constant:
- digit-sequenceopt . digit-sequence
- digit-sequence .
-(6.4.4.2) exponent-part:
- e signopt digit-sequence
- E signopt digit-sequence
-(6.4.4.2) sign: one of
- + -
-
-
-
-[page 457] (Contents)
-
-(6.4.4.2) digit-sequence:
- digit
- digit-sequence digit
-(6.4.4.2) hexadecimal-fractional-constant:
- hexadecimal-digit-sequenceopt .
- hexadecimal-digit-sequence
- hexadecimal-digit-sequence .
-(6.4.4.2) binary-exponent-part:
- p signopt digit-sequence
- P signopt digit-sequence
-(6.4.4.2) hexadecimal-digit-sequence:
- hexadecimal-digit
- hexadecimal-digit-sequence hexadecimal-digit
-(6.4.4.2) floating-suffix: one of
- f l F L
-(6.4.4.3) enumeration-constant:
- identifier
-(6.4.4.4) character-constant:
- ' c-char-sequence '
- L' c-char-sequence '
- u' c-char-sequence '
- U' c-char-sequence '
-(6.4.4.4) c-char-sequence:
- c-char
- c-char-sequence c-char
-(6.4.4.4) c-char:
- any member of the source character set except
- the single-quote ', backslash \, or new-line character
- escape-sequence
-(6.4.4.4) escape-sequence:
- simple-escape-sequence
- octal-escape-sequence
- hexadecimal-escape-sequence
- universal-character-name
-
-
-
-
-[page 458] (Contents)
-
-(6.4.4.4) simple-escape-sequence: one of
- \' \" \? \\
- \a \b \f \n \r \t \v
-(6.4.4.4) octal-escape-sequence:
- \ octal-digit
- \ octal-digit octal-digit
- \ octal-digit octal-digit octal-digit
-(6.4.4.4) hexadecimal-escape-sequence:
- \x hexadecimal-digit
- hexadecimal-escape-sequence hexadecimal-digit
-A.1.6 String literals
-(6.4.5) string-literal:
- encoding-prefixopt " s-char-sequenceopt "
-(6.4.5) encoding-prefix:
- u8
- u
- U
- L
-(6.4.5) s-char-sequence:
- s-char
- s-char-sequence s-char
-(6.4.5) s-char:
- any member of the source character set except
- the double-quote ", backslash \, or new-line character
- escape-sequence
-A.1.7 Punctuators
-(6.4.6) punctuator: one of
- [ ] ( ) { } . ->
- ++ -- & * + - ~ !
- / % << >> < > <= >= == != ^ | && ||
- ? : ; ...
- = *= /= %= += -= <<= >>= &= ^= |=
- , # ##
- <: :> <% %> %: %:%:
-
-
-
-
-[page 459] (Contents)
-
-A.1.8 Header names
-(6.4.7) header-name:
- < h-char-sequence >
- " q-char-sequence "
-(6.4.7) h-char-sequence:
- h-char
- h-char-sequence h-char
-(6.4.7) h-char:
- any member of the source character set except
- the new-line character and >
-(6.4.7) q-char-sequence:
- q-char
- q-char-sequence q-char
-(6.4.7) q-char:
- any member of the source character set except
- the new-line character and "
-A.1.9 Preprocessing numbers
-(6.4.8) pp-number:
- digit
- . digit
- pp-number digit
- pp-number identifier-nondigit
- pp-number e sign
- pp-number E sign
- pp-number p sign
- pp-number P sign
- pp-number .
-
-
-
-
-[page 460] (Contents)
-
-A.2 Phrase structure grammar
-A.2.1 Expressions
-(6.5.1) primary-expression:
- identifier
- constant
- string-literal
- ( expression )
- generic-selection
-(6.5.1.1) generic-selection:
- _Generic ( assignment-expression , generic-assoc-list )
-(6.5.1.1) generic-assoc-list:
- generic-association
- generic-assoc-list , generic-association
-(6.5.1.1) generic-association:
- type-name : assignment-expression
- default : assignment-expression
-(6.5.2) postfix-expression:
- primary-expression
- postfix-expression [ expression ]
- postfix-expression ( argument-expression-listopt )
- postfix-expression . identifier
- postfix-expression -> identifier
- postfix-expression ++
- postfix-expression --
- ( type-name ) { initializer-list }
- ( type-name ) { initializer-list , }
-(6.5.2) argument-expression-list:
- assignment-expression
- argument-expression-list , assignment-expression
-(6.5.3) unary-expression:
- postfix-expression
- ++ unary-expression
- -- unary-expression
- unary-operator cast-expression
- sizeof unary-expression
- sizeof ( type-name )
- alignof ( type-name )
-
-[page 461] (Contents)
-
-(6.5.3) unary-operator: one of
- & * + - ~ !
-(6.5.4) cast-expression:
- unary-expression
- ( type-name ) cast-expression
-(6.5.5) multiplicative-expression:
- cast-expression
- multiplicative-expression * cast-expression
- multiplicative-expression / cast-expression
- multiplicative-expression % cast-expression
-(6.5.6) additive-expression:
- multiplicative-expression
- additive-expression + multiplicative-expression
- additive-expression - multiplicative-expression
-(6.5.7) shift-expression:
- additive-expression
- shift-expression << additive-expression
- shift-expression >> additive-expression
-(6.5.8) relational-expression:
- shift-expression
- relational-expression < shift-expression
- relational-expression > shift-expression
- relational-expression <= shift-expression
- relational-expression >= shift-expression
-(6.5.9) equality-expression:
- relational-expression
- equality-expression == relational-expression
- equality-expression != relational-expression
-(6.5.10) AND-expression:
- equality-expression
- AND-expression & equality-expression
-(6.5.11) exclusive-OR-expression:
- AND-expression
- exclusive-OR-expression ^ AND-expression
-
-
-
-
-[page 462] (Contents)
-
-(6.5.12) inclusive-OR-expression:
- exclusive-OR-expression
- inclusive-OR-expression | exclusive-OR-expression
-(6.5.13) logical-AND-expression:
- inclusive-OR-expression
- logical-AND-expression && inclusive-OR-expression
-(6.5.14) logical-OR-expression:
- logical-AND-expression
- logical-OR-expression || logical-AND-expression
-(6.5.15) conditional-expression:
- logical-OR-expression
- logical-OR-expression ? expression : conditional-expression
-(6.5.16) assignment-expression:
- conditional-expression
- unary-expression assignment-operator assignment-expression
-(6.5.16) assignment-operator: one of
- = *= /= %= += -= <<= >>= &= ^= |=
-(6.5.17) expression:
- assignment-expression
- expression , assignment-expression
-(6.6) constant-expression:
- conditional-expression
-A.2.2 Declarations
-(6.7) declaration:
- declaration-specifiers init-declarator-listopt ;
- static_assert-declaration
-(6.7) declaration-specifiers:
- storage-class-specifier declaration-specifiersopt
- type-specifier declaration-specifiersopt
- type-qualifier declaration-specifiersopt
- function-specifier declaration-specifiersopt
- alignment-specifier declaration-specifiersopt
-(6.7) init-declarator-list:
- init-declarator
- init-declarator-list , init-declarator
-
-
-[page 463] (Contents)
-
-(6.7) init-declarator:
- declarator
- declarator = initializer
-(6.7.1) storage-class-specifier:
- typedef
- extern
- static
- _Thread_local
- auto
- register
-(6.7.2) type-specifier:
- void
- char
- short
- int
- long
- float
- double
- signed
- unsigned
- _Bool
- _Complex
- atomic-type-specifier
- struct-or-union-specifier
- enum-specifier
- typedef-name
-(6.7.2.1) struct-or-union-specifier:
- struct-or-union identifieropt { struct-declaration-list }
- struct-or-union identifier
-(6.7.2.1) struct-or-union:
- struct
- union
-(6.7.2.1) struct-declaration-list:
- struct-declaration
- struct-declaration-list struct-declaration
-(6.7.2.1) struct-declaration:
- specifier-qualifier-list struct-declarator-listopt ;
- static_assert-declaration
-
-[page 464] (Contents)
-
-(6.7.2.1) specifier-qualifier-list:
- type-specifier specifier-qualifier-listopt
- type-qualifier specifier-qualifier-listopt
-(6.7.2.1) struct-declarator-list:
- struct-declarator
- struct-declarator-list , struct-declarator
-(6.7.2.1) struct-declarator:
- declarator
- declaratoropt : constant-expression
-(6.7.2.2) enum-specifier:
- enum identifieropt { enumerator-list }
- enum identifieropt { enumerator-list , }
- enum identifier
-(6.7.2.2) enumerator-list:
- enumerator
- enumerator-list , enumerator
-(6.7.2.2) enumerator:
- enumeration-constant
- enumeration-constant = constant-expression
-(6.7.2.4) atomic-type-specifier:
- _Atomic ( type-name )
-(6.7.3) type-qualifier:
- const
- restrict
- volatile
- _Atomic
-(6.7.4) function-specifier:
- inline
- _Noreturn
-(6.7.5) alignment-specifier:
- _Alignas ( type-name )
- _Alignas ( constant-expression )
-(6.7.6) declarator:
- pointeropt direct-declarator
-
-
-
-[page 465] (Contents)
-
-(6.7.6) direct-declarator:
- identifier
- ( declarator )
- direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
- direct-declarator [ static type-qualifier-listopt assignment-expression ]
- direct-declarator [ type-qualifier-list static assignment-expression ]
- direct-declarator [ type-qualifier-listopt * ]
- direct-declarator ( parameter-type-list )
- direct-declarator ( identifier-listopt )
-(6.7.6) pointer:
- * type-qualifier-listopt
- * type-qualifier-listopt pointer
-(6.7.6) type-qualifier-list:
- type-qualifier
- type-qualifier-list type-qualifier
-(6.7.6) parameter-type-list:
- parameter-list
- parameter-list , ...
-(6.7.6) parameter-list:
- parameter-declaration
- parameter-list , parameter-declaration
-(6.7.6) parameter-declaration:
- declaration-specifiers declarator
- declaration-specifiers abstract-declaratoropt
-(6.7.6) identifier-list:
- identifier
- identifier-list , identifier
-(6.7.7) type-name:
- specifier-qualifier-list abstract-declaratoropt
-(6.7.7) abstract-declarator:
- pointer
- pointeropt direct-abstract-declarator
-
-
-
-
-[page 466] (Contents)
-
-(6.7.7) direct-abstract-declarator:
- ( abstract-declarator )
- direct-abstract-declaratoropt [ type-qualifier-listopt
- assignment-expressionopt ]
- direct-abstract-declaratoropt [ static type-qualifier-listopt
- assignment-expression ]
- direct-abstract-declaratoropt [ type-qualifier-list static
- assignment-expression ]
- direct-abstract-declaratoropt [ * ]
- direct-abstract-declaratoropt ( parameter-type-listopt )
-(6.7.8) typedef-name:
- identifier
-(6.7.9) initializer:
- assignment-expression
- { initializer-list }
- { initializer-list , }
-(6.7.9) initializer-list:
- designationopt initializer
- initializer-list , designationopt initializer
-(6.7.9) designation:
- designator-list =
-(6.7.9) designator-list:
- designator
- designator-list designator
-(6.7.9) designator:
- [ constant-expression ]
- . identifier
-(6.7.10) static_assert-declaration:
- _Static_assert ( constant-expression , string-literal ) ;
-
-
-
-
-[page 467] (Contents)
-
-A.2.3 Statements
-(6.8) statement:
- labeled-statement
- compound-statement
- expression-statement
- selection-statement
- iteration-statement
- jump-statement
-(6.8.1) labeled-statement:
- identifier : statement
- case constant-expression : statement
- default : statement
-(6.8.2) compound-statement:
- { block-item-listopt }
-(6.8.2) block-item-list:
- block-item
- block-item-list block-item
-(6.8.2) block-item:
- declaration
- statement
-(6.8.3) expression-statement:
- expressionopt ;
-(6.8.4) selection-statement:
- if ( expression ) statement
- if ( expression ) statement else statement
- switch ( expression ) statement
-(6.8.5) iteration-statement:
- while ( expression ) statement
- do statement while ( expression ) ;
- for ( expressionopt ; expressionopt ; expressionopt ) statement
- for ( declaration expressionopt ; expressionopt ) statement
-(6.8.6) jump-statement:
- goto identifier ;
- continue ;
- break ;
- return expressionopt ;
-
-[page 468] (Contents)
-
-A.2.4 External definitions
-(6.9) translation-unit:
- external-declaration
- translation-unit external-declaration
-(6.9) external-declaration:
- function-definition
- declaration
-(6.9.1) function-definition:
- declaration-specifiers declarator declaration-listopt compound-statement
-(6.9.1) declaration-list:
- declaration
- declaration-list declaration
-A.3 Preprocessing directives
-(6.10) preprocessing-file:
- groupopt
-(6.10) group:
- group-part
- group group-part
-(6.10) group-part:
- if-section
- control-line
- text-line
- # non-directive
-(6.10) if-section:
- if-group elif-groupsopt else-groupopt endif-line
-(6.10) if-group:
- # if constant-expression new-line groupopt
- # ifdef identifier new-line groupopt
- # ifndef identifier new-line groupopt
-(6.10) elif-groups:
- elif-group
- elif-groups elif-group
-(6.10) elif-group:
- # elif constant-expression new-line groupopt
-
-
-[page 469] (Contents)
-
-(6.10) else-group:
- # else new-line groupopt
-(6.10) endif-line:
- # endif new-line
-(6.10) control-line:
- # include pp-tokens new-line
- # define identifier replacement-list new-line
- # define identifier lparen identifier-listopt )
- replacement-list new-line
- # define identifier lparen ... ) replacement-list new-line
- # define identifier lparen identifier-list , ... )
- replacement-list new-line
- # undef identifier new-line
- # line pp-tokens new-line
- # error pp-tokensopt new-line
- # pragma pp-tokensopt new-line
- # new-line
-(6.10) text-line:
- pp-tokensopt new-line
-(6.10) non-directive:
- pp-tokens new-line
-(6.10) lparen:
- a ( character not immediately preceded by white-space
-(6.10) replacement-list:
- pp-tokensopt
-(6.10) pp-tokens:
- preprocessing-token
- pp-tokens preprocessing-token
-(6.10) new-line:
- the new-line character
-
-
-
-
-[page 470] (Contents)
-
- Annex B
- (informative)
- Library summary
-B.1 Diagnostics <assert.h>
- NDEBUG
- static_assert
- void assert(scalar expression);
-B.2 Complex <complex.h>
- __STDC_NO_COMPLEX__ imaginary
- complex _Imaginary_I
- _Complex_I I
+
++ EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably + modified types. A jump within the scope, however, is permitted. +
+ goto lab3; // invalid: going INTO scope of VLA.
+ {
+ double a[n];
+ a[j] = 4.4;
+ lab3:
+ a[j] = 3.3;
+ goto lab4; // valid: going WITHIN scope of VLA.
+ a[j] = 5.5;
+ lab4:
+ a[j] = 6.6;
+ }
+ goto lab4; // invalid: going INTO scope of VLA.
+
+
+
++ A continue statement shall appear only in or as a loop body. +
+ A continue statement causes a jump to the loop-continuation portion of the smallest + enclosing iteration statement; that is, to the end of the loop body. More precisely, in each + of the statements + while (/* ... */) { do { for (/* ... */) { +
+ /* ... */ /* ... */ /* ... */ + continue; continue; continue; + /* ... */ /* ... */ /* ... */ ++ contin: ; contin: ; contin: ; + } } while (/* ... */); } + unless the continue statement shown is in an enclosed iteration statement (in which + case it is interpreted within that statement), it is equivalent to goto contin;.159) + +
159) Following the contin: label is a null statement. + + +
+ A break statement shall appear only in or as a switch body or loop body. +
+ A break statement terminates execution of the smallest enclosing switch or iteration + statement. + + + + + +
+ A return statement with an expression shall not appear in a function whose return type + is void. A return statement without an expression shall only appear in a function + whose return type is void. +
+ A return statement terminates execution of the current function and returns control to + its caller. A function may have any number of return statements. +
+ If a return statement with an expression is executed, the value of the expression is + returned to the caller as the value of the function call expression. If the expression has a + type different from the return type of the function in which it appears, the value is + converted as if by assignment to an object having the return type of the function.160) +
+ EXAMPLE In: +
+ struct s { double i; } f(void);
+ union {
+ struct {
+ int f1;
+ struct s f2;
+ } u1;
+ struct {
+ struct s f3;
+ int f4;
+ } u2;
+ } g;
+ struct s f(void)
+ {
+ return g.u1.f2;
+ }
+ /* ... */
+ g.u2.f3 = f();
+
+ there is no undefined behavior, although there would be if the assignment were done directly (without using
+ a function call to fetch the value).
+
+
+
+
+
+
+160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not + apply to the case of function return. The representation of floating-point values may have wider range + or precision than implied by the type; a cast may be used to remove this extra range and precision. + + +
+
+ translation-unit: + external-declaration + translation-unit external-declaration + external-declaration: + function-definition + declaration ++
+ The storage-class specifiers auto and register shall not appear in the declaration + specifiers in an external declaration. +
+ There shall be no more than one external definition for each identifier declared with + internal linkage in a translation unit. Moreover, if an identifier declared with internal + linkage is used in an expression (other than as a part of the operand of a sizeof + operator whose result is an integer constant), there shall be exactly one external definition + for the identifier in the translation unit. +
+ As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit, + which consists of a sequence of external declarations. These are described as ''external'' + because they appear outside any function (and hence have file scope). As discussed in + 6.7, a declaration that also causes storage to be reserved for an object or a function named + by the identifier is a definition. +
+ An external definition is an external declaration that is also a definition of a function + (other than an inline definition) or an object. If an identifier declared with external + linkage is used in an expression (other than as part of the operand of a sizeof operator + whose result is an integer constant), somewhere in the entire program there shall be + exactly one external definition for the identifier; otherwise, there shall be no more than + one.161) + + + + + + +
161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no + external definition for it. + + +
+
+ function-definition: + declaration-specifiers declarator declaration-listopt compound-statement + declaration-list: + declaration + declaration-list declaration ++
+ The identifier declared in a function definition (which is the name of the function) shall + have a function type, as specified by the declarator portion of the function definition.162) +
+ The return type of a function shall be void or a complete object type other than array + type. +
+ The storage-class specifier, if any, in the declaration specifiers shall be either extern or + static. +
+ If the declarator includes a parameter type list, the declaration of each parameter shall + include an identifier, except for the special case of a parameter list consisting of a single + parameter of type void, in which case there shall not be an identifier. No declaration list + shall follow. +
+ If the declarator includes an identifier list, each declaration in the declaration list shall + have at least one declarator, those declarators shall declare only identifiers from the + identifier list, and every identifier in the identifier list shall be declared. An identifier + declared as a typedef name shall not be redeclared as a parameter. The declarations in the + declaration list shall contain no storage-class specifier other than register and no + initializations. + + + + +
+ The declarator in a function definition specifies the name of the function being defined + and the identifiers of its parameters. If the declarator includes a parameter type list, the + list also specifies the types of all the parameters; such a declarator also serves as a + function prototype for later calls to the same function in the same translation unit. If the + declarator includes an identifier list,163) the types of the parameters shall be declared in a + following declaration list. In either case, the type of each parameter is adjusted as + described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object + type. +
+ If a function that accepts a variable number of arguments is defined without a parameter + type list that ends with the ellipsis notation, the behavior is undefined. +
+ Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout + of the storage for parameters is unspecified. +
+ On entry to the function, the size expressions of each variably modified parameter are + evaluated and the value of each argument expression is converted to the type of the + corresponding parameter as if by assignment. (Array expressions and function + designators as arguments were converted to pointers before the call.) +
+ After all parameters have been assigned, the compound statement that constitutes the + body of the function definition is executed. +
+ If the } that terminates a function is reached, and the value of the function call is used by + the caller, the behavior is undefined. +
+ EXAMPLE 1 In the following: +
+ extern int max(int a, int b)
+ {
+ return a > b ? a : b;
+ }
+
+ extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
+ function declarator; and
+
+ { return a > b ? a : b; }
+
+ is the function body. The following similar definition uses the identifier-list form for the parameter
+ declarations:
+
+
+
+
+
+
+ extern int max(a, b)
+ int a, b;
+ {
+ return a > b ? a : b;
+ }
+
+ Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
+ that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
+ to the function, whereas the second form does not.
+
++ EXAMPLE 2 To pass one function to another, one might say +
+ int f(void); + /* ... */ + g(f); ++ Then the definition of g might read +
+ void g(int (*funcp)(void))
+ {
+ /* ... */
+ (*funcp)(); /* or funcp(); ... */
+ }
+
+ or, equivalently,
+
+ void g(int func(void))
+ {
+ /* ... */
+ func(); /* or (*func)(); ... */
+ }
+
+
+
+162) The intent is that the type category in a function definition cannot be inherited from a typedef:
+
+
+ typedef int F(void); // type F is ''function with no parameters
+ // returning int''
+ F f, g; // f and g both have type compatible with F
+ F f { /* ... */ } // WRONG: syntax/constraint error
+ F g() { /* ... */ } // WRONG: declares that g returns a function
+ int f(void) { /* ... */ } // RIGHT: f has type compatible with F
+ int g() { /* ... */ } // RIGHT: g has type compatible with F
+ F *e(void) { /* ... */ } // e returns a pointer to a function
+ F *((e))(void) { /* ... */ } // same: parentheses irrelevant
+ int (*fp)(void); // fp points to a function that has type F
+ F *Fp; // Fp points to a function that has type F
+
+
+
163) See ''future language directions'' (6.11.7). + +
164) A parameter identifier cannot be redeclared in the function body except in an enclosed block. + + +
+ If the declaration of an identifier for an object has file scope and an initializer, the + declaration is an external definition for the identifier. +
+ A declaration of an identifier for an object that has file scope without an initializer, and + without a storage-class specifier or with the storage-class specifier static, constitutes a + tentative definition. If a translation unit contains one or more tentative definitions for an + identifier, and the translation unit contains no external definition for that identifier, then + the behavior is exactly as if the translation unit contains a file scope declaration of that + identifier, with the composite type as of the end of the translation unit, with an initializer + equal to 0. +
+ If the declaration of an identifier for an object is a tentative definition and has internal + linkage, the declared type shall not be an incomplete type. + +
+ EXAMPLE 1 +
+ int i1 = 1; // definition, external linkage + static int i2 = 2; // definition, internal linkage + extern int i3 = 3; // definition, external linkage + int i4; // tentative definition, external linkage + static int i5; // tentative definition, internal linkage + int i1; // valid tentative definition, refers to previous + int i2; // 6.2.2 renders undefined, linkage disagreement + int i3; // valid tentative definition, refers to previous + int i4; // valid tentative definition, refers to previous + int i5; // 6.2.2 renders undefined, linkage disagreement + extern int i1; // refers to previous, whose linkage is external + extern int i2; // refers to previous, whose linkage is internal + extern int i3; // refers to previous, whose linkage is external + extern int i4; // refers to previous, whose linkage is external + extern int i5; // refers to previous, whose linkage is internal ++ +
+ EXAMPLE 2 If at the end of the translation unit containing +
+ int i[]; ++ the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to + zero on program startup. + + +
+ +
+ preprocessing-file: + groupopt + group: + group-part + group group-part + group-part: + if-section + control-line + text-line + # non-directive + if-section: + if-group elif-groupsopt else-groupopt endif-line + if-group: + # if constant-expression new-line groupopt + # ifdef identifier new-line groupopt + # ifndef identifier new-line groupopt + elif-groups: + elif-group + elif-groups elif-group + elif-group: + # elif constant-expression new-line groupopt + else-group: + # else new-line groupopt + endif-line: + # endif new-line + control-line: + # include pp-tokens new-line + # define identifier replacement-list new-line + # define identifier lparen identifier-listopt ) + replacement-list new-line + # define identifier lparen ... ) replacement-list new-line + # define identifier lparen identifier-list , ... ) + replacement-list new-line + # undef identifier new-line + # line pp-tokens new-line + # error pp-tokensopt new-line + # pragma pp-tokensopt new-line + # new-line + text-line: + pp-tokensopt new-line + non-directive: + pp-tokens new-line + lparen: + a ( character not immediately preceded by white-space + replacement-list: + pp-tokensopt + pp-tokens: + preprocessing-token + pp-tokens preprocessing-token + new-line: + the new-line character ++
+ A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the + following constraints: The first token in the sequence is a # preprocessing token that (at + the start of translation phase 4) is either the first character in the source file (optionally + after white space containing no new-line characters) or that follows white space + containing at least one new-line character. The last token in the sequence is the first new- + line character that follows the first token in the sequence.165) A new-line character ends + the preprocessing directive even if it occurs within what would otherwise be an + + + invocation of a function-like macro. +
+ A text line shall not begin with a # preprocessing token. A non-directive shall not begin + with any of the directive names appearing in the syntax. +
+ When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any + sequence of preprocessing tokens to occur between the directive name and the following + new-line character. +
+ The only white-space characters that shall appear between preprocessing tokens within a + preprocessing directive (from just after the introducing # preprocessing token through + just before the terminating new-line character) are space and horizontal-tab (including + spaces that have replaced comments or possibly other white-space characters in + translation phase 3). +
+ The implementation can process and skip sections of source files conditionally, include + other source files, and replace macros. These capabilities are called preprocessing, + because conceptually they occur before translation of the resulting translation unit. +
+ The preprocessing tokens within a preprocessing directive are not subject to macro + expansion unless otherwise stated. +
+ EXAMPLE In: +
+ #define EMPTY + EMPTY # include <file.h> ++ the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not + begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been + replaced. + + +
165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic + significance, as all white space is equivalent except in certain situations during preprocessing (see the + # character string literal creation operator in 6.10.3.2, for example). + + +
+ The expression that controls conditional inclusion shall be an integer constant expression + except that: identifiers (including those lexically identical to keywords) are interpreted as * + described below;166) and it may contain unary operator expressions of the form +
+ defined identifier ++ or +
+ defined ( identifier ) ++ which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is + + + + predefined or if it has been the subject of a #define preprocessing directive without an + intervening #undef directive with the same subject identifier), 0 if it is not. +
+ Each preprocessing token that remains (in the list of preprocessing tokens that will + become the controlling expression) after all macro replacements have occurred shall be in + the lexical form of a token (6.4). +
+ Preprocessing directives of the forms +
+ # if constant-expression new-line groupopt + # elif constant-expression new-line groupopt ++ check whether the controlling constant expression evaluates to nonzero. +
+ Prior to evaluation, macro invocations in the list of preprocessing tokens that will become + the controlling constant expression are replaced (except for those macro names modified + by the defined unary operator), just as in normal text. If the token defined is + generated as a result of this replacement process or use of the defined unary operator + does not match one of the two specified forms prior to macro replacement, the behavior is + undefined. After all replacements due to macro expansion and the defined unary + operator have been performed, all remaining identifiers (including those lexically + identical to keywords) are replaced with the pp-number 0, and then each preprocessing + token is converted into a token. The resulting tokens compose the controlling constant + expression which is evaluated according to the rules of 6.6. For the purposes of this + token conversion and evaluation, all signed integer types and all unsigned integer types + act as if they have the same representation as, respectively, the types intmax_t and + uintmax_t defined in the header <stdint.h>.167) This includes interpreting + character constants, which may involve converting escape sequences into execution + character set members. Whether the numeric value for these character constants matches + the value obtained when an identical character constant occurs in an expression (other + than within a #if or #elif directive) is implementation-defined.168) Also, whether a + single-character character constant may have a negative value is implementation-defined. + + + + + +
+ Preprocessing directives of the forms +
+ # ifdef identifier new-line groupopt + # ifndef identifier new-line groupopt ++ check whether the identifier is or is not currently defined as a macro name. Their + conditions are equivalent to #if defined identifier and #if !defined identifier + respectively. +
+ Each directive's condition is checked in order. If it evaluates to false (zero), the group + that it controls is skipped: directives are processed only through the name that determines + the directive in order to keep track of the level of nested conditionals; the rest of the + directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the + group. Only the first group whose control condition evaluates to true (nonzero) is + processed. If none of the conditions evaluates to true, and there is a #else directive, the + group controlled by the #else is processed; lacking a #else directive, all the groups + until the #endif are skipped.169) +
Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest + integer types (7.20.1.5). + +
166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers + either are or are not macro names -- there simply are no keywords, enumeration constants, etc. + +
167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant + 0x8000 is signed and positive within a #if expression even though it would be unsigned in + translation phase 7. + +
168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to + evaluate to the same value in these two contexts. + #if 'z' - 'a' == 25 + if ('z' - 'a' == 25) + +
169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive + before the terminating new-line character. However, comments may appear anywhere in a source file, + including within a preprocessing directive. + + +
+ A #include directive shall identify a header or source file that can be processed by the + implementation. +
+ A preprocessing directive of the form +
+ # include <h-char-sequence> new-line ++ searches a sequence of implementation-defined places for a header identified uniquely by + the specified sequence between the < and > delimiters, and causes the replacement of that + directive by the entire contents of the header. How the places are specified or the header + identified is implementation-defined. +
+ A preprocessing directive of the form +
+ # include "q-char-sequence" new-line ++ causes the replacement of that directive by the entire contents of the source file identified + by the specified sequence between the " delimiters. The named source file is searched + + + + for in an implementation-defined manner. If this search is not supported, or if the search + fails, the directive is reprocessed as if it read +
+ # include <h-char-sequence> new-line ++ with the identical contained sequence (including > characters, if any) from the original + directive. +
+ A preprocessing directive of the form +
+ # include pp-tokens new-line ++ (that does not match one of the two previous forms) is permitted. The preprocessing + tokens after include in the directive are processed just as in normal text. (Each + identifier currently defined as a macro name is replaced by its replacement list of + preprocessing tokens.) The directive resulting after all replacements shall match one of + the two previous forms.170) The method by which a sequence of preprocessing tokens + between a < and a > preprocessing token pair or a pair of " characters is combined into a + single header name preprocessing token is implementation-defined. +
+ The implementation shall provide unique mappings for sequences consisting of one or + more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The + first character shall not be a digit. The implementation may ignore distinctions of + alphabetical case and restrict the mapping to eight significant characters before the + period. +
+ A #include preprocessing directive may appear in a source file that has been read + because of a #include directive in another file, up to an implementation-defined + nesting limit (see 5.2.4.1). +
+ EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following: +
+ #include <stdio.h> + #include "myprog.h" ++ + + + + +
+ EXAMPLE 2 This illustrates macro-replaced #include directives: +
+ #if VERSION == 1 + #define INCFILE "vers1.h" + #elif VERSION == 2 + #define INCFILE "vers2.h" // and so on + #else + #define INCFILE "versN.h" + #endif + #include INCFILE ++ +
Forward references: macro replacement (6.10.3). + +
170) Note that adjacent string literals are not concatenated into a single string literal (see the translation + phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive. + + +
+ Two replacement lists are identical if and only if the preprocessing tokens in both have + the same number, ordering, spelling, and white-space separation, where all white-space + separations are considered identical. +
+ An identifier currently defined as an object-like macro shall not be redefined by another + #define preprocessing directive unless the second definition is an object-like macro + definition and the two replacement lists are identical. Likewise, an identifier currently + defined as a function-like macro shall not be redefined by another #define + preprocessing directive unless the second definition is a function-like macro definition + that has the same number and spelling of parameters, and the two replacement lists are + identical. +
+ There shall be white-space between the identifier and the replacement list in the definition + of an object-like macro. +
+ If the identifier-list in the macro definition does not end with an ellipsis, the number of + arguments (including those arguments consisting of no preprocessing tokens) in an + invocation of a function-like macro shall equal the number of parameters in the macro + definition. Otherwise, there shall be more arguments in the invocation than there are + parameters in the macro definition (excluding the ...). There shall exist a ) + preprocessing token that terminates the invocation. +
+ The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like + macro that uses the ellipsis notation in the parameters. +
+ A parameter identifier in a function-like macro shall be uniquely declared within its + scope. +
+ The identifier immediately following the define is called the macro name. There is one + name space for macro names. Any white-space characters preceding or following the + replacement list of preprocessing tokens are not considered part of the replacement list + + for either form of macro. +
+ If a # preprocessing token, followed by an identifier, occurs lexically at the point at which + a preprocessing directive could begin, the identifier is not subject to macro replacement. +
+ A preprocessing directive of the form +
+ # define identifier replacement-list new-line ++ defines an object-like macro that causes each subsequent instance of the macro name171) + to be replaced by the replacement list of preprocessing tokens that constitute the + remainder of the directive. The replacement list is then rescanned for more macro names + as specified below. +
+ A preprocessing directive of the form +
+ # define identifier lparen identifier-listopt ) replacement-list new-line + # define identifier lparen ... ) replacement-list new-line + # define identifier lparen identifier-list , ... ) replacement-list new-line ++ defines a function-like macro with parameters, whose use is similar syntactically to a + function call. The parameters are specified by the optional list of identifiers, whose scope + extends from their declaration in the identifier list until the new-line character that + terminates the #define preprocessing directive. Each subsequent instance of the + function-like macro name followed by a ( as the next preprocessing token introduces the + sequence of preprocessing tokens that is replaced by the replacement list in the definition + (an invocation of the macro). The replaced sequence of preprocessing tokens is + terminated by the matching ) preprocessing token, skipping intervening matched pairs of + left and right parenthesis preprocessing tokens. Within the sequence of preprocessing + tokens making up an invocation of a function-like macro, new-line is considered a normal + white-space character. +
+ The sequence of preprocessing tokens bounded by the outside-most matching parentheses + forms the list of arguments for the function-like macro. The individual arguments within + the list are separated by comma preprocessing tokens, but comma preprocessing tokens + between matching inner parentheses do not separate arguments. If there are sequences of + preprocessing tokens within the list of arguments that would otherwise act as + preprocessing directives,172) the behavior is undefined. +
+ If there is a ... in the identifier-list in the macro definition, then the trailing arguments, + including any separating comma preprocessing tokens, are merged to form a single item: + + + + the variable arguments. The number of arguments so combined is such that, following + merger, the number of arguments is one more than the number of parameters in the macro + definition (excluding the ...). + +
171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens, + not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they + are never scanned for macro names or parameters. + +
172) Despite the name, a non-directive is a preprocessing directive. + + +
+ After the arguments for the invocation of a function-like macro have been identified, + argument substitution takes place. A parameter in the replacement list, unless preceded + by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is + replaced by the corresponding argument after all macros contained therein have been + expanded. Before being substituted, each argument's preprocessing tokens are + completely macro replaced as if they formed the rest of the preprocessing file; no other + preprocessing tokens are available. +
+ An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it + were a parameter, and the variable arguments shall form the preprocessing tokens used to + replace it. + +
+ Each # preprocessing token in the replacement list for a function-like macro shall be + followed by a parameter as the next preprocessing token in the replacement list. +
+ If, in the replacement list, a parameter is immediately preceded by a # preprocessing + token, both are replaced by a single character string literal preprocessing token that + contains the spelling of the preprocessing token sequence for the corresponding + argument. Each occurrence of white space between the argument's preprocessing tokens + becomes a single space character in the character string literal. White space before the + first preprocessing token and after the last preprocessing token composing the argument + is deleted. Otherwise, the original spelling of each preprocessing token in the argument + is retained in the character string literal, except for special handling for producing the + spelling of string literals and character constants: a \ character is inserted before each " + and \ character of a character constant or string literal (including the delimiting " + characters), except that it is implementation-defined whether a \ character is inserted + before the \ character beginning a universal character name. If the replacement that + results is not a valid character string literal, the behavior is undefined. The character + string literal corresponding to an empty argument is "". The order of evaluation of # and + ## operators is unspecified. + + +
+ A ## preprocessing token shall not occur at the beginning or at the end of a replacement + list for either form of macro definition. +
+ If, in the replacement list of a function-like macro, a parameter is immediately preceded + or followed by a ## preprocessing token, the parameter is replaced by the corresponding + argument's preprocessing token sequence; however, if an argument consists of no + preprocessing tokens, the parameter is replaced by a placemarker preprocessing token + instead.173) +
+ For both object-like and function-like macro invocations, before the replacement list is + reexamined for more macro names to replace, each instance of a ## preprocessing token + in the replacement list (not from an argument) is deleted and the preceding preprocessing + token is concatenated with the following preprocessing token. Placemarker + preprocessing tokens are handled specially: concatenation of two placemarkers results in + a single placemarker preprocessing token, and concatenation of a placemarker with a + non-placemarker preprocessing token results in the non-placemarker preprocessing token. + If the result is not a valid preprocessing token, the behavior is undefined. The resulting + token is available for further macro replacement. The order of evaluation of ## operators + is unspecified. +
+ EXAMPLE In the following fragment: +
+ #define hash_hash # ## # + #define mkstr(a) # a + #define in_between(a) mkstr(a) + #define join(c, d) in_between(c hash_hash d) + char p[] = join(x, y); // equivalent to + // char p[] = "x ## y"; ++ The expansion produces, at various stages: +
+ join(x, y) + in_between(x hash_hash y) + in_between(x ## y) + mkstr(x ## y) + "x ## y" ++ In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but + this new token is not the ## operator. + + + + +
173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that + exist only within translation phase 4. + + +
+ After all parameters in the replacement list have been substituted and # and ## + processing has taken place, all placemarker preprocessing tokens are removed. The + resulting preprocessing token sequence is then rescanned, along with all subsequent + preprocessing tokens of the source file, for more macro names to replace. +
+ If the name of the macro being replaced is found during this scan of the replacement list + (not including the rest of the source file's preprocessing tokens), it is not replaced. + Furthermore, if any nested replacements encounter the name of the macro being replaced, + it is not replaced. These nonreplaced macro name preprocessing tokens are no longer + available for further replacement even if they are later (re)examined in contexts in which + that macro name preprocessing token would otherwise have been replaced. +
+ The resulting completely macro-replaced preprocessing token sequence is not processed + as a preprocessing directive even if it resembles one, but all pragma unary operator + expressions within it are then processed as specified in 6.10.9 below. + +
+ A macro definition lasts (independent of block structure) until a corresponding #undef + directive is encountered or (if none is encountered) until the end of the preprocessing + translation unit. Macro definitions have no significance after translation phase 4. +
+ A preprocessing directive of the form +
+ # undef identifier new-line ++ causes the specified identifier no longer to be defined as a macro name. It is ignored if + the specified identifier is not currently defined as a macro name. +
+ EXAMPLE 1 The simplest use of this facility is to define a ''manifest constant'', as in +
+ #define TABSIZE 100 + int table[TABSIZE]; ++ +
+ EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments. + It has the advantages of working for any compatible types of the arguments and of generating in-line code + without the overhead of function calling. It has the disadvantages of evaluating one or the other of its + arguments a second time (including side effects) and generating more code than a function if invoked + several times. It also cannot have its address taken, as it has none. +
+ #define max(a, b) ((a) > (b) ? (a) : (b)) ++ The parentheses ensure that the arguments and the resulting expression are bound properly. + +
+ EXAMPLE 3 To illustrate the rules for redefinition and reexamination, the sequence +
+ #define x 3
+ #define f(a) f(x * (a))
+ #undef x
+ #define x 2
+ #define g f
+ #define z z[0]
+ #define h g(~
+ #define m(a) a(w)
+ #define w 0,1
+ #define t(a) a
+ #define p() int
+ #define q(x) x
+ #define r(x,y) x ## y
+ #define str(x) # x
+ f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
+ g(x+(3,4)-w) | h 5) & m
+ (f)^m(m);
+ p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
+ char c[2][6] = { str(hello), str() };
+
+ results in
+
+ f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
+ f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
+ int i[] = { 1, 23, 4, 5, };
+ char c[2][6] = { "hello", "" };
+
+
++ EXAMPLE 4 To illustrate the rules for creating character string literals and concatenating tokens, the + sequence +
+ #define str(s) # s
+ #define xstr(s) str(s)
+ #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
+ x ## s, x ## t)
+ #define INCFILE(n) vers ## n
+ #define glue(a, b) a ## b
+ #define xglue(a, b) glue(a, b)
+ #define HIGHLOW "hello"
+ #define LOW LOW ", world"
+ debug(1, 2);
+ fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
+ == 0) str(: @\n), s);
+ #include xstr(INCFILE(2).h)
+ glue(HIGH, LOW);
+ xglue(HIGH, LOW)
+
+ results in
+
+
+ printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
+ fputs(
+ "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
+ s);
+ #include "vers2.h" (after macro replacement, before file access)
+ "hello";
+ "hello" ", world"
+
+ or, after concatenation of the character string literals,
+
+ printf("x1= %d, x2= %s", x1, x2);
+ fputs(
+ "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
+ s);
+ #include "vers2.h" (after macro replacement, before file access)
+ "hello";
+ "hello, world"
+
+ Space around the # and ## tokens in the macro definition is optional.
+
++ EXAMPLE 5 To illustrate the rules for placemarker preprocessing tokens, the sequence +
+ #define t(x,y,z) x ## y ## z
+ int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
+ t(10,,), t(,11,), t(,,12), t(,,) };
+
+ results in
+
+ int j[] = { 123, 45, 67, 89,
+ 10, 11, 12, };
+
+
++ EXAMPLE 6 To demonstrate the redefinition rules, the following sequence is valid. +
+ #define OBJ_LIKE (1-1) + #define OBJ_LIKE /* white space */ (1-1) /* other */ + #define FUNC_LIKE(a) ( a ) + #define FUNC_LIKE( a )( /* note the white space */ \ + a /* other stuff on this line + */ ) ++ But the following redefinitions are invalid: +
+ #define OBJ_LIKE (0) // different token sequence + #define OBJ_LIKE (1 - 1) // different white space + #define FUNC_LIKE(b) ( a ) // different parameter usage + #define FUNC_LIKE(b) ( b ) // different parameter spelling ++ +
+ EXAMPLE 7 Finally, to show the variable argument list macro facilities: + +
+ #define debug(...) fprintf(stderr, __VA_ARGS__)
+ #define showlist(...) puts(#__VA_ARGS__)
+ #define report(test, ...) ((test)?puts(#test):\
+ printf(__VA_ARGS__))
+ debug("Flag");
+ debug("X = %d\n", x);
+ showlist(The first, second, and third items.);
+ report(x>y, "x is %d but y is %d", x, y);
+
+ results in
+
+ fprintf(stderr, "Flag" );
+ fprintf(stderr, "X = %d\n", x );
+ puts( "The first, second, and third items." );
+ ((x>y)?puts("x>y"):
+ printf("x is %d but y is %d", x, y));
+
+
+
++ The string literal of a #line directive, if present, shall be a character string literal. +
+ The line number of the current source line is one greater than the number of new-line + characters read or introduced in translation phase 1 (5.1.1.2) while processing the source + file to the current token. +
+ A preprocessing directive of the form +
+ # line digit-sequence new-line ++ causes the implementation to behave as if the following sequence of source lines begins + with a source line that has a line number as specified by the digit sequence (interpreted as + a decimal integer). The digit sequence shall not specify zero, nor a number greater than + 2147483647. +
+ A preprocessing directive of the form +
+ # line digit-sequence "s-char-sequenceopt" new-line ++ sets the presumed line number similarly and changes the presumed name of the source + file to be the contents of the character string literal. +
+ A preprocessing directive of the form +
+ # line pp-tokens new-line ++ (that does not match one of the two previous forms) is permitted. The preprocessing + tokens after line on the directive are processed just as in normal text (each identifier + currently defined as a macro name is replaced by its replacement list of preprocessing + tokens). The directive resulting after all replacements shall match one of the two + previous forms and is then processed as appropriate. + + +
+ A preprocessing directive of the form +
+ # error pp-tokensopt new-line ++ causes the implementation to produce a diagnostic message that includes the specified + sequence of preprocessing tokens. + +
+ A preprocessing directive of the form +
+ # pragma pp-tokensopt new-line ++ where the preprocessing token STDC does not immediately follow pragma in the + directive (prior to any macro replacement)174) causes the implementation to behave in an + implementation-defined manner. The behavior might cause translation to fail or cause the + translator or the resulting program to behave in a non-conforming manner. Any such + pragma that is not recognized by the implementation is ignored. +
+ If the preprocessing token STDC does immediately follow pragma in the directive (prior + to any macro replacement), then no macro replacement is performed on the directive, and + the directive shall have one of the following forms175) whose meanings are described + elsewhere: +
+ #pragma STDC FP_CONTRACT on-off-switch + #pragma STDC FENV_ACCESS on-off-switch + #pragma STDC CX_LIMITED_RANGE on-off-switch + on-off-switch: one of + ON OFF DEFAULT ++
Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma + (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4). + + + + + + +
174) An implementation is not required to perform macro replacement in pragmas, but it is permitted + except for in standard pragmas (where STDC immediately follows pragma). If the result of macro + replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still + implementation-defined; an implementation is permitted to behave as if it were the standard pragma, + but is not required to. + +
175) See ''future language directions'' (6.11.8). + + +
+ A preprocessing directive of the form +
+ # new-line ++ has no effect. + +
+ The values of the predefined macros listed in the following subclauses176) (except for + __FILE__ and __LINE__) remain constant throughout the translation unit. +
+ None of these macro names, nor the identifier defined, shall be the subject of a + #define or a #undef preprocessing directive. Any other predefined macro names + shall begin with a leading underscore followed by an uppercase letter or a second + underscore. +
+ The implementation shall not predefine the macro __cplusplus, nor shall it define it + in any standard header. +
Forward references: standard headers (7.1.2). + +
176) See ''future language directions'' (6.11.9). + + +
+ The following macro names shall be defined by the implementation: + __DATE__ The date of translation of the preprocessing translation unit: a character +
+ string literal of the form "Mmm dd yyyy", where the names of the + months are the same as those generated by the asctime function, and the + first character of dd is a space character if the value is less than 10. If the + date of translation is not available, an implementation-defined valid date + shall be supplied. ++ __FILE__ The presumed name of the current source file (a character string literal).177) + __LINE__ The presumed line number (within the current source file) of the current +
+ source line (an integer constant).177) ++ __STDC__ The integer constant 1, intended to indicate a conforming implementation. + __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted +
+ implementation or the integer constant 0 if it is not. ++ + + + + + __STDC_VERSION__ The integer constant 201ymmL.178) + __TIME__ The time of translation of the preprocessing translation unit: a character +
+ string literal of the form "hh:mm:ss" as in the time generated by the + asctime function. If the time of translation is not available, an + implementation-defined valid time shall be supplied. ++
Forward references: the asctime function (7.26.3.1). + +
177) The presumed source file name and line number can be changed by the #line directive. + +
178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in + ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will + remain an integer constant of type long int that is increased with each revision of this International + Standard. + + +
+ The following macro names are conditionally defined by the implementation: + __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example, +
+ 199712L). If this symbol is defined, then every character in the Unicode + required set, when stored in an object of type wchar_t, has the same + value as the short identifier of that character. The Unicode required set + consists of all the characters that are defined by ISO/IEC 10646, along with + all amendments and technical corrigenda, as of the specified year and + month. If some other encoding is used, the macro shall not be defined and + the actual encoding used is implementation-defined. ++ __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in +
+ the encoding for wchar_t, a member of the basic character set need not + have a code value equal to its value when used as the lone character in an + integer character constant. ++ __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type +
+ char16_t are UTF-16 encoded. If some other encoding is used, the + macro shall not be defined and the actual encoding used is implementation- + defined. ++ __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type +
+ char32_t are UTF-32 encoded. If some other encoding is used, the + macro shall not be defined and the actual encoding used is implementation- + defined. ++
Forward references: common definitions (7.19), unicode utilities (7.27). + + + + + + +
+ The following macro names are conditionally defined by the implementation: + __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to +
+ the specifications in annex L (Analyzability). ++ __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the +
+ specifications in annex F (IEC 60559 floating-point arithmetic). ++ __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate +
+ adherence to the specifications in annex G (IEC 60559 compatible complex + arithmetic). ++ __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support +
+ for the extensions defined in annex K (Bounds-checking interfaces).179) ++ __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the +
+ implementation does not support complex types or the <complex.h> + header. ++ __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the +
+ implementation does not support atomic types (including the _Atomic + type qualifier and the <stdatomic.h> header) or the <threads.h> + header. ++ __STDC_NO_VLA__ The integer constant 1, intended to indicate that the +
+ implementation does not support variable length arrays or variably + modified types. ++
+ An implementation that defines __STDC_NO_COMPLEX__ shall not define + __STDC_IEC_559_COMPLEX__. + +
179) The intention is that this will remain an integer constant of type long int that is increased with + each revision of this International Standard. + + +
+ A unary operator expression of the form: +
+ _Pragma ( string-literal ) ++ is processed as follows: The string literal is destringized by deleting the L prefix, if + present, deleting the leading and trailing double-quotes, replacing each escape sequence + \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The + resulting sequence of characters is processed through translation phase 3 to produce + preprocessing tokens that are executed as if they were the pp-tokens in a pragma + + + + directive. The original four preprocessing tokens in the unary operator expression are + removed. +
+ EXAMPLE A directive of the form: +
+ #pragma listing on "..\listing.dir" ++ can also be expressed as: +
+ _Pragma ( "listing on \"..\\listing.dir\"" ) ++ The latter form is processed in the same way whether it appears literally as shown, or results from macro + replacement, as in: + +
+ #define LISTING(x) PRAGMA(listing on #x) + #define PRAGMA(x) _Pragma(#x) + LISTING ( ..\listing.dir ) ++ +
+ Future standardization may include additional floating-point types, including those with + greater range, precision, or both than long double. + +
+ Declaring an identifier with internal linkage at file scope without the static storage- + class specifier is an obsolescent feature. + +
+ Restriction of the significance of an external name to fewer than 255 characters + (considering each universal character name or extended source character as a single + character) is an obsolescent feature that is a concession to existing implementations. + +
+ Lowercase letters as escape sequences are reserved for future standardization. Other + characters may be used in extensions. + +
+ The placement of a storage-class specifier other than at the beginning of the declaration + specifiers in a declaration is an obsolescent feature. + +
+ The use of function declarators with empty parentheses (not prototype-format parameter + type declarators) is an obsolescent feature. + +
+ The use of function definitions with separate parameter identifier and declaration lists + (not prototype-format parameter type and identifier declarators) is an obsolescent feature. + +
+ Pragmas whose first preprocessing token is STDC are reserved for future standardization. + +
+ Macro names beginning with __STDC_ are reserved for future standardization. + + +
+ A string is a contiguous sequence of characters terminated by and including the first null + character. The term multibyte string is sometimes used instead to emphasize special + processing given to multibyte characters contained in the string or to avoid confusion + with a wide string. A pointer to a string is a pointer to its initial (lowest addressed) + character. The length of a string is the number of bytes preceding the null character and + the value of a string is the sequence of the values of the contained characters, in order. +
+ The decimal-point character is the character used by functions that convert floating-point + numbers to or from character sequences to denote the beginning of the fractional part of + such character sequences.180) It is represented in the text and examples by a period, but + may be changed by the setlocale function. +
+ A null wide character is a wide character with code value zero. +
+ A wide string is a contiguous sequence of wide characters terminated by and including + the first null wide character. A pointer to a wide string is a pointer to its initial (lowest + addressed) wide character. The length of a wide string is the number of wide characters + preceding the null wide character and the value of a wide string is the sequence of code + values of the contained wide characters, in order. +
+ A shift sequence is a contiguous sequence of bytes within a multibyte string that + (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a + corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte + character.181) +
Forward references: character handling (7.4), the setlocale function (7.11.1.1). + + + + + + +
180) The functions that make use of the decimal-point character are the numeric conversion functions + (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2). + +
181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large + enough to count all the bytes in any complete multibyte character plus at least one adjacent shift + sequence of maximum length. Whether these counts provide for more than one shift sequence is the + implementation's choice. + + +
+ Each library function is declared, with a type that includes a prototype, in a header,182) + whose contents are made available by the #include preprocessing directive. The + header declares a set of related functions, plus any necessary types and additional macros + needed to facilitate their use. Declarations of types described in this clause shall not + include type qualifiers, unless explicitly stated otherwise. +
+ The standard headers are183) +
+ <assert.h> <iso646.h> <stdarg.h> <string.h> + <complex.h> <limits.h> <stdatomic.h> <tgmath.h> + <ctype.h> <locale.h> <stdbool.h> <threads.h> + <errno.h> <math.h> <stddef.h> <time.h> + <fenv.h> <setjmp.h> <stdint.h> <uchar.h> + <float.h> <signal.h> <stdio.h> <wchar.h> + <inttypes.h> <stdalign.h> <stdlib.h> <wctype.h> ++
+ If a file with the same name as one of the above < and > delimited sequences, not + provided as part of the implementation, is placed in any of the standard places that are + searched for included source files, the behavior is undefined. +
+ Standard headers may be included in any order; each may be included more than once in + a given scope, with no effect different from being included only once, except that the + effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If + used, a header shall be included outside of any external declaration or definition, and it + shall first be included before the first reference to any of the functions or objects it + declares, or to any of the types or macros it defines. However, if an identifier is declared + or defined in more than one header, the second and subsequent associated headers may be + included after the initial reference to the identifier. The program shall not have any + macros with names lexically identical to keywords currently defined prior to the + inclusion. +
+ Any definition of an object-like macro described in this clause shall expand to code that is + fully protected by parentheses where necessary, so that it groups in an arbitrary + expression as if it were a single identifier. +
+ Any declaration of a library function shall have external linkage. + + + + + +
+ A summary of the contents of the standard headers is given in annex B. +
Forward references: diagnostics (7.2). + +
182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names + necessarily valid source file names. + +
183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that + implementations need not support; see 6.10.8.3. + + +
+ Each header declares or defines all identifiers listed in its associated subclause, and + optionally declares or defines identifiers listed in its associated future library directions + subclause and identifiers which are always reserved either for any use or for use as file + scope identifiers. +
+ No other identifiers are reserved. If the program declares or defines an identifier in a + context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved + identifier as a macro name, the behavior is undefined. +
+ If the program removes (with #undef) any macro definition of an identifier in the first + group listed above, the behavior is undefined. + + + + + + +
184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp, + va_copy, and va_end. + + +
+ Each of the following statements applies unless explicitly stated otherwise in the detailed + descriptions that follow: If an argument to a function has an invalid value (such as a value + outside the domain of the function, or a pointer outside the address space of the program, + or a null pointer, or a pointer to non-modifiable storage when the corresponding + parameter is not const-qualified) or a type (after promotion) not expected by a function + with variable number of arguments, the behavior is undefined. If a function argument is + described as being an array, the pointer actually passed to the function shall have a value + such that all address computations and accesses to objects (that would be valid if the + pointer did point to the first element of such an array) are in fact valid. Any function + declared in a header may be additionally implemented as a function-like macro defined in + the header, so if a library function is declared explicitly when its header is included, one + of the techniques shown below can be used to ensure the declaration is not affected by + such a macro. Any macro definition of a function can be suppressed locally by enclosing + the name of the function in parentheses, because the name is then not followed by the left + parenthesis that indicates expansion of a macro function name. For the same syntactic + reason, it is permitted to take the address of a library function even if it is also defined as + a macro.185) The use of #undef to remove any macro definition will also ensure that an + actual function is referred to. Any invocation of a library function that is implemented as + a macro shall expand to code that evaluates each of its arguments exactly once, fully + protected by parentheses where necessary, so it is generally safe to use arbitrary + expressions as arguments.186) Likewise, those function-like macros described in the + following subclauses may be invoked in an expression anywhere a function with a + compatible return type could be called.187) All object-like macros listed as expanding to + + + + integer constant expressions shall additionally be suitable for use in #if preprocessing + directives. +
+ Provided that a library function can be declared without reference to any type defined in a + header, it is also permissible to declare the function and use it without including its + associated header. +
+ There is a sequence point immediately before a library function returns. +
+ The functions in the standard library are not guaranteed to be reentrant and may modify + objects with static or thread storage duration.188) +
+ Unless explicitly stated otherwise in the detailed descriptions that follow, library + functions shall prevent data races as follows: A library function shall not directly or + indirectly access objects accessible by threads other than the current thread unless the + objects are accessed directly or indirectly via the function's arguments. A library + function shall not directly or indirectly modify objects accessible by threads other than + the current thread unless the objects are accessed directly or indirectly via the function's + non-const arguments.189) Implementations may share their own internal objects between + threads if the objects are not visible to users and are protected against data races. +
+ Unless otherwise specified, library functions shall perform all operations solely within the + current thread if those operations have effects that are visible to users.190) +
+ EXAMPLE The function atoi may be used in any of several ways: +
+ #include <stdlib.h> + const char *str; + /* ... */ + i = atoi(str); ++
+ #include <stdlib.h> + #undef atoi + const char *str; + /* ... */ + i = atoi(str); ++ or +
+ #include <stdlib.h> + const char *str; + /* ... */ + i = (atoi)(str); ++
+ extern int atoi(const char *); + const char *str; + /* ... */ + i = atoi(str); ++
185) This means that an implementation shall provide an actual function for each library function, even if it + also provides a macro for that function. + +
186) Such macros might not contain the sequence points that the corresponding function calls do. + +
187) Because external identifiers and some macro names beginning with an underscore are reserved,
+ implementations may provide special semantics for such names. For example, the identifier
+ _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
+ appropriate header could specify
+
+
+ #define abs(x) _BUILTIN_abs(x)
+
+ for a compiler whose code generator will accept it.
+ In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
+ function may write
+
+
+ #undef abs
+
+ whether the implementation's header provides a macro implementation of abs or a built-in
+ implementation. The prototype for the function, which precedes and is hidden by any macro
+ definition, is thereby revealed also.
+
+
188) Thus, a signal handler cannot, in general, call standard library functions. + +
189) This means, for example, that an implementation is not permitted to use a static object for internal + purposes without synchronization because it could cause a data race even in programs that do not + explicitly share objects between threads. + +
190) This allows implementations to parallelize operations if there are no visible side effects. + + +
+ The header <assert.h> defines the assert and static_assert macros and + refers to another macro, +
+ NDEBUG ++ which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the + point in the source file where <assert.h> is included, the assert macro is defined + simply as +
+ #define assert(ignore) ((void)0) ++ The assert macro is redefined according to the current state of NDEBUG each time that + <assert.h> is included. +
+ The assert macro shall be implemented as a macro, not as an actual function. If the + macro definition is suppressed in order to access an actual function, the behavior is + undefined. +
+ The macro +
+ static_assert ++ expands to _Static_assert. + +
+
+ #include <assert.h> + void assert(scalar expression); ++
+ The assert macro puts diagnostic tests into programs; it expands to a void expression. + When it is executed, if expression (which shall have a scalar type) is false (that is, + compares equal to 0), the assert macro writes information about the particular call that + failed (including the text of the argument, the name of the source file, the source line + number, and the name of the enclosing function -- the latter are respectively the values of + the preprocessing macros __FILE__ and __LINE__ and of the identifier + __func__) on the standard error stream in an implementation-defined format.191) It + then calls the abort function. + + + + +
+ The assert macro returns no value. +
Forward references: the abort function (7.22.4.1). + + +
191) The message written might be of the form: + Assertion failed: expression, function abc, file xyz, line nnn. + + +
+ The header <complex.h> defines macros and declares functions that support complex + arithmetic.192) +
+ Implementations that define the macro __STDC_NO_COMPLEX__ need not provide + this header nor support any of its facilities. +
+ Each synopsis specifies a family of functions consisting of a principal function with one + or more double complex parameters and a double complex or double return + value; and other functions with the same name but with f and l suffixes which are + corresponding functions with float and long double parameters and return values. +
+ The macro +
+ complex ++ expands to _Complex; the macro +
+ _Complex_I ++ expands to a constant expression of type const float _Complex, with the value of + the imaginary unit.193) +
+ The macros +
+ imaginary ++ and +
+ _Imaginary_I ++ are defined if and only if the implementation supports imaginary types;194) if defined, + they expand to _Imaginary and a constant expression of type const float + _Imaginary with the value of the imaginary unit. +
+ The macro +
+ I ++ expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not + defined, I shall expand to _Complex_I. +
+ Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then + redefine the macros complex, imaginary, and I. + + +
Forward references: IEC 60559-compatible complex arithmetic (annex G). + +
192) See ''future library directions'' (7.30.1). + +
193) The imaginary unit is a number i such that i 2 = -1. + +
194) A specification for imaginary types is in informative annex G. + + +
+ Values are interpreted as radians, not degrees. An implementation may set errno but is + not required to. + +
+ Some of the functions below have branch cuts, across which the function is + discontinuous. For implementations with a signed zero (including all IEC 60559 + implementations) that follow the specifications of annex G, the sign of zero distinguishes + one side of a cut from another so the function is continuous (except for format + limitations) as the cut is approached from either side. For example, for the square root + function, which has a branch cut along the negative real axis, the top of the cut, with + imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with + imaginary part -0, maps to the negative imaginary axis. +
+ Implementations that do not support a signed zero (see annex F) cannot distinguish the + sides of branch cuts. These implementations shall map a cut so the function is continuous + as the cut is approached coming around the finite endpoint of the cut in a counter + clockwise direction. (Branch cuts for the functions specified here have just one finite + endpoint.) For example, for the square root function, coming counter clockwise around + the finite endpoint of the cut along the negative real axis approaches the cut from above, + so the cut maps to the positive imaginary axis. + +
+
+ #include <complex.h> #pragma STDC CX_LIMITED_RANGE on-off-switch - double complex cacos(double complex z); - float complex cacosf(float complex z); - long double complex cacosl(long double complex z); - double complex casin(double complex z); - float complex casinf(float complex z); - long double complex casinl(long double complex z); ++
+ The usual mathematical formulas for complex multiply, divide, and absolute value are + problematic because of their treatment of infinities and because of undue overflow and + underflow. The CX_LIMITED_RANGE pragma can be used to inform the + implementation that (where the state is ''on'') the usual mathematical formulas are + acceptable.195) The pragma can occur either outside external declarations or preceding all + explicit declarations and statements inside a compound statement. When outside external + declarations, the pragma takes effect from its occurrence until another + CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit. + When inside a compound statement, the pragma takes effect from its occurrence until + another CX_LIMITED_RANGE pragma is encountered (including within a nested + compound statement), or until the end of the compound statement; at the end of a + compound statement the state for the pragma is restored to its condition just before the + + compound statement. If this pragma is used in any other context, the behavior is + undefined. The default state for the pragma is ''off''. + +
195) The purpose of the pragma is to allow the implementation to use the formulas:
+
+
+ (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
+ (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
+ | x + iy | = (sqrt) x 2 + y 2
+ -----
+
+ where the programmer can determine they are safe.
+
+
+
+
+ #include <complex.h> + double complex cacos(double complex z); + float complex cacosf(float complex z); + long double complex cacosl(long double complex z); ++
+ The cacos functions compute the complex arc cosine of z, with branch cuts outside the + interval [-1, +1] along the real axis. +
+ The cacos functions return the complex arc cosine value, in the range of a strip + mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the + real axis. + +
+
+ #include <complex.h> + double complex casin(double complex z); + float complex casinf(float complex z); + long double complex casinl(long double complex z); ++
+ The casin functions compute the complex arc sine of z, with branch cuts outside the + interval [-1, +1] along the real axis. +
+ The casin functions return the complex arc sine value, in the range of a strip + mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2] + + + along the real axis. + +
+
+ #include <complex.h> double complex catan(double complex z); float complex catanf(float complex z); long double complex catanl(long double complex z); ++
+ The catan functions compute the complex arc tangent of z, with branch cuts outside the + interval [-i, +i] along the imaginary axis. +
+ The catan functions return the complex arc tangent value, in the range of a strip + mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2] + along the real axis. + +
+
+ #include <complex.h> double complex ccos(double complex z); float complex ccosf(float complex z); long double complex ccosl(long double complex z); ++
+ The ccos functions compute the complex cosine of z. +
+ The ccos functions return the complex cosine value. + +
+
+ #include <complex.h> double complex csin(double complex z); float complex csinf(float complex z); long double complex csinl(long double complex z); - double complex ctan(double complex z); - float complex ctanf(float complex z); - long double complex ctanl(long double complex z); - double complex cacosh(double complex z); - float complex cacoshf(float complex z); - long double complex cacoshl(long double complex z); - double complex casinh(double complex z); - float complex casinhf(float complex z); - long double complex casinhl(long double complex z); - -[page 471] (Contents) - - double complex catanh(double complex z); - float complex catanhf(float complex z); - long double complex catanhl(long double complex z); - double complex ccosh(double complex z); - float complex ccoshf(float complex z); - long double complex ccoshl(long double complex z); - double complex csinh(double complex z); - float complex csinhf(float complex z); - long double complex csinhl(long double complex z); - double complex ctanh(double complex z); - float complex ctanhf(float complex z); - long double complex ctanhl(long double complex z); - double complex cexp(double complex z); - float complex cexpf(float complex z); - long double complex cexpl(long double complex z); - double complex clog(double complex z); - float complex clogf(float complex z); - long double complex clogl(long double complex z); - double cabs(double complex z); - float cabsf(float complex z); - long double cabsl(long double complex z); - double complex cpow(double complex x, double complex y); - float complex cpowf(float complex x, float complex y); - long double complex cpowl(long double complex x, - long double complex y); - double complex csqrt(double complex z); - float complex csqrtf(float complex z); - long double complex csqrtl(long double complex z); - double carg(double complex z); - float cargf(float complex z); - long double cargl(long double complex z); - double cimag(double complex z); - float cimagf(float complex z); - long double cimagl(long double complex z); - double complex CMPLX(double x, double y); - float complex CMPLXF(float x, float y); - long double complex CMPLXL(long double x, long double y); - double complex conj(double complex z); - float complex conjf(float complex z); - long double complex conjl(long double complex z); - double complex cproj(double complex z); - -[page 472] (Contents) - - float complex cprojf(float complex z); - long double complex cprojl(long double complex z); - double creal(double complex z); - float crealf(float complex z); - long double creall(long double complex z); -B.3 Character handling <ctype.h> - int isalnum(int c); - int isalpha(int c); - int isblank(int c); - int iscntrl(int c); - int isdigit(int c); - int isgraph(int c); - int islower(int c); - int isprint(int c); - int ispunct(int c); - int isspace(int c); - int isupper(int c); - int isxdigit(int c); - int tolower(int c); - int toupper(int c); -B.4 Errors <errno.h> - EDOM EILSEQ ERANGE errno - __STDC_WANT_LIB_EXT1__ - errno_t -B.5 Floating-point environment <fenv.h> - fenv_t FE_OVERFLOW FE_TOWARDZERO - fexcept_t FE_UNDERFLOW FE_UPWARD - FE_DIVBYZERO FE_ALL_EXCEPT FE_DFL_ENV - FE_INEXACT FE_DOWNWARD - FE_INVALID FE_TONEAREST - #pragma STDC FENV_ACCESS on-off-switch - int feclearexcept(int excepts); - int fegetexceptflag(fexcept_t *flagp, int excepts); - int feraiseexcept(int excepts); - int fesetexceptflag(const fexcept_t *flagp, - int excepts); - int fetestexcept(int excepts); - -[page 473] (Contents) - - int fegetround(void); - int fesetround(int round); - int fegetenv(fenv_t *envp); - int feholdexcept(fenv_t *envp); - int fesetenv(const fenv_t *envp); - int feupdateenv(const fenv_t *envp); -B.6 Characteristics of floating types <float.h> - FLT_ROUNDS DBL_DIG FLT_MAX - FLT_EVAL_METHOD LDBL_DIG DBL_MAX - FLT_HAS_SUBNORM FLT_MIN_EXP LDBL_MAX - DBL_HAS_SUBNORM DBL_MIN_EXP FLT_EPSILON - LDBL_HAS_SUBNORM LDBL_MIN_EXP DBL_EPSILON - FLT_RADIX FLT_MIN_10_EXP LDBL_EPSILON - FLT_MANT_DIG DBL_MIN_10_EXP FLT_MIN - DBL_MANT_DIG LDBL_MIN_10_EXP DBL_MIN - LDBL_MANT_DIG FLT_MAX_EXP LDBL_MIN - FLT_DECIMAL_DIG DBL_MAX_EXP FLT_TRUE_MIN - DBL_DECIMAL_DIG LDBL_MAX_EXP DBL_TRUE_MIN - LDBL_DECIMAL_DIG FLT_MAX_10_EXP LDBL_TRUE_MIN - DECIMAL_DIG DBL_MAX_10_EXP - FLT_DIG LDBL_MAX_10_EXP -B.7 Format conversion of integer types <inttypes.h> - imaxdiv_t - PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR - PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR - PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR - PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR - PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR - PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR - SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR - SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR - SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR - SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR - SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR - intmax_t imaxabs(intmax_t j); - imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); - intmax_t strtoimax(const char * restrict nptr, - char ** restrict endptr, int base); - -[page 474] (Contents) - ++
+ The csin functions compute the complex sine of z. + +
+ The csin functions return the complex sine value. + +
+
+ #include <complex.h> + double complex ctan(double complex z); + float complex ctanf(float complex z); + long double complex ctanl(long double complex z); ++
+ The ctan functions compute the complex tangent of z. +
+ The ctan functions return the complex tangent value. + +
+
+ #include <complex.h> + double complex cacosh(double complex z); + float complex cacoshf(float complex z); + long double complex cacoshl(long double complex z); ++
+ The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch + cut at values less than 1 along the real axis. +
+ The cacosh functions return the complex arc hyperbolic cosine value, in the range of a + half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the + imaginary axis. + +
+ +
+ #include <complex.h> + double complex casinh(double complex z); + float complex casinhf(float complex z); + long double complex casinhl(long double complex z); ++
+ The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts + outside the interval [-i, +i] along the imaginary axis. +
+ The casinh functions return the complex arc hyperbolic sine value, in the range of a + strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2] + along the imaginary axis. + +
+
+ #include <complex.h> + double complex catanh(double complex z); + float complex catanhf(float complex z); + long double complex catanhl(long double complex z); ++
+ The catanh functions compute the complex arc hyperbolic tangent of z, with branch + cuts outside the interval [-1, +1] along the real axis. +
+ The catanh functions return the complex arc hyperbolic tangent value, in the range of a + strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2] + along the imaginary axis. + +
+
+ #include <complex.h> + double complex ccosh(double complex z); + float complex ccoshf(float complex z); + long double complex ccoshl(long double complex z); ++
+ The ccosh functions compute the complex hyperbolic cosine of z. +
+ The ccosh functions return the complex hyperbolic cosine value. + + +
+
+ #include <complex.h> + double complex csinh(double complex z); + float complex csinhf(float complex z); + long double complex csinhl(long double complex z); ++
+ The csinh functions compute the complex hyperbolic sine of z. +
+ The csinh functions return the complex hyperbolic sine value. + +
+
+ #include <complex.h> + double complex ctanh(double complex z); + float complex ctanhf(float complex z); + long double complex ctanhl(long double complex z); ++
+ The ctanh functions compute the complex hyperbolic tangent of z. +
+ The ctanh functions return the complex hyperbolic tangent value. + +
+
+ #include <complex.h> + double complex cexp(double complex z); + float complex cexpf(float complex z); + long double complex cexpl(long double complex z); ++
+ The cexp functions compute the complex base-e exponential of z. +
+ The cexp functions return the complex base-e exponential value. + + +
+
+ #include <complex.h> + double complex clog(double complex z); + float complex clogf(float complex z); + long double complex clogl(long double complex z); ++
+ The clog functions compute the complex natural (base-e) logarithm of z, with a branch + cut along the negative real axis. +
+ The clog functions return the complex natural logarithm value, in the range of a strip + mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the + imaginary axis. + +
+
+ #include <complex.h> + double cabs(double complex z); + float cabsf(float complex z); + long double cabsl(long double complex z); ++
+ The cabs functions compute the complex absolute value (also called norm, modulus, or + magnitude) of z. +
+ The cabs functions return the complex absolute value. + +
+ +
+ #include <complex.h> + double complex cpow(double complex x, double complex y); + float complex cpowf(float complex x, float complex y); + long double complex cpowl(long double complex x, + long double complex y); ++
+ The cpow functions compute the complex power function xy , with a branch cut for the + first parameter along the negative real axis. +
+ The cpow functions return the complex power function value. + +
+
+ #include <complex.h> + double complex csqrt(double complex z); + float complex csqrtf(float complex z); + long double complex csqrtl(long double complex z); ++
+ The csqrt functions compute the complex square root of z, with a branch cut along the + negative real axis. +
+ The csqrt functions return the complex square root value, in the range of the right half- + plane (including the imaginary axis). + +
+
+ #include <complex.h> + double carg(double complex z); + float cargf(float complex z); + long double cargl(long double complex z); ++
+ The carg functions compute the argument (also called phase angle) of z, with a branch + cut along the negative real axis. +
+ The carg functions return the value of the argument in the interval [-pi , +pi ]. + + +
+
+ #include <complex.h> + double cimag(double complex z); + float cimagf(float complex z); + long double cimagl(long double complex z); ++
+ The cimag functions compute the imaginary part of z.196) +
+ The cimag functions return the imaginary part value (as a real). + +
196) For a variable z of complex type, z == creal(z) + cimag(z)*I. + + +
+
+ #include <complex.h> + double complex CMPLX(double x, double y); + float complex CMPLXF(float x, float y); + long double complex CMPLXL(long double x, long double y); ++
+ The CMPLX macros expand to an expression of the specified complex type, with the real + part having the (converted) value of x and the imaginary part having the (converted) + value of y. +
+ The resulting expression should be suitable for use as an initializer for an object with + static or thread storage duration, provided both arguments are likewise suitable. +
+ The CMPLX macros return the complex value x + i y. +
+ NOTE These macros act as if the implementation supported imaginary types and the definitions were: +
+ #define CMPLX(x, y) ((double complex)((double)(x) + \ + _Imaginary_I * (double)(y))) + #define CMPLXF(x, y) ((float complex)((float)(x) + \ + _Imaginary_I * (float)(y))) + #define CMPLXL(x, y) ((long double complex)((long double)(x) + \ + _Imaginary_I * (long double)(y))) ++ + + + + + +
+
+ #include <complex.h> + double complex conj(double complex z); + float complex conjf(float complex z); + long double complex conjl(long double complex z); ++
+ The conj functions compute the complex conjugate of z, by reversing the sign of its + imaginary part. +
+ The conj functions return the complex conjugate value. + +
+
+ #include <complex.h> + double complex cproj(double complex z); + float complex cprojf(float complex z); + long double complex cprojl(long double complex z); ++
+ The cproj functions compute a projection of z onto the Riemann sphere: z projects to + z except that all complex infinities (even those with one infinite part and one NaN part) + project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is + equivalent to +
+ INFINITY + I * copysign(0.0, cimag(z)) ++
+ The cproj functions return the value of the projection onto the Riemann sphere. + +
+
+ #include <complex.h> + double creal(double complex z); + float crealf(float complex z); + long double creall(long double complex z); ++
+ The creal functions compute the real part of z.197) + +
+ The creal functions return the real part value. + + + + + + +
197) For a variable z of complex type, z == creal(z) + cimag(z)*I. + + +
+ The header <ctype.h> declares several functions useful for classifying and mapping + characters.198) In all cases the argument is an int, the value of which shall be + representable as an unsigned char or shall equal the value of the macro EOF. If the + argument has any other value, the behavior is undefined. +
+ The behavior of these functions is affected by the current locale. Those functions that + have locale-specific aspects only when not in the "C" locale are noted below. +
+ The term printing character refers to a member of a locale-specific set of characters, each + of which occupies one printing position on a display device; the term control character + refers to a member of a locale-specific set of characters that are not printing + characters.199) All letters and digits are printing characters. +
Forward references: EOF (7.21.1), localization (7.11). + +
198) See ''future library directions'' (7.30.2). + +
199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those + whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose + values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL). + + +
+ The functions in this subclause return nonzero (true) if and only if the value of the + argument c conforms to that in the description of the function. + +
+
+ #include <ctype.h> + int isalnum(int c); ++
+ The isalnum function tests for any character for which isalpha or isdigit is true. + +
+
+ #include <ctype.h> + int isalpha(int c); ++
+ The isalpha function tests for any character for which isupper or islower is true, + or any character that is one of a locale-specific set of alphabetic characters for which + + + + + none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale, + isalpha returns true only for the characters for which isupper or islower is true. + +
200) The functions islower and isupper test true or false separately for each of these additional + characters; all four combinations are possible. + + +
+
+ #include <ctype.h> + int isblank(int c); ++
+ The isblank function tests for any character that is a standard blank character or is one + of a locale-specific set of characters for which isspace is true and that is used to + separate words within a line of text. The standard blank characters are the following: + space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only + for the standard blank characters. + +
+
+ #include <ctype.h> + int iscntrl(int c); ++
+ The iscntrl function tests for any control character. + +
+
+ #include <ctype.h> + int isdigit(int c); ++
+ The isdigit function tests for any decimal-digit character (as defined in 5.2.1). + +
+
+ #include <ctype.h> + int isgraph(int c); ++ + + + + +
+ The isgraph function tests for any printing character except space (' '). + +
+
+ #include <ctype.h> + int islower(int c); ++
+ The islower function tests for any character that is a lowercase letter or is one of a + locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or + isspace is true. In the "C" locale, islower returns true only for the lowercase + letters (as defined in 5.2.1). + +
+
+ #include <ctype.h> + int isprint(int c); ++
+ The isprint function tests for any printing character including space (' '). + +
+
+ #include <ctype.h> + int ispunct(int c); ++
+ The ispunct function tests for any printing character that is one of a locale-specific set + of punctuation characters for which neither isspace nor isalnum is true. In the "C" + locale, ispunct returns true for every printing character for which neither isspace + nor isalnum is true. + +
+
+ #include <ctype.h> + int isspace(int c); ++
+ The isspace function tests for any character that is a standard white-space character or + is one of a locale-specific set of characters for which isalnum is false. The standard + + white-space characters are the following: space (' '), form feed ('\f'), new-line + ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the + "C" locale, isspace returns true only for the standard white-space characters. + +
+
+ #include <ctype.h> + int isupper(int c); ++
+ The isupper function tests for any character that is an uppercase letter or is one of a + locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or + isspace is true. In the "C" locale, isupper returns true only for the uppercase + letters (as defined in 5.2.1). + +
+
+ #include <ctype.h> + int isxdigit(int c); ++
+ The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1). + +
+
+ #include <ctype.h> + int tolower(int c); ++
+ The tolower function converts an uppercase letter to a corresponding lowercase letter. +
+ If the argument is a character for which isupper is true and there are one or more + corresponding characters, as specified by the current locale, for which islower is true, + the tolower function returns one of the corresponding characters (always the same one + for any given locale); otherwise, the argument is returned unchanged. + + +
+
+ #include <ctype.h> + int toupper(int c); ++
+ The toupper function converts a lowercase letter to a corresponding uppercase letter. +
+ If the argument is a character for which islower is true and there are one or more + corresponding characters, as specified by the current locale, for which isupper is true, + the toupper function returns one of the corresponding characters (always the same one + for any given locale); otherwise, the argument is returned unchanged. + + +
+ The header <errno.h> defines several macros, all relating to the reporting of error + conditions. +
+ The macros are +
+ EDOM + EILSEQ + ERANGE ++ which expand to integer constant expressions with type int, distinct positive values, and + which are suitable for use in #if preprocessing directives; and +
+ errno ++ which expands to a modifiable lvalue201) that has type int and thread local storage + duration, the value of which is set to a positive error number by several library functions. + If a macro definition is suppressed in order to access an actual object, or a program + defines an identifier with the name errno, the behavior is undefined. +
+ The value of errno in the initial thread is zero at program startup (the initial value of + errno in other threads is an indeterminate value), but is never set to zero by any library + function.202) The value of errno may be set to nonzero by a library function call + whether or not there is an error, provided the use of errno is not documented in the + description of the function in this International Standard. +
+ Additional macro definitions, beginning with E and a digit or E and an uppercase + letter,203) may also be specified by the implementation. + + + + + + +
201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue + resulting from a function call (for example, *errno()). + +
202) Thus, a program that uses errno for error checking should set it to zero before a library function call, + then inspect it before a subsequent library function call. Of course, a library function can save the + value of errno on entry and then set it to zero, as long as the original value is restored if errno's + value is still zero just before the return. + +
203) See ''future library directions'' (7.30.3). + + +
+ The header <fenv.h> defines several macros, and declares types and functions that + provide access to the floating-point environment. The floating-point environment refers + collectively to any floating-point status flags and control modes supported by the + implementation.204) A floating-point status flag is a system variable whose value is set + (but never cleared) when a floating-point exception is raised, which occurs as a side effect + of exceptional floating-point arithmetic to provide auxiliary information.205) A floating- + point control mode is a system variable whose value may be set by the user to affect the + subsequent behavior of floating-point arithmetic. +
+ The floating-point environment has thread storage duration. The initial state for a + thread's floating-point environment is the current state of the floating-point environment + of the thread that creates it at the time of creation. +
+ Certain programming conventions support the intended model of use for the floating- + point environment:206) +
+ The type +
+ fenv_t ++ represents the entire floating-point environment. +
+ The type +
+ fexcept_t ++ represents the floating-point status flags collectively, including any status the + implementation associates with the flags. + + + +
+ Each of the macros +
+ FE_DIVBYZERO + FE_INEXACT + FE_INVALID + FE_OVERFLOW + FE_UNDERFLOW ++ is defined if and only if the implementation supports the floating-point exception by + means of the functions in 7.6.2.207) Additional implementation-defined floating-point + exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also + be specified by the implementation. The defined macros expand to integer constant + expressions with values such that bitwise ORs of all combinations of the macros result in + distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in + zero.208) +
+ The macro +
+ FE_ALL_EXCEPT ++ is simply the bitwise OR of all floating-point exception macros defined by the + implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0. +
+ Each of the macros +
+ FE_DOWNWARD + FE_TONEAREST + FE_TOWARDZERO + FE_UPWARD ++ is defined if and only if the implementation supports getting and setting the represented + rounding direction by means of the fegetround and fesetround functions. + Additional implementation-defined rounding directions, with macro definitions beginning + with FE_ and an uppercase letter, may also be specified by the implementation. The + defined macros expand to integer constant expressions whose values are distinct + nonnegative values.209) +
+ The macro + + + + +
+ FE_DFL_ENV ++ represents the default floating-point environment -- the one installed at program startup +
+ Additional implementation-defined environments, with macro definitions beginning with + FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may + also be specified by the implementation. + +
204) This header is designed to support the floating-point exception status flags and directed-rounding + control modes required by IEC 60559, and other similar floating-point state information. It is also + designed to facilitate code portability among all systems. + +
205) A floating-point status flag is not an object and can be set more than once within an expression. + +
206) With these conventions, a programmer can safely assume default floating-point control modes (or be + unaware of them). The responsibilities associated with accessing the floating-point environment fall + on the programmer or program that does so explicitly. + +
207) The implementation supports a floating-point exception if there are circumstances where a call to at + least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not + necessary for all the functions to succeed all the time. + +
208) The macros should be distinct powers of two. + +
209) Even though the rounding direction macros may expand to constants corresponding to the values of + FLT_ROUNDS, they are not required to do so. + + +
+
+ #include <fenv.h> + #pragma STDC FENV_ACCESS on-off-switch ++
+ The FENV_ACCESS pragma provides a means to inform the implementation when a + program might access the floating-point environment to test floating-point status flags or + run under non-default floating-point control modes.210) The pragma shall occur either + outside external declarations or preceding all explicit declarations and statements inside a + compound statement. When outside external declarations, the pragma takes effect from + its occurrence until another FENV_ACCESS pragma is encountered, or until the end of + the translation unit. When inside a compound statement, the pragma takes effect from its + occurrence until another FENV_ACCESS pragma is encountered (including within a + nested compound statement), or until the end of the compound statement; at the end of a + compound statement the state for the pragma is restored to its condition just before the + compound statement. If this pragma is used in any other context, the behavior is + undefined. If part of a program tests floating-point status flags, sets floating-point control + modes, or runs under non-default mode settings, but was translated with the state for the + FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or + ''off'') for the pragma is implementation-defined. (When execution passes from a part of + the program translated with FENV_ACCESS ''off'' to a part translated with + FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the + floating-point control modes have their default settings.) + + + + + +
+ EXAMPLE +
+ #include <fenv.h> + void f(double x) + { + #pragma STDC FENV_ACCESS ON + void g(double); + void h(double); + /* ... */ + g(x + 1); + h(x + 1); + /* ... */ + } ++
+ If the function g might depend on status flags set as a side effect of the first x + 1, or if the second + x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall + contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.211) + + +
210) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag + tests and mode changes (e.g., global common subexpression elimination, code motion, and constant + folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default + modes are in effect and the flags are not tested. + +
211) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other + hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is + ''off'', just one evaluation of x + 1 would suffice. + + +
+ The following functions provide access to the floating-point status flags.212) The int + input argument for the functions represents a subset of floating-point exceptions, and can + be zero or the bitwise OR of one or more floating-point exception macros, for example + FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these + functions is undefined. + +
212) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic + abstraction of flags that are either set or clear. An implementation may endow floating-point status + flags with more information -- for example, the address of the code which first raised the floating- + point exception; the functions fegetexceptflag and fesetexceptflag deal with the full + content of flags. + + +
+
+ #include <fenv.h> + int feclearexcept(int excepts); ++
+ The feclearexcept function attempts to clear the supported floating-point exceptions + represented by its argument. +
+ The feclearexcept function returns zero if the excepts argument is zero or if all + the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value. + + + + +
+
+ #include <fenv.h> + int fegetexceptflag(fexcept_t *flagp, + int excepts); ++
+ The fegetexceptflag function attempts to store an implementation-defined + representation of the states of the floating-point status flags indicated by the argument + excepts in the object pointed to by the argument flagp. +
+ The fegetexceptflag function returns zero if the representation was successfully + stored. Otherwise, it returns a nonzero value. + +
+
+ #include <fenv.h> + int feraiseexcept(int excepts); ++
+ The feraiseexcept function attempts to raise the supported floating-point exceptions + represented by its argument.213) The order in which these floating-point exceptions are + raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function + additionally raises the ''inexact'' floating-point exception whenever it raises the + ''overflow'' or ''underflow'' floating-point exception is implementation-defined. +
+ The feraiseexcept function returns zero if the excepts argument is zero or if all + the specified exceptions were successfully raised. Otherwise, it returns a nonzero value. + + + + + + +
213) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations. + Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification + in F.8.6 is in the same spirit. + + +
+
+ #include <fenv.h> + int fesetexceptflag(const fexcept_t *flagp, + int excepts); ++
+ The fesetexceptflag function attempts to set the floating-point status flags + indicated by the argument excepts to the states stored in the object pointed to by + flagp. The value of *flagp shall have been set by a previous call to + fegetexceptflag whose second argument represented at least those floating-point + exceptions represented by the argument excepts. This function does not raise floating- + point exceptions, but only sets the state of the flags. +
+ The fesetexceptflag function returns zero if the excepts argument is zero or if + all the specified flags were successfully set to the appropriate state. Otherwise, it returns + a nonzero value. + +
+
+ #include <fenv.h> + int fetestexcept(int excepts); ++
+ The fetestexcept function determines which of a specified subset of the floating- + point exception flags are currently set. The excepts argument specifies the floating- + point status flags to be queried.214) +
+ The fetestexcept function returns the value of the bitwise OR of the floating-point + exception macros corresponding to the currently set floating-point exceptions included in + excepts. +
+ EXAMPLE Call f if ''invalid'' is set, then g if ''overflow'' is set: + + + + + +
+ #include <fenv.h> + /* ... */ + { + #pragma STDC FENV_ACCESS ON + int set_excepts; + feclearexcept(FE_INVALID | FE_OVERFLOW); + // maybe raise exceptions + set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW); + if (set_excepts & FE_INVALID) f(); + if (set_excepts & FE_OVERFLOW) g(); + /* ... */ + } ++ + +
214) This mechanism allows testing several floating-point exceptions with just one function call. + + +
+ The fegetround and fesetround functions provide control of rounding direction + modes. + +
+
+ #include <fenv.h> + int fegetround(void); ++
+ The fegetround function gets the current rounding direction. +
+ The fegetround function returns the value of the rounding direction macro + representing the current rounding direction or a negative value if there is no such + rounding direction macro or the current rounding direction is not determinable. + +
+
+ #include <fenv.h> + int fesetround(int round); ++
+ The fesetround function establishes the rounding direction represented by its + argument round. If the argument is not equal to the value of a rounding direction macro, + the rounding direction is not changed. +
+ The fesetround function returns zero if and only if the requested rounding direction + was established. + +
+ EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the + rounding direction fails. +
+ #include <fenv.h> + #include <assert.h> + void f(int round_dir) + { + #pragma STDC FENV_ACCESS ON + int save_round; + int setround_ok; + save_round = fegetround(); + setround_ok = fesetround(round_dir); + assert(setround_ok == 0); + /* ... */ + fesetround(save_round); + /* ... */ + } ++ + +
+ The functions in this section manage the floating-point environment -- status flags and + control modes -- as one entity. + +
+
+ #include <fenv.h> + int fegetenv(fenv_t *envp); ++
+ The fegetenv function attempts to store the current floating-point environment in the + object pointed to by envp. +
+ The fegetenv function returns zero if the environment was successfully stored. + Otherwise, it returns a nonzero value. + +
+
+ #include <fenv.h> + int feholdexcept(fenv_t *envp); ++
+ The feholdexcept function saves the current floating-point environment in the object + pointed to by envp, clears the floating-point status flags, and then installs a non-stop + (continue on floating-point exceptions) mode, if available, for all floating-point + exceptions.215) + +
+ The feholdexcept function returns zero if and only if non-stop floating-point + exception handling was successfully installed. + +
215) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap + handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For + such systems, the feholdexcept function can be used in conjunction with the feupdateenv + function to write routines that hide spurious floating-point exceptions from their callers. + + +
+
+ #include <fenv.h> + int fesetenv(const fenv_t *envp); ++
+ The fesetenv function attempts to establish the floating-point environment represented + by the object pointed to by envp. The argument envp shall point to an object set by a + call to fegetenv or feholdexcept, or equal a floating-point environment macro. + Note that fesetenv merely installs the state of the floating-point status flags + represented through its argument, and does not raise these floating-point exceptions. +
+ The fesetenv function returns zero if the environment was successfully established. + Otherwise, it returns a nonzero value. + +
+
+ #include <fenv.h> + int feupdateenv(const fenv_t *envp); ++
+ The feupdateenv function attempts to save the currently raised floating-point + exceptions in its automatic storage, install the floating-point environment represented by + the object pointed to by envp, and then raise the saved floating-point exceptions. The + argument envp shall point to an object set by a call to feholdexcept or fegetenv, + or equal a floating-point environment macro. +
+ The feupdateenv function returns zero if all the actions were successfully carried out. + Otherwise, it returns a nonzero value. + + + + + +
+ EXAMPLE Hide spurious underflow floating-point exceptions: + +
+ #include <fenv.h> + double f(double x) + { + #pragma STDC FENV_ACCESS ON + double result; + fenv_t save_env; + if (feholdexcept(&save_env)) + return /* indication of an environmental problem */; + // compute result + if (/* test spurious underflow */) + if (feclearexcept(FE_UNDERFLOW)) + return /* indication of an environmental problem */; + if (feupdateenv(&save_env)) + return /* indication of an environmental problem */; + return result; + } ++ +
+ The header <float.h> defines several macros that expand to various limits and + parameters of the standard floating-point types. +
+ The macros, their meanings, and the constraints (or restrictions) on their values are listed + in 5.2.4.2.2. + + +
+ The header <inttypes.h> includes the header <stdint.h> and extends it with + additional facilities provided by hosted implementations. +
+ It declares functions for manipulating greatest-width integers and converting numeric + character strings to greatest-width integers, and it declares the type +
+ imaxdiv_t ++ which is a structure type that is the type of the value returned by the imaxdiv function. + For each type declared in <stdint.h>, it defines corresponding macros for conversion + specifiers for use with the formatted input/output functions.216) +
Forward references: integer types <stdint.h> (7.20), formatted input/output + functions (7.21.6), formatted wide character input/output functions (7.28.2). + +
216) See ''future library directions'' (7.30.4). + + +
+ Each of the following object-like macros expands to a character string literal containing a * + conversion specifier, possibly modified by a length modifier, suitable for use within the + format argument of a formatted input/output function when converting the corresponding + integer type. These macro names have the general form of PRI (character string literals + for the fprintf and fwprintf family) or SCN (character string literals for the + fscanf and fwscanf family),217) followed by the conversion specifier, followed by a + name corresponding to a similar type name in 7.20.1. In these names, N represents the + width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a + format string to print the value of an integer of type int_fast32_t. +
+ The fprintf macros for signed integers are: +
+ PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR + PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR ++
+ The fprintf macros for unsigned integers are: +
+ PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR + PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR + PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR + PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR ++
+ The fscanf macros for signed integers are: + + + + +
+ SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR + SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR ++
+ The fscanf macros for unsigned integers are: +
+ SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR + SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR + SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR ++
+ For each type that the implementation provides in <stdint.h>, the corresponding + fprintf macros shall be defined and the corresponding fscanf macros shall be + defined unless the implementation does not have a suitable fscanf length modifier for + the type. +
+ EXAMPLE +
+ #include <inttypes.h> + #include <wchar.h> + int main(void) + { + uintmax_t i = UINTMAX_MAX; // this type always exists + wprintf(L"The largest integer value is %020" + PRIxMAX "\n", i); + return 0; + } ++ + +
217) Separate macros are given for use with fprintf and fscanf functions because, in the general case, + different format specifiers may be required for fprintf and fscanf, even when the type is the + same. + + +
+
+ #include <inttypes.h> + intmax_t imaxabs(intmax_t j); ++
+ The imaxabs function computes the absolute value of an integer j. If the result cannot + be represented, the behavior is undefined.218) +
+ The imaxabs function returns the absolute value. + + + + + + +
218) The absolute value of the most negative number cannot be represented in two's complement. + + +
+
+ #include <inttypes.h> + imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); ++
+ The imaxdiv function computes numer / denom and numer % denom in a single + operation. +
+ The imaxdiv function returns a structure of type imaxdiv_t comprising both the + quotient and the remainder. The structure shall contain (in either order) the members + quot (the quotient) and rem (the remainder), each of which has type intmax_t. If + either part of the result cannot be represented, the behavior is undefined. + +
+
+ #include <inttypes.h> + intmax_t strtoimax(const char * restrict nptr, + char ** restrict endptr, int base); uintmax_t strtoumax(const char * restrict nptr, - char ** restrict endptr, int base); - intmax_t wcstoimax(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - uintmax_t wcstoumax(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); -B.8 Alternative spellings <iso646.h> - and bitor not_eq xor - and_eq compl or xor_eq - bitand not or_eq -B.9 Sizes of integer types <limits.h> - CHAR_BIT CHAR_MAX INT_MIN ULONG_MAX - SCHAR_MIN MB_LEN_MAX INT_MAX LLONG_MIN - SCHAR_MAX SHRT_MIN UINT_MAX LLONG_MAX - UCHAR_MAX SHRT_MAX LONG_MIN ULLONG_MAX - CHAR_MIN USHRT_MAX LONG_MAX -B.10 Localization <locale.h> - struct lconv LC_ALL LC_CTYPE LC_NUMERIC - NULL LC_COLLATE LC_MONETARY LC_TIME - char *setlocale(int category, const char *locale); - struct lconv *localeconv(void); -B.11 Mathematics <math.h> - float_t FP_INFINITE FP_FAST_FMAL - double_t FP_NAN FP_ILOGB0 - HUGE_VAL FP_NORMAL FP_ILOGBNAN - HUGE_VALF FP_SUBNORMAL MATH_ERRNO - HUGE_VALL FP_ZERO MATH_ERREXCEPT - INFINITY FP_FAST_FMA math_errhandling - NAN FP_FAST_FMAF - #pragma STDC FP_CONTRACT on-off-switch - int fpclassify(real-floating x); - int isfinite(real-floating x); - int isinf(real-floating x); - int isnan(real-floating x); - int isnormal(real-floating x); - int signbit(real-floating x); -[page 475] (Contents) - - double acos(double x); - float acosf(float x); - long double acosl(long double x); - double asin(double x); - float asinf(float x); - long double asinl(long double x); - double atan(double x); - float atanf(float x); - long double atanl(long double x); - double atan2(double y, double x); - float atan2f(float y, float x); - long double atan2l(long double y, long double x); - double cos(double x); - float cosf(float x); - long double cosl(long double x); - double sin(double x); - float sinf(float x); - long double sinl(long double x); - double tan(double x); - float tanf(float x); - long double tanl(long double x); - double acosh(double x); - float acoshf(float x); - long double acoshl(long double x); - double asinh(double x); - float asinhf(float x); - long double asinhl(long double x); - double atanh(double x); - float atanhf(float x); - long double atanhl(long double x); - double cosh(double x); - float coshf(float x); - long double coshl(long double x); - double sinh(double x); - float sinhf(float x); - long double sinhl(long double x); - double tanh(double x); - float tanhf(float x); - long double tanhl(long double x); - double exp(double x); - float expf(float x); - -[page 476] (Contents) - - long double expl(long double x); - double exp2(double x); - float exp2f(float x); - long double exp2l(long double x); - double expm1(double x); - float expm1f(float x); - long double expm1l(long double x); - double frexp(double value, int *exp); - float frexpf(float value, int *exp); - long double frexpl(long double value, int *exp); - int ilogb(double x); - int ilogbf(float x); - int ilogbl(long double x); - double ldexp(double x, int exp); - float ldexpf(float x, int exp); - long double ldexpl(long double x, int exp); - double log(double x); - float logf(float x); - long double logl(long double x); - double log10(double x); - float log10f(float x); - long double log10l(long double x); - double log1p(double x); - float log1pf(float x); - long double log1pl(long double x); - double log2(double x); - float log2f(float x); - long double log2l(long double x); - double logb(double x); - float logbf(float x); - long double logbl(long double x); - double modf(double value, double *iptr); - float modff(float value, float *iptr); - long double modfl(long double value, long double *iptr); + char ** restrict endptr, int base); ++
+ The strtoimax and strtoumax functions are equivalent to the strtol, strtoll, + strtoul, and strtoull functions, except that the initial portion of the string is + converted to intmax_t and uintmax_t representation, respectively. +
+ The strtoimax and strtoumax functions return the converted value, if any. If no + conversion could be performed, zero is returned. If the correct value is outside the range + of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned + (according to the return type and sign of the value, if any), and the value of the macro + ERANGE is stored in errno. +
Forward references: the strtol, strtoll, strtoul, and strtoull functions + (7.22.1.4). + + +
+
+ #include <stddef.h> // for wchar_t + #include <inttypes.h> + intmax_t wcstoimax(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); + uintmax_t wcstoumax(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); ++
+ The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll, + wcstoul, and wcstoull functions except that the initial portion of the wide string is + converted to intmax_t and uintmax_t representation, respectively. +
+ The wcstoimax function returns the converted value, if any. If no conversion could be + performed, zero is returned. If the correct value is outside the range of representable + values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the + return type and sign of the value, if any), and the value of the macro ERANGE is stored in + errno. +
Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions + (7.28.4.1.2). + + +
+ The header <iso646.h> defines the following eleven macros (on the left) that expand + to the corresponding tokens (on the right): + +
+ and && + and_eq &= + bitand & + bitor | + compl ~ + not ! + not_eq != + or || + or_eq |= + xor ^ + xor_eq ^= ++ +
+ The header <limits.h> defines several macros that expand to various limits and + parameters of the standard integer types. +
+ The macros, their meanings, and the constraints (or restrictions) on their values are listed + in 5.2.4.2.1. + + +
+ The header <locale.h> declares two functions, one type, and defines several macros. +
+ The type is +
+ struct lconv ++ which contains members related to the formatting of numeric values. The structure shall + contain at least the following members, in any order. The semantics of the members and + their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have + the values specified in the comments. + +
+ char *decimal_point; // "." + char *thousands_sep; // "" + char *grouping; // "" + char *mon_decimal_point; // "" + char *mon_thousands_sep; // "" + char *mon_grouping; // "" + char *positive_sign; // "" + char *negative_sign; // "" + char *currency_symbol; // "" + char frac_digits; // CHAR_MAX + char p_cs_precedes; // CHAR_MAX + char n_cs_precedes; // CHAR_MAX + char p_sep_by_space; // CHAR_MAX + char n_sep_by_space; // CHAR_MAX + char p_sign_posn; // CHAR_MAX + char n_sign_posn; // CHAR_MAX + char *int_curr_symbol; // "" + char int_frac_digits; // CHAR_MAX + char int_p_cs_precedes; // CHAR_MAX + char int_n_cs_precedes; // CHAR_MAX + char int_p_sep_by_space; // CHAR_MAX + char int_n_sep_by_space; // CHAR_MAX + char int_p_sign_posn; // CHAR_MAX + char int_n_sign_posn; // CHAR_MAX ++
+ The macros defined are NULL (described in 7.19); and +
+ LC_ALL + LC_COLLATE + LC_CTYPE + LC_MONETARY + LC_NUMERIC + LC_TIME ++ which expand to integer constant expressions with distinct values, suitable for use as the + first argument to the setlocale function.219) Additional macro definitions, beginning + with the characters LC_ and an uppercase letter,220) may also be specified by the + implementation. + +
219) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C. + +
220) See ''future library directions'' (7.30.5). + + +
+
+ #include <locale.h> + char *setlocale(int category, const char *locale); ++
+ The setlocale function selects the appropriate portion of the program's locale as + specified by the category and locale arguments. The setlocale function may be + used to change or query the program's entire current locale or portions thereof. The value + LC_ALL for category names the program's entire locale; the other values for + category name only a portion of the program's locale. LC_COLLATE affects the + behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of + the character handling functions221) and the multibyte and wide character functions. + LC_MONETARY affects the monetary formatting information returned by the + localeconv function. LC_NUMERIC affects the decimal-point character for the + formatted input/output functions and the string conversion functions, as well as the + nonmonetary formatting information returned by the localeconv function. LC_TIME + affects the behavior of the strftime and wcsftime functions. +
+ A value of "C" for locale specifies the minimal environment for C translation; a value + of "" for locale specifies the locale-specific native environment. Other + implementation-defined strings may be passed as the second argument to setlocale. + + +
+ At program startup, the equivalent of +
+ setlocale(LC_ALL, "C"); ++ is executed. +
+ A call to the setlocale function may introduce a data race with other calls to the + setlocale function or with calls to functions that are affected by the current locale. + The implementation shall behave as if no library function calls the setlocale function. +
+ If a pointer to a string is given for locale and the selection can be honored, the + setlocale function returns a pointer to the string associated with the specified + category for the new locale. If the selection cannot be honored, the setlocale + function returns a null pointer and the program's locale is not changed. +
+ A null pointer for locale causes the setlocale function to return a pointer to the + string associated with the category for the program's current locale; the program's + locale is not changed.222) +
+ The pointer to string returned by the setlocale function is such that a subsequent call + with that string value and its associated category will restore that part of the program's + locale. The string pointed to shall not be modified by the program, but may be + overwritten by a subsequent call to the setlocale function. +
Forward references: formatted input/output functions (7.21.6), multibyte/wide + character conversion functions (7.22.7), multibyte/wide string conversion functions + (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the + strftime function (7.26.3.5), the strxfrm function (7.23.4.5). + +
221) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and + isxdigit. + +
222) The implementation shall arrange to encode in a string the various categories due to a heterogeneous + locale when category has the value LC_ALL. + + +
+
+ #include <locale.h> + struct lconv *localeconv(void); ++
+ The localeconv function sets the components of an object with type struct lconv + with values appropriate for the formatting of numeric quantities (monetary and otherwise) + according to the rules of the current locale. + + + + +
+ The members of the structure with type char * are pointers to strings, any of which + (except decimal_point) can point to "", to indicate that the value is not available in + the current locale or is of zero length. Apart from grouping and mon_grouping, the + strings shall start and end in the initial shift state. The members with type char are + nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not + available in the current locale. The members include the following: + char *decimal_point +
+ The decimal-point character used to format nonmonetary quantities. ++ char *thousands_sep +
+ The character used to separate groups of digits before the decimal-point + character in formatted nonmonetary quantities. ++ char *grouping +
+ A string whose elements indicate the size of each group of digits in + formatted nonmonetary quantities. ++ char *mon_decimal_point +
+ The decimal-point used to format monetary quantities. ++ char *mon_thousands_sep +
+ The separator for groups of digits before the decimal-point in formatted + monetary quantities. ++ char *mon_grouping +
+ A string whose elements indicate the size of each group of digits in + formatted monetary quantities. ++ char *positive_sign +
+ The string used to indicate a nonnegative-valued formatted monetary + quantity. ++ char *negative_sign +
+ The string used to indicate a negative-valued formatted monetary quantity. ++ char *currency_symbol +
+ The local currency symbol applicable to the current locale. ++ char frac_digits +
+ The number of fractional digits (those after the decimal-point) to be + displayed in a locally formatted monetary quantity. ++ char p_cs_precedes + +
+ Set to 1 or 0 if the currency_symbol respectively precedes or + succeeds the value for a nonnegative locally formatted monetary quantity. ++ char n_cs_precedes +
+ Set to 1 or 0 if the currency_symbol respectively precedes or + succeeds the value for a negative locally formatted monetary quantity. ++ char p_sep_by_space +
+ Set to a value indicating the separation of the currency_symbol, the + sign string, and the value for a nonnegative locally formatted monetary + quantity. ++ char n_sep_by_space +
+ Set to a value indicating the separation of the currency_symbol, the + sign string, and the value for a negative locally formatted monetary + quantity. ++ char p_sign_posn +
+ Set to a value indicating the positioning of the positive_sign for a + nonnegative locally formatted monetary quantity. ++ char n_sign_posn +
+ Set to a value indicating the positioning of the negative_sign for a + negative locally formatted monetary quantity. ++ char *int_curr_symbol +
+ The international currency symbol applicable to the current locale. The + first three characters contain the alphabetic international currency symbol + in accordance with those specified in ISO 4217. The fourth character + (immediately preceding the null character) is the character used to separate + the international currency symbol from the monetary quantity. ++ char int_frac_digits +
+ The number of fractional digits (those after the decimal-point) to be + displayed in an internationally formatted monetary quantity. ++ char int_p_cs_precedes +
+ Set to 1 or 0 if the int_curr_symbol respectively precedes or + succeeds the value for a nonnegative internationally formatted monetary + quantity. ++ char int_n_cs_precedes +
+ Set to 1 or 0 if the int_curr_symbol respectively precedes or + succeeds the value for a negative internationally formatted monetary + quantity. ++ char int_p_sep_by_space + +
+ Set to a value indicating the separation of the int_curr_symbol, the + sign string, and the value for a nonnegative internationally formatted + monetary quantity. ++ char int_n_sep_by_space +
+ Set to a value indicating the separation of the int_curr_symbol, the + sign string, and the value for a negative internationally formatted monetary + quantity. ++ char int_p_sign_posn +
+ Set to a value indicating the positioning of the positive_sign for a + nonnegative internationally formatted monetary quantity. ++ char int_n_sign_posn +
+ Set to a value indicating the positioning of the negative_sign for a + negative internationally formatted monetary quantity. ++
+ The elements of grouping and mon_grouping are interpreted according to the + following: + CHAR_MAX No further grouping is to be performed. + 0 The previous element is to be repeatedly used for the remainder of the +
+ digits. ++ other The integer value is the number of digits that compose the current group. +
+ The next element is examined to determine the size of the next group of + digits before the current group. ++
+ The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space, + and int_n_sep_by_space are interpreted according to the following: + 0 No space separates the currency symbol and value. + 1 If the currency symbol and sign string are adjacent, a space separates them from the +
+ value; otherwise, a space separates the currency symbol from the value. ++ 2 If the currency symbol and sign string are adjacent, a space separates them; +
+ otherwise, a space separates the sign string from the value. ++ For int_p_sep_by_space and int_n_sep_by_space, the fourth character of + int_curr_symbol is used instead of a space. +
+ The values of p_sign_posn, n_sign_posn, int_p_sign_posn, and + int_n_sign_posn are interpreted according to the following: + 0 Parentheses surround the quantity and currency symbol. + 1 The sign string precedes the quantity and currency symbol. + 2 The sign string succeeds the quantity and currency symbol. + 3 The sign string immediately precedes the currency symbol. + 4 The sign string immediately succeeds the currency symbol. + +
+ The implementation shall behave as if no library function calls the localeconv + function. +
+ The localeconv function returns a pointer to the filled-in object. The structure + pointed to by the return value shall not be modified by the program, but may be + overwritten by a subsequent call to the localeconv function. In addition, calls to the + setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may + overwrite the contents of the structure. +
+ EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format + monetary quantities. +
+ Local format International format ++ + Country Positive Negative Positive Negative + + Country1 1.234,56 mk -1.234,56 mk FIM 1.234,56 FIM -1.234,56 + Country2 L.1.234 -L.1.234 ITL 1.234 -ITL 1.234 + Country3 fl. 1.234,56 fl. -1.234,56 NLG 1.234,56 NLG -1.234,56 + Country4 SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56 CHF 1,234.56C +
+ For these four countries, the respective values for the monetary members of the structure returned by + localeconv could be: +
+ Country1 Country2 Country3 Country4 ++ + mon_decimal_point "," "" "," "." + mon_thousands_sep "." "." "." "," + mon_grouping "\3" "\3" "\3" "\3" + positive_sign "" "" "" "" + negative_sign "-" "-" "-" "C" + currency_symbol "mk" "L." "\u0192" "SFrs." + frac_digits 2 0 2 2 + p_cs_precedes 0 1 1 1 + n_cs_precedes 0 1 1 1 + p_sep_by_space 1 0 1 0 + n_sep_by_space 1 0 2 0 + p_sign_posn 1 1 1 1 + n_sign_posn 1 1 4 2 + int_curr_symbol "FIM " "ITL " "NLG " "CHF " + int_frac_digits 2 0 2 2 + int_p_cs_precedes 1 1 1 1 + int_n_cs_precedes 1 1 1 1 + int_p_sep_by_space 1 1 1 1 + int_n_sep_by_space 2 1 2 1 + int_p_sign_posn 1 1 1 1 + int_n_sign_posn 4 1 4 2 + +
+ EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members + affect the formatted value. +
+ p_sep_by_space ++ + p_cs_precedes p_sign_posn 0 1 2 + +
+ 0 0 (1.25$) (1.25 $) (1.25$) + 1 +1.25$ +1.25 $ + 1.25$ + 2 1.25$+ 1.25 $+ 1.25$ + + 3 1.25+$ 1.25 +$ 1.25+ $ + 4 1.25$+ 1.25 $+ 1.25$ + ++ + +
+ 1 0 ($1.25) ($ 1.25) ($1.25) + 1 +$1.25 +$ 1.25 + $1.25 + 2 $1.25+ $ 1.25+ $1.25 + + 3 +$1.25 +$ 1.25 + $1.25 + 4 $+1.25 $+ 1.25 $ +1.25 ++ +
+ The header <math.h> declares two types and many mathematical functions and defines + several macros. Most synopses specify a family of functions consisting of a principal + function with one or more double parameters, a double return value, or both; and + other functions with the same name but with f and l suffixes, which are corresponding + functions with float and long double parameters, return values, or both.223) + Integer arithmetic functions and conversion functions are discussed later. +
+ The types +
+ float_t + double_t ++ are floating types at least as wide as float and double, respectively, and such that + double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0, + float_t and double_t are float and double, respectively; if + FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals + 2, they are both long double; and for other values of FLT_EVAL_METHOD, they are + otherwise implementation-defined.224) +
+ The macro +
+ HUGE_VAL ++ expands to a positive double constant expression, not necessarily representable as a + float. The macros +
+ HUGE_VALF + HUGE_VALL ++ are respectively float and long double analogs of HUGE_VAL.225) +
+ The macro +
+ INFINITY ++ expands to a constant expression of type float representing positive or unsigned + infinity, if available; else to a positive constant of type float that overflows at + + + + + translation time.226) +
+ The macro +
+ NAN ++ is defined if and only if the implementation supports quiet NaNs for the float type. It + expands to a constant expression of type float representing a quiet NaN. +
+ The number classification macros +
+ FP_INFINITE + FP_NAN + FP_NORMAL + FP_SUBNORMAL + FP_ZERO ++ represent the mutually exclusive kinds of floating-point values. They expand to integer + constant expressions with distinct values. Additional implementation-defined floating- + point classifications, with macro definitions beginning with FP_ and an uppercase letter, + may also be specified by the implementation. +
+ The macro +
+ FP_FAST_FMA ++ is optionally defined. If defined, it indicates that the fma function generally executes + about as fast as, or faster than, a multiply and an add of double operands.227) The + macros +
+ FP_FAST_FMAF + FP_FAST_FMAL ++ are, respectively, float and long double analogs of FP_FAST_FMA. If defined, + these macros expand to the integer constant 1. +
+ The macros +
+ FP_ILOGB0 + FP_ILOGBNAN ++ expand to integer constant expressions whose values are returned by ilogb(x) if x is + zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or + -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN. + + + +
+ The macros +
+ MATH_ERRNO + MATH_ERREXCEPT ++ expand to the integer constants 1 and 2, respectively; the macro +
+ math_errhandling ++ expands to an expression that has type int and the value MATH_ERRNO, + MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is + constant for the duration of the program. It is unspecified whether + math_errhandling is a macro or an identifier with external linkage. If a macro + definition is suppressed or a program defines an identifier with the name + math_errhandling, the behavior is undefined. If the expression + math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation + shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in + <fenv.h>. + +
223) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments + and return values in wider format than the synopsis prototype indicates. + +
224) The types float_t and double_t are intended to be the implementation's most efficient types at + least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the + type float_t is the narrowest type used by the implementation to evaluate floating expressions. + +
225) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that + supports infinities. + +
226) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic. + +
227) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented + directly with a hardware multiply-add instruction. Software implementations are expected to be + substantially slower. + + +
+ The behavior of each of the functions in <math.h> is specified for all representable + values of its input arguments, except where stated otherwise. Each function shall execute + as if it were a single operation without raising SIGFPE and without generating any of the + floating-point exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect + the result of the function. +
+ For all functions, a domain error occurs if an input argument is outside the domain over + which the mathematical function is defined. The description of each function lists any + required domain errors; an implementation may define additional domain errors, provided + that such errors are consistent with the mathematical definition of the function.228) On a + domain error, the function returns an implementation-defined value; if the integer + expression math_errhandling & MATH_ERRNO is nonzero, the integer expression + errno acquires the value EDOM; if the integer expression math_errhandling & + MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised. +
+ Similarly, a pole error (also known as a singularity or infinitary) occurs if the + mathematical function has an exact infinite result as the finite input argument(s) are + approached in the limit (for example, log(0.0)). The description of each function lists + any required pole errors; an implementation may define additional pole errors, provided + that such errors are consistent with the mathematical definition of the function. On a pole + error, the function returns an implementation-defined value; if the integer expression + + + + math_errhandling & MATH_ERRNO is nonzero, the integer expression errno + acquires the value ERANGE; if the integer expression math_errhandling & + MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised. +
+ Likewise, a range error occurs if the mathematical result of the function cannot be + represented in an object of the specified type, due to extreme magnitude. +
+ A floating result overflows if the magnitude of the mathematical result is finite but so + large that the mathematical result cannot be represented without extraordinary roundoff + error in an object of the specified type. If a floating result overflows and default rounding + is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or * + HUGE_VALL according to the return type, with the same sign as the correct value of the + function; if the integer expression math_errhandling & MATH_ERRNO is nonzero, + the integer expression errno acquires the value ERANGE; if the integer expression + math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating- + point exception is raised. +
+ The result underflows if the magnitude of the mathematical result is so small that the + mathematical result cannot be represented, without extraordinary roundoff error, in an + object of the specified type.229) If the result underflows, the function returns an + implementation-defined value whose magnitude is no greater than the smallest + normalized positive number in the specified type; if the integer expression + math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the + value ERANGE is implementation-defined; if the integer expression + math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow'' + floating-point exception is raised is implementation-defined. +
+ If a domain, pole, or range error occurs and the integer expression + math_errhandling & MATH_ERRNO is zero,230) then errno shall either be set to + the value corresponding to the error or left unmodified. If no such error occurs, errno + shall be left unmodified regardless of the setting of math_errhandling. + + + + + + +
228) In an implementation that supports infinities, this allows an infinity as an argument to be a domain + error if the mathematical domain of the function does not include the infinity. + +
229) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and + also ''flush-to-zero'' underflow. + +
230) Math errors are being indicated by the floating-point exception flags rather than by errno. + + +
+
+ #include <math.h> + #pragma STDC FP_CONTRACT on-off-switch ++
+ The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the + state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur + either outside external declarations or preceding all explicit declarations and statements + inside a compound statement. When outside external declarations, the pragma takes + effect from its occurrence until another FP_CONTRACT pragma is encountered, or until + the end of the translation unit. When inside a compound statement, the pragma takes + effect from its occurrence until another FP_CONTRACT pragma is encountered + (including within a nested compound statement), or until the end of the compound + statement; at the end of a compound statement the state for the pragma is restored to its + condition just before the compound statement. If this pragma is used in any other + context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is + implementation-defined. + +
+ In the synopses in this subclause, real-floating indicates that the argument shall be an + expression of real floating type. + +
+
+ #include <math.h> + int fpclassify(real-floating x); ++
+ The fpclassify macro classifies its argument value as NaN, infinite, normal, + subnormal, zero, or into another implementation-defined category. First, an argument + represented in a format wider than its semantic type is converted to its semantic type. + Then classification is based on the type of the argument.231) +
+ The fpclassify macro returns the value of the number classification macro + appropriate to the value of its argument. * + + + + +
231) Since an expression can be evaluated with more range and precision than its type has, it is important to + know the type that classification is based on. For example, a normal long double value might + become subnormal when converted to double, and zero when converted to float. + + +
+
+ #include <math.h> + int isfinite(real-floating x); ++
+ The isfinite macro determines whether its argument has a finite value (zero, + subnormal, or normal, and not infinite or NaN). First, an argument represented in a + format wider than its semantic type is converted to its semantic type. Then determination + is based on the type of the argument. +
+ The isfinite macro returns a nonzero value if and only if its argument has a finite + value. + +
+
+ #include <math.h> + int isinf(real-floating x); ++
+ The isinf macro determines whether its argument value is an infinity (positive or + negative). First, an argument represented in a format wider than its semantic type is + converted to its semantic type. Then determination is based on the type of the argument. +
+ The isinf macro returns a nonzero value if and only if its argument has an infinite + value. + +
+
+ #include <math.h> + int isnan(real-floating x); ++
+ The isnan macro determines whether its argument value is a NaN. First, an argument + represented in a format wider than its semantic type is converted to its semantic type. + Then determination is based on the type of the argument.232) + + + +
+ The isnan macro returns a nonzero value if and only if its argument has a NaN value. + +
232) For the isnan macro, the type for determination does not matter unless the implementation supports + NaNs in the evaluation type but not in the semantic type. + + +
+
+ #include <math.h> + int isnormal(real-floating x); ++
+ The isnormal macro determines whether its argument value is normal (neither zero, + subnormal, infinite, nor NaN). First, an argument represented in a format wider than its + semantic type is converted to its semantic type. Then determination is based on the type + of the argument. +
+ The isnormal macro returns a nonzero value if and only if its argument has a normal + value. + +
+
+ #include <math.h> + int signbit(real-floating x); ++
+ The signbit macro determines whether the sign of its argument value is negative.233) +
+ The signbit macro returns a nonzero value if and only if the sign of its argument value + is negative. + + + + + + +
233) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is + unsigned, it is treated as positive. + + +
+
+ #include <math.h> + double acos(double x); + float acosf(float x); + long double acosl(long double x); ++
+ The acos functions compute the principal value of the arc cosine of x. A domain error + occurs for arguments not in the interval [-1, +1]. +
+ The acos functions return arccos x in the interval [0, pi ] radians. + +
+
+ #include <math.h> + double asin(double x); + float asinf(float x); + long double asinl(long double x); ++
+ The asin functions compute the principal value of the arc sine of x. A domain error + occurs for arguments not in the interval [-1, +1]. +
+ The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians. + +
+
+ #include <math.h> + double atan(double x); + float atanf(float x); + long double atanl(long double x); ++
+ The atan functions compute the principal value of the arc tangent of x. + +
+ The atan functions return arctan x in the interval [-pi /2, +pi /2] radians. + +
+
+ #include <math.h> + double atan2(double y, double x); + float atan2f(float y, float x); + long double atan2l(long double y, long double x); ++
+ The atan2 functions compute the value of the arc tangent of y/x, using the signs of both + arguments to determine the quadrant of the return value. A domain error may occur if + both arguments are zero. +
+ The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians. + +
+
+ #include <math.h> + double cos(double x); + float cosf(float x); + long double cosl(long double x); ++
+ The cos functions compute the cosine of x (measured in radians). +
+ The cos functions return cos x. + +
+
+ #include <math.h> + double sin(double x); + float sinf(float x); + long double sinl(long double x); ++
+ The sin functions compute the sine of x (measured in radians). + +
+ The sin functions return sin x. + +
+
+ #include <math.h> + double tan(double x); + float tanf(float x); + long double tanl(long double x); ++
+ The tan functions return the tangent of x (measured in radians). +
+ The tan functions return tan x. + +
+
+ #include <math.h> + double acosh(double x); + float acoshf(float x); + long double acoshl(long double x); ++
+ The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain + error occurs for arguments less than 1. +
+ The acosh functions return arcosh x in the interval [0, +(inf)]. + +
+
+ #include <math.h> + double asinh(double x); + float asinhf(float x); + long double asinhl(long double x); ++
+ The asinh functions compute the arc hyperbolic sine of x. + +
+ The asinh functions return arsinh x. + +
+
+ #include <math.h> + double atanh(double x); + float atanhf(float x); + long double atanhl(long double x); ++
+ The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs + for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals + -1 or +1. +
+ The atanh functions return artanh x. + +
+
+ #include <math.h> + double cosh(double x); + float coshf(float x); + long double coshl(long double x); ++
+ The cosh functions compute the hyperbolic cosine of x. A range error occurs if the + magnitude of x is too large. +
+ The cosh functions return cosh x. + +
+
+ #include <math.h> + double sinh(double x); + float sinhf(float x); + long double sinhl(long double x); ++
+ The sinh functions compute the hyperbolic sine of x. A range error occurs if the + magnitude of x is too large. + +
+ The sinh functions return sinh x. + +
+
+ #include <math.h> + double tanh(double x); + float tanhf(float x); + long double tanhl(long double x); ++
+ The tanh functions compute the hyperbolic tangent of x. +
+ The tanh functions return tanh x. + +
+
+ #include <math.h> + double exp(double x); + float expf(float x); + long double expl(long double x); ++
+ The exp functions compute the base-e exponential of x. A range error occurs if the + magnitude of x is too large. +
+ The exp functions return ex . + +
+
+ #include <math.h> + double exp2(double x); + float exp2f(float x); + long double exp2l(long double x); ++
+ The exp2 functions compute the base-2 exponential of x. A range error occurs if the + magnitude of x is too large. + +
+ The exp2 functions return 2x . + +
+
+ #include <math.h> + double expm1(double x); + float expm1f(float x); + long double expm1l(long double x); ++
+ The expm1 functions compute the base-e exponential of the argument, minus 1. A range + error occurs if x is too large.234) +
+ The expm1 functions return ex - 1. + +
234) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1. + + +
+
+ #include <math.h> + double frexp(double value, int *exp); + float frexpf(float value, int *exp); + long double frexpl(long double value, int *exp); ++
+ The frexp functions break a floating-point number into a normalized fraction and an + integral power of 2. They store the integer in the int object pointed to by exp. +
+ If value is not a floating-point number or if the integral power of 2 is outside the range + of int, the results are unspecified. Otherwise, the frexp functions return the value x, + such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp . + If value is zero, both parts of the result are zero. + + + + + + +
+
+ #include <math.h> + int ilogb(double x); + int ilogbf(float x); + int ilogbl(long double x); ++
+ The ilogb functions extract the exponent of x as a signed int value. If x is zero they + compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is + a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling + the corresponding logb function and casting the returned value to type int. A domain + error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside + the range of the return type, the numeric result is unspecified. +
+ The ilogb functions return the exponent of x as a signed int value. +
Forward references: the logb functions (7.12.6.11). + +
+
+ #include <math.h> + double ldexp(double x, int exp); + float ldexpf(float x, int exp); + long double ldexpl(long double x, int exp); ++
+ The ldexp functions multiply a floating-point number by an integral power of 2. A + range error may occur. +
+ The ldexp functions return x x 2exp . + +
+ +
+ #include <math.h> + double log(double x); + float logf(float x); + long double logl(long double x); ++
+ The log functions compute the base-e (natural) logarithm of x. A domain error occurs if + the argument is negative. A pole error may occur if the argument is zero. +
+ The log functions return loge x. + +
+
+ #include <math.h> + double log10(double x); + float log10f(float x); + long double log10l(long double x); ++
+ The log10 functions compute the base-10 (common) logarithm of x. A domain error + occurs if the argument is negative. A pole error may occur if the argument is zero. +
+ The log10 functions return log10 x. + +
+
+ #include <math.h> + double log1p(double x); + float log1pf(float x); + long double log1pl(long double x); ++
+ The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.235) + A domain error occurs if the argument is less than -1. A pole error may occur if the + argument equals -1. +
+ The log1p functions return loge (1 + x). + + + + + + +
235) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x). + + +
+
+ #include <math.h> + double log2(double x); + float log2f(float x); + long double log2l(long double x); ++
+ The log2 functions compute the base-2 logarithm of x. A domain error occurs if the + argument is less than zero. A pole error may occur if the argument is zero. +
+ The log2 functions return log2 x. + +
+
+ #include <math.h> + double logb(double x); + float logbf(float x); + long double logbl(long double x); ++
+ The logb functions extract the exponent of x, as a signed integer value in floating-point + format. If x is subnormal it is treated as though it were normalized; thus, for positive + finite x, +
+ 1 <= x x FLT_RADIX-logb(x) < FLT_RADIX ++ A domain error or pole error may occur if the argument is zero. +
+ The logb functions return the signed exponent of x. + +
+
+ #include <math.h> + double modf(double value, double *iptr); + float modff(float value, float *iptr); + long double modfl(long double value, long double *iptr); ++
+ The modf functions break the argument value into integral and fractional parts, each of + which has the same type and sign as the argument. They store the integral part (in + + floating-point format) in the object pointed to by iptr. +
+ The modf functions return the signed fractional part of value. + +
+
+ #include <math.h> double scalbn(double x, int n); float scalbnf(float x, int n); long double scalbnl(long double x, int n); double scalbln(double x, long int n); float scalblnf(float x, long int n); long double scalblnl(long double x, long int n); ++
+ The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not + normally by computing FLT_RADIXn explicitly. A range error may occur. +
+ The scalbn and scalbln functions return x x FLT_RADIXn . + +
+
+ #include <math.h> double cbrt(double x); - -[page 477] (Contents) - - float cbrtf(float x); - long double cbrtl(long double x); - double fabs(double x); - float fabsf(float x); - long double fabsl(long double x); - double hypot(double x, double y); - float hypotf(float x, float y); - long double hypotl(long double x, long double y); - double pow(double x, double y); - float powf(float x, float y); - long double powl(long double x, long double y); - double sqrt(double x); - float sqrtf(float x); - long double sqrtl(long double x); - double erf(double x); - float erff(float x); - long double erfl(long double x); - double erfc(double x); - float erfcf(float x); - long double erfcl(long double x); - double lgamma(double x); - float lgammaf(float x); - long double lgammal(long double x); - double tgamma(double x); - float tgammaf(float x); - long double tgammal(long double x); - double ceil(double x); - float ceilf(float x); - long double ceill(long double x); - double floor(double x); - float floorf(float x); - long double floorl(long double x); - double nearbyint(double x); - float nearbyintf(float x); - long double nearbyintl(long double x); - double rint(double x); - float rintf(float x); - long double rintl(long double x); - long int lrint(double x); - long int lrintf(float x); - long int lrintl(long double x); - -[page 478] (Contents) - - long long int llrint(double x); - long long int llrintf(float x); - long long int llrintl(long double x); + float cbrtf(float x); + long double cbrtl(long double x); ++
+ The cbrt functions compute the real cube root of x. +
+ The cbrt functions return x1/3 . + + +
+
+ #include <math.h> + double fabs(double x); + float fabsf(float x); + long double fabsl(long double x); ++
+ The fabs functions compute the absolute value of a floating-point number x. +
+ The fabs functions return | x |. + +
+
+ #include <math.h> + double hypot(double x, double y); + float hypotf(float x, float y); + long double hypotl(long double x, long double y); ++
+ The hypot functions compute the square root of the sum of the squares of x and y, + without undue overflow or underflow. A range error may occur. +
+
+ The hypot functions return (sqrt)x2 + y2 . +
+ - + ----- ++ +
+
+ #include <math.h> + double pow(double x, double y); + float powf(float x, float y); + long double powl(long double x, long double y); ++
+ The pow functions compute x raised to the power y. A domain error occurs if x is finite + and negative and y is finite and not an integer value. A range error may occur. A domain + error may occur if x is zero and y is zero. A domain error or pole error may occur if x is + zero and y is less than zero. + +
+ The pow functions return xy . + +
+
+ #include <math.h> + double sqrt(double x); + float sqrtf(float x); + long double sqrtl(long double x); ++
+ The sqrt functions compute the nonnegative square root of x. A domain error occurs if + the argument is less than zero. +
+ The sqrt functions return (sqrt)x. +
+ - + - ++ +
+
+ #include <math.h> + double erf(double x); + float erff(float x); + long double erfl(long double x); ++
+ The erf functions compute the error function of x. +
+
+ 2 x + (integral) e-t dt. + 2 ++ The erf functions return erf x = +
+ (sqrt)pi + - + - 0 ++ + +
+
+ #include <math.h> + double erfc(double x); + float erfcf(float x); + long double erfcl(long double x); ++
+ The erfc functions compute the complementary error function of x. A range error + occurs if x is too large. + +
+
+ 2 (inf) + (integral) e-t dt. + 2 ++ The erfc functions return erfc x = 1 - erf x = +
+ (sqrt)pi + - + - x ++ + +
+
+ #include <math.h> + double lgamma(double x); + float lgammaf(float x); + long double lgammal(long double x); ++
+ The lgamma functions compute the natural logarithm of the absolute value of gamma of + x. A range error occurs if x is too large. A pole error may occur if x is a negative integer + or zero. +
+ The lgamma functions return loge | (Gamma)(x) |. + +
+
+ #include <math.h> + double tgamma(double x); + float tgammaf(float x); + long double tgammal(long double x); ++
+ The tgamma functions compute the gamma function of x. A domain error or pole error + may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is + too large and may occur if the magnitude of x is too small. +
+ The tgamma functions return (Gamma)(x). + + +
+
+ #include <math.h> + double ceil(double x); + float ceilf(float x); + long double ceill(long double x); ++
+ The ceil functions compute the smallest integer value not less than x. +
+ The ceil functions return [^x^], expressed as a floating-point number. + +
+
+ #include <math.h> + double floor(double x); + float floorf(float x); + long double floorl(long double x); ++
+ The floor functions compute the largest integer value not greater than x. +
+ The floor functions return [_x_], expressed as a floating-point number. + +
+
+ #include <math.h> + double nearbyint(double x); + float nearbyintf(float x); + long double nearbyintl(long double x); ++
+ The nearbyint functions round their argument to an integer value in floating-point + format, using the current rounding direction and without raising the ''inexact'' floating- + point exception. + +
+ The nearbyint functions return the rounded integer value. + +
+
+ #include <math.h> + double rint(double x); + float rintf(float x); + long double rintl(long double x); ++
+ The rint functions differ from the nearbyint functions (7.12.9.3) only in that the + rint functions may raise the ''inexact'' floating-point exception if the result differs in + value from the argument. +
+ The rint functions return the rounded integer value. + +
+
+ #include <math.h> + long int lrint(double x); + long int lrintf(float x); + long int lrintl(long double x); + long long int llrint(double x); + long long int llrintf(float x); + long long int llrintl(long double x); ++
+ The lrint and llrint functions round their argument to the nearest integer value, + rounding according to the current rounding direction. If the rounded value is outside the + range of the return type, the numeric result is unspecified and a domain error or range + error may occur. +
+ The lrint and llrint functions return the rounded integer value. + + +
+
+ #include <math.h> double round(double x); float roundf(float x); long double roundl(long double x); ++
+ The round functions round their argument to the nearest integer value in floating-point + format, rounding halfway cases away from zero, regardless of the current rounding + direction. +
+ The round functions return the rounded integer value. + +
+
+ #include <math.h> long int lround(double x); long int lroundf(float x); long int lroundl(long double x); long long int llround(double x); long long int llroundf(float x); long long int llroundl(long double x); ++
+ The lround and llround functions round their argument to the nearest integer value, + rounding halfway cases away from zero, regardless of the current rounding direction. If + the rounded value is outside the range of the return type, the numeric result is unspecified + and a domain error or range error may occur. +
+ The lround and llround functions return the rounded integer value. + +
+ +
+ #include <math.h> double trunc(double x); float truncf(float x); long double truncl(long double x); - double fmod(double x, double y); - float fmodf(float x, float y); - long double fmodl(long double x, long double y); - double remainder(double x, double y); - float remainderf(float x, float y); - long double remainderl(long double x, long double y); ++
+ The trunc functions round their argument to the integer value, in floating format, + nearest to but no larger in magnitude than the argument. +
+ The trunc functions return the truncated integer value. + +
+
+ #include <math.h> + double fmod(double x, double y); + float fmodf(float x, float y); + long double fmodl(long double x, long double y); ++
+ The fmod functions compute the floating-point remainder of x/y. +
+ The fmod functions return the value x - ny, for some integer n such that, if y is nonzero, + the result has the same sign as x and magnitude less than the magnitude of y. If y is zero, + whether a domain error occurs or the fmod functions return zero is implementation- + defined. + +
+
+ #include <math.h> + double remainder(double x, double y); + float remainderf(float x, float y); + long double remainderl(long double x, long double y); ++
+ The remainder functions compute the remainder x REM y required by IEC 60559.236) + + + + + +
+ The remainder functions return x REM y. If y is zero, whether a domain error occurs + or the functions return zero is implementation defined. + +
236) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the + mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever + | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for * + all implementations. + + +
+
+ #include <math.h> double remquo(double x, double y, int *quo); float remquof(float x, float y, int *quo); long double remquol(long double x, long double y, int *quo); ++
+ The remquo functions compute the same remainder as the remainder functions. In + the object pointed to by quo they store a value whose sign is the sign of x/y and whose + magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where + n is an implementation-defined integer greater than or equal to 3. +
+ The remquo functions return x REM y. If y is zero, the value stored in the object + pointed to by quo is unspecified and whether a domain error occurs or the functions + return zero is implementation defined. + +
+
+ #include <math.h> double copysign(double x, double y); float copysignf(float x, float y); long double copysignl(long double x, long double y); - double nan(const char *tagp); - float nanf(const char *tagp); - long double nanl(const char *tagp); - double nextafter(double x, double y); - float nextafterf(float x, float y); - long double nextafterl(long double x, long double y); - double nexttoward(double x, long double y); - float nexttowardf(float x, long double y); - long double nexttowardl(long double x, long double y); - double fdim(double x, double y); - float fdimf(float x, float y); - long double fdiml(long double x, long double y); - double fmax(double x, double y); - -[page 479] (Contents) - - float fmaxf(float x, float y); - long double fmaxl(long double x, long double y); - double fmin(double x, double y); - float fminf(float x, float y); - long double fminl(long double x, long double y); - double fma(double x, double y, double z); - float fmaf(float x, float y, float z); - long double fmal(long double x, long double y, - long double z); - int isgreater(real-floating x, real-floating y); - int isgreaterequal(real-floating x, real-floating y); - int isless(real-floating x, real-floating y); - int islessequal(real-floating x, real-floating y); - int islessgreater(real-floating x, real-floating y); - int isunordered(real-floating x, real-floating y); -B.12 Nonlocal jumps <setjmp.h> - jmp_buf - int setjmp(jmp_buf env); - _Noreturn void longjmp(jmp_buf env, int val); -B.13 Signal handling <signal.h> - sig_atomic_t SIG_IGN SIGILL SIGTERM - SIG_DFL SIGABRT SIGINT - SIG_ERR SIGFPE SIGSEGV - void (*signal(int sig, void (*func)(int)))(int); - int raise(int sig); - - - - -[page 480] (Contents) - -B.14 Alignment <stdalign.h> - alignas - __alignas_is_defined -B.15 Variable arguments <stdarg.h> - va_list - type va_arg(va_list ap, type); - void va_copy(va_list dest, va_list src); - void va_end(va_list ap); - void va_start(va_list ap, parmN); -B.16 Atomics <stdatomic.h> - ATOMIC_CHAR_LOCK_FREE atomic_uint - ATOMIC_CHAR16_T_LOCK_FREE atomic_long - ATOMIC_CHAR32_T_LOCK_FREE atomic_ulong - ATOMIC_WCHAR_T_LOCK_FREE atomic_llong - ATOMIC_SHORT_LOCK_FREE atomic_ullong - ATOMIC_INT_LOCK_FREE atomic_char16_t - ATOMIC_LONG_LOCK_FREE atomic_char32_t - ATOMIC_LLONG_LOCK_FREE atomic_wchar_t - ATOMIC_ADDRESS_LOCK_FREE atomic_int_least8_t - ATOMIC_FLAG_INIT atomic_uint_least8_t - memory_order atomic_int_least16_t - atomic_flag atomic_uint_least16_t - atomic_bool atomic_int_least32_t - atomic_address atomic_uint_least32_t - memory_order_relaxed atomic_int_least64_t - memory_order_consume atomic_uint_least64_t - memory_order_acquire atomic_int_fast8_t - memory_order_release atomic_uint_fast8_t - memory_order_acq_rel atomic_int_fast16_t - memory_order_seq_cst atomic_uint_fast16_t - atomic_char atomic_int_fast32_t - atomic_schar atomic_uint_fast32_t - atomic_uchar atomic_int_fast64_t - atomic_short atomic_uint_fast64_t - atomic_ushort atomic_intptr_t - atomic_int atomic_uintptr_t - - - -[page 481] (Contents) - - atomic_size_t atomic_intmax_t - atomic_ptrdiff_t atomic_uintmax_t - #define ATOMIC_VAR_INIT(C value) - void atomic_init(volatile A *obj, C value); - type kill_dependency(type y); - void atomic_thread_fence(memory_order order); - void atomic_signal_fence(memory_order order); - _Bool atomic_is_lock_free(atomic_type const volatile *obj); - void atomic_store(volatile A *object, C desired); - void atomic_store_explicit(volatile A *object, - C desired, memory_order order); - C atomic_load(volatile A *object); - C atomic_load_explicit(volatile A *object, - memory_order order); - C atomic_exchange(volatile A *object, C desired); - C atomic_exchange_explicit(volatile A *object, - C desired, memory_order order); - _Bool atomic_compare_exchange_strong(volatile A *object, - C *expected, C desired); - _Bool atomic_compare_exchange_strong_explicit( - volatile A *object, C *expected, C desired, - memory_order success, memory_order failure); - _Bool atomic_compare_exchange_weak(volatile A *object, - C *expected, C desired); - _Bool atomic_compare_exchange_weak_explicit( - volatile A *object, C *expected, C desired, - memory_order success, memory_order failure); - C atomic_fetch_key(volatile A *object, M operand); - C atomic_fetch_key_explicit(volatile A *object, - M operand, memory_order order); - bool atomic_flag_test_and_set( - volatile atomic_flag *object); - bool atomic_flag_test_and_set_explicit( - volatile atomic_flag *object, memory_order order); - void atomic_flag_clear(volatile atomic_flag *object); - void atomic_flag_clear_explicit( - volatile atomic_flag *object, memory_order order); - - - - -[page 482] (Contents) - -B.17 Boolean type and values <stdbool.h> - bool - true - false - __bool_true_false_are_defined -B.18 Common definitions <stddef.h> - ptrdiff_t max_align_t NULL - size_t wchar_t - offsetof(type, member-designator) - __STDC_WANT_LIB_EXT1__ - rsize_t -B.19 Integer types <stdint.h> - intN_t INT_LEASTN_MIN PTRDIFF_MAX - uintN_t INT_LEASTN_MAX SIG_ATOMIC_MIN - int_leastN_t UINT_LEASTN_MAX SIG_ATOMIC_MAX - uint_leastN_t INT_FASTN_MIN SIZE_MAX - int_fastN_t INT_FASTN_MAX WCHAR_MIN - uint_fastN_t UINT_FASTN_MAX WCHAR_MAX - intptr_t INTPTR_MIN WINT_MIN - uintptr_t INTPTR_MAX WINT_MAX - intmax_t UINTPTR_MAX INTN_C(value) - uintmax_t INTMAX_MIN UINTN_C(value) - INTN_MIN INTMAX_MAX INTMAX_C(value) - INTN_MAX UINTMAX_MAX UINTMAX_C(value) - UINTN_MAX PTRDIFF_MIN - __STDC_WANT_LIB_EXT1__ - RSIZE_MAX - - - - -[page 483] (Contents) - -B.20 Input/output <stdio.h> - size_t _IOLBF FILENAME_MAX TMP_MAX - FILE _IONBF L_tmpnam stderr - fpos_t BUFSIZ SEEK_CUR stdin - NULL EOF SEEK_END stdout - _IOFBF FOPEN_MAX SEEK_SET - int remove(const char *filename); - int rename(const char *old, const char *new); - FILE *tmpfile(void); - char *tmpnam(char *s); - int fclose(FILE *stream); - int fflush(FILE *stream); - FILE *fopen(const char * restrict filename, - const char * restrict mode); - FILE *freopen(const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - void setbuf(FILE * restrict stream, - char * restrict buf); - int setvbuf(FILE * restrict stream, - char * restrict buf, - int mode, size_t size); - int fprintf(FILE * restrict stream, - const char * restrict format, ...); - int fscanf(FILE * restrict stream, - const char * restrict format, ...); - int printf(const char * restrict format, ...); - int scanf(const char * restrict format, ...); - int snprintf(char * restrict s, size_t n, - const char * restrict format, ...); - int sprintf(char * restrict s, - const char * restrict format, ...); - int sscanf(const char * restrict s, - const char * restrict format, ...); - int vfprintf(FILE * restrict stream, - const char * restrict format, va_list arg); - int vfscanf(FILE * restrict stream, - const char * restrict format, va_list arg); - int vprintf(const char * restrict format, va_list arg); - int vscanf(const char * restrict format, va_list arg); - -[page 484] (Contents) - ++
+ The copysign functions produce a value with the magnitude of x and the sign of y. + They produce a NaN (with the sign of y) if x is a NaN. On implementations that + represent a signed zero but do not treat negative zero consistently in arithmetic + operations, the copysign functions regard the sign of zero as positive. +
+ The copysign functions return a value with the magnitude of x and the sign of y. + + +
+
+ #include <math.h> + double nan(const char *tagp); + float nanf(const char *tagp); + long double nanl(const char *tagp); ++
+ The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char- + sequence)", (char**) NULL); the call nan("") is equivalent to + strtod("NAN()", (char**) NULL). If tagp does not point to an n-char + sequence or an empty string, the call is equivalent to strtod("NAN", (char**) + NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof + and strtold. +
+ The nan functions return a quiet NaN, if available, with content indicated through tagp. + If the implementation does not support quiet NaNs, the functions return zero. +
Forward references: the strtod, strtof, and strtold functions (7.22.1.3). + +
+
+ #include <math.h> + double nextafter(double x, double y); + float nextafterf(float x, float y); + long double nextafterl(long double x, long double y); ++
+ The nextafter functions determine the next representable value, in the type of the + function, after x in the direction of y, where x and y are first converted to the type of the + function.237) The nextafter functions return y if x equals y. A range error may occur + if the magnitude of x is the largest finite value representable in the type and the result is + infinite or not representable in the type. +
+ The nextafter functions return the next representable value in the specified format + after x in the direction of y. + + + + +
237) The argument values are converted to the type of the function, even by a macro implementation of the + function. + + +
+
+ #include <math.h> + double nexttoward(double x, long double y); + float nexttowardf(float x, long double y); + long double nexttowardl(long double x, long double y); ++
+ The nexttoward functions are equivalent to the nextafter functions except that the + second parameter has type long double and the functions return y converted to the + type of the function if x equals y.238) + +
238) The result of the nexttoward functions is determined in the type of the function, without loss of + range or precision in a floating second argument. + + +
+
+ #include <math.h> + double fdim(double x, double y); + float fdimf(float x, float y); + long double fdiml(long double x, long double y); ++
+ The fdim functions determine the positive difference between their arguments: +
+ {x - y if x > y
+ {
+ {+0 if x <= y
+
+ A range error may occur.
++ The fdim functions return the positive difference value. + +
+
+ #include <math.h> + double fmax(double x, double y); + float fmaxf(float x, float y); + long double fmaxl(long double x, long double y); ++ + + + +
+ The fmax functions determine the maximum numeric value of their arguments.239) +
+ The fmax functions return the maximum numeric value of their arguments. + +
239) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the + fmax functions choose the numeric value. See F.10.9.2. + + +
+
+ #include <math.h> + double fmin(double x, double y); + float fminf(float x, float y); + long double fminl(long double x, long double y); ++
+ The fmin functions determine the minimum numeric value of their arguments.240) +
+ The fmin functions return the minimum numeric value of their arguments. + +
240) The fmin functions are analogous to the fmax functions in their treatment of NaNs. + + +
+
+ #include <math.h> + double fma(double x, double y, double z); + float fmaf(float x, float y, float z); + long double fmal(long double x, long double y, + long double z); ++
+ The fma functions compute (x x y) + z, rounded as one ternary operation: they compute + the value (as if) to infinite precision and round once to the result format, according to the + current rounding mode. A range error may occur. +
+ The fma functions return (x x y) + z, rounded as one ternary operation. + + + + + + +
+ The relational and equality operators support the usual mathematical relationships + between numeric values. For any ordered pair of numeric values exactly one of the + relationships -- less, greater, and equal -- is true. Relational operators may raise the + ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a + numeric value, or for two NaNs, just the unordered relationship is true.241) The following + subclauses provide macros that are quiet (non floating-point exception raising) versions + of the relational operators, and other comparison macros that facilitate writing efficient + code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In + the synopses in this subclause, real-floating indicates that the argument shall be an + expression of real floating type242) (both arguments need not have the same type).243) + +
241) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if + the operands compare unordered, as an error indicator for programs written without consideration of + NaNs; the result in these cases is false. + +
242) If any argument is of integer type, or any other type that is not a real floating type, the behavior is + undefined. + +
243) Whether an argument represented in a format wider than its semantic type is converted to the semantic + type is unspecified. + + +
+
+ #include <math.h> + int isgreater(real-floating x, real-floating y); ++
+ The isgreater macro determines whether its first argument is greater than its second + argument. The value of isgreater(x, y) is always equal to (x) > (y); however, + unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point + exception when x and y are unordered. +
+ The isgreater macro returns the value of (x) > (y). + +
+
+ #include <math.h> + int isgreaterequal(real-floating x, real-floating y); ++ + + + + +
+ The isgreaterequal macro determines whether its first argument is greater than or + equal to its second argument. The value of isgreaterequal(x, y) is always equal + to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does + not raise the ''invalid'' floating-point exception when x and y are unordered. +
+ The isgreaterequal macro returns the value of (x) >= (y). + +
+
+ #include <math.h> + int isless(real-floating x, real-floating y); ++
+ The isless macro determines whether its first argument is less than its second + argument. The value of isless(x, y) is always equal to (x) < (y); however, + unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point + exception when x and y are unordered. +
+ The isless macro returns the value of (x) < (y). + +
+
+ #include <math.h> + int islessequal(real-floating x, real-floating y); ++
+ The islessequal macro determines whether its first argument is less than or equal to + its second argument. The value of islessequal(x, y) is always equal to + (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise + the ''invalid'' floating-point exception when x and y are unordered. +
+ The islessequal macro returns the value of (x) <= (y). + + +
+
+ #include <math.h> + int islessgreater(real-floating x, real-floating y); ++
+ The islessgreater macro determines whether its first argument is less than or + greater than its second argument. The islessgreater(x, y) macro is similar to + (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise + the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x + and y twice). +
+ The islessgreater macro returns the value of (x) < (y) || (x) > (y). + +
+
+ #include <math.h> + int isunordered(real-floating x, real-floating y); ++
+ The isunordered macro determines whether its arguments are unordered. +
+ The isunordered macro returns 1 if its arguments are unordered and 0 otherwise. + + +
+ The header <setjmp.h> defines the macro setjmp, and declares one function and + one type, for bypassing the normal function call and return discipline.244) +
+ The type declared is +
+ jmp_buf ++ which is an array type suitable for holding the information needed to restore a calling + environment. The environment of a call to the setjmp macro consists of information + sufficient for a call to the longjmp function to return execution to the correct block and + invocation of that block, were it called recursively. It does not include the state of the + floating-point status flags, of open files, or of any other component of the abstract + machine. +
+ It is unspecified whether setjmp is a macro or an identifier declared with external + linkage. If a macro definition is suppressed in order to access an actual function, or a + program defines an external identifier with the name setjmp, the behavior is undefined. + +
244) These functions are useful for dealing with unusual conditions encountered in a low-level function of + a program. + + +
+
+ #include <setjmp.h> + int setjmp(jmp_buf env); ++
+ The setjmp macro saves its calling environment in its jmp_buf argument for later use + by the longjmp function. +
+ If the return is from a direct invocation, the setjmp macro returns the value zero. If the + return is from a call to the longjmp function, the setjmp macro returns a nonzero + value. +
+ An invocation of the setjmp macro shall appear only in one of the following contexts: +
+ If the invocation appears in any other context, the behavior is undefined. + +
+
+ #include <setjmp.h> + _Noreturn void longjmp(jmp_buf env, int val); ++
+ The longjmp function restores the environment saved by the most recent invocation of + the setjmp macro in the same invocation of the program with the corresponding + jmp_buf argument. If there has been no such invocation, or if the function containing + the invocation of the setjmp macro has terminated execution245) in the interim, or if the + invocation of the setjmp macro was within the scope of an identifier with variably + modified type and execution has left that scope in the interim, the behavior is undefined. +
+ All accessible objects have values, and all other components of the abstract machine246) + have state, as of the time the longjmp function was called, except that the values of + objects of automatic storage duration that are local to the function containing the + invocation of the corresponding setjmp macro that do not have volatile-qualified type + and have been changed between the setjmp invocation and longjmp call are + indeterminate. +
+ After longjmp is completed, program execution continues as if the corresponding + invocation of the setjmp macro had just returned the value specified by val. The + longjmp function cannot cause the setjmp macro to return the value 0; if val is 0, + the setjmp macro returns the value 1. +
+ EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation + might cause memory associated with a variable length array object to be squandered. + + + + + + +
+ #include <setjmp.h> + jmp_buf buf; + void g(int n); + void h(int n); + int n = 6; + void f(void) + { + int x[n]; // valid: f is not terminated + setjmp(buf); + g(n); + } + void g(int n) + { + int a[n]; // a may remain allocated + h(n); + } + void h(int n) + { + int b[n]; // b may remain allocated + longjmp(buf, 2); // might cause memory loss + } ++ +
245) For example, by executing a return statement or because another longjmp call has caused a + transfer to a setjmp invocation in a function earlier in the set of nested calls. + +
246) This includes, but is not limited to, the floating-point status flags and the state of open files. + + +
+ The header <signal.h> declares a type and two functions and defines several macros, + for handling various signals (conditions that may be reported during program execution). +
+ The type defined is +
+ sig_atomic_t ++ which is the (possibly volatile-qualified) integer type of an object that can be accessed as + an atomic entity, even in the presence of asynchronous interrupts. +
+ The macros defined are +
+ SIG_DFL + SIG_ERR + SIG_IGN ++ which expand to constant expressions with distinct values that have type compatible with + the second argument to, and the return value of, the signal function, and whose values + compare unequal to the address of any declarable function; and the following, which + expand to positive integer constant expressions with type int and distinct values that are + the signal numbers, each corresponding to the specified condition: +
+ SIGABRT abnormal termination, such as is initiated by the abort function + SIGFPE an erroneous arithmetic operation, such as zero divide or an operation + resulting in overflow + SIGILL detection of an invalid function image, such as an invalid instruction + SIGINT receipt of an interactive attention signal + SIGSEGV an invalid access to storage + SIGTERM a termination request sent to the program ++
+ An implementation need not generate any of these signals, except as a result of explicit + calls to the raise function. Additional signals and pointers to undeclarable functions, + with macro definitions beginning, respectively, with the letters SIG and an uppercase + letter or with SIG_ and an uppercase letter,247) may also be specified by the + implementation. The complete set of signals, their semantics, and their default handling + is implementation-defined; all signal numbers shall be positive. + + + + + + +
247) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms + (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation, + and termination. + + +
+
+ #include <signal.h> + void (*signal(int sig, void (*func)(int)))(int); ++
+ The signal function chooses one of three ways in which receipt of the signal number + sig is to be subsequently handled. If the value of func is SIG_DFL, default handling + for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored. + Otherwise, func shall point to a function to be called when that signal occurs. An + invocation of such a function because of a signal, or (recursively) of any further functions + called by that invocation (other than functions in the standard library),248) is called a + signal handler. +
+ When a signal occurs and func points to a function, it is implementation-defined + whether the equivalent of signal(sig, SIG_DFL); is executed or the + implementation prevents some implementation-defined set of signals (at least including + sig) from occurring until the current signal handling has completed; in the case of + SIGILL, the implementation may alternatively define that no action is taken. Then the + equivalent of (*func)(sig); is executed. If and when the function returns, if the + value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined + value corresponding to a computational exception, the behavior is undefined; otherwise + the program will resume execution at the point it was interrupted. +
+ If the signal occurs as the result of calling the abort or raise function, the signal + handler shall not call the raise function. +
+ If the signal occurs other than as the result of calling the abort or raise function, the + behavior is undefined if the signal handler refers to any object with static or thread + storage duration that is not a lock-free atomic object other than by assigning a value to an + object declared as volatile sig_atomic_t, or the signal handler calls any function + in the standard library other than the abort function, the _Exit function, the + quick_exit function, or the signal function with the first argument equal to the + signal number corresponding to the signal that caused the invocation of the handler. + Furthermore, if such a call to the signal function results in a SIG_ERR return, the + value of errno is indeterminate.249) + + + +
+ At program startup, the equivalent of +
+ signal(sig, SIG_IGN); ++ may be executed for some signals selected in an implementation-defined manner; the + equivalent of +
+ signal(sig, SIG_DFL); ++ is executed for all other signals defined by the implementation. +
+ The implementation shall behave as if no library function calls the signal function. +
+ If the request can be honored, the signal function returns the value of func for the + most recent successful call to signal for the specified signal sig. Otherwise, a value of + SIG_ERR is returned and a positive value is stored in errno. +
Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the + _Exit function (7.22.4.5), the quick_exit function (7.22.4.7). + +
248) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler + called via the abort function). + +
249) If any signal is generated by an asynchronous signal handler, the behavior is undefined. + + +
+
+ #include <signal.h> + int raise(int sig); ++
+ The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a + signal handler is called, the raise function shall not return until after the signal handler + does. +
+ The raise function returns zero if successful, nonzero if unsuccessful. + + +
+ The header <stdalign.h> defines two macros. +
+ The macro +
+ alignas ++ expands to _Alignas. +
+ The remaining macro is suitable for use in #if preprocessing directives. It is +
+ __alignas_is_defined ++ which expands to the integer constant 1. + + +
+ The header <stdarg.h> declares a type and defines four macros, for advancing + through a list of arguments whose number and types are not known to the called function + when it is translated. +
+ A function may be called with a variable number of arguments of varying types. As + described in 6.9.1, its parameter list contains one or more parameters. The rightmost + parameter plays a special role in the access mechanism, and will be designated parmN in + this description. +
+ The type declared is +
+ va_list ++ which is a complete object type suitable for holding information needed by the macros + va_start, va_arg, va_end, and va_copy. If access to the varying arguments is + desired, the called function shall declare an object (generally referred to as ap in this + subclause) having type va_list. The object ap may be passed as an argument to + another function; if that function invokes the va_arg macro with parameter ap, the + value of ap in the calling function is indeterminate and shall be passed to the va_end + macro prior to any further reference to ap.250) + +
250) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which + case the original function may make further use of the original list after the other function returns. + + +
+ The va_start and va_arg macros described in this subclause shall be implemented + as macros, not functions. It is unspecified whether va_copy and va_end are macros or + identifiers declared with external linkage. If a macro definition is suppressed in order to + access an actual function, or a program defines an external identifier with the same name, + the behavior is undefined. Each invocation of the va_start and va_copy macros + shall be matched by a corresponding invocation of the va_end macro in the same + function. + +
+
+ #include <stdarg.h> + type va_arg(va_list ap, type); ++
+ The va_arg macro expands to an expression that has the specified type and the value of + the next argument in the call. The parameter ap shall have been initialized by the + va_start or va_copy macro (without an intervening invocation of the va_end + + + macro for the same ap). Each invocation of the va_arg macro modifies ap so that the + values of successive arguments are returned in turn. The parameter type shall be a type + name specified such that the type of a pointer to an object that has the specified type can + be obtained simply by postfixing a * to type. If there is no actual next argument, or if + type is not compatible with the type of the actual next argument (as promoted according + to the default argument promotions), the behavior is undefined, except for the following + cases: +
+ The first invocation of the va_arg macro after that of the va_start macro returns the + value of the argument after that specified by parmN . Successive invocations return the + values of the remaining arguments in succession. + +
+
+ #include <stdarg.h> + void va_copy(va_list dest, va_list src); ++
+ The va_copy macro initializes dest as a copy of src, as if the va_start macro had + been applied to dest followed by the same sequence of uses of the va_arg macro as + had previously been used to reach the present state of src. Neither the va_copy nor + va_start macro shall be invoked to reinitialize dest without an intervening + invocation of the va_end macro for the same dest. +
+ The va_copy macro returns no value. + +
+
+ #include <stdarg.h> + void va_end(va_list ap); ++
+ The va_end macro facilitates a normal return from the function whose variable + argument list was referred to by the expansion of the va_start macro, or the function + containing the expansion of the va_copy macro, that initialized the va_list ap. The + va_end macro may modify ap so that it is no longer usable (without being reinitialized + + by the va_start or va_copy macro). If there is no corresponding invocation of the + va_start or va_copy macro, or if the va_end macro is not invoked before the + return, the behavior is undefined. +
+ The va_end macro returns no value. + +
+
+ #include <stdarg.h> + void va_start(va_list ap, parmN); ++
+ The va_start macro shall be invoked before any access to the unnamed arguments. +
+ The va_start macro initializes ap for subsequent use by the va_arg and va_end + macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap + without an intervening invocation of the va_end macro for the same ap. +
+ The parameter parmN is the identifier of the rightmost parameter in the variable + parameter list in the function definition (the one just before the , ...). If the parameter + parmN is declared with the register storage class, with a function or array type, or + with a type that is not compatible with the type that results after application of the default + argument promotions, the behavior is undefined. +
+ The va_start macro returns no value. +
+ EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not + more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of + pointers is specified by the first argument to f1. + +
+ #include <stdarg.h> + #define MAXARGS 31 + void f1(int n_ptrs, ...) + { + va_list ap; + char *array[MAXARGS]; + int ptr_no = 0; + if (n_ptrs > MAXARGS) + n_ptrs = MAXARGS; + va_start(ap, n_ptrs); + while (ptr_no < n_ptrs) + array[ptr_no++] = va_arg(ap, char *); + va_end(ap); + f2(n_ptrs, array); + } ++ Each call to f1 is required to have visible the definition of the function or a declaration such as +
+ void f1(int, ...); ++ +
+ EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the + indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list + is gathered again and passed to function f4. + +
+ #include <stdarg.h> + #define MAXARGS 31 + void f3(int n_ptrs, int f4_after, ...) + { + va_list ap, ap_save; + char *array[MAXARGS]; + int ptr_no = 0; + if (n_ptrs > MAXARGS) + n_ptrs = MAXARGS; + va_start(ap, f4_after); + while (ptr_no < n_ptrs) { + array[ptr_no++] = va_arg(ap, char *); + if (ptr_no == f4_after) + va_copy(ap_save, ap); + } + va_end(ap); + f2(n_ptrs, array); + // Now process the saved copy. + n_ptrs -= f4_after; + ptr_no = 0; + while (ptr_no < n_ptrs) + array[ptr_no++] = va_arg(ap_save, char *); + va_end(ap_save); + f4(n_ptrs, array); + } ++ +
+ The header <stdatomic.h> defines several macros and declares several types and + functions for performing atomic operations on data shared between threads. +
+ Implementations that define the macro __STDC_NO_THREADS__ need not provide + this header nor support any of its facilities. +
+ The macros defined are the atomic lock-free macros +
+ ATOMIC_CHAR_LOCK_FREE + ATOMIC_CHAR16_T_LOCK_FREE + ATOMIC_CHAR32_T_LOCK_FREE + ATOMIC_WCHAR_T_LOCK_FREE + ATOMIC_SHORT_LOCK_FREE + ATOMIC_INT_LOCK_FREE + ATOMIC_LONG_LOCK_FREE + ATOMIC_LLONG_LOCK_FREE + ATOMIC_ADDRESS_LOCK_FREE ++ which indicate the lock-free property of the corresponding atomic types (both signed and + unsigned); and +
+ ATOMIC_FLAG_INIT ++ which expands to an initializer for an object of type atomic_flag. +
+ The types include +
+ memory_order ++ which is an enumerated type whose enumerators identify memory ordering constraints; +
+ atomic_flag ++ which is a structure type representing a lock-free, primitive atomic flag; +
+ atomic_bool ++ which is a structure type representing the atomic analog of the type _Bool; +
+ atomic_address ++ which is a structure type representing the atomic analog of a pointer type; and several + atomic analogs of integer types. +
+ In the following operation definitions: +
+ NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not + changed in the standard. This qualification means that volatility is preserved when applying these + operations to volatile objects. + + +
+
+ #include <stdatomic.h> + #define ATOMIC_VAR_INIT(C value) ++
+ The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an + atomic object of a type that is initialization-compatible with value. An atomic object + with automatic storage duration that is not explicitly initialized using + ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero) + initialization for objects with static or thread-local storage duration is guaranteed to + produce a valid state. +
+ Concurrent access to the variable being initialized, even via an atomic operation, + constitutes a data race. +
+ EXAMPLE +
+ atomic_int guide = ATOMIC_VAR_INIT(42); ++ + +
+
+ #include <stdatomic.h> + void atomic_init(volatile A *obj, C value); ++
+ The atomic_init generic function initializes the atomic object pointed to by obj to + the value value, while also initializing any additional state that the implementation + might need to carry for the atomic object. + +
+ Although this function initializes an atomic object, it does not avoid data races; + concurrent access to the variable being initialized, even via an atomic operation, + constitutes a data race. +
+ The atomic_init generic function returns no value. +
+ EXAMPLE +
+ atomic_int guide; + atomic_init(&guide, 42); ++ + +
+ The enumerated type memory_order specifies the detailed regular (non-atomic) + memory synchronization operations as defined in 5.1.2.4 and may provide for operation + ordering. Its enumeration constants are as follows: +
+ memory_order_relaxed + memory_order_consume + memory_order_acquire + memory_order_release + memory_order_acq_rel + memory_order_seq_cst ++
+ For memory_order_relaxed, no operation orders memory. +
+ For memory_order_release, memory_order_acq_rel, and + memory_order_seq_cst, a store operation performs a release operation on the + affected memory location. +
+ For memory_order_acquire, memory_order_acq_rel, and + memory_order_seq_cst, a load operation performs an acquire operation on the + affected memory location. +
+ For memory_order_consume, a load operation performs a consume operation on the + affected memory location. +
+ For memory_order_seq_cst, there shall be a single total order S on all operations, + consistent with the ''happens before'' order and modification orders for all affected + locations, such that each memory_order_seq_cst operation that loads a value + observes either the last preceding modification according to this order S, or the result of + an operation that is not memory_order_seq_cst. +
+ NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to + an order that does include lock and unlock operations, since the ordering between those is already included + in the ''happens before'' ordering. + +
+ NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to + memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic + + object be indivisible with respect to all other atomic accesses to that object. + +
+ For an atomic operation B that reads the value of an atomic object M, if there is a + memory_order_seq_cst fence X sequenced before B, then B observes either the + last memory_order_seq_cst modification of M preceding X in the total order S or + a later modification of M in its modification order. +
+ For atomic operations A and B on an atomic object M, where A modifies M and B takes + its value, if there is a memory_order_seq_cst fence X such that A is sequenced + before X and B follows X in S, then B observes either the effects of A or a later + modification of M in its modification order. +
+ For atomic operations A and B on an atomic object M, where A modifies M and B takes + its value, if there are memory_order_seq_cst fences X and Y such that A is + sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes + either the effects of A or a later modification of M in its modification order. +
+ Atomic read-modify-write operations shall always read the last value (in the modification + order) stored before the write associated with the read-modify-write operation. +
+ An atomic store shall only store a value that has been computed from constants and + program input values by a finite sequence of program evaluations, such that each + evaluation observes the values of variables as computed by the last prior assignment in + the sequence.251) The ordering of evaluations in this sequence shall be such that +
+ NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when + relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this + sequence out of thread order. For example, with x and y initially zero, +
+ // Thread 1: + r1 = atomic_load_explicit(&y, memory_order_relaxed); + atomic_store_explicit(&x, r1, memory_order_relaxed); ++ +
+ // Thread 2: + r2 = atomic_load_explicit(&x, memory_order_relaxed); + atomic_store_explicit(&y, 42, memory_order_relaxed); ++ is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of: + + + + + +
+ atomic_store_explicit(&y, 42, memory_order_relaxed); + r1 = atomic_load_explicit(&y, memory_order_relaxed); + atomic_store_explicit(&x, r1, memory_order_relaxed); + r2 = atomic_load_explicit(&x, memory_order_relaxed); ++ On the other hand, +
+ // Thread 1: + r1 = atomic_load_explicit(&y, memory_order_relaxed); + atomic_store_explicit(&x, r1, memory_order_relaxed); ++ +
+ // Thread 2: + r2 = atomic_load_explicit(&x, memory_order_relaxed); + atomic_store_explicit(&y, r2, memory_order_relaxed); ++ is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results + in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with + weaker than memory_order_acq_rel ordering, the second requirement has no impact. + +
+ The requirements do not forbid r1 == 42 && r2 == 42 in the following example, + with x and y initially zero: +
+ // Thread 1: + r1 = atomic_load_explicit(&x, memory_order_relaxed); + if (r1 == 42) + atomic_store_explicit(&y, r1, memory_order_relaxed); ++ +
+ // Thread 2: + r2 = atomic_load_explicit(&y, memory_order_relaxed); + if (r2 == 42) + atomic_store_explicit(&x, 42, memory_order_relaxed); ++ However, this is not useful behavior, and implementations should not allow it. +
+ Implementations should make atomic stores visible to atomic loads within a reasonable + amount of time. + +
251) Among other implications, atomic variables shall not decay. + + +
+
+ #include <stdatomic.h> + type kill_dependency(type y); ++
+ The kill_dependency macro terminates a dependency chain; the argument does not + carry a dependency to the return value. + +
+ The kill_dependency macro returns the value of y. + +
+ This subclause introduces synchronization primitives called fences. Fences can have + acquire semantics, release semantics, or both. A fence with acquire semantics is called + an acquire fence; a fence with release semantics is called a release fence. +
+ A release fence A synchronizes with an acquire fence B if there exist atomic operations + X and Y , both operating on some atomic object M, such that A is sequenced before X, X + modifies M, Y is sequenced before B, and Y reads the value written by X or a value + written by any side effect in the hypothetical release sequence X would head if it were a + release operation. +
+ A release fence A synchronizes with an atomic operation B that performs an acquire + operation on an atomic object M if there exists an atomic operation X such that A is + sequenced before X, X modifies M, and B reads the value written by X or a value written + by any side effect in the hypothetical release sequence X would head if it were a release + operation. +
+ An atomic operation A that is a release operation on an atomic object M synchronizes + with an acquire fence B if there exists some atomic operation X on M such that X is + sequenced before B and reads the value written by A or a value written by any side effect + in the release sequence headed by A. + +
+
+ #include <stdatomic.h> + void atomic_thread_fence(memory_order order); ++
+ Depending on the value of order, this operation: +
+ The atomic_thread_fence function returns no value. + +
+
+ #include <stdatomic.h> + void atomic_signal_fence(memory_order order); ++
+ Equivalent to atomic_thread_fence(order), except that ''synchronizes with'' + relationships are established only between a thread and a signal handler executed in the + same thread. +
+ NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions + performed by the thread become visible to the signal handler. + +
+ NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with + atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would + have inserted are not emitted. + +
+ The atomic_signal_fence function returns no value. + +
+ The atomic lock-free macros indicate the lock-free property of integer and address atomic + types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that + the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free. +
+ NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same + memory location via two different addresses will communicate atomically. The implementation should not + depend on any per-process state. This restriction enables communication via memory mapped into a + process more than once and memory shared between two processes. + + +
+
+ #include <stdatomic.h> + _Bool atomic_is_lock_free(atomic_type const volatile *obj); ++
+ The atomic_is_lock_free generic function indicates whether or not the object + pointed to by obj is lock-free. atomic_type can be any atomic type. +
+ The atomic_is_lock_free generic function returns nonzero (true) if and only if the + object's operations are lock-free. The result of a lock-free query on one object cannot be + + inferred from the result of a lock-free query on another object. + +
+ For each line in the following table, the atomic type name is declared as the + corresponding direct type. + +
+ Atomic type name Direct type + atomic_char _Atomic char + atomic_schar _Atomic signed char + atomic_uchar _Atomic unsigned char + atomic_short _Atomic short + atomic_ushort _Atomic unsigned short + atomic_int _Atomic int + atomic_uint _Atomic unsigned int + atomic_long _Atomic long + atomic_ulong _Atomic unsigned long + atomic_llong _Atomic long long + atomic_ullong _Atomic unsigned long long + atomic_char16_t _Atomic char16_t + atomic_char32_t _Atomic char32_t + atomic_wchar_t _Atomic wchar_t + atomic_int_least8_t _Atomic int_least8_t + atomic_uint_least8_t _Atomic uint_least8_t + atomic_int_least16_t _Atomic int_least16_t + atomic_uint_least16_t _Atomic uint_least16_t + atomic_int_least32_t _Atomic int_least32_t + atomic_uint_least32_t _Atomic uint_least32_t + atomic_int_least64_t _Atomic int_least64_t + atomic_uint_least64_t _Atomic uint_least64_t + atomic_int_fast8_t _Atomic int_fast8_t + atomic_uint_fast8_t _Atomic uint_fast8_t + atomic_int_fast16_t _Atomic int_fast16_t + atomic_uint_fast16_t _Atomic uint_fast16_t + atomic_int_fast32_t _Atomic int_fast32_t + atomic_uint_fast32_t _Atomic uint_fast32_t + atomic_int_fast64_t _Atomic int_fast64_t + atomic_uint_fast64_t _Atomic uint_fast64_t + atomic_intptr_t _Atomic intptr_t + atomic_uintptr_t _Atomic uintptr_t + atomic_size_t _Atomic size_t + atomic_ptrdiff_t _Atomic ptrdiff_t + atomic_intmax_t _Atomic intmax_t + atomic_uintmax_t _Atomic uintmax_t ++
+ The semantics of the operations on these types are defined in 7.17.7. +
+ The atomic_bool type provides an atomic boolean. + +
+ The atomic_address type provides atomic void * operations. The unit of + addition/subtraction shall be one byte. +
+ NOTE The representation of atomic integer and address types need not have the same size as their + corresponding regular types. They should have the same size whenever possible, as it eases effort required + to port existing code. + + +
+ There are only a few kinds of operations on atomic types, though there are many + instances of those kinds. This subclause specifies each general kind. + +
+
+ #include <stdatomic.h> + void atomic_store(volatile A *object, C desired); + void atomic_store_explicit(volatile A *object, + C desired, memory_order order); ++
+ The order argument shall not be memory_order_acquire, + memory_order_consume, nor memory_order_acq_rel. Atomically replace the + value pointed to by object with the value of desired. Memory is affected according + to the value of order. +
+ The atomic_store generic functions return no value. + +
+
+ #include <stdatomic.h> + C atomic_load(volatile A *object); + C atomic_load_explicit(volatile A *object, + memory_order order); ++
+ The order argument shall not be memory_order_release nor + memory_order_acq_rel. Memory is affected according to the value of order. +
+
+ #include <stdatomic.h> + C atomic_exchange(volatile A *object, C desired); + C atomic_exchange_explicit(volatile A *object, + C desired, memory_order order); ++
+ Atomically replace the value pointed to by object with desired. Memory is affected + according to the value of order. These operations are read-modify-write operations + (5.1.2.4). +
+ Atomically returns the value pointed to by object immediately before the effects. + +
+
+ #include <stdatomic.h> + _Bool atomic_compare_exchange_strong(volatile A *object, + C *expected, C desired); + _Bool atomic_compare_exchange_strong_explicit( + volatile A *object, C *expected, C desired, + memory_order success, memory_order failure); + _Bool atomic_compare_exchange_weak(volatile A *object, + C *expected, C desired); + _Bool atomic_compare_exchange_weak_explicit( + volatile A *object, C *expected, C desired, + memory_order success, memory_order failure); ++
+ The failure argument shall not be memory_order_release nor + memory_order_acq_rel. The failure argument shall be no stronger than the + success argument. Atomically, compares the value pointed to by object for equality + with that in expected, and if true, replaces the value pointed to by object with + desired, and if false, updates the value in expected with the value pointed to by + object. Further, if the comparison is true, memory is affected according to the value of + success, and if the comparison is false, memory is affected according to the value of + failure. These operations are atomic read-modify-write operations (5.1.2.4). +
+ NOTE 1 The effect of the compare-and-exchange operations is + +
+ if (*object == *expected) + *object = desired; + else + *expected = *object; ++ +
+ The weak compare-and-exchange operations may fail spuriously, that is, return zero + while leaving the value pointed to by expected unchanged. +
+ NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of + machines, e.g. load-locked store-conditional machines. + +
+ EXAMPLE A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will + be in a loop. +
+ exp = atomic_load(&cur);
+ do {
+ des = function(exp);
+ } while (!atomic_compare_exchange_weak(&cur, &exp, des));
+
+ When a compare-and-exchange is in a loop, the weak version will yield better performance on some
+ platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
+ strong one is preferable.
+
++ The result of the comparison. + +
+ The following operations perform arithmetic and bitwise computations. All of these + operations are applicable to an object of any atomic integer type. Only addition and + subtraction are applicable to atomic_address. None of these operations is applicable + to atomic_bool. The key, operator, and computation correspondence is: + key op computation + add + addition + sub - subtraction + or | bitwise inclusive or + xor ^ bitwise exclusive or + and & bitwise and +
+
+ #include <stdatomic.h> + C atomic_fetch_key(volatile A *object, M operand); + C atomic_fetch_key_explicit(volatile A *object, + M operand, memory_order order); ++
+ Atomically replaces the value pointed to by object with the result of the computation + applied to the value pointed to by object and the given operand. Memory is affected + according to the value of order. These operations are atomic read-modify-write + + operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's + complement representation with silent wrap-around on overflow; there are no undefined + results. For address types, the result may be an undefined address, but the operations + otherwise have no undefined behavior. +
+ Atomically, the value pointed to by object immediately before the effects. +
+ NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the + operation of the corresponding op= compound assignment operators. The only differences are that the + compound assignment operators are not guaranteed to operate atomically, and the value yielded by a + compound assignment operator is the updated value of the object, whereas the value returned by the + atomic_fetch and modify generic functions is the previous value of the atomic object. + + +
+ The atomic_flag type provides the classic test-and-set functionality. It has two + states, set and clear. +
+ Operations on an object of type atomic_flag shall be lock free. +
+ NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so + the atomic_flag type is the minimum hardware-implemented type needed to conform to this + International standard. The remaining types can be emulated with atomic_flag, though with less than + ideal properties. + +
+ The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the + clear state. An atomic_flag that is not explicitly initialized with + ATOMIC_FLAG_INIT is initially in an indeterminate state. +
+ EXAMPLE +
+ atomic_flag guard = ATOMIC_FLAG_INIT; ++ + +
+
+ #include <stdatomic.h> + bool atomic_flag_test_and_set( + volatile atomic_flag *object); + bool atomic_flag_test_and_set_explicit( + volatile atomic_flag *object, memory_order order); ++
+ Atomically sets the value pointed to by object to true. Memory is affected according + to the value of order. These operations are atomic read-modify-write operations + (5.1.2.4). + +
+ Atomically, the value of the object immediately before the effects. + +
+
+ #include <stdatomic.h> + void atomic_flag_clear(volatile atomic_flag *object); + void atomic_flag_clear_explicit( + volatile atomic_flag *object, memory_order order); ++
+ The order argument shall not be memory_order_acquire nor + memory_order_acq_rel. Atomically sets the value pointed to by object to false. + Memory is affected according to the value of order. +
+ The atomic_flag_clear functions return no value. + + +
+ The header <stdbool.h> defines four macros. +
+ The macro +
+ bool ++ expands to _Bool. +
+ The remaining three macros are suitable for use in #if preprocessing directives. They + are +
+ true ++ which expands to the integer constant 1, +
+ false ++ which expands to the integer constant 0, and +
+ __bool_true_false_are_defined ++ which expands to the integer constant 1. +
+ Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then + redefine the macros bool, true, and false.252) + + + + + + +
252) See ''future library directions'' (7.30.7). + + +
+ The header <stddef.h> defines the following macros and declares the following types. + Some are also defined in other headers, as noted in their respective subclauses. +
+ The types are +
+ ptrdiff_t ++ which is the signed integer type of the result of subtracting two pointers; +
+ size_t ++ which is the unsigned integer type of the result of the sizeof operator; +
+ max_align_t ++ which is an object type whose alignment is as great as is supported by the implementation + in all contexts; and +
+ wchar_t ++ which is an integer type whose range of values can represent distinct codes for all + members of the largest extended character set specified among the supported locales; the + null character shall have the code value zero. Each member of the basic character set + shall have a code value equal to its value when used as the lone character in an integer + character constant if an implementation does not define + __STDC_MB_MIGHT_NEQ_WC__. +
+ The macros are +
+ NULL ++ which expands to an implementation-defined null pointer constant; and +
+ offsetof(type, member-designator) ++ which expands to an integer constant expression that has type size_t, the value of + which is the offset in bytes, to the structure member (designated by member-designator), + from the beginning of its structure (designated by type). The type and member designator + shall be such that given +
+ static type t; ++ then the expression &(t.member-designator) evaluates to an address constant. (If the + specified member is a bit-field, the behavior is undefined.) +
+ The types used for size_t and ptrdiff_t should not have an integer conversion rank + greater than that of signed long int unless the implementation supports objects + large enough to make this necessary. + +
Forward references: localization (7.11). + + +
+ The header <stdint.h> declares sets of integer types having specified widths, and + defines corresponding sets of macros.253) It also defines macros that specify limits of + integer types corresponding to types defined in other standard headers. +
+ Types are defined in the following categories: +
+ Corresponding macros specify limits of the declared types and construct suitable + constants. +
+ For each type described herein that the implementation provides,254) <stdint.h> shall + declare that typedef name and define the associated macros. Conversely, for each type + described herein that the implementation does not provide, <stdint.h> shall not + declare that typedef name nor shall it define the associated macros. An implementation + shall provide those types described as ''required'', but need not provide any of the others + (described as ''optional''). + +
253) See ''future library directions'' (7.30.8). + +
254) Some of these types may denote implementation-defined extended integer types. + + +
+ When typedef names differing only in the absence or presence of the initial u are defined, + they shall denote corresponding signed and unsigned types as described in 6.2.5; an + implementation providing one of these corresponding types shall also provide the other. +
+ In the following descriptions, the symbol N represents an unsigned decimal integer with + no leading zeros (e.g., 8 or 24, but not 04 or 048). + + + + + + +
+ The typedef name intN_t designates a signed integer type with width N , no padding + bits, and a two's complement representation. Thus, int8_t denotes such a signed + integer type with a width of exactly 8 bits. +
+ The typedef name uintN_t designates an unsigned integer type with width N and no + padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of + exactly 24 bits. +
+ These types are optional. However, if an implementation provides integer types with + widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a + two's complement representation, it shall define the corresponding typedef names. + +
+ The typedef name int_leastN_t designates a signed integer type with a width of at + least N , such that no signed integer type with lesser size has at least the specified width. + Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits. +
+ The typedef name uint_leastN_t designates an unsigned integer type with a width + of at least N , such that no unsigned integer type with lesser size has at least the specified + width. Thus, uint_least16_t denotes an unsigned integer type with a width of at + least 16 bits. +
+ The following types are required: +
+ int_least8_t uint_least8_t + int_least16_t uint_least16_t + int_least32_t uint_least32_t + int_least64_t uint_least64_t ++ All other types of this form are optional. + +
+ Each of the following types designates an integer type that is usually fastest255) to operate + with among all integer types that have at least the specified width. +
+ The typedef name int_fastN_t designates the fastest signed integer type with a width + of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer + type with a width of at least N . + + + + + +
+ The following types are required: +
+ int_fast8_t uint_fast8_t + int_fast16_t uint_fast16_t + int_fast32_t uint_fast32_t + int_fast64_t uint_fast64_t ++ All other types of this form are optional. + +
255) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear + grounds for choosing one type over another, it will simply pick some integer type satisfying the + signedness and width requirements. + + +
+ The following type designates a signed integer type with the property that any valid + pointer to void can be converted to this type, then converted back to pointer to void, + and the result will compare equal to the original pointer: +
+ intptr_t ++ The following type designates an unsigned integer type with the property that any valid + pointer to void can be converted to this type, then converted back to pointer to void, + and the result will compare equal to the original pointer: +
+ uintptr_t ++ These types are optional. + +
+ The following type designates a signed integer type capable of representing any value of + any signed integer type: +
+ intmax_t ++ The following type designates an unsigned integer type capable of representing any value + of any unsigned integer type: +
+ uintmax_t ++ These types are required. + +
+ The following object-like macros specify the minimum and maximum limits of the types * + declared in <stdint.h>. Each macro name corresponds to a similar type name in + 7.20.1. +
+ Each instance of any defined macro shall be replaced by a constant expression suitable + for use in #if preprocessing directives, and this expression shall have the same type as + would an expression that is an object of the corresponding type converted according to + the integer promotions. Its implementation-defined value shall be equal to or greater in + magnitude (absolute value) than the corresponding value given below, with the same sign, + except where stated to be exactly the given value. + + +
+
+ INTN_MIN exactly -(2 N -1 ) ++
+ INTN_MAX exactly 2 N -1 - 1 ++
+
+ INT_LEASTN_MIN -(2 N -1 - 1) ++
+ INT_LEASTN_MAX 2 N -1 - 1 ++
+
+ INT_FASTN_MIN -(2 N -1 - 1) ++
+
+ INTPTR_MIN -(215 - 1) ++
+
+ The following object-like macros specify the minimum and maximum limits of integer * + types corresponding to types defined in other standard headers. +
+ Each instance of these macros shall be replaced by a constant expression suitable for use + in #if preprocessing directives, and this expression shall have the same type as would an + expression that is an object of the corresponding type converted according to the integer + promotions. Its implementation-defined value shall be equal to or greater in magnitude + (absolute value) than the corresponding value given below, with the same sign. An + implementation shall define only the macros corresponding to those typedef names it + actually provides.256) +
+ If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of + SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX + shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer + type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of + SIG_ATOMIC_MAX shall be no less than 255. +
+ If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN + shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127; + otherwise, wchar_t is defined as an unsigned integer type, and the value of + WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.257) +
+ If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall + be no greater than -32767 and the value of WINT_MAX shall be no less than 32767; + otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN + shall be 0 and the value of WINT_MAX shall be no less than 65535. + +
256) A freestanding implementation need not provide all of these types. + +
257) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended + character set. + + +
+ The following function-like macros expand to integer constants suitable for initializing * + objects that have integer types corresponding to types defined in <stdint.h>. Each + macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5. +
+ The argument in any instance of these macros shall be an unsuffixed integer constant (as + defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type. +
+ Each invocation of one of these macros shall expand to an integer constant expression + suitable for use in #if preprocessing directives. The type of the expression shall have + the same type as would an expression of the corresponding type converted according to + the integer promotions. The value of the expression shall be that of the argument. + +
+ The macro INTN_C(value) shall expand to an integer constant expression + corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand + to an integer constant expression corresponding to the type uint_leastN_t. For + example, if uint_least64_t is a name for the type unsigned long long int, + then UINT64_C(0x123) might expand to the integer constant 0x123ULL. + + + + + + +
+ The following macro expands to an integer constant expression having the value specified + by its argument and the type intmax_t: +
+ INTMAX_C(value) ++ The following macro expands to an integer constant expression having the value specified + by its argument and the type uintmax_t: + +
+ UINTMAX_C(value) ++ +
+ The header <stdio.h> defines several macros, and declares three types and many + functions for performing input and output. +
+ The types declared are size_t (described in 7.19); +
+ FILE ++ which is an object type capable of recording all the information needed to control a + stream, including its file position indicator, a pointer to its associated buffer (if any), an + error indicator that records whether a read/write error has occurred, and an end-of-file + indicator that records whether the end of the file has been reached; and +
+ fpos_t ++ which is a complete object type other than an array type capable of recording all the + information needed to specify uniquely every position within a file. +
+ The macros are NULL (described in 7.19); +
+ _IOFBF + _IOLBF + _IONBF ++ which expand to integer constant expressions with distinct values, suitable for use as the + third argument to the setvbuf function; +
+ BUFSIZ ++ which expands to an integer constant expression that is the size of the buffer used by the + setbuf function; +
+ EOF ++ which expands to an integer constant expression, with type int and a negative value, that + is returned by several functions to indicate end-of-file, that is, no more input from a + stream; +
+ FOPEN_MAX ++ which expands to an integer constant expression that is the minimum number of files that + the implementation guarantees can be open simultaneously; +
+ FILENAME_MAX ++ which expands to an integer constant expression that is the size needed for an array of + char large enough to hold the longest file name string that the implementation + + guarantees can be opened;258) +
+ L_tmpnam ++ which expands to an integer constant expression that is the size needed for an array of + char large enough to hold a temporary file name string generated by the tmpnam + function; +
+ SEEK_CUR + SEEK_END + SEEK_SET ++ which expand to integer constant expressions with distinct values, suitable for use as the + third argument to the fseek function; +
+ TMP_MAX ++ which expands to an integer constant expression that is the minimum number of unique + file names that can be generated by the tmpnam function; +
+ stderr + stdin + stdout ++ which are expressions of type ''pointer to FILE'' that point to the FILE objects + associated, respectively, with the standard error, input, and output streams. +
+ The header <wchar.h> declares a number of functions useful for wide character input + and output. The wide character input/output functions described in that subclause + provide operations analogous to most of those described here, except that the + fundamental units internal to the program are wide characters. The external + representation (in the file) is a sequence of ''generalized'' multibyte characters, as + described further in 7.21.3. +
+ The input/output functions are given the following collective terms: +
Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the + tmpnam function (7.21.4.4), <wchar.h> (7.28). + +
258) If the implementation imposes no practical limit on the length of file name strings, the value of + FILENAME_MAX should instead be the recommended size of an array intended to hold a file name + string. Of course, file name string contents are subject to other system-specific constraints; therefore + all possible strings of length FILENAME_MAX cannot be expected to be opened successfully. + + +
+ Input and output, whether to or from physical devices such as terminals and tape drives, + or whether to or from files supported on structured storage devices, are mapped into + logical data streams, whose properties are more uniform than their various inputs and + outputs. Two forms of mapping are supported, for text streams and for binary + streams.259) +
+ A text stream is an ordered sequence of characters composed into lines, each line + consisting of zero or more characters plus a terminating new-line character. Whether the + last line requires a terminating new-line character is implementation-defined. Characters + may have to be added, altered, or deleted on input and output to conform to differing + conventions for representing text in the host environment. Thus, there need not be a one- + to-one correspondence between the characters in a stream and those in the external + representation. Data read in from a text stream will necessarily compare equal to the data + that were earlier written out to that stream only if: the data consist only of printing + characters and the control characters horizontal tab and new-line; no new-line character is + immediately preceded by space characters; and the last character is a new-line character. + Whether space characters that are written out immediately before a new-line character + appear when read in is implementation-defined. +
+ A binary stream is an ordered sequence of characters that can transparently record + internal data. Data read in from a binary stream shall compare equal to the data that were + earlier written out to that stream, under the same implementation. Such a stream may, + however, have an implementation-defined number of null characters appended to the end + of the stream. +
+ Each stream has an orientation. After a stream is associated with an external file, but + before any operations are performed on it, the stream is without orientation. Once a wide + character input/output function has been applied to a stream without orientation, the + + + + stream becomes a wide-oriented stream. Similarly, once a byte input/output function has + been applied to a stream without orientation, the stream becomes a byte-oriented stream. + Only a call to the freopen function or the fwide function can otherwise alter the + orientation of a stream. (A successful call to freopen removes any orientation.)260) +
+ Byte input/output functions shall not be applied to a wide-oriented stream and wide + character input/output functions shall not be applied to a byte-oriented stream. The + remaining stream operations do not affect, and are not affected by, a stream's orientation, + except for the following additional restrictions: +
+ Each wide-oriented stream has an associated mbstate_t object that stores the current + parse state of the stream. A successful call to fgetpos stores a representation of the + value of this mbstate_t object as part of the value of the fpos_t object. A later + successful call to fsetpos using the same stored fpos_t value restores the value of + the associated mbstate_t object as well as the position within the controlled stream. +
+ An implementation shall support text files with lines containing at least 254 characters, + including the terminating new-line character. The value of the macro BUFSIZ shall be at + least 256. +
Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5), + mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function + (7.21.9.3). + + + + + + +
259) An implementation need not distinguish between text streams and binary streams. In such an + implementation, there need be no new-line characters in a text stream nor any limit to the length of a + line. + +
260) The three predefined streams stdin, stdout, and stderr are unoriented at program startup. + + +
+ A stream is associated with an external file (which may be a physical device) by opening + a file, which may involve creating a new file. Creating an existing file causes its former + contents to be discarded, if necessary. If a file can support positioning requests (such as a + disk file, as opposed to a terminal), then a file position indicator associated with the + stream is positioned at the start (character number zero) of the file, unless the file is + opened with append mode in which case it is implementation-defined whether the file + position indicator is initially positioned at the beginning or the end of the file. The file + position indicator is maintained by subsequent reads, writes, and positioning requests, to + facilitate an orderly progression through the file. +
+ Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text + stream causes the associated file to be truncated beyond that point is implementation- + defined. +
+ When a stream is unbuffered, characters are intended to appear from the source or at the + destination as soon as possible. Otherwise characters may be accumulated and + transmitted to or from the host environment as a block. When a stream is fully buffered, + characters are intended to be transmitted to or from the host environment as a block when + a buffer is filled. When a stream is line buffered, characters are intended to be + transmitted to or from the host environment as a block when a new-line character is + encountered. Furthermore, characters are intended to be transmitted as a block to the host + environment when a buffer is filled, when input is requested on an unbuffered stream, or + when input is requested on a line buffered stream that requires the transmission of + characters from the host environment. Support for these characteristics is + implementation-defined, and may be affected via the setbuf and setvbuf functions. +
+ A file may be disassociated from a controlling stream by closing the file. Output streams + are flushed (any unwritten buffer contents are transmitted to the host environment) before + the stream is disassociated from the file. The value of a pointer to a FILE object is + indeterminate after the associated file is closed (including the standard text streams). + Whether a file of zero length (on which no characters have been written by an output + stream) actually exists is implementation-defined. +
+ The file may be subsequently reopened, by the same or another program execution, and + its contents reclaimed or modified (if it can be repositioned at its start). If the main + function returns to its original caller, or if the exit function is called, all open files are + closed (hence all output streams are flushed) before program termination. Other paths to + program termination, such as calling the abort function, need not close all files + properly. +
+ The address of the FILE object used to control a stream may be significant; a copy of a + FILE object need not serve in place of the original. + +
+ At program startup, three text streams are predefined and need not be opened explicitly +
+ Functions that open additional (nontemporary) files require a file name, which is a string. + The rules for composing valid file names are implementation-defined. Whether the same + file can be simultaneously open multiple times is also implementation-defined. +
+ Although both text and binary wide-oriented streams are conceptually sequences of wide + characters, the external file associated with a wide-oriented stream is a sequence of + multibyte characters, generalized as follows: +
+ Moreover, the encodings used for multibyte characters may differ among files. Both the + nature and choice of such encodings are implementation-defined. +
+ The wide character input functions read multibyte characters from the stream and convert + them to wide characters as if they were read by successive calls to the fgetwc function. + Each conversion occurs as if by a call to the mbrtowc function, with the conversion state + described by the stream's own mbstate_t object. The byte input functions read + characters from the stream as if by successive calls to the fgetc function. +
+ The wide character output functions convert wide characters to multibyte characters and + write them to the stream as if they were written by successive calls to the fputwc + function. Each conversion occurs as if by a call to the wcrtomb function, with the + conversion state described by the stream's own mbstate_t object. The byte output + functions write characters to the stream as if by successive calls to the fputc function. +
+ In some cases, some of the byte input/output functions also perform conversions between + multibyte characters and wide characters. These conversions also occur as if by calls to + the mbrtowc and wcrtomb functions. +
+ An encoding error occurs if the character sequence presented to the underlying + mbrtowc function does not form a valid (generalized) multibyte character, or if the code + value passed to the underlying wcrtomb does not correspond to a valid (generalized) + + + + multibyte character. The wide character input/output functions and the byte input/output + functions store the value of the macro EILSEQ in errno if and only if an encoding error + occurs. +
+ The value of FOPEN_MAX shall be at least eight, including the three standard text + streams. +
Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the + fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function + (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the + fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function + (7.28.6.3.2), the wcrtomb function (7.28.6.3.3). + +
261) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has + undefined behavior for a binary stream (because of possible trailing null characters) or for any stream + with state-dependent encoding that does not assuredly end in the initial shift state. + + +
+
+ #include <stdio.h> + int remove(const char *filename); ++
+ The remove function causes the file whose name is the string pointed to by filename + to be no longer accessible by that name. A subsequent attempt to open that file using that + name will fail, unless it is created anew. If the file is open, the behavior of the remove + function is implementation-defined. +
+ The remove function returns zero if the operation succeeds, nonzero if it fails. + +
+
+ #include <stdio.h> + int rename(const char *old, const char *new); ++
+ The rename function causes the file whose name is the string pointed to by old to be + henceforth known by the name given by the string pointed to by new. The file named + old is no longer accessible by that name. If a file named by the string pointed to by new + exists prior to the call to the rename function, the behavior is implementation-defined. + +
+ The rename function returns zero if the operation succeeds, nonzero if it fails,262) in + which case if the file existed previously it is still known by its original name. + +
262) Among the reasons the implementation may cause the rename function to fail are that the file is open + or that it is necessary to copy its contents to effectuate its renaming. + + +
+
+ #include <stdio.h> + FILE *tmpfile(void); ++
+ The tmpfile function creates a temporary binary file that is different from any other + existing file and that will automatically be removed when it is closed or at program + termination. If the program terminates abnormally, whether an open temporary file is + removed is implementation-defined. The file is opened for update with "wb+" mode. +
+ It should be possible to open at least TMP_MAX temporary files during the lifetime of the + program (this limit may be shared with tmpnam) and there should be no limit on the + number simultaneously open other than this limit and any limit on the number of open + files (FOPEN_MAX). +
+ The tmpfile function returns a pointer to the stream of the file that it created. If the file + cannot be created, the tmpfile function returns a null pointer. +
Forward references: the fopen function (7.21.5.3). + +
+
+ #include <stdio.h> + char *tmpnam(char *s); ++
+ The tmpnam function generates a string that is a valid file name and that is not the same + as the name of an existing file.263) The function is potentially capable of generating at + + + + least TMP_MAX different strings, but any or all of them may already be in use by existing + files and thus not be suitable return values. +
+ The tmpnam function generates a different string each time it is called. +
+ Calls to the tmpnam function with a null pointer argument may introduce data races with + each other. The implementation shall behave as if no library function calls the tmpnam + function. +
+ If no suitable string can be generated, the tmpnam function returns a null pointer. + Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an + internal static object and returns a pointer to that object (subsequent calls to the tmpnam + function may modify the same object). If the argument is not a null pointer, it is assumed + to point to an array of at least L_tmpnam chars; the tmpnam function writes its result + in that array and returns the argument as its value. +
+ The value of the macro TMP_MAX shall be at least 25. + +
263) Files created using strings generated by the tmpnam function are temporary only in the sense that + their names should not collide with those generated by conventional naming rules for the + implementation. It is still necessary to use the remove function to remove such files when their use + is ended, and before program termination. + + +
+
+ #include <stdio.h> + int fclose(FILE *stream); ++
+ A successful call to the fclose function causes the stream pointed to by stream to be + flushed and the associated file to be closed. Any unwritten buffered data for the stream + are delivered to the host environment to be written to the file; any unread buffered data + are discarded. Whether or not the call succeeds, the stream is disassociated from the file + and any buffer set by the setbuf or setvbuf function is disassociated from the stream + (and deallocated if it was automatically allocated). +
+ The fclose function returns zero if the stream was successfully closed, or EOF if any + errors were detected. + + +
+
+ #include <stdio.h> + int fflush(FILE *stream); ++
+ If stream points to an output stream or an update stream in which the most recent + operation was not input, the fflush function causes any unwritten data for that stream + to be delivered to the host environment to be written to the file; otherwise, the behavior is + undefined. +
+ If stream is a null pointer, the fflush function performs this flushing action on all + streams for which the behavior is defined above. +
+ The fflush function sets the error indicator for the stream and returns EOF if a write + error occurs, otherwise it returns zero. +
Forward references: the fopen function (7.21.5.3). + +
+
+ #include <stdio.h> + FILE *fopen(const char * restrict filename, + const char * restrict mode); ++
+ The fopen function opens the file whose name is the string pointed to by filename, + and associates a stream with it. +
+ The argument mode points to a string. If the string is one of the following, the file is + open in the indicated mode. Otherwise, the behavior is undefined.264) + r open text file for reading + w truncate to zero length or create text file for writing + wx create text file for writing + a append; open or create text file for writing at end-of-file + rb open binary file for reading + wb truncate to zero length or create binary file for writing + + + + wbx create binary file for writing + ab append; open or create binary file for writing at end-of-file + r+ open text file for update (reading and writing) + w+ truncate to zero length or create text file for update + w+x create text file for update + a+ append; open or create text file for update, writing at end-of-file + r+b or rb+ open binary file for update (reading and writing) + w+b or wb+ truncate to zero length or create binary file for update + w+bx or wb+x create binary file for update + a+b or ab+ append; open or create binary file for update, writing at end-of-file +
+ Opening a file with read mode ('r' as the first character in the mode argument) fails if + the file does not exist or cannot be read. +
+ Opening a file with exclusive mode ('x' as the last character in the mode argument) + fails if the file already exists or cannot be created. Otherwise, the file is created with + exclusive (also known as non-shared) access to the extent that the underlying system + supports exclusive access. +
+ Opening a file with append mode ('a' as the first character in the mode argument) + causes all subsequent writes to the file to be forced to the then current end-of-file, + regardless of intervening calls to the fseek function. In some implementations, opening + a binary file with append mode ('b' as the second or third character in the above list of + mode argument values) may initially position the file position indicator for the stream + beyond the last data written, because of null character padding. +
+ When a file is opened with update mode ('+' as the second or third character in the + above list of mode argument values), both input and output may be performed on the + associated stream. However, output shall not be directly followed by input without an + intervening call to the fflush function or to a file positioning function (fseek, + fsetpos, or rewind), and input shall not be directly followed by output without an + intervening call to a file positioning function, unless the input operation encounters end- + of-file. Opening (or creating) a text file with update mode may instead open (or create) a + binary stream in some implementations. +
+ When opened, a stream is fully buffered if and only if it can be determined not to refer to + an interactive device. The error and end-of-file indicators for the stream are cleared. +
+ The fopen function returns a pointer to the object controlling the stream. If the open + operation fails, fopen returns a null pointer. +
Forward references: file positioning functions (7.21.9). + + +
264) If the string begins with one of the above sequences, the implementation might choose to ignore the + remaining characters, or it might use them to select different kinds of a file (some of which might not + conform to the properties in 7.21.2). + + +
+
+ #include <stdio.h> + FILE *freopen(const char * restrict filename, + const char * restrict mode, + FILE * restrict stream); ++
+ The freopen function opens the file whose name is the string pointed to by filename + and associates the stream pointed to by stream with it. The mode argument is used just + as in the fopen function.265) +
+ If filename is a null pointer, the freopen function attempts to change the mode of + the stream to that specified by mode, as if the name of the file currently associated with + the stream had been used. It is implementation-defined which changes of mode are + permitted (if any), and under what circumstances. +
+ The freopen function first attempts to close any file that is associated with the specified + stream. Failure to close the file is ignored. The error and end-of-file indicators for the + stream are cleared. +
+ The freopen function returns a null pointer if the open operation fails. Otherwise, + freopen returns the value of stream. + +
265) The primary use of the freopen function is to change the file associated with a standard text stream + (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value + returned by the fopen function may be assigned. + + +
+
+ #include <stdio.h> + void setbuf(FILE * restrict stream, + char * restrict buf); ++
+ Except that it returns no value, the setbuf function is equivalent to the setvbuf + function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf + is a null pointer), with the value _IONBF for mode. + + + + + +
+ The setbuf function returns no value. +
Forward references: the setvbuf function (7.21.5.6). + +
+
+ #include <stdio.h> + int setvbuf(FILE * restrict stream, + char * restrict buf, + int mode, size_t size); ++
+ The setvbuf function may be used only after the stream pointed to by stream has + been associated with an open file and before any other operation (other than an + unsuccessful call to setvbuf) is performed on the stream. The argument mode + determines how stream will be buffered, as follows: _IOFBF causes input/output to be + fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes + input/output to be unbuffered. If buf is not a null pointer, the array it points to may be + used instead of a buffer allocated by the setvbuf function266) and the argument size + specifies the size of the array; otherwise, size may determine the size of a buffer + allocated by the setvbuf function. The contents of the array at any time are + indeterminate. +
+ The setvbuf function returns zero on success, or nonzero if an invalid value is given + for mode or if the request cannot be honored. + + + + + + +
266) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed + before a buffer that has automatic storage duration is deallocated upon block exit. + + +
+ The formatted input/output functions shall behave as if there is a sequence point after the + actions associated with each specifier.267) + +
267) The fprintf functions perform writes to memory for the %n specifier. + + +
+
+ #include <stdio.h> + int fprintf(FILE * restrict stream, + const char * restrict format, ...); ++
+ The fprintf function writes output to the stream pointed to by stream, under control + of the string pointed to by format that specifies how subsequent arguments are + converted for output. If there are insufficient arguments for the format, the behavior is + undefined. If the format is exhausted while arguments remain, the excess arguments are + evaluated (as always) but are otherwise ignored. The fprintf function returns when + the end of the format string is encountered. +
+ The format shall be a multibyte character sequence, beginning and ending in its initial + shift state. The format is composed of zero or more directives: ordinary multibyte + characters (not %), which are copied unchanged to the output stream; and conversion + specifications, each of which results in fetching zero or more subsequent arguments, + converting them, if applicable, according to the corresponding conversion specifier, and + then writing the result to the output stream. +
+ Each conversion specification is introduced by the character %. After the %, the following + appear in sequence: +
+ As noted above, a field width, or precision, or both, may be indicated by an asterisk. In + this case, an int argument supplies the field width or precision. The arguments + specifying field width, or precision, or both, shall appear (in that order) before the + argument (if any) to be converted. A negative field width argument is taken as a - flag + followed by a positive field width. A negative precision argument is taken as if the + precision were omitted. +
+ The flag characters and their meanings are: + - The result of the conversion is left-justified within the field. (It is right-justified if +
+ this flag is not specified.) ++ + The result of a signed conversion always begins with a plus or minus sign. (It +
+ begins with a sign only when a negative value is converted if this flag is not + specified.)269) ++ space If the first character of a signed conversion is not a sign, or if a signed conversion +
+ results in no characters, a space is prefixed to the result. If the space and + flags + both appear, the space flag is ignored. ++ # The result is converted to an ''alternative form''. For o conversion, it increases +
+ the precision, if and only if necessary, to force the first digit of the result to be a + zero (if the value and precision are both 0, a single 0 is printed). For x (or X) + conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, + and G conversions, the result of converting a floating-point number always + contains a decimal-point character, even if no digits follow it. (Normally, a + decimal-point character appears in the result of these conversions only if a digit + follows it.) For g and G conversions, trailing zeros are not removed from the + result. For other conversions, the behavior is undefined. ++ 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros +
+ (following any indication of sign or base) are used to pad to the field width rather + than performing space padding, except when converting an infinity or NaN. If the + 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X ++ + + +
+ conversions, if a precision is specified, the 0 flag is ignored. For other + conversions, the behavior is undefined. ++
+ The length modifiers and their meanings are: + hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ signed char or unsigned char argument (the argument will have + been promoted according to the integer promotions, but its value shall be + converted to signed char or unsigned char before printing); or that + a following n conversion specifier applies to a pointer to a signed char + argument. ++ h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ short int or unsigned short int argument (the argument will + have been promoted according to the integer promotions, but its value shall + be converted to short int or unsigned short int before printing); + or that a following n conversion specifier applies to a pointer to a short + int argument. ++ l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ long int or unsigned long int argument; that a following n + conversion specifier applies to a pointer to a long int argument; that a + following c conversion specifier applies to a wint_t argument; that a + following s conversion specifier applies to a pointer to a wchar_t + argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion + specifier. ++ ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ long long int or unsigned long long int argument; or that a + following n conversion specifier applies to a pointer to a long long int + argument. ++ j Specifies that a following d, i, o, u, x, or X conversion specifier applies to +
+ an intmax_t or uintmax_t argument; or that a following n conversion + specifier applies to a pointer to an intmax_t argument. ++ z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ size_t or the corresponding signed integer type argument; or that a + following n conversion specifier applies to a pointer to a signed integer type + corresponding to size_t argument. ++ t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a + +
+ ptrdiff_t or the corresponding unsigned integer type argument; or that a + following n conversion specifier applies to a pointer to a ptrdiff_t + argument. ++ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier +
+ applies to a long double argument. ++ If a length modifier appears with any conversion specifier other than as specified above, + the behavior is undefined. +
+ The conversion specifiers and their meanings are: + d,i The int argument is converted to signed decimal in the style [-]dddd. The +
+ precision specifies the minimum number of digits to appear; if the value + being converted can be represented in fewer digits, it is expanded with + leading zeros. The default precision is 1. The result of converting a zero + value with a precision of zero is no characters. ++ o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned +
+ decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the + letters abcdef are used for x conversion and the letters ABCDEF for X + conversion. The precision specifies the minimum number of digits to appear; + if the value being converted can be represented in fewer digits, it is expanded + with leading zeros. The default precision is 1. The result of converting a + zero value with a precision of zero is no characters. ++ f,F A double argument representing a floating-point number is converted to +
+ decimal notation in the style [-]ddd.ddd, where the number of digits after + the decimal-point character is equal to the precision specification. If the + precision is missing, it is taken as 6; if the precision is zero and the # flag is + not specified, no decimal-point character appears. If a decimal-point + character appears, at least one digit appears before it. The value is rounded to + the appropriate number of digits. + A double argument representing an infinity is converted in one of the styles + [-]inf or [-]infinity -- which style is implementation-defined. A + double argument representing a NaN is converted in one of the styles + [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of + any n-char-sequence, is implementation-defined. The F conversion specifier + produces INF, INFINITY, or NAN instead of inf, infinity, or nan, + respectively.270) ++ e,E A double argument representing a floating-point number is converted in the +
+ style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the + argument is nonzero) before the decimal-point character and the number of + digits after it is equal to the precision; if the precision is missing, it is taken as ++ + + +
+ 6; if the precision is zero and the # flag is not specified, no decimal-point + character appears. The value is rounded to the appropriate number of digits. + The E conversion specifier produces a number with E instead of e + introducing the exponent. The exponent always contains at least two digits, + and only as many more digits as necessary to represent the exponent. If the + value is zero, the exponent is zero. + A double argument representing an infinity or NaN is converted in the style + of an f or F conversion specifier. ++ g,G A double argument representing a floating-point number is converted in +
+ style f or e (or in style F or E in the case of a G conversion specifier), + depending on the value converted and the precision. Let P equal the + precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero. + Then, if a conversion with style E would have an exponent of X: + -- if P > X >= -4, the conversion is with style f (or F) and precision + P - (X + 1). + -- otherwise, the conversion is with style e (or E) and precision P - 1. + Finally, unless the # flag is used, any trailing zeros are removed from the + fractional portion of the result and the decimal-point character is removed if + there is no fractional portion remaining. + A double argument representing an infinity or NaN is converted in the style + of an f or F conversion specifier. ++ a,A A double argument representing a floating-point number is converted in the +
+ style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is + nonzero if the argument is a normalized floating-point number and is + otherwise unspecified) before the decimal-point character271) and the number + of hexadecimal digits after it is equal to the precision; if the precision is + missing and FLT_RADIX is a power of 2, then the precision is sufficient for + an exact representation of the value; if the precision is missing and + FLT_RADIX is not a power of 2, then the precision is sufficient to ++ + + + + +
+ distinguish272) values of type double, except that trailing zeros may be + omitted; if the precision is zero and the # flag is not specified, no decimal- + point character appears. The letters abcdef are used for a conversion and + the letters ABCDEF for A conversion. The A conversion specifier produces a + number with X and P instead of x and p. The exponent always contains at + least one digit, and only as many more digits as necessary to represent the + decimal exponent of 2. If the value is zero, the exponent is zero. + A double argument representing an infinity or NaN is converted in the style + of an f or F conversion specifier. ++ c If no l length modifier is present, the int argument is converted to an +
+ unsigned char, and the resulting character is written. + If an l length modifier is present, the wint_t argument is converted as if by + an ls conversion specification with no precision and an argument that points + to the initial element of a two-element array of wchar_t, the first element + containing the wint_t argument to the lc conversion specification and the + second a null wide character. ++ s If no l length modifier is present, the argument shall be a pointer to the initial +
+ element of an array of character type.273) Characters from the array are + written up to (but not including) the terminating null character. If the + precision is specified, no more than that many bytes are written. If the + precision is not specified or is greater than the size of the array, the array shall + contain a null character. + If an l length modifier is present, the argument shall be a pointer to the initial + element of an array of wchar_t type. Wide characters from the array are + converted to multibyte characters (each as if by a call to the wcrtomb + function, with the conversion state described by an mbstate_t object + initialized to zero before the first wide character is converted) up to and + including a terminating null wide character. The resulting multibyte + characters are written up to (but not including) the terminating null character + (byte). If no precision is specified, the array shall contain a null wide + character. If a precision is specified, no more than that many bytes are + written (including shift sequences, if any), and the array shall contain a null + wide character if, to equal the multibyte character sequence length given by ++ + +
+ the precision, the function would need to access a wide character one past the + end of the array. In no case is a partial multibyte character written.274) ++ p The argument shall be a pointer to void. The value of the pointer is +
+ converted to a sequence of printing characters, in an implementation-defined + manner. ++ n The argument shall be a pointer to signed integer into which is written the +
+ number of characters written to the output stream so far by this call to + fprintf. No argument is converted, but one is consumed. If the conversion + specification includes any flags, a field width, or a precision, the behavior is + undefined. ++ % A % character is written. No argument is converted. The complete +
+ conversion specification shall be %%. ++
+ If a conversion specification is invalid, the behavior is undefined.275) If any argument is + not the correct type for the corresponding conversion specification, the behavior is + undefined. +
+ In no case does a nonexistent or small field width cause truncation of a field; if the result + of a conversion is wider than the field width, the field is expanded to contain the + conversion result. +
+ For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded + to a hexadecimal floating number with the given precision. +
+ For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly + representable in the given precision, the result should be one of the two adjacent numbers + in hexadecimal floating style with the given precision, with the extra stipulation that the + error should have a correct sign for the current rounding direction. +
+ For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most + DECIMAL_DIG, then the result should be correctly rounded.276) If the number of + significant decimal digits is more than DECIMAL_DIG but the source value is exactly + representable with DECIMAL_DIG digits, then the result should be an exact + representation with trailing zeros. Otherwise, the source value is bounded by two + adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value + + + + of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that + the error should have a correct sign for the current rounding direction. +
+ The fprintf function returns the number of characters transmitted, or a negative value + if an output or encoding error occurred. +
+ The number of characters that can be produced by any single conversion shall be at least + 4095. +
+ EXAMPLE 1 To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal + places: +
+ #include <math.h> + #include <stdio.h> + /* ... */ + char *weekday, *month; // pointers to strings + int day, hour, min; + fprintf(stdout, "%s, %s %d, %.2d:%.2d\n", + weekday, month, day, hour, min); + fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0)); ++ +
+ EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the + members of the extended character set that consist of more than one byte each consist of exactly two bytes, + the first of which is denoted here by a and the second by an uppercase letter. +
+ Given the following wide string with length seven, +
+ static wchar_t wstr[] = L" X Yabc Z W"; ++ the seven calls +
+ fprintf(stdout, "|1234567890123|\n"); + fprintf(stdout, "|%13ls|\n", wstr); + fprintf(stdout, "|%-13.9ls|\n", wstr); + fprintf(stdout, "|%13.10ls|\n", wstr); + fprintf(stdout, "|%13.11ls|\n", wstr); + fprintf(stdout, "|%13.15ls|\n", &wstr[2]); + fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]); ++ will print the following seven lines: +
+ |1234567890123| + | X Yabc Z W| + | X Yabc Z | + | X Yabc Z| + | X Yabc Z W| + | abc Z W| + | Z| ++ +
Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3). + + +
268) Note that 0 is taken as a flag, not as the beginning of a field width. + +
269) The results of all floating conversions of a negative zero, and of negative values that round to zero, + include a minus sign. + +
270) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning; + the # and 0 flag characters have no effect. + +
271) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so + that subsequent digits align to nibble (4-bit) boundaries. + +
272) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is + FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p + might suffice depending on the implementation's scheme for determining the digit to the left of the + decimal-point character. + +
273) No special provisions are made for multibyte characters. + +
274) Redundant shift sequences may result if multibyte characters have a state-dependent encoding. + +
275) See ''future library directions'' (7.30.9). + +
276) For binary-to-decimal conversion, the result format's values are the numbers representable with the + given format specifier. The number of significant digits is determined by the format specifier, and in + the case of fixed-point conversion by the source value as well. + + +
+
+ #include <stdio.h> + int fscanf(FILE * restrict stream, + const char * restrict format, ...); ++
+ The fscanf function reads input from the stream pointed to by stream, under control + of the string pointed to by format that specifies the admissible input sequences and how + they are to be converted for assignment, using subsequent arguments as pointers to the + objects to receive the converted input. If there are insufficient arguments for the format, + the behavior is undefined. If the format is exhausted while arguments remain, the excess + arguments are evaluated (as always) but are otherwise ignored. +
+ The format shall be a multibyte character sequence, beginning and ending in its initial + shift state. The format is composed of zero or more directives: one or more white-space + characters, an ordinary multibyte character (neither % nor a white-space character), or a + conversion specification. Each conversion specification is introduced by the character %. + After the %, the following appear in sequence: +
+ The fscanf function executes each directive of the format in turn. When all directives + have been executed, or if a directive fails (as detailed below), the function returns. + Failures are described as input failures (due to the occurrence of an encoding error or the + unavailability of input characters), or matching failures (due to inappropriate input). +
+ A directive composed of white-space character(s) is executed by reading input up to the + first non-white-space character (which remains unread), or until no more characters can + be read. +
+ A directive that is an ordinary multibyte character is executed by reading the next + characters of the stream. If any of those characters differ from the ones composing the + directive, the directive fails and the differing and subsequent characters remain unread. + Similarly, if end-of-file, an encoding error, or a read error prevents a character from being + read, the directive fails. +
+ A directive that is a conversion specification defines a set of matching input sequences, as + described below for each specifier. A conversion specification is executed in the + + following steps: +
+ Input white-space characters (as specified by the isspace function) are skipped, unless + the specification includes a [, c, or n specifier.277) +
+ An input item is read from the stream, unless the specification includes an n specifier. An + input item is defined as the longest sequence of input characters which does not exceed + any specified field width and which is, or is a prefix of, a matching input sequence.278) + The first character, if any, after the input item remains unread. If the length of the input + item is zero, the execution of the directive fails; this condition is a matching failure unless + end-of-file, an encoding error, or a read error prevented input from the stream, in which + case it is an input failure. +
+ Except in the case of a % specifier, the input item (or, in the case of a %n directive, the + count of input characters) is converted to a type appropriate to the conversion specifier. If + the input item is not a matching sequence, the execution of the directive fails: this + condition is a matching failure. Unless assignment suppression was indicated by a *, the + result of the conversion is placed in the object pointed to by the first argument following + the format argument that has not already received a conversion result. If this object + does not have an appropriate type, or if the result of the conversion cannot be represented + in the object, the behavior is undefined. +
+ The length modifiers and their meanings are: + hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to signed char or unsigned char. ++ h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to short int or unsigned short + int. ++ l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to long int or unsigned long + int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to + an argument with type pointer to double; or that a following c, s, or [ + conversion specifier applies to an argument with type pointer to wchar_t. ++ ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to long long int or unsigned + long long int. ++ + + + + j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to intmax_t or uintmax_t. ++ z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to size_t or the corresponding signed + integer type. ++ t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to ptrdiff_t or the corresponding + unsigned integer type. ++ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier +
+ applies to an argument with type pointer to long double. ++ If a length modifier appears with any conversion specifier other than as specified above, + the behavior is undefined. +
+ The conversion specifiers and their meanings are: + d Matches an optionally signed decimal integer, whose format is the same as +
+ expected for the subject sequence of the strtol function with the value 10 + for the base argument. The corresponding argument shall be a pointer to + signed integer. ++ i Matches an optionally signed integer, whose format is the same as expected +
+ for the subject sequence of the strtol function with the value 0 for the + base argument. The corresponding argument shall be a pointer to signed + integer. ++ o Matches an optionally signed octal integer, whose format is the same as +
+ expected for the subject sequence of the strtoul function with the value 8 + for the base argument. The corresponding argument shall be a pointer to + unsigned integer. ++ u Matches an optionally signed decimal integer, whose format is the same as +
+ expected for the subject sequence of the strtoul function with the value 10 + for the base argument. The corresponding argument shall be a pointer to + unsigned integer. ++ x Matches an optionally signed hexadecimal integer, whose format is the same +
+ as expected for the subject sequence of the strtoul function with the value + 16 for the base argument. The corresponding argument shall be a pointer to + unsigned integer. ++ a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose + +
+ format is the same as expected for the subject sequence of the strtod + function. The corresponding argument shall be a pointer to floating. ++ c Matches a sequence of characters of exactly the number specified by the field +
+ width (1 if no field width is present in the directive).279) + If no l length modifier is present, the corresponding argument shall be a + pointer to the initial element of a character array large enough to accept the + sequence. No null character is added. + If an l length modifier is present, the input shall be a sequence of multibyte + characters that begins in the initial shift state. Each multibyte character in the + sequence is converted to a wide character as if by a call to the mbrtowc + function, with the conversion state described by an mbstate_t object + initialized to zero before the first multibyte character is converted. The + corresponding argument shall be a pointer to the initial element of an array of + wchar_t large enough to accept the resulting sequence of wide characters. + No null wide character is added. ++ s Matches a sequence of non-white-space characters.279) +
+ If no l length modifier is present, the corresponding argument shall be a + pointer to the initial element of a character array large enough to accept the + sequence and a terminating null character, which will be added automatically. + If an l length modifier is present, the input shall be a sequence of multibyte + characters that begins in the initial shift state. Each multibyte character is + converted to a wide character as if by a call to the mbrtowc function, with + the conversion state described by an mbstate_t object initialized to zero + before the first multibyte character is converted. The corresponding argument + shall be a pointer to the initial element of an array of wchar_t large enough + to accept the sequence and the terminating null wide character, which will be + added automatically. ++ [ Matches a nonempty sequence of characters from a set of expected characters +
+ (the scanset).279) + If no l length modifier is present, the corresponding argument shall be a + pointer to the initial element of a character array large enough to accept the + sequence and a terminating null character, which will be added automatically. + If an l length modifier is present, the input shall be a sequence of multibyte + characters that begins in the initial shift state. Each multibyte character is + converted to a wide character as if by a call to the mbrtowc function, with + the conversion state described by an mbstate_t object initialized to zero ++ + +
+ before the first multibyte character is converted. The corresponding argument + shall be a pointer to the initial element of an array of wchar_t large enough + to accept the sequence and the terminating null wide character, which will be + added automatically. + The conversion specifier includes all subsequent characters in the format + string, up to and including the matching right bracket (]). The characters + between the brackets (the scanlist) compose the scanset, unless the character + after the left bracket is a circumflex (^), in which case the scanset contains all + characters that do not appear in the scanlist between the circumflex and the + right bracket. If the conversion specifier begins with [] or [^], the right + bracket character is in the scanlist and the next following right bracket + character is the matching right bracket that ends the specification; otherwise + the first following right bracket character is the one that ends the + specification. If a - character is in the scanlist and is not the first, nor the + second where the first character is a ^, nor the last character, the behavior is + implementation-defined. ++ p Matches an implementation-defined set of sequences, which should be the +
+ same as the set of sequences that may be produced by the %p conversion of + the fprintf function. The corresponding argument shall be a pointer to a + pointer to void. The input item is converted to a pointer value in an + implementation-defined manner. If the input item is a value converted earlier + during the same program execution, the pointer that results shall compare + equal to that value; otherwise the behavior of the %p conversion is undefined. ++ n No input is consumed. The corresponding argument shall be a pointer to +
+ signed integer into which is to be written the number of characters read from + the input stream so far by this call to the fscanf function. Execution of a + %n directive does not increment the assignment count returned at the + completion of execution of the fscanf function. No argument is converted, + but one is consumed. If the conversion specification includes an assignment- + suppressing character or a field width, the behavior is undefined. ++ % Matches a single % character; no conversion or assignment occurs. The +
+ complete conversion specification shall be %%. ++
+ If a conversion specification is invalid, the behavior is undefined.280) +
+ The conversion specifiers A, E, F, G, and X are also valid and behave the same as, + respectively, a, e, f, g, and x. + + + + +
+ Trailing white space (including new-line characters) is left unread unless matched by a + directive. The success of literal matches and suppressed assignments is not directly + determinable other than via the %n directive. +
+ The fscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the function returns the + number of input items assigned, which can be fewer than provided for, or even zero, in + the event of an early matching failure. +
+ EXAMPLE 1 The call: +
+ #include <stdio.h> + /* ... */ + int n, i; float x; char name[50]; + n = fscanf(stdin, "%d%f%s", &i, &x, name); ++ with the input line: +
+ 25 54.32E-1 thompson ++ will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence + thompson\0. + +
+ EXAMPLE 2 The call: +
+ #include <stdio.h> + /* ... */ + int i; float x; char name[50]; + fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name); ++ with input: +
+ 56789 0123 56a72 ++ will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the + sequence 56\0. The next character read from the input stream will be a. + +
+ EXAMPLE 3 To accept repeatedly from stdin a quantity, a unit of measure, and an item name: +
+ #include <stdio.h> + /* ... */ + int count; float quant; char units[21], item[21]; + do { + count = fscanf(stdin, "%f%20s of %20s", &quant, units, item); + fscanf(stdin,"%*[^\n]"); + } while (!feof(stdin) && !ferror(stdin)); ++
+ If the stdin stream contains the following lines: + +
+ 2 quarts of oil + -12.8degrees Celsius + lots of luck + 10.0LBS of + dirt + 100ergs of energy ++ the execution of the above example will be analogous to the following assignments: +
+ quant = 2; strcpy(units, "quarts"); strcpy(item, "oil"); + count = 3; + quant = -12.8; strcpy(units, "degrees"); + count = 2; // "C" fails to match "o" + count = 0; // "l" fails to match "%f" + quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt"); + count = 3; + count = 0; // "100e" fails to match "%f" + count = EOF; ++ +
+ EXAMPLE 4 In: +
+ #include <stdio.h> + /* ... */ + int d1, d2, n1, n2, i; + i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2); ++ the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value + of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i. + +
+ EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the + members of the extended character set that consist of more than one byte each consist of exactly two bytes, + the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as + such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes + entry into the alternate shift state. +
+ After the call: +
+ #include <stdio.h> + /* ... */ + char str[50]; + fscanf(stdin, "a%s", str); ++ with the input line: +
+ a(uparrow) X Y(downarrow) bc ++ str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte + characters, in the more general case) appears to be a single-byte white-space character. +
+ In contrast, after the call: +
+ #include <stdio.h> + #include <stddef.h> + /* ... */ + wchar_t wstr[50]; + fscanf(stdin, "a%ls", wstr); ++ with the same input line, wstr will contain the two wide characters that correspond to X and Y and a + terminating null wide character. +
+ However, the call: + +
+ #include <stdio.h> + #include <stddef.h> + /* ... */ + wchar_t wstr[50]; + fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr); ++ with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format + string. +
+ Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte + character Y, after the call: +
+ #include <stdio.h> + #include <stddef.h> + /* ... */ + wchar_t wstr[50]; + fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr); ++ with the same input line, zero will again be returned, but stdin will be left with a partially consumed + multibyte character. + +
Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the + strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state + (7.28.6), the wcrtomb function (7.28.6.3.3). + +
277) These white-space characters are not counted against a specified field width. + +
278) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences + that are acceptable to strtod, strtol, etc., are unacceptable to fscanf. + +
279) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [ + conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The + resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state. + +
280) See ''future library directions'' (7.30.9). + + +
+
+ #include <stdio.h> + int printf(const char * restrict format, ...); ++
+ The printf function is equivalent to fprintf with the argument stdout interposed + before the arguments to printf. +
+ The printf function returns the number of characters transmitted, or a negative value if + an output or encoding error occurred. + +
+
+ #include <stdio.h> + int scanf(const char * restrict format, ...); ++
+ The scanf function is equivalent to fscanf with the argument stdin interposed + before the arguments to scanf. + +
+ The scanf function returns the value of the macro EOF if an input failure occurs before + the first conversion (if any) has completed. Otherwise, the scanf function returns the + number of input items assigned, which can be fewer than provided for, or even zero, in + the event of an early matching failure. + +
+
+ #include <stdio.h> + int snprintf(char * restrict s, size_t n, + const char * restrict format, ...); ++
+ The snprintf function is equivalent to fprintf, except that the output is written into + an array (specified by argument s) rather than to a stream. If n is zero, nothing is written, + and s may be a null pointer. Otherwise, output characters beyond the n-1st are + discarded rather than being written to the array, and a null character is written at the end + of the characters actually written into the array. If copying takes place between objects + that overlap, the behavior is undefined. +
+ The snprintf function returns the number of characters that would have been written + had n been sufficiently large, not counting the terminating null character, or a negative + value if an encoding error occurred. Thus, the null-terminated output has been + completely written if and only if the returned value is nonnegative and less than n. + +
+
+ #include <stdio.h> + int sprintf(char * restrict s, + const char * restrict format, ...); ++
+ The sprintf function is equivalent to fprintf, except that the output is written into + an array (specified by the argument s) rather than to a stream. A null character is written + at the end of the characters written; it is not counted as part of the returned value. If + copying takes place between objects that overlap, the behavior is undefined. +
+ The sprintf function returns the number of characters written in the array, not + counting the terminating null character, or a negative value if an encoding error occurred. + + +
+
+ #include <stdio.h> + int sscanf(const char * restrict s, + const char * restrict format, ...); ++
+ The sscanf function is equivalent to fscanf, except that input is obtained from a + string (specified by the argument s) rather than from a stream. Reaching the end of the + string is equivalent to encountering end-of-file for the fscanf function. If copying + takes place between objects that overlap, the behavior is undefined. +
+ The sscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the sscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdarg.h> + #include <stdio.h> + int vfprintf(FILE * restrict stream, + const char * restrict format, + va_list arg); ++
+ The vfprintf function is equivalent to fprintf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vfprintf function does not invoke the + va_end macro.281) +
+ The vfprintf function returns the number of characters transmitted, or a negative + value if an output or encoding error occurred. +
+ EXAMPLE The following shows the use of the vfprintf function in a general error-reporting routine. + + + + + +
+ #include <stdarg.h> + #include <stdio.h> + void error(char *function_name, char *format, ...) + { + va_list args; + va_start(args, format); + // print out name of function causing error + fprintf(stderr, "ERROR in %s: ", function_name); + // print out remainder of message + vfprintf(stderr, format, args); + va_end(args); + } ++ + +
281) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and + vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate. + + +
+
+ #include <stdarg.h> + #include <stdio.h> + int vfscanf(FILE * restrict stream, + const char * restrict format, + va_list arg); ++
+ The vfscanf function is equivalent to fscanf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vfscanf function does not invoke the + va_end macro.281) +
+ The vfscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the vfscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdarg.h> + #include <stdio.h> + int vprintf(const char * restrict format, + va_list arg); ++
+ The vprintf function is equivalent to printf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + + possibly subsequent va_arg calls). The vprintf function does not invoke the + va_end macro.281) +
+ The vprintf function returns the number of characters transmitted, or a negative value + if an output or encoding error occurred. + +
+
+ #include <stdarg.h> + #include <stdio.h> + int vscanf(const char * restrict format, + va_list arg); ++
+ The vscanf function is equivalent to scanf, with the variable argument list replaced + by arg, which shall have been initialized by the va_start macro (and possibly + subsequent va_arg calls). The vscanf function does not invoke the va_end + macro.281) +
+ The vscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the vscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdarg.h> + #include <stdio.h> int vsnprintf(char * restrict s, size_t n, - const char * restrict format, va_list arg); - int vsprintf(char * restrict s, - const char * restrict format, va_list arg); - int vsscanf(const char * restrict s, - const char * restrict format, va_list arg); - int fgetc(FILE *stream); - char *fgets(char * restrict s, int n, - FILE * restrict stream); - int fputc(int c, FILE *stream); - int fputs(const char * restrict s, - FILE * restrict stream); - int getc(FILE *stream); + const char * restrict format, + va_list arg); ++
+ The vsnprintf function is equivalent to snprintf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vsnprintf function does not invoke the + va_end macro.281) If copying takes place between objects that overlap, the behavior is + undefined. + +
+ The vsnprintf function returns the number of characters that would have been written + had n been sufficiently large, not counting the terminating null character, or a negative + value if an encoding error occurred. Thus, the null-terminated output has been + completely written if and only if the returned value is nonnegative and less than n. + +
+
+ #include <stdarg.h> + #include <stdio.h> + int vsprintf(char * restrict s, + const char * restrict format, + va_list arg); ++
+ The vsprintf function is equivalent to sprintf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vsprintf function does not invoke the + va_end macro.281) If copying takes place between objects that overlap, the behavior is + undefined. +
+ The vsprintf function returns the number of characters written in the array, not + counting the terminating null character, or a negative value if an encoding error occurred. + +
+
+ #include <stdarg.h> + #include <stdio.h> + int vsscanf(const char * restrict s, + const char * restrict format, + va_list arg); ++
+ The vsscanf function is equivalent to sscanf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vsscanf function does not invoke the + va_end macro.281) +
+ The vsscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the vsscanf function + + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdio.h> + int fgetc(FILE *stream); ++
+ If the end-of-file indicator for the input stream pointed to by stream is not set and a + next character is present, the fgetc function obtains that character as an unsigned + char converted to an int and advances the associated file position indicator for the + stream (if defined). +
+ If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end- + of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the + fgetc function returns the next character from the input stream pointed to by stream. + If a read error occurs, the error indicator for the stream is set and the fgetc function + returns EOF.282) + +
282) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. + + +
+
+ #include <stdio.h> + char *fgets(char * restrict s, int n, + FILE * restrict stream); ++
+ The fgets function reads at most one less than the number of characters specified by n + from the stream pointed to by stream into the array pointed to by s. No additional + characters are read after a new-line character (which is retained) or after end-of-file. A + null character is written immediately after the last character read into the array. +
+ The fgets function returns s if successful. If end-of-file is encountered and no + characters have been read into the array, the contents of the array remain unchanged and a + null pointer is returned. If a read error occurs during the operation, the array contents are + indeterminate and a null pointer is returned. + + + +
+
+ #include <stdio.h> + int fputc(int c, FILE *stream); ++
+ The fputc function writes the character specified by c (converted to an unsigned + char) to the output stream pointed to by stream, at the position indicated by the + associated file position indicator for the stream (if defined), and advances the indicator + appropriately. If the file cannot support positioning requests, or if the stream was opened + with append mode, the character is appended to the output stream. +
+ The fputc function returns the character written. If a write error occurs, the error + indicator for the stream is set and fputc returns EOF. + +
+
+ #include <stdio.h> + int fputs(const char * restrict s, + FILE * restrict stream); ++
+ The fputs function writes the string pointed to by s to the stream pointed to by + stream. The terminating null character is not written. +
+ The fputs function returns EOF if a write error occurs; otherwise it returns a + nonnegative value. + +
+
+ #include <stdio.h> + int getc(FILE *stream); ++
+ The getc function is equivalent to fgetc, except that if it is implemented as a macro, it + may evaluate stream more than once, so the argument should never be an expression + with side effects. + +
+ The getc function returns the next character from the input stream pointed to by + stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and + getc returns EOF. If a read error occurs, the error indicator for the stream is set and + getc returns EOF. + +
+
+ #include <stdio.h> int getchar(void); - int putc(int c, FILE *stream); * ++
+ The getchar function is equivalent to getc with the argument stdin. +
+ The getchar function returns the next character from the input stream pointed to by + stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and + getchar returns EOF. If a read error occurs, the error indicator for the stream is set and + getchar returns EOF. * + +
+
+ #include <stdio.h> + int putc(int c, FILE *stream); ++
+ The putc function is equivalent to fputc, except that if it is implemented as a macro, it + may evaluate stream more than once, so that argument should never be an expression + with side effects. +
+ The putc function returns the character written. If a write error occurs, the error + indicator for the stream is set and putc returns EOF. + +
+
+ #include <stdio.h> int putchar(int c); - int puts(const char *s); - int ungetc(int c, FILE *stream); - size_t fread(void * restrict ptr, - size_t size, size_t nmemb, - FILE * restrict stream); - size_t fwrite(const void * restrict ptr, - size_t size, size_t nmemb, - FILE * restrict stream); - int fgetpos(FILE * restrict stream, - fpos_t * restrict pos); ++
+ The putchar function is equivalent to putc with the second argument stdout. + +
+ The putchar function returns the character written. If a write error occurs, the error + indicator for the stream is set and putchar returns EOF. + +
+
+ #include <stdio.h> + int puts(const char *s); ++
+ The puts function writes the string pointed to by s to the stream pointed to by stdout, + and appends a new-line character to the output. The terminating null character is not + written. +
+ The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative + value. + +
+
+ #include <stdio.h> + int ungetc(int c, FILE *stream); ++
+ The ungetc function pushes the character specified by c (converted to an unsigned + char) back onto the input stream pointed to by stream. Pushed-back characters will be + returned by subsequent reads on that stream in the reverse order of their pushing. A + successful intervening call (with the stream pointed to by stream) to a file positioning + function (fseek, fsetpos, or rewind) discards any pushed-back characters for the + stream. The external storage corresponding to the stream is unchanged. +
+ One character of pushback is guaranteed. If the ungetc function is called too many + times on the same stream without an intervening read or file positioning operation on that + stream, the operation may fail. +
+ If the value of c equals that of the macro EOF, the operation fails and the input stream is + unchanged. +
+ A successful call to the ungetc function clears the end-of-file indicator for the stream. + The value of the file position indicator for the stream after reading or discarding all + pushed-back characters shall be the same as it was before the characters were pushed + back. For a text stream, the value of its file position indicator after a successful call to the + ungetc function is unspecified until all pushed-back characters are read or discarded. + + For a binary stream, its file position indicator is decremented by each successful call to + the ungetc function; if its value was zero before a call, it is indeterminate after the + call.283) +
+ The ungetc function returns the character pushed back after conversion, or EOF if the + operation fails. +
Forward references: file positioning functions (7.21.9). + +
283) See ''future library directions'' (7.30.9). + + +
+
+ #include <stdio.h> + size_t fread(void * restrict ptr, + size_t size, size_t nmemb, + FILE * restrict stream); ++
+ The fread function reads, into the array pointed to by ptr, up to nmemb elements + whose size is specified by size, from the stream pointed to by stream. For each + object, size calls are made to the fgetc function and the results stored, in the order + read, in an array of unsigned char exactly overlaying the object. The file position + indicator for the stream (if defined) is advanced by the number of characters successfully + read. If an error occurs, the resulting value of the file position indicator for the stream is + indeterminate. If a partial element is read, its value is indeterminate. +
+ The fread function returns the number of elements successfully read, which may be + less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero, + fread returns zero and the contents of the array and the state of the stream remain + unchanged. + + + + + + +
+
+ #include <stdio.h> + size_t fwrite(const void * restrict ptr, + size_t size, size_t nmemb, + FILE * restrict stream); ++
+ The fwrite function writes, from the array pointed to by ptr, up to nmemb elements + whose size is specified by size, to the stream pointed to by stream. For each object, + size calls are made to the fputc function, taking the values (in order) from an array of + unsigned char exactly overlaying the object. The file position indicator for the + stream (if defined) is advanced by the number of characters successfully written. If an + error occurs, the resulting value of the file position indicator for the stream is + indeterminate. +
+ The fwrite function returns the number of elements successfully written, which will be + less than nmemb only if a write error is encountered. If size or nmemb is zero, + fwrite returns zero and the state of the stream remains unchanged. + +
+
+ #include <stdio.h> + int fgetpos(FILE * restrict stream, + fpos_t * restrict pos); ++
+ The fgetpos function stores the current values of the parse state (if any) and file + position indicator for the stream pointed to by stream in the object pointed to by pos. + The values stored contain unspecified information usable by the fsetpos function for + repositioning the stream to its position at the time of the call to the fgetpos function. +
+ If successful, the fgetpos function returns zero; on failure, the fgetpos function + returns nonzero and stores an implementation-defined positive value in errno. +
Forward references: the fsetpos function (7.21.9.3). + + +
+
+ #include <stdio.h> int fseek(FILE *stream, long int offset, int whence); ++
+ The fseek function sets the file position indicator for the stream pointed to by stream. + If a read or write error occurs, the error indicator for the stream is set and fseek fails. +
+ For a binary stream, the new position, measured in characters from the beginning of the + file, is obtained by adding offset to the position specified by whence. The specified + position is the beginning of the file if whence is SEEK_SET, the current value of the file + position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not + meaningfully support fseek calls with a whence value of SEEK_END. +
+ For a text stream, either offset shall be zero, or offset shall be a value returned by + an earlier successful call to the ftell function on a stream associated with the same file + and whence shall be SEEK_SET. +
+ After determining the new position, a successful call to the fseek function undoes any + effects of the ungetc function on the stream, clears the end-of-file indicator for the + stream, and then establishes the new position. After a successful fseek call, the next + operation on an update stream may be either input or output. +
+ The fseek function returns nonzero only for a request that cannot be satisfied. +
Forward references: the ftell function (7.21.9.4). + +
+
+ #include <stdio.h> int fsetpos(FILE *stream, const fpos_t *pos); - long int ftell(FILE *stream); - void rewind(FILE *stream); ++
+ The fsetpos function sets the mbstate_t object (if any) and file position indicator + for the stream pointed to by stream according to the value of the object pointed to by + pos, which shall be a value obtained from an earlier successful call to the fgetpos + function on a stream associated with the same file. If a read or write error occurs, the + error indicator for the stream is set and fsetpos fails. +
+ A successful call to the fsetpos function undoes any effects of the ungetc function + on the stream, clears the end-of-file indicator for the stream, and then establishes the new + parse state and position. After a successful fsetpos call, the next operation on an + + update stream may be either input or output. +
+ If successful, the fsetpos function returns zero; on failure, the fsetpos function + returns nonzero and stores an implementation-defined positive value in errno. + +
+
+ #include <stdio.h> + long int ftell(FILE *stream); ++
+ The ftell function obtains the current value of the file position indicator for the stream + pointed to by stream. For a binary stream, the value is the number of characters from + the beginning of the file. For a text stream, its file position indicator contains unspecified + information, usable by the fseek function for returning the file position indicator for the + stream to its position at the time of the ftell call; the difference between two such + return values is not necessarily a meaningful measure of the number of characters written + or read. +
+ If successful, the ftell function returns the current value of the file position indicator + for the stream. On failure, the ftell function returns -1L and stores an + implementation-defined positive value in errno. + +
+
+ #include <stdio.h> + void rewind(FILE *stream); ++
+ The rewind function sets the file position indicator for the stream pointed to by + stream to the beginning of the file. It is equivalent to +
+ (void)fseek(stream, 0L, SEEK_SET) ++ except that the error indicator for the stream is also cleared. +
+ The rewind function returns no value. + + +
+
+ #include <stdio.h> void clearerr(FILE *stream); ++
+ The clearerr function clears the end-of-file and error indicators for the stream pointed + to by stream. +
+ The clearerr function returns no value. + +
+
+ #include <stdio.h> int feof(FILE *stream); ++
+ The feof function tests the end-of-file indicator for the stream pointed to by stream. +
+ The feof function returns nonzero if and only if the end-of-file indicator is set for + stream. + +
+
+ #include <stdio.h> int ferror(FILE *stream); - void perror(const char *s); - __STDC_WANT_LIB_EXT1__ - L_tmpnam_s TMP_MAX_S errno_t rsize_t - errno_t tmpfile_s(FILE * restrict * restrict streamptr); - errno_t tmpnam_s(char *s, rsize_t maxsize); - - - -[page 485] (Contents) - - errno_t fopen_s(FILE * restrict * restrict streamptr, - const char * restrict filename, - const char * restrict mode); - errno_t freopen_s(FILE * restrict * restrict newstreamptr, - const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - int fprintf_s(FILE * restrict stream, - const char * restrict format, ...); - int fscanf_s(FILE * restrict stream, - const char * restrict format, ...); - int printf_s(const char * restrict format, ...); - int scanf_s(const char * restrict format, ...); - int snprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - int sprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - int sscanf_s(const char * restrict s, - const char * restrict format, ...); - int vfprintf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - int vfscanf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - int vprintf_s(const char * restrict format, - va_list arg); - int vscanf_s(const char * restrict format, - va_list arg); - int vsnprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - int vsprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - int vsscanf_s(const char * restrict s, - const char * restrict format, - va_list arg); - char *gets_s(char *s, rsize_t n); - - - -[page 486] (Contents) - -B.21 General utilities <stdlib.h> - size_t ldiv_t EXIT_FAILURE MB_CUR_MAX - wchar_t lldiv_t EXIT_SUCCESS - div_t NULL RAND_MAX - double atof(const char *nptr); - int atoi(const char *nptr); - long int atol(const char *nptr); - long long int atoll(const char *nptr); ++
+ The ferror function tests the error indicator for the stream pointed to by stream. +
+ The ferror function returns nonzero if and only if the error indicator is set for + stream. + + +
+
+ #include <stdio.h> + void perror(const char *s); ++
+ The perror function maps the error number in the integer expression errno to an + error message. It writes a sequence of characters to the standard error stream thus: first + (if s is not a null pointer and the character pointed to by s is not the null character), the + string pointed to by s followed by a colon (:) and a space; then an appropriate error + message string followed by a new-line character. The contents of the error message + strings are the same as those returned by the strerror function with argument errno. +
+ The perror function returns no value. +
Forward references: the strerror function (7.23.6.2). + + +
+ The header <stdlib.h> declares five types and several functions of general utility, and + defines several macros.284) +
+ The types declared are size_t and wchar_t (both described in 7.19), +
+ div_t ++ which is a structure type that is the type of the value returned by the div function, +
+ ldiv_t ++ which is a structure type that is the type of the value returned by the ldiv function, and +
+ lldiv_t ++ which is a structure type that is the type of the value returned by the lldiv function. +
+ The macros defined are NULL (described in 7.19); +
+ EXIT_FAILURE ++ and +
+ EXIT_SUCCESS ++ which expand to integer constant expressions that can be used as the argument to the + exit function to return unsuccessful or successful termination status, respectively, to the + host environment; +
+ RAND_MAX ++ which expands to an integer constant expression that is the maximum value returned by + the rand function; and +
+ MB_CUR_MAX ++ which expands to a positive integer expression with type size_t that is the maximum + number of bytes in a multibyte character for the extended character set specified by the + current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX. + + + + + + +
284) See ''future library directions'' (7.30.10). + + +
+ The functions atof, atoi, atol, and atoll need not affect the value of the integer + expression errno on an error. If the value of the result cannot be represented, the + behavior is undefined. + +
+
+ #include <stdlib.h> + double atof(const char *nptr); ++
+ The atof function converts the initial portion of the string pointed to by nptr to + double representation. Except for the behavior on error, it is equivalent to +
+ strtod(nptr, (char **)NULL) ++
+ The atof function returns the converted value. +
Forward references: the strtod, strtof, and strtold functions (7.22.1.3). + +
+
+ #include <stdlib.h> + int atoi(const char *nptr); + long int atol(const char *nptr); + long long int atoll(const char *nptr); ++
+ The atoi, atol, and atoll functions convert the initial portion of the string pointed + to by nptr to int, long int, and long long int representation, respectively. + Except for the behavior on error, they are equivalent to +
+ atoi: (int)strtol(nptr, (char **)NULL, 10) + atol: strtol(nptr, (char **)NULL, 10) + atoll: strtoll(nptr, (char **)NULL, 10) ++
+ The atoi, atol, and atoll functions return the converted value. +
Forward references: the strtol, strtoll, strtoul, and strtoull functions + (7.22.1.4). + + +
+
+ #include <stdlib.h> double strtod(const char * restrict nptr, char ** restrict endptr); float strtof(const char * restrict nptr, char ** restrict endptr); long double strtold(const char * restrict nptr, char ** restrict endptr); - long int strtol(const char * restrict nptr, - char ** restrict endptr, int base); - long long int strtoll(const char * restrict nptr, - char ** restrict endptr, int base); - unsigned long int strtoul( - const char * restrict nptr, - char ** restrict endptr, int base); - unsigned long long int strtoull( - const char * restrict nptr, - char ** restrict endptr, int base); - int rand(void); - void srand(unsigned int seed); - void *aligned_alloc(size_t alignment, size_t size); - void *calloc(size_t nmemb, size_t size); - void free(void *ptr); - void *malloc(size_t size); - void *realloc(void *ptr, size_t size); - _Noreturn void abort(void); ++
+ The strtod, strtof, and strtold functions convert the initial portion of the string + pointed to by nptr to double, float, and long double representation, + respectively. First, they decompose the input string into three parts: an initial, possibly + empty, sequence of white-space characters (as specified by the isspace function), a + subject sequence resembling a floating-point constant or representing an infinity or NaN; + and a final string of one or more unrecognized characters, including the terminating null + character of the input string. Then, they attempt to convert the subject sequence to a + floating-point number, and return the result. +
+ The expected form of the subject sequence is an optional plus or minus sign, then one of + the following: +
+ n-char-sequence: + digit + nondigit + n-char-sequence digit + n-char-sequence nondigit ++
+ If the subject sequence has the expected form for a floating-point number, the sequence of + characters starting with the first digit or the decimal-point character (whichever occurs + first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the + + decimal-point character is used in place of a period, and that if neither an exponent part + nor a decimal-point character appears in a decimal floating point number, or if a binary + exponent part does not appear in a hexadecimal floating point number, an exponent part + of the appropriate type with value zero is assumed to follow the last digit in the string. If + the subject sequence begins with a minus sign, the sequence is interpreted as negated.285) + A character sequence INF or INFINITY is interpreted as an infinity, if representable in + the return type, else like a floating constant that is too large for the range of the return + type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet + NaN, if supported in the return type, else like a subject sequence part that does not have + the expected form; the meaning of the n-char sequences is implementation-defined.286) A + pointer to the final string is stored in the object pointed to by endptr, provided that + endptr is not a null pointer. +
+ If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the + value resulting from the conversion is correctly rounded. +
+ In other than the "C" locale, additional locale-specific subject sequence forms may be + accepted. +
+ If the subject sequence is empty or does not have the expected form, no conversion is + performed; the value of nptr is stored in the object pointed to by endptr, provided + that endptr is not a null pointer. +
+ If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and + the result is not exactly representable, the result should be one of the two numbers in the + appropriate internal format that are adjacent to the hexadecimal floating source value, + with the extra stipulation that the error should have a correct sign for the current rounding + direction. +
+ If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in + <float.h>) significant digits, the result should be correctly rounded. If the subject + sequence D has the decimal form and more than DECIMAL_DIG significant digits, + consider the two bounding, adjacent decimal strings L and U, both having + DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U. + The result should be one of the (equal or adjacent) values that would be obtained by + correctly rounding L and U according to the current rounding direction, with the extra + + + stipulation that the error with respect to D should have a correct sign for the current + rounding direction.287) +
+ The functions return the converted value, if any. If no conversion could be performed, + zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), + plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the + return type and sign of the value), and the value of the macro ERANGE is stored in + errno. If the result underflows (7.12.1), the functions return a value whose magnitude is + no greater than the smallest normalized positive number in the return type; whether + errno acquires the value ERANGE is implementation-defined. + +
285) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by + negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two + methods may yield different results if rounding is toward positive or negative infinity. In either case, + the functions honor the sign of zero if floating-point arithmetic supports signed zeros. + +
286) An implementation may use the n-char sequence to determine extra information to be represented in + the NaN's significand. + +
287) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round + to the same internal floating value, but if not will round to adjacent values. + + +
+
+ #include <stdlib.h> + long int strtol( + const char * restrict nptr, + char ** restrict endptr, + int base); + long long int strtoll( + const char * restrict nptr, + char ** restrict endptr, + int base); + unsigned long int strtoul( + const char * restrict nptr, + char ** restrict endptr, + int base); + unsigned long long int strtoull( + const char * restrict nptr, + char ** restrict endptr, + int base); ++
+ The strtol, strtoll, strtoul, and strtoull functions convert the initial + portion of the string pointed to by nptr to long int, long long int, unsigned + long int, and unsigned long long int representation, respectively. First, + they decompose the input string into three parts: an initial, possibly empty, sequence of + white-space characters (as specified by the isspace function), a subject sequence + + + + resembling an integer represented in some radix determined by the value of base, and a + final string of one or more unrecognized characters, including the terminating null + character of the input string. Then, they attempt to convert the subject sequence to an + integer, and return the result. +
+ If the value of base is zero, the expected form of the subject sequence is that of an + integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but + not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the + expected form of the subject sequence is a sequence of letters and digits representing an + integer with the radix specified by base, optionally preceded by a plus or minus sign, + but not including an integer suffix. The letters from a (or A) through z (or Z) are + ascribed the values 10 through 35; only letters and digits whose ascribed values are less + than that of base are permitted. If the value of base is 16, the characters 0x or 0X may + optionally precede the sequence of letters and digits, following the sign if present. +
+ The subject sequence is defined as the longest initial subsequence of the input string, + starting with the first non-white-space character, that is of the expected form. The subject + sequence contains no characters if the input string is empty or consists entirely of white + space, or if the first non-white-space character is other than a sign or a permissible letter + or digit. +
+ If the subject sequence has the expected form and the value of base is zero, the sequence + of characters starting with the first digit is interpreted as an integer constant according to + the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base + is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value + as given above. If the subject sequence begins with a minus sign, the value resulting from + the conversion is negated (in the return type). A pointer to the final string is stored in the + object pointed to by endptr, provided that endptr is not a null pointer. +
+ In other than the "C" locale, additional locale-specific subject sequence forms may be + accepted. +
+ If the subject sequence is empty or does not have the expected form, no conversion is + performed; the value of nptr is stored in the object pointed to by endptr, provided + that endptr is not a null pointer. +
+ The strtol, strtoll, strtoul, and strtoull functions return the converted + value, if any. If no conversion could be performed, zero is returned. If the correct value + is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, + LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type + and sign of the value, if any), and the value of the macro ERANGE is stored in errno. + + +
+
+ #include <stdlib.h> + int rand(void); ++
+ The rand function computes a sequence of pseudo-random integers in the range 0 to + RAND_MAX.288) +
+ The rand function is not required to avoid data races. The implementation shall behave + as if no library function calls the rand function. +
+ The rand function returns a pseudo-random integer. +
+ The value of the RAND_MAX macro shall be at least 32767. + +
288) There are no guarantees as to the quality of the random sequence produced and some implementations + are known to produce sequences with distressingly non-random low-order bits. Applications with + particular requirements should use a generator that is known to be sufficient for their needs. + + +
+
+ #include <stdlib.h> + void srand(unsigned int seed); ++
+ The srand function uses the argument as a seed for a new sequence of pseudo-random + numbers to be returned by subsequent calls to rand. If srand is then called with the + same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is + called before any calls to srand have been made, the same sequence shall be generated + as when srand is first called with a seed value of 1. +
+ The implementation shall behave as if no library function calls the srand function. +
+ The srand function returns no value. + + + + + +
+ EXAMPLE The following functions define a portable implementation of rand and srand. +
+ static unsigned long int next = 1;
+ int rand(void) // RAND_MAX assumed to be 32767
+ {
+ next = next * 1103515245 + 12345;
+ return (unsigned int)(next/65536) % 32768;
+ }
+ void srand(unsigned int seed)
+ {
+ next = seed;
+ }
+
+
+
++ The order and contiguity of storage allocated by successive calls to the + aligned_alloc, calloc, malloc, and realloc functions is unspecified. The + pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to + a pointer to any type of object with a fundamental alignment requirement and then used + to access such an object or an array of such objects in the space allocated (until the space + is explicitly deallocated). The lifetime of an allocated object extends from the allocation + until the deallocation. Each such allocation shall yield a pointer to an object disjoint from + any other object. The pointer returned points to the start (lowest byte address) of the + allocated space. If the space cannot be allocated, a null pointer is returned. If the size of + the space requested is zero, the behavior is implementation-defined: either a null pointer + is returned, or the behavior is as if the size were some nonzero value, except that the + returned pointer shall not be used to access an object. + +
+
+ #include <stdlib.h> + void *aligned_alloc(size_t alignment, size_t size); ++
+ The aligned_alloc function allocates space for an object whose alignment is + specified by alignment, whose size is specified by size, and whose value is + indeterminate. The value of alignment shall be a valid alignment supported by the + implementation and the value of size shall be an integral multiple of alignment. +
+ The aligned_alloc function returns either a null pointer or a pointer to the allocated + space. + + +
+
+ #include <stdlib.h> + void *calloc(size_t nmemb, size_t size); ++
+ The calloc function allocates space for an array of nmemb objects, each of whose size + is size. The space is initialized to all bits zero.289) +
+ The calloc function returns either a null pointer or a pointer to the allocated space. + +
289) Note that this need not be the same as the representation of floating-point zero or a null pointer + constant. + + +
+
+ #include <stdlib.h> + void free(void *ptr); ++
+ The free function causes the space pointed to by ptr to be deallocated, that is, made + available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if + the argument does not match a pointer earlier returned by a memory management + function, or if the space has been deallocated by a call to free or realloc, the + behavior is undefined. +
+ The free function returns no value. + +
+
+ #include <stdlib.h> + void *malloc(size_t size); ++
+ The malloc function allocates space for an object whose size is specified by size and + whose value is indeterminate. + + + + + +
+ The malloc function returns either a null pointer or a pointer to the allocated space. + +
+
+ #include <stdlib.h> + void *realloc(void *ptr, size_t size); ++
+ The realloc function deallocates the old object pointed to by ptr and returns a + pointer to a new object that has the size specified by size. The contents of the new + object shall be the same as that of the old object prior to deallocation, up to the lesser of + the new and old sizes. Any bytes in the new object beyond the size of the old object have + indeterminate values. +
+ If ptr is a null pointer, the realloc function behaves like the malloc function for the + specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory + management function, or if the space has been deallocated by a call to the free or + realloc function, the behavior is undefined. If memory for the new object cannot be + allocated, the old object is not deallocated and its value is unchanged. +
+ The realloc function returns a pointer to the new object (which may have the same + value as a pointer to the old object), or a null pointer if the new object could not be + allocated. + +
+
+ #include <stdlib.h> + _Noreturn void abort(void); ++
+ The abort function causes abnormal program termination to occur, unless the signal + SIGABRT is being caught and the signal handler does not return. Whether open streams + with unwritten buffered data are flushed, open streams are closed, or temporary files are + removed is implementation-defined. An implementation-defined form of the status + unsuccessful termination is returned to the host environment by means of the function + call raise(SIGABRT). + +
+ The abort function does not return to its caller. + +
+
+ #include <stdlib.h> int atexit(void (*func)(void)); ++
+ The atexit function registers the function pointed to by func, to be called without + arguments at normal program termination.290) +
+ The implementation shall support the registration of at least 32 functions. +
+ The atexit function returns zero if the registration succeeds, nonzero if it fails. +
Forward references: the at_quick_exit function (7.22.4.3), the exit function + (7.22.4.4). + +
290) The atexit function registrations are distinct from the at_quick_exit registrations, so + applications may need to call both registration functions with the same argument. + + +
+
+ #include <stdlib.h> int at_quick_exit(void (*func)(void)); - _Noreturn void exit(int status); - _Noreturn void _Exit(int status); - char *getenv(const char *name); - _Noreturn void quick_exit(int status); - int system(const char *string); - - -[page 487] (Contents) - - void *bsearch(const void *key, const void *base, - size_t nmemb, size_t size, - int (*compar)(const void *, const void *)); - void qsort(void *base, size_t nmemb, size_t size, - int (*compar)(const void *, const void *)); - int abs(int j); - long int labs(long int j); - long long int llabs(long long int j); - div_t div(int numer, int denom); - ldiv_t ldiv(long int numer, long int denom); - lldiv_t lldiv(long long int numer, - long long int denom); - int mblen(const char *s, size_t n); - int mbtowc(wchar_t * restrict pwc, - const char * restrict s, size_t n); - int wctomb(char *s, wchar_t wchar); - size_t mbstowcs(wchar_t * restrict pwcs, - const char * restrict s, size_t n); - size_t wcstombs(char * restrict s, - const wchar_t * restrict pwcs, size_t n); - __STDC_WANT_LIB_EXT1__ - errno_t - rsize_t - constraint_handler_t - constraint_handler_t set_constraint_handler_s( - constraint_handler_t handler); - void abort_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - void ignore_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - errno_t getenv_s(size_t * restrict len, - char * restrict value, rsize_t maxsize, - const char * restrict name); - - - - -[page 488] (Contents) - - void *bsearch_s(const void *key, const void *base, - rsize_t nmemb, rsize_t size, - int (*compar)(const void *k, const void *y, - void *context), - void *context); - errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, - int (*compar)(const void *x, const void *y, - void *context), - void *context); - errno_t wctomb_s(int * restrict status, - char * restrict s, - rsize_t smax, - wchar_t wc); - errno_t mbstowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char * restrict src, rsize_t len); - errno_t wcstombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t * restrict src, rsize_t len); -B.22 String handling <string.h> - size_t - NULL - void *memcpy(void * restrict s1, - const void * restrict s2, size_t n); - void *memmove(void *s1, const void *s2, size_t n); - char *strcpy(char * restrict s1, - const char * restrict s2); - char *strncpy(char * restrict s1, - const char * restrict s2, size_t n); - char *strcat(char * restrict s1, - const char * restrict s2); - char *strncat(char * restrict s1, - const char * restrict s2, size_t n); - int memcmp(const void *s1, const void *s2, size_t n); - int strcmp(const char *s1, const char *s2); ++
+ The at_quick_exit function registers the function pointed to by func, to be called + without arguments should quick_exit be called.291) +
+ The implementation shall support the registration of at least 32 functions. +
+ The at_quick_exit function returns zero if the registration succeeds, nonzero if it + fails. +
Forward references: the quick_exit function (7.22.4.7). + + + + +
291) The at_quick_exit function registrations are distinct from the atexit registrations, so + applications may need to call both registration functions with the same argument. + + +
+
+ #include <stdlib.h> + _Noreturn void exit(int status); ++
+ The exit function causes normal program termination to occur. No functions registered + by the at_quick_exit function are called. If a program calls the exit function + more than once, or calls the quick_exit function in addition to the exit function, the + behavior is undefined. +
+ First, all functions registered by the atexit function are called, in the reverse order of + their registration,292) except that a function is called after any previously registered + functions that had already been called at the time it was registered. If, during the call to + any such function, a call to the longjmp function is made that would terminate the call + to the registered function, the behavior is undefined. +
+ Next, all open streams with unwritten buffered data are flushed, all open streams are + closed, and all files created by the tmpfile function are removed. +
+ Finally, control is returned to the host environment. If the value of status is zero or + EXIT_SUCCESS, an implementation-defined form of the status successful termination is + returned. If the value of status is EXIT_FAILURE, an implementation-defined form + of the status unsuccessful termination is returned. Otherwise the status returned is + implementation-defined. +
+ The exit function cannot return to its caller. + +
292) Each function is called as many times as it was registered, and in the correct order with respect to + other registered functions. + + +
+
+ #include <stdlib.h> + _Noreturn void _Exit(int status); ++
+ The _Exit function causes normal program termination to occur and control to be + returned to the host environment. No functions registered by the atexit function, the + at_quick_exit function, or signal handlers registered by the signal function are + called. The status returned to the host environment is determined in the same way as for + + + + the exit function (7.22.4.4). Whether open streams with unwritten buffered data are + flushed, open streams are closed, or temporary files are removed is implementation- + defined. +
+ The _Exit function cannot return to its caller. + +
+
+ #include <stdlib.h> + char *getenv(const char *name); ++
+ The getenv function searches an environment list, provided by the host environment, + for a string that matches the string pointed to by name. The set of environment names + and the method for altering the environment list are implementation-defined. The + getenv function need not avoid data races with other threads of execution that modify + the environment list.293) +
+ The implementation shall behave as if no library function calls the getenv function. +
+ The getenv function returns a pointer to a string associated with the matched list + member. The string pointed to shall not be modified by the program, but may be + overwritten by a subsequent call to the getenv function. If the specified name cannot + be found, a null pointer is returned. + +
293) Many implementations provide non-standard functions that modify the environment list. + + +
+
+ #include <stdlib.h> + _Noreturn void quick_exit(int status); ++
+ The quick_exit function causes normal program termination to occur. No functions + registered by the atexit function or signal handlers registered by the signal function + are called. If a program calls the quick_exit function more than once, or calls the + exit function in addition to the quick_exit function, the behavior is undefined. +
+ The quick_exit function first calls all functions registered by the at_quick_exit + function, in the reverse order of their registration,294) except that a function is called after + + + + any previously registered functions that had already been called at the time it was + registered. If, during the call to any such function, a call to the longjmp function is + made that would terminate the call to the registered function, the behavior is undefined. +
+ Then control is returned to the host environment by means of the function call + _Exit(status). +
+ The quick_exit function cannot return to its caller. + +
294) Each function is called as many times as it was registered, and in the correct order with respect to + other registered functions. + + +
+
+ #include <stdlib.h> + int system(const char *string); ++
+ If string is a null pointer, the system function determines whether the host + environment has a command processor. If string is not a null pointer, the system + function passes the string pointed to by string to that command processor to be + executed in a manner which the implementation shall document; this might then cause the + program calling system to behave in a non-conforming manner or to terminate. +
+ If the argument is a null pointer, the system function returns nonzero only if a + command processor is available. If the argument is not a null pointer, and the system + function does return, it returns an implementation-defined value. + +
+ These utilities make use of a comparison function to search or sort arrays of unspecified + type. Where an argument declared as size_t nmemb specifies the length of the array + for a function, nmemb can have the value zero on a call to that function; the comparison + function is not called, a search finds no matching element, and sorting performs no + rearrangement. Pointer arguments on such a call shall still have valid values, as described + in 7.1.4. +
+ The implementation shall ensure that the second argument of the comparison function + (when called from bsearch), or both arguments (when called from qsort), are + pointers to elements of the array.295) The first argument when called from bsearch + shall equal key. + + + + +
+ The comparison function shall not alter the contents of the array. The implementation + may reorder elements of the array between calls to the comparison function, but shall not + alter the contents of any individual element. +
+ When the same objects (consisting of size bytes, irrespective of their current positions + in the array) are passed more than once to the comparison function, the results shall be + consistent with one another. That is, for qsort they shall define a total ordering on the + array, and for bsearch the same object shall always compare the same way with the + key. +
+ A sequence point occurs immediately before and immediately after each call to the + comparison function, and also between any call to the comparison function and any + movement of the objects passed as arguments to that call. + +
295) That is, if the value passed is p, then the following expressions are always nonzero:
+
+
+ ((char *)p - (char *)base) % size == 0
+ (char *)p >= (char *)base
+ (char *)p < (char *)base + nmemb * size
+
+
+
+
+
+
+ #include <stdlib.h> + void *bsearch(const void *key, const void *base, + size_t nmemb, size_t size, + int (*compar)(const void *, const void *)); ++
+ The bsearch function searches an array of nmemb objects, the initial element of which + is pointed to by base, for an element that matches the object pointed to by key. The + size of each element of the array is specified by size. +
+ The comparison function pointed to by compar is called with two arguments that point + to the key object and to an array element, in that order. The function shall return an + integer less than, equal to, or greater than zero if the key object is considered, + respectively, to be less than, to match, or to be greater than the array element. The array + shall consist of: all the elements that compare less than, all the elements that compare + equal to, and all the elements that compare greater than the key object, in that order.296) +
+ The bsearch function returns a pointer to a matching element of the array, or a null + pointer if no match is found. If two elements compare as equal, which element is + + + + matched is unspecified. + +
296) In practice, the entire array is sorted according to the comparison function. + + +
+
+ #include <stdlib.h> + void qsort(void *base, size_t nmemb, size_t size, + int (*compar)(const void *, const void *)); ++
+ The qsort function sorts an array of nmemb objects, the initial element of which is + pointed to by base. The size of each object is specified by size. +
+ The contents of the array are sorted into ascending order according to a comparison + function pointed to by compar, which is called with two arguments that point to the + objects being compared. The function shall return an integer less than, equal to, or + greater than zero if the first argument is considered to be respectively less than, equal to, + or greater than the second. +
+ If two elements compare as equal, their order in the resulting sorted array is unspecified. +
+ The qsort function returns no value. + +
+
+ #include <stdlib.h> + int abs(int j); + long int labs(long int j); + long long int llabs(long long int j); ++
+ The abs, labs, and llabs functions compute the absolute value of an integer j. If the + result cannot be represented, the behavior is undefined.297) +
+ The abs, labs, and llabs, functions return the absolute value. + + + + + + +
297) The absolute value of the most negative number cannot be represented in two's complement. + + +
+
+ #include <stdlib.h> + div_t div(int numer, int denom); + ldiv_t ldiv(long int numer, long int denom); + lldiv_t lldiv(long long int numer, long long int denom); ++
+ The div, ldiv, and lldiv, functions compute numer / denom and numer % + denom in a single operation. +
+ The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and + lldiv_t, respectively, comprising both the quotient and the remainder. The structures + shall contain (in either order) the members quot (the quotient) and rem (the remainder), + each of which has the same type as the arguments numer and denom. If either part of + the result cannot be represented, the behavior is undefined. + +
+ The behavior of the multibyte character functions is affected by the LC_CTYPE category + of the current locale. For a state-dependent encoding, each function is placed into its + initial conversion state at program startup and can be returned to that state by a call for + which its character pointer argument, s, is a null pointer. Subsequent calls with s as + other than a null pointer cause the internal conversion state of the function to be altered as + necessary. A call with s as a null pointer causes these functions to return a nonzero value + if encodings have state dependency, and zero otherwise.298) Changing the LC_CTYPE + category causes the conversion state of these functions to be indeterminate. + +
298) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide + character codes, but are grouped with an adjacent multibyte character. + + +
+
+ #include <stdlib.h> + int mblen(const char *s, size_t n); ++
+ If s is not a null pointer, the mblen function determines the number of bytes contained + in the multibyte character pointed to by s. Except that the conversion state of the + mbtowc function is not affected, it is equivalent to + + + + +
+ mbtowc((wchar_t *)0, (const char *)0, 0); + mbtowc((wchar_t *)0, s, n); ++
+ The implementation shall behave as if no library function calls the mblen function. +
+ If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte + character encodings, respectively, do or do not have state-dependent encodings. If s is + not a null pointer, the mblen function either returns 0 (if s points to the null character), + or returns the number of bytes that are contained in the multibyte character (if the next n + or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid + multibyte character). +
Forward references: the mbtowc function (7.22.7.2). + +
+
+ #include <stdlib.h> + int mbtowc(wchar_t * restrict pwc, + const char * restrict s, + size_t n); ++
+ If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with + the byte pointed to by s to determine the number of bytes needed to complete the next + multibyte character (including any shift sequences). If the function determines that the + next multibyte character is complete and valid, it determines the value of the + corresponding wide character and then, if pwc is not a null pointer, stores that value in + the object pointed to by pwc. If the corresponding wide character is the null wide + character, the function is left in the initial conversion state. +
+ The implementation shall behave as if no library function calls the mbtowc function. +
+ If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte + character encodings, respectively, do or do not have state-dependent encodings. If s is + not a null pointer, the mbtowc function either returns 0 (if s points to the null character), + or returns the number of bytes that are contained in the converted multibyte character (if + the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not + form a valid multibyte character). +
+ In no case will the value returned be greater than n or the value of the MB_CUR_MAX + macro. + + +
+
+ #include <stdlib.h> + int wctomb(char *s, wchar_t wc); ++
+ The wctomb function determines the number of bytes needed to represent the multibyte + character corresponding to the wide character given by wc (including any shift + sequences), and stores the multibyte character representation in the array whose first + element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters + are stored. If wc is a null wide character, a null byte is stored, preceded by any shift + sequence needed to restore the initial shift state, and the function is left in the initial + conversion state. +
+ The implementation shall behave as if no library function calls the wctomb function. +
+ If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte + character encodings, respectively, do or do not have state-dependent encodings. If s is + not a null pointer, the wctomb function returns -1 if the value of wc does not correspond + to a valid multibyte character, or returns the number of bytes that are contained in the + multibyte character corresponding to the value of wc. +
+ In no case will the value returned be greater than the value of the MB_CUR_MAX macro. + +
+ The behavior of the multibyte string functions is affected by the LC_CTYPE category of + the current locale. + +
+
+ #include <stdlib.h> + size_t mbstowcs(wchar_t * restrict pwcs, + const char * restrict s, + size_t n); ++
+ The mbstowcs function converts a sequence of multibyte characters that begins in the + initial shift state from the array pointed to by s into a sequence of corresponding wide + characters and stores not more than n wide characters into the array pointed to by pwcs. + No multibyte characters that follow a null character (which is converted into a null wide + character) will be examined or converted. Each multibyte character is converted as if by + a call to the mbtowc function, except that the conversion state of the mbtowc function is + + not affected. +
+ No more than n elements will be modified in the array pointed to by pwcs. If copying + takes place between objects that overlap, the behavior is undefined. +
+ If an invalid multibyte character is encountered, the mbstowcs function returns + (size_t)(-1). Otherwise, the mbstowcs function returns the number of array + elements modified, not including a terminating null wide character, if any.299) + +
299) The array will not be null-terminated if the value returned is n. + + +
+
+ #include <stdlib.h> + size_t wcstombs(char * restrict s, + const wchar_t * restrict pwcs, + size_t n); ++
+ The wcstombs function converts a sequence of wide characters from the array pointed + to by pwcs into a sequence of corresponding multibyte characters that begins in the + initial shift state, and stores these multibyte characters into the array pointed to by s, + stopping if a multibyte character would exceed the limit of n total bytes or if a null + character is stored. Each wide character is converted as if by a call to the wctomb + function, except that the conversion state of the wctomb function is not affected. +
+ No more than n bytes will be modified in the array pointed to by s. If copying takes place + between objects that overlap, the behavior is undefined. +
+ If a wide character is encountered that does not correspond to a valid multibyte character, + the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function + returns the number of bytes modified, not including a terminating null character, if + any.299) + + + + + + +
+ The header <string.h> declares one type and several functions, and defines one + macro useful for manipulating arrays of character type and other objects treated as arrays + of character type.300) The type is size_t and the macro is NULL (both described in + 7.19). Various methods are used for determining the lengths of the arrays, but in all cases + a char * or void * argument points to the initial (lowest addressed) character of the + array. If an array is accessed beyond the end of an object, the behavior is undefined. +
+ Where an argument declared as size_t n specifies the length of the array for a + function, n can have the value zero on a call to that function. Unless explicitly stated + otherwise in the description of a particular function in this subclause, pointer arguments + on such a call shall still have valid values, as described in 7.1.4. On such a call, a + function that locates a character finds no occurrence, a function that compares two + character sequences returns zero, and a function that copies characters copies zero + characters. +
+ For all functions in this subclause, each character shall be interpreted as if it had the type + unsigned char (and therefore every possible object representation is valid and has a + different value). + +
300) See ''future library directions'' (7.30.11). + + +
+
+ #include <string.h> + void *memcpy(void * restrict s1, + const void * restrict s2, + size_t n); ++
+ The memcpy function copies n characters from the object pointed to by s2 into the + object pointed to by s1. If copying takes place between objects that overlap, the behavior + is undefined. +
+ The memcpy function returns the value of s1. + + + + + + +
+
+ #include <string.h> + void *memmove(void *s1, const void *s2, size_t n); ++
+ The memmove function copies n characters from the object pointed to by s2 into the + object pointed to by s1. Copying takes place as if the n characters from the object + pointed to by s2 are first copied into a temporary array of n characters that does not + overlap the objects pointed to by s1 and s2, and then the n characters from the + temporary array are copied into the object pointed to by s1. +
+ The memmove function returns the value of s1. + +
+
+ #include <string.h> + char *strcpy(char * restrict s1, + const char * restrict s2); ++
+ The strcpy function copies the string pointed to by s2 (including the terminating null + character) into the array pointed to by s1. If copying takes place between objects that + overlap, the behavior is undefined. +
+ The strcpy function returns the value of s1. + +
+
+ #include <string.h> + char *strncpy(char * restrict s1, + const char * restrict s2, + size_t n); ++
+ The strncpy function copies not more than n characters (characters that follow a null + character are not copied) from the array pointed to by s2 to the array pointed to by + + s1.301) If copying takes place between objects that overlap, the behavior is undefined. +
+ If the array pointed to by s2 is a string that is shorter than n characters, null characters + are appended to the copy in the array pointed to by s1, until n characters in all have been + written. +
+ The strncpy function returns the value of s1. + +
301) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will + not be null-terminated. + + +
+
+ #include <string.h> + char *strcat(char * restrict s1, + const char * restrict s2); ++
+ The strcat function appends a copy of the string pointed to by s2 (including the + terminating null character) to the end of the string pointed to by s1. The initial character + of s2 overwrites the null character at the end of s1. If copying takes place between + objects that overlap, the behavior is undefined. +
+ The strcat function returns the value of s1. + +
+
+ #include <string.h> + char *strncat(char * restrict s1, + const char * restrict s2, + size_t n); ++
+ The strncat function appends not more than n characters (a null character and + characters that follow it are not appended) from the array pointed to by s2 to the end of + the string pointed to by s1. The initial character of s2 overwrites the null character at the + end of s1. A terminating null character is always appended to the result.302) If copying + + + takes place between objects that overlap, the behavior is undefined. +
+ The strncat function returns the value of s1. +
Forward references: the strlen function (7.23.6.3). + +
302) Thus, the maximum number of characters that can end up in the array pointed to by s1 is + strlen(s1)+n+1. + + +
+ The sign of a nonzero value returned by the comparison functions memcmp, strcmp, + and strncmp is determined by the sign of the difference between the values of the first + pair of characters (both interpreted as unsigned char) that differ in the objects being + compared. + +
+
+ #include <string.h> + int memcmp(const void *s1, const void *s2, size_t n); ++
+ The memcmp function compares the first n characters of the object pointed to by s1 to + the first n characters of the object pointed to by s2.303) +
+ The memcmp function returns an integer greater than, equal to, or less than zero, + accordingly as the object pointed to by s1 is greater than, equal to, or less than the object + pointed to by s2. + +
303) The contents of ''holes'' used as padding for purposes of alignment within structure objects are + indeterminate. Strings shorter than their allocated space and unions may also cause problems in + comparison. + + +
+
+ #include <string.h> + int strcmp(const char *s1, const char *s2); ++
+ The strcmp function compares the string pointed to by s1 to the string pointed to by + s2. +
+ The strcmp function returns an integer greater than, equal to, or less than zero, + accordingly as the string pointed to by s1 is greater than, equal to, or less than the string + + + pointed to by s2. + +
+
+ #include <string.h> int strcoll(const char *s1, const char *s2); ++
+ The strcoll function compares the string pointed to by s1 to the string pointed to by + s2, both interpreted as appropriate to the LC_COLLATE category of the current locale. +
+ The strcoll function returns an integer greater than, equal to, or less than zero, + accordingly as the string pointed to by s1 is greater than, equal to, or less than the string + pointed to by s2 when both are interpreted as appropriate to the current locale. + +
+
+ #include <string.h> int strncmp(const char *s1, const char *s2, size_t n); ++
+ The strncmp function compares not more than n characters (characters that follow a + null character are not compared) from the array pointed to by s1 to the array pointed to + by s2. +
+ The strncmp function returns an integer greater than, equal to, or less than zero, + accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal + to, or less than the possibly null-terminated array pointed to by s2. + +
+
+ #include <string.h> size_t strxfrm(char * restrict s1, - const char * restrict s2, size_t n); - void *memchr(const void *s, int c, size_t n); -[page 489] (Contents) - - char *strchr(const char *s, int c); - size_t strcspn(const char *s1, const char *s2); - char *strpbrk(const char *s1, const char *s2); - char *strrchr(const char *s, int c); - size_t strspn(const char *s1, const char *s2); - char *strstr(const char *s1, const char *s2); - char *strtok(char * restrict s1, - const char * restrict s2); - void *memset(void *s, int c, size_t n); - char *strerror(int errnum); - size_t strlen(const char *s); - __STDC_WANT_LIB_EXT1__ - errno_t - rsize_t - errno_t memcpy_s(void * restrict s1, rsize_t s1max, - const void * restrict s2, rsize_t n); - errno_t memmove_s(void *s1, rsize_t s1max, - const void *s2, rsize_t n); - errno_t strcpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - errno_t strncpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - errno_t strcat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - errno_t strncat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - char *strtok_s(char * restrict s1, - rsize_t * restrict s1max, - const char * restrict s2, - char ** restrict ptr); - errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) - errno_t strerror_s(char *s, rsize_t maxsize, - errno_t errnum); - size_t strerrorlen_s(errno_t errnum); - -[page 490] (Contents) - - size_t strnlen_s(const char *s, size_t maxsize); -B.23 Type-generic math <tgmath.h> - acos sqrt fmod nextafter - asin fabs frexp nexttoward - atan atan2 hypot remainder - acosh cbrt ilogb remquo - asinh ceil ldexp rint - atanh copysign lgamma round - cos erf llrint scalbn - sin erfc llround scalbln - tan exp2 log10 tgamma - cosh expm1 log1p trunc - sinh fdim log2 carg - tanh floor logb cimag - exp fma lrint conj - log fmax lround cproj - pow fmin nearbyint creal -B.24 Threads <threads.h> - ONCE_FLAG_INIT mtx_plain - TSS_DTOR_ITERATIONS mtx_recursive - cnd_t mtx_timed - thrd_t mtx_try - tss_t thrd_timeout - mtx_t thrd_success - tss_dtor_t thrd_busy - thrd_start_t thrd_error - once_flag thrd_nomem + const char * restrict s2, + size_t n); ++
+ The strxfrm function transforms the string pointed to by s2 and places the resulting + string into the array pointed to by s1. The transformation is such that if the strcmp + function is applied to two transformed strings, it returns a value greater than, equal to, or + + less than zero, corresponding to the result of the strcoll function applied to the same + two original strings. No more than n characters are placed into the resulting array + pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to + be a null pointer. If copying takes place between objects that overlap, the behavior is + undefined. +
+ The strxfrm function returns the length of the transformed string (not including the + terminating null character). If the value returned is n or more, the contents of the array + pointed to by s1 are indeterminate. +
+ EXAMPLE The value of the following expression is the size of the array needed to hold the + transformation of the string pointed to by s. +
+ 1 + strxfrm(NULL, s, 0) ++ + +
+
+ #include <string.h> + void *memchr(const void *s, int c, size_t n); ++
+ The memchr function locates the first occurrence of c (converted to an unsigned + char) in the initial n characters (each interpreted as unsigned char) of the object + pointed to by s. The implementation shall behave as if it reads the characters sequentially + and stops as soon as a matching character is found. +
+ The memchr function returns a pointer to the located character, or a null pointer if the + character does not occur in the object. + +
+
+ #include <string.h> + char *strchr(const char *s, int c); ++
+ The strchr function locates the first occurrence of c (converted to a char) in the + string pointed to by s. The terminating null character is considered to be part of the + string. + +
+ The strchr function returns a pointer to the located character, or a null pointer if the + character does not occur in the string. + +
+
+ #include <string.h> + size_t strcspn(const char *s1, const char *s2); ++
+ The strcspn function computes the length of the maximum initial segment of the string + pointed to by s1 which consists entirely of characters not from the string pointed to by + s2. +
+ The strcspn function returns the length of the segment. + +
+
+ #include <string.h> + char *strpbrk(const char *s1, const char *s2); ++
+ The strpbrk function locates the first occurrence in the string pointed to by s1 of any + character from the string pointed to by s2. +
+ The strpbrk function returns a pointer to the character, or a null pointer if no character + from s2 occurs in s1. + +
+
+ #include <string.h> + char *strrchr(const char *s, int c); ++
+ The strrchr function locates the last occurrence of c (converted to a char) in the + string pointed to by s. The terminating null character is considered to be part of the + string. + +
+ The strrchr function returns a pointer to the character, or a null pointer if c does not + occur in the string. + +
+
+ #include <string.h> + size_t strspn(const char *s1, const char *s2); ++
+ The strspn function computes the length of the maximum initial segment of the string + pointed to by s1 which consists entirely of characters from the string pointed to by s2. +
+ The strspn function returns the length of the segment. + +
+
+ #include <string.h> + char *strstr(const char *s1, const char *s2); ++
+ The strstr function locates the first occurrence in the string pointed to by s1 of the + sequence of characters (excluding the terminating null character) in the string pointed to + by s2. +
+ The strstr function returns a pointer to the located string, or a null pointer if the string + is not found. If s2 points to a string with zero length, the function returns s1. + +
+
+ #include <string.h> + char *strtok(char * restrict s1, + const char * restrict s2); ++
+ A sequence of calls to the strtok function breaks the string pointed to by s1 into a + sequence of tokens, each of which is delimited by a character from the string pointed to + by s2. The first call in the sequence has a non-null first argument; subsequent calls in the + sequence have a null first argument. The separator string pointed to by s2 may be + different from call to call. + +
+ The first call in the sequence searches the string pointed to by s1 for the first character + that is not contained in the current separator string pointed to by s2. If no such character + is found, then there are no tokens in the string pointed to by s1 and the strtok function + returns a null pointer. If such a character is found, it is the start of the first token. +
+ The strtok function then searches from there for a character that is contained in the + current separator string. If no such character is found, the current token extends to the + end of the string pointed to by s1, and subsequent searches for a token will return a null + pointer. If such a character is found, it is overwritten by a null character, which + terminates the current token. The strtok function saves a pointer to the following + character, from which the next search for a token will start. +
+ Each subsequent call, with a null pointer as the value of the first argument, starts + searching from the saved pointer and behaves as described above. +
+ The strtok function is not required to avoid data races. The implementation shall + behave as if no library function calls the strtok function. +
+ The strtok function returns a pointer to the first character of a token, or a null pointer + if there is no token. +
+ EXAMPLE +
+ #include <string.h> + static char str[] = "?a???b,,,#c"; + char *t; + t = strtok(str, "?"); // t points to the token "a" + t = strtok(NULL, ","); // t points to the token "??b" + t = strtok(NULL, "#,"); // t points to the token "c" + t = strtok(NULL, "?"); // t is a null pointer ++ + +
+
+ #include <string.h> + void *memset(void *s, int c, size_t n); ++
+ The memset function copies the value of c (converted to an unsigned char) into + each of the first n characters of the object pointed to by s. +
+ The memset function returns the value of s. + + +
+
+ #include <string.h> + char *strerror(int errnum); ++
+ The strerror function maps the number in errnum to a message string. Typically, + the values for errnum come from errno, but strerror shall map any value of type + int to a message. +
+ The strerror function is not required to avoid data races. The implementation shall + behave as if no library function calls the strerror function. +
+ The strerror function returns a pointer to the string, the contents of which are locale- + specific. The array pointed to shall not be modified by the program, but may be + overwritten by a subsequent call to the strerror function. + +
+
+ #include <string.h> + size_t strlen(const char *s); ++
+ The strlen function computes the length of the string pointed to by s. +
+ The strlen function returns the number of characters that precede the terminating null + character. + + +
+ The header <tgmath.h> includes the headers <math.h> and <complex.h> and + defines several type-generic macros. +
+ Of the <math.h> and <complex.h> functions without an f (float) or l (long + double) suffix, several have one or more parameters whose corresponding real type is + double. For each such function, except modf, there is a corresponding type-generic + macro.304) The parameters whose corresponding real type is double in the function + synopsis are generic parameters. Use of the macro invokes a function whose + corresponding real type and type domain are determined by the arguments for the generic + parameters.305) +
+ Use of the macro invokes a function whose generic parameters have the corresponding + real type determined as follows: +
+ For each unsuffixed function in <math.h> for which there is a function in + <complex.h> with the same name except for a c prefix, the corresponding type- + generic macro (for both functions) has the same name as the function in <math.h>. The + corresponding type-generic macro for fabs and cabs is fabs. + + + + + +
+ <math.h> <complex.h> type-generic + function function macro + acos cacos acos + asin casin asin + atan catan atan + acosh cacosh acosh + asinh casinh asinh + atanh catanh atanh + cos ccos cos + sin csin sin + tan ctan tan + cosh ccosh cosh + sinh csinh sinh + tanh ctanh tanh + exp cexp exp + log clog log + pow cpow pow + sqrt csqrt sqrt + fabs cabs fabs ++ If at least one argument for a generic parameter is complex, then use of the macro invokes + a complex function; otherwise, use of the macro invokes a real function. +
+ For each unsuffixed function in <math.h> without a c-prefixed counterpart in + <complex.h> (except modf), the corresponding type-generic macro has the same + name as the function. These type-generic macros are: +
+ atan2 fma llround remainder + cbrt fmax log10 remquo + ceil fmin log1p rint + copysign fmod log2 round + erf frexp logb scalbn + erfc hypot lrint scalbln + exp2 ilogb lround tgamma + expm1 ldexp nearbyint trunc + fdim lgamma nextafter + floor llrint nexttoward ++ If all arguments for generic parameters are real, then use of the macro invokes a real + function; otherwise, use of the macro results in undefined behavior. + +
+ For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a + function in <math.h>, the corresponding type-generic macro has the same name as the + function. These type-generic macros are: +
+ carg conj creal + cimag cproj ++ Use of the macro with any real or complex argument invokes a complex function. +
+ EXAMPLE With the declarations +
+ #include <tgmath.h> + int n; + float f; + double d; + long double ld; + float complex fc; + double complex dc; + long double complex ldc; ++ functions invoked by use of type-generic macros are shown in the following table: + +
+ macro use invokes + exp(n) exp(n), the function + acosh(f) acoshf(f) + sin(d) sin(d), the function + atan(ld) atanl(ld) + log(fc) clogf(fc) + sqrt(dc) csqrt(dc) + pow(ldc, f) cpowl(ldc, f) + remainder(n, n) remainder(n, n), the function + nextafter(d, f) nextafter(d, f), the function + nexttoward(f, ld) nexttowardf(f, ld) + copysign(n, ld) copysignl(n, ld) + ceil(fc) undefined behavior + rint(dc) undefined behavior + fmax(ldc, ld) undefined behavior + carg(n) carg(n), the function + cproj(f) cprojf(f) + creal(d) creal(d), the function + cimag(ld) cimagl(ld) + fabs(fc) cabsf(fc) + carg(dc) carg(dc), the function + cproj(ldc) cprojl(ldc) ++ +
304) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to + make available the corresponding ordinary function. + +
305) If the type of the argument is not compatible with the type of the parameter for the selected function, + the behavior is undefined. + + +
+ The header <threads.h> defines macros, and declares types, enumeration constants, + and functions that support multiple threads of execution. +
+ Implementations that define the macro __STDC_NO_THREADS__ need not provide + this header nor support any of its facilities. +
+ The macros are +
+ ONCE_FLAG_INIT ++ which expands to a value that can be used to initialize an object of type once_flag; + and +
+ TSS_DTOR_ITERATIONS ++ which expands to an integer constant expression representing the maximum number of + times that destructors will be called when a thread terminates. +
+ The types are +
+ cnd_t ++ which is a complete object type that holds an identifier for a condition variable; +
+ thrd_t ++ which is a complete object type that holds an identifier for a thread; +
+ tss_t ++ which is a complete object type that holds an identifier for a thread-specific storage + pointer; +
+ mtx_t ++ which is a complete object type that holds an identifier for a mutex; +
+ tss_dtor_t ++ which is the function pointer type void (*)(void*), used for a destructor for a + thread-specific storage pointer; +
+ thrd_start_t ++ which is the function pointer type int (*)(void*) that is passed to thrd_create + to create a new thread; +
+ once_flag ++ which is a complete object type that holds a flag for use by call_once; and + +
xtime
- void call_once(once_flag *flag, void (*func)(void));
- int cnd_broadcast(cnd_t *cond);
- void cnd_destroy(cnd_t *cond);
- int cnd_init(cnd_t *cond);
- int cnd_signal(cnd_t *cond);
- int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
- const xtime *xt);
- int cnd_wait(cnd_t *cond, mtx_t *mtx);
- void mtx_destroy(mtx_t *mtx);
- int mtx_init(mtx_t *mtx, int type);
- int mtx_lock(mtx_t *mtx);
-[page 491] (Contents)
-
- int mtx_timedlock(mtx_t *mtx, const xtime *xt);
- int mtx_trylock(mtx_t *mtx);
- int mtx_unlock(mtx_t *mtx);
- int thrd_create(thrd_t *thr, thrd_start_t func,
- void *arg);
- thrd_t thrd_current(void);
- int thrd_detach(thrd_t thr);
- int thrd_equal(thrd_t thr0, thrd_t thr1);
- void thrd_exit(int res);
- int thrd_join(thrd_t thr, int *res);
- void thrd_sleep(const xtime *xt);
- void thrd_yield(void);
- int tss_create(tss_t *key, tss_dtor_t dtor);
- void tss_delete(tss_t key);
- void *tss_get(tss_t key);
- int tss_set(tss_t key, void *val);
- int xtime_get(xtime *xt, int base);
-B.25 Date and time <time.h>
- NULL size_t time_t
- CLOCKS_PER_SEC clock_t struct tm
- clock_t clock(void);
- double difftime(time_t time1, time_t time0);
- time_t mktime(struct tm *timeptr);
- time_t time(time_t *timer);
- char *asctime(const struct tm *timeptr);
- char *ctime(const time_t *timer);
- struct tm *gmtime(const time_t *timer);
- struct tm *localtime(const time_t *timer);
- size_t strftime(char * restrict s,
- size_t maxsize,
- const char * restrict format,
- const struct tm * restrict timeptr);
- __STDC_WANT_LIB_EXT1__
- errno_t
- rsize_t
- errno_t asctime_s(char *s, rsize_t maxsize,
- const struct tm *timeptr);
-
-
-
-[page 492] (Contents)
-
- errno_t ctime_s(char *s, rsize_t maxsize,
- const time_t *timer);
- struct tm *gmtime_s(const time_t * restrict timer,
- struct tm * restrict result);
- struct tm *localtime_s(const time_t * restrict timer,
- struct tm * restrict result);
-B.26 Unicode utilities <uchar.h>
- mbstate_t size_t char16_t char32_t
- size_t mbrtoc16(char16_t * restrict pc16,
- const char * restrict s, size_t n,
- mbstate_t * restrict ps);
- size_t c16rtomb(char * restrict s, char16_t c16,
- mbstate_t * restrict ps);
- size_t mbrtoc32(char32_t * restrict pc32,
- const char * restrict s, size_t n,
- mbstate_t * restrict ps);
- size_t c32rtomb(char * restrict s, char32_t c32,
- mbstate_t * restrict ps);
-B.27 Extended multibyte/wide character utilities <wchar.h>
- wchar_t wint_t WCHAR_MAX
- size_t struct tm WCHAR_MIN
- mbstate_t NULL WEOF
- int fwprintf(FILE * restrict stream,
- const wchar_t * restrict format, ...);
- int fwscanf(FILE * restrict stream,
- const wchar_t * restrict format, ...);
- int swprintf(wchar_t * restrict s, size_t n,
- const wchar_t * restrict format, ...);
- int swscanf(const wchar_t * restrict s,
- const wchar_t * restrict format, ...);
+
+ which is a structure type that holds a time specified in seconds and nanoseconds. The
+ structure shall contain at least the following members, in any order.
++ time_t sec; + long nsec; ++
+ The enumeration constants are +
+ mtx_plain ++ which is passed to mtx_init to create a mutex object that supports neither timeout nor + test and return; +
+ mtx_recursive ++ which is passed to mtx_init to create a mutex object that supports recursive locking; +
+ mtx_timed ++ which is passed to mtx_init to create a mutex object that supports timeout; +
+ mtx_try ++ which is passed to mtx_init to create a mutex object that supports test and return; +
+ thrd_timeout ++ which is returned by a timed wait function to indicate that the time specified in the call + was reached without acquiring the requested resource; +
+ thrd_success ++ which is returned by a function to indicate that the requested operation succeeded; +
+ thrd_busy ++ which is returned by a function to indicate that the requested operation failed because a + resource requested by a test and return function is already in use; +
+ thrd_error ++ which is returned by a function to indicate that the requested operation failed; and +
+ thrd_nomem ++ which is returned by a function to indicate that the requested operation failed because it + was unable to allocate memory. + + +
+
+ #include <threads.h> + void call_once(once_flag *flag, void (*func)(void)); ++
+ The call_once function uses the once_flag pointed to by flag to ensure that + func is called exactly once, the first time the call_once function is called with that + value of flag. Completion of an effective call to the call_once function synchronizes + with all subsequent calls to the call_once function with the same value of flag. +
+ The call_once function returns no value. + +
+
+ #include <threads.h> + int cnd_broadcast(cnd_t *cond); ++
+ The cnd_broadcast function unblocks all of the threads that are blocked on the + condition variable pointed to by cond at the time of the call. If no threads are blocked + on the condition variable pointed to by cond at the time of the call, the function does + nothing. +
+ The cnd_broadcast function returns thrd_success on success, or thrd_error + if the request could not be honored. + +
+
+ #include <threads.h> + void cnd_destroy(cnd_t *cond); ++
+ The cnd_destroy function releases all resources used by the condition variable + pointed to by cond. The cnd_destroy function requires that no threads be blocked + waiting for the condition variable pointed to by cond. + +
+ The cnd_destroy function returns no value. + +
+
+ #include <threads.h> + int cnd_init(cnd_t *cond); ++
+ The cnd_init function creates a condition variable. If it succeeds it sets the variable + pointed to by cond to a value that uniquely identifies the newly created condition + variable. A thread that calls cnd_wait on a newly created condition variable will + block. +
+ The cnd_init function returns thrd_success on success, or thrd_nomem if no + memory could be allocated for the newly created condition, or thrd_error if the + request could not be honored. + +
+
+ #include <threads.h> + int cnd_signal(cnd_t *cond); ++
+ The cnd_signal function unblocks one of the threads that are blocked on the + condition variable pointed to by cond at the time of the call. If no threads are blocked + on the condition variable at the time of the call, the function does nothing and return + success. +
+ The cnd_signal function returns thrd_success on success or thrd_error if + the request could not be honored. + +
+ +
+ #include <threads.h> + int cnd_timedwait(cnd_t *cond, mtx_t *mtx, + const xtime *xt); ++
+ The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and + endeavors to block until the condition variable pointed to by cond is signaled by a call to + cnd_signal or to cnd_broadcast, or until after the time specified by the xtime + object pointed to by xt. When the calling thread becomes unblocked it locks the variable + pointed to by mtx before it returns. The cnd_timedwait function requires that the + mutex pointed to by mtx be locked by the calling thread. +
+ The cnd_timedwait function returns thrd_success upon success, or + thrd_timeout if the time specified in the call was reached without acquiring the + requested resource, or thrd_error if the request could not be honored. + +
+
+ #include <threads.h> + int cnd_wait(cnd_t *cond, mtx_t *mtx); ++
+ The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors + to block until the condition variable pointed to by cond is signaled by a call to + cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it + locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is + not locked by the calling thread, the cnd_wait function will act as if the abort + function is called. +
+ The cnd_wait function returns thrd_success on success or thrd_error if the + request could not be honored. + +
+
+ #include <threads.h> + void mtx_destroy(mtx_t *mtx); ++
+ The mtx_destroy function releases any resources used by the mutex pointed to by + mtx. No threads can be blocked waiting for the mutex pointed to by mtx. + +
+ The mtx_destroy function returns no value. + +
+
+ #include <threads.h> + int mtx_init(mtx_t *mtx, int type); ++
+ The mtx_init function creates a mutex object with properties indicated by type, + which must have one of the six values: + mtx_plain for a simple non-recursive mutex, + mtx_timed for a non-recursive mutex that supports timeout, + mtx_try for a non-recursive mutex that supports test and return, + mtx_plain | mtx_recursive for a simple recursive mutex, + mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or + mtx_try | mtx_recursive for a recursive mutex that supports test and return. +
+ If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that + uniquely identifies the newly created mutex. +
+ The mtx_init function returns thrd_success on success, or thrd_error if the + request could not be honored. + +
+
+ #include <threads.h> + int mtx_lock(mtx_t *mtx); ++
+ The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex + is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock + on the same mutex shall synchronize with this operation. +
+ The mtx_lock function returns thrd_success on success, or thrd_busy if the + resource requested is already in use, or thrd_error if the request could not be + honored. + + +
+
+ #include <threads.h> + int mtx_timedlock(mtx_t *mtx, const xtime *xt); ++
+ The mtx_timedlock function endeavors to block until it locks the mutex pointed to by + mtx or until the time specified by the xtime object xt has passed. The specified mutex + shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same + mutex shall synchronize with this operation. +
+ The mtx_timedlock function returns thrd_success on success, or thrd_busy + if the resource requested is already in use, or thrd_timeout if the time specified was + reached without acquiring the requested resource, or thrd_error if the request could + not be honored. + +
+
+ #include <threads.h> + int mtx_trylock(mtx_t *mtx); ++
+ The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The + specified mutex shall support either test and return or timeout. If the mutex is already + locked, the function returns without blocking. If the operation succeeds, prior calls to + mtx_unlock on the same mutex shall synchronize with this operation. +
+ The mtx_trylock function returns thrd_success on success, or thrd_busy if + the resource requested is already in use, or thrd_error if the request could not be + honored. + +
+
+ #include <threads.h> + int mtx_unlock(mtx_t *mtx); ++
+ The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to + by mtx shall be locked by the calling thread. + +
+ The mtx_unlock function returns thrd_success on success or thrd_error if + the request could not be honored. + +
+
+ #include <threads.h> + int thrd_create(thrd_t *thr, thrd_start_t func, + void *arg); ++
+ The thrd_create function creates a new thread executing func(arg). If the + thrd_create function succeeds, it sets the object pointed to by thr to the identifier of + the newly created thread. (A thread's identifier may be reused for a different thread once + the original thread has exited and either been detached or joined to another thread.) The + completion of the thrd_create function synchronizes with the beginning of the + execution of the new thread. +
+ The thrd_create function returns thrd_success on success, or thrd_nomem if + no memory could be allocated for the thread requested, or thrd_error if the request + could not be honored. + +
+
+ #include <threads.h> + thrd_t thrd_current(void); ++
+ The thrd_current function identifies the thread that called it. +
+ The thrd_current function returns the identifier of the thread that called it. + +
+ +
+ #include <threads.h> + int thrd_detach(thrd_t thr); ++
+ The thrd_detach function tells the operating system to dispose of any resources + allocated to the thread identified by thr when that thread terminates. The thread + identified by thr shall not have been previously detached or joined with another thread. +
+ The thrd_detach function returns thrd_success on success or thrd_error if + the request could not be honored. + +
+
+ #include <threads.h> + int thrd_equal(thrd_t thr0, thrd_t thr1); ++
+ The thrd_equal function will determine whether the thread identified by thr0 refers + to the thread identified by thr1. +
+ The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to + different threads. Otherwise the thrd_equal function returns a nonzero value. + +
+
+ #include <threads.h> + void thrd_exit(int res); ++
+ The thrd_exit function terminates execution of the calling thread and sets its result + code to res. +
+ The thrd_exit function returns no value. + +
+
+ #include <threads.h> + int thrd_join(thrd_t thr, int *res); ++
+ The thrd_join function joins the thread identified by thr with the current thread by + blocking until the other thread has terminated. If the parameter res is not a null pointer, + + it stores the thread's result code in the integer pointed to by res. The termination of the + other thread synchronizes with the completion of the thrd_join function. The thread + identified by thr shall not have been previously detached or joined with another thread. +
+ The thrd_join function returns thrd_success on success or thrd_error if the + request could not be honored. + +
+
+ #include <threads.h> + void thrd_sleep(const xtime *xt); ++
+ The thrd_sleep function suspends execution of the calling thread until after the time + specified by the xtime object pointed to by xt. +
+ The thrd_sleep function returns no value. + +
+
+ #include <threads.h> + void thrd_yield(void); ++
+ The thrd_yield function endeavors to permit other threads to run, even if the current + thread would ordinarily continue to run. +
+ The thrd_yield function returns no value. + +
+
+ #include <threads.h> + int tss_create(tss_t *key, tss_dtor_t dtor); ++
+ The tss_create function creates a thread-specific storage pointer with destructor + dtor, which may be null. + +
+ If the tss_create function is successful, it sets the thread-specific storage pointed to + by key to a value that uniquely identifies the newly created pointer and returns + thrd_success; otherwise, thrd_error is returned and the thread-specific storage + pointed to by key is set to an undefined value. + +
+
+ #include <threads.h> + void tss_delete(tss_t key); ++
+ The tss_delete function releases any resources used by the thread-specific storage + identified by key. +
+ The tss_delete function returns no value. + +
+
+ #include <threads.h> + void *tss_get(tss_t key); ++
+ The tss_get function returns the value for the current thread held in the thread-specific + storage identified by key. +
+ The tss_get function returns the value for the current thread if successful, or zero if + unsuccessful. + +
+
+ #include <threads.h> + int tss_set(tss_t key, void *val); ++
+ The tss_set function sets the value for the current thread held in the thread-specific + storage identified by key to val. + +
+ The tss_set function returns thrd_success on success or thrd_error if the + request could not be honored. + +
+
+ #include <threads.h> + int xtime_get(xtime *xt, int base); ++
+ The xtime_get function sets the xtime object pointed to by xt to hold the current + time based on the time base base. +
+ If the xtime_get function is successful it returns the nonzero value base, which must + be TIME_UTC; otherwise, it returns zero.306) + + + + + + +
306) Although an xtime object describes times with nanosecond resolution, the actual resolution in an + xtime object is system dependent. + + +
+ The header <time.h> defines two macros, and declares several types and functions for + manipulating time. Many functions deal with a calendar time that represents the current + date (according to the Gregorian calendar) and time. Some functions deal with local + time, which is the calendar time expressed for some specific time zone, and with Daylight + Saving Time, which is a temporary change in the algorithm for determining local time. + The local time zone and Daylight Saving Time are implementation-defined. +
+ The macros defined are NULL (described in 7.19); and +
+ CLOCKS_PER_SEC ++ which expands to an expression with type clock_t (described below) that is the + number per second of the value returned by the clock function. +
+ The types declared are size_t (described in 7.19); +
+ clock_t ++ and +
+ time_t ++ which are arithmetic types capable of representing times; and +
+ struct tm ++ which holds the components of a calendar time, called the broken-down time. +
+ The range and precision of times representable in clock_t and time_t are + implementation-defined. The tm structure shall contain at least the following members, + in any order. The semantics of the members and their normal ranges are expressed in the + comments.307) +
+ int tm_sec; // seconds after the minute -- [0, 60] + int tm_min; // minutes after the hour -- [0, 59] + int tm_hour; // hours since midnight -- [0, 23] + int tm_mday; // day of the month -- [1, 31] + int tm_mon; // months since January -- [0, 11] + int tm_year; // years since 1900 + int tm_wday; // days since Sunday -- [0, 6] + int tm_yday; // days since January 1 -- [0, 365] + int tm_isdst; // Daylight Saving Time flag ++ + + + + The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight + Saving Time is not in effect, and negative if the information is not available. + +
307) The range [0, 60] for tm_sec allows for a positive leap second. + + +
+
+ #include <time.h> + clock_t clock(void); ++
+ The clock function determines the processor time used. +
+ The clock function returns the implementation's best approximation to the processor + time used by the program since the beginning of an implementation-defined era related + only to the program invocation. To determine the time in seconds, the value returned by + the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If + the processor time used is not available or its value cannot be represented, the function + returns the value (clock_t)(-1).308) + +
308) In order to measure the time spent in a program, the clock function should be called at the start of + the program and its return value subtracted from the value returned by subsequent calls. + + +
+
+ #include <time.h> + double difftime(time_t time1, time_t time0); ++
+ The difftime function computes the difference between two calendar times: time1 - + time0. +
+ The difftime function returns the difference expressed in seconds as a double. + + + + + + +
+
+ #include <time.h> + time_t mktime(struct tm *timeptr); ++
+ The mktime function converts the broken-down time, expressed as local time, in the + structure pointed to by timeptr into a calendar time value with the same encoding as + that of the values returned by the time function. The original values of the tm_wday + and tm_yday components of the structure are ignored, and the original values of the + other components are not restricted to the ranges indicated above.309) On successful + completion, the values of the tm_wday and tm_yday components of the structure are + set appropriately, and the other components are set to represent the specified calendar + time, but with their values forced to the ranges indicated above; the final value of + tm_mday is not set until tm_mon and tm_year are determined. +
+ The mktime function returns the specified calendar time encoded as a value of type + time_t. If the calendar time cannot be represented, the function returns the value + (time_t)(-1). +
+ EXAMPLE What day of the week is July 4, 2001? +
+ #include <stdio.h> + #include <time.h> + static const char *const wday[] = { + "Sunday", "Monday", "Tuesday", "Wednesday", + "Thursday", "Friday", "Saturday", "-unknown-" + }; + struct tm time_str; + /* ... */ ++ + + + + +
+ time_str.tm_year = 2001 - 1900;
+ time_str.tm_mon = 7 - 1;
+ time_str.tm_mday = 4;
+ time_str.tm_hour = 0;
+ time_str.tm_min = 0;
+ time_str.tm_sec = 1;
+ time_str.tm_isdst = -1;
+ if (mktime(&time_str) == (time_t)(-1))
+ time_str.tm_wday = 7;
+ printf("%s\n", wday[time_str.tm_wday]);
+
+
+
+309) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that + Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value + causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time. + + +
+
+ #include <time.h> + time_t time(time_t *timer); ++
+ The time function determines the current calendar time. The encoding of the value is + unspecified. +
+ The time function returns the implementation's best approximation to the current + calendar time. The value (time_t)(-1) is returned if the calendar time is not + available. If timer is not a null pointer, the return value is also assigned to the object it + points to. + +
+ Except for the strftime function, these functions each return a pointer to one of two + types of static objects: a broken-down time structure or an array of char. Execution of + any of the functions that return a pointer to one of these object types may overwrite the + information in any object of the same type pointed to by the value returned from any + previous call to any of them and the functions are not required to avoid data races. The + implementation shall behave as if no other library functions call these functions. + +
+
+ #include <time.h> + char *asctime(const struct tm *timeptr); ++
+ The asctime function converts the broken-down time in the structure pointed to by + timeptr into a string in the form + +
+ Sun Sep 16 01:03:52 1973\n\0 ++ using the equivalent of the following algorithm. + char *asctime(const struct tm *timeptr) + { +
+ static const char wday_name[7][3] = {
+ "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+ };
+ static const char mon_name[12][3] = {
+ "Jan", "Feb", "Mar", "Apr", "May", "Jun",
+ "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
+ };
+ static char result[26];
+ sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
+ wday_name[timeptr->tm_wday],
+ mon_name[timeptr->tm_mon],
+ timeptr->tm_mday, timeptr->tm_hour,
+ timeptr->tm_min, timeptr->tm_sec,
+ 1900 + timeptr->tm_year);
+ return result;
+
+ }
++ If any of the fields of the broken-down time contain values that are outside their normal + ranges,310) the behavior of the asctime function is undefined. Likewise, if the + calculated year exceeds four digits or is less than the year 1000, the behavior is + undefined. +
+ The asctime function returns a pointer to the string. + +
+
+ #include <time.h> + char *ctime(const time_t *timer); ++
+ The ctime function converts the calendar time pointed to by timer to local time in the + form of a string. It is equivalent to +
+ asctime(localtime(timer)) ++ + + + +
+ The ctime function returns the pointer returned by the asctime function with that + broken-down time as argument. +
Forward references: the localtime function (7.26.3.4). + +
+
+ #include <time.h> + struct tm *gmtime(const time_t *timer); ++
+ The gmtime function converts the calendar time pointed to by timer into a broken- + down time, expressed as UTC. +
+ The gmtime function returns a pointer to the broken-down time, or a null pointer if the + specified time cannot be converted to UTC. + +
+
+ #include <time.h> + struct tm *localtime(const time_t *timer); ++
+ The localtime function converts the calendar time pointed to by timer into a + broken-down time, expressed as local time. +
+ The localtime function returns a pointer to the broken-down time, or a null pointer if + the specified time cannot be converted to local time. + +
+ +
+ #include <time.h> + size_t strftime(char * restrict s, + size_t maxsize, + const char * restrict format, + const struct tm * restrict timeptr); ++
+ The strftime function places characters into the array pointed to by s as controlled by + the string pointed to by format. The format shall be a multibyte character sequence, + beginning and ending in its initial shift state. The format string consists of zero or + more conversion specifiers and ordinary multibyte characters. A conversion specifier + consists of a % character, possibly followed by an E or O modifier character (described + below), followed by a character that determines the behavior of the conversion specifier. + All ordinary multibyte characters (including the terminating null character) are copied + unchanged into the array. If copying takes place between objects that overlap, the + behavior is undefined. No more than maxsize characters are placed into the array. +
+ Each conversion specifier is replaced by appropriate characters as described in the + following list. The appropriate characters are determined using the LC_TIME category + of the current locale and by the values of zero or more members of the broken-down time + structure pointed to by timeptr, as specified in brackets in the description. If any of + the specified values is outside the normal range, the characters stored are unspecified. + %a is replaced by the locale's abbreviated weekday name. [tm_wday] + %A is replaced by the locale's full weekday name. [tm_wday] + %b is replaced by the locale's abbreviated month name. [tm_mon] + %B is replaced by the locale's full month name. [tm_mon] + %c is replaced by the locale's appropriate date and time representation. [all specified +
+ in 7.26.1] ++ %C is replaced by the year divided by 100 and truncated to an integer, as a decimal +
+ number (00-99). [tm_year] ++ %d is replaced by the day of the month as a decimal number (01-31). [tm_mday] + %D is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year] + %e is replaced by the day of the month as a decimal number (1-31); a single digit is +
+ preceded by a space. [tm_mday] ++ %F is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon, +
+ tm_mday] ++ %g is replaced by the last 2 digits of the week-based year (see below) as a decimal +
+ number (00-99). [tm_year, tm_wday, tm_yday] ++ %G is replaced by the week-based year (see below) as a decimal number (e.g., 1997). +
+ [tm_year, tm_wday, tm_yday] ++ %h is equivalent to ''%b''. [tm_mon] + %H is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour] + %I is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour] + %j is replaced by the day of the year as a decimal number (001-366). [tm_yday] + %m is replaced by the month as a decimal number (01-12). [tm_mon] + %M is replaced by the minute as a decimal number (00-59). [tm_min] + %n is replaced by a new-line character. + + %p is replaced by the locale's equivalent of the AM/PM designations associated with a +
+ 12-hour clock. [tm_hour] ++ %r is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec] + %R is equivalent to ''%H:%M''. [tm_hour, tm_min] + %S is replaced by the second as a decimal number (00-60). [tm_sec] + %t is replaced by a horizontal-tab character. + %T is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min, +
+ tm_sec] ++ %u is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday +
+ is 1. [tm_wday] ++ %U is replaced by the week number of the year (the first Sunday as the first day of week +
+ 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday] ++ %V is replaced by the ISO 8601 week number (see below) as a decimal number +
+ (01-53). [tm_year, tm_wday, tm_yday] ++ %w is replaced by the weekday as a decimal number (0-6), where Sunday is 0. +
+ [tm_wday] ++ %W is replaced by the week number of the year (the first Monday as the first day of +
+ week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday] ++ %x is replaced by the locale's appropriate date representation. [all specified in 7.26.1] + %X is replaced by the locale's appropriate time representation. [all specified in 7.26.1] + %y is replaced by the last 2 digits of the year as a decimal number (00-99). +
+ [tm_year] ++ %Y is replaced by the year as a decimal number (e.g., 1997). [tm_year] + %z is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4 +
+ hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time + zone is determinable. [tm_isdst] ++ %Z is replaced by the locale's time zone name or abbreviation, or by no characters if no +
+ time zone is determinable. [tm_isdst] ++ %% is replaced by %. +
+ Some conversion specifiers can be modified by the inclusion of an E or O modifier + character to indicate an alternative format or specification. If the alternative format or + specification does not exist for the current locale, the modifier is ignored. + %Ec is replaced by the locale's alternative date and time representation. + %EC is replaced by the name of the base year (period) in the locale's alternative +
+ representation. ++ %Ex is replaced by the locale's alternative date representation. + %EX is replaced by the locale's alternative time representation. + %Ey is replaced by the offset from %EC (year only) in the locale's alternative +
+ representation. ++ %EY is replaced by the locale's full alternative year representation. + + %Od is replaced by the day of the month, using the locale's alternative numeric symbols +
+ (filled as needed with leading zeros, or with leading spaces if there is no alternative + symbol for zero). ++ %Oe is replaced by the day of the month, using the locale's alternative numeric symbols +
+ (filled as needed with leading spaces). ++ %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric +
+ symbols. ++ %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric +
+ symbols. ++ %Om is replaced by the month, using the locale's alternative numeric symbols. + %OM is replaced by the minutes, using the locale's alternative numeric symbols. + %OS is replaced by the seconds, using the locale's alternative numeric symbols. + %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative +
+ representation, where Monday is 1. ++ %OU is replaced by the week number, using the locale's alternative numeric symbols. + %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric +
+ symbols. ++ %Ow is replaced by the weekday as a number, using the locale's alternative numeric +
+ symbols. ++ %OW is replaced by the week number of the year, using the locale's alternative numeric +
+ symbols. ++ %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric +
+ symbols. ++
+ %g, %G, and %V give values according to the ISO 8601 week-based year. In this system, + weeks begin on a Monday and week 1 of the year is the week that includes January 4th, + which is also the week that includes the first Thursday of the year, and is also the first + week that contains at least four days in the year. If the first Monday of January is the + 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus, + for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If + December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of + the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and + %V is replaced by 01. +
+ If a conversion specifier is not one of the above, the behavior is undefined. +
+ In the "C" locale, the E and O modifiers are ignored and the replacement strings for the + following specifiers are: + %a the first three characters of %A. + %A one of ''Sunday'', ''Monday'', ... , ''Saturday''. + %b the first three characters of %B. + %B one of ''January'', ''February'', ... , ''December''. + %c equivalent to ''%a %b %e %T %Y''. + + %p one of ''AM'' or ''PM''. + %r equivalent to ''%I:%M:%S %p''. + %x equivalent to ''%m/%d/%y''. + %X equivalent to %T. + %Z implementation-defined. +
+ If the total number of resulting characters including the terminating null character is not + more than maxsize, the strftime function returns the number of characters placed + into the array pointed to by s not including the terminating null character. Otherwise, + zero is returned and the contents of the array are indeterminate. + + +
+ The header <uchar.h> declares types and functions for manipulating Unicode + characters. +
+ The types declared are mbstate_t (described in 7.29.1) and size_t (described in + 7.19); +
+ char16_t ++ which is an unsigned integer type used for 16-bit characters and is the same type as + uint_least16_t (described in 7.20.1.2); and +
+ char32_t ++ which is an unsigned integer type used for 32-bit characters and is the same type as + uint_least32_t (also described in 7.20.1.2). + +
+ These functions have a parameter, ps, of type pointer to mbstate_t that points to an + object that can completely describe the current conversion state of the associated + multibyte character sequence, which the functions alter as necessary. If ps is a null + pointer, each function uses its own internal mbstate_t object instead, which is + initialized at program startup to the initial conversion state; the functions are not required + to avoid data races in this case. The implementation behaves as if no library function + calls these functions with a null pointer for ps. + +
+
+ #include <uchar.h> + size_t mbrtoc16(char16_t * restrict pc16, + const char * restrict s, size_t n, + mbstate_t * restrict ps); ++
+ If s is a null pointer, the mbrtoc16 function is equivalent to the call: +
+ mbrtoc16(NULL, "", 1, ps) ++ In this case, the values of the parameters pc16 and n are ignored. +
+ If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with + the byte pointed to by s to determine the number of bytes needed to complete the next + multibyte character (including any shift sequences). If the function determines that the + next multibyte character is complete and valid, it determines the values of the + corresponding wide characters and then, if pc16 is not a null pointer, stores the value of + the first (or only) such character in the object pointed to by pc16. Subsequent calls will + + store successive wide characters without consuming any additional input until all the + characters have been stored. If the corresponding wide character is the null wide + character, the resulting state described is the initial conversion state. +
+ The mbrtoc16 function returns the first of the following that applies (given the current + conversion state): + 0 if the next n or fewer bytes complete the multibyte character that +
+ corresponds to the null wide character (which is the value stored). ++ between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte +
+ character (which is the value stored); the value returned is the number + of bytes that complete the multibyte character. ++ (size_t)(-3) if the next character resulting from a previous call has been stored (no +
+ bytes from the input have been consumed by this call). ++ (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) +
+ multibyte character, and all n bytes have been processed (no value is + stored).311) ++ (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes +
+ do not contribute to a complete and valid multibyte character (no + value is stored); the value of the macro EILSEQ is stored in errno, + and the conversion state is unspecified. ++ +
311) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a + sequence of redundant shift sequences (for implementations with state-dependent encodings). + + +
+
+ #include <uchar.h> + size_t c16rtomb(char * restrict s, char16_t c16, + mbstate_t * restrict ps); ++
+ If s is a null pointer, the c16rtomb function is equivalent to the call +
+ c16rtomb(buf, L'\0', ps) ++ where buf is an internal buffer. +
+ If s is not a null pointer, the c16rtomb function determines the number of bytes needed + to represent the multibyte character that corresponds to the wide character given by c16 + (including any shift sequences), and stores the multibyte character representation in the + + + + array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If + c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed + to restore the initial shift state; the resulting state described is the initial conversion state. +
+ The c16rtomb function returns the number of bytes stored in the array object (including + any shift sequences). When c16 is not a valid wide character, an encoding error occurs: + the function stores the value of the macro EILSEQ in errno and returns + (size_t)(-1); the conversion state is unspecified. + +
+
+ #include <uchar.h> + size_t mbrtoc32(char32_t * restrict pc32, + const char * restrict s, size_t n, + mbstate_t * restrict ps); ++
+ If s is a null pointer, the mbrtoc32 function is equivalent to the call: +
+ mbrtoc32(NULL, "", 1, ps) ++ In this case, the values of the parameters pc32 and n are ignored. +
+ If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with + the byte pointed to by s to determine the number of bytes needed to complete the next + multibyte character (including any shift sequences). If the function determines that the + next multibyte character is complete and valid, it determines the values of the + corresponding wide characters and then, if pc32 is not a null pointer, stores the value of + the first (or only) such character in the object pointed to by pc32. Subsequent calls will + store successive wide characters without consuming any additional input until all the + characters have been stored. If the corresponding wide character is the null wide + character, the resulting state described is the initial conversion state. +
+ The mbrtoc32 function returns the first of the following that applies (given the current + conversion state): + 0 if the next n or fewer bytes complete the multibyte character that +
+ corresponds to the null wide character (which is the value stored). ++ between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte + +
+ character (which is the value stored); the value returned is the number + of bytes that complete the multibyte character. ++ (size_t)(-3) if the next character resulting from a previous call has been stored (no +
+ bytes from the input have been consumed by this call). ++ (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) +
+ multibyte character, and all n bytes have been processed (no value is + stored).312) ++ (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes +
+ do not contribute to a complete and valid multibyte character (no + value is stored); the value of the macro EILSEQ is stored in errno, + and the conversion state is unspecified. ++ +
312) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a + sequence of redundant shift sequences (for implementations with state-dependent encodings). + + +
+
+ #include <uchar.h> + size_t c32rtomb(char * restrict s, char32_t c32, + mbstate_t * restrict ps); ++
+ If s is a null pointer, the c32rtomb function is equivalent to the call +
+ c32rtomb(buf, L'\0', ps) ++ where buf is an internal buffer. +
+ If s is not a null pointer, the c32rtomb function determines the number of bytes needed + to represent the multibyte character that corresponds to the wide character given by c32 + (including any shift sequences), and stores the multibyte character representation in the + array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If + c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed + to restore the initial shift state; the resulting state described is the initial conversion state. +
+ The c32rtomb function returns the number of bytes stored in the array object (including + any shift sequences). When c32 is not a valid wide character, an encoding error occurs: + the function stores the value of the macro EILSEQ in errno and returns + (size_t)(-1); the conversion state is unspecified. + + + + + + +
+ The header <wchar.h> defines four macros, and declares four data types, one tag, and + many functions.313) +
+ The types declared are wchar_t and size_t (both described in 7.19); +
+ mbstate_t ++ which is a complete object type other than an array type that can hold the conversion state + information necessary to convert between sequences of multibyte characters and wide + characters; +
+ wint_t ++ which is an integer type unchanged by default argument promotions that can hold any + value corresponding to members of the extended character set, as well as at least one + value that does not correspond to any member of the extended character set (see WEOF + below);314) and +
+ struct tm ++ which is declared as an incomplete structure type (the contents are described in 7.26.1). +
+ The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX + (described in 7.20.3); and +
+ WEOF ++ which expands to a constant expression of type wint_t whose value does not + correspond to any member of the extended character set.315) It is accepted (and returned) + by several functions in this subclause to indicate end-of-file, that is, no more input from a + stream. It is also used as a wide character value that does not correspond to any member + of the extended character set. +
+ The functions declared are grouped as follows: +
+ Unless explicitly stated otherwise, if the execution of a function described in this + subclause causes copying to take place between objects that overlap, the behavior is + undefined. + +
313) See ''future library directions'' (7.30.12). + +
314) wchar_t and wint_t can be the same integer type. + +
315) The value of the macro WEOF may differ from that of EOF and need not be negative. + + +
+ The formatted wide character input/output functions shall behave as if there is a sequence + point after the actions associated with each specifier.316) + +
316) The fwprintf functions perform writes to memory for the %n specifier. + + +
+
+ #include <stdio.h> + #include <wchar.h> + int fwprintf(FILE * restrict stream, + const wchar_t * restrict format, ...); ++
+ The fwprintf function writes output to the stream pointed to by stream, under + control of the wide string pointed to by format that specifies how subsequent arguments + are converted for output. If there are insufficient arguments for the format, the behavior + is undefined. If the format is exhausted while arguments remain, the excess arguments + are evaluated (as always) but are otherwise ignored. The fwprintf function returns + when the end of the format string is encountered. +
+ The format is composed of zero or more directives: ordinary wide characters (not %), + which are copied unchanged to the output stream; and conversion specifications, each of + which results in fetching zero or more subsequent arguments, converting them, if + applicable, according to the corresponding conversion specifier, and then writing the + result to the output stream. +
+ Each conversion specification is introduced by the wide character %. After the %, the + following appear in sequence: +
+ As noted above, a field width, or precision, or both, may be indicated by an asterisk. In + this case, an int argument supplies the field width or precision. The arguments + specifying field width, or precision, or both, shall appear (in that order) before the + argument (if any) to be converted. A negative field width argument is taken as a - flag + followed by a positive field width. A negative precision argument is taken as if the + precision were omitted. +
+ The flag wide characters and their meanings are: + - The result of the conversion is left-justified within the field. (It is right-justified if +
+ this flag is not specified.) ++ + The result of a signed conversion always begins with a plus or minus sign. (It +
+ begins with a sign only when a negative value is converted if this flag is not + specified.)318) ++ space If the first wide character of a signed conversion is not a sign, or if a signed +
+ conversion results in no wide characters, a space is prefixed to the result. If the + space and + flags both appear, the space flag is ignored. ++ # The result is converted to an ''alternative form''. For o conversion, it increases +
+ the precision, if and only if necessary, to force the first digit of the result to be a + zero (if the value and precision are both 0, a single 0 is printed). For x (or X) + conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g, ++ + + +
+ and G conversions, the result of converting a floating-point number always + contains a decimal-point wide character, even if no digits follow it. (Normally, a + decimal-point wide character appears in the result of these conversions only if a + digit follows it.) For g and G conversions, trailing zeros are not removed from the + result. For other conversions, the behavior is undefined. ++ 0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros +
+ (following any indication of sign or base) are used to pad to the field width rather + than performing space padding, except when converting an infinity or NaN. If the + 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X + conversions, if a precision is specified, the 0 flag is ignored. For other + conversions, the behavior is undefined. ++
+ The length modifiers and their meanings are: + hh Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ signed char or unsigned char argument (the argument will have + been promoted according to the integer promotions, but its value shall be + converted to signed char or unsigned char before printing); or that + a following n conversion specifier applies to a pointer to a signed char + argument. ++ h Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ short int or unsigned short int argument (the argument will + have been promoted according to the integer promotions, but its value shall + be converted to short int or unsigned short int before printing); + or that a following n conversion specifier applies to a pointer to a short + int argument. ++ l (ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ long int or unsigned long int argument; that a following n + conversion specifier applies to a pointer to a long int argument; that a + following c conversion specifier applies to a wint_t argument; that a + following s conversion specifier applies to a pointer to a wchar_t + argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion + specifier. ++ ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ long long int or unsigned long long int argument; or that a + following n conversion specifier applies to a pointer to a long long int + argument. ++ j Specifies that a following d, i, o, u, x, or X conversion specifier applies to + +
+ an intmax_t or uintmax_t argument; or that a following n conversion + specifier applies to a pointer to an intmax_t argument. ++ z Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ size_t or the corresponding signed integer type argument; or that a + following n conversion specifier applies to a pointer to a signed integer type + corresponding to size_t argument. ++ t Specifies that a following d, i, o, u, x, or X conversion specifier applies to a +
+ ptrdiff_t or the corresponding unsigned integer type argument; or that a + following n conversion specifier applies to a pointer to a ptrdiff_t + argument. ++ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier +
+ applies to a long double argument. ++ If a length modifier appears with any conversion specifier other than as specified above, + the behavior is undefined. +
+ The conversion specifiers and their meanings are: + d,i The int argument is converted to signed decimal in the style [-]dddd. The +
+ precision specifies the minimum number of digits to appear; if the value + being converted can be represented in fewer digits, it is expanded with + leading zeros. The default precision is 1. The result of converting a zero + value with a precision of zero is no wide characters. ++ o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned +
+ decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the + letters abcdef are used for x conversion and the letters ABCDEF for X + conversion. The precision specifies the minimum number of digits to appear; + if the value being converted can be represented in fewer digits, it is expanded + with leading zeros. The default precision is 1. The result of converting a + zero value with a precision of zero is no wide characters. ++ f,F A double argument representing a floating-point number is converted to + +
+ decimal notation in the style [-]ddd.ddd, where the number of digits after + the decimal-point wide character is equal to the precision specification. If the + precision is missing, it is taken as 6; if the precision is zero and the # flag is + not specified, no decimal-point wide character appears. If a decimal-point + wide character appears, at least one digit appears before it. The value is + rounded to the appropriate number of digits. + A double argument representing an infinity is converted in one of the styles + [-]inf or [-]infinity -- which style is implementation-defined. A + double argument representing a NaN is converted in one of the styles + [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of + any n-wchar-sequence, is implementation-defined. The F conversion + specifier produces INF, INFINITY, or NAN instead of inf, infinity, or + nan, respectively.319) ++ e,E A double argument representing a floating-point number is converted in the +
+ style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the + argument is nonzero) before the decimal-point wide character and the number + of digits after it is equal to the precision; if the precision is missing, it is taken + as 6; if the precision is zero and the # flag is not specified, no decimal-point + wide character appears. The value is rounded to the appropriate number of + digits. The E conversion specifier produces a number with E instead of e + introducing the exponent. The exponent always contains at least two digits, + and only as many more digits as necessary to represent the exponent. If the + value is zero, the exponent is zero. + A double argument representing an infinity or NaN is converted in the style + of an f or F conversion specifier. ++ g,G A double argument representing a floating-point number is converted in +
+ style f or e (or in style F or E in the case of a G conversion specifier), + depending on the value converted and the precision. Let P equal the + precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero. + Then, if a conversion with style E would have an exponent of X: + -- if P > X >= -4, the conversion is with style f (or F) and precision + P - (X + 1). + -- otherwise, the conversion is with style e (or E) and precision P - 1. + Finally, unless the # flag is used, any trailing zeros are removed from the + fractional portion of the result and the decimal-point wide character is + removed if there is no fractional portion remaining. + A double argument representing an infinity or NaN is converted in the style + of an f or F conversion specifier. ++ a,A A double argument representing a floating-point number is converted in the +
+ style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is + nonzero if the argument is a normalized floating-point number and is + otherwise unspecified) before the decimal-point wide character320) and the + number of hexadecimal digits after it is equal to the precision; if the precision + is missing and FLT_RADIX is a power of 2, then the precision is sufficient ++ + + +
+ for an exact representation of the value; if the precision is missing and + FLT_RADIX is not a power of 2, then the precision is sufficient to + distinguish321) values of type double, except that trailing zeros may be + omitted; if the precision is zero and the # flag is not specified, no decimal- + point wide character appears. The letters abcdef are used for a conversion + and the letters ABCDEF for A conversion. The A conversion specifier + produces a number with X and P instead of x and p. The exponent always + contains at least one digit, and only as many more digits as necessary to + represent the decimal exponent of 2. If the value is zero, the exponent is + zero. + A double argument representing an infinity or NaN is converted in the style + of an f or F conversion specifier. ++ c If no l length modifier is present, the int argument is converted to a wide +
+ character as if by calling btowc and the resulting wide character is written. + If an l length modifier is present, the wint_t argument is converted to + wchar_t and written. ++ s If no l length modifier is present, the argument shall be a pointer to the initial +
+ element of a character array containing a multibyte character sequence + beginning in the initial shift state. Characters from the array are converted as + if by repeated calls to the mbrtowc function, with the conversion state + described by an mbstate_t object initialized to zero before the first + multibyte character is converted, and written up to (but not including) the + terminating null wide character. If the precision is specified, no more than + that many wide characters are written. If the precision is not specified or is + greater than the size of the converted array, the converted array shall contain a + null wide character. + If an l length modifier is present, the argument shall be a pointer to the initial + element of an array of wchar_t type. Wide characters from the array are + written up to (but not including) a terminating null wide character. If the + precision is specified, no more than that many wide characters are written. If + the precision is not specified or is greater than the size of the array, the array + shall contain a null wide character. ++ p The argument shall be a pointer to void. The value of the pointer is +
+ converted to a sequence of printing wide characters, in an implementation- ++ + +
+ defined manner. ++ n The argument shall be a pointer to signed integer into which is written the +
+ number of wide characters written to the output stream so far by this call to + fwprintf. No argument is converted, but one is consumed. If the + conversion specification includes any flags, a field width, or a precision, the + behavior is undefined. ++ % A % wide character is written. No argument is converted. The complete +
+ conversion specification shall be %%. ++
+ If a conversion specification is invalid, the behavior is undefined.322) If any argument is + not the correct type for the corresponding conversion specification, the behavior is + undefined. +
+ In no case does a nonexistent or small field width cause truncation of a field; if the result + of a conversion is wider than the field width, the field is expanded to contain the + conversion result. +
+ For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded + to a hexadecimal floating number with the given precision. +
+ For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly + representable in the given precision, the result should be one of the two adjacent numbers + in hexadecimal floating style with the given precision, with the extra stipulation that the + error should have a correct sign for the current rounding direction. +
+ For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most + DECIMAL_DIG, then the result should be correctly rounded.323) If the number of + significant decimal digits is more than DECIMAL_DIG but the source value is exactly + representable with DECIMAL_DIG digits, then the result should be an exact + representation with trailing zeros. Otherwise, the source value is bounded by two + adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value + of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that + the error should have a correct sign for the current rounding direction. +
+ The fwprintf function returns the number of wide characters transmitted, or a negative + value if an output or encoding error occurred. + + +
+ The number of wide characters that can be produced by any single conversion shall be at + least 4095. +
+ EXAMPLE To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal + places: +
+ #include <math.h> + #include <stdio.h> + #include <wchar.h> + /* ... */ + wchar_t *weekday, *month; // pointers to wide strings + int day, hour, min; + fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n", + weekday, month, day, hour, min); + fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0)); ++ +
Forward references: the btowc function (7.28.6.1.1), the mbrtowc function + (7.28.6.3.2). + +
317) Note that 0 is taken as a flag, not as the beginning of a field width. + +
318) The results of all floating conversions of a negative zero, and of negative values that round to zero, + include a minus sign. + +
319) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual + meaning; the # and 0 flag wide characters have no effect. + +
320) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide + character so that subsequent digits align to nibble (4-bit) boundaries. + +
321) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is + FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p + might suffice depending on the implementation's scheme for determining the digit to the left of the + decimal-point wide character. + +
322) See ''future library directions'' (7.30.12). + +
323) For binary-to-decimal conversion, the result format's values are the numbers representable with the + given format specifier. The number of significant digits is determined by the format specifier, and in + the case of fixed-point conversion by the source value as well. + + +
+
+ #include <stdio.h> + #include <wchar.h> + int fwscanf(FILE * restrict stream, + const wchar_t * restrict format, ...); ++
+ The fwscanf function reads input from the stream pointed to by stream, under + control of the wide string pointed to by format that specifies the admissible input + sequences and how they are to be converted for assignment, using subsequent arguments + as pointers to the objects to receive the converted input. If there are insufficient + arguments for the format, the behavior is undefined. If the format is exhausted while + arguments remain, the excess arguments are evaluated (as always) but are otherwise + ignored. +
+ The format is composed of zero or more directives: one or more white-space wide + characters, an ordinary wide character (neither % nor a white-space wide character), or a + conversion specification. Each conversion specification is introduced by the wide + character %. After the %, the following appear in sequence: +
+ The fwscanf function executes each directive of the format in turn. When all directives + have been executed, or if a directive fails (as detailed below), the function returns. + Failures are described as input failures (due to the occurrence of an encoding error or the + unavailability of input characters), or matching failures (due to inappropriate input). +
+ A directive composed of white-space wide character(s) is executed by reading input up to + the first non-white-space wide character (which remains unread), or until no more wide + characters can be read. +
+ A directive that is an ordinary wide character is executed by reading the next wide + character of the stream. If that wide character differs from the directive, the directive + fails and the differing and subsequent wide characters remain unread. Similarly, if end- + of-file, an encoding error, or a read error prevents a wide character from being read, the + directive fails. +
+ A directive that is a conversion specification defines a set of matching input sequences, as + described below for each specifier. A conversion specification is executed in the + following steps: +
+ Input white-space wide characters (as specified by the iswspace function) are skipped, + unless the specification includes a [, c, or n specifier.324) +
+ An input item is read from the stream, unless the specification includes an n specifier. An + input item is defined as the longest sequence of input wide characters which does not + exceed any specified field width and which is, or is a prefix of, a matching input + sequence.325) The first wide character, if any, after the input item remains unread. If the + length of the input item is zero, the execution of the directive fails; this condition is a + matching failure unless end-of-file, an encoding error, or a read error prevented input + from the stream, in which case it is an input failure. +
+ Except in the case of a % specifier, the input item (or, in the case of a %n directive, the + count of input wide characters) is converted to a type appropriate to the conversion + specifier. If the input item is not a matching sequence, the execution of the directive fails: + this condition is a matching failure. Unless assignment suppression was indicated by a *, + the result of the conversion is placed in the object pointed to by the first argument + following the format argument that has not already received a conversion result. If this + + + + object does not have an appropriate type, or if the result of the conversion cannot be + represented in the object, the behavior is undefined. +
+ The length modifiers and their meanings are: + hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to signed char or unsigned char. ++ h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to short int or unsigned short + int. ++ l (ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to long int or unsigned long + int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to + an argument with type pointer to double; or that a following c, s, or [ + conversion specifier applies to an argument with type pointer to wchar_t. ++ ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to long long int or unsigned + long long int. ++ j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to intmax_t or uintmax_t. ++ z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to size_t or the corresponding signed + integer type. ++ t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies +
+ to an argument with type pointer to ptrdiff_t or the corresponding + unsigned integer type. ++ L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier +
+ applies to an argument with type pointer to long double. ++ If a length modifier appears with any conversion specifier other than as specified above, + the behavior is undefined. +
+ The conversion specifiers and their meanings are: + d Matches an optionally signed decimal integer, whose format is the same as +
+ expected for the subject sequence of the wcstol function with the value 10 + for the base argument. The corresponding argument shall be a pointer to + signed integer. ++ i Matches an optionally signed integer, whose format is the same as expected + +
+ for the subject sequence of the wcstol function with the value 0 for the + base argument. The corresponding argument shall be a pointer to signed + integer. ++ o Matches an optionally signed octal integer, whose format is the same as +
+ expected for the subject sequence of the wcstoul function with the value 8 + for the base argument. The corresponding argument shall be a pointer to + unsigned integer. ++ u Matches an optionally signed decimal integer, whose format is the same as +
+ expected for the subject sequence of the wcstoul function with the value 10 + for the base argument. The corresponding argument shall be a pointer to + unsigned integer. ++ x Matches an optionally signed hexadecimal integer, whose format is the same +
+ as expected for the subject sequence of the wcstoul function with the value + 16 for the base argument. The corresponding argument shall be a pointer to + unsigned integer. ++ a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose +
+ format is the same as expected for the subject sequence of the wcstod + function. The corresponding argument shall be a pointer to floating. ++ c Matches a sequence of wide characters of exactly the number specified by the +
+ field width (1 if no field width is present in the directive). + If no l length modifier is present, characters from the input field are + converted as if by repeated calls to the wcrtomb function, with the + conversion state described by an mbstate_t object initialized to zero + before the first wide character is converted. The corresponding argument + shall be a pointer to the initial element of a character array large enough to + accept the sequence. No null character is added. + If an l length modifier is present, the corresponding argument shall be a + pointer to the initial element of an array of wchar_t large enough to accept + the sequence. No null wide character is added. ++ s Matches a sequence of non-white-space wide characters. + +
+ If no l length modifier is present, characters from the input field are + converted as if by repeated calls to the wcrtomb function, with the + conversion state described by an mbstate_t object initialized to zero + before the first wide character is converted. The corresponding argument + shall be a pointer to the initial element of a character array large enough to + accept the sequence and a terminating null character, which will be added + automatically. + If an l length modifier is present, the corresponding argument shall be a + pointer to the initial element of an array of wchar_t large enough to accept + the sequence and the terminating null wide character, which will be added + automatically. ++ [ Matches a nonempty sequence of wide characters from a set of expected +
+ characters (the scanset). + If no l length modifier is present, characters from the input field are + converted as if by repeated calls to the wcrtomb function, with the + conversion state described by an mbstate_t object initialized to zero + before the first wide character is converted. The corresponding argument + shall be a pointer to the initial element of a character array large enough to + accept the sequence and a terminating null character, which will be added + automatically. + If an l length modifier is present, the corresponding argument shall be a + pointer to the initial element of an array of wchar_t large enough to accept + the sequence and the terminating null wide character, which will be added + automatically. + The conversion specifier includes all subsequent wide characters in the + format string, up to and including the matching right bracket (]). The wide + characters between the brackets (the scanlist) compose the scanset, unless the + wide character after the left bracket is a circumflex (^), in which case the + scanset contains all wide characters that do not appear in the scanlist between + the circumflex and the right bracket. If the conversion specifier begins with + [] or [^], the right bracket wide character is in the scanlist and the next + following right bracket wide character is the matching right bracket that ends + the specification; otherwise the first following right bracket wide character is + the one that ends the specification. If a - wide character is in the scanlist and + is not the first, nor the second where the first wide character is a ^, nor the + last character, the behavior is implementation-defined. ++ p Matches an implementation-defined set of sequences, which should be the +
+ same as the set of sequences that may be produced by the %p conversion of + the fwprintf function. The corresponding argument shall be a pointer to a + pointer to void. The input item is converted to a pointer value in an + implementation-defined manner. If the input item is a value converted earlier + during the same program execution, the pointer that results shall compare + equal to that value; otherwise the behavior of the %p conversion is undefined. ++ n No input is consumed. The corresponding argument shall be a pointer to + +
+ signed integer into which is to be written the number of wide characters read + from the input stream so far by this call to the fwscanf function. Execution + of a %n directive does not increment the assignment count returned at the + completion of execution of the fwscanf function. No argument is + converted, but one is consumed. If the conversion specification includes an + assignment-suppressing wide character or a field width, the behavior is + undefined. ++ % Matches a single % wide character; no conversion or assignment occurs. The +
+ complete conversion specification shall be %%. ++
+ If a conversion specification is invalid, the behavior is undefined.326) +
+ The conversion specifiers A, E, F, G, and X are also valid and behave the same as, + respectively, a, e, f, g, and x. +
+ Trailing white space (including new-line wide characters) is left unread unless matched + by a directive. The success of literal matches and suppressed assignments is not directly + determinable other than via the %n directive. +
+ The fwscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the function returns the + number of input items assigned, which can be fewer than provided for, or even zero, in + the event of an early matching failure. +
+ EXAMPLE 1 The call: +
+ #include <stdio.h> + #include <wchar.h> + /* ... */ + int n, i; float x; wchar_t name[50]; + n = fwscanf(stdin, L"%d%f%ls", &i, &x, name); ++ with the input line: +
+ 25 54.32E-1 thompson ++ will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence + thompson\0. + +
+ EXAMPLE 2 The call: +
+ #include <stdio.h> + #include <wchar.h> + /* ... */ + int i; float x; double y; + fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y); ++ with input: +
+ 56789 0123 56a72 ++ will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value + 56.0. The next wide character read from the input stream will be a. + + + +
Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the + wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb + function (7.28.6.3.3). + +
324) These white-space wide characters are not counted against a specified field width. + +
325) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some + sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf. + +
326) See ''future library directions'' (7.30.12). + + +
+
+ #include <wchar.h> + int swprintf(wchar_t * restrict s, + size_t n, + const wchar_t * restrict format, ...); ++
+ The swprintf function is equivalent to fwprintf, except that the argument s + specifies an array of wide characters into which the generated output is to be written, + rather than written to a stream. No more than n wide characters are written, including a + terminating null wide character, which is always added (unless n is zero). +
+ The swprintf function returns the number of wide characters written in the array, not + counting the terminating null wide character, or a negative value if an encoding error + occurred or if n or more wide characters were requested to be written. + +
+
+ #include <wchar.h> + int swscanf(const wchar_t * restrict s, + const wchar_t * restrict format, ...); ++
+ The swscanf function is equivalent to fwscanf, except that the argument s specifies a + wide string from which the input is to be obtained, rather than from a stream. Reaching + the end of the wide string is equivalent to encountering end-of-file for the fwscanf + function. +
+ The swscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the swscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + + +
+
+ #include <stdarg.h> + #include <stdio.h> + #include <wchar.h> int vfwprintf(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - int vfwscanf(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - int vswprintf(wchar_t * restrict s, size_t n, - const wchar_t * restrict format, va_list arg); - - - -[page 493] (Contents) - - int vswscanf(const wchar_t * restrict s, - const wchar_t * restrict format, va_list arg); - int vwprintf(const wchar_t * restrict format, - va_list arg); - int vwscanf(const wchar_t * restrict format, - va_list arg); - int wprintf(const wchar_t * restrict format, ...); - int wscanf(const wchar_t * restrict format, ...); - wint_t fgetwc(FILE *stream); - wchar_t *fgetws(wchar_t * restrict s, int n, - FILE * restrict stream); - wint_t fputwc(wchar_t c, FILE *stream); - int fputws(const wchar_t * restrict s, - FILE * restrict stream); - int fwide(FILE *stream, int mode); - wint_t getwc(FILE *stream); - wint_t getwchar(void); - wint_t putwc(wchar_t c, FILE *stream); - wint_t putwchar(wchar_t c); - wint_t ungetwc(wint_t c, FILE *stream); - double wcstod(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - float wcstof(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - long double wcstold(const wchar_t * restrict nptr, - wchar_t ** restrict endptr); - long int wcstol(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - long long int wcstoll(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - unsigned long int wcstoul(const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - unsigned long long int wcstoull( - const wchar_t * restrict nptr, - wchar_t ** restrict endptr, int base); - wchar_t *wcscpy(wchar_t * restrict s1, - const wchar_t * restrict s2); - wchar_t *wcsncpy(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - - - -[page 494] (Contents) - - wchar_t *wmemcpy(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, - size_t n); - wchar_t *wcscat(wchar_t * restrict s1, - const wchar_t * restrict s2); - wchar_t *wcsncat(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); - int wcscmp(const wchar_t *s1, const wchar_t *s2); - int wcscoll(const wchar_t *s1, const wchar_t *s2); - int wcsncmp(const wchar_t *s1, const wchar_t *s2, - size_t n); - size_t wcsxfrm(wchar_t * restrict s1, - const wchar_t * restrict s2, size_t n); + const wchar_t * restrict format, + va_list arg); ++
+ The vfwprintf function is equivalent to fwprintf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vfwprintf function does not invoke the + va_end macro.327) +
+ The vfwprintf function returns the number of wide characters transmitted, or a + negative value if an output or encoding error occurred. +
+ EXAMPLE The following shows the use of the vfwprintf function in a general error-reporting + routine. +
+ #include <stdarg.h> + #include <stdio.h> + #include <wchar.h> + void error(char *function_name, wchar_t *format, ...) + { + va_list args; + va_start(args, format); + // print out name of function causing error + fwprintf(stderr, L"ERROR in %s: ", function_name); + // print out remainder of message + vfwprintf(stderr, format, args); + va_end(args); + } ++ + + + + + +
327) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf + invoke the va_arg macro, the value of arg after the return is indeterminate. + + +
+
+ #include <stdarg.h> + #include <stdio.h> + #include <wchar.h> + int vfwscanf(FILE * restrict stream, + const wchar_t * restrict format, + va_list arg); ++
+ The vfwscanf function is equivalent to fwscanf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vfwscanf function does not invoke the + va_end macro.327) +
+ The vfwscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the vfwscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdarg.h> + #include <wchar.h> + int vswprintf(wchar_t * restrict s, + size_t n, + const wchar_t * restrict format, + va_list arg); ++
+ The vswprintf function is equivalent to swprintf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vswprintf function does not invoke the + va_end macro.327) +
+ The vswprintf function returns the number of wide characters written in the array, not + counting the terminating null wide character, or a negative value if an encoding error + occurred or if n or more wide characters were requested to be generated. + + +
+
+ #include <stdarg.h> + #include <wchar.h> + int vswscanf(const wchar_t * restrict s, + const wchar_t * restrict format, + va_list arg); ++
+ The vswscanf function is equivalent to swscanf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vswscanf function does not invoke the + va_end macro.327) +
+ The vswscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the vswscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdarg.h> + #include <wchar.h> + int vwprintf(const wchar_t * restrict format, + va_list arg); ++
+ The vwprintf function is equivalent to wprintf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vwprintf function does not invoke the + va_end macro.327) +
+ The vwprintf function returns the number of wide characters transmitted, or a negative + value if an output or encoding error occurred. + + +
+
+ #include <stdarg.h> + #include <wchar.h> + int vwscanf(const wchar_t * restrict format, + va_list arg); ++
+ The vwscanf function is equivalent to wscanf, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vwscanf function does not invoke the + va_end macro.327) +
+ The vwscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the vwscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <wchar.h> + int wprintf(const wchar_t * restrict format, ...); ++
+ The wprintf function is equivalent to fwprintf with the argument stdout + interposed before the arguments to wprintf. +
+ The wprintf function returns the number of wide characters transmitted, or a negative + value if an output or encoding error occurred. + +
+
+ #include <wchar.h> + int wscanf(const wchar_t * restrict format, ...); ++
+ The wscanf function is equivalent to fwscanf with the argument stdin interposed + before the arguments to wscanf. + +
+ The wscanf function returns the value of the macro EOF if an input failure occurs + before the first conversion (if any) has completed. Otherwise, the wscanf function + returns the number of input items assigned, which can be fewer than provided for, or even + zero, in the event of an early matching failure. + +
+
+ #include <stdio.h> + #include <wchar.h> + wint_t fgetwc(FILE *stream); ++
+ If the end-of-file indicator for the input stream pointed to by stream is not set and a + next wide character is present, the fgetwc function obtains that wide character as a + wchar_t converted to a wint_t and advances the associated file position indicator for + the stream (if defined). +
+ If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end- + of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise, + the fgetwc function returns the next wide character from the input stream pointed to by + stream. If a read error occurs, the error indicator for the stream is set and the fgetwc + function returns WEOF. If an encoding error occurs (including too few bytes), the value of + the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.328) + +
328) An end-of-file and a read error can be distinguished by use of the feof and ferror functions. + Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs. + + +
+
+ #include <stdio.h> + #include <wchar.h> + wchar_t *fgetws(wchar_t * restrict s, + int n, FILE * restrict stream); ++
+ The fgetws function reads at most one less than the number of wide characters + specified by n from the stream pointed to by stream into the array pointed to by s. No + + + + additional wide characters are read after a new-line wide character (which is retained) or + after end-of-file. A null wide character is written immediately after the last wide + character read into the array. +
+ The fgetws function returns s if successful. If end-of-file is encountered and no + characters have been read into the array, the contents of the array remain unchanged and a + null pointer is returned. If a read or encoding error occurs during the operation, the array + contents are indeterminate and a null pointer is returned. + +
+
+ #include <stdio.h> + #include <wchar.h> + wint_t fputwc(wchar_t c, FILE *stream); ++
+ The fputwc function writes the wide character specified by c to the output stream + pointed to by stream, at the position indicated by the associated file position indicator + for the stream (if defined), and advances the indicator appropriately. If the file cannot + support positioning requests, or if the stream was opened with append mode, the + character is appended to the output stream. +
+ The fputwc function returns the wide character written. If a write error occurs, the + error indicator for the stream is set and fputwc returns WEOF. If an encoding error + occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF. + +
+
+ #include <stdio.h> + #include <wchar.h> + int fputws(const wchar_t * restrict s, + FILE * restrict stream); ++
+ The fputws function writes the wide string pointed to by s to the stream pointed to by + stream. The terminating null wide character is not written. +
+ The fputws function returns EOF if a write or encoding error occurs; otherwise, it + returns a nonnegative value. + + +
+
+ #include <stdio.h> + #include <wchar.h> + int fwide(FILE *stream, int mode); ++
+ The fwide function determines the orientation of the stream pointed to by stream. If + mode is greater than zero, the function first attempts to make the stream wide oriented. If + mode is less than zero, the function first attempts to make the stream byte oriented.329) + Otherwise, mode is zero and the function does not alter the orientation of the stream. +
+ The fwide function returns a value greater than zero if, after the call, the stream has + wide orientation, a value less than zero if the stream has byte orientation, or zero if the + stream has no orientation. + +
329) If the orientation of the stream has already been determined, fwide does not change it. + + +
+
+ #include <stdio.h> + #include <wchar.h> + wint_t getwc(FILE *stream); ++
+ The getwc function is equivalent to fgetwc, except that if it is implemented as a + macro, it may evaluate stream more than once, so the argument should never be an + expression with side effects. +
+ The getwc function returns the next wide character from the input stream pointed to by + stream, or WEOF. + +
+
+ #include <wchar.h> + wint_t getwchar(void); ++ + + + + +
+ The getwchar function is equivalent to getwc with the argument stdin. +
+ The getwchar function returns the next wide character from the input stream pointed to + by stdin, or WEOF. + +
+
+ #include <stdio.h> + #include <wchar.h> + wint_t putwc(wchar_t c, FILE *stream); ++
+ The putwc function is equivalent to fputwc, except that if it is implemented as a + macro, it may evaluate stream more than once, so that argument should never be an + expression with side effects. +
+ The putwc function returns the wide character written, or WEOF. + +
+
+ #include <wchar.h> + wint_t putwchar(wchar_t c); ++
+ The putwchar function is equivalent to putwc with the second argument stdout. +
+ The putwchar function returns the character written, or WEOF. + +
+
+ #include <stdio.h> + #include <wchar.h> + wint_t ungetwc(wint_t c, FILE *stream); ++
+ The ungetwc function pushes the wide character specified by c back onto the input + stream pointed to by stream. Pushed-back wide characters will be returned by + subsequent reads on that stream in the reverse order of their pushing. A successful + + intervening call (with the stream pointed to by stream) to a file positioning function + (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the + stream. The external storage corresponding to the stream is unchanged. +
+ One wide character of pushback is guaranteed, even if the call to the ungetwc function + follows just after a call to a formatted wide character input function fwscanf, + vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times + on the same stream without an intervening read or file positioning operation on that + stream, the operation may fail. +
+ If the value of c equals that of the macro WEOF, the operation fails and the input stream is + unchanged. +
+ A successful call to the ungetwc function clears the end-of-file indicator for the stream. + The value of the file position indicator for the stream after reading or discarding all + pushed-back wide characters is the same as it was before the wide characters were pushed + back. For a text or binary stream, the value of its file position indicator after a successful + call to the ungetwc function is unspecified until all pushed-back wide characters are + read or discarded. +
+ The ungetwc function returns the wide character pushed back, or WEOF if the operation + fails. + +
+ The header <wchar.h> declares a number of functions useful for wide string + manipulation. Various methods are used for determining the lengths of the arrays, but in + all cases a wchar_t * argument points to the initial (lowest addressed) element of the + array. If an array is accessed beyond the end of an object, the behavior is undefined. +
+ Where an argument declared as size_t n determines the length of the array for a + function, n can have the value zero on a call to that function. Unless explicitly stated + otherwise in the description of a particular function in this subclause, pointer arguments + on such a call shall still have valid values, as described in 7.1.4. On such a call, a + function that locates a wide character finds no occurrence, a function that compares two + wide character sequences returns zero, and a function that copies wide characters copies + zero wide characters. + + +
+
+ #include <wchar.h> + double wcstod(const wchar_t * restrict nptr, + wchar_t ** restrict endptr); + float wcstof(const wchar_t * restrict nptr, + wchar_t ** restrict endptr); + long double wcstold(const wchar_t * restrict nptr, + wchar_t ** restrict endptr); ++
+ The wcstod, wcstof, and wcstold functions convert the initial portion of the wide + string pointed to by nptr to double, float, and long double representation, + respectively. First, they decompose the input string into three parts: an initial, possibly + empty, sequence of white-space wide characters (as specified by the iswspace + function), a subject sequence resembling a floating-point constant or representing an + infinity or NaN; and a final wide string of one or more unrecognized wide characters, + including the terminating null wide character of the input wide string. Then, they attempt + to convert the subject sequence to a floating-point number, and return the result. +
+ The expected form of the subject sequence is an optional plus or minus sign, then one of + the following: +
+ n-wchar-sequence: + digit + nondigit + n-wchar-sequence digit + n-wchar-sequence nondigit ++
+ If the subject sequence has the expected form for a floating-point number, the sequence of + wide characters starting with the first digit or the decimal-point wide character + (whichever occurs first) is interpreted as a floating constant according to the rules of + 6.4.4.2, except that the decimal-point wide character is used in place of a period, and that + if neither an exponent part nor a decimal-point wide character appears in a decimal + floating point number, or if a binary exponent part does not appear in a hexadecimal + floating point number, an exponent part of the appropriate type with value zero is + assumed to follow the last digit in the string. If the subject sequence begins with a minus + sign, the sequence is interpreted as negated.330) A wide character sequence INF or + INFINITY is interpreted as an infinity, if representable in the return type, else like a + floating constant that is too large for the range of the return type. A wide character + sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported + in the return type, else like a subject sequence part that does not have the expected form; + the meaning of the n-wchar sequences is implementation-defined.331) A pointer to the + final wide string is stored in the object pointed to by endptr, provided that endptr is + not a null pointer. +
+ If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the + value resulting from the conversion is correctly rounded. +
+ In other than the "C" locale, additional locale-specific subject sequence forms may be + accepted. +
+ If the subject sequence is empty or does not have the expected form, no conversion is + performed; the value of nptr is stored in the object pointed to by endptr, provided + that endptr is not a null pointer. +
+ If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and + the result is not exactly representable, the result should be one of the two numbers in the + appropriate internal format that are adjacent to the hexadecimal floating source value, + with the extra stipulation that the error should have a correct sign for the current rounding + direction. + + + + +
+ If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in + <float.h>) significant digits, the result should be correctly rounded. If the subject + sequence D has the decimal form and more than DECIMAL_DIG significant digits, + consider the two bounding, adjacent decimal strings L and U, both having + DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U. + The result should be one of the (equal or adjacent) values that would be obtained by + correctly rounding L and U according to the current rounding direction, with the extra + stipulation that the error with respect to D should have a correct sign for the current + rounding direction.332) +
+ The functions return the converted value, if any. If no conversion could be performed, + zero is returned. If the correct value overflows and default rounding is in effect (7.12.1), + plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the + return type and sign of the value), and the value of the macro ERANGE is stored in + errno. If the result underflows (7.12.1), the functions return a value whose magnitude is + no greater than the smallest normalized positive number in the return type; whether + errno acquires the value ERANGE is implementation-defined. + + + + + + +
330) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by + negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two + methods may yield different results if rounding is toward positive or negative infinity. In either case, + the functions honor the sign of zero if floating-point arithmetic supports signed zeros. + +
331) An implementation may use the n-wchar sequence to determine extra information to be represented in + the NaN's significand. + +
332) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round + to the same internal floating value, but if not will round to adjacent values. + + +
+
+ #include <wchar.h> + long int wcstol( + const wchar_t * restrict nptr, + wchar_t ** restrict endptr, + int base); + long long int wcstoll( + const wchar_t * restrict nptr, + wchar_t ** restrict endptr, + int base); + unsigned long int wcstoul( + const wchar_t * restrict nptr, + wchar_t ** restrict endptr, + int base); + unsigned long long int wcstoull( + const wchar_t * restrict nptr, + wchar_t ** restrict endptr, + int base); ++
+ The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial + portion of the wide string pointed to by nptr to long int, long long int, + unsigned long int, and unsigned long long int representation, + respectively. First, they decompose the input string into three parts: an initial, possibly + empty, sequence of white-space wide characters (as specified by the iswspace + function), a subject sequence resembling an integer represented in some radix determined + by the value of base, and a final wide string of one or more unrecognized wide + characters, including the terminating null wide character of the input wide string. Then, + they attempt to convert the subject sequence to an integer, and return the result. +
+ If the value of base is zero, the expected form of the subject sequence is that of an + integer constant as described for the corresponding single-byte characters in 6.4.4.1, + optionally preceded by a plus or minus sign, but not including an integer suffix. If the + value of base is between 2 and 36 (inclusive), the expected form of the subject sequence + is a sequence of letters and digits representing an integer with the radix specified by + base, optionally preceded by a plus or minus sign, but not including an integer suffix. + The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only + letters and digits whose ascribed values are less than that of base are permitted. If the + value of base is 16, the wide characters 0x or 0X may optionally precede the sequence + of letters and digits, following the sign if present. + +
+ The subject sequence is defined as the longest initial subsequence of the input wide + string, starting with the first non-white-space wide character, that is of the expected form. + The subject sequence contains no wide characters if the input wide string is empty or + consists entirely of white space, or if the first non-white-space wide character is other + than a sign or a permissible letter or digit. +
+ If the subject sequence has the expected form and the value of base is zero, the sequence + of wide characters starting with the first digit is interpreted as an integer constant + according to the rules of 6.4.4.1. If the subject sequence has the expected form and the + value of base is between 2 and 36, it is used as the base for conversion, ascribing to each + letter its value as given above. If the subject sequence begins with a minus sign, the value + resulting from the conversion is negated (in the return type). A pointer to the final wide + string is stored in the object pointed to by endptr, provided that endptr is not a null + pointer. +
+ In other than the "C" locale, additional locale-specific subject sequence forms may be + accepted. +
+ If the subject sequence is empty or does not have the expected form, no conversion is + performed; the value of nptr is stored in the object pointed to by endptr, provided + that endptr is not a null pointer. +
+ The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted + value, if any. If no conversion could be performed, zero is returned. If the correct value + is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, + LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type + sign of the value, if any), and the value of the macro ERANGE is stored in errno. + +
+
+ #include <wchar.h> + wchar_t *wcscpy(wchar_t * restrict s1, + const wchar_t * restrict s2); ++
+ The wcscpy function copies the wide string pointed to by s2 (including the terminating + null wide character) into the array pointed to by s1. +
+ The wcscpy function returns the value of s1. + + +
+
+ #include <wchar.h> + wchar_t *wcsncpy(wchar_t * restrict s1, + const wchar_t * restrict s2, + size_t n); ++
+ The wcsncpy function copies not more than n wide characters (those that follow a null + wide character are not copied) from the array pointed to by s2 to the array pointed to by + s1.333) +
+ If the array pointed to by s2 is a wide string that is shorter than n wide characters, null + wide characters are appended to the copy in the array pointed to by s1, until n wide + characters in all have been written. +
+ The wcsncpy function returns the value of s1. + +
333) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the + result will not be null-terminated. + + +
+
+ #include <wchar.h> + wchar_t *wmemcpy(wchar_t * restrict s1, + const wchar_t * restrict s2, + size_t n); ++
+ The wmemcpy function copies n wide characters from the object pointed to by s2 to the + object pointed to by s1. +
+ The wmemcpy function returns the value of s1. + + + + + + +
+
+ #include <wchar.h> + wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, + size_t n); ++
+ The wmemmove function copies n wide characters from the object pointed to by s2 to + the object pointed to by s1. Copying takes place as if the n wide characters from the + object pointed to by s2 are first copied into a temporary array of n wide characters that + does not overlap the objects pointed to by s1 or s2, and then the n wide characters from + the temporary array are copied into the object pointed to by s1. +
+ The wmemmove function returns the value of s1. + +
+
+ #include <wchar.h> + wchar_t *wcscat(wchar_t * restrict s1, + const wchar_t * restrict s2); ++
+ The wcscat function appends a copy of the wide string pointed to by s2 (including the + terminating null wide character) to the end of the wide string pointed to by s1. The initial + wide character of s2 overwrites the null wide character at the end of s1. +
+ The wcscat function returns the value of s1. + +
+
+ #include <wchar.h> + wchar_t *wcsncat(wchar_t * restrict s1, + const wchar_t * restrict s2, + size_t n); ++
+ The wcsncat function appends not more than n wide characters (a null wide character + and those that follow it are not appended) from the array pointed to by s2 to the end of + + the wide string pointed to by s1. The initial wide character of s2 overwrites the null + wide character at the end of s1. A terminating null wide character is always appended to + the result.334) +
+ The wcsncat function returns the value of s1. + +
334) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is + wcslen(s1)+n+1. + + +
+ Unless explicitly stated otherwise, the functions described in this subclause order two + wide characters the same way as two integers of the underlying integer type designated + by wchar_t. + +
+
+ #include <wchar.h> + int wcscmp(const wchar_t *s1, const wchar_t *s2); ++
+ The wcscmp function compares the wide string pointed to by s1 to the wide string + pointed to by s2. +
+ The wcscmp function returns an integer greater than, equal to, or less than zero, + accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the + wide string pointed to by s2. + +
+
+ #include <wchar.h> + int wcscoll(const wchar_t *s1, const wchar_t *s2); ++
+ The wcscoll function compares the wide string pointed to by s1 to the wide string + pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the + current locale. +
+ The wcscoll function returns an integer greater than, equal to, or less than zero, + accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the + + + + wide string pointed to by s2 when both are interpreted as appropriate to the current + locale. + +
+
+ #include <wchar.h> + int wcsncmp(const wchar_t *s1, const wchar_t *s2, + size_t n); ++
+ The wcsncmp function compares not more than n wide characters (those that follow a + null wide character are not compared) from the array pointed to by s1 to the array + pointed to by s2. +
+ The wcsncmp function returns an integer greater than, equal to, or less than zero, + accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal + to, or less than the possibly null-terminated array pointed to by s2. + +
+
+ #include <wchar.h> + size_t wcsxfrm(wchar_t * restrict s1, + const wchar_t * restrict s2, + size_t n); ++
+ The wcsxfrm function transforms the wide string pointed to by s2 and places the + resulting wide string into the array pointed to by s1. The transformation is such that if + the wcscmp function is applied to two transformed wide strings, it returns a value greater + than, equal to, or less than zero, corresponding to the result of the wcscoll function + applied to the same two original wide strings. No more than n wide characters are placed + into the resulting array pointed to by s1, including the terminating null wide character. If + n is zero, s1 is permitted to be a null pointer. +
+ The wcsxfrm function returns the length of the transformed wide string (not including + the terminating null wide character). If the value returned is n or greater, the contents of + the array pointed to by s1 are indeterminate. +
+ EXAMPLE The value of the following expression is the length of the array needed to hold the + transformation of the wide string pointed to by s: + +
+ 1 + wcsxfrm(NULL, s, 0) ++ + +
+
+ #include <wchar.h> int wmemcmp(const wchar_t *s1, const wchar_t *s2, size_t n); ++
+ The wmemcmp function compares the first n wide characters of the object pointed to by + s1 to the first n wide characters of the object pointed to by s2. +
+ The wmemcmp function returns an integer greater than, equal to, or less than zero, + accordingly as the object pointed to by s1 is greater than, equal to, or less than the object + pointed to by s2. + +
+
+ #include <wchar.h> wchar_t *wcschr(const wchar_t *s, wchar_t c); ++
+ The wcschr function locates the first occurrence of c in the wide string pointed to by s. + The terminating null wide character is considered to be part of the wide string. +
+ The wcschr function returns a pointer to the located wide character, or a null pointer if + the wide character does not occur in the wide string. + +
+
+ #include <wchar.h> size_t wcscspn(const wchar_t *s1, const wchar_t *s2); - wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2); - wchar_t *wcsrchr(const wchar_t *s, wchar_t c); - size_t wcsspn(const wchar_t *s1, const wchar_t *s2); ++
+ The wcscspn function computes the length of the maximum initial segment of the wide + string pointed to by s1 which consists entirely of wide characters not from the wide + string pointed to by s2. + +
+ The wcscspn function returns the length of the segment. + +
+
+ #include <wchar.h> + wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2); ++
+ The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of + any wide character from the wide string pointed to by s2. +
+ The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if + no wide character from s2 occurs in s1. + +
+
+ #include <wchar.h> + wchar_t *wcsrchr(const wchar_t *s, wchar_t c); ++
+ The wcsrchr function locates the last occurrence of c in the wide string pointed to by + s. The terminating null wide character is considered to be part of the wide string. +
+ The wcsrchr function returns a pointer to the wide character, or a null pointer if c does + not occur in the wide string. + +
+
+ #include <wchar.h> + size_t wcsspn(const wchar_t *s1, const wchar_t *s2); ++
+ The wcsspn function computes the length of the maximum initial segment of the wide + string pointed to by s1 which consists entirely of wide characters from the wide string + pointed to by s2. +
+ The wcsspn function returns the length of the segment. + + +
+
+ #include <wchar.h> wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2); ++
+ The wcsstr function locates the first occurrence in the wide string pointed to by s1 of + the sequence of wide characters (excluding the terminating null wide character) in the + wide string pointed to by s2. +
+ The wcsstr function returns a pointer to the located wide string, or a null pointer if the + wide string is not found. If s2 points to a wide string with zero length, the function + returns s1. + +
+
+ #include <wchar.h> wchar_t *wcstok(wchar_t * restrict s1, const wchar_t * restrict s2, wchar_t ** restrict ptr); - wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n); ++
+ A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into + a sequence of tokens, each of which is delimited by a wide character from the wide string + pointed to by s2. The third argument points to a caller-provided wchar_t pointer into + which the wcstok function stores information necessary for it to continue scanning the + same wide string. +
+ The first call in a sequence has a non-null first argument and stores an initial value in the + object pointed to by ptr. Subsequent calls in the sequence have a null first argument and + the object pointed to by ptr is required to have the value stored by the previous call in + the sequence, which is then updated. The separator wide string pointed to by s2 may be + different from call to call. +
+ The first call in the sequence searches the wide string pointed to by s1 for the first wide + character that is not contained in the current separator wide string pointed to by s2. If no + such wide character is found, then there are no tokens in the wide string pointed to by s1 + and the wcstok function returns a null pointer. If such a wide character is found, it is + the start of the first token. +
+ The wcstok function then searches from there for a wide character that is contained in + the current separator wide string. If no such wide character is found, the current token + + extends to the end of the wide string pointed to by s1, and subsequent searches in the + same wide string for a token return a null pointer. If such a wide character is found, it is + overwritten by a null wide character, which terminates the current token. +
+ In all cases, the wcstok function stores sufficient information in the pointer pointed to + by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer + value for ptr, shall start searching just past the element overwritten by a null wide + character (if any). +
+ The wcstok function returns a pointer to the first wide character of a token, or a null + pointer if there is no token. +
+ EXAMPLE +
+ #include <wchar.h> + static wchar_t str1[] = L"?a???b,,,#c"; + static wchar_t str2[] = L"\t \t"; + wchar_t *t, *ptr1, *ptr2; + t = wcstok(str1, L"?", &ptr1); // t points to the token L"a" + t = wcstok(NULL, L",", &ptr1); // t points to the token L"??b" + t = wcstok(str2, L" \t", &ptr2); // t is a null pointer + t = wcstok(NULL, L"#,", &ptr1); // t points to the token L"c" + t = wcstok(NULL, L"?", &ptr1); // t is a null pointer ++ + +
+
+ #include <wchar.h> + wchar_t *wmemchr(const wchar_t *s, wchar_t c, + size_t n); ++
+ The wmemchr function locates the first occurrence of c in the initial n wide characters of + the object pointed to by s. +
+ The wmemchr function returns a pointer to the located wide character, or a null pointer if + the wide character does not occur in the object. + + +
+
+ #include <wchar.h> size_t wcslen(const wchar_t *s); ++
+ The wcslen function computes the length of the wide string pointed to by s. +
+ The wcslen function returns the number of wide characters that precede the terminating + null wide character. + +
+
+ #include <wchar.h> wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n); - size_t wcsftime(wchar_t * restrict s, size_t maxsize, ++
+ The wmemset function copies the value of c into each of the first n wide characters of + the object pointed to by s. +
+ The wmemset function returns the value of s. + +
+
+ #include <time.h> + #include <wchar.h> + size_t wcsftime(wchar_t * restrict s, + size_t maxsize, const wchar_t * restrict format, const struct tm * restrict timeptr); ++
+ The wcsftime function is equivalent to the strftime function, except that: +
+ If the total number of resulting wide characters including the terminating null wide + character is not more than maxsize, the wcsftime function returns the number of + wide characters placed into the array pointed to by s not including the terminating null + wide character. Otherwise, zero is returned and the contents of the array are + indeterminate. + +
+ The header <wchar.h> declares an extended set of functions useful for conversion + between multibyte characters and wide characters. +
+ Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and + 7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used + to describe the current conversion state from a particular multibyte character sequence to + a wide character sequence (or the reverse) under the rules of a particular setting for the + LC_CTYPE category of the current locale. +
+ The initial conversion state corresponds, for a conversion in either direction, to the + beginning of a new multibyte character in the initial shift state. A zero-valued + mbstate_t object is (at least) one way to describe an initial conversion state. A zero- + valued mbstate_t object can be used to initiate conversion involving any multibyte + character sequence, in any LC_CTYPE category setting. If an mbstate_t object has + been altered by any of the functions described in this subclause, and is then used with a + different multibyte character sequence, or in the other conversion direction, or with a + different LC_CTYPE category setting than on earlier function calls, the behavior is + undefined.335) +
+ On entry, each function takes the described conversion state (either internal or pointed to + by an argument) as current. The conversion state described by the referenced object is + altered as needed to track the shift state, and the position within a multibyte character, for + the associated multibyte character sequence. + + + + + + +
335) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and + mbsrtowcs functions as long as they are used to step sequentially through the same multibyte + character string. + + +
+
+ #include <wchar.h> * wint_t btowc(int c); ++
+ The btowc function determines whether c constitutes a valid single-byte character in the + initial shift state. +
+ The btowc function returns WEOF if c has the value EOF or if (unsigned char)c + does not constitute a valid single-byte character in the initial shift state. Otherwise, it + returns the wide character representation of that character. + +
+
+ #include <wchar.h> * int wctob(wint_t c); ++
+ The wctob function determines whether c corresponds to a member of the extended + character set whose multibyte character representation is a single byte when in the initial + shift state. +
+ The wctob function returns EOF if c does not correspond to a multibyte character with + length one in the initial shift state. Otherwise, it returns the single-byte representation of + that character as an unsigned char converted to an int. + +
+
+ #include <wchar.h> int mbsinit(const mbstate_t *ps); - size_t mbrlen(const char * restrict s, size_t n, - mbstate_t * restrict ps); - size_t mbrtowc(wchar_t * restrict pwc, - const char * restrict s, size_t n, - mbstate_t * restrict ps); ++
+ If ps is not a null pointer, the mbsinit function determines whether the referenced + mbstate_t object describes an initial conversion state. + +
+ The mbsinit function returns nonzero if ps is a null pointer or if the referenced object + describes an initial conversion state; otherwise, it returns zero. + +
+ These functions differ from the corresponding multibyte character functions of 7.22.7 + (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type + pointer to mbstate_t that points to an object that can completely describe the current + conversion state of the associated multibyte character sequence. If ps is a null pointer, + each function uses its own internal mbstate_t object instead, which is initialized at + program startup to the initial conversion state; the functions are not required to avoid data + races in this case. The implementation behaves as if no library function calls these + functions with a null pointer for ps. +
+ Also unlike their corresponding functions, the return value does not represent whether the + encoding is state-dependent. + +
+
+ #include <wchar.h> + size_t mbrlen(const char * restrict s, + size_t n, + mbstate_t * restrict ps); ++
+ The mbrlen function is equivalent to the call: +
+ mbrtowc(NULL, s, n, ps != NULL ? ps : &internal) ++ where internal is the mbstate_t object for the mbrlen function, except that the + expression designated by ps is evaluated only once. +
+ The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2), + or (size_t)(-1). +
Forward references: the mbrtowc function (7.28.6.3.2). + + +
+
+ #include <wchar.h> + size_t mbrtowc(wchar_t * restrict pwc, + const char * restrict s, + size_t n, + mbstate_t * restrict ps); ++
+ If s is a null pointer, the mbrtowc function is equivalent to the call: +
+ mbrtowc(NULL, "", 1, ps) ++ In this case, the values of the parameters pwc and n are ignored. +
+ If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with + the byte pointed to by s to determine the number of bytes needed to complete the next + multibyte character (including any shift sequences). If the function determines that the + next multibyte character is complete and valid, it determines the value of the + corresponding wide character and then, if pwc is not a null pointer, stores that value in + the object pointed to by pwc. If the corresponding wide character is the null wide + character, the resulting state described is the initial conversion state. +
+ The mbrtowc function returns the first of the following that applies (given the current + conversion state): + 0 if the next n or fewer bytes complete the multibyte character that +
+ corresponds to the null wide character (which is the value stored). ++ between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte +
+ character (which is the value stored); the value returned is the number + of bytes that complete the multibyte character. ++ (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid) +
+ multibyte character, and all n bytes have been processed (no value is + stored).336) ++ (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes +
+ do not contribute to a complete and valid multibyte character (no + value is stored); the value of the macro EILSEQ is stored in errno, + and the conversion state is unspecified. ++ + + +
336) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a + sequence of redundant shift sequences (for implementations with state-dependent encodings). + + +
+
+ #include <wchar.h> + size_t wcrtomb(char * restrict s, + wchar_t wc, + mbstate_t * restrict ps); ++
+ If s is a null pointer, the wcrtomb function is equivalent to the call +
+ wcrtomb(buf, L'\0', ps) ++ where buf is an internal buffer. +
+ If s is not a null pointer, the wcrtomb function determines the number of bytes needed + to represent the multibyte character that corresponds to the wide character given by wc + (including any shift sequences), and stores the multibyte character representation in the + array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If + wc is a null wide character, a null byte is stored, preceded by any shift sequence needed + to restore the initial shift state; the resulting state described is the initial conversion state. +
+ The wcrtomb function returns the number of bytes stored in the array object (including + any shift sequences). When wc is not a valid wide character, an encoding error occurs: + the function stores the value of the macro EILSEQ in errno and returns + (size_t)(-1); the conversion state is unspecified. + +
+ These functions differ from the corresponding multibyte string functions of 7.22.8 + (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to + mbstate_t that points to an object that can completely describe the current conversion + state of the associated multibyte character sequence. If ps is a null pointer, each function + uses its own internal mbstate_t object instead, which is initialized at program startup + to the initial conversion state; the functions are not required to avoid data races in this + case. The implementation behaves as if no library function calls these functions with a + null pointer for ps. +
+ Also unlike their corresponding functions, the conversion source parameter, src, has a + pointer-to-pointer type. When the function is storing the results of conversions (that is, + when dst is not a null pointer), the pointer object pointed to by this parameter is updated + to reflect the amount of the source processed by that invocation. + + +
+
+ #include <wchar.h> + size_t mbsrtowcs(wchar_t * restrict dst, + const char ** restrict src, + size_t len, + mbstate_t * restrict ps); ++
+ The mbsrtowcs function converts a sequence of multibyte characters that begins in the + conversion state described by the object pointed to by ps, from the array indirectly + pointed to by src into a sequence of corresponding wide characters. If dst is not a null + pointer, the converted characters are stored into the array pointed to by dst. Conversion + continues up to and including a terminating null character, which is also stored. + Conversion stops earlier in two cases: when a sequence of bytes is encountered that does + not form a valid multibyte character, or (if dst is not a null pointer) when len wide + characters have been stored into the array pointed to by dst.337) Each conversion takes + place as if by a call to the mbrtowc function. +
+ If dst is not a null pointer, the pointer object pointed to by src is assigned either a null + pointer (if conversion stopped due to reaching a terminating null character) or the address + just past the last multibyte character converted (if any). If conversion stopped due to + reaching a terminating null character and if dst is not a null pointer, the resulting state + described is the initial conversion state. +
+ If the input conversion encounters a sequence of bytes that do not form a valid multibyte + character, an encoding error occurs: the mbsrtowcs function stores the value of the + macro EILSEQ in errno and returns (size_t)(-1); the conversion state is + unspecified. Otherwise, it returns the number of multibyte characters successfully + converted, not including the terminating null character (if any). + + + + + + +
337) Thus, the value of len is ignored if dst is a null pointer. + + +
+
+ #include <wchar.h> + size_t wcsrtombs(char * restrict dst, + const wchar_t ** restrict src, + size_t len, + mbstate_t * restrict ps); ++
+ The wcsrtombs function converts a sequence of wide characters from the array + indirectly pointed to by src into a sequence of corresponding multibyte characters that + begins in the conversion state described by the object pointed to by ps. If dst is not a + null pointer, the converted characters are then stored into the array pointed to by dst. + Conversion continues up to and including a terminating null wide character, which is also + stored. Conversion stops earlier in two cases: when a wide character is reached that does + not correspond to a valid multibyte character, or (if dst is not a null pointer) when the + next multibyte character would exceed the limit of len total bytes to be stored into the + array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb + function.338) +
+ If dst is not a null pointer, the pointer object pointed to by src is assigned either a null + pointer (if conversion stopped due to reaching a terminating null wide character) or the + address just past the last wide character converted (if any). If conversion stopped due to + reaching a terminating null wide character, the resulting state described is the initial + conversion state. +
+ If conversion stops because a wide character is reached that does not correspond to a + valid multibyte character, an encoding error occurs: the wcsrtombs function stores the + value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion + state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte + character sequence, not including the terminating null character (if any). + + + + + + +
338) If conversion stops because a terminating null wide character has been reached, the bytes stored + include those necessary to reach the initial shift state immediately before the null byte. + + +
+ The header <wctype.h> defines one macro, and declares three data types and many + functions.339) +
+ The types declared are +
+ wint_t ++ described in 7.28.1; +
+ wctrans_t ++ which is a scalar type that can hold values which represent locale-specific character + mappings; and +
+ wctype_t ++ which is a scalar type that can hold values which represent locale-specific character + classifications. +
+ The macro defined is WEOF (described in 7.28.1). +
+ The functions declared are grouped as follows: +
+ For all functions described in this subclause that accept an argument of type wint_t, the + value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If + this argument has any other value, the behavior is undefined. +
+ The behavior of these functions is affected by the LC_CTYPE category of the current + locale. + + + + + + +
339) See ''future library directions'' (7.30.13). + + +
+ The header <wctype.h> declares several functions useful for classifying wide + characters. +
+ The term printing wide character refers to a member of a locale-specific set of wide + characters, each of which occupies at least one printing position on a display device. The + term control wide character refers to a member of a locale-specific set of wide characters + that are not printing wide characters. + +
+ The functions in this subclause return nonzero (true) if and only if the value of the + argument wc conforms to that in the description of the function. +
+ Each of the following functions returns true for each wide character that corresponds (as + if by a call to the wctob function) to a single-byte character for which the corresponding + character classification function from 7.4.1 returns true, except that the iswgraph and + iswpunct functions may differ with respect to wide characters other than L' ' that are + both printing and white-space wide characters.340) +
Forward references: the wctob function (7.28.6.1.2). + +
340) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call + iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true + (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc) + && iswspace(wc) is true, but not both. + + +
+
+ #include <wctype.h> + int iswalnum(wint_t wc); ++
+ The iswalnum function tests for any wide character for which iswalpha or + iswdigit is true. + +
+
+ #include <wctype.h> + int iswalpha(wint_t wc); ++
+ The iswalpha function tests for any wide character for which iswupper or + iswlower is true, or any wide character that is one of a locale-specific set of alphabetic + + + wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace + is true.341) + +
341) The functions iswlower and iswupper test true or false separately for each of these additional + wide characters; all four combinations are possible. + + +
+
+ #include <wctype.h> + int iswblank(wint_t wc); ++
+ The iswblank function tests for any wide character that is a standard blank wide + character or is one of a locale-specific set of wide characters for which iswspace is true + and that is used to separate words within a line of text. The standard blank wide + characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C" + locale, iswblank returns true only for the standard blank characters. + +
+
+ #include <wctype.h> + int iswcntrl(wint_t wc); ++
+ The iswcntrl function tests for any control wide character. + +
+
+ #include <wctype.h> + int iswdigit(wint_t wc); ++
+ The iswdigit function tests for any wide character that corresponds to a decimal-digit + character (as defined in 5.2.1). + +
+
+ #include <wctype.h> + int iswgraph(wint_t wc); ++ + + + + +
+ The iswgraph function tests for any wide character for which iswprint is true and + iswspace is false.342) + +
342) Note that the behavior of the iswgraph and iswpunct functions may differ from their + corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution + characters other than ' '. + + +
+
+ #include <wctype.h> + int iswlower(wint_t wc); ++
+ The iswlower function tests for any wide character that corresponds to a lowercase + letter or is one of a locale-specific set of wide characters for which none of iswcntrl, + iswdigit, iswpunct, or iswspace is true. + +
+
+ #include <wctype.h> + int iswprint(wint_t wc); ++
+ The iswprint function tests for any printing wide character. + +
+
+ #include <wctype.h> + int iswpunct(wint_t wc); ++
+ The iswpunct function tests for any printing wide character that is one of a locale- + specific set of punctuation wide characters for which neither iswspace nor iswalnum + is true.342) + +
+
+ #include <wctype.h> + int iswspace(wint_t wc); ++ + + + +
+ The iswspace function tests for any wide character that corresponds to a locale-specific + set of white-space wide characters for which none of iswalnum, iswgraph, or + iswpunct is true. + +
+
+ #include <wctype.h> + int iswupper(wint_t wc); ++
+ The iswupper function tests for any wide character that corresponds to an uppercase + letter or is one of a locale-specific set of wide characters for which none of iswcntrl, + iswdigit, iswpunct, or iswspace is true. + +
+
+ #include <wctype.h> + int iswxdigit(wint_t wc); ++
+ The iswxdigit function tests for any wide character that corresponds to a + hexadecimal-digit character (as defined in 6.4.4.1). + +
+ The functions wctype and iswctype provide extensible wide character classification + as well as testing equivalent to that performed by the functions described in the previous + subclause (7.29.2.1). + +
+
+ #include <wctype.h> + int iswctype(wint_t wc, wctype_t desc); ++
+ The iswctype function determines whether the wide character wc has the property + described by desc. The current setting of the LC_CTYPE category shall be the same as + during the call to wctype that returned the value desc. +
+ Each of the following expressions has a truth-value equivalent to the call to the wide + character classification function (7.29.2.1) in the comment that follows the expression: + +
+ iswctype(wc, wctype("alnum")) // iswalnum(wc)
+ iswctype(wc, wctype("alpha")) // iswalpha(wc)
+ iswctype(wc, wctype("blank")) // iswblank(wc)
+ iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
+ iswctype(wc, wctype("digit")) // iswdigit(wc)
+ iswctype(wc, wctype("graph")) // iswgraph(wc)
+ iswctype(wc, wctype("lower")) // iswlower(wc)
+ iswctype(wc, wctype("print")) // iswprint(wc)
+ iswctype(wc, wctype("punct")) // iswpunct(wc)
+ iswctype(wc, wctype("space")) // iswspace(wc)
+ iswctype(wc, wctype("upper")) // iswupper(wc)
+ iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
+
++ The iswctype function returns nonzero (true) if and only if the value of the wide + character wc has the property described by desc. If desc is zero, the iswctype + function returns zero (false). +
Forward references: the wctype function (7.29.2.2.2). + +
+
+ #include <wctype.h> + wctype_t wctype(const char *property); ++
+ The wctype function constructs a value with type wctype_t that describes a class of + wide characters identified by the string argument property. +
+ The strings listed in the description of the iswctype function shall be valid in all + locales as property arguments to the wctype function. +
+ If property identifies a valid class of wide characters according to the LC_CTYPE + category of the current locale, the wctype function returns a nonzero value that is valid + as the second argument to the iswctype function; otherwise, it returns zero. + + +
+ The header <wctype.h> declares several functions useful for mapping wide characters. + +
+
+ #include <wctype.h> + wint_t towlower(wint_t wc); ++
+ The towlower function converts an uppercase letter to a corresponding lowercase letter. +
+ If the argument is a wide character for which iswupper is true and there are one or + more corresponding wide characters, as specified by the current locale, for which + iswlower is true, the towlower function returns one of the corresponding wide + characters (always the same one for any given locale); otherwise, the argument is + returned unchanged. + +
+
+ #include <wctype.h> + wint_t towupper(wint_t wc); ++
+ The towupper function converts a lowercase letter to a corresponding uppercase letter. +
+ If the argument is a wide character for which iswlower is true and there are one or + more corresponding wide characters, as specified by the current locale, for which + iswupper is true, the towupper function returns one of the corresponding wide + characters (always the same one for any given locale); otherwise, the argument is + returned unchanged. + +
+ The functions wctrans and towctrans provide extensible wide character mapping as + well as case mapping equivalent to that performed by the functions described in the + previous subclause (7.29.3.1). + + +
+
+ #include <wctype.h> + wint_t towctrans(wint_t wc, wctrans_t desc); ++
+ The towctrans function maps the wide character wc using the mapping described by + desc. The current setting of the LC_CTYPE category shall be the same as during the call + to wctrans that returned the value desc. +
+ Each of the following expressions behaves the same as the call to the wide character case + mapping function (7.29.3.1) in the comment that follows the expression: +
+ towctrans(wc, wctrans("tolower")) // towlower(wc)
+ towctrans(wc, wctrans("toupper")) // towupper(wc)
+
++ The towctrans function returns the mapped value of wc using the mapping described + by desc. If desc is zero, the towctrans function returns the value of wc. + +
+
+ #include <wctype.h> + wctrans_t wctrans(const char *property); ++
+ The wctrans function constructs a value with type wctrans_t that describes a + mapping between wide characters identified by the string argument property. +
+ The strings listed in the description of the towctrans function shall be valid in all + locales as property arguments to the wctrans function. +
+ If property identifies a valid mapping of wide characters according to the LC_CTYPE + category of the current locale, the wctrans function returns a nonzero value that is valid + as the second argument to the towctrans function; otherwise, it returns zero. + + +
+ The following names are grouped under individual headers for convenience. All external + names described below are reserved no matter what headers are included by the program. + +
+ The function names +
+ cerf cexpm1 clog2 + cerfc clog10 clgamma + cexp2 clog1p ctgamma ++ and the same names suffixed with f or l may be added to the declarations in the + <complex.h> header. + +
+ Function names that begin with either is or to, and a lowercase letter may be added to + the declarations in the <ctype.h> header. + +
+ Macros that begin with E and a digit or E and an uppercase letter may be added to the + declarations in the <errno.h> header. + +
+ Macro names beginning with PRI or SCN followed by any lowercase letter or X may be + added to the macros defined in the <inttypes.h> header. + +
+ Macros that begin with LC_ and an uppercase letter may be added to the definitions in + the <locale.h> header. + +
+ Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase + letter may be added to the definitions in the <signal.h> header. + +
+ The ability to undefine and perhaps then redefine the macros bool, true, and false is + an obsolescent feature. + +
+ Typedef names beginning with int or uint and ending with _t may be added to the + types defined in the <stdint.h> header. Macro names beginning with INT or UINT + and ending with _MAX, _MIN, or _C may be added to the macros defined in the + <stdint.h> header. + + +
+ Lowercase letters may be added to the conversion specifiers and length modifiers in + fprintf and fscanf. Other characters may be used in extensions. +
+ The use of ungetc on a binary stream where the file position indicator is zero prior to * + the call is an obsolescent feature. + +
+ Function names that begin with str and a lowercase letter may be added to the + declarations in the <stdlib.h> header. + +
+ Function names that begin with str, mem, or wcs and a lowercase letter may be added + to the declarations in the <string.h> header. + +
+ Function names that begin with wcs and a lowercase letter may be added to the + declarations in the <wchar.h> header. +
+ Lowercase letters may be added to the conversion specifiers and length modifiers in + fwprintf and fwscanf. Other characters may be used in extensions. + +
+ Function names that begin with is or to and a lowercase letter may be added to the + declarations in the <wctype.h> header. + + +
+ (informative) + Language syntax summary ++
+ NOTE The notation is described in 6.1. + + +
+ keyword + identifier + constant + string-literal + punctuator ++ (6.4) preprocessing-token: + +
+ header-name + identifier + pp-number + character-constant + string-literal + punctuator + each non-white-space character that cannot be one of the above ++ +
+ alignof goto union + auto if unsigned + break inline void + case int volatile + char long while + const register _Alignas + continue restrict _Atomic + default return _Bool + do short _Complex + double signed _Generic + else sizeof _Imaginary + enum static _Noreturn + extern struct _Static_assert + float switch _Thread_local + for typedef ++ +
+ identifier-nondigit + identifier identifier-nondigit + identifier digit ++ (6.4.2.1) identifier-nondigit: +
+ nondigit + universal-character-name + other implementation-defined characters ++ (6.4.2.1) nondigit: one of +
+ _ a b c d e f g h i j k l m + n o p q r s t u v w x y z + A B C D E F G H I J K L M + N O P Q R S T U V W X Y Z ++ (6.4.2.1) digit: one of + +
+ 0 1 2 3 4 5 6 7 8 9 ++ +
+ \u hex-quad + \U hex-quad hex-quad ++ (6.4.3) hex-quad: +
+ hexadecimal-digit hexadecimal-digit + hexadecimal-digit hexadecimal-digit ++ +
+ integer-constant + floating-constant + enumeration-constant + character-constant ++ (6.4.4.1) integer-constant: +
+ decimal-constant integer-suffixopt + octal-constant integer-suffixopt + hexadecimal-constant integer-suffixopt ++ (6.4.4.1) decimal-constant: +
+ nonzero-digit + decimal-constant digit ++ (6.4.4.1) octal-constant: +
+ 0 + octal-constant octal-digit ++ (6.4.4.1) hexadecimal-constant: +
+ hexadecimal-prefix hexadecimal-digit + hexadecimal-constant hexadecimal-digit ++ (6.4.4.1) hexadecimal-prefix: one of +
+ 0x 0X ++ (6.4.4.1) nonzero-digit: one of +
+ 1 2 3 4 5 6 7 8 9 ++ (6.4.4.1) octal-digit: one of + +
+ 0 1 2 3 4 5 6 7 ++ (6.4.4.1) hexadecimal-digit: one of +
+ 0 1 2 3 4 5 6 7 8 9 + a b c d e f + A B C D E F ++ (6.4.4.1) integer-suffix: +
+ unsigned-suffix long-suffixopt + unsigned-suffix long-long-suffix + long-suffix unsigned-suffixopt + long-long-suffix unsigned-suffixopt ++ (6.4.4.1) unsigned-suffix: one of +
+ u U ++ (6.4.4.1) long-suffix: one of +
+ l L ++ (6.4.4.1) long-long-suffix: one of +
+ ll LL ++ (6.4.4.2) floating-constant: +
+ decimal-floating-constant + hexadecimal-floating-constant ++ (6.4.4.2) decimal-floating-constant: +
+ fractional-constant exponent-partopt floating-suffixopt + digit-sequence exponent-part floating-suffixopt ++ (6.4.4.2) hexadecimal-floating-constant: +
+ hexadecimal-prefix hexadecimal-fractional-constant + binary-exponent-part floating-suffixopt + hexadecimal-prefix hexadecimal-digit-sequence + binary-exponent-part floating-suffixopt ++ (6.4.4.2) fractional-constant: +
+ digit-sequenceopt . digit-sequence + digit-sequence . ++ (6.4.4.2) exponent-part: +
+ e signopt digit-sequence + E signopt digit-sequence ++ (6.4.4.2) sign: one of + +
+ + - ++ (6.4.4.2) digit-sequence: +
+ digit + digit-sequence digit ++ (6.4.4.2) hexadecimal-fractional-constant: +
+ hexadecimal-digit-sequenceopt . + hexadecimal-digit-sequence + hexadecimal-digit-sequence . ++ (6.4.4.2) binary-exponent-part: +
+ p signopt digit-sequence + P signopt digit-sequence ++ (6.4.4.2) hexadecimal-digit-sequence: +
+ hexadecimal-digit + hexadecimal-digit-sequence hexadecimal-digit ++ (6.4.4.2) floating-suffix: one of +
+ f l F L ++ (6.4.4.3) enumeration-constant: +
+ identifier ++ (6.4.4.4) character-constant: +
+ ' c-char-sequence ' + L' c-char-sequence ' + u' c-char-sequence ' + U' c-char-sequence ' ++ (6.4.4.4) c-char-sequence: +
+ c-char + c-char-sequence c-char ++ (6.4.4.4) c-char: +
+ any member of the source character set except + the single-quote ', backslash \, or new-line character + escape-sequence ++ (6.4.4.4) escape-sequence: + +
+ simple-escape-sequence + octal-escape-sequence + hexadecimal-escape-sequence + universal-character-name ++ (6.4.4.4) simple-escape-sequence: one of +
+ \' \" \? \\ + \a \b \f \n \r \t \v ++ (6.4.4.4) octal-escape-sequence: +
+ \ octal-digit + \ octal-digit octal-digit + \ octal-digit octal-digit octal-digit ++ (6.4.4.4) hexadecimal-escape-sequence: +
+ \x hexadecimal-digit + hexadecimal-escape-sequence hexadecimal-digit ++ +
+ encoding-prefixopt " s-char-sequenceopt " ++ (6.4.5) encoding-prefix: +
+ u8 + u + U + L ++ (6.4.5) s-char-sequence: +
+ s-char + s-char-sequence s-char ++ (6.4.5) s-char: +
+ any member of the source character set except + the double-quote ", backslash \, or new-line character + escape-sequence ++ +
+ [ ] ( ) { } . ->
+ ++ -- & * + - ~ !
+ / % << >> < > <= >= == != ^ | && ||
+ ? : ; ...
+ = *= /= %= += -= <<= >>= &= ^= |=
+ , # ##
+ <: :> <% %> %: %:%:
+
+
++ < h-char-sequence > + " q-char-sequence " ++ (6.4.7) h-char-sequence: +
+ h-char + h-char-sequence h-char ++ (6.4.7) h-char: +
+ any member of the source character set except + the new-line character and > ++ (6.4.7) q-char-sequence: +
+ q-char + q-char-sequence q-char ++ (6.4.7) q-char: +
+ any member of the source character set except + the new-line character and " ++
+ digit + . digit + pp-number digit + pp-number identifier-nondigit + pp-number e sign + pp-number E sign + pp-number p sign + pp-number P sign + pp-number . ++ +
+ identifier + constant + string-literal + ( expression ) + generic-selection ++ (6.5.1.1) generic-selection: +
+ _Generic ( assignment-expression , generic-assoc-list ) ++ (6.5.1.1) generic-assoc-list: +
+ generic-association + generic-assoc-list , generic-association ++ (6.5.1.1) generic-association: +
+ type-name : assignment-expression + default : assignment-expression ++ (6.5.2) postfix-expression: +
+ primary-expression
+ postfix-expression [ expression ]
+ postfix-expression ( argument-expression-listopt )
+ postfix-expression . identifier
+ postfix-expression -> identifier
+ postfix-expression ++
+ postfix-expression --
+ ( type-name ) { initializer-list }
+ ( type-name ) { initializer-list , }
+
+ (6.5.2) argument-expression-list:
++ assignment-expression + argument-expression-list , assignment-expression ++ (6.5.3) unary-expression: + +
+ postfix-expression + ++ unary-expression + -- unary-expression + unary-operator cast-expression + sizeof unary-expression + sizeof ( type-name ) + alignof ( type-name ) ++ (6.5.3) unary-operator: one of +
+ & * + - ~ ! ++ (6.5.4) cast-expression: +
+ unary-expression + ( type-name ) cast-expression ++ (6.5.5) multiplicative-expression: +
+ cast-expression + multiplicative-expression * cast-expression + multiplicative-expression / cast-expression + multiplicative-expression % cast-expression ++ (6.5.6) additive-expression: +
+ multiplicative-expression + additive-expression + multiplicative-expression + additive-expression - multiplicative-expression ++ (6.5.7) shift-expression: +
+ additive-expression + shift-expression << additive-expression + shift-expression >> additive-expression ++ (6.5.8) relational-expression: +
+ shift-expression + relational-expression < shift-expression + relational-expression > shift-expression + relational-expression <= shift-expression + relational-expression >= shift-expression ++ (6.5.9) equality-expression: +
+ relational-expression + equality-expression == relational-expression + equality-expression != relational-expression ++ (6.5.10) AND-expression: +
+ equality-expression + AND-expression & equality-expression ++ (6.5.11) exclusive-OR-expression: + +
+ AND-expression + exclusive-OR-expression ^ AND-expression ++ (6.5.12) inclusive-OR-expression: +
+ exclusive-OR-expression + inclusive-OR-expression | exclusive-OR-expression ++ (6.5.13) logical-AND-expression: +
+ inclusive-OR-expression + logical-AND-expression && inclusive-OR-expression ++ (6.5.14) logical-OR-expression: +
+ logical-AND-expression + logical-OR-expression || logical-AND-expression ++ (6.5.15) conditional-expression: +
+ logical-OR-expression + logical-OR-expression ? expression : conditional-expression ++ (6.5.16) assignment-expression: +
+ conditional-expression + unary-expression assignment-operator assignment-expression ++ (6.5.16) assignment-operator: one of +
+ = *= /= %= += -= <<= >>= &= ^= |= ++ (6.5.17) expression: +
+ assignment-expression + expression , assignment-expression ++ (6.6) constant-expression: +
+ conditional-expression ++ +
+ declaration-specifiers init-declarator-listopt ; + static_assert-declaration ++ (6.7) declaration-specifiers: +
+ storage-class-specifier declaration-specifiersopt + type-specifier declaration-specifiersopt + type-qualifier declaration-specifiersopt + function-specifier declaration-specifiersopt + alignment-specifier declaration-specifiersopt ++ (6.7) init-declarator-list: + +
+ init-declarator + init-declarator-list , init-declarator ++ (6.7) init-declarator: +
+ declarator + declarator = initializer ++ (6.7.1) storage-class-specifier: +
+ typedef + extern + static + _Thread_local + auto + register ++ (6.7.2) type-specifier: +
+ void + char + short + int + long + float + double + signed + unsigned + _Bool + _Complex + atomic-type-specifier + struct-or-union-specifier + enum-specifier + typedef-name ++ (6.7.2.1) struct-or-union-specifier: +
+ struct-or-union identifieropt { struct-declaration-list }
+ struct-or-union identifier
+
+ (6.7.2.1) struct-or-union:
++ struct + union ++ (6.7.2.1) struct-declaration-list: +
+ struct-declaration + struct-declaration-list struct-declaration ++ (6.7.2.1) struct-declaration: + +
+ specifier-qualifier-list struct-declarator-listopt ; + static_assert-declaration ++ (6.7.2.1) specifier-qualifier-list: +
+ type-specifier specifier-qualifier-listopt + type-qualifier specifier-qualifier-listopt ++ (6.7.2.1) struct-declarator-list: +
+ struct-declarator + struct-declarator-list , struct-declarator ++ (6.7.2.1) struct-declarator: +
+ declarator + declaratoropt : constant-expression ++ (6.7.2.2) enum-specifier: +
+ enum identifieropt { enumerator-list }
+ enum identifieropt { enumerator-list , }
+ enum identifier
+
+ (6.7.2.2) enumerator-list:
++ enumerator + enumerator-list , enumerator ++ (6.7.2.2) enumerator: +
+ enumeration-constant + enumeration-constant = constant-expression ++ (6.7.2.4) atomic-type-specifier: +
+ _Atomic ( type-name ) ++ (6.7.3) type-qualifier: +
+ const + restrict + volatile + _Atomic ++ (6.7.4) function-specifier: +
+ inline + _Noreturn ++ (6.7.5) alignment-specifier: +
+ _Alignas ( type-name ) + _Alignas ( constant-expression ) ++ (6.7.6) declarator: + +
+ pointeropt direct-declarator ++ (6.7.6) direct-declarator: +
+ identifier + ( declarator ) + direct-declarator [ type-qualifier-listopt assignment-expressionopt ] + direct-declarator [ static type-qualifier-listopt assignment-expression ] + direct-declarator [ type-qualifier-list static assignment-expression ] + direct-declarator [ type-qualifier-listopt * ] + direct-declarator ( parameter-type-list ) + direct-declarator ( identifier-listopt ) ++ (6.7.6) pointer: +
+ * type-qualifier-listopt + * type-qualifier-listopt pointer ++ (6.7.6) type-qualifier-list: +
+ type-qualifier + type-qualifier-list type-qualifier ++ (6.7.6) parameter-type-list: +
+ parameter-list + parameter-list , ... ++ (6.7.6) parameter-list: +
+ parameter-declaration + parameter-list , parameter-declaration ++ (6.7.6) parameter-declaration: +
+ declaration-specifiers declarator + declaration-specifiers abstract-declaratoropt ++ (6.7.6) identifier-list: +
+ identifier + identifier-list , identifier ++ (6.7.7) type-name: +
+ specifier-qualifier-list abstract-declaratoropt ++ (6.7.7) abstract-declarator: + +
+ pointer + pointeropt direct-abstract-declarator ++ (6.7.7) direct-abstract-declarator: +
+ ( abstract-declarator ) + direct-abstract-declaratoropt [ type-qualifier-listopt + assignment-expressionopt ] + direct-abstract-declaratoropt [ static type-qualifier-listopt + assignment-expression ] + direct-abstract-declaratoropt [ type-qualifier-list static + assignment-expression ] + direct-abstract-declaratoropt [ * ] + direct-abstract-declaratoropt ( parameter-type-listopt ) ++ (6.7.8) typedef-name: +
+ identifier ++ (6.7.9) initializer: +
+ assignment-expression
+ { initializer-list }
+ { initializer-list , }
+
+ (6.7.9) initializer-list:
++ designationopt initializer + initializer-list , designationopt initializer ++ (6.7.9) designation: +
+ designator-list = ++ (6.7.9) designator-list: +
+ designator + designator-list designator ++ (6.7.9) designator: +
+ [ constant-expression ] + . identifier ++ (6.7.10) static_assert-declaration: + +
+ _Static_assert ( constant-expression , string-literal ) ; ++ +
+ labeled-statement + compound-statement + expression-statement + selection-statement + iteration-statement + jump-statement ++ (6.8.1) labeled-statement: +
+ identifier : statement + case constant-expression : statement + default : statement ++ (6.8.2) compound-statement: +
+ { block-item-listopt }
+
+ (6.8.2) block-item-list:
++ block-item + block-item-list block-item ++ (6.8.2) block-item: +
+ declaration + statement ++ (6.8.3) expression-statement: +
+ expressionopt ; ++ (6.8.4) selection-statement: +
+ if ( expression ) statement + if ( expression ) statement else statement + switch ( expression ) statement ++ (6.8.5) iteration-statement: +
+ while ( expression ) statement + do statement while ( expression ) ; + for ( expressionopt ; expressionopt ; expressionopt ) statement + for ( declaration expressionopt ; expressionopt ) statement ++ (6.8.6) jump-statement: + +
+ goto identifier ; + continue ; + break ; + return expressionopt ; ++ +
+ external-declaration + translation-unit external-declaration ++ (6.9) external-declaration: +
+ function-definition + declaration ++ (6.9.1) function-definition: +
+ declaration-specifiers declarator declaration-listopt compound-statement ++ (6.9.1) declaration-list: +
+ declaration + declaration-list declaration ++ +
+ groupopt ++ (6.10) group: +
+ group-part + group group-part ++ (6.10) group-part: +
+ if-section + control-line + text-line + # non-directive ++ (6.10) if-section: +
+ if-group elif-groupsopt else-groupopt endif-line ++ (6.10) if-group: +
+ # if constant-expression new-line groupopt + # ifdef identifier new-line groupopt + # ifndef identifier new-line groupopt ++ (6.10) elif-groups: +
+ elif-group + elif-groups elif-group ++ (6.10) elif-group: + +
+ # elif constant-expression new-line groupopt ++ (6.10) else-group: +
+ # else new-line groupopt ++ (6.10) endif-line: +
+ # endif new-line ++ (6.10) control-line: +
+ # include pp-tokens new-line + # define identifier replacement-list new-line + # define identifier lparen identifier-listopt ) + replacement-list new-line + # define identifier lparen ... ) replacement-list new-line + # define identifier lparen identifier-list , ... ) + replacement-list new-line + # undef identifier new-line + # line pp-tokens new-line + # error pp-tokensopt new-line + # pragma pp-tokensopt new-line + # new-line ++ (6.10) text-line: +
+ pp-tokensopt new-line ++ (6.10) non-directive: +
+ pp-tokens new-line ++ (6.10) lparen: +
+ a ( character not immediately preceded by white-space ++ (6.10) replacement-list: +
+ pp-tokensopt ++ (6.10) pp-tokens: +
+ preprocessing-token + pp-tokens preprocessing-token ++ (6.10) new-line: + +
+ the new-line character ++ +
+ (informative) + Library summary ++ +
+ NDEBUG + static_assert + void assert(scalar expression); ++ +
+ __STDC_NO_COMPLEX__ imaginary + complex _Imaginary_I + _Complex_I I + #pragma STDC CX_LIMITED_RANGE on-off-switch + double complex cacos(double complex z); + float complex cacosf(float complex z); + long double complex cacosl(long double complex z); + double complex casin(double complex z); + float complex casinf(float complex z); + long double complex casinl(long double complex z); + double complex catan(double complex z); + float complex catanf(float complex z); + long double complex catanl(long double complex z); + double complex ccos(double complex z); + float complex ccosf(float complex z); + long double complex ccosl(long double complex z); + double complex csin(double complex z); + float complex csinf(float complex z); + long double complex csinl(long double complex z); + double complex ctan(double complex z); + float complex ctanf(float complex z); + long double complex ctanl(long double complex z); + double complex cacosh(double complex z); + float complex cacoshf(float complex z); + long double complex cacoshl(long double complex z); + double complex casinh(double complex z); + float complex casinhf(float complex z); + long double complex casinhl(long double complex z); + double complex catanh(double complex z); + float complex catanhf(float complex z); + long double complex catanhl(long double complex z); + double complex ccosh(double complex z); + float complex ccoshf(float complex z); + long double complex ccoshl(long double complex z); + double complex csinh(double complex z); + float complex csinhf(float complex z); + long double complex csinhl(long double complex z); + double complex ctanh(double complex z); + float complex ctanhf(float complex z); + long double complex ctanhl(long double complex z); + double complex cexp(double complex z); + float complex cexpf(float complex z); + long double complex cexpl(long double complex z); + double complex clog(double complex z); + float complex clogf(float complex z); + long double complex clogl(long double complex z); + double cabs(double complex z); + float cabsf(float complex z); + long double cabsl(long double complex z); + double complex cpow(double complex x, double complex y); + float complex cpowf(float complex x, float complex y); + long double complex cpowl(long double complex x, + long double complex y); + double complex csqrt(double complex z); + float complex csqrtf(float complex z); + long double complex csqrtl(long double complex z); + double carg(double complex z); + float cargf(float complex z); + long double cargl(long double complex z); + double cimag(double complex z); + float cimagf(float complex z); + long double cimagl(long double complex z); + double complex CMPLX(double x, double y); + float complex CMPLXF(float x, float y); + long double complex CMPLXL(long double x, long double y); + double complex conj(double complex z); + float complex conjf(float complex z); + long double complex conjl(long double complex z); + double complex cproj(double complex z); + float complex cprojf(float complex z); + long double complex cprojl(long double complex z); + double creal(double complex z); + float crealf(float complex z); + long double creall(long double complex z); ++ +
+ int isalnum(int c); + int isalpha(int c); + int isblank(int c); + int iscntrl(int c); + int isdigit(int c); + int isgraph(int c); + int islower(int c); + int isprint(int c); + int ispunct(int c); + int isspace(int c); + int isupper(int c); + int isxdigit(int c); + int tolower(int c); + int toupper(int c); ++ +
+ EDOM EILSEQ ERANGE errno + __STDC_WANT_LIB_EXT1__ + errno_t ++ +
+ fenv_t FE_OVERFLOW FE_TOWARDZERO + fexcept_t FE_UNDERFLOW FE_UPWARD + FE_DIVBYZERO FE_ALL_EXCEPT FE_DFL_ENV + FE_INEXACT FE_DOWNWARD + FE_INVALID FE_TONEAREST + #pragma STDC FENV_ACCESS on-off-switch + int feclearexcept(int excepts); + int fegetexceptflag(fexcept_t *flagp, int excepts); + int feraiseexcept(int excepts); + int fesetexceptflag(const fexcept_t *flagp, + int excepts); + int fetestexcept(int excepts); + int fegetround(void); + int fesetround(int round); + int fegetenv(fenv_t *envp); + int feholdexcept(fenv_t *envp); + int fesetenv(const fenv_t *envp); + int feupdateenv(const fenv_t *envp); ++ +
+ FLT_ROUNDS DBL_DIG FLT_MAX + FLT_EVAL_METHOD LDBL_DIG DBL_MAX + FLT_HAS_SUBNORM FLT_MIN_EXP LDBL_MAX + DBL_HAS_SUBNORM DBL_MIN_EXP FLT_EPSILON + LDBL_HAS_SUBNORM LDBL_MIN_EXP DBL_EPSILON + FLT_RADIX FLT_MIN_10_EXP LDBL_EPSILON + FLT_MANT_DIG DBL_MIN_10_EXP FLT_MIN + DBL_MANT_DIG LDBL_MIN_10_EXP DBL_MIN + LDBL_MANT_DIG FLT_MAX_EXP LDBL_MIN + FLT_DECIMAL_DIG DBL_MAX_EXP FLT_TRUE_MIN + DBL_DECIMAL_DIG LDBL_MAX_EXP DBL_TRUE_MIN + LDBL_DECIMAL_DIG FLT_MAX_10_EXP LDBL_TRUE_MIN + DECIMAL_DIG DBL_MAX_10_EXP + FLT_DIG LDBL_MAX_10_EXP ++ +
+ imaxdiv_t + PRIdN PRIdLEASTN PRIdFASTN PRIdMAX PRIdPTR + PRIiN PRIiLEASTN PRIiFASTN PRIiMAX PRIiPTR + PRIoN PRIoLEASTN PRIoFASTN PRIoMAX PRIoPTR + PRIuN PRIuLEASTN PRIuFASTN PRIuMAX PRIuPTR + PRIxN PRIxLEASTN PRIxFASTN PRIxMAX PRIxPTR + PRIXN PRIXLEASTN PRIXFASTN PRIXMAX PRIXPTR + SCNdN SCNdLEASTN SCNdFASTN SCNdMAX SCNdPTR + SCNiN SCNiLEASTN SCNiFASTN SCNiMAX SCNiPTR + SCNoN SCNoLEASTN SCNoFASTN SCNoMAX SCNoPTR + SCNuN SCNuLEASTN SCNuFASTN SCNuMAX SCNuPTR + SCNxN SCNxLEASTN SCNxFASTN SCNxMAX SCNxPTR + intmax_t imaxabs(intmax_t j); + imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); + intmax_t strtoimax(const char * restrict nptr, + char ** restrict endptr, int base); + uintmax_t strtoumax(const char * restrict nptr, + char ** restrict endptr, int base); + intmax_t wcstoimax(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); + uintmax_t wcstoumax(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); ++ +
+ and bitor not_eq xor + and_eq compl or xor_eq + bitand not or_eq ++ +
+ CHAR_BIT CHAR_MAX INT_MIN ULONG_MAX + SCHAR_MIN MB_LEN_MAX INT_MAX LLONG_MIN + SCHAR_MAX SHRT_MIN UINT_MAX LLONG_MAX + UCHAR_MAX SHRT_MAX LONG_MIN ULLONG_MAX + CHAR_MIN USHRT_MAX LONG_MAX ++ +
+ struct lconv LC_ALL LC_CTYPE LC_NUMERIC + NULL LC_COLLATE LC_MONETARY LC_TIME + char *setlocale(int category, const char *locale); + struct lconv *localeconv(void); ++ +
+ float_t FP_INFINITE FP_FAST_FMAL + double_t FP_NAN FP_ILOGB0 + HUGE_VAL FP_NORMAL FP_ILOGBNAN + HUGE_VALF FP_SUBNORMAL MATH_ERRNO + HUGE_VALL FP_ZERO MATH_ERREXCEPT + INFINITY FP_FAST_FMA math_errhandling + NAN FP_FAST_FMAF + #pragma STDC FP_CONTRACT on-off-switch + int fpclassify(real-floating x); + int isfinite(real-floating x); + int isinf(real-floating x); + int isnan(real-floating x); + int isnormal(real-floating x); + int signbit(real-floating x); + double acos(double x); + float acosf(float x); + long double acosl(long double x); + double asin(double x); + float asinf(float x); + long double asinl(long double x); + double atan(double x); + float atanf(float x); + long double atanl(long double x); + double atan2(double y, double x); + float atan2f(float y, float x); + long double atan2l(long double y, long double x); + double cos(double x); + float cosf(float x); + long double cosl(long double x); + double sin(double x); + float sinf(float x); + long double sinl(long double x); + double tan(double x); + float tanf(float x); + long double tanl(long double x); + double acosh(double x); + float acoshf(float x); + long double acoshl(long double x); + double asinh(double x); + float asinhf(float x); + long double asinhl(long double x); + double atanh(double x); + float atanhf(float x); + long double atanhl(long double x); + double cosh(double x); + float coshf(float x); + long double coshl(long double x); + double sinh(double x); + float sinhf(float x); + long double sinhl(long double x); + double tanh(double x); + float tanhf(float x); + long double tanhl(long double x); + double exp(double x); + float expf(float x); + long double expl(long double x); + double exp2(double x); + float exp2f(float x); + long double exp2l(long double x); + double expm1(double x); + float expm1f(float x); + long double expm1l(long double x); + double frexp(double value, int *exp); + float frexpf(float value, int *exp); + long double frexpl(long double value, int *exp); + int ilogb(double x); + int ilogbf(float x); + int ilogbl(long double x); + double ldexp(double x, int exp); + float ldexpf(float x, int exp); + long double ldexpl(long double x, int exp); + double log(double x); + float logf(float x); + long double logl(long double x); + double log10(double x); + float log10f(float x); + long double log10l(long double x); + double log1p(double x); + float log1pf(float x); + long double log1pl(long double x); + double log2(double x); + float log2f(float x); + long double log2l(long double x); + double logb(double x); + float logbf(float x); + long double logbl(long double x); + double modf(double value, double *iptr); + float modff(float value, float *iptr); + long double modfl(long double value, long double *iptr); + double scalbn(double x, int n); + float scalbnf(float x, int n); + long double scalbnl(long double x, int n); + double scalbln(double x, long int n); + float scalblnf(float x, long int n); + long double scalblnl(long double x, long int n); + double cbrt(double x); + float cbrtf(float x); + long double cbrtl(long double x); + double fabs(double x); + float fabsf(float x); + long double fabsl(long double x); + double hypot(double x, double y); + float hypotf(float x, float y); + long double hypotl(long double x, long double y); + double pow(double x, double y); + float powf(float x, float y); + long double powl(long double x, long double y); + double sqrt(double x); + float sqrtf(float x); + long double sqrtl(long double x); + double erf(double x); + float erff(float x); + long double erfl(long double x); + double erfc(double x); + float erfcf(float x); + long double erfcl(long double x); + double lgamma(double x); + float lgammaf(float x); + long double lgammal(long double x); + double tgamma(double x); + float tgammaf(float x); + long double tgammal(long double x); + double ceil(double x); + float ceilf(float x); + long double ceill(long double x); + double floor(double x); + float floorf(float x); + long double floorl(long double x); + double nearbyint(double x); + float nearbyintf(float x); + long double nearbyintl(long double x); + double rint(double x); + float rintf(float x); + long double rintl(long double x); + long int lrint(double x); + long int lrintf(float x); + long int lrintl(long double x); + long long int llrint(double x); + long long int llrintf(float x); + long long int llrintl(long double x); + double round(double x); + float roundf(float x); + long double roundl(long double x); + long int lround(double x); + long int lroundf(float x); + long int lroundl(long double x); + long long int llround(double x); + long long int llroundf(float x); + long long int llroundl(long double x); + double trunc(double x); + float truncf(float x); + long double truncl(long double x); + double fmod(double x, double y); + float fmodf(float x, float y); + long double fmodl(long double x, long double y); + double remainder(double x, double y); + float remainderf(float x, float y); + long double remainderl(long double x, long double y); + double remquo(double x, double y, int *quo); + float remquof(float x, float y, int *quo); + long double remquol(long double x, long double y, + int *quo); + double copysign(double x, double y); + float copysignf(float x, float y); + long double copysignl(long double x, long double y); + double nan(const char *tagp); + float nanf(const char *tagp); + long double nanl(const char *tagp); + double nextafter(double x, double y); + float nextafterf(float x, float y); + long double nextafterl(long double x, long double y); + double nexttoward(double x, long double y); + float nexttowardf(float x, long double y); + long double nexttowardl(long double x, long double y); + double fdim(double x, double y); + float fdimf(float x, float y); + long double fdiml(long double x, long double y); + double fmax(double x, double y); + float fmaxf(float x, float y); + long double fmaxl(long double x, long double y); + double fmin(double x, double y); + float fminf(float x, float y); + long double fminl(long double x, long double y); + double fma(double x, double y, double z); + float fmaf(float x, float y, float z); + long double fmal(long double x, long double y, + long double z); + int isgreater(real-floating x, real-floating y); + int isgreaterequal(real-floating x, real-floating y); + int isless(real-floating x, real-floating y); + int islessequal(real-floating x, real-floating y); + int islessgreater(real-floating x, real-floating y); + int isunordered(real-floating x, real-floating y); ++ +
+ jmp_buf + int setjmp(jmp_buf env); + _Noreturn void longjmp(jmp_buf env, int val); ++ +
+ sig_atomic_t SIG_IGN SIGILL SIGTERM + SIG_DFL SIGABRT SIGINT + SIG_ERR SIGFPE SIGSEGV + void (*signal(int sig, void (*func)(int)))(int); + int raise(int sig); ++ +
+ alignas + __alignas_is_defined ++ +
+ va_list + type va_arg(va_list ap, type); + void va_copy(va_list dest, va_list src); + void va_end(va_list ap); + void va_start(va_list ap, parmN); ++ +
+ ATOMIC_CHAR_LOCK_FREE atomic_uint + ATOMIC_CHAR16_T_LOCK_FREE atomic_long + ATOMIC_CHAR32_T_LOCK_FREE atomic_ulong + ATOMIC_WCHAR_T_LOCK_FREE atomic_llong + ATOMIC_SHORT_LOCK_FREE atomic_ullong + ATOMIC_INT_LOCK_FREE atomic_char16_t + ATOMIC_LONG_LOCK_FREE atomic_char32_t + ATOMIC_LLONG_LOCK_FREE atomic_wchar_t + ATOMIC_ADDRESS_LOCK_FREE atomic_int_least8_t + ATOMIC_FLAG_INIT atomic_uint_least8_t + memory_order atomic_int_least16_t + atomic_flag atomic_uint_least16_t + atomic_bool atomic_int_least32_t + atomic_address atomic_uint_least32_t + memory_order_relaxed atomic_int_least64_t + memory_order_consume atomic_uint_least64_t + memory_order_acquire atomic_int_fast8_t + memory_order_release atomic_uint_fast8_t + memory_order_acq_rel atomic_int_fast16_t + memory_order_seq_cst atomic_uint_fast16_t + atomic_char atomic_int_fast32_t + atomic_schar atomic_uint_fast32_t + atomic_uchar atomic_int_fast64_t + atomic_short atomic_uint_fast64_t + atomic_ushort atomic_intptr_t + atomic_int atomic_uintptr_t + atomic_size_t atomic_intmax_t + atomic_ptrdiff_t atomic_uintmax_t + #define ATOMIC_VAR_INIT(C value) + void atomic_init(volatile A *obj, C value); + type kill_dependency(type y); + void atomic_thread_fence(memory_order order); + void atomic_signal_fence(memory_order order); + _Bool atomic_is_lock_free(atomic_type const volatile *obj); + void atomic_store(volatile A *object, C desired); + void atomic_store_explicit(volatile A *object, + C desired, memory_order order); + C atomic_load(volatile A *object); + C atomic_load_explicit(volatile A *object, + memory_order order); + C atomic_exchange(volatile A *object, C desired); + C atomic_exchange_explicit(volatile A *object, + C desired, memory_order order); + _Bool atomic_compare_exchange_strong(volatile A *object, + C *expected, C desired); + _Bool atomic_compare_exchange_strong_explicit( + volatile A *object, C *expected, C desired, + memory_order success, memory_order failure); + _Bool atomic_compare_exchange_weak(volatile A *object, + C *expected, C desired); + _Bool atomic_compare_exchange_weak_explicit( + volatile A *object, C *expected, C desired, + memory_order success, memory_order failure); + C atomic_fetch_key(volatile A *object, M operand); + C atomic_fetch_key_explicit(volatile A *object, + M operand, memory_order order); + bool atomic_flag_test_and_set( + volatile atomic_flag *object); + bool atomic_flag_test_and_set_explicit( + volatile atomic_flag *object, memory_order order); + void atomic_flag_clear(volatile atomic_flag *object); + void atomic_flag_clear_explicit( + volatile atomic_flag *object, memory_order order); ++ +
+ bool + true + false + __bool_true_false_are_defined ++ +
+ ptrdiff_t max_align_t NULL + size_t wchar_t + offsetof(type, member-designator) + __STDC_WANT_LIB_EXT1__ + rsize_t ++ +
+ intN_t INT_LEASTN_MIN PTRDIFF_MAX + uintN_t INT_LEASTN_MAX SIG_ATOMIC_MIN + int_leastN_t UINT_LEASTN_MAX SIG_ATOMIC_MAX + uint_leastN_t INT_FASTN_MIN SIZE_MAX + int_fastN_t INT_FASTN_MAX WCHAR_MIN + uint_fastN_t UINT_FASTN_MAX WCHAR_MAX + intptr_t INTPTR_MIN WINT_MIN + uintptr_t INTPTR_MAX WINT_MAX + intmax_t UINTPTR_MAX INTN_C(value) + uintmax_t INTMAX_MIN UINTN_C(value) + INTN_MIN INTMAX_MAX INTMAX_C(value) + INTN_MAX UINTMAX_MAX UINTMAX_C(value) + UINTN_MAX PTRDIFF_MIN + __STDC_WANT_LIB_EXT1__ + RSIZE_MAX ++ +
+ size_t _IOLBF FILENAME_MAX TMP_MAX + FILE _IONBF L_tmpnam stderr + fpos_t BUFSIZ SEEK_CUR stdin + NULL EOF SEEK_END stdout + _IOFBF FOPEN_MAX SEEK_SET + int remove(const char *filename); + int rename(const char *old, const char *new); + FILE *tmpfile(void); + char *tmpnam(char *s); + int fclose(FILE *stream); + int fflush(FILE *stream); + FILE *fopen(const char * restrict filename, + const char * restrict mode); + FILE *freopen(const char * restrict filename, + const char * restrict mode, + FILE * restrict stream); + void setbuf(FILE * restrict stream, + char * restrict buf); + int setvbuf(FILE * restrict stream, + char * restrict buf, + int mode, size_t size); + int fprintf(FILE * restrict stream, + const char * restrict format, ...); + int fscanf(FILE * restrict stream, + const char * restrict format, ...); + int printf(const char * restrict format, ...); + int scanf(const char * restrict format, ...); + int snprintf(char * restrict s, size_t n, + const char * restrict format, ...); + int sprintf(char * restrict s, + const char * restrict format, ...); + int sscanf(const char * restrict s, + const char * restrict format, ...); + int vfprintf(FILE * restrict stream, + const char * restrict format, va_list arg); + int vfscanf(FILE * restrict stream, + const char * restrict format, va_list arg); + int vprintf(const char * restrict format, va_list arg); + int vscanf(const char * restrict format, va_list arg); + int vsnprintf(char * restrict s, size_t n, + const char * restrict format, va_list arg); + int vsprintf(char * restrict s, + const char * restrict format, va_list arg); + int vsscanf(const char * restrict s, + const char * restrict format, va_list arg); + int fgetc(FILE *stream); + char *fgets(char * restrict s, int n, + FILE * restrict stream); + int fputc(int c, FILE *stream); + int fputs(const char * restrict s, + FILE * restrict stream); + int getc(FILE *stream); + int getchar(void); + int putc(int c, FILE *stream); * + int putchar(int c); + int puts(const char *s); + int ungetc(int c, FILE *stream); + size_t fread(void * restrict ptr, + size_t size, size_t nmemb, + FILE * restrict stream); + size_t fwrite(const void * restrict ptr, + size_t size, size_t nmemb, + FILE * restrict stream); + int fgetpos(FILE * restrict stream, + fpos_t * restrict pos); + int fseek(FILE *stream, long int offset, int whence); + int fsetpos(FILE *stream, const fpos_t *pos); + long int ftell(FILE *stream); + void rewind(FILE *stream); + void clearerr(FILE *stream); + int feof(FILE *stream); + int ferror(FILE *stream); + void perror(const char *s); + __STDC_WANT_LIB_EXT1__ + L_tmpnam_s TMP_MAX_S errno_t rsize_t + errno_t tmpfile_s(FILE * restrict * restrict streamptr); + errno_t tmpnam_s(char *s, rsize_t maxsize); + errno_t fopen_s(FILE * restrict * restrict streamptr, + const char * restrict filename, + const char * restrict mode); + errno_t freopen_s(FILE * restrict * restrict newstreamptr, + const char * restrict filename, + const char * restrict mode, + FILE * restrict stream); + int fprintf_s(FILE * restrict stream, + const char * restrict format, ...); + int fscanf_s(FILE * restrict stream, + const char * restrict format, ...); + int printf_s(const char * restrict format, ...); + int scanf_s(const char * restrict format, ...); + int snprintf_s(char * restrict s, rsize_t n, + const char * restrict format, ...); + int sprintf_s(char * restrict s, rsize_t n, + const char * restrict format, ...); + int sscanf_s(const char * restrict s, + const char * restrict format, ...); + int vfprintf_s(FILE * restrict stream, + const char * restrict format, + va_list arg); + int vfscanf_s(FILE * restrict stream, + const char * restrict format, + va_list arg); + int vprintf_s(const char * restrict format, + va_list arg); + int vscanf_s(const char * restrict format, + va_list arg); + int vsnprintf_s(char * restrict s, rsize_t n, + const char * restrict format, + va_list arg); + int vsprintf_s(char * restrict s, rsize_t n, + const char * restrict format, + va_list arg); + int vsscanf_s(const char * restrict s, + const char * restrict format, + va_list arg); + char *gets_s(char *s, rsize_t n); ++ +
+ size_t ldiv_t EXIT_FAILURE MB_CUR_MAX + wchar_t lldiv_t EXIT_SUCCESS + div_t NULL RAND_MAX + double atof(const char *nptr); + int atoi(const char *nptr); + long int atol(const char *nptr); + long long int atoll(const char *nptr); + double strtod(const char * restrict nptr, + char ** restrict endptr); + float strtof(const char * restrict nptr, + char ** restrict endptr); + long double strtold(const char * restrict nptr, + char ** restrict endptr); + long int strtol(const char * restrict nptr, + char ** restrict endptr, int base); + long long int strtoll(const char * restrict nptr, + char ** restrict endptr, int base); + unsigned long int strtoul( + const char * restrict nptr, + char ** restrict endptr, int base); + unsigned long long int strtoull( + const char * restrict nptr, + char ** restrict endptr, int base); + int rand(void); + void srand(unsigned int seed); + void *aligned_alloc(size_t alignment, size_t size); + void *calloc(size_t nmemb, size_t size); + void free(void *ptr); + void *malloc(size_t size); + void *realloc(void *ptr, size_t size); + _Noreturn void abort(void); + int atexit(void (*func)(void)); + int at_quick_exit(void (*func)(void)); + _Noreturn void exit(int status); + _Noreturn void _Exit(int status); + char *getenv(const char *name); + _Noreturn void quick_exit(int status); + int system(const char *string); + void *bsearch(const void *key, const void *base, + size_t nmemb, size_t size, + int (*compar)(const void *, const void *)); + void qsort(void *base, size_t nmemb, size_t size, + int (*compar)(const void *, const void *)); + int abs(int j); + long int labs(long int j); + long long int llabs(long long int j); + div_t div(int numer, int denom); + ldiv_t ldiv(long int numer, long int denom); + lldiv_t lldiv(long long int numer, + long long int denom); + int mblen(const char *s, size_t n); + int mbtowc(wchar_t * restrict pwc, + const char * restrict s, size_t n); + int wctomb(char *s, wchar_t wchar); + size_t mbstowcs(wchar_t * restrict pwcs, + const char * restrict s, size_t n); + size_t wcstombs(char * restrict s, + const wchar_t * restrict pwcs, size_t n); + __STDC_WANT_LIB_EXT1__ + errno_t + rsize_t + constraint_handler_t + constraint_handler_t set_constraint_handler_s( + constraint_handler_t handler); + void abort_handler_s( + const char * restrict msg, + void * restrict ptr, + errno_t error); + void ignore_handler_s( + const char * restrict msg, + void * restrict ptr, + errno_t error); + errno_t getenv_s(size_t * restrict len, + char * restrict value, rsize_t maxsize, + const char * restrict name); + void *bsearch_s(const void *key, const void *base, + rsize_t nmemb, rsize_t size, + int (*compar)(const void *k, const void *y, + void *context), + void *context); + errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, + int (*compar)(const void *x, const void *y, + void *context), + void *context); + errno_t wctomb_s(int * restrict status, + char * restrict s, + rsize_t smax, + wchar_t wc); + errno_t mbstowcs_s(size_t * restrict retval, + wchar_t * restrict dst, rsize_t dstmax, + const char * restrict src, rsize_t len); + errno_t wcstombs_s(size_t * restrict retval, + char * restrict dst, rsize_t dstmax, + const wchar_t * restrict src, rsize_t len); ++ +
+ size_t + NULL + void *memcpy(void * restrict s1, + const void * restrict s2, size_t n); + void *memmove(void *s1, const void *s2, size_t n); + char *strcpy(char * restrict s1, + const char * restrict s2); + char *strncpy(char * restrict s1, + const char * restrict s2, size_t n); + char *strcat(char * restrict s1, + const char * restrict s2); + char *strncat(char * restrict s1, + const char * restrict s2, size_t n); + int memcmp(const void *s1, const void *s2, size_t n); + int strcmp(const char *s1, const char *s2); + int strcoll(const char *s1, const char *s2); + int strncmp(const char *s1, const char *s2, size_t n); + size_t strxfrm(char * restrict s1, + const char * restrict s2, size_t n); + void *memchr(const void *s, int c, size_t n); + char *strchr(const char *s, int c); + size_t strcspn(const char *s1, const char *s2); + char *strpbrk(const char *s1, const char *s2); + char *strrchr(const char *s, int c); + size_t strspn(const char *s1, const char *s2); + char *strstr(const char *s1, const char *s2); + char *strtok(char * restrict s1, + const char * restrict s2); + void *memset(void *s, int c, size_t n); + char *strerror(int errnum); + size_t strlen(const char *s); + __STDC_WANT_LIB_EXT1__ + errno_t + rsize_t + errno_t memcpy_s(void * restrict s1, rsize_t s1max, + const void * restrict s2, rsize_t n); + errno_t memmove_s(void *s1, rsize_t s1max, + const void *s2, rsize_t n); + errno_t strcpy_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2); + errno_t strncpy_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2, + rsize_t n); + errno_t strcat_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2); + errno_t strncat_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2, + rsize_t n); + char *strtok_s(char * restrict s1, + rsize_t * restrict s1max, + const char * restrict s2, + char ** restrict ptr); + errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) + errno_t strerror_s(char *s, rsize_t maxsize, + errno_t errnum); + size_t strerrorlen_s(errno_t errnum); + size_t strnlen_s(const char *s, size_t maxsize); ++ +
+ acos sqrt fmod nextafter + asin fabs frexp nexttoward + atan atan2 hypot remainder + acosh cbrt ilogb remquo + asinh ceil ldexp rint + atanh copysign lgamma round + cos erf llrint scalbn + sin erfc llround scalbln + tan exp2 log10 tgamma + cosh expm1 log1p trunc + sinh fdim log2 carg + tanh floor logb cimag + exp fma lrint conj + log fmax lround cproj + pow fmin nearbyint creal ++ +
+ ONCE_FLAG_INIT mtx_plain + TSS_DTOR_ITERATIONS mtx_recursive + cnd_t mtx_timed + thrd_t mtx_try + tss_t thrd_timeout + mtx_t thrd_success + tss_dtor_t thrd_busy + thrd_start_t thrd_error + once_flag thrd_nomem + xtime + void call_once(once_flag *flag, void (*func)(void)); + int cnd_broadcast(cnd_t *cond); + void cnd_destroy(cnd_t *cond); + int cnd_init(cnd_t *cond); + int cnd_signal(cnd_t *cond); + int cnd_timedwait(cnd_t *cond, mtx_t *mtx, + const xtime *xt); + int cnd_wait(cnd_t *cond, mtx_t *mtx); + void mtx_destroy(mtx_t *mtx); + int mtx_init(mtx_t *mtx, int type); + int mtx_lock(mtx_t *mtx); + int mtx_timedlock(mtx_t *mtx, const xtime *xt); + int mtx_trylock(mtx_t *mtx); + int mtx_unlock(mtx_t *mtx); + int thrd_create(thrd_t *thr, thrd_start_t func, + void *arg); + thrd_t thrd_current(void); + int thrd_detach(thrd_t thr); + int thrd_equal(thrd_t thr0, thrd_t thr1); + void thrd_exit(int res); + int thrd_join(thrd_t thr, int *res); + void thrd_sleep(const xtime *xt); + void thrd_yield(void); + int tss_create(tss_t *key, tss_dtor_t dtor); + void tss_delete(tss_t key); + void *tss_get(tss_t key); + int tss_set(tss_t key, void *val); + int xtime_get(xtime *xt, int base); ++ +
+ NULL size_t time_t + CLOCKS_PER_SEC clock_t struct tm + clock_t clock(void); + double difftime(time_t time1, time_t time0); + time_t mktime(struct tm *timeptr); + time_t time(time_t *timer); + char *asctime(const struct tm *timeptr); + char *ctime(const time_t *timer); + struct tm *gmtime(const time_t *timer); + struct tm *localtime(const time_t *timer); + size_t strftime(char * restrict s, + size_t maxsize, + const char * restrict format, + const struct tm * restrict timeptr); + __STDC_WANT_LIB_EXT1__ + errno_t + rsize_t + errno_t asctime_s(char *s, rsize_t maxsize, + const struct tm *timeptr); + errno_t ctime_s(char *s, rsize_t maxsize, + const time_t *timer); + struct tm *gmtime_s(const time_t * restrict timer, + struct tm * restrict result); + struct tm *localtime_s(const time_t * restrict timer, + struct tm * restrict result); ++ +
+ mbstate_t size_t char16_t char32_t + size_t mbrtoc16(char16_t * restrict pc16, + const char * restrict s, size_t n, + mbstate_t * restrict ps); + size_t c16rtomb(char * restrict s, char16_t c16, + mbstate_t * restrict ps); + size_t mbrtoc32(char32_t * restrict pc32, + const char * restrict s, size_t n, + mbstate_t * restrict ps); + size_t c32rtomb(char * restrict s, char32_t c32, + mbstate_t * restrict ps); ++ +
+ wchar_t wint_t WCHAR_MAX + size_t struct tm WCHAR_MIN + mbstate_t NULL WEOF + int fwprintf(FILE * restrict stream, + const wchar_t * restrict format, ...); + int fwscanf(FILE * restrict stream, + const wchar_t * restrict format, ...); + int swprintf(wchar_t * restrict s, size_t n, + const wchar_t * restrict format, ...); + int swscanf(const wchar_t * restrict s, + const wchar_t * restrict format, ...); + int vfwprintf(FILE * restrict stream, + const wchar_t * restrict format, va_list arg); + int vfwscanf(FILE * restrict stream, + const wchar_t * restrict format, va_list arg); + int vswprintf(wchar_t * restrict s, size_t n, + const wchar_t * restrict format, va_list arg); + int vswscanf(const wchar_t * restrict s, + const wchar_t * restrict format, va_list arg); + int vwprintf(const wchar_t * restrict format, + va_list arg); + int vwscanf(const wchar_t * restrict format, + va_list arg); + int wprintf(const wchar_t * restrict format, ...); + int wscanf(const wchar_t * restrict format, ...); + wint_t fgetwc(FILE *stream); + wchar_t *fgetws(wchar_t * restrict s, int n, + FILE * restrict stream); + wint_t fputwc(wchar_t c, FILE *stream); + int fputws(const wchar_t * restrict s, + FILE * restrict stream); + int fwide(FILE *stream, int mode); + wint_t getwc(FILE *stream); + wint_t getwchar(void); + wint_t putwc(wchar_t c, FILE *stream); + wint_t putwchar(wchar_t c); + wint_t ungetwc(wint_t c, FILE *stream); + double wcstod(const wchar_t * restrict nptr, + wchar_t ** restrict endptr); + float wcstof(const wchar_t * restrict nptr, + wchar_t ** restrict endptr); + long double wcstold(const wchar_t * restrict nptr, + wchar_t ** restrict endptr); + long int wcstol(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); + long long int wcstoll(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); + unsigned long int wcstoul(const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); + unsigned long long int wcstoull( + const wchar_t * restrict nptr, + wchar_t ** restrict endptr, int base); + wchar_t *wcscpy(wchar_t * restrict s1, + const wchar_t * restrict s2); + wchar_t *wcsncpy(wchar_t * restrict s1, + const wchar_t * restrict s2, size_t n); + wchar_t *wmemcpy(wchar_t * restrict s1, + const wchar_t * restrict s2, size_t n); + wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2, + size_t n); + wchar_t *wcscat(wchar_t * restrict s1, + const wchar_t * restrict s2); + wchar_t *wcsncat(wchar_t * restrict s1, + const wchar_t * restrict s2, size_t n); + int wcscmp(const wchar_t *s1, const wchar_t *s2); + int wcscoll(const wchar_t *s1, const wchar_t *s2); + int wcsncmp(const wchar_t *s1, const wchar_t *s2, + size_t n); + size_t wcsxfrm(wchar_t * restrict s1, + const wchar_t * restrict s2, size_t n); + int wmemcmp(const wchar_t *s1, const wchar_t *s2, + size_t n); + wchar_t *wcschr(const wchar_t *s, wchar_t c); + size_t wcscspn(const wchar_t *s1, const wchar_t *s2); + wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2); + wchar_t *wcsrchr(const wchar_t *s, wchar_t c); + size_t wcsspn(const wchar_t *s1, const wchar_t *s2); + wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2); + wchar_t *wcstok(wchar_t * restrict s1, + const wchar_t * restrict s2, + wchar_t ** restrict ptr); + wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n); + size_t wcslen(const wchar_t *s); + wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n); + size_t wcsftime(wchar_t * restrict s, size_t maxsize, + const wchar_t * restrict format, + const struct tm * restrict timeptr); + wint_t btowc(int c); + int wctob(wint_t c); + int mbsinit(const mbstate_t *ps); + size_t mbrlen(const char * restrict s, size_t n, + mbstate_t * restrict ps); + size_t mbrtowc(wchar_t * restrict pwc, + const char * restrict s, size_t n, + mbstate_t * restrict ps); + size_t wcrtomb(char * restrict s, wchar_t wc, + mbstate_t * restrict ps); + size_t mbsrtowcs(wchar_t * restrict dst, + const char ** restrict src, size_t len, + mbstate_t * restrict ps); + size_t wcsrtombs(char * restrict dst, + const wchar_t ** restrict src, size_t len, + mbstate_t * restrict ps); + __STDC_WANT_LIB_EXT1__ + errno_t + rsize_t + int fwprintf_s(FILE * restrict stream, + const wchar_t * restrict format, ...); + int fwscanf_s(FILE * restrict stream, + const wchar_t * restrict format, ...); + int snwprintf_s(wchar_t * restrict s, + rsize_t n, + const wchar_t * restrict format, ...); + int swprintf_s(wchar_t * restrict s, rsize_t n, + const wchar_t * restrict format, ...); + int swscanf_s(const wchar_t * restrict s, + const wchar_t * restrict format, ...); + int vfwprintf_s(FILE * restrict stream, + const wchar_t * restrict format, + va_list arg); + int vfwscanf_s(FILE * restrict stream, + const wchar_t * restrict format, va_list arg); + int vsnwprintf_s(wchar_t * restrict s, + rsize_t n, + const wchar_t * restrict format, + va_list arg); + int vswprintf_s(wchar_t * restrict s, + rsize_t n, + const wchar_t * restrict format, + va_list arg); + int vswscanf_s(const wchar_t * restrict s, + const wchar_t * restrict format, + va_list arg); + int vwprintf_s(const wchar_t * restrict format, + va_list arg); + int vwscanf_s(const wchar_t * restrict format, + va_list arg); + int wprintf_s(const wchar_t * restrict format, ...); + int wscanf_s(const wchar_t * restrict format, ...); + errno_t wcscpy_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2); + errno_t wcsncpy_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2, + rsize_t n); + errno_t wmemcpy_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2, + rsize_t n); + errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, + const wchar_t *s2, rsize_t n); + errno_t wcscat_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2); + errno_t wcsncat_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2, + rsize_t n); + wchar_t *wcstok_s(wchar_t * restrict s1, + rsize_t * restrict s1max, + const wchar_t * restrict s2, + wchar_t ** restrict ptr); + size_t wcsnlen_s(const wchar_t *s, size_t maxsize); + errno_t wcrtomb_s(size_t * restrict retval, + char * restrict s, rsize_t smax, + wchar_t wc, mbstate_t * restrict ps); + errno_t mbsrtowcs_s(size_t * restrict retval, + wchar_t * restrict dst, rsize_t dstmax, + const char ** restrict src, rsize_t len, + mbstate_t * restrict ps); + errno_t wcsrtombs_s(size_t * restrict retval, + char * restrict dst, rsize_t dstmax, + const wchar_t ** restrict src, rsize_t len, + mbstate_t * restrict ps); ++ +
+ wint_t wctrans_t wctype_t WEOF + int iswalnum(wint_t wc); + int iswalpha(wint_t wc); + int iswblank(wint_t wc); + int iswcntrl(wint_t wc); + int iswdigit(wint_t wc); + int iswgraph(wint_t wc); + int iswlower(wint_t wc); + int iswprint(wint_t wc); + int iswpunct(wint_t wc); + int iswspace(wint_t wc); + int iswupper(wint_t wc); + int iswxdigit(wint_t wc); + int iswctype(wint_t wc, wctype_t desc); + wctype_t wctype(const char *property); + wint_t towlower(wint_t wc); + wint_t towupper(wint_t wc); + wint_t towctrans(wint_t wc, wctrans_t desc); + wctrans_t wctrans(const char *property); ++ +
+ (informative) + Sequence points ++
+ The following are the sequence points described in 5.1.2.3: +
+ (normative) + Universal character names for identifiers ++
+ This clause lists the hexadecimal code values that are valid in universal character names + in identifiers. + +
+ 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6, + 00D8-00F6, 00F8-00FF +
+ 0100-167F, 1681-180D, 180F-1FFF +
+ 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F +
+ 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF +
+ 3004-3007, 3021-302F, 3031-303F +
+ 3040-D7FF +
+ F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD +
+ 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD, + 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD, + B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD + +
+ 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F + + +
+ (informative) + Implementation limits ++
+ The contents of the header <limits.h> are given below, in alphabetical order. The + minimum magnitudes shown shall be replaced by implementation-defined magnitudes + with the same sign. The values shall all be constant expressions suitable for use in #if + preprocessing directives. The components are described further in 5.2.4.2.1. +
+ #define CHAR_BIT 8 + #define CHAR_MAX UCHAR_MAX or SCHAR_MAX + #define CHAR_MIN 0 or SCHAR_MIN + #define INT_MAX +32767 + #define INT_MIN -32767 + #define LONG_MAX +2147483647 + #define LONG_MIN -2147483647 + #define LLONG_MAX +9223372036854775807 + #define LLONG_MIN -9223372036854775807 + #define MB_LEN_MAX 1 + #define SCHAR_MAX +127 + #define SCHAR_MIN -127 + #define SHRT_MAX +32767 + #define SHRT_MIN -32767 + #define UCHAR_MAX 255 + #define USHRT_MAX 65535 + #define UINT_MAX 65535 + #define ULONG_MAX 4294967295 + #define ULLONG_MAX 18446744073709551615 ++
+ The contents of the header <float.h> are given below. All integer values, except + FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing + directives; all floating values shall be constant expressions. The components are + described further in 5.2.4.2.2. +
+ The values given in the following list shall be replaced by implementation-defined + expressions: +
+ #define FLT_EVAL_METHOD + #define FLT_ROUNDS ++
+ The values given in the following list shall be replaced by implementation-defined + constant expressions that are greater or equal in magnitude (absolute value) to those + shown, with the same sign: + +
+ #define DLB_DECIMAL_DIG 10 + #define DBL_DIG 10 + #define DBL_MANT_DIG + #define DBL_MAX_10_EXP +37 + #define DBL_MAX_EXP + #define DBL_MIN_10_EXP -37 + #define DBL_MIN_EXP + #define DECIMAL_DIG 10 + #define FLT_DECIMAL_DIG 6 + #define FLT_DIG 6 + #define FLT_MANT_DIG + #define FLT_MAX_10_EXP +37 + #define FLT_MAX_EXP + #define FLT_MIN_10_EXP -37 + #define FLT_MIN_EXP + #define FLT_RADIX 2 + #define LDLB_DECIMAL_DIG 10 + #define LDBL_DIG 10 + #define LDBL_MANT_DIG + #define LDBL_MAX_10_EXP +37 + #define LDBL_MAX_EXP + #define LDBL_MIN_10_EXP -37 + #define LDBL_MIN_EXP ++
+ The values given in the following list shall be replaced by implementation-defined + constant expressions with values that are greater than or equal to those shown: +
+ #define DBL_MAX 1E+37 + #define FLT_MAX 1E+37 + #define LDBL_MAX 1E+37 ++
+ The values given in the following list shall be replaced by implementation-defined + constant expressions with (positive) values that are less than or equal to those shown: + +
+ #define DBL_EPSILON 1E-9 + #define DBL_MIN 1E-37 + #define FLT_EPSILON 1E-5 + #define FLT_MIN 1E-37 + #define LDBL_EPSILON 1E-9 + #define LDBL_MIN 1E-37 ++ +
+ (normative) + IEC 60559 floating-point arithmetic ++ +
+ This annex specifies C language support for the IEC 60559 floating-point standard. The + IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for + microprocessor systems, second edition (IEC 60559:1989), previously designated + IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic + (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point + Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove + dependencies on radix and word length. IEC 60559 generally refers to the floating-point + standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that + defines __STDC_IEC_559__ shall conform to the specifications in this annex.343) + Where a binding between the C language and IEC 60559 is indicated, the + IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since + negative and positive infinity are representable in IEC 60559 formats, all real numbers lie + within the range of representable values. + +
343) Implementations that do not define __STDC_IEC_559__ are not required to conform to these + specifications. + + +
+ The C floating types match the IEC 60559 formats as follows: +
+ The long double type should match an IEC 60559 extended format. + +
344) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit + and quadruple 128-bit IEC 60559 formats. + +
345) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include + all double values. + + +
+ This specification does not define the behavior of signaling NaNs.346) It generally uses + the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan + functions in <math.h> provide designations for IEC 60559 NaNs and infinities. + +
346) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are + sufficient for closure of the arithmetic. + + +
+ C operators and functions provide IEC 60559 required and recommended facilities as + listed below. +
+ If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised + (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part + of the floating value exceeds the range of the integer type, then the ''invalid'' floating- + point exception is raised and the resulting value is unspecified. Otherwise, the resulting + value is determined by 6.3.1.4. Conversion of an integral floating value that does not + exceed the range of the integer type raises no floating-point exceptions; whether + conversion of a non-integral floating value raises the ''inexact'' floating-point exception is + unspecified.347) + +
347) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer + conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those + cases where it matters, library functions can be used to effect such conversions with or without raising + the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in + <math.h>. + + +
+ Conversion from the widest supported IEC 60559 format to decimal with + DECIMAL_DIG digits and back is the identity function.348) +
+ Conversions involving IEC 60559 formats follow all pertinent recommended practice. In + particular, conversion between any supported IEC 60559 format and decimal with + DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current + rounding mode), which assures that conversion from the widest supported IEC 60559 + format to decimal with DECIMAL_DIG digits and back is the identity function. + + + + +
+ Functions such as strtod that convert character sequences to floating types honor the + rounding direction. Hence, if the rounding direction might be upward or downward, the + implementation cannot convert a minus-signed sequence by negating the converted + unsigned sequence. + +
348) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported, + DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest + IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and + DBL_DIG are 18 and 15, respectively, for these formats.) + + +
349) Assignment removes any extra range and precision. + + +
+ A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed + zeros, subnormals, and the rounding directions in a manner consistent with the basic + arithmetic operations covered by IEC 60559. +
+ A contracted expression should raise floating-point exceptions in a manner generally + consistent with the basic arithmetic operations. * + +
+ The floating-point environment defined in <fenv.h> includes the IEC 60559 floating- + point exception status flags and directed-rounding control modes. It includes also + IEC 60559 dynamic rounding precision and trap enablement modes, if the + implementation supports them.350) + +
350) This specification does not require dynamic rounding precision nor trap enablement modes. + + +
+ IEC 60559 requires that floating-point operations implicitly raise floating-point exception + status flags, and that rounding control modes can be set explicitly to affect result values of + floating-point operations. When the state for the FENV_ACCESS pragma (defined in + <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects + which respect sequence points.351) + + + + + + +
351) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating- + point control modes will be the default ones and the floating-point status flags will not be tested, + which allows certain optimizations (see F.9). + + +
+ During translation the IEC 60559 default modes are in effect: +
+ The implementation should produce a diagnostic message for each translation-time + floating-point exception, other than ''inexact'';352) the implementation should then + proceed with the translation of the program. + +
352) As floating constants are converted to appropriate internal representations at translation time, their + conversion is subject to default rounding modes and raises no execution-time floating-point exceptions + (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example + strtod, provide execution-time conversion of numeric strings. + + +
+ At program startup the floating-point environment is initialized as prescribed by + IEC 60559: +
+ An arithmetic constant expression of floating type, other than one in an initializer for an + object that has static or thread storage duration, is evaluated (as if) during execution; thus, + it is affected by any operative floating-point control modes and raises floating-point + exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma + is ''on'').353) +
+ EXAMPLE + + + + +
+ #include <fenv.h> + #pragma STDC FENV_ACCESS ON + void f(void) + { + float w[] = { 0.0/0.0 }; // raises an exception + static float x = 0.0/0.0; // does not raise an exception + float y = 0.0/0.0; // raises an exception + double z = 0.0/0.0; // raises an exception + /* ... */ + } ++
+ For the static initialization, the division is done at translation time, raising no (execution-time) floating- + point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at + execution time. + + +
353) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0
+ are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
+ 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the
+ efficiency of translation-time evaluation through static initialization, such as
+
+
+ const static double one_third = 1.0/3.0;
+
+
+
+
+ All computation for automatic initialization is done (as if) at execution time; thus, it is + affected by any operative modes and raises floating-point exceptions as required by + IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation + for initialization of objects that have static or thread storage duration is done (as if) at + translation time. +
+ EXAMPLE +
+ #include <fenv.h> + #pragma STDC FENV_ACCESS ON + void f(void) + { + float u[] = { 1.1e75 }; // raises exceptions + static float v = 1.1e75; // does not raise exceptions + float w = 1.1e75; // raises exceptions + double x = 1.1e75; // may raise exceptions + float y = 1.1e75f; // may raise exceptions + long double z = 1.1e75; // does not raise exceptions + /* ... */ + } ++
+ The static initialization of v raises no (execution-time) floating-point exceptions because its computation is + done at translation time. The automatic initialization of u and w require an execution-time conversion to + float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations + of x and y entail execution-time conversion; however, in some expression evaluation methods, the + conversions is not to a narrower format, in which case no floating-point exception is raised.354) The + automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating- + point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to + + + + + their internal representations occur at translation time in all cases. + + +
354) Use of float_t and double_t variables increases the likelihood of translation-time computation.
+ For example, the automatic initialization
+
+
+ double_t x = 1.1e75;
+
+ could be done at translation time, regardless of the expression evaluation method.
+
+
+
+ Operations defined in 6.5 and functions and macros defined for the standard libraries + change floating-point status flags and control modes just as indicated by their + specifications (including conformance to IEC 60559). They do not change flags or modes + (so as to be detectable by the user) in any other cases. +
+ If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559 + valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and + ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised + before ''inexact''. + +
+ This section identifies code transformations that might subvert IEC 60559-specified + behavior, and others that do not. + +
+ Floating-point arithmetic operations and external function calls may entail side effects + which optimization shall honor, at least where the state of the FENV_ACCESS pragma is + ''on''. The flags and modes in the floating-point environment may be regarded as global + variables; floating-point operations (+, *, etc.) implicitly read the modes and write the + flags. +
+ Concern about side effects may inhibit code motion and removal of seemingly useless + code. For example, in +
+ #include <fenv.h> + #pragma STDC FENV_ACCESS ON + void f(double x) + { + /* ... */ + for (i = 0; i < n; i++) x + 1; + /* ... */ + } ++ x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop + body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of + course these optimizations are valid if the implementation can rule out the nettlesome + cases.) +
+ This specification does not require support for trap handlers that maintain information + about the order or count of floating-point exceptions. Therefore, between function calls, + floating-point exceptions need not be precise: the actual order and number of occurrences + of floating-point exceptions (> 1) may vary from what the source code expresses. Thus, + + the preceding loop could be treated as +
+ if (0 < n) x + 1; ++ +
+ x/2 <-> x x 0.5 Although similar transformations involving inexact constants +
+ generally do not yield numerically equivalent expressions, if the + constants are exact then such transformations can be made on + IEC 60559 machines and others that round perfectly. ++ 1 x x and x/1 -> x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559 +
+ machines, among others).355) ++ x/x -> 1.0 The expressions x/x and 1.0 are not equivalent if x can be zero, +
+ infinite, or NaN. ++ x - y <-> x + (-y) The expressions x - y, x + (-y), and (-y) + x are equivalent (on +
+ IEC 60559 machines, among others). ++ x - y <-> -(y - x) The expressions x - y and -(y - x) are not equivalent because 1 - 1 +
+ is +0 but -(1 - 1) is -0 (in the default rounding direction).356) ++ x - x -> 0.0 The expressions x - x and 0.0 are not equivalent if x is a NaN or +
+ infinite. ++ 0 x x -> 0.0 The expressions 0 x x and 0.0 are not equivalent if x is a NaN, +
+ infinite, or -0. ++ x+0-> x The expressions x + 0 and x are not equivalent if x is -0, because +
+ (-0) + (+0) yields +0 (in the default rounding direction), not -0. ++ x-0-> x (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but +
+ +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the + FENV_ACCESS pragma is ''off'', promising default rounding, then + the implementation can replace x - 0 by x, even if x might be zero. ++ -x <-> 0 - x The expressions -x and 0 - x are not equivalent if x is +0, because +
+ -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is + downward). ++ + + +
355) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and + other transformations that remove arithmetic operators. + +
356) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
+ Examples include:
+
+
+ 1/(1/ (+-) (inf)) is (+-) (inf)
+
+ and
+
+
+ conj(csqrt(z)) is csqrt(conj(z)),
+
+ for complex z.
+
+
+
+ x != x -> false The expression x != x is true if x is a NaN. + x = x -> true The expression x = x is false if x is a NaN. + x < y -> isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these +
+ expressions are not equivalent because of side effects when x or y is a + NaN and the state of the FENV_ACCESS pragma is ''on''. This + transformation, which would be desirable if extra code were required + to cause the ''invalid'' floating-point exception for unordered cases, + could be performed provided the state of the FENV_ACCESS pragma + is ''off''. ++ The sense of relational operators shall be maintained. This includes handling unordered + cases as expressed by the source code. +
+ EXAMPLE +
+ // calls g and raises ''invalid'' if a and b are unordered + if (a < b) + f(); + else + g(); ++ is not equivalent to +
+ // calls f and raises ''invalid'' if a and b are unordered + if (a >= b) + g(); + else + f(); ++ nor to +
+ // calls f without raising ''invalid'' if a and b are unordered + if (isgreaterequal(a,b)) + g(); + else + f(); ++ nor, unless the state of the FENV_ACCESS pragma is ''off'', to +
+ // calls g without raising ''invalid'' if a and b are unordered + if (isless(a,b)) + f(); + else + g(); ++ but is equivalent to + +
+ if (!(a < b)) + g(); + else + f(); ++ + +
+ The implementation shall honor floating-point exceptions raised by execution-time + constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4 + and F.8.5.) An operation on constants that raises no floating-point exception can be + folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a + further check is required to assure that changing the rounding direction to downward does + not alter the sign of the result,357) and implementations that support dynamic rounding + precision modes shall assure further that the result of the operation raises no floating- + point exception when converted to the semantic type of the operation. + +
357) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward. + + +
+ This subclause contains specifications of <math.h> facilities that are particularly suited + for IEC 60559 implementations. +
+ The Standard C macro HUGE_VAL and its float and long double analogs, + HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive + infinities. +
+ Special cases for functions in <math.h> are covered directly or indirectly by + IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The + other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and + (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags + in a manner consistent with the basic arithmetic operations covered by IEC 60559. +
+ The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a + nonzero value. +
+ The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in + subsequent subclauses of this annex. +
+ The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of + rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value + whose magnitude is too large. +
+ The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially + subnormal or zero) and suffers loss of accuracy.358) + + + +
+ Whether or when library functions raise the ''inexact'' floating-point exception is + unspecified, unless explicitly specified otherwise. +
+ Whether or when library functions raise an undeserved ''underflow'' floating-point + exception is unspecified.359) Otherwise, as implied by F.8.6, the <math.h> functions do + not raise spurious floating-point exceptions (detectable by the user), other than the + ''inexact'' floating-point exception. +
+ Whether the functions honor the rounding direction mode is implementation-defined, + unless explicitly specified otherwise. +
+ Functions with a NaN argument return a NaN result and raise no floating-point exception, + except where stated otherwise. +
+ The specifications in the following subclauses append to the definitions in <math.h>. + For families of functions, the specifications apply to all of the functions even though only + the principal function is shown. Unless otherwise specified, where the symbol ''(+-)'' + occurs in both an argument and the result, the result has the same sign as the argument. +
+ If a function with one or more NaN arguments returns a NaN result, the result should be + the same as one of the NaN arguments (after possible type conversion), except perhaps + for the sign. + +
358) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on + when the floating-point exception is raised. + +
359) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if + avoiding them would be too costly. + + +
+
+
+
+
360) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise + the ''divide-by-zero'' floating-point exception. + + +
+
+
+
+
+
+
+
+
+
+
+
+
+
+ frexp raises no floating-point exceptions. +
+ When the radix of the argument is a power of 2, the returned value is exact and is + independent of the current rounding direction mode. +
+ On a binary system, the body of the frexp function might be +
+ {
+ *exp = (value == 0) ? 0 : (int)(1 + logb(value));
+ return scalbn(value, -(*exp));
+ }
+
+
++ When the correct result is representable in the range of the return type, the returned value + is exact and is independent of the current rounding direction mode. +
+ If the correct result is outside the range of the return type, the numeric result is + unspecified and the ''invalid'' floating-point exception is raised. + + +
+ On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp). + +
+
+
+
+
+
+ The returned value is exact and is independent of the current rounding direction mode. + + +
+
+ The returned values are exact and are independent of the current rounding direction + mode. +
+ modf behaves as though implemented by +
+ #include <math.h> + #include <fenv.h> + #pragma STDC FENV_ACCESS ON + double modf(double value, double *iptr) + { + int save_round = fegetround(); + fesetround(FE_TOWARDZERO); + *iptr = nearbyint(value); + fesetround(save_round); + return copysign( + isinf(value) ? 0.0 : + value - (*iptr), value); + } ++ +
+
+ If the calculation does not overflow or underflow, the returned value is exact and + independent of the current rounding direction mode. + + +
+
+
+ The returned value is exact and is independent of the current rounding direction mode. + +
+
+
+ sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value + is dependent on the current rounding direction mode. + +
+
+
+
+
+
+ The returned value is independent of the current rounding direction mode. +
+ The double version of ceil behaves as though implemented by +
+ #include <math.h> + #include <fenv.h> + #pragma STDC FENV_ACCESS ON + double ceil(double x) + { + double result; + int save_round = fegetround(); + fesetround(FE_UPWARD); + result = rint(x); // or nearbyint instead of rint + fesetround(save_round); + return result; + } ++
+ The ceil functions may, but are not required to, raise the ''inexact'' floating-point + exception for finite non-integer arguments, as this implementation does. + +
+
+ The returned value and is independent of the current rounding direction mode. +
+ See the sample implementation for ceil in F.10.6.1. The floor functions may, but are + not required to, raise the ''inexact'' floating-point exception for finite non-integer + arguments, as that implementation does. + +
+ The nearbyint functions use IEC 60559 rounding according to the current rounding + direction. They do not raise the ''inexact'' floating-point exception if the result differs in + value from the argument. +
+ The rint functions differ from the nearbyint functions only in that they do raise the + ''inexact'' floating-point exception if the result differs in value from the argument. + +
+ The lrint and llrint functions provide floating-to-integer conversion as prescribed + by IEC 60559. They round according to the current rounding direction. If the rounded + value is outside the range of the return type, the numeric result is unspecified and the + ''invalid'' floating-point exception is raised. When they raise no other floating-point + exception and the result differs from the argument, they raise the ''inexact'' floating-point + exception. + +
+
+ The returned value is independent of the current rounding direction mode. +
+ The double version of round behaves as though implemented by +
+ #include <math.h> + #include <fenv.h> + #pragma STDC FENV_ACCESS ON + double round(double x) + { + double result; + fenv_t save_env; + feholdexcept(&save_env); + result = rint(x); + if (fetestexcept(FE_INEXACT)) { + fesetround(FE_TOWARDZERO); + result = rint(copysign(0.5 + fabs(x), x)); + } + feupdateenv(&save_env); + return result; + } ++ The round functions may, but are not required to, raise the ''inexact'' floating-point + exception for finite non-integer numeric arguments, as this implementation does. + + +
+ The lround and llround functions differ from the lrint and llrint functions + with the default rounding direction just in that the lround and llround functions + round halfway cases away from zero and need not raise the ''inexact'' floating-point + exception for non-integer arguments that round to within the range of the return type. + +
+ The trunc functions use IEC 60559 rounding toward zero (regardless of the current + rounding direction). The returned value is exact. +
+ The returned value is independent of the current rounding direction mode. The trunc + functions may, but are not required to, raise the ''inexact'' floating-point exception for + finite non-integer arguments. + +
+
+ When subnormal results are supported, the returned value is exact and is independent of + the current rounding direction mode. +
+ The double version of fmod behaves as though implemented by + +
+ #include <math.h> + #include <fenv.h> + #pragma STDC FENV_ACCESS ON + double fmod(double x, double y) + { + double result; + result = remainder(fabs(x), (y = fabs(y))); + if (signbit(result)) result += y; + return copysign(result, x); + } ++ +
+ The remainder functions are fully specified as a basic arithmetic operation in + IEC 60559. +
+ When subnormal results are supported, the returned value is exact and is independent of + the current rounding direction mode. + +
+ The remquo functions follow the specifications for the remainder functions. They + have no further specifications special to IEC 60559 implementations. +
+ When subnormal results are supported, the returned value is exact and is independent of + the current rounding direction mode. + +
+ copysign is specified in the Appendix to IEC 60559. +
+ The returned value is exact and is independent of the current rounding direction mode. + +
+ All IEC 60559 implementations support quiet NaNs, in all floating formats. +
+ The returned value is exact and is independent of the current rounding direction mode. + +
+
+ Even though underflow or overflow can occur, the returned value is independent of the + current rounding direction mode. + +
+ No additional requirements beyond those on nextafter. +
+ Even though underflow or overflow can occur, the returned value is independent of the + current rounding direction mode. + + +
+ No additional requirements. + +
+ If just one argument is a NaN, the fmax functions return the other argument (if both + arguments are NaNs, the functions return a NaN). +
+ The returned value is exact and is independent of the current rounding direction mode. +
+ The body of the fmax function might be361) +
+ { return (isgreaterequal(x, y) ||
+ isnan(y)) ? x : y; }
+
+
+361) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would + return +0; however, implementation in software might be impractical. + + +
+ The fmin functions are analogous to the fmax functions (see F.10.9.2). +
+ The returned value is exact and is independent of the current rounding direction mode. + +
+
+ Relational operators and their corresponding comparison macros (7.12.14) produce + equivalent result values, even if argument values are represented in wider formats. Thus, + comparison macro arguments represented in formats wider than their semantic types are + not converted to the semantic types, unless the wide evaluation method converts operands + of relational operators to their semantic types. The standard wide evaluation methods + characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert + operands of relational operators to their semantic types. + + +
+ (normative) + IEC 60559-compatible complex arithmetic ++ +
+ This annex supplements annex F to specify complex arithmetic for compatibility with + IEC 60559 real floating-point arithmetic. An implementation that defines * + __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.362) + +
362) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform + to these specifications. + + +
+ There is a new keyword _Imaginary, which is used to specify imaginary types. It is + used as a type specifier within declaration specifiers in the same way as _Complex is + (thus, _Imaginary float is a valid type name). +
+ There are three imaginary types, designated as float _Imaginary, double + _Imaginary, and long double _Imaginary. The imaginary types (along with + the real floating and complex types) are floating types. +
+ For imaginary types, the corresponding real type is given by deleting the keyword + _Imaginary from the type name. +
+ Each imaginary type has the same representation and alignment requirements as the + corresponding real type. The value of an object of imaginary type is the value of the real + representation times the imaginary unit. +
+ The imaginary type domain comprises the imaginary types. + +
+ A complex or imaginary value with at least one infinite part is regarded as an infinity + (even if its other part is a NaN). A complex or imaginary value is a finite number if each + of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is + a zero if each of its parts is a zero. + + + + + + +
+ Conversions among imaginary types follow rules analogous to those for real floating + types. + +
+ When a value of imaginary type is converted to a real type other than _Bool,363) the + result is a positive zero. +
+ When a value of real type is converted to an imaginary type, the result is a positive + imaginary zero. + +
+ When a value of imaginary type is converted to a complex type, the real part of the + complex result value is a positive zero and the imaginary part of the complex result value + is determined by the conversion rules for the corresponding real types. +
+ When a value of complex type is converted to an imaginary type, the real part of the + complex value is discarded and the value of the imaginary part is converted according to + the conversion rules for the corresponding real types. + +
+ The following subclauses supplement 6.5 in order to specify the type of the result for an + operation with an imaginary operand. +
+ For most operand types, the value of the result of a binary operator with an imaginary or + complex operand is completely determined, with reference to real arithmetic, by the usual + mathematical formula. For some operand types, the usual mathematical formula is + problematic because of its treatment of infinities and because of undue overflow or + underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is + not completely determined. + + + + + + +
+ If one operand has real type and the other operand has imaginary type, then the result has + imaginary type. If both operands have imaginary type, then the result has real type. (If + either operand has complex type, then the result has complex type.) +
+ If the operands are not both complex, then the result and floating-point exception + behavior of the * operator is defined by the usual mathematical formula: +
+ * u iv u + iv ++ +
+ x xu i(xv) (xu) + i(xv) ++ +
+ iy i(yu) -yv (-yv) + i(yu) ++ +
+ x + iy (xu) + i(yu) (-yv) + i(xv) ++
+ If the second operand is not complex, then the result and floating-point exception + behavior of the / operator is defined by the usual mathematical formula: +
+ / u iv ++ +
+ x x/u i(-x/v) ++ +
+ iy i(y/u) y/v ++ +
+ x + iy (x/u) + i(y/u) (y/v) + i(-x/v) ++
+ The * and / operators satisfy the following infinity properties for all real, imaginary, and + complex operands:364) +
+ If both operands of the * operator are complex or if the second operand of the / operator + is complex, the operator raises floating-point exceptions if appropriate for the calculation + of the parts of the result, and may raise spurious floating-point exceptions. +
+ EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note + that the imaginary unit I has imaginary type (see G.6). + +
+ #include <math.h> + #include <complex.h> + /* Multiply z * w ... */ + double complex _Cmultd(double complex z, double complex w) + { + #pragma STDC FP_CONTRACT OFF + double a, b, c, d, ac, bd, ad, bc, x, y; + a = creal(z); b = cimag(z); + c = creal(w); d = cimag(w); + ac = a * c; bd = b * d; + ad = a * d; bc = b * c; + x = ac - bd; y = ad + bc; + if (isnan(x) && isnan(y)) { + /* Recover infinities that computed as NaN+iNaN ... */ + int recalc = 0; + if ( isinf(a) || isinf(b) ) { // z is infinite + /* "Box" the infinity and change NaNs in the other factor to 0 */ + a = copysign(isinf(a) ? 1.0 : 0.0, a); + b = copysign(isinf(b) ? 1.0 : 0.0, b); + if (isnan(c)) c = copysign(0.0, c); + if (isnan(d)) d = copysign(0.0, d); + recalc = 1; + } + if ( isinf(c) || isinf(d) ) { // w is infinite + /* "Box" the infinity and change NaNs in the other factor to 0 */ + c = copysign(isinf(c) ? 1.0 : 0.0, c); + d = copysign(isinf(d) ? 1.0 : 0.0, d); + if (isnan(a)) a = copysign(0.0, a); + if (isnan(b)) b = copysign(0.0, b); + recalc = 1; + } + if (!recalc && (isinf(ac) || isinf(bd) || + isinf(ad) || isinf(bc))) { + /* Recover infinities from overflow by changing NaNs to 0 ... */ + if (isnan(a)) a = copysign(0.0, a); + if (isnan(b)) b = copysign(0.0, b); + if (isnan(c)) c = copysign(0.0, c); + if (isnan(d)) d = copysign(0.0, d); + recalc = 1; + } + if (recalc) { + x = INFINITY * ( a * c - b * d ); + y = INFINITY * ( a * d + b * c ); + } + } + return x + I * y; + } ++
+ This implementation achieves the required treatment of infinities at the cost of only one isnan test in + ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur. + +
+ EXAMPLE 2 Division of two double _Complex operands could be implemented as follows. + +
+ #include <math.h> + #include <complex.h> + /* Divide z / w ... */ + double complex _Cdivd(double complex z, double complex w) + { + #pragma STDC FP_CONTRACT OFF + double a, b, c, d, logbw, denom, x, y; + int ilogbw = 0; + a = creal(z); b = cimag(z); + c = creal(w); d = cimag(w); + logbw = logb(fmax(fabs(c), fabs(d))); + if (logbw == INFINITY) { + ilogbw = (int)logbw; + c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw); + } + denom = c * c + d * d; + x = scalbn((a * c + b * d) / denom, -ilogbw); + y = scalbn((b * c - a * d) / denom, -ilogbw); + /* Recover infinities and zeros that computed as NaN+iNaN; */ + /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */ + if (isnan(x) && isnan(y)) { + if ((denom == 0.0) && + (!isnan(a) || !isnan(b))) { + x = copysign(INFINITY, c) * a; + y = copysign(INFINITY, c) * b; + } + else if ((isinf(a) || isinf(b)) && + isfinite(c) && isfinite(d)) { + a = copysign(isinf(a) ? 1.0 : 0.0, a); + b = copysign(isinf(b) ? 1.0 : 0.0, b); + x = INFINITY * ( a * c + b * d ); + y = INFINITY * ( b * c - a * d ); + } + else if (isinf(logbw) && + isfinite(a) && isfinite(b)) { + c = copysign(isinf(c) ? 1.0 : 0.0, c); + d = copysign(isinf(d) ? 1.0 : 0.0, d); + x = 0.0 * ( a * c + b * d ); + y = 0.0 * ( b * c - a * d ); + } + } + return x + I * y; + } ++
+ Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than + for multiplication. In the spirit of the multiplication example above, this code does not defend against + overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of + with division, provides better roundoff characteristics. + + +
364) These properties are already implied for those cases covered in the tables, but are required for all cases + (at least where the state for CX_LIMITED_RANGE is ''off''). + + +
+ If both operands have imaginary type, then the result has imaginary type. (If one operand + has real type and the other operand has imaginary type, or if either operand has complex + type, then the result has complex type.) +
+ In all cases the result and floating-point exception behavior of a + or - operator is defined + by the usual mathematical formula: +
+ + or - u iv u + iv ++ +
+ x x(+-)u x (+-) iv (x (+-) u) (+-) iv ++ +
+ iy (+-)u + iy i(y (+-) v) (+-)u + i(y (+-) v) ++ +
+ x + iy (x (+-) u) + iy x + i(y (+-) v) (x (+-) u) + i(y (+-) v) ++ +
+ The macros +
+ imaginary ++ and +
+ _Imaginary_I ++ are defined, respectively, as _Imaginary and a constant expression of type const + float _Imaginary with the value of the imaginary unit. The macro +
+ I ++ is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding + the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro + imaginary. +
+ This subclause contains specifications for the <complex.h> functions that are + particularly suited to IEC 60559 implementations. For families of functions, the + specifications apply to all of the functions even though only the principal function is + + shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument + and the result, the result has the same sign as the argument. +
+ The functions are continuous onto both sides of their branch cuts, taking into account the + sign of zero. For example, csqrt(-2 (+-) i0) = (+-)i(sqrt)2. - +
+ Since complex and imaginary values are composed of real values, each function may be + regarded as computing real values from real values. Except as noted, the functions treat + real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a + manner consistent with the specifications for real functions in F.10.365) +
+ The functions cimag, conj, cproj, and creal are fully specified for all + implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating- + point exceptions. +
+ Each of the functions cabs and carg is specified by a formula in terms of a real + function (whose special cases are covered in annex F): +
+ cabs(x + iy) = hypot(x, y) + carg(x + iy) = atan2(y, x) ++
+ Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by + a formula in terms of other complex functions (whose special cases are specified below): +
+ casin(z) = -i casinh(iz) + catan(z) = -i catanh(iz) + ccos(z) = ccosh(iz) + csin(z) = -i csinh(iz) + ctan(z) = -i ctanh(iz) ++
+ For the other functions, the following subclauses specify behavior for special cases, + including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For + families of functions, the specifications apply to all of the functions even though only the + principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the + specifications for the upper half-plane imply the specifications for the lower half-plane; if + the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the + specifications for the first quadrant imply the specifications for the other three quadrants. +
+ In the following subclauses, cis(y) is defined as cos(y) + i sin(y). + + + + + + +
365) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its + other part is a NaN. + + +
+
+
+
+
+
+
+
+
+
+ The cpow functions raise floating-point exceptions if appropriate for the calculation of + the parts of the result, and may also raise spurious floating-point exceptions.366) + +
366) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding + implementations that treat special cases more carefully. + + +
+
+ Type-generic macros that accept complex arguments also accept imaginary arguments. If + an argument is imaginary, the macro expands to an expression whose type is real, + imaginary, or complex, as appropriate for the particular function: if the argument is + imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the + types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and + the types of the others are complex. +
+ Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh, + sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real + functions: + +
+ cos(iy) = cosh(y) + sin(iy) = i sinh(y) + tan(iy) = i tanh(y) + cosh(iy) = cos(y) + sinh(iy) = i sin(y) + tanh(iy) = i tan(y) + asin(iy) = i asinh(y) + atan(iy) = i atanh(y) + asinh(iy) = i asin(y) + atanh(iy) = i atan(y) ++ +
+ (informative) + Language independent arithmetic ++ +
+ This annex documents the extent to which the C language supports the ISO/IEC 10967-1 + standard for language-independent arithmetic (LIA-1). LIA-1 is more general than + IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics. + +
+ The relevant C arithmetic types meet the requirements of LIA-1 types if an + implementation adds notification of exceptional arithmetic operations and meets the 1 + unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8). + +
+ The LIA-1 data type Boolean is implemented by the C data type bool with values of + true and false, all from <stdbool.h>. + +
+ The signed C integer types int, long int, long long int, and the corresponding + unsigned types are compatible with LIA-1. If an implementation adds support for the + LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are + LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense + in that overflows or out-of-bounds results silently wrap. An implementation that defines + signed integer types as also being modulo need not detect integer overflow, in which case, + only integer divide-by-zero need be detected. +
+ The parameters for the integer data types can be accessed by the following: + maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX, +
+ ULLONG_MAX ++ minint INT_MIN, LONG_MIN, LLONG_MIN +
+ The parameter ''bounded'' is always true, and is not provided. The parameter ''minint'' + is always 0 for the unsigned types, and is not provided for those types. + + +
+ The integer operations on integer types are the following: + addI x + y + subI x - y + mulI x * y + divI, divtI x / y + remI, remtI x % y + negI -x + absI abs(x), labs(x), llabs(x) + eqI x == y + neqI x != y + lssI x < y + leqI x <= y + gtrI x > y + geqI x >= y + where x and y are expressions of the same integer type. + +
+ The C floating-point types float, double, and long double are compatible with + LIA-1. If an implementation adds support for the LIA-1 exceptional values + ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant + with LIA-1. An implementation that uses IEC 60559 floating-point formats and + operations (see annex F) along with IEC 60559 status flags and traps has LIA-1 + conformant types. + +
+ The parameters for a floating point data type can be accessed by the following: + r FLT_RADIX + p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG + emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP + emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP +
+ The derived constants for the floating point types are accessed by the following: + + fmax FLT_MAX, DBL_MAX, LDBL_MAX + fminN FLT_MIN, DBL_MIN, LDBL_MIN + epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON + rnd_style FLT_ROUNDS + +
+ The floating-point operations on floating-point types are the following: + addF x + y + subF x - y + mulF x * y + divF x / y + negF -x + absF fabsf(x), fabs(x), fabsl(x) + exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x) + scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n), +
+ scalblnf(x, li), scalbln(x, li), scalblnl(x, li) ++ intpartF modff(x, &y), modf(x, &y), modfl(x, &y) + fractpartF modff(x, &y), modf(x, &y), modfl(x, &y) + eqF x == y + neqF x != y + lssF x < y + leqF x <= y + gtrF x > y + geqF x >= y + where x and y are expressions of the same floating point type, n is of type int, and li + is of type long int. + +
+ The C Standard requires all floating types to use the same radix and rounding style, so + that only one identifier for each is provided to map to LIA-1. +
+ The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles: + truncate FLT_ROUNDS == 0 + + nearest FLT_ROUNDS == 1 + other FLT_ROUNDS != 0 && FLT_ROUNDS != 1 + provided that an implementation extends FLT_ROUNDS to cover the rounding style used + in all relevant LIA-1 operations, not just addition as in C. + +
+ The LIA-1 type conversions are the following type casts: + cvtI' -> I (int)i, (long int)i, (long long int)i, +
+ (unsigned int)i, (unsigned long int)i, + (unsigned long long int)i ++ cvtF -> I (int)x, (long int)x, (long long int)x, +
+ (unsigned int)x, (unsigned long int)x, + (unsigned long long int)x ++ cvtI -> F (float)i, (double)i, (long double)i + cvtF' -> F (float)x, (double)x, (long double)x +
+ In the above conversions from floating to integer, the use of (cast)x can be replaced with + (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x), + (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer + conversion functions, lrint(), llrint(), lround(), and llround(), can be + used. They all meet LIA-1's requirements on floating to integer rounding for in-range + values. For out-of-range values, the conversions shall silently wrap for the modulo types. +
+ The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g., + fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x), + 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0 + to 65535.0 which can then be cast to unsigned short int. But, the + remainder() function is not useful for doing silent wrapping to signed integer types, + e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the + range -32767.0 to +32768.0 which is not, in general, in the range of signed short + int. +
+ C's conversions (casts) from floating-point to floating-point can meet LIA-1 + requirements if an implementation uses round-to-nearest (IEC 60559 default). +
+ C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an + implementation uses round-to-nearest. + + +
+ Notification is the process by which a user or program is informed that an exceptional + arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C + allows an implementation to cause a notification to occur when any arithmetic operation + returns an exceptional value as defined in LIA-1 clause 5. + +
+ LIA-1 requires at least the following two alternatives for handling of notifications: + setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and- + resume. +
+ An implementation need only support a given notification alternative for the entire + program. An implementation may support the ability to switch between notification + alternatives during execution, but is not required to do so. An implementation can + provide separate selection for each kind of notification, but this is not required. +
+ C allows an implementation to provide notification. C's SIGFPE (for traps) and + FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators) + can provide LIA-1 notification. +
+ C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can + provide trap-and-terminate behavior, except for those LIA-1 operations implemented by + math library function calls. User-provided signal handlers for SIGFPE allow for trap- + and-resume behavior with the same constraint. + +
+ C's <fenv.h> status flags are compatible with the LIA-1 indicators. +
+ The following mapping is for floating-point types: + undefined FE_INVALID, FE_DIVBYZERO + floating_overflow FE_OVERFLOW + underflow FE_UNDERFLOW +
+ The floating-point indicator interrogation and manipulation operations are: + set_indicators feraiseexcept(i) + clear_indicators feclearexcept(i) + test_indicators fetestexcept(i) + current_indicators fetestexcept(FE_ALL_EXCEPT) + where i is an expression of type int representing a subset of the LIA-1 indicators. +
+ C allows an implementation to provide the following LIA-1 required behavior: at + program termination if any indicator is set the implementation shall send an unambiguous + + and ''hard to ignore'' message (see LIA-1 subclause 6.1.2) +
+ LIA-1 does not make the distinction between floating-point and integer for ''undefined''. + This documentation makes that distinction because <fenv.h> covers only the floating- + point indicators. + +
+ C is compatible with LIA-1's trap requirements for arithmetic operations, but not for + math library functions (which are not permitted to invoke a user's signal handler for + SIGFPE). An implementation can provide an alternative of notification through + termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3). +
+ LIA-1 does not require that traps be precise. +
+ C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions, + if there is any signal raised for them. +
+ C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic + exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism + allows trap-and-terminate (either default implementation behavior or user replacement for + it) or trap-and-resume, at the programmer's option. + + +
+ (informative) + Common warnings ++
+ An implementation may generate warnings in many situations, none of which are + specified as part of this International Standard. The following are a few of the more + common situations. +
+
+ (informative) + Portability issues ++
+ This annex collects some information about portability that appears in this International + Standard. + +
+ The following are unspecified: +
+ The behavior is undefined in the following circumstances: +
+ A conforming implementation is required to document its choice of behavior in each of + the areas listed in this subclause. The following are implementation-defined: + + +
+
+
+
+
+
+
+
+
+
+
+
+
+
+ The following characteristics of a hosted environment are locale-specific and are required + to be documented by the implementation: +
+ The following extensions are widely used in many systems, but are not portable to all + implementations. The inclusion of any extension that may cause a strictly conforming + program to become invalid renders an implementation nonconforming. Examples of such + extensions are new keywords, extra library functions declared in standard headers, or + predefined macros with names that do not begin with an underscore. + +
+ In a hosted environment, the main function receives a third argument, char *envp[], + that points to a null-terminated array of pointers to char, each of which points to a string + that provides information about the environment for this execution of the program + (5.1.2.2.1). + +
+ Characters other than the underscore _, letters, and digits, that are not part of the basic + source character set (such as the dollar sign $, or characters in national character sets) + may appear in an identifier (6.4.2). + +
+ All characters in identifiers (with or without external linkage) are significant (6.4.2). + +
+ A function identifier, or the identifier of an object the declaration of which contains the + keyword extern, has file scope (6.2.1). + +
+ String literals are modifiable (in which case, identical string literals should denote distinct + objects) (6.4.5). + + +
+ Additional arithmetic types, such as __int128 or double double, and their + appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have + more range or precision than long double, may be used for evaluating expressions of + other floating types, and may be used to define float_t or double_t. + +
+ A pointer to an object or to void may be cast to a pointer to a function, allowing data to + be invoked as a function (6.5.4). +
+ A pointer to a function may be cast to a pointer to an object or to void, allowing a + function to be inspected or modified (for example, by a debugger) (6.5.4). + +
+ A bit-field may be declared with a type other than _Bool, unsigned int, or + signed int, with an appropriate maximum width (6.7.2.1). + +
+ The fortran function specifier may be used in a function declaration to indicate that + calls suitable for FORTRAN should be generated, or that a different representation for the + external name is to be generated (6.7.4). + +
+ The asm keyword may be used to insert assembly language directly into the translator + output (6.8). The most common implementation is via a statement of the form: +
+ asm ( character-string-literal ); ++ +
+ There may be more than one external definition for the identifier of an object, with or + without the explicit use of the keyword extern; if the definitions disagree, or more than + one is initialized, the behavior is undefined (6.9.2). + +
+ Macro names that do not begin with an underscore, describing the translation and + execution environments, are defined by the implementation before translation begins + (6.10.8). + + +
+ If any floating-point status flags are set on normal termination after all calls to functions + registered by the atexit function have been made (see 7.22.4.4), the implementation + writes some diagnostics indicating the fact to the stderr stream, if it is still open, + +
+ Handlers for specific signals are called with extra arguments in addition to the signal + number (7.14.1.1). + +
+ Additional mappings from files to streams are supported (7.21.2). +
+ Additional file-opening modes may be specified by characters appended to the mode + argument of the fopen function (7.21.5.3). + +
+ The file position indicator is decremented by each successful call to the ungetc or + ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10, + 7.28.3.10). + +
+ Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors + instead of, or in addition to, setting errno or raising floating-point exceptions (7.3, + 7.12). + + +
+ (normative) + Bounds-checking interfaces ++ +
+ Traditionally, the C Library has contained many functions that trust the programmer to + provide output character arrays big enough to hold the result being produced. Not only + do these functions not check that the arrays are big enough, they frequently lack the + information needed to perform such checks. While it is possible to write safe, robust, and + error-free code using the existing library, the library tends to promote programming styles + that lead to mysterious failures if a result is too big for the provided array. +
+ A common programming style is to declare character arrays large enough to handle most + practical cases. However, if these arrays are not large enough to handle the resulting + strings, data can be written past the end of the array overwriting other data and program + structures. The program never gets any indication that a problem exists, and so never has + a chance to recover or to fail gracefully. +
+ Worse, this style of programming has compromised the security of computers and + networks. Buffer overflows can often be exploited to run arbitrary code with the + permissions of the vulnerable (defective) program. +
+ If the programmer writes runtime checks to verify lengths before calling library + functions, then those runtime checks frequently duplicate work done inside the library + functions, which discover string lengths as a side effect of doing their job. +
+ This annex provides alternative library functions that promote safer, more secure + programming. The alternative functions verify that output buffers are large enough for + the intended result and return a failure indicator if they are not. Data is never written past + the end of an array. All string results are null terminated. +
+ This annex also addresses another problem that complicates writing robust code: + functions that are not reentrant because they return pointers to static objects owned by the + function. Such functions can be troublesome since a previously returned result can + change if the function is called again, perhaps by another thread. + + +
+ This annex specifies a series of optional extensions that can be useful in the mitigation of + security vulnerabilities in programs, and comprise new functions, macros, and types + declared or defined in existing standard headers. +
+ An implementation that defines __STDC_LIB_EXT1__ shall conform to the + specifications in this annex.367) +
+ Subclause K.3 should be read as if it were merged into the parallel structure of named + subclauses of clause 7. + +
367) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these + specifications. + + +
+ The functions, macros, and types declared or defined in K.3 and its subclauses are not + declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is + defined as a macro which expands to the integer constant 0 at the point in the source file + where the appropriate header is first included. +
+ The functions, macros, and types declared or defined in K.3 and its subclauses are + declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is + defined as a macro which expands to the integer constant 1 at the point in the source file + where the appropriate header is first included.368) +
+ It is implementation-defined whether the functions, macros, and types declared or defined + in K.3 and its subclauses are declared or defined by their respective headers if + __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file + where the appropriate header is first included.369) +
+ Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be + defined identically for all inclusions of any headers from subclause K.3. If + __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the + implementation shall issue a diagnostic as if a preprocessor error directive were used. + + + + +
368) Future revisions of this International Standard may define meanings for other values of + __STDC_WANT_LIB_EXT1__. + +
369) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in + headers. All other names are not reserved, and a conforming implementation is not permitted to use + them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an + unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the + implementation is not conforming. + + +
+ Each macro name in any of the following subclauses is reserved for use as specified if it + is defined by any of its associated headers when included; unless explicitly stated + otherwise (see 7.1.4). +
+ All identifiers with external linkage in any of the following subclauses are reserved for + use as identifiers with external linkage if any of them are used by the program. None of + them are reserved if none of them are used. +
+ Each identifier with file scope listed in any of the following subclauses is reserved for use + as a macro name and as an identifier with file scope in the same name space if it is + defined by any of its associated headers when included. + +
+ An implementation may set errno for the functions defined in this annex, but is not + required to. + +
+ Most functions in this annex include as part of their specification a list of runtime- + constraints. These runtime-constraints are requirements on the program using the + library.370) +
+ Implementations shall verify that the runtime-constraints for a function are not violated + by the program. If a runtime-constraint is violated, the implementation shall call the + currently registered runtime-constraint handler (see set_constraint_handler_s + in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library + function result in only one call to the runtime-constraint handler. It is unspecified which + one of the multiple runtime-constraint violations cause the handler to be called. +
+ If the runtime-constraints section for a function states an action to be performed when a + runtime-constraint violation occurs, the function shall perform the action before calling + the runtime-constraint handler. If the runtime-constraints section lists actions that are + prohibited when a runtime-constraint violation occurs, then such actions are prohibited to + the function both before calling the handler and after the handler returns. +
+ The runtime-constraint handler might not return. If the handler does return, the library + function whose runtime-constraint was violated shall return some indication of failure as + given by the returns section in the function's specification. + + + + + +
370) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still + exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a + runtime-constraint violation by calling the runtime-constraint handler. This license comes directly + from the definition of undefined behavior. + + +
+ The header <errno.h> defines a type. +
+ The type is +
+ errno_t ++ which is type int.371) + +
371) As a matter of programming style, errno_t may be used as the type of something that deals only + with the values that might be found in errno. For example, a function which returns the value of + errno might be declared as having the return type errno_t. + + +
+ The header <stddef.h> defines a type. +
+ The type is +
+ rsize_t ++ which is the type size_t.372) + +
372) See the description of the RSIZE_MAX macro in <stdint.h>. + + +
+ The header <stdint.h> defines a macro. +
+ The macro is +
+ RSIZE_MAX ++ which expands to a value373) of type size_t. Functions that have parameters of type + rsize_t consider it a runtime-constraint violation if the values of those parameters are + greater than RSIZE_MAX. +
+ Extremely large object sizes are frequently a sign that an object's size was calculated + incorrectly. For example, negative numbers appear as very large positive numbers when + converted to an unsigned type like size_t. Also, some implementations do not support + objects as large as the maximum value that can be represented by type size_t. +
+ For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect + programming errors. For implementations targeting machines with large address spaces, + it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest + object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of + some legitimate, but very large, objects. Implementations targeting machines with small + address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there + + + is no object size that is considered a runtime-constraint violation. + +
373) The macro RSIZE_MAX need not expand to a constant expression. + + +
+ The header <stdio.h> defines several macros and two types. +
+ The macros are +
+ L_tmpnam_s ++ which expands to an integer constant expression that is the size needed for an array of + char large enough to hold a temporary file name string generated by the tmpnam_s + function; +
+ TMP_MAX_S ++ which expands to an integer constant expression that is the maximum number of unique + file names that can be generated by the tmpnam_s function. +
+ The types are +
+ errno_t ++ which is type int; and +
+ rsize_t ++ which is the type size_t. +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + errno_t tmpfile_s(FILE * restrict * restrict streamptr); ++ Runtime-constraints +
+ streamptr shall not be a null pointer. +
+ If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file. +
+ The tmpfile_s function creates a temporary binary file that is different from any other + existing file and that will automatically be removed when it is closed or at program + termination. If the program terminates abnormally, whether an open temporary file is + removed is implementation-defined. The file is opened for update with "wb+" mode + with the meaning that mode has in the fopen_s function (including the mode's effect + on exclusive access and file permissions). + +
+ If the file was created successfully, then the pointer to FILE pointed to by streamptr + will be set to the pointer to the object controlling the opened file. Otherwise, the pointer + to FILE pointed to by streamptr will be set to a null pointer. +
+ The tmpfile_s function returns zero if it created the file. If it did not create the file or + there was a runtime-constraint violation, tmpfile_s returns a nonzero value. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + errno_t tmpnam_s(char *s, rsize_t maxsize); ++ Runtime-constraints +
+ s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX. + maxsize shall be greater than the length of the generated file name string. +
+ The tmpnam_s function generates a string that is a valid file name and that is not the + same as the name of an existing file.374) The function is potentially capable of generating + TMP_MAX_S different strings, but any or all of them may already be in use by existing + files and thus not be suitable return values. The lengths of these strings shall be less than + the value of the L_tmpnam_s macro. +
+ The tmpnam_s function generates a different string each time it is called. +
+ It is assumed that s points to an array of at least maxsize characters. This array will be + set to generated string, as specified below. + + + + +
+ The implementation shall behave as if no library function except tmpnam calls the + tmpnam_s function.375) +
+ After a program obtains a file name using the tmpnam_s function and before the + program creates a file with that name, the possibility exists that someone else may create + a file with that same name. To avoid this race condition, the tmpfile_s function + should be used instead of tmpnam_s when possible. One situation that requires the use + of the tmpnam_s function is when the program needs to create a temporary directory + rather than a temporary file. +
+ If no suitable string can be generated, or if there is a runtime-constraint violation, the + tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize + is greater than zero) and returns a nonzero value. +
+ Otherwise, the tmpnam_s function writes the string in the array pointed to by s and + returns zero. +
+ The value of the macro TMP_MAX_S shall be at least 25. + +
374) Files created using strings generated by the tmpnam_s function are temporary only in the sense that + their names should not collide with those generated by conventional naming rules for the + implementation. It is still necessary to use the remove function to remove such files when their use + is ended, and before program termination. Implementations should take care in choosing the patterns + used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the + race condition and possible conflict when multiple programs run simultaneously by the same user + generate the same temporary file names. + +
375) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming + convention for temporary files), but this is not required. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + errno_t fopen_s(FILE * restrict * restrict streamptr, + const char * restrict filename, + const char * restrict mode); ++ Runtime-constraints +
+ None of streamptr, filename, or mode shall be a null pointer. +
+ If there is a runtime-constraint violation, fopen_s does not attempt to open a file. + Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the + null pointer. + + + + + +
+ The fopen_s function opens the file whose name is the string pointed to by + filename, and associates a stream with it. +
+ The mode string shall be as described for fopen, with the addition that modes starting + with the character 'w' or 'a' may be preceded by the character 'u', see below: + uw truncate to zero length or create text file for writing, default +
+ permissions ++ uwx create text file for writing, default permissions + ua append; open or create text file for writing at end-of-file, default +
+ permissions ++ uwb truncate to zero length or create binary file for writing, default +
+ permissions ++ uwbx create binary file for writing, default permissions + uab append; open or create binary file for writing at end-of-file, default +
+ permissions ++ uw+ truncate to zero length or create text file for update, default +
+ permissions ++ uw+x create text file for update, default permissions + ua+ append; open or create text file for update, writing at end-of-file, +
+ default permissions ++ uw+b or uwb+ truncate to zero length or create binary file for update, default +
+ permissions ++ uw+bx or uwb+x create binary file for update, default permissions + ua+b or uab+ append; open or create binary file for update, writing at end-of-file, +
+ default permissions ++
+ Opening a file with exclusive mode ('x' as the last character in the mode argument) + fails if the file already exists or cannot be created. +
+ To the extent that the underlying system supports the concepts, files opened for writing + shall be opened with exclusive (also known as non-shared) access. If the file is being + created, and the first character of the mode string is not 'u', to the extent that the + underlying system supports it, the file shall have a file permission that prevents other + users on the system from accessing the file. If the file is being created and first character + of the mode string is 'u', then by the time the file has been closed, it shall have the + system default file access permissions.376) +
+ If the file was opened successfully, then the pointer to FILE pointed to by streamptr + will be set to the pointer to the object controlling the opened file. Otherwise, the pointer + + + + to FILE pointed to by streamptr will be set to a null pointer. +
+ The fopen_s function returns zero if it opened the file. If it did not open the file or if + there was a runtime-constraint violation, fopen_s returns a nonzero value. + +
376) These are the same permissions that the file would have been created with by fopen. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + errno_t freopen_s(FILE * restrict * restrict newstreamptr, + const char * restrict filename, + const char * restrict mode, + FILE * restrict stream); ++ Runtime-constraints +
+ None of newstreamptr, mode, and stream shall be a null pointer. +
+ If there is a runtime-constraint violation, freopen_s neither attempts to close any file + associated with stream nor attempts to open a file. Furthermore, if newstreamptr is + not a null pointer, fopen_s sets *newstreamptr to the null pointer. +
+ The freopen_s function opens the file whose name is the string pointed to by + filename and associates the stream pointed to by stream with it. The mode + argument has the same meaning as in the fopen_s function (including the mode's effect + on exclusive access and file permissions). +
+ If filename is a null pointer, the freopen_s function attempts to change the mode of + the stream to that specified by mode, as if the name of the file currently associated with + the stream had been used. It is implementation-defined which changes of mode are + permitted (if any), and under what circumstances. +
+ The freopen_s function first attempts to close any file that is associated with stream. + Failure to close the file is ignored. The error and end-of-file indicators for the stream are + cleared. +
+ If the file was opened successfully, then the pointer to FILE pointed to by + newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE + pointed to by newstreamptr will be set to a null pointer. +
+ The freopen_s function returns zero if it opened the file. If it did not open the file or + there was a runtime-constraint violation, freopen_s returns a nonzero value. + + +
+ Unless explicitly stated otherwise, if the execution of a function described in this + subclause causes copying to take place between objects that overlap, the objects take on + unspecified values. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int fprintf_s(FILE * restrict stream, + const char * restrict format, ...); ++ Runtime-constraints +
+ Neither stream nor format shall be a null pointer. The %n specifier377) (modified or + not by flags, field width, or precision) shall not appear in the string pointed to by + format. Any argument to fprintf_s corresponding to a %s specifier shall not be a + null pointer. +
+ If there is a runtime-constraint violation,378) the fprintf_s function does not attempt + to produce further output, and it is unspecified to what extent fprintf_s produced + output before discovering the runtime-constraint violation. +
+ The fprintf_s function is equivalent to the fprintf function except for the explicit + runtime-constraints listed above. +
+ The fprintf_s function returns the number of characters transmitted, or a negative + value if an output error, encoding error, or runtime-constraint violation occurred. + + + + + + +
377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + +
378) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an + implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- + constraint violation. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int fscanf_s(FILE * restrict stream, + const char * restrict format, ...); ++ Runtime-constraints +
+ Neither stream nor format shall be a null pointer. Any argument indirected though in + order to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation,379) the fscanf_s function does not attempt to + perform further input, and it is unspecified to what extent fscanf_s performed input + before discovering the runtime-constraint violation. +
+ The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion + specifiers apply to a pair of arguments (unless assignment suppression is indicated by a + *). The first of these arguments is the same as for fscanf. That argument is + immediately followed in the argument list by the second argument, which has type + rsize_t and gives the number of elements in the array pointed to by the first argument + of the pair. If the first argument points to a scalar object, it is considered to be an array of + one element.380) +
+ A matching failure occurs if the number of elements in a receiving object is insufficient to + hold the converted input (including any trailing null character). +
+ The fscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + + + fscanf_s function returns the number of input items assigned, which can be fewer than + provided for, or even zero, in the event of an early matching failure. +
+ EXAMPLE 1 The call: +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + /* ... */ + int n, i; float x; char name[50]; + n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50); ++ with the input line: +
+ 25 54.32E-1 thompson ++ will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence + thompson\0. + +
+ EXAMPLE 2 The call: +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + /* ... */ + int n; char s[5]; + n = fscanf_s(stdin, "%s", s, sizeof s); ++ with the input line: +
+ hello ++ will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an + array of six characters to store it. + + +
379) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an + implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- + constraint violation. + +
380) If the format is known at translation time, an implementation may issue a diagnostic for any argument + used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an + argument of a type compatible with rsize_t. A limited amount of checking may be done if even if + the format is not known at translation time. For example, an implementation may issue a diagnostic + for each argument after format that has of type pointer to one of char, signed char, + unsigned char, or void that is not followed by an argument of a type compatible with + rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier + using the hh length modifier, a length argument must follow the pointer argument. Another useful + diagnostic could flag any non-pointer argument following format that did not have a type + compatible with rsize_t. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int printf_s(const char * restrict format, ...); ++ Runtime-constraints +
+ format shall not be a null pointer. The %n specifier381) (modified or not by flags, field + width, or precision) shall not appear in the string pointed to by format. Any argument + to printf_s corresponding to a %s specifier shall not be a null pointer. +
+ If there is a runtime-constraint violation, the printf_s function does not attempt to + produce further output, and it is unspecified to what extent printf_s produced output + before discovering the runtime-constraint violation. + + + +
+ The printf_s function is equivalent to the printf function except for the explicit + runtime-constraints listed above. +
+ The printf_s function returns the number of characters transmitted, or a negative + value if an output error, encoding error, or runtime-constraint violation occurred. + +
381) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int scanf_s(const char * restrict format, ...); ++ Runtime-constraints +
+ format shall not be a null pointer. Any argument indirected though in order to store + converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the scanf_s function does not attempt to + perform further input, and it is unspecified to what extent scanf_s performed input + before discovering the runtime-constraint violation. +
+ The scanf_s function is equivalent to fscanf_s with the argument stdin + interposed before the arguments to scanf_s. +
+ The scanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + scanf_s function returns the number of input items assigned, which can be fewer than + provided for, or even zero, in the event of an early matching failure. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int snprintf_s(char * restrict s, rsize_t n, + const char * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or + precision) shall not appear in the string pointed to by format. Any argument to + + snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding + error shall occur. +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the + null character. +
+ The snprintf_s function is equivalent to the snprintf function except for the + explicit runtime-constraints listed above. +
+ The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the + array pointed to by s. +
+ The snprintf_s function returns the number of characters that would have been + written had n been sufficiently large, not counting the terminating null character, or a + negative value if a runtime-constraint violation occurred. Thus, the null-terminated + output has been completely written if and only if the returned value is nonnegative and + less than n. + +
382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int sprintf_s(char * restrict s, rsize_t n, + const char * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The number of characters (including the trailing null) required for the + result to be written to the array pointed to by s shall not be greater than n. The %n + specifier383) (modified or not by flags, field width, or precision) shall not appear in the + string pointed to by format. Any argument to sprintf_s corresponding to a %s + specifier shall not be a null pointer. No encoding error shall occur. + + + + +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the + null character. +
+ The sprintf_s function is equivalent to the sprintf function except for the + parameter n and the explicit runtime-constraints listed above. +
+ The sprintf_s function, unlike snprintf_s, treats a result too big for the array + pointed to by s as a runtime-constraint violation. +
+ If no runtime-constraint violation occurred, the sprintf_s function returns the number + of characters written in the array, not counting the terminating null character. If an + encoding error occurred, sprintf_s returns a negative value. If any other runtime- + constraint violation occurred, sprintf_s returns zero. + +
383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + int sscanf_s(const char * restrict s, + const char * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. Any argument indirected though in order + to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the sscanf_s function does not attempt to + perform further input, and it is unspecified to what extent sscanf_s performed input + before discovering the runtime-constraint violation. +
+ The sscanf_s function is equivalent to fscanf_s, except that input is obtained from + a string (specified by the argument s) rather than from a stream. Reaching the end of the + string is equivalent to encountering end-of-file for the fscanf_s function. If copying + takes place between objects that overlap, the objects take on unspecified values. +
+ The sscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + sscanf_s function returns the number of input items assigned, which can be fewer than + provided for, or even zero, in the event of an early matching failure. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vfprintf_s(FILE * restrict stream, + const char * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither stream nor format shall be a null pointer. The %n specifier384) (modified or + not by flags, field width, or precision) shall not appear in the string pointed to by + format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a + null pointer. +
+ If there is a runtime-constraint violation, the vfprintf_s function does not attempt to + produce further output, and it is unspecified to what extent vfprintf_s produced + output before discovering the runtime-constraint violation. +
+ The vfprintf_s function is equivalent to the vfprintf function except for the + explicit runtime-constraints listed above. +
+ The vfprintf_s function returns the number of characters transmitted, or a negative + value if an output error, encoding error, or runtime-constraint violation occurred. + +
384) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vfscanf_s(FILE * restrict stream, + const char * restrict format, + va_list arg); ++ + + + + + Runtime-constraints +
+ Neither stream nor format shall be a null pointer. Any argument indirected though in + order to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vfscanf_s function does not attempt to + perform further input, and it is unspecified to what extent vfscanf_s performed input + before discovering the runtime-constraint violation. +
+ The vfscanf_s function is equivalent to fscanf_s, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vfscanf_s function does not invoke the + va_end macro.385) +
+ The vfscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + vfscanf_s function returns the number of input items assigned, which can be fewer + than provided for, or even zero, in the event of an early matching failure. + +
385) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, + vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is + indeterminate. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vprintf_s(const char * restrict format, + va_list arg); ++ Runtime-constraints +
+ format shall not be a null pointer. The %n specifier386) (modified or not by flags, field + width, or precision) shall not appear in the string pointed to by format. Any argument + to vprintf_s corresponding to a %s specifier shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vprintf_s function does not attempt to + produce further output, and it is unspecified to what extent vprintf_s produced output + before discovering the runtime-constraint violation. + + +
+ The vprintf_s function is equivalent to the vprintf function except for the explicit + runtime-constraints listed above. +
+ The vprintf_s function returns the number of characters transmitted, or a negative + value if an output error, encoding error, or runtime-constraint violation occurred. + +
386) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vscanf_s(const char * restrict format, + va_list arg); ++ Runtime-constraints +
+ format shall not be a null pointer. Any argument indirected though in order to store + converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vscanf_s function does not attempt to + perform further input, and it is unspecified to what extent vscanf_s performed input + before discovering the runtime-constraint violation. +
+ The vscanf_s function is equivalent to scanf_s, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vscanf_s function does not invoke the + va_end macro.387) +
+ The vscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + vscanf_s function returns the number of input items assigned, which can be fewer than + provided for, or even zero, in the event of an early matching failure. + + + + + + +
387) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, + vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is + indeterminate. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vsnprintf_s(char * restrict s, rsize_t n, + const char * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The %n specifier388) (modified or not by flags, field width, or + precision) shall not appear in the string pointed to by format. Any argument to + vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding + error shall occur. +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the + null character. +
+ The vsnprintf_s function is equivalent to the vsnprintf function except for the + explicit runtime-constraints listed above. +
+ The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within + the array pointed to by s. +
+ The vsnprintf_s function returns the number of characters that would have been + written had n been sufficiently large, not counting the terminating null character, or a + negative value if a runtime-constraint violation occurred. Thus, the null-terminated + output has been completely written if and only if the returned value is nonnegative and + less than n. + + + + + + +
388) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vsprintf_s(char * restrict s, rsize_t n, + const char * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The number of characters (including the trailing null) required for the + result to be written to the array pointed to by s shall not be greater than n. The %n + specifier389) (modified or not by flags, field width, or precision) shall not appear in the + string pointed to by format. Any argument to vsprintf_s corresponding to a %s + specifier shall not be a null pointer. No encoding error shall occur. +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the + null character. +
+ The vsprintf_s function is equivalent to the vsprintf function except for the + parameter n and the explicit runtime-constraints listed above. +
+ The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array + pointed to by s as a runtime-constraint violation. +
+ If no runtime-constraint violation occurred, the vsprintf_s function returns the + number of characters written in the array, not counting the terminating null character. If + an encoding error occurred, vsprintf_s returns a negative value. If any other + runtime-constraint violation occurred, vsprintf_s returns zero. + + + + + + +
389) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed + at by format when those characters are not a interpreted as a %n specifier. For example, if the entire + format string was %%n. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + int vsscanf_s(const char * restrict s, + const char * restrict format, va_list arg); - int wprintf_s(const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. Any argument indirected though in order + to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vsscanf_s function does not attempt to + perform further input, and it is unspecified to what extent vsscanf_s performed input + before discovering the runtime-constraint violation. +
+ The vsscanf_s function is equivalent to sscanf_s, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vsscanf_s function does not invoke the + va_end macro.390) +
+ The vsscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + vscanf_s function returns the number of input items assigned, which can be fewer than + provided for, or even zero, in the event of an early matching failure. + +
390) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, + vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is + indeterminate. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + char *gets_s(char *s, rsize_t n); ++ + + + + + Runtime-constraints +
+ s shall not be a null pointer. n shall neither be equal to zero nor be greater than + RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading + n-1 characters from stdin.391) +
+ If there is a runtime-constraint violation, s[0] is set to the null character, and characters + are read and discarded from stdin until a new-line character is read, or end-of-file or a + read error occurs. +
+ The gets_s function reads at most one less than the number of characters specified by n + from the stream pointed to by stdin, into the array pointed to by s. No additional + characters are read after a new-line character (which is discarded) or after end-of-file. + The discarded new-line character does not count towards number of characters read. A + null character is written immediately after the last character read into the array. +
+ If end-of-file is encountered and no characters have been read into the array, or if a read + error occurs during the operation, then s[0] is set to the null character, and the other + elements of s take unspecified values. +
+ The fgets function allows properly-written programs to safely process input lines too + long to store in the result array. In general this requires that callers of fgets pay + attention to the presence or absence of a new-line character in the result array. Consider + using fgets (along with any needed processing based on new-line characters) instead of + gets_s. +
+ The gets_s function returns s if successful. If there was a runtime-constraint violation, + or if end-of-file is encountered and no characters have been read into the array, or if a + read error occurs during the operation, then a null pointer is returned. + + + + + + +
391) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for + a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a + one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets + expect such a relationship. + + +
+ The header <stdlib.h> defines three types. +
+ The types are +
+ errno_t ++ which is type int; and +
+ rsize_t ++ which is the type size_t; and +
+ constraint_handler_t ++ which has the following definition +
+ typedef void (*constraint_handler_t)( + const char * restrict msg, + void * restrict ptr, + errno_t error); ++ +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + constraint_handler_t set_constraint_handler_s( + constraint_handler_t handler); ++
+ The set_constraint_handler_s function sets the runtime-constraint handler to + be handler. The runtime-constraint handler is the function to be called when a library + function detects a runtime-constraint violation. Only the most recent handler registered + with set_constraint_handler_s is called when a runtime-constraint violation + occurs. +
+ When the handler is called, it is passed the following arguments in the following order: +
+ The implementation has a default constraint handler that is used if no calls to the + set_constraint_handler_s function have been made. The behavior of the + default handler is implementation-defined, and it may cause the program to exit or abort. +
+ If the handler argument to set_constraint_handler_s is a null pointer, the + implementation default handler becomes the current constraint handler. +
+ The set_constraint_handler_s function returns a pointer to the previously + registered handler.392) + +
392) If the previous handler was registered by calling set_constraint_handler_s with a null + pointer argument, a pointer to the implementation default handler is returned (not NULL). + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + void abort_handler_s( + const char * restrict msg, + void * restrict ptr, + errno_t error); ++
+ A pointer to the abort_handler_s function shall be a suitable argument to the + set_constraint_handler_s function. +
+ The abort_handler_s function writes a message on the standard error stream in an + implementation-defined format. The message shall include the string pointed to by msg. + The abort_handler_s function then calls the abort function.393) +
+ The abort_handler_s function does not return to its caller. + + + + + + +
393) Many implementations invoke a debugger when the abort function is called. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + void ignore_handler_s( + const char * restrict msg, + void * restrict ptr, + errno_t error); ++
+ A pointer to the ignore_handler_s function shall be a suitable argument to the + set_constraint_handler_s function. +
+ The ignore_handler_s function simply returns to its caller.394) +
+ The ignore_handler_s function returns no value. + +
394) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in + which a runtime-constraint violation occurs will return to its caller. The caller can determine whether + a runtime-constraint violation occurred based on the library function's specification (usually, the + library function returns a nonzero errno_t). + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + errno_t getenv_s(size_t * restrict len, + char * restrict value, rsize_t maxsize, + const char * restrict name); ++ Runtime-constraints +
+ name shall not be a null pointer. maxsize shall neither equal zero nor be greater than + RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer. +
+ If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len + is not null), and the environment list is not searched. +
+ The getenv_s function searches an environment list, provided by the host environment, + for a string that matches the string pointed to by name. + + + +
+ If that name is found then getenv_s performs the following actions. If len is not a + null pointer, the length of the string associated with the matched list member is stored in + the integer pointed to by len. If the length of the associated string is less than maxsize, + then the associated string is copied to the array pointed to by value. +
+ If that name is not found then getenv_s performs the following actions. If len is not + a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than + zero, then value[0] is set to the null character. +
+ The set of environment names and the method for altering the environment list are + implementation-defined. +
+ The getenv_s function returns zero if the specified name is found and the associated + string was successfully stored in value. Otherwise, a nonzero value is returned. + +
+ These utilities make use of a comparison function to search or sort arrays of unspecified + type. Where an argument declared as size_t nmemb specifies the length of the array + for a function, if nmemb has the value zero on a call to that function, then the comparison + function is not called, a search finds no matching element, sorting performs no + rearrangement, and the pointer to the array may be null. +
+ The implementation shall ensure that the second argument of the comparison function + (when called from bsearch_s), or both arguments (when called from qsort_s), are + pointers to elements of the array.395) The first argument when called from bsearch_s + shall equal key. +
+ The comparison function shall not alter the contents of either the array or search key. The + implementation may reorder elements of the array between calls to the comparison + function, but shall not otherwise alter the contents of any individual element. +
+ When the same objects (consisting of size bytes, irrespective of their current positions + in the array) are passed more than once to the comparison function, the results shall be + consistent with one another. That is, for qsort_s they shall define a total ordering on + the array, and for bsearch_s the same object shall always compare the same way with + the key. + + + + + +
+ A sequence point occurs immediately before and immediately after each call to the + comparison function, and also between any call to the comparison function and any + movement of the objects passed as arguments to that call. + +
395) That is, if the value passed is p, then the following expressions are always valid and nonzero:
+
+
+ ((char *)p - (char *)base) % size == 0
+ (char *)p >= (char *)base
+ (char *)p < (char *)base + nmemb * size
+
+
+
+
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + void *bsearch_s(const void *key, const void *base, + rsize_t nmemb, rsize_t size, + int (*compar)(const void *k, const void *y, + void *context), + void *context); ++ Runtime-constraints +
+ Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to + zero, then none of key, base, or compar shall be a null pointer. +
+ If there is a runtime-constraint violation, the bsearch_s function does not search the + array. +
+ The bsearch_s function searches an array of nmemb objects, the initial element of + which is pointed to by base, for an element that matches the object pointed to by key. + The size of each element of the array is specified by size. +
+ The comparison function pointed to by compar is called with three arguments. The first + two point to the key object and to an array element, in that order. The function shall + return an integer less than, equal to, or greater than zero if the key object is considered, + respectively, to be less than, to match, or to be greater than the array element. The array + shall consist of: all the elements that compare less than, all the elements that compare + equal to, and all the elements that compare greater than the key object, in that order.396) + The third argument to the comparison function is the context argument passed to + bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison + function.397) + + + + + +
+ The bsearch_s function returns a pointer to a matching element of the array, or a null + pointer if no match is found or there is a runtime-constraint violation. If two elements + compare as equal, which element is matched is unspecified. + +
396) In practice, this means that the entire array has been sorted according to the comparison function. + +
397) The context argument is for the use of the comparison function in performing its duties. For + example, it might specify a collating sequence used by the comparison function. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, + int (*compar)(const void *x, const void *y, + void *context), + void *context); ++ Runtime-constraints +
+ Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to + zero, then neither base nor compar shall be a null pointer. +
+ If there is a runtime-constraint violation, the qsort_s function does not sort the array. +
+ The qsort_s function sorts an array of nmemb objects, the initial element of which is + pointed to by base. The size of each object is specified by size. +
+ The contents of the array are sorted into ascending order according to a comparison + function pointed to by compar, which is called with three arguments. The first two + point to the objects being compared. The function shall return an integer less than, equal + to, or greater than zero if the first argument is considered to be respectively less than, + equal to, or greater than the second. The third argument to the comparison function is the + context argument passed to qsort_s. The sole use of context by qsort_s is to + pass it to the comparison function.398) +
+ If two elements compare as equal, their relative order in the resulting sorted array is + unspecified. +
+ The qsort_s function returns zero if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + + + + + + +
398) The context argument is for the use of the comparison function in performing its duties. For + example, it might specify a collating sequence used by the comparison function. + + +
+ The behavior of the multibyte character functions is affected by the LC_CTYPE category + of the current locale. For a state-dependent encoding, each function is placed into its + initial conversion state by a call for which its character pointer argument, s, is a null + pointer. Subsequent calls with s as other than a null pointer cause the internal conversion + state of the function to be altered as necessary. A call with s as a null pointer causes + these functions to set the int pointed to by their status argument to a nonzero value if + encodings have state dependency, and zero otherwise.399) Changing the LC_CTYPE + category causes the conversion state of these functions to be indeterminate. + +
399) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide + character codes, but are grouped with an adjacent multibyte character. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdlib.h> + errno_t wctomb_s(int * restrict status, + char * restrict s, + rsize_t smax, + wchar_t wc); ++ Runtime-constraints +
+ Let n denote the number of bytes needed to represent the multibyte character + corresponding to the wide character given by wc (including any shift sequences). +
+ If s is not a null pointer, then smax shall not be less than n, and smax shall not be + greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero. +
+ If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to + by status, and if s is not a null pointer, no more than smax elements in the array + pointed to by s will be accessed. +
+ The wctomb_s function determines n and stores the multibyte character representation + of wc in the array whose first element is pointed to by s (if s is not a null pointer). The + number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide + character, a null byte is stored, preceded by any shift sequence needed to restore the + initial shift state, and the function is left in the initial conversion state. +
+ The implementation shall behave as if no library function calls the wctomb_s function. + + + + + +
+ If s is a null pointer, the wctomb_s function stores into the int pointed to by status a + nonzero or zero value, if multibyte character encodings, respectively, do or do not have + state-dependent encodings. +
+ If s is not a null pointer, the wctomb_s function stores into the int pointed to by + status either n or -1 if wc, respectively, does or does not correspond to a valid + multibyte character. +
+ In no case will the int pointed to by status be set to a value greater than the + MB_CUR_MAX macro. +
+ The wctomb_s function returns zero if successful, and a nonzero value if there was a + runtime-constraint violation or wc did not correspond to a valid multibyte character. + +
+ The behavior of the multibyte string functions is affected by the LC_CTYPE category of + the current locale. + +
+
+ #include <stdlib.h> + errno_t mbstowcs_s(size_t * restrict retval, + wchar_t * restrict dst, rsize_t dstmax, + const char * restrict src, rsize_t len); ++ Runtime-constraints +
+ Neither retval nor src shall be a null pointer. If dst is not a null pointer, then + neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, + then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal + zero. If dst is not a null pointer and len is not less than dstmax, then a null character + shall occur within the first dstmax multibyte characters of the array pointed to by src. +
+ If there is a runtime-constraint violation, then mbstowcs_s does the following. If + retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If + dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, + then mbstowcs_s sets dst[0] to the null wide character. +
+ The mbstowcs_s function converts a sequence of multibyte characters that begins in + the initial shift state from the array pointed to by src into a sequence of corresponding + wide characters. If dst is not a null pointer, the converted characters are stored into the + array pointed to by dst. Conversion continues up to and including a terminating null + character, which is also stored. Conversion stops earlier in two cases: when a sequence of + + bytes is encountered that does not form a valid multibyte character, or (if dst is not a + null pointer) when len wide characters have been stored into the array pointed to by + dst.400) If dst is not a null pointer and no null wide character was stored into the array + pointed to by dst, then dst[len] is set to the null wide character. Each conversion + takes place as if by a call to the mbrtowc function. +
+ Regardless of whether dst is or is not a null pointer, if the input conversion encounters a + sequence of bytes that do not form a valid multibyte character, an encoding error occurs: + the mbstowcs_s function stores the value (size_t)(-1) into *retval. + Otherwise, the mbstowcs_s function stores into *retval the number of multibyte + characters successfully converted, not including the terminating null character (if any). +
+ All elements following the terminating null wide character (if any) written by + mbstowcs_s in the array of dstmax wide characters pointed to by dst take + unspecified values when mbstowcs_s returns.401) +
+ If copying takes place between objects that overlap, the objects take on unspecified + values. +
+ The mbstowcs_s function returns zero if no runtime-constraint violation and no + encoding error occurred. Otherwise, a nonzero value is returned. + +
400) Thus, the value of len is ignored if dst is a null pointer. + +
401) This allows an implementation to attempt converting the multibyte string before discovering a + terminating null character did not occur where required. + + +
+
+ #include <stdlib.h> + errno_t wcstombs_s(size_t * restrict retval, + char * restrict dst, rsize_t dstmax, + const wchar_t * restrict src, rsize_t len); ++ Runtime-constraints +
+ Neither retval nor src shall be a null pointer. If dst is not a null pointer, then + neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, + then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal + zero. If dst is not a null pointer and len is not less than dstmax, then the conversion + shall have been stopped (see below) because a terminating null wide character was + reached or because an encoding error occurred. + + + + + +
+ If there is a runtime-constraint violation, then wcstombs_s does the following. If + retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If + dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, + then wcstombs_s sets dst[0] to the null character. +
+ The wcstombs_s function converts a sequence of wide characters from the array + pointed to by src into a sequence of corresponding multibyte characters that begins in + the initial shift state. If dst is not a null pointer, the converted characters are then stored + into the array pointed to by dst. Conversion continues up to and including a terminating + null wide character, which is also stored. Conversion stops earlier in two cases: +
+ Regardless of whether dst is or is not a null pointer, if the input conversion encounters a + wide character that does not correspond to a valid multibyte character, an encoding error + occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval. + Otherwise, the wcstombs_s function stores into *retval the number of bytes in the + resulting multibyte character sequence, not including the terminating null character (if + any). +
+ All elements following the terminating null character (if any) written by wcstombs_s + in the array of dstmax elements pointed to by dst take unspecified values when + wcstombs_s returns.403) +
+ If copying takes place between objects that overlap, the objects take on unspecified + values. + + + +
+ The wcstombs_s function returns zero if no runtime-constraint violation and no + encoding error occurred. Otherwise, a nonzero value is returned. + +
402) If conversion stops because a terminating null wide character has been reached, the bytes stored + include those necessary to reach the initial shift state immediately before the null byte. However, if + the conversion stops before a terminating null wide character has been reached, the result will be null + terminated, but might not end in the initial shift state. + +
403) When len is not less than dstmax, the implementation might fill the array before discovering a + runtime-constraint violation. + + +
+ The header <string.h> defines two types. +
+ The types are +
+ errno_t ++ which is type int; and +
+ rsize_t ++ which is the type size_t. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t memcpy_s(void * restrict s1, rsize_t s1max, + const void * restrict s2, rsize_t n); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between + objects that overlap. +
+ If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first + s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is + not greater than RSIZE_MAX. +
+ The memcpy_s function copies n characters from the object pointed to by s2 into the + object pointed to by s1. +
+ The memcpy_s function returns zero if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t memmove_s(void *s1, rsize_t s1max, + const void *s2, rsize_t n); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. n shall not be greater than s1max. +
+ If there is a runtime-constraint violation, the memmove_s function stores zeros in the + first s1max characters of the object pointed to by s1 if s1 is not a null pointer and + s1max is not greater than RSIZE_MAX. +
+ The memmove_s function copies n characters from the object pointed to by s2 into the + object pointed to by s1. This copying takes place as if the n characters from the object + pointed to by s2 are first copied into a temporary array of n characters that does not + overlap the objects pointed to by s1 or s2, and then the n characters from the temporary + array are copied into the object pointed to by s1. +
+ The memmove_s function returns zero if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t strcpy_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. + s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max). + Copying shall not take place between objects that overlap. +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the + null character. + +
+ The strcpy_s function copies the string pointed to by s2 (including the terminating + null character) into the array pointed to by s1. +
+ All elements following the terminating null character (if any) written by strcpy_s in + the array of s1max characters pointed to by s1 take unspecified values when + strcpy_s returns.404) +
+ The strcpy_s function returns zero405) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + +
404) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if + any of those characters are null. Such an approach might write a character to every element of s1 + before discovering that the first element should be set to the null character. + +
405) A zero return value implies that all of the requested characters from the string pointed to by s2 fit + within the array pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t strncpy_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2, + rsize_t n); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max + shall be greater than strnlen_s(s2, s1max). Copying shall not take place between + objects that overlap. +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the + null character. +
+ The strncpy_s function copies not more than n successive characters (characters that + follow a null character are not copied) from the array pointed to by s2 to the array + pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null + character. + + + +
+ All elements following the terminating null character (if any) written by strncpy_s in + the array of s1max characters pointed to by s1 take unspecified values when + strncpy_s returns.406) +
+ The strncpy_s function returns zero407) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. +
+ EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result + will not be null terminated or that characters will be written past the end of the destination array. +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + /* ... */ + char src1[100] = "hello"; + char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'}; + char dst1[6], dst2[5], dst3[5]; + int r1, r2, r3; + r1 = strncpy_s(dst1, 6, src1, 100); + r2 = strncpy_s(dst2, 5, src2, 7); + r3 = strncpy_s(dst3, 5, src2, 4); ++ The first call will assign to r1 the value zero and to dst1 the sequence hello\0. + The second call will assign to r2 a nonzero value and to dst2 the sequence \0. + The third call will assign to r3 the value zero and to dst3 the sequence good\0. + + +
406) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if + any of those characters are null. Such an approach might write a character to every element of s1 + before discovering that the first element should be set to the null character. + +
407) A zero return value implies that all of the requested characters from the string pointed to by s2 fit + within the array pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t strcat_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2); ++ Runtime-constraints +
+ Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to + strcat_s. + + + + + +
+ Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. + s1max shall not equal zero. m shall not equal zero.408) m shall be greater than + strnlen_s(s2, m). Copying shall not take place between objects that overlap. +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the + null character. +
+ The strcat_s function appends a copy of the string pointed to by s2 (including the + terminating null character) to the end of the string pointed to by s1. The initial character + from s2 overwrites the null character at the end of s1. +
+ All elements following the terminating null character (if any) written by strcat_s in + the array of s1max characters pointed to by s1 take unspecified values when + strcat_s returns.409) +
+ The strcat_s function returns zero410) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + +
408) Zero means that s1 was not null terminated upon entry to strcat_s. + +
409) This allows an implementation to append characters from s2 to s1 while simultaneously checking if + any of those characters are null. Such an approach might write a character to every element of s1 + before discovering that the first element should be set to the null character. + +
410) A zero return value implies that all of the requested characters from the string pointed to by s2 were + appended to the string pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t strncat_s(char * restrict s1, + rsize_t s1max, + const char * restrict s2, + rsize_t n); ++ Runtime-constraints +
+ Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to + strncat_s. +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.411) If n is not less + + + + than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take + place between objects that overlap. +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the + null character. +
+ The strncat_s function appends not more than n successive characters (characters + that follow a null character are not copied) from the array pointed to by s2 to the end of + the string pointed to by s1. The initial character from s2 overwrites the null character at + the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to + a null character. +
+ All elements following the terminating null character (if any) written by strncat_s in + the array of s1max characters pointed to by s1 take unspecified values when + strncat_s returns.412) +
+ The strncat_s function returns zero413) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. +
+ EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result + will not be null terminated or that characters will be written past the end of the destination array. +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + /* ... */ + char s1[100] = "good"; + char s2[6] = "hello"; + char s3[6] = "hello"; + char s4[7] = "abc"; + char s5[1000] = "bye"; + int r1, r2, r3, r4; + r1 = strncat_s(s1, 100, s5, 1000); + r2 = strncat_s(s2, 6, "", 1); + r3 = strncat_s(s3, 6, "X", 2); + r4 = strncat_s(s4, 7, "defghijklmn", 3); ++ After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0. + + + + + After the second call r2 will have the value zero and s2 will contain the sequence hello\0. + After the third call r3 will have a nonzero value and s3 will contain the sequence \0. + After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0. + + +
411) Zero means that s1 was not null terminated upon entry to strncat_s. + +
412) This allows an implementation to append characters from s2 to s1 while simultaneously checking if + any of those characters are null. Such an approach might write a character to every element of s1 + before discovering that the first element should be set to the null character. + +
413) A zero return value implies that all of the requested characters from the string pointed to by s2 were + appended to the string pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + char *strtok_s(char * restrict s1, + rsize_t * restrict s1max, + const char * restrict s2, + char ** restrict ptr); ++ Runtime-constraints +
+ None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr + shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. + The end of the token found shall occur within the first *s1max characters of s1 for the + first call, and shall occur within the first *s1max characters of where searching resumes + on subsequent calls. +
+ If there is a runtime-constraint violation, the strtok_s function does not indirect + through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. +
+ A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a + sequence of tokens, each of which is delimited by a character from the string pointed to + by s2. The fourth argument points to a caller-provided char pointer into which the + strtok_s function stores information necessary for it to continue scanning the same + string. +
+ The first call in a sequence has a non-null first argument and s1max points to an object + whose value is the number of elements in the character array pointed to by the first + argument. The first call stores an initial value in the object pointed to by ptr and + updates the value pointed to by s1max to reflect the number of elements that remain in + relation to ptr. Subsequent calls in the sequence have a null first argument and the + objects pointed to by s1max and ptr are required to have the values stored by the + previous call in the sequence, which are then updated. The separator string pointed to by + s2 may be different from call to call. +
+ The first call in the sequence searches the string pointed to by s1 for the first character + that is not contained in the current separator string pointed to by s2. If no such character + is found, then there are no tokens in the string pointed to by s1 and the strtok_s + function returns a null pointer. If such a character is found, it is the start of the first token. + +
+ The strtok_s function then searches from there for the first character in s1 that is + contained in the current separator string. If no such character is found, the current token + extends to the end of the string pointed to by s1, and subsequent searches in the same + string for a token return a null pointer. If such a character is found, it is overwritten by a + null character, which terminates the current token. +
+ In all cases, the strtok_s function stores sufficient information in the pointer pointed + to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer + value for ptr, shall start searching just past the element overwritten by a null character + (if any). +
+ The strtok_s function returns a pointer to the first character of a token, or a null + pointer if there is no token or there is a runtime-constraint violation. +
+ EXAMPLE +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + static char str1[] = "?a???b,,,#c"; + static char str2[] = "\t \t"; + char *t, *ptr1, *ptr2; + rsize_t max1 = sizeof(str1); + rsize_t max2 = sizeof(str2); + t = strtok_s(str1, &max1, "?", &ptr1); // t points to the token "a" + t = strtok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b" + t = strtok_s(str2, &max2, " \t", &ptr2); // t is a null pointer + t = strtok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c" + t = strtok_s(NULL, &max1, "?", &ptr1); // t is a null pointer ++ + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) ++ Runtime-constraints +
+ s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n + shall not be greater than smax. +
+ If there is a runtime-constraint violation, then if s is not a null pointer and smax is not + greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an + unsigned char) into each of the first smax characters of the object pointed to by s. + +
+ The memset_s function copies the value of c (converted to an unsigned char) into + each of the first n characters of the object pointed to by s. Unlike memset, any call to + the memset_s function shall be evaluated strictly according to the rules of the abstract + machine as described in (5.1.2.3). That is, any call to the memset_s function shall + assume that the memory indicated by s and n may be accessible in the future and thus + must contain the values indicated by c. +
+ The memset_s function returns zero if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + errno_t strerror_s(char *s, rsize_t maxsize, + errno_t errnum); ++ Runtime-constraints +
+ s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX. + maxsize shall not equal zero. +
+ If there is a runtime-constraint violation, then the array (if any) pointed to by s is not + modified. +
+ The strerror_s function maps the number in errnum to a locale-specific message + string. Typically, the values for errnum come from errno, but strerror_s shall + map any value of type int to a message. +
+ If the length of the desired string is less than maxsize, then the string is copied to the + array pointed to by s. +
+ Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied + from the string to the array pointed to by s and then s[maxsize-1] is set to the null + character. Then, if maxsize is greater than 3, then s[maxsize-2], + s[maxsize-3], and s[maxsize-4] are set to the character period (.). +
+ The strerror_s function returns zero if the length of the desired string was less than + maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s + function returns a nonzero value. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + size_t strerrorlen_s(errno_t errnum); ++
+ The strerrorlen_s function calculates the length of the (untruncated) locale-specific + message string that the strerror_s function maps to errnum. +
+ The strerrorlen_s function returns the number of characters (not including the null + character) in the full message string. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <string.h> + size_t strnlen_s(const char *s, size_t maxsize); ++
+ The strnlen_s function computes the length of the string pointed to by s. +
+ If s is a null pointer,414) then the strnlen_s function returns zero. +
+ Otherwise, the strnlen_s function returns the number of characters that precede the + terminating null character. If there is no null character in the first maxsize characters of + s then strnlen_s returns maxsize. At most the first maxsize characters of s shall + be accessed by strnlen_s. + + + + + + +
414) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints + along with the values returned for a null pointer or an unterminated string argument make + strnlen_s useful in algorithms that gracefully handle such exceptional data. + + +
+ The header <time.h> defines two types. +
+ The types are +
+ errno_t ++ which is type int; and +
+ rsize_t ++ which is the type size_t. + +
+ A broken-down time is normalized if the values of the members of the tm structure are in + their normal rages.415) + +
415) The normal ranges are defined in 7.26.1. + + +
+ Like the strftime function, the asctime_s and ctime_s functions do not return a + pointer to a static object, and other library functions are permitted to call them. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <time.h> + errno_t asctime_s(char *s, rsize_t maxsize, + const struct tm *timeptr); ++ Runtime-constraints +
+ Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and + shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr + shall be normalized. The calendar year represented by the broken-down time pointed to + by timeptr shall not be less than calendar year 0 and shall not be greater than calendar + year 9999. +
+ If there is a runtime-constraint violation, there is no attempt to convert the time, and + s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is + not greater than RSIZE_MAX. +
+ The asctime_s function converts the normalized broken-down time in the structure + pointed to by timeptr into a 26 character (including the null character) string in the + + + + form +
+ Sun Sep 16 01:03:52 1973\n\0 ++ The fields making up this string are (in order): +
+ The asctime_s function returns zero if the time was successfully converted and stored + into the array pointed to by s. Otherwise, it returns a nonzero value. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <time.h> + errno_t ctime_s(char *s, rsize_t maxsize, + const time_t *timer); ++ Runtime-constraints +
+ Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and + shall not be greater than RSIZE_MAX. +
+ If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null + pointer and maxsize is not equal zero and is not greater than RSIZE_MAX. +
+ The ctime_s function converts the calendar time pointed to by timer to local time in + the form of a string. It is equivalent to +
+ asctime_s(s, maxsize, localtime_s(timer)) ++
+ The ctime_s function returns zero if the time was successfully converted and stored + into the array pointed to by s. Otherwise, it returns a nonzero value. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <time.h> + struct tm *gmtime_s(const time_t * restrict timer, + struct tm * restrict result); ++ Runtime-constraints +
+ Neither timer nor result shall be a null pointer. +
+ If there is a runtime-constraint violation, there is no attempt to convert the time. +
+ The gmtime_s function converts the calendar time pointed to by timer into a broken- + down time, expressed as UTC. The broken-down time is stored in the structure pointed + + to by result. +
+ The gmtime_s function returns result, or a null pointer if the specified time cannot + be converted to UTC or there is a runtime-constraint violation. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <time.h> + struct tm *localtime_s(const time_t * restrict timer, + struct tm * restrict result); ++ Runtime-constraints +
+ Neither timer nor result shall be a null pointer. +
+ If there is a runtime-constraint violation, there is no attempt to convert the time. +
+ The localtime_s function converts the calendar time pointed to by timer into a + broken-down time, expressed as local time. The broken-down time is stored in the + structure pointed to by result. +
+ The localtime_s function returns result, or a null pointer if the specified time + cannot be converted to local time or there is a runtime-constraint violation. + +
+ The header <wchar.h> defines two types. +
+ The types are +
+ errno_t ++ which is type int; and +
+ rsize_t ++ which is the type size_t. +
+ Unless explicitly stated otherwise, if the execution of a function described in this + subclause causes copying to take place between objects that overlap, the objects take on + unspecified values. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + int fwprintf_s(FILE * restrict stream, + const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ Neither stream nor format shall be a null pointer. The %n specifier416) (modified or + not by flags, field width, or precision) shall not appear in the wide string pointed to by + format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a + null pointer. +
+ If there is a runtime-constraint violation, the fwprintf_s function does not attempt to + produce further output, and it is unspecified to what extent fwprintf_s produced + output before discovering the runtime-constraint violation. +
+ The fwprintf_s function is equivalent to the fwprintf function except for the + explicit runtime-constraints listed above. +
+ The fwprintf_s function returns the number of wide characters transmitted, or a + negative value if an output error, encoding error, or runtime-constraint violation occurred. + +
416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdio.h> + #include <wchar.h> + int fwscanf_s(FILE * restrict stream, + const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ Neither stream nor format shall be a null pointer. Any argument indirected though in + order to store converted input shall not be a null pointer. + + + +
+ If there is a runtime-constraint violation, the fwscanf_s function does not attempt to + perform further input, and it is unspecified to what extent fwscanf_s performed input + before discovering the runtime-constraint violation. +
+ The fwscanf_s function is equivalent to fwscanf except that the c, s, and [ + conversion specifiers apply to a pair of arguments (unless assignment suppression is + indicated by a *). The first of these arguments is the same as for fwscanf. That + argument is immediately followed in the argument list by the second argument, which has + type size_t and gives the number of elements in the array pointed to by the first + argument of the pair. If the first argument points to a scalar object, it is considered to be + an array of one element.417) +
+ A matching failure occurs if the number of elements in a receiving object is insufficient to + hold the converted input (including any trailing null character). +
+ The fwscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + fwscanf_s function returns the number of input items assigned, which can be fewer + than provided for, or even zero, in the event of an early matching failure. + +
417) If the format is known at translation time, an implementation may issue a diagnostic for any argument + used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an + argument of a type compatible with rsize_t. A limited amount of checking may be done if even if + the format is not known at translation time. For example, an implementation may issue a diagnostic + for each argument after format that has of type pointer to one of char, signed char, + unsigned char, or void that is not followed by an argument of a type compatible with + rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier + using the hh length modifier, a length argument must follow the pointer argument. Another useful + diagnostic could flag any non-pointer argument following format that did not have a type + compatible with rsize_t. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + int snwprintf_s(wchar_t * restrict s, + rsize_t n, + const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The %n specifier418) (modified or not by flags, field width, or + + + precision) shall not appear in the wide string pointed to by format. Any argument to + snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding + error shall occur. +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the + null wide character. +
+ The snwprintf_s function is equivalent to the swprintf function except for the + explicit runtime-constraints listed above. +
+ The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within + the array pointed to by s. +
+ The snwprintf_s function returns the number of wide characters that would have + been written had n been sufficiently large, not counting the terminating wide null + character, or a negative value if a runtime-constraint violation occurred. Thus, the null- + terminated output has been completely written if and only if the returned value is + nonnegative and less than n. + +
418) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + int swprintf_s(wchar_t * restrict s, rsize_t n, + const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The number of wide characters (including the trailing null) required + for the result to be written to the array pointed to by s shall not be greater than n. The %n + specifier419) (modified or not by flags, field width, or precision) shall not appear in the + wide string pointed to by format. Any argument to swprintf_s corresponding to a + %s specifier shall not be a null pointer. No encoding error shall occur. + + + +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the + null wide character. +
+ The swprintf_s function is equivalent to the swprintf function except for the + explicit runtime-constraints listed above. +
+ The swprintf_s function, unlike snwprintf_s, treats a result too big for the array + pointed to by s as a runtime-constraint violation. +
+ If no runtime-constraint violation occurred, the swprintf_s function returns the + number of wide characters written in the array, not counting the terminating null wide + character. If an encoding error occurred or if n or more wide characters are requested to + be written, swprintf_s returns a negative value. If any other runtime-constraint + violation occurred, swprintf_s returns zero. + +
419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + int swscanf_s(const wchar_t * restrict s, + const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. Any argument indirected though in order + to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the swscanf_s function does not attempt to + perform further input, and it is unspecified to what extent swscanf_s performed input + before discovering the runtime-constraint violation. +
+ The swscanf_s function is equivalent to fwscanf_s, except that the argument s + specifies a wide string from which the input is to be obtained, rather than from a stream. + Reaching the end of the wide string is equivalent to encountering end-of-file for the + fwscanf_s function. +
+ The swscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + swscanf_s function returns the number of input items assigned, which can be fewer + than provided for, or even zero, in the event of an early matching failure. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + #include <wchar.h> + int vfwprintf_s(FILE * restrict stream, + const wchar_t * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither stream nor format shall be a null pointer. The %n specifier420) (modified or + not by flags, field width, or precision) shall not appear in the wide string pointed to by + format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be + a null pointer. +
+ If there is a runtime-constraint violation, the vfwprintf_s function does not attempt + to produce further output, and it is unspecified to what extent vfwprintf_s produced + output before discovering the runtime-constraint violation. +
+ The vfwprintf_s function is equivalent to the vfwprintf function except for the + explicit runtime-constraints listed above. +
+ The vfwprintf_s function returns the number of wide characters transmitted, or a + negative value if an output error, encoding error, or runtime-constraint violation occurred. + +
420) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <stdio.h> + #include <wchar.h> + int vfwscanf_s(FILE * restrict stream, + const wchar_t * restrict format, va_list arg); ++ + + + + Runtime-constraints +
+ Neither stream nor format shall be a null pointer. Any argument indirected though in + order to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to + perform further input, and it is unspecified to what extent vfwscanf_s performed input + before discovering the runtime-constraint violation. +
+ The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument + list replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the + va_end macro.421) +
+ The vfwscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + vfwscanf_s function returns the number of input items assigned, which can be fewer + than provided for, or even zero, in the event of an early matching failure. + +
421) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the + value of arg after the return is indeterminate. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <wchar.h> + int vsnwprintf_s(wchar_t * restrict s, + rsize_t n, + const wchar_t * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The %n specifier422) (modified or not by flags, field width, or + precision) shall not appear in the wide string pointed to by format. Any argument to + vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No + encoding error shall occur. + + +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to + the null wide character. +
+ The vsnwprintf_s function is equivalent to the vswprintf function except for the + explicit runtime-constraints listed above. +
+ The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit + within the array pointed to by s. +
+ The vsnwprintf_s function returns the number of wide characters that would have + been written had n been sufficiently large, not counting the terminating null character, or + a negative value if a runtime-constraint violation occurred. Thus, the null-terminated + output has been completely written if and only if the returned value is nonnegative and + less than n. + +
422) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <wchar.h> + int vswprintf_s(wchar_t * restrict s, + rsize_t n, + const wchar_t * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater + than RSIZE_MAX. The number of wide characters (including the trailing null) required + for the result to be written to the array pointed to by s shall not be greater than n. The %n + specifier423) (modified or not by flags, field width, or precision) shall not appear in the + wide string pointed to by format. Any argument to vswprintf_s corresponding to a + %s specifier shall not be a null pointer. No encoding error shall occur. +
+ If there is a runtime-constraint violation, then if s is not a null pointer and n is greater + than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the + null wide character. + + +
+ The vswprintf_s function is equivalent to the vswprintf function except for the + explicit runtime-constraints listed above. +
+ The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the + array pointed to by s as a runtime-constraint violation. +
+ If no runtime-constraint violation occurred, the vswprintf_s function returns the + number of wide characters written in the array, not counting the terminating null wide + character. If an encoding error occurred or if n or more wide characters are requested to + be written, vswprintf_s returns a negative value. If any other runtime-constraint + violation occurred, vswprintf_s returns zero. + +
423) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <wchar.h> + int vswscanf_s(const wchar_t * restrict s, + const wchar_t * restrict format, + va_list arg); ++ Runtime-constraints +
+ Neither s nor format shall be a null pointer. Any argument indirected though in order + to store converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vswscanf_s function does not attempt to + perform further input, and it is unspecified to what extent vswscanf_s performed input + before discovering the runtime-constraint violation. +
+ The vswscanf_s function is equivalent to swscanf_s, with the variable argument + list replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vswscanf_s function does not invoke the + va_end macro.424) + + + + + +
+ The vswscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + vswscanf_s function returns the number of input items assigned, which can be fewer + than provided for, or even zero, in the event of an early matching failure. + +
424) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the + value of arg after the return is indeterminate. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <wchar.h> + int vwprintf_s(const wchar_t * restrict format, + va_list arg); ++ Runtime-constraints +
+ format shall not be a null pointer. The %n specifier425) (modified or not by flags, field + width, or precision) shall not appear in the wide string pointed to by format. Any + argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vwprintf_s function does not attempt to + produce further output, and it is unspecified to what extent vwprintf_s produced + output before discovering the runtime-constraint violation. +
+ The vwprintf_s function is equivalent to the vwprintf function except for the + explicit runtime-constraints listed above. +
+ The vwprintf_s function returns the number of wide characters transmitted, or a + negative value if an output error, encoding error, or runtime-constraint violation occurred. + + + + + + +
425) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <stdarg.h> + #include <wchar.h> + int vwscanf_s(const wchar_t * restrict format, + va_list arg); ++ Runtime-constraints +
+ format shall not be a null pointer. Any argument indirected though in order to store + converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the vwscanf_s function does not attempt to + perform further input, and it is unspecified to what extent vwscanf_s performed input + before discovering the runtime-constraint violation. +
+ The vwscanf_s function is equivalent to wscanf_s, with the variable argument list + replaced by arg, which shall have been initialized by the va_start macro (and + possibly subsequent va_arg calls). The vwscanf_s function does not invoke the + va_end macro.426) +
+ The vwscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + vwscanf_s function returns the number of input items assigned, which can be fewer + than provided for, or even zero, in the event of an early matching failure. + +
426) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the + value of arg after the return is indeterminate. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + int wprintf_s(const wchar_t * restrict format, ...); ++ Runtime-constraints +
+ format shall not be a null pointer. The %n specifier427) (modified or not by flags, field + + + width, or precision) shall not appear in the wide string pointed to by format. Any + argument to wprintf_s corresponding to a %s specifier shall not be a null pointer. +
+ If there is a runtime-constraint violation, the wprintf_s function does not attempt to + produce further output, and it is unspecified to what extent wprintf_s produced output + before discovering the runtime-constraint violation. +
+ The wprintf_s function is equivalent to the wprintf function except for the explicit + runtime-constraints listed above. +
+ The wprintf_s function returns the number of wide characters transmitted, or a + negative value if an output error, encoding error, or runtime-constraint violation occurred. + +
427) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide + string pointed at by format when those wide characters are not a interpreted as a %n specifier. For + example, if the entire format string was L"%%n". + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> int wscanf_s(const wchar_t * restrict format, ...); - errno_t wcscpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - errno_t wcsncpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - errno_t wmemcpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); ++ Runtime-constraints +
+ format shall not be a null pointer. Any argument indirected though in order to store + converted input shall not be a null pointer. +
+ If there is a runtime-constraint violation, the wscanf_s function does not attempt to + perform further input, and it is unspecified to what extent wscanf_s performed input + before discovering the runtime-constraint violation. +
+ The wscanf_s function is equivalent to fwscanf_s with the argument stdin + interposed before the arguments to wscanf_s. +
+ The wscanf_s function returns the value of the macro EOF if an input failure occurs + before any conversion or if there is a runtime-constraint violation. Otherwise, the + wscanf_s function returns the number of input items assigned, which can be fewer than + provided for, or even zero, in the event of an early matching failure. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + errno_t wcscpy_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. + s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max). + Copying shall not take place between objects that overlap. +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the + null wide character. +
+ The wcscpy_s function copies the wide string pointed to by s2 (including the + terminating null wide character) into the array pointed to by s1. +
+ All elements following the terminating null wide character (if any) written by + wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified + values when wcscpy_s returns.428) +
+ The wcscpy_s function returns zero429) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + + + + + + +
428) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking + if any of those wide characters are null. Such an approach might write a wide character to every + element of s1 before discovering that the first element should be set to the null wide character. + +
429) A zero return value implies that all of the requested wide characters from the string pointed to by s2 + fit within the array pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + errno_t wcsncpy_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2, + rsize_t n); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max + shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between + objects that overlap. +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the + null wide character. +
+ The wcsncpy_s function copies not more than n successive wide characters (wide + characters that follow a null wide character are not copied) from the array pointed to by + s2 to the array pointed to by s1. If no null wide character was copied from s2, then + s1[n] is set to a null wide character. +
+ All elements following the terminating null wide character (if any) written by + wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified + values when wcsncpy_s returns.430) +
+ The wcsncpy_s function returns zero431) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. +
+ EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the + result will not be null terminated or that wide characters will be written past the end of the destination + array. + + + + + +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + /* ... */ + wchar_t src1[100] = L"hello"; + wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'}; + wchar_t dst1[6], dst2[5], dst3[5]; + int r1, r2, r3; + r1 = wcsncpy_s(dst1, 6, src1, 100); + r2 = wcsncpy_s(dst2, 5, src2, 7); + r3 = wcsncpy_s(dst3, 5, src2, 4); ++ The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0. + The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0. + The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0. + + +
430) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking + if any of those wide characters are null. Such an approach might write a wide character to every + element of s1 before discovering that the first element should be set to the null wide character. + +
431) A zero return value implies that all of the requested wide characters from the string pointed to by s2 + fit within the array pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + errno_t wmemcpy_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2, + rsize_t n); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between + objects that overlap. +
+ If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the + first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and + s1max is not greater than RSIZE_MAX. +
+ The wmemcpy_s function copies n successive wide characters from the object pointed + to by s2 into the object pointed to by s1. +
+ The wmemcpy_s function returns zero if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, const wchar_t *s2, rsize_t n); ++ Runtime-constraints +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. n shall not be greater than s1max. +
+ If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the + first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and + s1max is not greater than RSIZE_MAX. +
+ The wmemmove_s function copies n successive wide characters from the object pointed + to by s2 into the object pointed to by s1. This copying takes place as if the n wide + characters from the object pointed to by s2 are first copied into a temporary array of n + wide characters that does not overlap the objects pointed to by s1 or s2, and then the n + wide characters from the temporary array are copied into the object pointed to by s1. +
+ The wmemmove_s function returns zero if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> errno_t wcscat_s(wchar_t * restrict s1, rsize_t s1max, const wchar_t * restrict s2); - errno_t wcsncat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - wchar_t *wcstok_s(wchar_t * restrict s1, - rsize_t * restrict s1max, - const wchar_t * restrict s2, - wchar_t ** restrict ptr); ++ Runtime-constraints +
+ Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to + wcscat_s. +
+ Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. + s1max shall not equal zero. m shall not equal zero.432) m shall be greater than + wcsnlen_s(s2, m). Copying shall not take place between objects that overlap. + +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the + null wide character. +
+ The wcscat_s function appends a copy of the wide string pointed to by s2 (including + the terminating null wide character) to the end of the wide string pointed to by s1. The + initial wide character from s2 overwrites the null wide character at the end of s1. +
+ All elements following the terminating null wide character (if any) written by + wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified + values when wcscat_s returns.433) +
+ The wcscat_s function returns zero434) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. + +
432) Zero means that s1 was not null terminated upon entry to wcscat_s. + +
433) This allows an implementation to append wide characters from s2 to s1 while simultaneously + checking if any of those wide characters are null. Such an approach might write a wide character to + every element of s1 before discovering that the first element should be set to the null wide character. + +
434) A zero return value implies that all of the requested wide characters from the wide string pointed to by + s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + errno_t wcsncat_s(wchar_t * restrict s1, + rsize_t s1max, + const wchar_t * restrict s2, + rsize_t n); ++ Runtime-constraints +
+ Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to + wcsncat_s. +
+ Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than + RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.435) If n is not less + than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take + place between objects that overlap. + + + +
+ If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is + greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the + null wide character. +
+ The wcsncat_s function appends not more than n successive wide characters (wide + characters that follow a null wide character are not copied) from the array pointed to by + s2 to the end of the wide string pointed to by s1. The initial wide character from s2 + overwrites the null wide character at the end of s1. If no null wide character was copied + from s2, then s1[s1max-m+n] is set to a null wide character. +
+ All elements following the terminating null wide character (if any) written by + wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified + values when wcsncat_s returns.436) +
+ The wcsncat_s function returns zero437) if there was no runtime-constraint violation. + Otherwise, a nonzero value is returned. +
+ EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the + result will not be null terminated or that wide characters will be written past the end of the destination + array. +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + /* ... */ + wchar_t s1[100] = L"good"; + wchar_t s2[6] = L"hello"; + wchar_t s3[6] = L"hello"; + wchar_t s4[7] = L"abc"; + wchar_t s5[1000] = L"bye"; + int r1, r2, r3, r4; + r1 = wcsncat_s(s1, 100, s5, 1000); + r2 = wcsncat_s(s2, 6, L"", 1); + r3 = wcsncat_s(s3, 6, L"X", 2); + r4 = wcsncat_s(s4, 7, L"defghijklmn", 3); ++ After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0. + After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0. + After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0. + After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0. + + + + + + +
435) Zero means that s1 was not null terminated upon entry to wcsncat_s. + +
436) This allows an implementation to append wide characters from s2 to s1 while simultaneously + checking if any of those wide characters are null. Such an approach might write a wide character to + every element of s1 before discovering that the first element should be set to the null wide character. + +
437) A zero return value implies that all of the requested wide characters from the wide string pointed to by + s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. + + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + wchar_t *wcstok_s(wchar_t * restrict s1, + rsize_t * restrict s1max, + const wchar_t * restrict s2, + wchar_t ** restrict ptr); ++ Runtime-constraints +
+ None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr + shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. + The end of the token found shall occur within the first *s1max wide characters of s1 for + the first call, and shall occur within the first *s1max wide characters of where searching + resumes on subsequent calls. +
+ If there is a runtime-constraint violation, the wcstok_s function does not indirect + through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. +
+ A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1 + into a sequence of tokens, each of which is delimited by a wide character from the wide + string pointed to by s2. The fourth argument points to a caller-provided wchar_t + pointer into which the wcstok_s function stores information necessary for it to + continue scanning the same wide string. +
+ The first call in a sequence has a non-null first argument and s1max points to an object + whose value is the number of elements in the wide character array pointed to by the first + argument. The first call stores an initial value in the object pointed to by ptr and + updates the value pointed to by s1max to reflect the number of elements that remain in + relation to ptr. Subsequent calls in the sequence have a null first argument and the + objects pointed to by s1max and ptr are required to have the values stored by the + previous call in the sequence, which are then updated. The separator wide string pointed + to by s2 may be different from call to call. +
+ The first call in the sequence searches the wide string pointed to by s1 for the first wide + character that is not contained in the current separator wide string pointed to by s2. If no + such wide character is found, then there are no tokens in the wide string pointed to by s1 + and the wcstok_s function returns a null pointer. If such a wide character is found, it is + the start of the first token. + +
+ The wcstok_s function then searches from there for the first wide character in s1 that + is contained in the current separator wide string. If no such wide character is found, the + current token extends to the end of the wide string pointed to by s1, and subsequent + searches in the same wide string for a token return a null pointer. If such a wide character + is found, it is overwritten by a null wide character, which terminates the current token. +
+ In all cases, the wcstok_s function stores sufficient information in the pointer pointed + to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer + value for ptr, shall start searching just past the element overwritten by a null wide + character (if any). +
+ The wcstok_s function returns a pointer to the first wide character of a token, or a null + pointer if there is no token or there is a runtime-constraint violation. +
+ EXAMPLE +
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> + static wchar_t str1[] = L"?a???b,,,#c"; + static wchar_t str2[] = L"\t \t"; + wchar_t *t, *ptr1, *ptr2; + rsize_t max1 = wcslen(str1)+1; + rsize_t max2 = wcslen(str2)+1; + t = wcstok_s(str1, &max1, "?", &ptr1); // t points to the token "a" + t = wcstok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b" + t = wcstok_s(str2, &max2, " \t", &ptr2); // t is a null pointer + t = wcstok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c" + t = wcstok_s(NULL, &max1, "?", &ptr1); // t is a null pointer ++ + +
+
+ #define __STDC_WANT_LIB_EXT1__ 1 + #include <wchar.h> size_t wcsnlen_s(const wchar_t *s, size_t maxsize); - errno_t wcrtomb_s(size_t * restrict retval, - char * restrict s, rsize_t smax, - wchar_t wc, mbstate_t * restrict ps); ++
+ The wcsnlen_s function computes the length of the wide string pointed to by s. +
+ If s is a null pointer,438) then the wcsnlen_s function returns zero. +
+ Otherwise, the wcsnlen_s function returns the number of wide characters that precede + the terminating null wide character. If there is no null wide character in the first + maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first + + maxsize wide characters of s shall be accessed by wcsnlen_s. + +
438) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints + along with the values returned for a null pointer or an unterminated wide string argument make + wcsnlen_s useful in algorithms that gracefully handle such exceptional data. + + +
+ Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the + conversion state) to be a null pointer. + +
+
+ #include <wchar.h> + errno_t wcrtomb_s(size_t * restrict retval, + char * restrict s, rsize_t smax, + wchar_t wc, mbstate_t * restrict ps); ++ Runtime-constraints +
+ Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax + shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer, + then smax shall be not be less than the number of bytes to be stored in the array pointed + to by s. If s is a null pointer, then smax shall equal zero. +
+ If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is + not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then + wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then + wcrtomb_s sets *retval to (size_t)(-1). +
+ If s is a null pointer, the wcrtomb_s function is equivalent to the call +
+ wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps) ++ where retval and buf are internal variables of the appropriate types, and the size of + buf is greater than MB_CUR_MAX. +
+ If s is not a null pointer, the wcrtomb_s function determines the number of bytes + needed to represent the multibyte character that corresponds to the wide character given + by wc (including any shift sequences), and stores the multibyte character representation + in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are + stored. If wc is a null wide character, a null byte is stored, preceded by any shift + sequence needed to restore the initial shift state; the resulting state described is the initial + conversion state. + + +
+ If wc does not correspond to a valid multibyte character, an encoding error occurs: the + wcrtomb_s function stores the value (size_t)(-1) into *retval and the + conversion state is unspecified. Otherwise, the wcrtomb_s function stores into + *retval the number of bytes (including any shift sequences) stored in the array pointed + to by s. +
+ The wcrtomb_s function returns zero if no runtime-constraint violation and no + encoding error occurred. Otherwise, a nonzero value is returned. + +
+ Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not + permit the ps parameter (the pointer to the conversion state) to be a null pointer. + +
+
+ #include <wchar.h> errno_t mbsrtowcs_s(size_t * restrict retval, wchar_t * restrict dst, rsize_t dstmax, const char ** restrict src, rsize_t len, mbstate_t * restrict ps); - - - - -[page 497] (Contents) - - errno_t wcsrtombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t ** restrict src, rsize_t len, - mbstate_t * restrict ps); -B.28 Wide character classification and mapping utilities <wctype.h> - wint_t wctrans_t wctype_t WEOF - int iswalnum(wint_t wc); - int iswalpha(wint_t wc); - int iswblank(wint_t wc); - int iswcntrl(wint_t wc); - int iswdigit(wint_t wc); - int iswgraph(wint_t wc); - int iswlower(wint_t wc); - int iswprint(wint_t wc); - int iswpunct(wint_t wc); - int iswspace(wint_t wc); - int iswupper(wint_t wc); - int iswxdigit(wint_t wc); - int iswctype(wint_t wc, wctype_t desc); - wctype_t wctype(const char *property); - wint_t towlower(wint_t wc); - wint_t towupper(wint_t wc); - wint_t towctrans(wint_t wc, wctrans_t desc); - wctrans_t wctrans(const char *property); - - - - -[page 498] (Contents) - - Annex C - (informative) - Sequence points -1 The following are the sequence points described in 5.1.2.3: - -- Between the evaluations of the function designator and actual arguments in a function - call and the actual call. (6.5.2.2). - -- Between the evaluations of the first and second operands of the following operators: - logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17). * - -- Between the evaluations of the first operand of the conditional ? : operator and - whichever of the second and third operands is evaluated (6.5.15). - -- The end of a full declarator: declarators (6.7.6); - -- Between the evaluation of a full expression and the next full expression to be - evaluated. The following are full expressions: an initializer that is not part of a - compound literal (6.7.9); the expression in an expression statement (6.8.3); the - controlling expression of a selection statement (if or switch) (6.8.4); the - controlling expression of a while or do statement (6.8.5); each of the (optional) - expressions of a for statement (6.8.5.3); the (optional) expression in a return - statement (6.8.6.4). - -- Immediately before a library function returns (7.1.4). - -- After the actions associated with each formatted input/output function conversion - specifier (7.21.6, 7.28.2). - -- Immediately before and immediately after each call to a comparison function, and - also between any call to a comparison function and any movement of the objects - passed as arguments to that call (7.22.5). - - - - -[page 499] (Contents) - - Annex D - (normative) - Universal character names for identifiers -1 This clause lists the hexadecimal code values that are valid in universal character names - in identifiers. - D.1 Ranges of characters allowed -1 00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6, - 00D8-00F6, 00F8-00FF -2 0100-167F, 1681-180D, 180F-1FFF -3 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F -4 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF -5 3004-3007, 3021-302F, 3031-303F -6 3040-D7FF -7 F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD -8 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD, - 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD, - B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD - D.2 Ranges of characters disallowed initially -1 0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F - - - - -[page 500] (Contents) - - Annex E - (informative) - Implementation limits -1 The contents of the header <limits.h> are given below, in alphabetical order. The - minimum magnitudes shown shall be replaced by implementation-defined magnitudes - with the same sign. The values shall all be constant expressions suitable for use in #if - preprocessing directives. The components are described further in 5.2.4.2.1. - #define CHAR_BIT 8 - #define CHAR_MAX UCHAR_MAX or SCHAR_MAX - #define CHAR_MIN 0 or SCHAR_MIN - #define INT_MAX +32767 - #define INT_MIN -32767 - #define LONG_MAX +2147483647 - #define LONG_MIN -2147483647 - #define LLONG_MAX +9223372036854775807 - #define LLONG_MIN -9223372036854775807 - #define MB_LEN_MAX 1 - #define SCHAR_MAX +127 - #define SCHAR_MIN -127 - #define SHRT_MAX +32767 - #define SHRT_MIN -32767 - #define UCHAR_MAX 255 - #define USHRT_MAX 65535 - #define UINT_MAX 65535 - #define ULONG_MAX 4294967295 - #define ULLONG_MAX 18446744073709551615 -2 The contents of the header <float.h> are given below. All integer values, except - FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing - directives; all floating values shall be constant expressions. The components are - described further in 5.2.4.2.2. -3 The values given in the following list shall be replaced by implementation-defined - expressions: - #define FLT_EVAL_METHOD - #define FLT_ROUNDS -4 The values given in the following list shall be replaced by implementation-defined - constant expressions that are greater or equal in magnitude (absolute value) to those - shown, with the same sign: -[page 501] (Contents) - - #define DLB_DECIMAL_DIG 10 - #define DBL_DIG 10 - #define DBL_MANT_DIG - #define DBL_MAX_10_EXP +37 - #define DBL_MAX_EXP - #define DBL_MIN_10_EXP -37 - #define DBL_MIN_EXP - #define DECIMAL_DIG 10 - #define FLT_DECIMAL_DIG 6 - #define FLT_DIG 6 - #define FLT_MANT_DIG - #define FLT_MAX_10_EXP +37 - #define FLT_MAX_EXP - #define FLT_MIN_10_EXP -37 - #define FLT_MIN_EXP - #define FLT_RADIX 2 - #define LDLB_DECIMAL_DIG 10 - #define LDBL_DIG 10 - #define LDBL_MANT_DIG - #define LDBL_MAX_10_EXP +37 - #define LDBL_MAX_EXP - #define LDBL_MIN_10_EXP -37 - #define LDBL_MIN_EXP -5 The values given in the following list shall be replaced by implementation-defined - constant expressions with values that are greater than or equal to those shown: - #define DBL_MAX 1E+37 - #define FLT_MAX 1E+37 - #define LDBL_MAX 1E+37 -6 The values given in the following list shall be replaced by implementation-defined - constant expressions with (positive) values that are less than or equal to those shown: - #define DBL_EPSILON 1E-9 - #define DBL_MIN 1E-37 - #define FLT_EPSILON 1E-5 - #define FLT_MIN 1E-37 - #define LDBL_EPSILON 1E-9 - #define LDBL_MIN 1E-37 - - - - -[page 502] (Contents) - - Annex F - (normative) - IEC 60559 floating-point arithmetic - F.1 Introduction -1 This annex specifies C language support for the IEC 60559 floating-point standard. The - IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for - microprocessor systems, second edition (IEC 60559:1989), previously designated - IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic - (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point - Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove - dependencies on radix and word length. IEC 60559 generally refers to the floating-point - standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that - defines __STDC_IEC_559__ shall conform to the specifications in this annex.343) - Where a binding between the C language and IEC 60559 is indicated, the - IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since - negative and positive infinity are representable in IEC 60559 formats, all real numbers lie - within the range of representable values. - F.2 Types -1 The C floating types match the IEC 60559 formats as follows: - -- The float type matches the IEC 60559 single format. - -- The double type matches the IEC 60559 double format. - -- The long double type matches an IEC 60559 extended format,344) else a - non-IEC 60559 extended format, else the IEC 60559 double format. - Any non-IEC 60559 extended format used for the long double type shall have more - precision than IEC 60559 double and at least the range of IEC 60559 double.345) - - - - - 343) Implementations that do not define __STDC_IEC_559__ are not required to conform to these - specifications. - 344) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit - and quadruple 128-bit IEC 60559 formats. - 345) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include - all double values. - -[page 503] (Contents) - - Recommended practice -2 The long double type should match an IEC 60559 extended format. - F.2.1 Infinities, signed zeros, and NaNs -1 This specification does not define the behavior of signaling NaNs.346) It generally uses - the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan - functions in <math.h> provide designations for IEC 60559 NaNs and infinities. - F.3 Operators and functions -1 C operators and functions provide IEC 60559 required and recommended facilities as - listed below. - -- The +, -, *, and / operators provide the IEC 60559 add, subtract, multiply, and - divide operations. - -- The sqrt functions in <math.h> provide the IEC 60559 square root operation. - -- The remainder functions in <math.h> provide the IEC 60559 remainder - operation. The remquo functions in <math.h> provide the same operation but - with additional information. - -- The rint functions in <math.h> provide the IEC 60559 operation that rounds a - floating-point number to an integer value (in the same precision). The nearbyint - functions in <math.h> provide the nearbyinteger function recommended in the - Appendix to ANSI/IEEE 854. - -- The conversions for floating types provide the IEC 60559 conversions between - floating-point precisions. - -- The conversions from integer to floating types provide the IEC 60559 conversions - from integer to floating point. - -- The conversions from floating to integer types provide IEC 60559-like conversions - but always round toward zero. - -- The lrint and llrint functions in <math.h> provide the IEC 60559 - conversions, which honor the directed rounding mode, from floating point to the - long int and long long int integer formats. The lrint and llrint - functions can be used to implement IEC 60559 conversions from floating to other - integer formats. - -- The translation time conversion of floating constants and the strtod, strtof, - strtold, fprintf, fscanf, and related library functions in <stdlib.h>, - - - 346) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are - sufficient for closure of the arithmetic. - -[page 504] (Contents) - - <stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The - strtold function in <stdlib.h> provides the conv function recommended in the - Appendix to ANSI/IEEE 854. --- The relational and equality operators provide IEC 60559 comparisons. IEC 60559 - identifies a need for additional comparison predicates to facilitate writing code that - accounts for NaNs. The comparison macros (isgreater, isgreaterequal, - isless, islessequal, islessgreater, and isunordered) in <math.h> - supplement the language operators to address this need. The islessgreater and - isunordered macros provide respectively a quiet version of the <> predicate and - the unordered predicate recommended in the Appendix to IEC 60559. --- The feclearexcept, feraiseexcept, and fetestexcept functions in - <fenv.h> provide the facility to test and alter the IEC 60559 floating-point - exception status flags. The fegetexceptflag and fesetexceptflag - functions in <fenv.h> provide the facility to save and restore all five status flags at - one time. These functions are used in conjunction with the type fexcept_t and the - floating-point exception macros (FE_INEXACT, FE_DIVBYZERO, - FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>. --- The fegetround and fesetround functions in <fenv.h> provide the facility - to select among the IEC 60559 directed rounding modes represented by the rounding - direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD, - FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the - IEC 60559 directed rounding modes. --- The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in - <fenv.h> provide a facility to manage the floating-point environment, comprising - the IEC 60559 status flags and control modes. --- The copysign functions in <math.h> provide the copysign function - recommended in the Appendix to IEC 60559. --- The fabs functions in <math.h> provide the abs function recommended in the - Appendix to IEC 60559. --- The unary minus (-) operator provides the unary minus (-) operation recommended - in the Appendix to IEC 60559. --- The scalbn and scalbln functions in <math.h> provide the scalb function - recommended in the Appendix to IEC 60559. --- The logb functions in <math.h> provide the logb function recommended in the - Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854. --- The nextafter and nexttoward functions in <math.h> provide the nextafter - function recommended in the Appendix to IEC 60559 (but with a minor change to - -[page 505] (Contents) - - better handle signed zeros). - -- The isfinite macro in <math.h> provides the finite function recommended in - the Appendix to IEC 60559. - -- The isnan macro in <math.h> provides the isnan function recommended in the - Appendix to IEC 60559. - -- The signbit macro and the fpclassify macro in <math.h>, used in - conjunction with the number classification macros (FP_NAN, FP_INFINITE, - FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class - function recommended in the Appendix to IEC 60559 (except that the classification - macros defined in 7.12.3 do not distinguish signaling from quiet NaNs). - F.4 Floating to integer conversion -1 If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised - (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part - of the floating value exceeds the range of the integer type, then the ''invalid'' floating- - point exception is raised and the resulting value is unspecified. Otherwise, the resulting - value is determined by 6.3.1.4. Conversion of an integral floating value that does not - exceed the range of the integer type raises no floating-point exceptions; whether - conversion of a non-integral floating value raises the ''inexact'' floating-point exception is - unspecified.347) - F.5 Binary-decimal conversion -1 Conversion from the widest supported IEC 60559 format to decimal with - DECIMAL_DIG digits and back is the identity function.348) -2 Conversions involving IEC 60559 formats follow all pertinent recommended practice. In - particular, conversion between any supported IEC 60559 format and decimal with - DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current - rounding mode), which assures that conversion from the widest supported IEC 60559 - format to decimal with DECIMAL_DIG digits and back is the identity function. - - - - 347) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer - conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those - cases where it matters, library functions can be used to effect such conversions with or without raising - the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in - <math.h>. - 348) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported, - DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest - IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and - DBL_DIG are 18 and 15, respectively, for these formats.) - -[page 506] (Contents) - -3 Functions such as strtod that convert character sequences to floating types honor the - rounding direction. Hence, if the rounding direction might be upward or downward, the - implementation cannot convert a minus-signed sequence by negating the converted - unsigned sequence. - F.6 The return statement - If the return expression is evaluated in a floating-point format different from the return - type, the expression is converted as if by assignment349) to the return type of the function - and the resulting value is returned to the caller. - F.7 Contracted expressions -1 A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed - zeros, subnormals, and the rounding directions in a manner consistent with the basic - arithmetic operations covered by IEC 60559. - Recommended practice -2 A contracted expression should raise floating-point exceptions in a manner generally - consistent with the basic arithmetic operations. * - F.8 Floating-point environment -1 The floating-point environment defined in <fenv.h> includes the IEC 60559 floating- - point exception status flags and directed-rounding control modes. It includes also - IEC 60559 dynamic rounding precision and trap enablement modes, if the - implementation supports them.350) - F.8.1 Environment management -1 IEC 60559 requires that floating-point operations implicitly raise floating-point exception - status flags, and that rounding control modes can be set explicitly to affect result values of - floating-point operations. When the state for the FENV_ACCESS pragma (defined in - <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects - which respect sequence points.351) - - - - - 349) Assignment removes any extra range and precision. - 350) This specification does not require dynamic rounding precision nor trap enablement modes. - 351) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating- - point control modes will be the default ones and the floating-point status flags will not be tested, - which allows certain optimizations (see F.9). - -[page 507] (Contents) - - F.8.2 Translation -1 During translation the IEC 60559 default modes are in effect: - -- The rounding direction mode is rounding to nearest. - -- The rounding precision mode (if supported) is set so that results are not shortened. - -- Trapping or stopping (if supported) is disabled on all floating-point exceptions. - Recommended practice -2 The implementation should produce a diagnostic message for each translation-time - floating-point exception, other than ''inexact'';352) the implementation should then - proceed with the translation of the program. - F.8.3 Execution -1 At program startup the floating-point environment is initialized as prescribed by - IEC 60559: - -- All floating-point exception status flags are cleared. - -- The rounding direction mode is rounding to nearest. - -- The dynamic rounding precision mode (if supported) is set so that results are not - shortened. - -- Trapping or stopping (if supported) is disabled on all floating-point exceptions. - F.8.4 Constant expressions -1 An arithmetic constant expression of floating type, other than one in an initializer for an - object that has static or thread storage duration, is evaluated (as if) during execution; thus, - it is affected by any operative floating-point control modes and raises floating-point - exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma - is ''on'').353) -2 EXAMPLE - - - - 352) As floating constants are converted to appropriate internal representations at translation time, their - conversion is subject to default rounding modes and raises no execution-time floating-point exceptions - (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example - strtod, provide execution-time conversion of numeric strings. - 353) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0 - are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and - 1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the - efficiency of translation-time evaluation through static initialization, such as - const static double one_third = 1.0/3.0; - - -[page 508] (Contents) - - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - void f(void) - { - float w[] = { 0.0/0.0 }; // raises an exception - static float x = 0.0/0.0; // does not raise an exception - float y = 0.0/0.0; // raises an exception - double z = 0.0/0.0; // raises an exception - /* ... */ - } -3 For the static initialization, the division is done at translation time, raising no (execution-time) floating- - point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at - execution time. - - F.8.5 Initialization -1 All computation for automatic initialization is done (as if) at execution time; thus, it is - affected by any operative modes and raises floating-point exceptions as required by - IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation - for initialization of objects that have static or thread storage duration is done (as if) at - translation time. -2 EXAMPLE - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - void f(void) - { - float u[] = { 1.1e75 }; // raises exceptions - static float v = 1.1e75; // does not raise exceptions - float w = 1.1e75; // raises exceptions - double x = 1.1e75; // may raise exceptions - float y = 1.1e75f; // may raise exceptions - long double z = 1.1e75; // does not raise exceptions - /* ... */ - } -3 The static initialization of v raises no (execution-time) floating-point exceptions because its computation is - done at translation time. The automatic initialization of u and w require an execution-time conversion to - float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations - of x and y entail execution-time conversion; however, in some expression evaluation methods, the - conversions is not to a narrower format, in which case no floating-point exception is raised.354) The - automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating- - point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to - - - - 354) Use of float_t and double_t variables increases the likelihood of translation-time computation. - For example, the automatic initialization - double_t x = 1.1e75; - could be done at translation time, regardless of the expression evaluation method. - -[page 509] (Contents) - - their internal representations occur at translation time in all cases. - - F.8.6 Changing the environment -1 Operations defined in 6.5 and functions and macros defined for the standard libraries - change floating-point status flags and control modes just as indicated by their - specifications (including conformance to IEC 60559). They do not change flags or modes - (so as to be detectable by the user) in any other cases. -2 If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559 - valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and - ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised - before ''inexact''. - F.9 Optimization -1 This section identifies code transformations that might subvert IEC 60559-specified - behavior, and others that do not. - F.9.1 Global transformations -1 Floating-point arithmetic operations and external function calls may entail side effects - which optimization shall honor, at least where the state of the FENV_ACCESS pragma is - ''on''. The flags and modes in the floating-point environment may be regarded as global - variables; floating-point operations (+, *, etc.) implicitly read the modes and write the - flags. -2 Concern about side effects may inhibit code motion and removal of seemingly useless - code. For example, in - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - void f(double x) - { - /* ... */ - for (i = 0; i < n; i++) x + 1; - /* ... */ - } - x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop - body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of - course these optimizations are valid if the implementation can rule out the nettlesome - cases.) -3 This specification does not require support for trap handlers that maintain information - about the order or count of floating-point exceptions. Therefore, between function calls, - floating-point exceptions need not be precise: the actual order and number of occurrences - of floating-point exceptions (> 1) may vary from what the source code expresses. Thus, -[page 510] (Contents) - - the preceding loop could be treated as - if (0 < n) x + 1; - F.9.2 Expression transformations -1 x/2 (<->) x x 0.5 Although similar transformations involving inexact constants - generally do not yield numerically equivalent expressions, if the - constants are exact then such transformations can be made on - IEC 60559 machines and others that round perfectly. - 1 x x and x/1 (->) x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559 - machines, among others).355) - x/x (->) 1.0 The expressions x/x and 1.0 are not equivalent if x can be zero, - infinite, or NaN. - x - y (<->) x + (-y) The expressions x - y, x + (-y), and (-y) + x are equivalent (on - IEC 60559 machines, among others). - x - y (<->) -(y - x) The expressions x - y and -(y - x) are not equivalent because 1 - 1 - is +0 but -(1 - 1) is -0 (in the default rounding direction).356) - x - x (->) 0.0 The expressions x - x and 0.0 are not equivalent if x is a NaN or - infinite. - 0 x x (->) 0.0 The expressions 0 x x and 0.0 are not equivalent if x is a NaN, - infinite, or -0. - x+0(->) x The expressions x + 0 and x are not equivalent if x is -0, because - (-0) + (+0) yields +0 (in the default rounding direction), not -0. - x-0(->) x (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but - +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the - FENV_ACCESS pragma is ''off'', promising default rounding, then - the implementation can replace x - 0 by x, even if x might be zero. - -x (<->) 0 - x The expressions -x and 0 - x are not equivalent if x is +0, because - -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is - downward). - - 355) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and - other transformations that remove arithmetic operators. - 356) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities. - Examples include: - 1/(1/ (+-) (inf)) is (+-) (inf) - and - conj(csqrt(z)) is csqrt(conj(z)), - for complex z. - -[page 511] (Contents) - - F.9.3 Relational operators -1 x != x (->) false The expression x != x is true if x is a NaN. - x = x (->) true The expression x = x is false if x is a NaN. - x < y (->) isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these - expressions are not equivalent because of side effects when x or y is a - NaN and the state of the FENV_ACCESS pragma is ''on''. This - transformation, which would be desirable if extra code were required - to cause the ''invalid'' floating-point exception for unordered cases, - could be performed provided the state of the FENV_ACCESS pragma - is ''off''. - The sense of relational operators shall be maintained. This includes handling unordered - cases as expressed by the source code. -2 EXAMPLE - // calls g and raises ''invalid'' if a and b are unordered - if (a < b) - f(); - else - g(); - is not equivalent to - // calls f and raises ''invalid'' if a and b are unordered - if (a >= b) - g(); - else - f(); - nor to - // calls f without raising ''invalid'' if a and b are unordered - if (isgreaterequal(a,b)) - g(); - else - f(); - nor, unless the state of the FENV_ACCESS pragma is ''off'', to - // calls g without raising ''invalid'' if a and b are unordered - if (isless(a,b)) - f(); - else - g(); - but is equivalent to - - - - -[page 512] (Contents) - - if (!(a < b)) - g(); - else - f(); - - F.9.4 Constant arithmetic -1 The implementation shall honor floating-point exceptions raised by execution-time - constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4 - and F.8.5.) An operation on constants that raises no floating-point exception can be - folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a - further check is required to assure that changing the rounding direction to downward does - not alter the sign of the result,357) and implementations that support dynamic rounding - precision modes shall assure further that the result of the operation raises no floating- - point exception when converted to the semantic type of the operation. - F.10 Mathematics <math.h> -1 This subclause contains specifications of <math.h> facilities that are particularly suited - for IEC 60559 implementations. -2 The Standard C macro HUGE_VAL and its float and long double analogs, - HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive - infinities. -3 Special cases for functions in <math.h> are covered directly or indirectly by - IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The - other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and - (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags - in a manner consistent with the basic arithmetic operations covered by IEC 60559. -4 The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a - nonzero value. -5 The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in - subsequent subclauses of this annex. -6 The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of - rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value - whose magnitude is too large. -7 The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially - subnormal or zero) and suffers loss of accuracy.358) - - - 357) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward. - 358) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on - when the floating-point exception is raised. - -[page 513] (Contents) - -8 Whether or when library functions raise the ''inexact'' floating-point exception is - unspecified, unless explicitly specified otherwise. -9 Whether or when library functions raise an undeserved ''underflow'' floating-point - exception is unspecified.359) Otherwise, as implied by F.8.6, the <math.h> functions do - not raise spurious floating-point exceptions (detectable by the user), other than the - ''inexact'' floating-point exception. -10 Whether the functions honor the rounding direction mode is implementation-defined, - unless explicitly specified otherwise. -11 Functions with a NaN argument return a NaN result and raise no floating-point exception, - except where stated otherwise. -12 The specifications in the following subclauses append to the definitions in <math.h>. - For families of functions, the specifications apply to all of the functions even though only - the principal function is shown. Unless otherwise specified, where the symbol ''(+-)'' - occurs in both an argument and the result, the result has the same sign as the argument. - Recommended practice -13 If a function with one or more NaN arguments returns a NaN result, the result should be - the same as one of the NaN arguments (after possible type conversion), except perhaps - for the sign. - F.10.1 Trigonometric functions - F.10.1.1 The acos functions -1 -- acos(1) returns +0. - -- acos(x) returns a NaN and raises the ''invalid'' floating-point exception for - | x | > 1. - F.10.1.2 The asin functions -1 -- asin((+-)0) returns (+-)0. - -- asin(x) returns a NaN and raises the ''invalid'' floating-point exception for - | x | > 1. - - - - - 359) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if - avoiding them would be too costly. - -[page 514] (Contents) - - F.10.1.3 The atan functions -1 -- atan((+-)0) returns (+-)0. - -- atan((+-)(inf)) returns (+-)pi /2. - F.10.1.4 The atan2 functions -1 -- atan2((+-)0, -0) returns (+-)pi .360) - -- atan2((+-)0, +0) returns (+-)0. - -- atan2((+-)0, x) returns (+-)pi for x < 0. - -- atan2((+-)0, x) returns (+-)0 for x > 0. - -- atan2(y, (+-)0) returns -pi /2 for y < 0. - -- atan2(y, (+-)0) returns pi /2 for y > 0. - -- atan2((+-)y, -(inf)) returns (+-)pi for finite y > 0. - -- atan2((+-)y, +(inf)) returns (+-)0 for finite y > 0. - -- atan2((+-)(inf), x) returns (+-)pi /2 for finite x. - -- atan2((+-)(inf), -(inf)) returns (+-)3pi /4. - -- atan2((+-)(inf), +(inf)) returns (+-)pi /4. - F.10.1.5 The cos functions -1 -- cos((+-)0) returns 1. - -- cos((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - F.10.1.6 The sin functions -1 -- sin((+-)0) returns (+-)0. - -- sin((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - F.10.1.7 The tan functions -1 -- tan((+-)0) returns (+-)0. - -- tan((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - - - - - 360) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise - the ''divide-by-zero'' floating-point exception. - -[page 515] (Contents) - - F.10.2 Hyperbolic functions - F.10.2.1 The acosh functions -1 -- acosh(1) returns +0. - -- acosh(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 1. - -- acosh(+(inf)) returns +(inf). - F.10.2.2 The asinh functions -1 -- asinh((+-)0) returns (+-)0. - -- asinh((+-)(inf)) returns (+-)(inf). - F.10.2.3 The atanh functions -1 -- atanh((+-)0) returns (+-)0. - -- atanh((+-)1) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception. - -- atanh(x) returns a NaN and raises the ''invalid'' floating-point exception for - | x | > 1. - F.10.2.4 The cosh functions -1 -- cosh((+-)0) returns 1. - -- cosh((+-)(inf)) returns +(inf). - F.10.2.5 The sinh functions -1 -- sinh((+-)0) returns (+-)0. - -- sinh((+-)(inf)) returns (+-)(inf). - F.10.2.6 The tanh functions -1 -- tanh((+-)0) returns (+-)0. - -- tanh((+-)(inf)) returns (+-)1. - F.10.3 Exponential and logarithmic functions - F.10.3.1 The exp functions -1 -- exp((+-)0) returns 1. - -- exp(-(inf)) returns +0. - -- exp(+(inf)) returns +(inf). - - - - -[page 516] (Contents) - - F.10.3.2 The exp2 functions -1 -- exp2((+-)0) returns 1. - -- exp2(-(inf)) returns +0. - -- exp2(+(inf)) returns +(inf). - F.10.3.3 The expm1 functions -1 -- expm1((+-)0) returns (+-)0. - -- expm1(-(inf)) returns -1. - -- expm1(+(inf)) returns +(inf). - F.10.3.4 The frexp functions -1 -- frexp((+-)0, exp) returns (+-)0, and stores 0 in the object pointed to by exp. - -- frexp((+-)(inf), exp) returns (+-)(inf), and stores an unspecified value in the object - pointed to by exp. - -- frexp(NaN, exp) stores an unspecified value in the object pointed to by exp - (and returns a NaN). -2 frexp raises no floating-point exceptions. -3 When the radix of the argument is a power of 2, the returned value is exact and is - independent of the current rounding direction mode. -4 On a binary system, the body of the frexp function might be - { - *exp = (value == 0) ? 0 : (int)(1 + logb(value)); - return scalbn(value, -(*exp)); - } - F.10.3.5 The ilogb functions -1 When the correct result is representable in the range of the return type, the returned value - is exact and is independent of the current rounding direction mode. -2 If the correct result is outside the range of the return type, the numeric result is - unspecified and the ''invalid'' floating-point exception is raised. - - - - -[page 517] (Contents) - - F.10.3.6 The ldexp functions -1 On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp). - F.10.3.7 The log functions -1 -- log((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log(1) returns +0. - -- log(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0. - -- log(+(inf)) returns +(inf). - F.10.3.8 The log10 functions -1 -- log10((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log10(1) returns +0. - -- log10(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0. - -- log10(+(inf)) returns +(inf). - F.10.3.9 The log1p functions -1 -- log1p((+-)0) returns (+-)0. - -- log1p(-1) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log1p(x) returns a NaN and raises the ''invalid'' floating-point exception for - x < -1. - -- log1p(+(inf)) returns +(inf). - F.10.3.10 The log2 functions -1 -- log2((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- log2(1) returns +0. - -- log2(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0. - -- log2(+(inf)) returns +(inf). - F.10.3.11 The logb functions -1 -- logb((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception. - -- logb((+-)(inf)) returns +(inf). -2 The returned value is exact and is independent of the current rounding direction mode. - - - - -[page 518] (Contents) - - F.10.3.12 The modf functions -1 -- modf((+-)x, iptr) returns a result with the same sign as x. - -- modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr. - -- modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a - NaN). -2 The returned values are exact and are independent of the current rounding direction - mode. -3 modf behaves as though implemented by - #include <math.h> - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - double modf(double value, double *iptr) - { - int save_round = fegetround(); - fesetround(FE_TOWARDZERO); - *iptr = nearbyint(value); - fesetround(save_round); - return copysign( - isinf(value) ? 0.0 : - value - (*iptr), value); - } - F.10.3.13 The scalbn and scalbln functions -1 -- scalbn((+-)0, n) returns (+-)0. - -- scalbn(x, 0) returns x. - -- scalbn((+-)(inf), n) returns (+-)(inf). -2 If the calculation does not overflow or underflow, the returned value is exact and - independent of the current rounding direction mode. - - - - -[page 519] (Contents) - - F.10.4 Power and absolute value functions - F.10.4.1 The cbrt functions -1 -- cbrt((+-)0) returns (+-)0. - -- cbrt((+-)(inf)) returns (+-)(inf). - F.10.4.2 The fabs functions -1 -- fabs((+-)0) returns +0. - -- fabs((+-)(inf)) returns +(inf). -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.4.3 The hypot functions -1 -- hypot(x, y), hypot(y, x), and hypot(x, -y) are equivalent. - -- hypot(x, (+-)0) is equivalent to fabs(x). - -- hypot((+-)(inf), y) returns +(inf), even if y is a NaN. - F.10.4.4 The pow functions -1 -- pow((+-)0, y) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception - for y an odd integer < 0. - -- pow((+-)0, y) returns +(inf) and raises the ''divide-by-zero'' floating-point exception - for y < 0, finite, and not an odd integer. - -- pow((+-)0, -(inf)) returns +(inf) and may raise the ''divide-by-zero'' floating-point - exception. - -- pow((+-)0, y) returns (+-)0 for y an odd integer > 0. - -- pow((+-)0, y) returns +0 for y > 0 and not an odd integer. - -- pow(-1, (+-)(inf)) returns 1. - -- pow(+1, y) returns 1 for any y, even a NaN. - -- pow(x, (+-)0) returns 1 for any x, even a NaN. - -- pow(x, y) returns a NaN and raises the ''invalid'' floating-point exception for - finite x < 0 and finite non-integer y. - -- pow(x, -(inf)) returns +(inf) for | x | < 1. - -- pow(x, -(inf)) returns +0 for | x | > 1. - -- pow(x, +(inf)) returns +0 for | x | < 1. - -- pow(x, +(inf)) returns +(inf) for | x | > 1. - - -[page 520] (Contents) - - -- pow(-(inf), y) returns -0 for y an odd integer < 0. - -- pow(-(inf), y) returns +0 for y < 0 and not an odd integer. - -- pow(-(inf), y) returns -(inf) for y an odd integer > 0. - -- pow(-(inf), y) returns +(inf) for y > 0 and not an odd integer. - -- pow(+(inf), y) returns +0 for y < 0. - -- pow(+(inf), y) returns +(inf) for y > 0. - F.10.4.5 The sqrt functions -1 sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value - is dependent on the current rounding direction mode. - F.10.5 Error and gamma functions - F.10.5.1 The erf functions -1 -- erf((+-)0) returns (+-)0. - -- erf((+-)(inf)) returns (+-)1. - F.10.5.2 The erfc functions -1 -- erfc(-(inf)) returns 2. - -- erfc(+(inf)) returns +0. - F.10.5.3 The lgamma functions -1 -- lgamma(1) returns +0. - -- lgamma(2) returns +0. - -- lgamma(x) returns +(inf) and raises the ''divide-by-zero'' floating-point exception for - x a negative integer or zero. - -- lgamma(-(inf)) returns +(inf). - -- lgamma(+(inf)) returns +(inf). - F.10.5.4 The tgamma functions -1 -- tgamma((+-)0) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception. - -- tgamma(x) returns a NaN and raises the ''invalid'' floating-point exception for x a - negative integer. - -- tgamma(-(inf)) returns a NaN and raises the ''invalid'' floating-point exception. - -- tgamma(+(inf)) returns +(inf). - - - -[page 521] (Contents) - - F.10.6 Nearest integer functions - F.10.6.1 The ceil functions -1 -- ceil((+-)0) returns (+-)0. - -- ceil((+-)(inf)) returns (+-)(inf). -2 The returned value is independent of the current rounding direction mode. -3 The double version of ceil behaves as though implemented by - #include <math.h> - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - double ceil(double x) - { - double result; - int save_round = fegetround(); - fesetround(FE_UPWARD); - result = rint(x); // or nearbyint instead of rint - fesetround(save_round); - return result; - } -4 The ceil functions may, but are not required to, raise the ''inexact'' floating-point - exception for finite non-integer arguments, as this implementation does. - F.10.6.2 The floor functions -1 -- floor((+-)0) returns (+-)0. - -- floor((+-)(inf)) returns (+-)(inf). -2 The returned value and is independent of the current rounding direction mode. -3 See the sample implementation for ceil in F.10.6.1. The floor functions may, but are - not required to, raise the ''inexact'' floating-point exception for finite non-integer - arguments, as that implementation does. - F.10.6.3 The nearbyint functions -1 The nearbyint functions use IEC 60559 rounding according to the current rounding - direction. They do not raise the ''inexact'' floating-point exception if the result differs in - value from the argument. - -- nearbyint((+-)0) returns (+-)0 (for all rounding directions). - -- nearbyint((+-)(inf)) returns (+-)(inf) (for all rounding directions). - - - -[page 522] (Contents) - - F.10.6.4 The rint functions -1 The rint functions differ from the nearbyint functions only in that they do raise the - ''inexact'' floating-point exception if the result differs in value from the argument. - F.10.6.5 The lrint and llrint functions -1 The lrint and llrint functions provide floating-to-integer conversion as prescribed - by IEC 60559. They round according to the current rounding direction. If the rounded - value is outside the range of the return type, the numeric result is unspecified and the - ''invalid'' floating-point exception is raised. When they raise no other floating-point - exception and the result differs from the argument, they raise the ''inexact'' floating-point - exception. - F.10.6.6 The round functions -1 -- round((+-)0) returns (+-)0. - -- round((+-)(inf)) returns (+-)(inf). -2 The returned value is independent of the current rounding direction mode. -3 The double version of round behaves as though implemented by - #include <math.h> - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - double round(double x) - { - double result; - fenv_t save_env; - feholdexcept(&save_env); - result = rint(x); - if (fetestexcept(FE_INEXACT)) { - fesetround(FE_TOWARDZERO); - result = rint(copysign(0.5 + fabs(x), x)); - } - feupdateenv(&save_env); - return result; - } - The round functions may, but are not required to, raise the ''inexact'' floating-point - exception for finite non-integer numeric arguments, as this implementation does. - - - - -[page 523] (Contents) - - F.10.6.7 The lround and llround functions -1 The lround and llround functions differ from the lrint and llrint functions - with the default rounding direction just in that the lround and llround functions - round halfway cases away from zero and need not raise the ''inexact'' floating-point - exception for non-integer arguments that round to within the range of the return type. - F.10.6.8 The trunc functions -1 The trunc functions use IEC 60559 rounding toward zero (regardless of the current - rounding direction). The returned value is exact. - -- trunc((+-)0) returns (+-)0. - -- trunc((+-)(inf)) returns (+-)(inf). -2 The returned value is independent of the current rounding direction mode. The trunc - functions may, but are not required to, raise the ''inexact'' floating-point exception for - finite non-integer arguments. - F.10.7 Remainder functions - F.10.7.1 The fmod functions -1 -- fmod((+-)0, y) returns (+-)0 for y not zero. - -- fmod(x, y) returns a NaN and raises the ''invalid'' floating-point exception for x - infinite or y zero (and neither is a NaN). - -- fmod(x, (+-)(inf)) returns x for x not infinite. -2 When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. -3 The double version of fmod behaves as though implemented by - #include <math.h> - #include <fenv.h> - #pragma STDC FENV_ACCESS ON - double fmod(double x, double y) - { - double result; - result = remainder(fabs(x), (y = fabs(y))); - if (signbit(result)) result += y; - return copysign(result, x); - } - - - - -[page 524] (Contents) - - F.10.7.2 The remainder functions -1 The remainder functions are fully specified as a basic arithmetic operation in - IEC 60559. -2 When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. - F.10.7.3 The remquo functions -1 The remquo functions follow the specifications for the remainder functions. They - have no further specifications special to IEC 60559 implementations. -2 When subnormal results are supported, the returned value is exact and is independent of - the current rounding direction mode. - F.10.8 Manipulation functions - F.10.8.1 The copysign functions -1 copysign is specified in the Appendix to IEC 60559. -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.8.2 The nan functions -1 All IEC 60559 implementations support quiet NaNs, in all floating formats. -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.8.3 The nextafter functions -1 -- nextafter(x, y) raises the ''overflow'' and ''inexact'' floating-point exceptions - for x finite and the function value infinite. - -- nextafter(x, y) raises the ''underflow'' and ''inexact'' floating-point - exceptions for the function value subnormal or zero and x != y. -2 Even though underflow or overflow can occur, the returned value is independent of the - current rounding direction mode. - F.10.8.4 The nexttoward functions -1 No additional requirements beyond those on nextafter. -2 Even though underflow or overflow can occur, the returned value is independent of the - current rounding direction mode. - - - - -[page 525] (Contents) - - F.10.9 Maximum, minimum, and positive difference functions - F.10.9.1 The fdim functions -1 No additional requirements. - F.10.9.2 The fmax functions -1 If just one argument is a NaN, the fmax functions return the other argument (if both - arguments are NaNs, the functions return a NaN). -2 The returned value is exact and is independent of the current rounding direction mode. -3 The body of the fmax function might be361) - { return (isgreaterequal(x, y) || - isnan(y)) ? x : y; } - F.10.9.3 The fmin functions -1 The fmin functions are analogous to the fmax functions (see F.10.9.2). -2 The returned value is exact and is independent of the current rounding direction mode. - F.10.10 Floating multiply-add - F.10.10.1 The fma functions -1 -- fma(x, y, z) computes xy + z, correctly rounded once. - -- fma(x, y, z) returns a NaN and optionally raises the ''invalid'' floating-point - exception if one of x and y is infinite, the other is zero, and z is a NaN. - -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if - one of x and y is infinite, the other is zero, and z is not a NaN. - -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if x - times y is an exact infinity and z is also an infinity but with the opposite sign. - - - - - 361) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would - return +0; however, implementation in software might be impractical. - -[page 526] (Contents) - - F.10.11 Comparison macros -1 Relational operators and their corresponding comparison macros (7.12.14) produce - equivalent result values, even if argument values are represented in wider formats. Thus, - comparison macro arguments represented in formats wider than their semantic types are - not converted to the semantic types, unless the wide evaluation method converts operands - of relational operators to their semantic types. The standard wide evaluation methods - characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert - operands of relational operators to their semantic types. - - - - -[page 527] (Contents) - - Annex G - (normative) - IEC 60559-compatible complex arithmetic - G.1 Introduction -1 This annex supplements annex F to specify complex arithmetic for compatibility with - IEC 60559 real floating-point arithmetic. An implementation that defines * - __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.362) - G.2 Types -1 There is a new keyword _Imaginary, which is used to specify imaginary types. It is - used as a type specifier within declaration specifiers in the same way as _Complex is - (thus, _Imaginary float is a valid type name). -2 There are three imaginary types, designated as float _Imaginary, double - _Imaginary, and long double _Imaginary. The imaginary types (along with - the real floating and complex types) are floating types. -3 For imaginary types, the corresponding real type is given by deleting the keyword - _Imaginary from the type name. -4 Each imaginary type has the same representation and alignment requirements as the - corresponding real type. The value of an object of imaginary type is the value of the real - representation times the imaginary unit. -5 The imaginary type domain comprises the imaginary types. - G.3 Conventions -1 A complex or imaginary value with at least one infinite part is regarded as an infinity - (even if its other part is a NaN). A complex or imaginary value is a finite number if each - of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is - a zero if each of its parts is a zero. - - - - - 362) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform - to these specifications. - -[page 528] (Contents) - - G.4 Conversions - G.4.1 Imaginary types -1 Conversions among imaginary types follow rules analogous to those for real floating - types. - G.4.2 Real and imaginary -1 When a value of imaginary type is converted to a real type other than _Bool,363) the - result is a positive zero. -2 When a value of real type is converted to an imaginary type, the result is a positive - imaginary zero. - G.4.3 Imaginary and complex -1 When a value of imaginary type is converted to a complex type, the real part of the - complex result value is a positive zero and the imaginary part of the complex result value - is determined by the conversion rules for the corresponding real types. -2 When a value of complex type is converted to an imaginary type, the real part of the - complex value is discarded and the value of the imaginary part is converted according to - the conversion rules for the corresponding real types. - G.5 Binary operators -1 The following subclauses supplement 6.5 in order to specify the type of the result for an - operation with an imaginary operand. -2 For most operand types, the value of the result of a binary operator with an imaginary or - complex operand is completely determined, with reference to real arithmetic, by the usual - mathematical formula. For some operand types, the usual mathematical formula is - problematic because of its treatment of infinities and because of undue overflow or - underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is - not completely determined. - - - - - 363) See 6.3.1.2. - -[page 529] (Contents) - - G.5.1 Multiplicative operators - Semantics -1 If one operand has real type and the other operand has imaginary type, then the result has - imaginary type. If both operands have imaginary type, then the result has real type. (If - either operand has complex type, then the result has complex type.) -2 If the operands are not both complex, then the result and floating-point exception - behavior of the * operator is defined by the usual mathematical formula: - * u iv u + iv - - x xu i(xv) (xu) + i(xv) - - iy i(yu) -yv (-yv) + i(yu) - - x + iy (xu) + i(yu) (-yv) + i(xv) -3 If the second operand is not complex, then the result and floating-point exception - behavior of the / operator is defined by the usual mathematical formula: - / u iv - - x x/u i(-x/v) - - iy i(y/u) y/v - - x + iy (x/u) + i(y/u) (y/v) + i(-x/v) -4 The * and / operators satisfy the following infinity properties for all real, imaginary, and - complex operands:364) - -- if one operand is an infinity and the other operand is a nonzero finite number or an - infinity, then the result of the * operator is an infinity; - -- if the first operand is an infinity and the second operand is a finite number, then the - result of the / operator is an infinity; - -- if the first operand is a finite number and the second operand is an infinity, then the - result of the / operator is a zero; - - - - - 364) These properties are already implied for those cases covered in the tables, but are required for all cases - (at least where the state for CX_LIMITED_RANGE is ''off''). - -[page 530] (Contents) - - -- if the first operand is a nonzero finite number or an infinity and the second operand is - a zero, then the result of the / operator is an infinity. -5 If both operands of the * operator are complex or if the second operand of the / operator - is complex, the operator raises floating-point exceptions if appropriate for the calculation - of the parts of the result, and may raise spurious floating-point exceptions. -6 EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note - that the imaginary unit I has imaginary type (see G.6). - #include <math.h> - #include <complex.h> - /* Multiply z * w ... */ - double complex _Cmultd(double complex z, double complex w) - { - #pragma STDC FP_CONTRACT OFF - double a, b, c, d, ac, bd, ad, bc, x, y; - a = creal(z); b = cimag(z); - c = creal(w); d = cimag(w); - ac = a * c; bd = b * d; - ad = a * d; bc = b * c; - x = ac - bd; y = ad + bc; - if (isnan(x) && isnan(y)) { - /* Recover infinities that computed as NaN+iNaN ... */ - int recalc = 0; - if ( isinf(a) || isinf(b) ) { // z is infinite - /* "Box" the infinity and change NaNs in the other factor to 0 */ - a = copysign(isinf(a) ? 1.0 : 0.0, a); - b = copysign(isinf(b) ? 1.0 : 0.0, b); - if (isnan(c)) c = copysign(0.0, c); - if (isnan(d)) d = copysign(0.0, d); - recalc = 1; - } - if ( isinf(c) || isinf(d) ) { // w is infinite - /* "Box" the infinity and change NaNs in the other factor to 0 */ - c = copysign(isinf(c) ? 1.0 : 0.0, c); - d = copysign(isinf(d) ? 1.0 : 0.0, d); - if (isnan(a)) a = copysign(0.0, a); - if (isnan(b)) b = copysign(0.0, b); - recalc = 1; - } - if (!recalc && (isinf(ac) || isinf(bd) || - isinf(ad) || isinf(bc))) { - /* Recover infinities from overflow by changing NaNs to 0 ... */ - if (isnan(a)) a = copysign(0.0, a); - if (isnan(b)) b = copysign(0.0, b); - if (isnan(c)) c = copysign(0.0, c); - if (isnan(d)) d = copysign(0.0, d); - recalc = 1; - } - if (recalc) { - -[page 531] (Contents) - - x = INFINITY * ( a * c - b * d ); - y = INFINITY * ( a * d + b * c ); - } - } - return x + I * y; - } -7 This implementation achieves the required treatment of infinities at the cost of only one isnan test in - ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur. - -8 EXAMPLE 2 Division of two double _Complex operands could be implemented as follows. - #include <math.h> - #include <complex.h> - /* Divide z / w ... */ - double complex _Cdivd(double complex z, double complex w) - { - #pragma STDC FP_CONTRACT OFF - double a, b, c, d, logbw, denom, x, y; - int ilogbw = 0; - a = creal(z); b = cimag(z); - c = creal(w); d = cimag(w); - logbw = logb(fmax(fabs(c), fabs(d))); - if (logbw == INFINITY) { - ilogbw = (int)logbw; - c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw); - } - denom = c * c + d * d; - x = scalbn((a * c + b * d) / denom, -ilogbw); - y = scalbn((b * c - a * d) / denom, -ilogbw); - /* Recover infinities and zeros that computed as NaN+iNaN; */ - /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */ - if (isnan(x) && isnan(y)) { - if ((denom == 0.0) && - (!isnan(a) || !isnan(b))) { - x = copysign(INFINITY, c) * a; - y = copysign(INFINITY, c) * b; - } - else if ((isinf(a) || isinf(b)) && - isfinite(c) && isfinite(d)) { - a = copysign(isinf(a) ? 1.0 : 0.0, a); - b = copysign(isinf(b) ? 1.0 : 0.0, b); - x = INFINITY * ( a * c + b * d ); - y = INFINITY * ( b * c - a * d ); - } - else if (isinf(logbw) && - isfinite(a) && isfinite(b)) { - c = copysign(isinf(c) ? 1.0 : 0.0, c); - d = copysign(isinf(d) ? 1.0 : 0.0, d); - x = 0.0 * ( a * c + b * d ); - y = 0.0 * ( b * c - a * d ); - -[page 532] (Contents) - - } - } - return x + I * y; - } -9 Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than - for multiplication. In the spirit of the multiplication example above, this code does not defend against - overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of - with division, provides better roundoff characteristics. - - G.5.2 Additive operators - Semantics -1 If both operands have imaginary type, then the result has imaginary type. (If one operand - has real type and the other operand has imaginary type, or if either operand has complex - type, then the result has complex type.) -2 In all cases the result and floating-point exception behavior of a + or - operator is defined - by the usual mathematical formula: - + or - u iv u + iv - - x x(+-)u x (+-) iv (x (+-) u) (+-) iv - - iy (+-)u + iy i(y (+-) v) (+-)u + i(y (+-) v) - - x + iy (x (+-) u) + iy x + i(y (+-) v) (x (+-) u) + i(y (+-) v) - G.6 Complex arithmetic <complex.h> -1 The macros - imaginary - and - _Imaginary_I - are defined, respectively, as _Imaginary and a constant expression of type const - float _Imaginary with the value of the imaginary unit. The macro - I - is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding - the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro - imaginary. -2 This subclause contains specifications for the <complex.h> functions that are - particularly suited to IEC 60559 implementations. For families of functions, the - specifications apply to all of the functions even though only the principal function is - -[page 533] (Contents) - - shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument - and the result, the result has the same sign as the argument. -3 The functions are continuous onto both sides of their branch cuts, taking into account the - sign of zero. For example, csqrt(-2 (+-) i0) = (+-)isqrt:2. - -4 Since complex and imaginary values are composed of real values, each function may be - regarded as computing real values from real values. Except as noted, the functions treat - real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a - manner consistent with the specifications for real functions in F.10.365) -5 The functions cimag, conj, cproj, and creal are fully specified for all - implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating- - point exceptions. -6 Each of the functions cabs and carg is specified by a formula in terms of a real - function (whose special cases are covered in annex F): - cabs(x + iy) = hypot(x, y) - carg(x + iy) = atan2(y, x) -7 Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by - a formula in terms of other complex functions (whose special cases are specified below): - casin(z) = -i casinh(iz) - catan(z) = -i catanh(iz) - ccos(z) = ccosh(iz) - csin(z) = -i csinh(iz) - ctan(z) = -i ctanh(iz) -8 For the other functions, the following subclauses specify behavior for special cases, - including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For - families of functions, the specifications apply to all of the functions even though only the - principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the - specifications for the upper half-plane imply the specifications for the lower half-plane; if - the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the - specifications for the first quadrant imply the specifications for the other three quadrants. -9 In the following subclauses, cis(y) is defined as cos(y) + i sin(y). - - - - - 365) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its - other part is a NaN. - -[page 534] (Contents) - - G.6.1 Trigonometric functions - G.6.1.1 The cacos functions -1 -- cacos(conj(z)) = conj(cacos(z)). - -- cacos((+-)0 + i0) returns pi /2 - i0. - -- cacos((+-)0 + iNaN) returns pi /2 + iNaN. - -- cacos(x + i (inf)) returns pi /2 - i (inf), for finite x. - -- cacos(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for nonzero finite x. - -- cacos(-(inf) + iy) returns pi - i (inf), for positive-signed finite y. - -- cacos(+(inf) + iy) returns +0 - i (inf), for positive-signed finite y. - -- cacos(-(inf) + i (inf)) returns 3pi /4 - i (inf). - -- cacos(+(inf) + i (inf)) returns pi /4 - i (inf). - -- cacos((+-)(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the - result is unspecified). - -- cacos(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite y. - -- cacos(NaN + i (inf)) returns NaN - i (inf). - -- cacos(NaN + iNaN) returns NaN + iNaN. - G.6.2 Hyperbolic functions - G.6.2.1 The cacosh functions -1 -- cacosh(conj(z)) = conj(cacosh(z)). - -- cacosh((+-)0 + i0) returns +0 + ipi /2. - -- cacosh(x + i (inf)) returns +(inf) + ipi /2, for finite x. - -- cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite x. - -- cacosh(-(inf) + iy) returns +(inf) + ipi , for positive-signed finite y. - -- cacosh(+(inf) + iy) returns +(inf) + i0, for positive-signed finite y. - -- cacosh(-(inf) + i (inf)) returns +(inf) + i3pi /4. - -- cacosh(+(inf) + i (inf)) returns +(inf) + ipi /4. - -- cacosh((+-)(inf) + iNaN) returns +(inf) + iNaN. - - -[page 535] (Contents) - - -- cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite y. - -- cacosh(NaN + i (inf)) returns +(inf) + iNaN. - -- cacosh(NaN + iNaN) returns NaN + iNaN. - G.6.2.2 The casinh functions -1 -- casinh(conj(z)) = conj(casinh(z)) and casinh is odd. - -- casinh(+0 + i0) returns 0 + i0. - -- casinh(x + i (inf)) returns +(inf) + ipi /2 for positive-signed finite x. - -- casinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite x. - -- casinh(+(inf) + iy) returns +(inf) + i0 for positive-signed finite y. - -- casinh(+(inf) + i (inf)) returns +(inf) + ipi /4. - -- casinh(+(inf) + iNaN) returns +(inf) + iNaN. - -- casinh(NaN + i0) returns NaN + i0. - -- casinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite nonzero y. - -- casinh(NaN + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result - is unspecified). - -- casinh(NaN + iNaN) returns NaN + iNaN. - G.6.2.3 The catanh functions -1 -- catanh(conj(z)) = conj(catanh(z)) and catanh is odd. - -- catanh(+0 + i0) returns +0 + i0. - -- catanh(+0 + iNaN) returns +0 + iNaN. - -- catanh(+1 + i0) returns +(inf) + i0 and raises the ''divide-by-zero'' floating-point - exception. - -- catanh(x + i (inf)) returns +0 + ipi /2, for finite positive-signed x. - -- catanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for nonzero finite x. - -- catanh(+(inf) + iy) returns +0 + ipi /2, for finite positive-signed y. - -- catanh(+(inf) + i (inf)) returns +0 + ipi /2. - -- catanh(+(inf) + iNaN) returns +0 + iNaN. - -[page 536] (Contents) - - -- catanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' - floating-point exception, for finite y. - -- catanh(NaN + i (inf)) returns (+-)0 + ipi /2 (where the sign of the real part of the result is - unspecified). - -- catanh(NaN + iNaN) returns NaN + iNaN. - G.6.2.4 The ccosh functions -1 -- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even. - -- ccosh(+0 + i0) returns 1 + i0. - -- ccosh(+0 + i (inf)) returns NaN (+-) i0 (where the sign of the imaginary part of the - result is unspecified) and raises the ''invalid'' floating-point exception. - -- ccosh(+0 + iNaN) returns NaN (+-) i0 (where the sign of the imaginary part of the - result is unspecified). - -- ccosh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for finite nonzero x. - -- ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite nonzero x. - -- ccosh(+(inf) + i0) returns +(inf) + i0. - -- ccosh(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y. - -- ccosh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is - unspecified) and raises the ''invalid'' floating-point exception. - -- ccosh(+(inf) + iNaN) returns +(inf) + iNaN. - -- ccosh(NaN + i0) returns NaN (+-) i0 (where the sign of the imaginary part of the - result is unspecified). - -- ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- ccosh(NaN + iNaN) returns NaN + iNaN. - G.6.2.5 The csinh functions -1 -- csinh(conj(z)) = conj(csinh(z)) and csinh is odd. - -- csinh(+0 + i0) returns +0 + i0. - -- csinh(+0 + i (inf)) returns (+-)0 + iNaN (where the sign of the real part of the result is - unspecified) and raises the ''invalid'' floating-point exception. - -- csinh(+0 + iNaN) returns (+-)0 + iNaN (where the sign of the real part of the result is - unspecified). -[page 537] (Contents) - - -- csinh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for positive finite x. - -- csinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite nonzero x. - -- csinh(+(inf) + i0) returns +(inf) + i0. - -- csinh(+(inf) + iy) returns +(inf) cis(y), for positive finite y. - -- csinh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is - unspecified) and raises the ''invalid'' floating-point exception. - -- csinh(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result - is unspecified). - -- csinh(NaN + i0) returns NaN + i0. - -- csinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- csinh(NaN + iNaN) returns NaN + iNaN. - G.6.2.6 The ctanh functions -1 -- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd. - -- ctanh(+0 + i0) returns +0 + i0. - -- ctanh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for finite x. - -- ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -- ctanh(+(inf) + iy) returns 1 + i0 sin(2y), for positive-signed finite y. - -- ctanh(+(inf) + i (inf)) returns 1 (+-) i0 (where the sign of the imaginary part of the result - is unspecified). - -- ctanh(+(inf) + iNaN) returns 1 (+-) i0 (where the sign of the imaginary part of the - result is unspecified). - -- ctanh(NaN + i0) returns NaN + i0. - -- ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- ctanh(NaN + iNaN) returns NaN + iNaN. - - - - -[page 538] (Contents) - - G.6.3 Exponential and logarithmic functions - G.6.3.1 The cexp functions -1 -- cexp(conj(z)) = conj(cexp(z)). - -- cexp((+-)0 + i0) returns 1 + i0. - -- cexp(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point - exception, for finite x. - -- cexp(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -- cexp(+(inf) + i0) returns +(inf) + i0. - -- cexp(-(inf) + iy) returns +0 cis(y), for finite y. - -- cexp(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y. - -- cexp(-(inf) + i (inf)) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts of - the result are unspecified). - -- cexp(+(inf) + i (inf)) returns (+-)(inf) + iNaN and raises the ''invalid'' floating-point - exception (where the sign of the real part of the result is unspecified). - -- cexp(-(inf) + iNaN) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts - of the result are unspecified). - -- cexp(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result - is unspecified). - -- cexp(NaN + i0) returns NaN + i0. - -- cexp(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for all nonzero numbers y. - -- cexp(NaN + iNaN) returns NaN + iNaN. - G.6.3.2 The clog functions -1 -- clog(conj(z)) = conj(clog(z)). - -- clog(-0 + i0) returns -(inf) + ipi and raises the ''divide-by-zero'' floating-point - exception. - -- clog(+0 + i0) returns -(inf) + i0 and raises the ''divide-by-zero'' floating-point - exception. - -- clog(x + i (inf)) returns +(inf) + ipi /2, for finite x. - -- clog(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -[page 539] (Contents) - - -- clog(-(inf) + iy) returns +(inf) + ipi , for finite positive-signed y. - -- clog(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y. - -- clog(-(inf) + i (inf)) returns +(inf) + i3pi /4. - -- clog(+(inf) + i (inf)) returns +(inf) + ipi /4. - -- clog((+-)(inf) + iNaN) returns +(inf) + iNaN. - -- clog(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite y. - -- clog(NaN + i (inf)) returns +(inf) + iNaN. - -- clog(NaN + iNaN) returns NaN + iNaN. - G.6.4 Power and absolute-value functions - G.6.4.1 The cpow functions -1 The cpow functions raise floating-point exceptions if appropriate for the calculation of - the parts of the result, and may also raise spurious floating-point exceptions.366) - G.6.4.2 The csqrt functions -1 -- csqrt(conj(z)) = conj(csqrt(z)). - -- csqrt((+-)0 + i0) returns +0 + i0. - -- csqrt(x + i (inf)) returns +(inf) + i (inf), for all x (including NaN). - -- csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite x. - -- csqrt(-(inf) + iy) returns +0 + i (inf), for finite positive-signed y. - -- csqrt(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y. - -- csqrt(-(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the - result is unspecified). - -- csqrt(+(inf) + iNaN) returns +(inf) + iNaN. - -- csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating- - point exception, for finite y. - -- csqrt(NaN + iNaN) returns NaN + iNaN. - - - - - 366) This allows cpow( z , c ) to be implemented as cexp(c clog( z )) without precluding - implementations that treat special cases more carefully. - -[page 540] (Contents) - - G.7 Type-generic math <tgmath.h> -1 Type-generic macros that accept complex arguments also accept imaginary arguments. If - an argument is imaginary, the macro expands to an expression whose type is real, - imaginary, or complex, as appropriate for the particular function: if the argument is - imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the - types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and - the types of the others are complex. -2 Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh, - sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real - functions: - cos(iy) = cosh(y) - sin(iy) = i sinh(y) - tan(iy) = i tanh(y) - cosh(iy) = cos(y) - sinh(iy) = i sin(y) - tanh(iy) = i tan(y) - asin(iy) = i asinh(y) - atan(iy) = i atanh(y) - asinh(iy) = i asin(y) - atanh(iy) = i atan(y) - - - - -[page 541] (Contents) - - Annex H - (informative) - Language independent arithmetic - H.1 Introduction -1 This annex documents the extent to which the C language supports the ISO/IEC 10967-1 - standard for language-independent arithmetic (LIA-1). LIA-1 is more general than - IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics. - H.2 Types -1 The relevant C arithmetic types meet the requirements of LIA-1 types if an - implementation adds notification of exceptional arithmetic operations and meets the 1 - unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8). - H.2.1 Boolean type -1 The LIA-1 data type Boolean is implemented by the C data type bool with values of - true and false, all from <stdbool.h>. - H.2.2 Integer types -1 The signed C integer types int, long int, long long int, and the corresponding - unsigned types are compatible with LIA-1. If an implementation adds support for the - LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are - LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense - in that overflows or out-of-bounds results silently wrap. An implementation that defines - signed integer types as also being modulo need not detect integer overflow, in which case, - only integer divide-by-zero need be detected. -2 The parameters for the integer data types can be accessed by the following: - maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX, - ULLONG_MAX - minint INT_MIN, LONG_MIN, LLONG_MIN -3 The parameter ''bounded'' is always true, and is not provided. The parameter ''minint'' - is always 0 for the unsigned types, and is not provided for those types. - - - - -[page 542] (Contents) - - H.2.2.1 Integer operations -1 The integer operations on integer types are the following: - addI x + y - subI x - y - mulI x * y - divI, divtI x / y - remI, remtI x % y - negI -x - absI abs(x), labs(x), llabs(x) - eqI x == y - neqI x != y - lssI x < y - leqI x <= y - gtrI x > y - geqI x >= y - where x and y are expressions of the same integer type. - H.2.3 Floating-point types -1 The C floating-point types float, double, and long double are compatible with - LIA-1. If an implementation adds support for the LIA-1 exceptional values - ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant - with LIA-1. An implementation that uses IEC 60559 floating-point formats and - operations (see annex F) along with IEC 60559 status flags and traps has LIA-1 - conformant types. - H.2.3.1 Floating-point parameters -1 The parameters for a floating point data type can be accessed by the following: - r FLT_RADIX - p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG - emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP - emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP -2 The derived constants for the floating point types are accessed by the following: - - -[page 543] (Contents) - - fmax FLT_MAX, DBL_MAX, LDBL_MAX - fminN FLT_MIN, DBL_MIN, LDBL_MIN - epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON - rnd_style FLT_ROUNDS - H.2.3.2 Floating-point operations -1 The floating-point operations on floating-point types are the following: - addF x + y - subF x - y - mulF x * y - divF x / y - negF -x - absF fabsf(x), fabs(x), fabsl(x) - exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x) - scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n), - scalblnf(x, li), scalbln(x, li), scalblnl(x, li) - intpartF modff(x, &y), modf(x, &y), modfl(x, &y) - fractpartF modff(x, &y), modf(x, &y), modfl(x, &y) - eqF x == y - neqF x != y - lssF x < y - leqF x <= y - gtrF x > y - geqF x >= y - where x and y are expressions of the same floating point type, n is of type int, and li - is of type long int. - H.2.3.3 Rounding styles -1 The C Standard requires all floating types to use the same radix and rounding style, so - that only one identifier for each is provided to map to LIA-1. -2 The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles: - truncate FLT_ROUNDS == 0 - - -[page 544] (Contents) - - nearest FLT_ROUNDS == 1 - other FLT_ROUNDS != 0 && FLT_ROUNDS != 1 - provided that an implementation extends FLT_ROUNDS to cover the rounding style used - in all relevant LIA-1 operations, not just addition as in C. - H.2.4 Type conversions -1 The LIA-1 type conversions are the following type casts: - cvtI' (->) I (int)i, (long int)i, (long long int)i, - (unsigned int)i, (unsigned long int)i, - (unsigned long long int)i - cvtF (->) I (int)x, (long int)x, (long long int)x, - (unsigned int)x, (unsigned long int)x, - (unsigned long long int)x - cvtI (->) F (float)i, (double)i, (long double)i - cvtF' (->) F (float)x, (double)x, (long double)x -2 In the above conversions from floating to integer, the use of (cast)x can be replaced with - (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x), - (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer - conversion functions, lrint(), llrint(), lround(), and llround(), can be - used. They all meet LIA-1's requirements on floating to integer rounding for in-range - values. For out-of-range values, the conversions shall silently wrap for the modulo types. -3 The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g., - fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x), - 65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0 - to 65535.0 which can then be cast to unsigned short int. But, the - remainder() function is not useful for doing silent wrapping to signed integer types, - e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the - range -32767.0 to +32768.0 which is not, in general, in the range of signed short - int. -4 C's conversions (casts) from floating-point to floating-point can meet LIA-1 - requirements if an implementation uses round-to-nearest (IEC 60559 default). -5 C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an - implementation uses round-to-nearest. - - - - -[page 545] (Contents) - - H.3 Notification -1 Notification is the process by which a user or program is informed that an exceptional - arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C - allows an implementation to cause a notification to occur when any arithmetic operation - returns an exceptional value as defined in LIA-1 clause 5. - H.3.1 Notification alternatives -1 LIA-1 requires at least the following two alternatives for handling of notifications: - setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and- - resume. -2 An implementation need only support a given notification alternative for the entire - program. An implementation may support the ability to switch between notification - alternatives during execution, but is not required to do so. An implementation can - provide separate selection for each kind of notification, but this is not required. -3 C allows an implementation to provide notification. C's SIGFPE (for traps) and - FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators) - can provide LIA-1 notification. -4 C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can - provide trap-and-terminate behavior, except for those LIA-1 operations implemented by - math library function calls. User-provided signal handlers for SIGFPE allow for trap- - and-resume behavior with the same constraint. - H.3.1.1 Indicators -1 C's <fenv.h> status flags are compatible with the LIA-1 indicators. -2 The following mapping is for floating-point types: - undefined FE_INVALID, FE_DIVBYZERO - floating_overflow FE_OVERFLOW - underflow FE_UNDERFLOW -3 The floating-point indicator interrogation and manipulation operations are: - set_indicators feraiseexcept(i) - clear_indicators feclearexcept(i) - test_indicators fetestexcept(i) - current_indicators fetestexcept(FE_ALL_EXCEPT) - where i is an expression of type int representing a subset of the LIA-1 indicators. -4 C allows an implementation to provide the following LIA-1 required behavior: at - program termination if any indicator is set the implementation shall send an unambiguous -[page 546] (Contents) - - and ''hard to ignore'' message (see LIA-1 subclause 6.1.2) -5 LIA-1 does not make the distinction between floating-point and integer for ''undefined''. - This documentation makes that distinction because <fenv.h> covers only the floating- - point indicators. - H.3.1.2 Traps -1 C is compatible with LIA-1's trap requirements for arithmetic operations, but not for - math library functions (which are not permitted to invoke a user's signal handler for - SIGFPE). An implementation can provide an alternative of notification through - termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3). -2 LIA-1 does not require that traps be precise. -3 C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions, - if there is any signal raised for them. -4 C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic - exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism - allows trap-and-terminate (either default implementation behavior or user replacement for - it) or trap-and-resume, at the programmer's option. - - - - -[page 547] (Contents) - - Annex I - (informative) - Common warnings -1 An implementation may generate warnings in many situations, none of which are - specified as part of this International Standard. The following are a few of the more - common situations. -2 -- A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3). - -- A block with initialization of an object that has automatic storage duration is jumped - into (6.2.4). - -- An implicit narrowing conversion is encountered, such as the assignment of a long - int or a double to an int, or a pointer to void to a pointer to any type other than - a character type (6.3). - -- A hexadecimal floating constant cannot be represented exactly in its evaluation format - (6.4.4.2). - -- An integer character constant includes more than one character or a wide character - constant includes more than one multibyte character (6.4.4.4). - -- The characters /* are found in a comment (6.4.7). - -- An ''unordered'' binary operator (not comma, &&, or ||) contains a side effect to an - lvalue in one operand, and a side effect to, or an access to the value of, the identical - lvalue in the other operand (6.5). - -- A function is called but no prototype has been supplied (6.5.2.2). - -- The arguments in a function call do not agree in number and type with those of the - parameters in a function definition that is not a prototype (6.5.2.2). - -- An object is defined but not used (6.7). - -- A value is given to an object of an enumerated type other than by assignment of an - enumeration constant that is a member of that type, or an enumeration object that has - the same type, or the value of a function that returns the same enumerated type - (6.7.2.2). - -- An aggregate has a partly bracketed initialization (6.7.8). - -- A statement cannot be reached (6.8). - -- A statement with no apparent effect is encountered (6.8). - -- A constant expression is used as the controlling expression of a selection statement - (6.8.4). -[page 548] (Contents) - --- An incorrectly formed preprocessing group is encountered while skipping a - preprocessing group (6.10.1). --- An unrecognized #pragma directive is encountered (6.10.6). - - - - -[page 549] (Contents) - - Annex J - (informative) - Portability issues -1 This annex collects some information about portability that appears in this International - Standard. - J.1 Unspecified behavior -1 The following are unspecified: - -- The manner and timing of static initialization (5.1.2). - -- The termination status returned to the hosted environment if the return type of main - is not compatible with int (5.1.2.2.3). - -- The behavior of the display device if a printing character is written when the active - position is at the final position of a line (5.2.2). - -- The behavior of the display device if a backspace character is written when the active - position is at the initial position of a line (5.2.2). - -- The behavior of the display device if a horizontal tab character is written when the - active position is at or past the last defined horizontal tabulation position (5.2.2). - -- The behavior of the display device if a vertical tab character is written when the active - position is at or past the last defined vertical tabulation position (5.2.2). - -- How an extended source character that does not correspond to a universal character - name counts toward the significant initial characters in an external identifier (5.2.4.1). - -- Many aspects of the representations of types (6.2.6). - -- The value of padding bytes when storing values in structures or unions (6.2.6.1). - -- The values of bytes that correspond to union members other than the one last stored - into (6.2.6.1). - -- The representation used when storing a value in an object that has more than one - object representation for that value (6.2.6.1). - -- The values of any padding bits in integer representations (6.2.6.2). - -- Whether certain operators can generate negative zeros and whether a negative zero - becomes a normal zero when stored in an object (6.2.6.2). - -- Whether two string literals result in distinct arrays (6.4.5). - -- The order in which subexpressions are evaluated and the order in which side effects - take place, except as specified for the function-call (), &&, ||, ? :, and comma -[page 550] (Contents) - - operators (6.5). --- The order in which the function designator, arguments, and subexpressions within the - arguments are evaluated in a function call (6.5.2.2). --- The order of side effects among compound literal initialization list expressions - (6.5.2.5). --- The order in which the operands of an assignment operator are evaluated (6.5.16). --- The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1). --- Whether a call to an inline function uses the inline definition or the external definition - of the function (6.7.4). --- Whether or not a size expression is evaluated when it is part of the operand of a - sizeof operator and changing the value of the size expression would not affect the - result of the operator (6.7.6.2). --- The order in which any side effects occur among the initialization list expressions in - an initializer (6.7.9). --- The layout of storage for function parameters (6.9.1). --- When a fully expanded macro replacement list contains a function-like macro name - as its last preprocessing token and the next preprocessing token from the source file is - a (, and the fully expanded replacement of that macro ends with the name of the first - macro and the next preprocessing token from the source file is again a (, whether that - is considered a nested replacement (6.10.3). --- The order in which # and ## operations are evaluated during macro substitution - (6.10.3.2, 6.10.3.3). --- The state of the floating-point status flags when execution passes from a part of the * - program translated with FENV_ACCESS ''off'' to a part translated with - FENV_ACCESS ''on'' (7.6.1). --- The order in which feraiseexcept raises floating-point exceptions, except as - stated in F.8.6 (7.6.2.3). --- Whether math_errhandling is a macro or an identifier with external linkage - (7.12). --- The results of the frexp functions when the specified value is not a floating-point - number (7.12.6.4). --- The numeric result of the ilogb functions when the correct value is outside the - range of the return type (7.12.6.5, F.10.3.5). --- The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5). - - -[page 551] (Contents) - --- The value stored by the remquo functions in the object pointed to by quo when y is - zero (7.12.10.3). --- Whether a comparison macro argument that is represented in a format wider than its - semantic type is converted to the semantic type (7.12.14). --- Whether setjmp is a macro or an identifier with external linkage (7.13). --- Whether va_copy and va_end are macros or identifiers with external linkage - (7.16.1). --- The hexadecimal digit before the decimal point when a non-normalized floating-point - number is printed with an a or A conversion specifier (7.21.6.1, 7.28.2.1). --- The value of the file position indicator after a successful call to the ungetc function - for a text stream, or the ungetwc function for any stream, until all pushed-back - characters are read or discarded (7.21.7.10, 7.28.3.10). --- The details of the value stored by the fgetpos function (7.21.9.1). --- The details of the value returned by the ftell function for a text stream (7.21.9.4). --- Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold - functions convert a minus-signed sequence to a negative number directly or by - negating the value resulting from converting the corresponding unsigned sequence - (7.22.1.3, 7.28.4.1.1). --- The order and contiguity of storage allocated by successive calls to the calloc, - malloc, and realloc functions (7.22.3). --- The amount of storage allocated by a successful call to the calloc, malloc, or - realloc function when 0 bytes was requested (7.22.3). --- Which of two elements that compare as equal is matched by the bsearch function - (7.22.5.1). --- The order of two elements that compare as equal in an array sorted by the qsort - function (7.22.5.2). --- The encoding of the calendar time returned by the time function (7.26.2.4). --- The characters stored by the strftime or wcsftime function if any of the time - values being converted is outside the normal range (7.26.3.5, 7.28.5.1). --- The conversion state after an encoding error occurs (7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, - 7.28.6.4.2, --- The resulting value when the ''invalid'' floating-point exception is raised during - IEC 60559 floating to integer conversion (F.4). - - - -[page 552] (Contents) - - -- Whether conversion of non-integer IEC 60559 floating values to integer raises the - ''inexact'' floating-point exception (F.4). - -- Whether or when library functions in <math.h> raise the ''inexact'' floating-point - exception in an IEC 60559 conformant implementation (F.10). - -- Whether or when library functions in <math.h> raise an undeserved ''underflow'' - floating-point exception in an IEC 60559 conformant implementation (F.10). - -- The exponent value stored by frexp for a NaN or infinity (F.10.3.4). - -- The numeric result returned by the lrint, llrint, lround, and llround - functions if the rounded value is outside the range of the return type (F.10.6.5, - F.10.6.7). - -- The sign of one part of the complex result of several math functions for certain - special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3, - G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2). - J.2 Undefined behavior -1 The behavior is undefined in the following circumstances: - -- A ''shall'' or ''shall not'' requirement that appears outside of a constraint is violated - (clause 4). - -- A nonempty source file does not end in a new-line character which is not immediately - preceded by a backslash character or ends in a partial preprocessing token or - comment (5.1.1.2). - -- Token concatenation produces a character sequence matching the syntax of a - universal character name (5.1.1.2). - -- A program in a hosted environment does not define a function named main using one - of the specified forms (5.1.2.2.1). - -- The execution of a program contains a data race (5.1.2.4). - -- A character not in the basic source character set is encountered in a source file, except - in an identifier, a character constant, a string literal, a header name, a comment, or a - preprocessing token that is never converted to a token (5.2.1). - -- An identifier, comment, string literal, character constant, or header name contains an - invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2). - -- The same identifier has both internal and external linkage in the same translation unit - (6.2.2). - -- An object is referred to outside of its lifetime (6.2.4). - - - -[page 553] (Contents) - --- The value of a pointer to an object whose lifetime has ended is used (6.2.4). --- The value of an object with automatic storage duration is used while it is - indeterminate (6.2.4, 6.7.9, 6.8). --- A trap representation is read by an lvalue expression that does not have character type - (6.2.6.1). --- A trap representation is produced by a side effect that modifies any part of the object - using an lvalue expression that does not have character type (6.2.6.1). --- The operands to certain operators are such that they could produce a negative zero - result, but the implementation does not support negative zeros (6.2.6.2). --- Two declarations of the same object or function specify types that are not compatible - (6.2.7). --- A program requires the formation of a composite type from a variable length array - type whose size is specified by an expression that is not evaluated (6.2.7). --- Conversion to or from an integer type produces a value outside the range that can be - represented (6.3.1.4). --- Demotion of one real floating type to another produces a value outside the range that - can be represented (6.3.1.5). --- An lvalue does not designate an object when evaluated (6.3.2.1). --- A non-array lvalue with an incomplete type is used in a context that requires the value - of the designated object (6.3.2.1). --- An lvalue designating an object of automatic storage duration that could have been - declared with the register storage class is used in a context that requires the value - of the designated object, but the object is uninitialized. (6.3.2.1). --- An lvalue having array type is converted to a pointer to the initial element of the - array, and the array object has register storage class (6.3.2.1). --- An attempt is made to use the value of a void expression, or an implicit or explicit - conversion (except to void) is applied to a void expression (6.3.2.2). --- Conversion of a pointer to an integer type produces a value outside the range that can - be represented (6.3.2.3). --- Conversion between two pointer types produces a result that is incorrectly aligned - (6.3.2.3). --- A pointer is used to call a function whose type is not compatible with the referenced - type (6.3.2.3). - - - -[page 554] (Contents) - --- An unmatched ' or " character is encountered on a logical source line during - tokenization (6.4). --- A reserved keyword token is used in translation phase 7 or 8 for some purpose other - than as a keyword (6.4.1). --- A universal character name in an identifier does not designate a character whose - encoding falls into one of the specified ranges (6.4.2.1). --- The initial character of an identifier is a universal character name designating a digit - (6.4.2.1). --- Two identifiers differ only in nonsignificant characters (6.4.2.1). --- The identifier __func__ is explicitly declared (6.4.2.2). --- The program attempts to modify a string literal (6.4.5). --- The characters ', \, ", //, or /* occur in the sequence between the < and > - delimiters, or the characters ', \, //, or /* occur in the sequence between the " - delimiters, in a header name preprocessing token (6.4.7). --- A side effect on a scalar object is unsequenced relative to either a different side effect - on the same scalar object or a value computation using the value of the same scalar - object (6.5). --- An exceptional condition occurs during the evaluation of an expression (6.5). --- An object has its stored value accessed other than by an lvalue of an allowable type - (6.5). --- For a call to a function without a function prototype in scope, the number of * - arguments does not equal the number of parameters (6.5.2.2). --- For call to a function without a function prototype in scope where the function is - defined with a function prototype, either the prototype ends with an ellipsis or the - types of the arguments after promotion are not compatible with the types of the - parameters (6.5.2.2). --- For a call to a function without a function prototype in scope where the function is not - defined with a function prototype, the types of the arguments after promotion are not - compatible with those of the parameters after promotion (with certain exceptions) - (6.5.2.2). --- A function is defined with a type that is not compatible with the type (of the - expression) pointed to by the expression that denotes the called function (6.5.2.2). --- A member of an atomic structure or union is accessed (6.5.2.3). --- The operand of the unary * operator has an invalid value (6.5.3.2). - - -[page 555] (Contents) - --- A pointer is converted to other than an integer or pointer type (6.5.4). --- The value of the second operand of the / or % operator is zero (6.5.5). --- Addition or subtraction of a pointer into, or just beyond, an array object and an - integer type produces a result that does not point into, or just beyond, the same array - object (6.5.6). --- Addition or subtraction of a pointer into, or just beyond, an array object and an - integer type produces a result that points just beyond the array object and is used as - the operand of a unary * operator that is evaluated (6.5.6). --- Pointers that do not point into, or just beyond, the same array object are subtracted - (6.5.6). --- An array subscript is out of range, even if an object is apparently accessible with the - given subscript (as in the lvalue expression a[1][7] given the declaration int - a[4][5]) (6.5.6). --- The result of subtracting two pointers is not representable in an object of type - ptrdiff_t (6.5.6). --- An expression is shifted by a negative number or by an amount greater than or equal - to the width of the promoted expression (6.5.7). --- An expression having signed promoted type is left-shifted and either the value of the - expression is negative or the result of shifting would be not be representable in the - promoted type (6.5.7). --- Pointers that do not point to the same aggregate or union (nor just beyond the same - array object) are compared using relational operators (6.5.8). --- An object is assigned to an inexactly overlapping object or to an exactly overlapping - object with incompatible type (6.5.16.1). --- An expression that is required to be an integer constant expression does not have an - integer type; has operands that are not integer constants, enumeration constants, - character constants, sizeof expressions whose results are integer constants, or - immediately-cast floating constants; or contains casts (outside operands to sizeof - operators) other than conversions of arithmetic types to integer types (6.6). --- A constant expression in an initializer is not, or does not evaluate to, one of the - following: an arithmetic constant expression, a null pointer constant, an address - constant, or an address constant for a complete object type plus or minus an integer - constant expression (6.6). --- An arithmetic constant expression does not have arithmetic type; has operands that - are not integer constants, floating constants, enumeration constants, character - constants, or sizeof expressions; or contains casts (outside operands to sizeof - -[page 556] (Contents) - - operators) other than conversions of arithmetic types to arithmetic types (6.6). --- The value of an object is accessed by an array-subscript [], member-access . or ->, - address &, or indirection * operator or a pointer cast in creating an address constant - (6.6). --- An identifier for an object is declared with no linkage and the type of the object is - incomplete after its declarator, or after its init-declarator if it has an initializer (6.7). --- A function is declared at block scope with an explicit storage-class specifier other - than extern (6.7.1). --- A structure or union is defined as containing no named members, no anonymous - structures, and no anonymous unions (6.7.2.1). --- An attempt is made to access, or generate a pointer to just past, a flexible array - member of a structure when the referenced object provides no elements for that array - (6.7.2.1). --- When the complete type is needed, an incomplete structure or union type is not - completed in the same scope by another declaration of the tag that defines the content - (6.7.2.3). --- An attempt is made to modify an object defined with a const-qualified type through - use of an lvalue with non-const-qualified type (6.7.3). --- An attempt is made to refer to an object defined with a volatile-qualified type through - use of an lvalue with non-volatile-qualified type (6.7.3). --- The specification of a function type includes any type qualifiers (6.7.3). * --- Two qualified types that are required to be compatible do not have the identically - qualified version of a compatible type (6.7.3). --- An object which has been modified is accessed through a restrict-qualified pointer to - a const-qualified type, or through a restrict-qualified pointer and another pointer that - are not both based on the same object (6.7.3.1). --- A restrict-qualified pointer is assigned a value based on another restricted pointer - whose associated block neither began execution before the block associated with this - pointer, nor ended before the assignment (6.7.3.1). --- A function with external linkage is declared with an inline function specifier, but is - not also defined in the same translation unit (6.7.4). --- A function declared with a _Noreturn function specifier returns to its caller (6.7.4). --- The definition of an object has an alignment specifier and another declaration of that - object has a different alignment specifier (6.7.5). - - -[page 557] (Contents) - --- Declarations of an object in different translation units have different alignment - specifiers (6.7.5). --- Two pointer types that are required to be compatible are not identically qualified, or - are not pointers to compatible types (6.7.6.1). --- The size expression in an array declaration is not a constant expression and evaluates - at program execution time to a nonpositive value (6.7.6.2). --- In a context requiring two array types to be compatible, they do not have compatible - element types, or their size specifiers evaluate to unequal values (6.7.6.2). --- A declaration of an array parameter includes the keyword static within the [ and - ] and the corresponding argument does not provide access to the first element of an - array with at least the specified number of elements (6.7.6.3). --- A storage-class specifier or type qualifier modifies the keyword void as a function - parameter type list (6.7.6.3). --- In a context requiring two function types to be compatible, they do not have - compatible return types, or their parameters disagree in use of the ellipsis terminator - or the number and type of parameters (after default argument promotion, when there - is no parameter type list or when one type is specified by a function definition with an - identifier list) (6.7.6.3). --- The value of an unnamed member of a structure or union is used (6.7.9). --- The initializer for a scalar is neither a single expression nor a single expression - enclosed in braces (6.7.9). --- The initializer for a structure or union object that has automatic storage duration is - neither an initializer list nor a single expression that has compatible structure or union - type (6.7.9). --- The initializer for an aggregate or union, other than an array initialized by a string - literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9). --- An identifier with external linkage is used, but in the program there does not exist - exactly one external definition for the identifier, or the identifier is not used and there - exist multiple external definitions for the identifier (6.9). --- A function definition includes an identifier list, but the types of the parameters are not - declared in a following declaration list (6.9.1). --- An adjusted parameter type in a function definition is not a complete object type - (6.9.1). --- A function that accepts a variable number of arguments is defined without a - parameter type list that ends with the ellipsis notation (6.9.1). - -[page 558] (Contents) - --- The } that terminates a function is reached, and the value of the function call is used - by the caller (6.9.1). --- An identifier for an object with internal linkage and an incomplete type is declared - with a tentative definition (6.9.2). --- The token defined is generated during the expansion of a #if or #elif - preprocessing directive, or the use of the defined unary operator does not match - one of the two specified forms prior to macro replacement (6.10.1). --- The #include preprocessing directive that results after expansion does not match - one of the two header name forms (6.10.2). --- The character sequence in an #include preprocessing directive does not start with a - letter (6.10.2). --- There are sequences of preprocessing tokens within the list of macro arguments that - would otherwise act as preprocessing directives (6.10.3). --- The result of the preprocessing operator # is not a valid character string literal - (6.10.3.2). --- The result of the preprocessing operator ## is not a valid preprocessing token - (6.10.3.3). --- The #line preprocessing directive that results after expansion does not match one of - the two well-defined forms, or its digit sequence specifies zero or a number greater - than 2147483647 (6.10.4). --- A non-STDC #pragma preprocessing directive that is documented as causing - translation failure or some other form of undefined behavior is encountered (6.10.6). --- A #pragma STDC preprocessing directive does not match one of the well-defined - forms (6.10.6). --- The name of a predefined macro, or the identifier defined, is the subject of a - #define or #undef preprocessing directive (6.10.8). --- An attempt is made to copy an object to an overlapping object by use of a library - function, other than as explicitly allowed (e.g., memmove) (clause 7). --- A file with the same name as one of the standard headers, not provided as part of the - implementation, is placed in any of the standard places that are searched for included - source files (7.1.2). --- A header is included within an external declaration or definition (7.1.2). --- A function, object, type, or macro that is specified as being declared or defined by - some standard header is used before any header that declares or defines it is included - (7.1.2). - -[page 559] (Contents) - --- A standard header is included while a macro is defined with the same name as a - keyword (7.1.2). --- The program attempts to declare a library function itself, rather than via a standard - header, but the declaration does not have external linkage (7.1.2). --- The program declares or defines a reserved identifier, other than as allowed by 7.1.4 - (7.1.3). --- The program removes the definition of a macro whose name begins with an - underscore and either an uppercase letter or another underscore (7.1.3). --- An argument to a library function has an invalid value or a type not expected by a - function with variable number of arguments (7.1.4). --- The pointer passed to a library function array parameter does not have a value such - that all address computations and object accesses are valid (7.1.4). --- The macro definition of assert is suppressed in order to access an actual function - (7.2). --- The argument to the assert macro does not have a scalar type (7.2). --- The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in - any context other than outside all external declarations or preceding all explicit - declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2). --- The value of an argument to a character handling function is neither equal to the value - of EOF nor representable as an unsigned char (7.4). --- A macro definition of errno is suppressed in order to access an actual object, or the - program defines an identifier with the name errno (7.5). --- Part of the program tests floating-point status flags, sets floating-point control modes, - or runs under non-default mode settings, but was translated with the state for the - FENV_ACCESS pragma ''off'' (7.6.1). --- The exception-mask argument for one of the functions that provide access to the - floating-point status flags has a nonzero value not obtained by bitwise OR of the - floating-point exception macros (7.6.2). --- The fesetexceptflag function is used to set floating-point status flags that were - not specified in the call to the fegetexceptflag function that provided the value - of the corresponding fexcept_t object (7.6.2.4). --- The argument to fesetenv or feupdateenv is neither an object set by a call to - fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4). --- The value of the result of an integer arithmetic or conversion function cannot be - represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.22.6.1, 7.22.6.2, 7.22.1). - -[page 560] (Contents) - --- The program modifies the string pointed to by the value returned by the setlocale - function (7.11.1.1). --- The program modifies the structure pointed to by the value returned by the - localeconv function (7.11.2.1). --- A macro definition of math_errhandling is suppressed or the program defines - an identifier with the name math_errhandling (7.12). --- An argument to a floating-point classification or comparison macro is not of real - floating type (7.12.3, 7.12.14). --- A macro definition of setjmp is suppressed in order to access an actual function, or - the program defines an external identifier with the name setjmp (7.13). --- An invocation of the setjmp macro occurs other than in an allowed context - (7.13.2.1). --- The longjmp function is invoked to restore a nonexistent environment (7.13.2.1). --- After a longjmp, there is an attempt to access the value of an object of automatic - storage duration that does not have volatile-qualified type, local to the function - containing the invocation of the corresponding setjmp macro, that was changed - between the setjmp invocation and longjmp call (7.13.2.1). --- The program specifies an invalid pointer to a signal handler function (7.14.1.1). --- A signal handler returns when the signal corresponded to a computational exception - (7.14.1.1). --- A signal occurs as the result of calling the abort or raise function, and the signal - handler calls the raise function (7.14.1.1). --- A signal occurs other than as the result of calling the abort or raise function, and - the signal handler refers to an object with static or thread storage duration that is not a - lock-free atomic object other than by assigning a value to an object declared as - volatile sig_atomic_t, or calls any function in the standard library other - than the abort function, the _Exit function, the quick_exit function, or the - signal function (for the same signal number) (7.14.1.1). --- The value of errno is referred to after a signal occurred other than as the result of - calling the abort or raise function and the corresponding signal handler obtained - a SIG_ERR return from a call to the signal function (7.14.1.1). --- A signal is generated by an asynchronous signal handler (7.14.1.1). --- A function with a variable number of arguments attempts to access its varying - arguments other than through a properly declared and initialized va_list object, or - before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4). - -[page 561] (Contents) - --- The macro va_arg is invoked using the parameter ap that was passed to a function - that invoked the macro va_arg with the same parameter (7.16). --- A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in - order to access an actual function, or the program defines an external identifier with - the name va_copy or va_end (7.16.1). --- The va_start or va_copy macro is invoked without a corresponding invocation - of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3, - 7.16.1.4). --- The type parameter to the va_arg macro is not such that a pointer to an object of - that type can be obtained simply by postfixing a * (7.16.1.1). --- The va_arg macro is invoked when there is no actual next argument, or with a - specified type that is not compatible with the promoted type of the actual next - argument, with certain exceptions (7.16.1.1). --- The va_copy or va_start macro is called to initialize a va_list that was - previously initialized by either macro without an intervening invocation of the - va_end macro for the same va_list (7.16.1.2, 7.16.1.4). --- The parameter parmN of a va_start macro is declared with the register - storage class, with a function or array type, or with a type that is not compatible with - the type that results after application of the default argument promotions (7.16.1.4). --- The member designator parameter of an offsetof macro is an invalid right - operand of the . operator for the type parameter, or designates a bit-field (7.19). --- The argument in an instance of one of the integer-constant macros is not a decimal, - octal, or hexadecimal constant, or it has a value that exceeds the limits for the - corresponding type (7.20.4). --- A byte input/output function is applied to a wide-oriented stream, or a wide character - input/output function is applied to a byte-oriented stream (7.21.2). --- Use is made of any portion of a file beyond the most recent wide character written to - a wide-oriented stream (7.21.2). --- The value of a pointer to a FILE object is used after the associated file is closed - (7.21.3). --- The stream for the fflush function points to an input stream or to an update stream - in which the most recent operation was input (7.21.5.2). --- The string pointed to by the mode argument in a call to the fopen function does not - exactly match one of the specified character sequences (7.21.5.3). --- An output operation on an update stream is followed by an input operation without an - intervening call to the fflush function or a file positioning function, or an input -[page 562] (Contents) - - operation on an update stream is followed by an output operation with an intervening - call to a file positioning function (7.21.5.3). --- An attempt is made to use the contents of the array that was supplied in a call to the - setvbuf function (7.21.5.6). --- There are insufficient arguments for the format in a call to one of the formatted - input/output functions, or an argument does not have an appropriate type (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- The format in a call to one of the formatted input/output functions or to the - strftime or wcsftime function is not a valid multibyte character sequence that - begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.26.3.5, 7.28.2.1, 7.28.2.2, - 7.28.5.1). --- In a call to one of the formatted output functions, a precision appears with a - conversion specifier other than those described (7.21.6.1, 7.28.2.1). --- A conversion specification for a formatted output function uses an asterisk to denote - an argument-supplied field width or precision, but the corresponding argument is not - provided (7.21.6.1, 7.28.2.1). --- A conversion specification for a formatted output function uses a # or 0 flag with a - conversion specifier other than those described (7.21.6.1, 7.28.2.1). --- A conversion specification for one of the formatted input/output functions uses a - length modifier with a conversion specifier other than those described (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- An s conversion specifier is encountered by one of the formatted output functions, - and the argument is missing the null terminator (unless a precision is specified that - does not require null termination) (7.21.6.1, 7.28.2.1). --- An n conversion specification for one of the formatted input/output functions includes - any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- A % conversion specifier is encountered by one of the formatted input/output - functions, but the complete conversion specification is not exactly %% (7.21.6.1, - 7.21.6.2, 7.28.2.1, 7.28.2.2). --- An invalid conversion specification is found in the format for one of the formatted - input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2, - 7.26.3.5, 7.28.2.1, 7.28.2.2, 7.28.5.1). --- The number of characters transmitted by a formatted output function is greater than - INT_MAX (7.21.6.1, 7.21.6.3, 7.21.6.8, 7.21.6.10). - - -[page 563] (Contents) - --- The result of a conversion by one of the formatted input functions cannot be - represented in the corresponding object, or the receiving object does not have an - appropriate type (7.21.6.2, 7.28.2.2). --- A c, s, or [ conversion specifier is encountered by one of the formatted input - functions, and the array pointed to by the corresponding argument is not large enough - to accept the input sequence (and a null terminator if the conversion specifier is s or - [) (7.21.6.2, 7.28.2.2). --- A c, s, or [ conversion specifier with an l qualifier is encountered by one of the - formatted input functions, but the input is not a valid multibyte character sequence - that begins in the initial shift state (7.21.6.2, 7.28.2.2). --- The input item for a %p conversion by one of the formatted input functions is not a - value converted earlier during the same program execution (7.21.6.2, 7.28.2.2). --- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, - vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or - vwscanf function is called with an improperly initialized va_list argument, or - the argument is used (other than in an invocation of va_end) after the function - returns (7.21.6.8, 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, - 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10). --- The contents of the array supplied in a call to the fgets or fgetws function are - used after a read error occurred (7.21.7.2, 7.28.3.2). --- The file position indicator for a binary stream is used after a call to the ungetc - function where its value was zero before the call (7.21.7.10). --- The file position indicator for a stream is used after an error occurred during a call to - the fread or fwrite function (7.21.8.1, 7.21.8.2). --- A partial element read by a call to the fread function is used (7.21.8.1). --- The fseek function is called for a text stream with a nonzero offset and either the - offset was not returned by a previous successful call to the ftell function on a - stream associated with the same file or whence is not SEEK_SET (7.21.9.2). --- The fsetpos function is called to set a position that was not returned by a previous - successful call to the fgetpos function on a stream associated with the same file - (7.21.9.3). --- A non-null pointer returned by a call to the calloc, malloc, or realloc function - with a zero requested size is used to access an object (7.22.3). --- The value of a pointer that refers to space deallocated by a call to the free or - realloc function is used (7.22.3). - - -[page 564] (Contents) - --- The alignment requested of the aligned_alloc function is not valid or not - supported by the implementation, or the size requested is not an integral multiple of - the alignment (7.22.3.1). --- The pointer argument to the free or realloc function does not match a pointer - earlier returned by a memory management function, or the space has been deallocated - by a call to free or realloc (7.22.3.3, 7.22.3.5). --- The value of the object allocated by the malloc function is used (7.22.3.4). --- The value of any bytes in a new object allocated by the realloc function beyond - the size of the old object are used (7.22.3.5). --- The program calls the exit or quick_exit function more than once, or calls both - functions (7.22.4.4, 7.22.4.7). --- During the call to a function registered with the atexit or at_quick_exit - function, a call is made to the longjmp function that would terminate the call to the - registered function (7.22.4.4, 7.22.4.7). --- The string set up by the getenv or strerror function is modified by the program - (7.22.4.6, 7.23.6.2). --- A command is executed through the system function in a way that is documented as - causing termination or some other form of undefined behavior (7.22.4.8). --- A searching or sorting utility function is called with an invalid pointer argument, even - if the number of elements is zero (7.22.5). --- The comparison function called by a searching or sorting utility function alters the - contents of the array being searched or sorted, or returns ordering values - inconsistently (7.22.5). --- The array being searched by the bsearch function does not have its elements in - proper order (7.22.5.1). --- The current conversion state is used by a multibyte/wide character conversion - function after changing the LC_CTYPE category (7.22.7). --- A string or wide string utility function is instructed to access an array beyond the end - of an object (7.23.1, 7.28.4). --- A string or wide string utility function is called with an invalid pointer argument, even - if the length is zero (7.23.1, 7.28.4). --- The contents of the destination array are used after a call to the strxfrm, - strftime, wcsxfrm, or wcsftime function in which the specified length was - too small to hold the entire null-terminated result (7.23.4.5, 7.26.3.5, 7.28.4.4.4, - 7.28.5.1). - -[page 565] (Contents) - - -- The first argument in the very first call to the strtok or wcstok is a null pointer - (7.23.5.8, 7.28.4.5.7). - -- The type of an argument to a type-generic macro is not compatible with the type of - the corresponding parameter of the selected function (7.24). - -- A complex argument is supplied for a generic parameter of a type-generic macro that - has no corresponding complex function (7.24). - -- At least one field of the broken-down time passed to asctime contains a value - outside its normal range, or the calculated year exceeds four digits or is less than the - year 1000 (7.26.3.1). - -- The argument corresponding to an s specifier without an l qualifier in a call to the - fwprintf function does not point to a valid multibyte character sequence that - begins in the initial shift state (7.28.2.11). - -- In a call to the wcstok function, the object pointed to by ptr does not have the - value stored by the previous call for the same wide string (7.28.4.5.7). - -- An mbstate_t object is used inappropriately (7.28.6). - -- The value of an argument of type wint_t to a wide character classification or case - mapping function is neither equal to the value of WEOF nor representable as a - wchar_t (7.29.1). - -- The iswctype function is called using a different LC_CTYPE category from the - one in effect for the call to the wctype function that returned the description - (7.29.2.2.1). - -- The towctrans function is called using a different LC_CTYPE category from the - one in effect for the call to the wctrans function that returned the description - (7.29.3.2.1). - J.3 Implementation-defined behavior -1 A conforming implementation is required to document its choice of behavior in each of - the areas listed in this subclause. The following are implementation-defined: - - - - -[page 566] (Contents) - - J.3.1 Translation -1 -- How a diagnostic is identified (3.10, 5.1.1.3). - -- Whether each nonempty sequence of white-space characters other than new-line is - retained or replaced by one space character in translation phase 3 (5.1.1.2). - J.3.2 Environment -1 -- The mapping between physical source file multibyte characters and the source - character set in translation phase 1 (5.1.1.2). - -- The name and type of the function called at program startup in a freestanding - environment (5.1.2.1). - -- The effect of program termination in a freestanding environment (5.1.2.1). - -- An alternative manner in which the main function may be defined (5.1.2.2.1). - -- The values given to the strings pointed to by the argv argument to main (5.1.2.2.1). - -- What constitutes an interactive device (5.1.2.3). - -- Whether a program can have more than one thread of execution in a freestanding - environment (5.1.2.4). - -- The set of signals, their semantics, and their default handling (7.14). - -- Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a - computational exception (7.14.1.1). - -- Signals for which the equivalent of signal(sig, SIG_IGN); is executed at - program startup (7.14.1.1). - -- The set of environment names and the method for altering the environment list used - by the getenv function (7.22.4.6). - -- The manner of execution of the string by the system function (7.22.4.8). - J.3.3 Identifiers -1 -- Which additional multibyte characters may appear in identifiers and their - correspondence to universal character names (6.4.2). - -- The number of significant initial characters in an identifier (5.2.4.1, 6.4.2). - - - - -[page 567] (Contents) - - J.3.4 Characters -1 -- The number of bits in a byte (3.6). - -- The values of the members of the execution character set (5.2.1). - -- The unique value of the member of the execution character set produced for each of - the standard alphabetic escape sequences (5.2.2). - -- The value of a char object into which has been stored any character other than a - member of the basic execution character set (6.2.5). - -- Which of signed char or unsigned char has the same range, representation, - and behavior as ''plain'' char (6.2.5, 6.3.1.1). - -- The mapping of members of the source character set (in character constants and string - literals) to members of the execution character set (6.4.4.4, 5.1.1.2). - -- The value of an integer character constant containing more than one character or - containing a character or escape sequence that does not map to a single-byte - execution character (6.4.4.4). - -- The value of a wide character constant containing more than one multibyte character - or a single multibyte character that maps to multiple members of the extended - execution character set, or containing a multibyte character or escape sequence not - represented in the extended execution character set (6.4.4.4). - -- The current locale used to convert a wide character constant consisting of a single - multibyte character that maps to a member of the extended execution character set - into a corresponding wide character code (6.4.4.4). - -- Whether differently-prefixed wide string literal tokens can be concatenated and, if so, - the treatment of the resulting multibyte character sequence (6.4.5). - -- The current locale used to convert a wide string literal into corresponding wide - character codes (6.4.5). - -- The value of a string literal containing a multibyte character or escape sequence not - represented in the execution character set (6.4.5). - -- The encoding of any of wchar_t, char16_t, and char32_t where the - corresponding standard encoding macro (__STDC_ISO_10646__, - __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.8.2). - - - - -[page 568] (Contents) - - J.3.5 Integers -1 -- Any extended integer types that exist in the implementation (6.2.5). - -- Whether signed integer types are represented using sign and magnitude, two's - complement, or ones' complement, and whether the extraordinary value is a trap - representation or an ordinary value (6.2.6.2). - -- The rank of any extended integer type relative to another extended integer type with - the same precision (6.3.1.1). - -- The result of, or the signal raised by, converting an integer to a signed integer type - when the value cannot be represented in an object of that type (6.3.1.3). - -- The results of some bitwise operations on signed integers (6.5). - J.3.6 Floating point -1 -- The accuracy of the floating-point operations and of the library functions in - <math.h> and <complex.h> that return floating-point results (5.2.4.2.2). - -- The accuracy of the conversions between floating-point internal representations and - string representations performed by the library functions in <stdio.h>, - <stdlib.h>, and <wchar.h> (5.2.4.2.2). - -- The rounding behaviors characterized by non-standard values of FLT_ROUNDS - (5.2.4.2.2). - -- The evaluation methods characterized by non-standard negative values of - FLT_EVAL_METHOD (5.2.4.2.2). - -- The direction of rounding when an integer is converted to a floating-point number that - cannot exactly represent the original value (6.3.1.4). - -- The direction of rounding when a floating-point number is converted to a narrower - floating-point number (6.3.1.5). - -- How the nearest representable value or the larger or smaller representable value - immediately adjacent to the nearest representable value is chosen for certain floating - constants (6.4.4.2). - -- Whether and how floating expressions are contracted when not disallowed by the - FP_CONTRACT pragma (6.5). - -- The default state for the FENV_ACCESS pragma (7.6.1). - -- Additional floating-point exceptions, rounding modes, environments, and - classifications, and their macro names (7.6, 7.12). - -- The default state for the FP_CONTRACT pragma (7.12.2). - - -[page 569] (Contents) - - J.3.7 Arrays and pointers -1 -- The result of converting a pointer to an integer or vice versa (6.3.2.3). - -- The size of the result of subtracting two pointers to elements of the same array - (6.5.6). - J.3.8 Hints -1 -- The extent to which suggestions made by using the register storage-class - specifier are effective (6.7.1). - -- The extent to which suggestions made by using the inline function specifier are - effective (6.7.4). - J.3.9 Structures, unions, enumerations, and bit-fields -1 -- Whether a ''plain'' int bit-field is treated as a signed int bit-field or as an - unsigned int bit-field (6.7.2, 6.7.2.1). - -- Allowable bit-field types other than _Bool, signed int, and unsigned int - (6.7.2.1). - -- Whether atomic types are permitted for bit-fields (6.7.2.1). - -- Whether a bit-field can straddle a storage-unit boundary (6.7.2.1). - -- The order of allocation of bit-fields within a unit (6.7.2.1). - -- The alignment of non-bit-field members of structures (6.7.2.1). This should present - no problem unless binary data written by one implementation is read by another. - -- The integer type compatible with each enumerated type (6.7.2.2). - J.3.10 Qualifiers -1 -- What constitutes an access to an object that has volatile-qualified type (6.7.3). - J.3.11 Preprocessing directives -1 -- The locations within #pragma directives where header name preprocessing tokens - are recognized (6.4, 6.4.7). - -- How sequences in both forms of header names are mapped to headers or external - source file names (6.4.7). - -- Whether the value of a character constant in a constant expression that controls - conditional inclusion matches the value of the same character constant in the - execution character set (6.10.1). - -- Whether the value of a single-character character constant in a constant expression - that controls conditional inclusion may have a negative value (6.10.1). - - -[page 570] (Contents) - - -- The places that are searched for an included < > delimited header, and how the places - are specified or the header is identified (6.10.2). - -- How the named source file is searched for in an included " " delimited header - (6.10.2). - -- The method by which preprocessing tokens (possibly resulting from macro - expansion) in a #include directive are combined into a header name (6.10.2). - -- The nesting limit for #include processing (6.10.2). - -- Whether the # operator inserts a \ character before the \ character that begins a - universal character name in a character constant or string literal (6.10.3.2). - -- The behavior on each recognized non-STDC #pragma directive (6.10.6). - -- The definitions for __DATE__ and __TIME__ when respectively, the date and - time of translation are not available (6.10.8.1). - J.3.12 Library functions -1 -- Any library facilities available to a freestanding program, other than the minimal set - required by clause 4 (5.1.2.1). - -- The format of the diagnostic printed by the assert macro (7.2.1.1). - -- The representation of the floating-point status flags stored by the - fegetexceptflag function (7.6.2.2). - -- Whether the feraiseexcept function raises the ''inexact'' floating-point - exception in addition to the ''overflow'' or ''underflow'' floating-point exception - (7.6.2.3). - -- Strings other than "C" and "" that may be passed as the second argument to the - setlocale function (7.11.1.1). - -- The types defined for float_t and double_t when the value of the - FLT_EVAL_METHOD macro is less than 0 (7.12). - -- Domain errors for the mathematics functions, other than those required by this - International Standard (7.12.1). - -- The values returned by the mathematics functions on domain errors or pole errors - (7.12.1). - -- The values returned by the mathematics functions on underflow range errors, whether - errno is set to the value of the macro ERANGE when the integer expression - math_errhandling & MATH_ERRNO is nonzero, and whether the ''underflow'' - floating-point exception is raised when the integer expression math_errhandling - & MATH_ERREXCEPT is nonzero. (7.12.1). - -[page 571] (Contents) - --- Whether a domain error occurs or zero is returned when an fmod function has a - second argument of zero (7.12.10.1). --- Whether a domain error occurs or zero is returned when a remainder function has - a second argument of zero (7.12.10.2). --- The base-2 logarithm of the modulus used by the remquo functions in reducing the - quotient (7.12.10.3). --- Whether a domain error occurs or zero is returned when a remquo function has a - second argument of zero (7.12.10.3). --- Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call - of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1). --- The null pointer constant to which the macro NULL expands (7.19). --- Whether the last line of a text stream requires a terminating new-line character - (7.21.2). --- Whether space characters that are written out to a text stream immediately before a - new-line character appear when read in (7.21.2). --- The number of null characters that may be appended to data written to a binary - stream (7.21.2). --- Whether the file position indicator of an append-mode stream is initially positioned at - the beginning or end of the file (7.21.3). --- Whether a write on a text stream causes the associated file to be truncated beyond that - point (7.21.3). --- The characteristics of file buffering (7.21.3). --- Whether a zero-length file actually exists (7.21.3). --- The rules for composing valid file names (7.21.3). --- Whether the same file can be simultaneously open multiple times (7.21.3). --- The nature and choice of encodings used for multibyte characters in files (7.21.3). --- The effect of the remove function on an open file (7.21.4.1). --- The effect if a file with the new name exists prior to a call to the rename function - (7.21.4.2). --- Whether an open temporary file is removed upon abnormal program termination - (7.21.4.3). --- Which changes of mode are permitted (if any), and under what circumstances - (7.21.5.4). - -[page 572] (Contents) - --- The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar - sequence printed for a NaN (7.21.6.1, 7.28.2.1). --- The output for %p conversion in the fprintf or fwprintf function (7.21.6.1, - 7.28.2.1). --- The interpretation of a - character that is neither the first nor the last character, nor - the second where a ^ character is the first, in the scanlist for %[ conversion in the - fscanf or fwscanf function (7.21.6.2, 7.28.2.1). --- The set of sequences matched by a %p conversion and the interpretation of the - corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.28.2.2). --- The value to which the macro errno is set by the fgetpos, fsetpos, or ftell - functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4). --- The meaning of any n-char or n-wchar sequence in a string representing a NaN that is - converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold - function (7.22.1.3, 7.28.4.1.1). --- Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold - function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.28.4.1.1). --- Whether the calloc, malloc, and realloc functions return a null pointer or a - pointer to an allocated object when the size requested is zero (7.22.3). --- Whether open streams with unwritten buffered data are flushed, open streams are - closed, or temporary files are removed when the abort or _Exit function is called - (7.22.4.1, 7.22.4.5). --- The termination status returned to the host environment by the abort, exit, - _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7). --- The value returned by the system function when its argument is not a null pointer - (7.22.4.8). --- The local time zone and Daylight Saving Time (7.26.1). --- The range and precision of times representable in clock_t and time_t (7.26). --- The era for the clock function (7.26.2.1). --- The replacement string for the %Z specifier to the strftime, and wcsftime - functions in the "C" locale (7.26.3.5, 7.28.5.1). --- Whether the functions in <math.h> honor the rounding direction mode in an - IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10). - - - - -[page 573] (Contents) - - J.3.13 Architecture -1 -- The values or expressions assigned to the macros specified in the headers - <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.20.2, 7.20.3). - -- The result of attempting to indirectly access an object with automatic or thread - storage duration from a thread other than the one with which it is associated (6.2.4). - -- The number, order, and encoding of bytes in any object (when not explicitly specified - in this International Standard) (6.2.6.1). - -- Whether any extended alignments are supported and the contexts in which they are - supported (6.2.8). - -- Valid alignment values other than those returned by an alignof expression for - fundamental types, if any (6.2.8). - -- The value of the result of the sizeof and alignof operators (6.5.3.4). - J.4 Locale-specific behavior -1 The following characteristics of a hosted environment are locale-specific and are required - to be documented by the implementation: - -- Additional members of the source and execution character sets beyond the basic - character set (5.2.1). - -- The presence, meaning, and representation of additional multibyte characters in the - execution character set beyond the basic character set (5.2.1.2). - -- The shift states used for the encoding of multibyte characters (5.2.1.2). - -- The direction of writing of successive printing characters (5.2.2). - -- The decimal-point character (7.1.1). - -- The set of printing characters (7.4, 7.29.2). - -- The set of control characters (7.4, 7.29.2). - -- The sets of characters tested for by the isalpha, isblank, islower, ispunct, - isspace, isupper, iswalpha, iswblank, iswlower, iswpunct, - iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10, - 7.4.1.11, 7.29.2.1.2, 7.29.2.1.3, 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, 7.29.2.1.11). - -- The native environment (7.11.1.1). - -- Additional subject sequences accepted by the numeric conversion functions (7.22.1, - 7.28.4.1). - -- The collation sequence of the execution character set (7.23.4.3, 7.28.4.4.2). - - -[page 574] (Contents) - - -- The contents of the error message strings set up by the strerror function - (7.23.6.2). - -- The formats for time and date (7.26.3.5, 7.28.5.1). - -- Character mappings that are supported by the towctrans function (7.29.1). - -- Character classifications that are supported by the iswctype function (7.29.1). - J.5 Common extensions -1 The following extensions are widely used in many systems, but are not portable to all - implementations. The inclusion of any extension that may cause a strictly conforming - program to become invalid renders an implementation nonconforming. Examples of such - extensions are new keywords, extra library functions declared in standard headers, or - predefined macros with names that do not begin with an underscore. - J.5.1 Environment arguments -1 In a hosted environment, the main function receives a third argument, char *envp[], - that points to a null-terminated array of pointers to char, each of which points to a string - that provides information about the environment for this execution of the program - (5.1.2.2.1). - J.5.2 Specialized identifiers -1 Characters other than the underscore _, letters, and digits, that are not part of the basic - source character set (such as the dollar sign $, or characters in national character sets) - may appear in an identifier (6.4.2). - J.5.3 Lengths and cases of identifiers -1 All characters in identifiers (with or without external linkage) are significant (6.4.2). - J.5.4 Scopes of identifiers -1 A function identifier, or the identifier of an object the declaration of which contains the - keyword extern, has file scope (6.2.1). - J.5.5 Writable string literals -1 String literals are modifiable (in which case, identical string literals should denote distinct - objects) (6.4.5). - - - - -[page 575] (Contents) - - J.5.6 Other arithmetic types -1 Additional arithmetic types, such as __int128 or double double, and their - appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have - more range or precision than long double, may be used for evaluating expressions of - other floating types, and may be used to define float_t or double_t. - J.5.7 Function pointer casts -1 A pointer to an object or to void may be cast to a pointer to a function, allowing data to - be invoked as a function (6.5.4). -2 A pointer to a function may be cast to a pointer to an object or to void, allowing a - function to be inspected or modified (for example, by a debugger) (6.5.4). - J.5.8 Extended bit-field types -1 A bit-field may be declared with a type other than _Bool, unsigned int, or - signed int, with an appropriate maximum width (6.7.2.1). - J.5.9 The fortran keyword -1 The fortran function specifier may be used in a function declaration to indicate that - calls suitable for FORTRAN should be generated, or that a different representation for the - external name is to be generated (6.7.4). - J.5.10 The asm keyword -1 The asm keyword may be used to insert assembly language directly into the translator - output (6.8). The most common implementation is via a statement of the form: - asm ( character-string-literal ); - J.5.11 Multiple external definitions -1 There may be more than one external definition for the identifier of an object, with or - without the explicit use of the keyword extern; if the definitions disagree, or more than - one is initialized, the behavior is undefined (6.9.2). - J.5.12 Predefined macro names -1 Macro names that do not begin with an underscore, describing the translation and - execution environments, are defined by the implementation before translation begins - (6.10.8). - - - - -[page 576] (Contents) - - J.5.13 Floating-point status flags -1 If any floating-point status flags are set on normal termination after all calls to functions - registered by the atexit function have been made (see 7.22.4.4), the implementation - writes some diagnostics indicating the fact to the stderr stream, if it is still open, - J.5.14 Extra arguments for signal handlers -1 Handlers for specific signals are called with extra arguments in addition to the signal - number (7.14.1.1). - J.5.15 Additional stream types and file-opening modes -1 Additional mappings from files to streams are supported (7.21.2). -2 Additional file-opening modes may be specified by characters appended to the mode - argument of the fopen function (7.21.5.3). - J.5.16 Defined file position indicator -1 The file position indicator is decremented by each successful call to the ungetc or - ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10, - 7.28.3.10). - J.5.17 Math error reporting -1 Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors - instead of, or in addition to, setting errno or raising floating-point exceptions (7.3, - 7.12). - - - - -[page 577] (Contents) - - Annex K - (normative) - Bounds-checking interfaces - K.1 Background -1 Traditionally, the C Library has contained many functions that trust the programmer to - provide output character arrays big enough to hold the result being produced. Not only - do these functions not check that the arrays are big enough, they frequently lack the - information needed to perform such checks. While it is possible to write safe, robust, and - error-free code using the existing library, the library tends to promote programming styles - that lead to mysterious failures if a result is too big for the provided array. -2 A common programming style is to declare character arrays large enough to handle most - practical cases. However, if these arrays are not large enough to handle the resulting - strings, data can be written past the end of the array overwriting other data and program - structures. The program never gets any indication that a problem exists, and so never has - a chance to recover or to fail gracefully. -3 Worse, this style of programming has compromised the security of computers and - networks. Buffer overflows can often be exploited to run arbitrary code with the - permissions of the vulnerable (defective) program. -4 If the programmer writes runtime checks to verify lengths before calling library - functions, then those runtime checks frequently duplicate work done inside the library - functions, which discover string lengths as a side effect of doing their job. -5 This annex provides alternative library functions that promote safer, more secure - programming. The alternative functions verify that output buffers are large enough for - the intended result and return a failure indicator if they are not. Data is never written past - the end of an array. All string results are null terminated. -6 This annex also addresses another problem that complicates writing robust code: - functions that are not reentrant because they return pointers to static objects owned by the - function. Such functions can be troublesome since a previously returned result can - change if the function is called again, perhaps by another thread. - - - - -[page 578] (Contents) - - K.2 Scope -1 This annex specifies a series of optional extensions that can be useful in the mitigation of - security vulnerabilities in programs, and comprise new functions, macros, and types - declared or defined in existing standard headers. -2 An implementation that defines __STDC_LIB_EXT1__ shall conform to the - specifications in this annex.367) -3 Subclause K.3 should be read as if it were merged into the parallel structure of named - subclauses of clause 7. - K.3 Library - K.3.1 Introduction - K.3.1.1 Standard headers -1 The functions, macros, and types declared or defined in K.3 and its subclauses are not - declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is - defined as a macro which expands to the integer constant 0 at the point in the source file - where the appropriate header is first included. -2 The functions, macros, and types declared or defined in K.3 and its subclauses are - declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is - defined as a macro which expands to the integer constant 1 at the point in the source file - where the appropriate header is first included.368) -3 It is implementation-defined whether the functions, macros, and types declared or defined - in K.3 and its subclauses are declared or defined by their respective headers if - __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file - where the appropriate header is first included.369) -4 Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be - defined identically for all inclusions of any headers from subclause K.3. If - __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the - implementation shall issue a diagnostic as if a preprocessor error directive were used. - - - 367) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these - specifications. - 368) Future revisions of this International Standard may define meanings for other values of - __STDC_WANT_LIB_EXT1__. - 369) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in - headers. All other names are not reserved, and a conforming implementation is not permitted to use - them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an - unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the - implementation is not conforming. - -[page 579] (Contents) - - K.3.1.2 Reserved identifiers -1 Each macro name in any of the following subclauses is reserved for use as specified if it - is defined by any of its associated headers when included; unless explicitly stated - otherwise (see 7.1.4). -2 All identifiers with external linkage in any of the following subclauses are reserved for - use as identifiers with external linkage if any of them are used by the program. None of - them are reserved if none of them are used. -3 Each identifier with file scope listed in any of the following subclauses is reserved for use - as a macro name and as an identifier with file scope in the same name space if it is - defined by any of its associated headers when included. - K.3.1.3 Use of errno -1 An implementation may set errno for the functions defined in this annex, but is not - required to. - K.3.1.4 Runtime-constraint violations -1 Most functions in this annex include as part of their specification a list of runtime- - constraints. These runtime-constraints are requirements on the program using the - library.370) -2 Implementations shall verify that the runtime-constraints for a function are not violated - by the program. If a runtime-constraint is violated, the implementation shall call the - currently registered runtime-constraint handler (see set_constraint_handler_s - in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library - function result in only one call to the runtime-constraint handler. It is unspecified which - one of the multiple runtime-constraint violations cause the handler to be called. -3 If the runtime-constraints section for a function states an action to be performed when a - runtime-constraint violation occurs, the function shall perform the action before calling - the runtime-constraint handler. If the runtime-constraints section lists actions that are - prohibited when a runtime-constraint violation occurs, then such actions are prohibited to - the function both before calling the handler and after the handler returns. -4 The runtime-constraint handler might not return. If the handler does return, the library - function whose runtime-constraint was violated shall return some indication of failure as - given by the returns section in the function's specification. - - - - 370) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still - exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a - runtime-constraint violation by calling the runtime-constraint handler. This license comes directly - from the definition of undefined behavior. - -[page 580] (Contents) - - K.3.2 Errors <errno.h> -1 The header <errno.h> defines a type. -2 The type is - errno_t - which is type int.371) - K.3.3 Common definitions <stddef.h> -1 The header <stddef.h> defines a type. -2 The type is - rsize_t - which is the type size_t.372) - K.3.4 Integer types <stdint.h> -1 The header <stdint.h> defines a macro. -2 The macro is - RSIZE_MAX - which expands to a value373) of type size_t. Functions that have parameters of type - rsize_t consider it a runtime-constraint violation if the values of those parameters are - greater than RSIZE_MAX. - Recommended practice -3 Extremely large object sizes are frequently a sign that an object's size was calculated - incorrectly. For example, negative numbers appear as very large positive numbers when - converted to an unsigned type like size_t. Also, some implementations do not support - objects as large as the maximum value that can be represented by type size_t. -4 For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect - programming errors. For implementations targeting machines with large address spaces, - it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest - object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of - some legitimate, but very large, objects. Implementations targeting machines with small - address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there - - 371) As a matter of programming style, errno_t may be used as the type of something that deals only - with the values that might be found in errno. For example, a function which returns the value of - errno might be declared as having the return type errno_t. - 372) See the description of the RSIZE_MAX macro in <stdint.h>. - 373) The macro RSIZE_MAX need not expand to a constant expression. - -[page 581] (Contents) - - is no object size that is considered a runtime-constraint violation. - K.3.5 Input/output <stdio.h> -1 The header <stdio.h> defines several macros and two types. -2 The macros are - L_tmpnam_s - which expands to an integer constant expression that is the size needed for an array of - char large enough to hold a temporary file name string generated by the tmpnam_s - function; - TMP_MAX_S - which expands to an integer constant expression that is the maximum number of unique - file names that can be generated by the tmpnam_s function. -3 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. - K.3.5.1 Operations on files - K.3.5.1.1 The tmpfile_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - errno_t tmpfile_s(FILE * restrict * restrict streamptr); - Runtime-constraints -2 streamptr shall not be a null pointer. -3 If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file. - Description -4 The tmpfile_s function creates a temporary binary file that is different from any other - existing file and that will automatically be removed when it is closed or at program - termination. If the program terminates abnormally, whether an open temporary file is - removed is implementation-defined. The file is opened for update with "wb+" mode - with the meaning that mode has in the fopen_s function (including the mode's effect - on exclusive access and file permissions). - - -[page 582] (Contents) - -5 If the file was created successfully, then the pointer to FILE pointed to by streamptr - will be set to the pointer to the object controlling the opened file. Otherwise, the pointer - to FILE pointed to by streamptr will be set to a null pointer. - Recommended practice - It should be possible to open at least TMP_MAX_S temporary files during the lifetime of - the program (this limit may be shared with tmpnam_s) and there should be no limit on - the number simultaneously open other than this limit and any limit on the number of open - files (FOPEN_MAX). - Returns -6 The tmpfile_s function returns zero if it created the file. If it did not create the file or - there was a runtime-constraint violation, tmpfile_s returns a nonzero value. - K.3.5.1.2 The tmpnam_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - errno_t tmpnam_s(char *s, rsize_t maxsize); - Runtime-constraints -2 s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX. - maxsize shall be greater than the length of the generated file name string. - Description -3 The tmpnam_s function generates a string that is a valid file name and that is not the - same as the name of an existing file.374) The function is potentially capable of generating - TMP_MAX_S different strings, but any or all of them may already be in use by existing - files and thus not be suitable return values. The lengths of these strings shall be less than - the value of the L_tmpnam_s macro. -4 The tmpnam_s function generates a different string each time it is called. -5 It is assumed that s points to an array of at least maxsize characters. This array will be - set to generated string, as specified below. - - - - 374) Files created using strings generated by the tmpnam_s function are temporary only in the sense that - their names should not collide with those generated by conventional naming rules for the - implementation. It is still necessary to use the remove function to remove such files when their use - is ended, and before program termination. Implementations should take care in choosing the patterns - used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the - race condition and possible conflict when multiple programs run simultaneously by the same user - generate the same temporary file names. - -[page 583] (Contents) - -6 The implementation shall behave as if no library function except tmpnam calls the - tmpnam_s function.375) - Recommended practice -7 After a program obtains a file name using the tmpnam_s function and before the - program creates a file with that name, the possibility exists that someone else may create - a file with that same name. To avoid this race condition, the tmpfile_s function - should be used instead of tmpnam_s when possible. One situation that requires the use - of the tmpnam_s function is when the program needs to create a temporary directory - rather than a temporary file. - Returns -8 If no suitable string can be generated, or if there is a runtime-constraint violation, the - tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize - is greater than zero) and returns a nonzero value. -9 Otherwise, the tmpnam_s function writes the string in the array pointed to by s and - returns zero. - Environmental limits -10 The value of the macro TMP_MAX_S shall be at least 25. - K.3.5.2 File access functions - K.3.5.2.1 The fopen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - errno_t fopen_s(FILE * restrict * restrict streamptr, - const char * restrict filename, - const char * restrict mode); - Runtime-constraints -2 None of streamptr, filename, or mode shall be a null pointer. -3 If there is a runtime-constraint violation, fopen_s does not attempt to open a file. - Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the - null pointer. - - - - - 375) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming - convention for temporary files), but this is not required. - -[page 584] (Contents) - - Description -4 The fopen_s function opens the file whose name is the string pointed to by - filename, and associates a stream with it. -5 The mode string shall be as described for fopen, with the addition that modes starting - with the character 'w' or 'a' may be preceded by the character 'u', see below: - uw truncate to zero length or create text file for writing, default - permissions - uwx create text file for writing, default permissions - ua append; open or create text file for writing at end-of-file, default - permissions - uwb truncate to zero length or create binary file for writing, default - permissions - uwbx create binary file for writing, default permissions - uab append; open or create binary file for writing at end-of-file, default - permissions - uw+ truncate to zero length or create text file for update, default - permissions - uw+x create text file for update, default permissions - ua+ append; open or create text file for update, writing at end-of-file, - default permissions - uw+b or uwb+ truncate to zero length or create binary file for update, default - permissions - uw+bx or uwb+x create binary file for update, default permissions - ua+b or uab+ append; open or create binary file for update, writing at end-of-file, - default permissions -6 Opening a file with exclusive mode ('x' as the last character in the mode argument) - fails if the file already exists or cannot be created. -7 To the extent that the underlying system supports the concepts, files opened for writing - shall be opened with exclusive (also known as non-shared) access. If the file is being - created, and the first character of the mode string is not 'u', to the extent that the - underlying system supports it, the file shall have a file permission that prevents other - users on the system from accessing the file. If the file is being created and first character - of the mode string is 'u', then by the time the file has been closed, it shall have the - system default file access permissions.376) -8 If the file was opened successfully, then the pointer to FILE pointed to by streamptr - will be set to the pointer to the object controlling the opened file. Otherwise, the pointer - - - 376) These are the same permissions that the file would have been created with by fopen. - -[page 585] (Contents) - - to FILE pointed to by streamptr will be set to a null pointer. - Returns -9 The fopen_s function returns zero if it opened the file. If it did not open the file or if - there was a runtime-constraint violation, fopen_s returns a nonzero value. - K.3.5.2.2 The freopen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - errno_t freopen_s(FILE * restrict * restrict newstreamptr, - const char * restrict filename, - const char * restrict mode, - FILE * restrict stream); - Runtime-constraints -2 None of newstreamptr, mode, and stream shall be a null pointer. -3 If there is a runtime-constraint violation, freopen_s neither attempts to close any file - associated with stream nor attempts to open a file. Furthermore, if newstreamptr is - not a null pointer, fopen_s sets *newstreamptr to the null pointer. - Description -4 The freopen_s function opens the file whose name is the string pointed to by - filename and associates the stream pointed to by stream with it. The mode - argument has the same meaning as in the fopen_s function (including the mode's effect - on exclusive access and file permissions). -5 If filename is a null pointer, the freopen_s function attempts to change the mode of - the stream to that specified by mode, as if the name of the file currently associated with - the stream had been used. It is implementation-defined which changes of mode are - permitted (if any), and under what circumstances. -6 The freopen_s function first attempts to close any file that is associated with stream. - Failure to close the file is ignored. The error and end-of-file indicators for the stream are - cleared. -7 If the file was opened successfully, then the pointer to FILE pointed to by - newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE - pointed to by newstreamptr will be set to a null pointer. - Returns -8 The freopen_s function returns zero if it opened the file. If it did not open the file or - there was a runtime-constraint violation, freopen_s returns a nonzero value. - -[page 586] (Contents) - - K.3.5.3 Formatted input/output functions -1 Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the objects take on - unspecified values. - K.3.5.3.1 The fprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int fprintf_s(FILE * restrict stream, - const char * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier377) (modified or - not by flags, field width, or precision) shall not appear in the string pointed to by - format. Any argument to fprintf_s corresponding to a %s specifier shall not be a - null pointer. -3 If there is a runtime-constraint violation,378) the fprintf_s function does not attempt - to produce further output, and it is unspecified to what extent fprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The fprintf_s function is equivalent to the fprintf function except for the explicit - runtime-constraints listed above. - Returns -5 The fprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - - - - - 377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - 378) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an - implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- - constraint violation. - -[page 587] (Contents) - - K.3.5.3.2 The fscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int fscanf_s(FILE * restrict stream, - const char * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation,379) the fscanf_s function does not attempt to - perform further input, and it is unspecified to what extent fscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion - specifiers apply to a pair of arguments (unless assignment suppression is indicated by a - *). The first of these arguments is the same as for fscanf. That argument is - immediately followed in the argument list by the second argument, which has type - rsize_t and gives the number of elements in the array pointed to by the first argument - of the pair. If the first argument points to a scalar object, it is considered to be an array of - one element.380) -5 A matching failure occurs if the number of elements in a receiving object is insufficient to - hold the converted input (including any trailing null character). - Returns -6 The fscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - - 379) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an - implementation may treat any unsupported specifiers in the string pointed to by format as a runtime- - constraint violation. - 380) If the format is known at translation time, an implementation may issue a diagnostic for any argument - used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an - argument of a type compatible with rsize_t. A limited amount of checking may be done if even if - the format is not known at translation time. For example, an implementation may issue a diagnostic - for each argument after format that has of type pointer to one of char, signed char, - unsigned char, or void that is not followed by an argument of a type compatible with - rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier - using the hh length modifier, a length argument must follow the pointer argument. Another useful - diagnostic could flag any non-pointer argument following format that did not have a type - compatible with rsize_t. - -[page 588] (Contents) - - fscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. -7 EXAMPLE 1 The call: - #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - /* ... */ - int n, i; float x; char name[50]; - n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50); - with the input line: - 25 54.32E-1 thompson - will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence - thompson\0. - -8 EXAMPLE 2 The call: - #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - /* ... */ - int n; char s[5]; - n = fscanf_s(stdin, "%s", s, sizeof s); - with the input line: - hello - will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an - array of six characters to store it. - - K.3.5.3.3 The printf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int printf_s(const char * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier381) (modified or not by flags, field - width, or precision) shall not appear in the string pointed to by format. Any argument - to printf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the printf_s function does not attempt to - produce further output, and it is unspecified to what extent printf_s produced output - before discovering the runtime-constraint violation. - - - 381) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 589] (Contents) - - Description -4 The printf_s function is equivalent to the printf function except for the explicit - runtime-constraints listed above. - Returns -5 The printf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.5.3.4 The scanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int scanf_s(const char * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the scanf_s function does not attempt to - perform further input, and it is unspecified to what extent scanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The scanf_s function is equivalent to fscanf_s with the argument stdin - interposed before the arguments to scanf_s. - Returns -5 The scanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - scanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - K.3.5.3.5 The snprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int snprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or - precision) shall not appear in the string pointed to by format. Any argument to -[page 590] (Contents) - - snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the - null character. - Description -4 The snprintf_s function is equivalent to the snprintf function except for the - explicit runtime-constraints listed above. -5 The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the - array pointed to by s. - Returns -6 The snprintf_s function returns the number of characters that would have been - written had n been sufficiently large, not counting the terminating null character, or a - negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - K.3.5.3.6 The sprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int sprintf_s(char * restrict s, rsize_t n, - const char * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of characters (including the trailing null) required for the - result to be written to the array pointed to by s shall not be greater than n. The %n - specifier383) (modified or not by flags, field width, or precision) shall not appear in the - string pointed to by format. Any argument to sprintf_s corresponding to a %s - specifier shall not be a null pointer. No encoding error shall occur. - - - - 382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - 383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 591] (Contents) - -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the - null character. - Description -4 The sprintf_s function is equivalent to the sprintf function except for the - parameter n and the explicit runtime-constraints listed above. -5 The sprintf_s function, unlike snprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the sprintf_s function returns the number - of characters written in the array, not counting the terminating null character. If an - encoding error occurred, sprintf_s returns a negative value. If any other runtime- - constraint violation occurred, sprintf_s returns zero. - K.3.5.3.7 The sscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - int sscanf_s(const char * restrict s, - const char * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the sscanf_s function does not attempt to - perform further input, and it is unspecified to what extent sscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The sscanf_s function is equivalent to fscanf_s, except that input is obtained from - a string (specified by the argument s) rather than from a stream. Reaching the end of the - string is equivalent to encountering end-of-file for the fscanf_s function. If copying - takes place between objects that overlap, the objects take on unspecified values. - Returns -5 The sscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - sscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - -[page 592] (Contents) - - K.3.5.3.8 The vfprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vfprintf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier384) (modified or - not by flags, field width, or precision) shall not appear in the string pointed to by - format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a - null pointer. -3 If there is a runtime-constraint violation, the vfprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vfprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The vfprintf_s function is equivalent to the vfprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The vfprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.5.3.9 The vfscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vfscanf_s(FILE * restrict stream, - const char * restrict format, - va_list arg); - - - - - 384) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 593] (Contents) - - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vfscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vfscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vfscanf_s function is equivalent to fscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfscanf_s function does not invoke the - va_end macro.385) - Returns -5 The vfscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vfscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.5.3.10 The vprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vprintf_s(const char * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier386) (modified or not by flags, field - width, or precision) shall not appear in the string pointed to by format. Any argument - to vprintf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the vprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vprintf_s produced output - before discovering the runtime-constraint violation. - - 385) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - 386) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 594] (Contents) - - Description -4 The vprintf_s function is equivalent to the vprintf function except for the explicit - runtime-constraints listed above. - Returns -5 The vprintf_s function returns the number of characters transmitted, or a negative - value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.5.3.11 The vscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vscanf_s(const char * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vscanf_s function is equivalent to scanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vscanf_s function does not invoke the - va_end macro.387) - Returns -5 The vscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - - - - - 387) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - -[page 595] (Contents) - - K.3.5.3.12 The vsnprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vsnprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier388) (modified or not by flags, field width, or - precision) shall not appear in the string pointed to by format. Any argument to - vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the - null character. - Description -4 The vsnprintf_s function is equivalent to the vsnprintf function except for the - explicit runtime-constraints listed above. -5 The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within - the array pointed to by s. - Returns -6 The vsnprintf_s function returns the number of characters that would have been - written had n been sufficiently large, not counting the terminating null character, or a - negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - - - - - 388) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 596] (Contents) - - K.3.5.3.13 The vsprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vsprintf_s(char * restrict s, rsize_t n, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of characters (including the trailing null) required for the - result to be written to the array pointed to by s shall not be greater than n. The %n - specifier389) (modified or not by flags, field width, or precision) shall not appear in the - string pointed to by format. Any argument to vsprintf_s corresponding to a %s - specifier shall not be a null pointer. No encoding error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the - null character. - Description -4 The vsprintf_s function is equivalent to the vsprintf function except for the - parameter n and the explicit runtime-constraints listed above. -5 The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the vsprintf_s function returns the - number of characters written in the array, not counting the terminating null character. If - an encoding error occurred, vsprintf_s returns a negative value. If any other - runtime-constraint violation occurred, vsprintf_s returns zero. - - - - - 389) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed - at by format when those characters are not a interpreted as a %n specifier. For example, if the entire - format string was %%n. - -[page 597] (Contents) - - K.3.5.3.14 The vsscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - int vsscanf_s(const char * restrict s, - const char * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vsscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vsscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vsscanf_s function is equivalent to sscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vsscanf_s function does not invoke the - va_end macro.390) - Returns -5 The vsscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - K.3.5.4 Character input/output functions - K.3.5.4.1 The gets_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - char *gets_s(char *s, rsize_t n); - - - - - 390) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s, - vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is - indeterminate. - -[page 598] (Contents) - - Runtime-constraints -2 s shall not be a null pointer. n shall neither be equal to zero nor be greater than - RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading - n-1 characters from stdin.391) -3 If there is a runtime-constraint violation, s[0] is set to the null character, and characters - are read and discarded from stdin until a new-line character is read, or end-of-file or a - read error occurs. - Description -4 The gets_s function reads at most one less than the number of characters specified by n - from the stream pointed to by stdin, into the array pointed to by s. No additional - characters are read after a new-line character (which is discarded) or after end-of-file. - The discarded new-line character does not count towards number of characters read. A - null character is written immediately after the last character read into the array. -5 If end-of-file is encountered and no characters have been read into the array, or if a read - error occurs during the operation, then s[0] is set to the null character, and the other - elements of s take unspecified values. - Recommended practice -6 The fgets function allows properly-written programs to safely process input lines too - long to store in the result array. In general this requires that callers of fgets pay - attention to the presence or absence of a new-line character in the result array. Consider - using fgets (along with any needed processing based on new-line characters) instead of - gets_s. - Returns -7 The gets_s function returns s if successful. If there was a runtime-constraint violation, - or if end-of-file is encountered and no characters have been read into the array, or if a - read error occurs during the operation, then a null pointer is returned. - - - - - 391) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for - a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a - one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets - expect such a relationship. - -[page 599] (Contents) - - K.3.6 General utilities <stdlib.h> -1 The header <stdlib.h> defines three types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t; and - constraint_handler_t - which has the following definition - typedef void (*constraint_handler_t)( - const char * restrict msg, - void * restrict ptr, - errno_t error); - K.3.6.1 Runtime-constraint handling - K.3.6.1.1 The set_constraint_handler_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - constraint_handler_t set_constraint_handler_s( - constraint_handler_t handler); - Description -2 The set_constraint_handler_s function sets the runtime-constraint handler to - be handler. The runtime-constraint handler is the function to be called when a library - function detects a runtime-constraint violation. Only the most recent handler registered - with set_constraint_handler_s is called when a runtime-constraint violation - occurs. -3 When the handler is called, it is passed the following arguments in the following order: - 1. A pointer to a character string describing the runtime-constraint violation. - 2. A null pointer or a pointer to an implementation defined object. - 3. If the function calling the handler has a return type declared as errno_t, the - return value of the function is passed. Otherwise, a positive value of type - errno_t is passed. - - - -[page 600] (Contents) - -4 The implementation has a default constraint handler that is used if no calls to the - set_constraint_handler_s function have been made. The behavior of the - default handler is implementation-defined, and it may cause the program to exit or abort. -5 If the handler argument to set_constraint_handler_s is a null pointer, the - implementation default handler becomes the current constraint handler. - Returns -6 The set_constraint_handler_s function returns a pointer to the previously - registered handler.392) - K.3.6.1.2 The abort_handler_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - void abort_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - Description -2 A pointer to the abort_handler_s function shall be a suitable argument to the - set_constraint_handler_s function. -3 The abort_handler_s function writes a message on the standard error stream in an - implementation-defined format. The message shall include the string pointed to by msg. - The abort_handler_s function then calls the abort function.393) - Returns -4 The abort_handler_s function does not return to its caller. - - - - - 392) If the previous handler was registered by calling set_constraint_handler_s with a null - pointer argument, a pointer to the implementation default handler is returned (not NULL). - 393) Many implementations invoke a debugger when the abort function is called. - -[page 601] (Contents) - - K.3.6.1.3 The ignore_handler_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - void ignore_handler_s( - const char * restrict msg, - void * restrict ptr, - errno_t error); - Description -2 A pointer to the ignore_handler_s function shall be a suitable argument to the - set_constraint_handler_s function. -3 The ignore_handler_s function simply returns to its caller.394) - Returns -4 The ignore_handler_s function returns no value. - K.3.6.2 Communication with the environment - K.3.6.2.1 The getenv_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - errno_t getenv_s(size_t * restrict len, - char * restrict value, rsize_t maxsize, - const char * restrict name); - Runtime-constraints -2 name shall not be a null pointer. maxsize shall neither equal zero nor be greater than - RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer. -3 If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len - is not null), and the environment list is not searched. - Description -4 The getenv_s function searches an environment list, provided by the host environment, - for a string that matches the string pointed to by name. - - - 394) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in - which a runtime-constraint violation occurs will return to its caller. The caller can determine whether - a runtime-constraint violation occurred based on the library function's specification (usually, the - library function returns a nonzero errno_t). - -[page 602] (Contents) - -5 If that name is found then getenv_s performs the following actions. If len is not a - null pointer, the length of the string associated with the matched list member is stored in - the integer pointed to by len. If the length of the associated string is less than maxsize, - then the associated string is copied to the array pointed to by value. -6 If that name is not found then getenv_s performs the following actions. If len is not - a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than - zero, then value[0] is set to the null character. -7 The set of environment names and the method for altering the environment list are - implementation-defined. - Returns -8 The getenv_s function returns zero if the specified name is found and the associated - string was successfully stored in value. Otherwise, a nonzero value is returned. - K.3.6.3 Searching and sorting utilities -1 These utilities make use of a comparison function to search or sort arrays of unspecified - type. Where an argument declared as size_t nmemb specifies the length of the array - for a function, if nmemb has the value zero on a call to that function, then the comparison - function is not called, a search finds no matching element, sorting performs no - rearrangement, and the pointer to the array may be null. -2 The implementation shall ensure that the second argument of the comparison function - (when called from bsearch_s), or both arguments (when called from qsort_s), are - pointers to elements of the array.395) The first argument when called from bsearch_s - shall equal key. -3 The comparison function shall not alter the contents of either the array or search key. The - implementation may reorder elements of the array between calls to the comparison - function, but shall not otherwise alter the contents of any individual element. -4 When the same objects (consisting of size bytes, irrespective of their current positions - in the array) are passed more than once to the comparison function, the results shall be - consistent with one another. That is, for qsort_s they shall define a total ordering on - the array, and for bsearch_s the same object shall always compare the same way with - the key. - - - - - 395) That is, if the value passed is p, then the following expressions are always valid and nonzero: - ((char *)p - (char *)base) % size == 0 - (char *)p >= (char *)base - (char *)p < (char *)base + nmemb * size - - -[page 603] (Contents) - -5 A sequence point occurs immediately before and immediately after each call to the - comparison function, and also between any call to the comparison function and any - movement of the objects passed as arguments to that call. - K.3.6.3.1 The bsearch_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - void *bsearch_s(const void *key, const void *base, - rsize_t nmemb, rsize_t size, - int (*compar)(const void *k, const void *y, - void *context), - void *context); - Runtime-constraints -2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to - zero, then none of key, base, or compar shall be a null pointer. -3 If there is a runtime-constraint violation, the bsearch_s function does not search the - array. - Description -4 The bsearch_s function searches an array of nmemb objects, the initial element of - which is pointed to by base, for an element that matches the object pointed to by key. - The size of each element of the array is specified by size. -5 The comparison function pointed to by compar is called with three arguments. The first - two point to the key object and to an array element, in that order. The function shall - return an integer less than, equal to, or greater than zero if the key object is considered, - respectively, to be less than, to match, or to be greater than the array element. The array - shall consist of: all the elements that compare less than, all the elements that compare - equal to, and all the elements that compare greater than the key object, in that order.396) - The third argument to the comparison function is the context argument passed to - bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison - function.397) - - - - - 396) In practice, this means that the entire array has been sorted according to the comparison function. - 397) The context argument is for the use of the comparison function in performing its duties. For - example, it might specify a collating sequence used by the comparison function. - -[page 604] (Contents) - - Returns -6 The bsearch_s function returns a pointer to a matching element of the array, or a null - pointer if no match is found or there is a runtime-constraint violation. If two elements - compare as equal, which element is matched is unspecified. - K.3.6.3.2 The qsort_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size, - int (*compar)(const void *x, const void *y, - void *context), - void *context); - Runtime-constraints -2 Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to - zero, then neither base nor compar shall be a null pointer. -3 If there is a runtime-constraint violation, the qsort_s function does not sort the array. - Description -4 The qsort_s function sorts an array of nmemb objects, the initial element of which is - pointed to by base. The size of each object is specified by size. -5 The contents of the array are sorted into ascending order according to a comparison - function pointed to by compar, which is called with three arguments. The first two - point to the objects being compared. The function shall return an integer less than, equal - to, or greater than zero if the first argument is considered to be respectively less than, - equal to, or greater than the second. The third argument to the comparison function is the - context argument passed to qsort_s. The sole use of context by qsort_s is to - pass it to the comparison function.398) -6 If two elements compare as equal, their relative order in the resulting sorted array is - unspecified. - Returns -7 The qsort_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - - 398) The context argument is for the use of the comparison function in performing its duties. For - example, it might specify a collating sequence used by the comparison function. - -[page 605] (Contents) - - K.3.6.4 Multibyte/wide character conversion functions -1 The behavior of the multibyte character functions is affected by the LC_CTYPE category - of the current locale. For a state-dependent encoding, each function is placed into its - initial conversion state by a call for which its character pointer argument, s, is a null - pointer. Subsequent calls with s as other than a null pointer cause the internal conversion - state of the function to be altered as necessary. A call with s as a null pointer causes - these functions to set the int pointed to by their status argument to a nonzero value if - encodings have state dependency, and zero otherwise.399) Changing the LC_CTYPE - category causes the conversion state of these functions to be indeterminate. - K.3.6.4.1 The wctomb_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdlib.h> - errno_t wctomb_s(int * restrict status, - char * restrict s, - rsize_t smax, - wchar_t wc); - Runtime-constraints -2 Let n denote the number of bytes needed to represent the multibyte character - corresponding to the wide character given by wc (including any shift sequences). -3 If s is not a null pointer, then smax shall not be less than n, and smax shall not be - greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero. -4 If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to - by status, and if s is not a null pointer, no more than smax elements in the array - pointed to by s will be accessed. - Description -5 The wctomb_s function determines n and stores the multibyte character representation - of wc in the array whose first element is pointed to by s (if s is not a null pointer). The - number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide - character, a null byte is stored, preceded by any shift sequence needed to restore the - initial shift state, and the function is left in the initial conversion state. -6 The implementation shall behave as if no library function calls the wctomb_s function. - - - - - 399) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide - character codes, but are grouped with an adjacent multibyte character. - -[page 606] (Contents) - -7 If s is a null pointer, the wctomb_s function stores into the int pointed to by status a - nonzero or zero value, if multibyte character encodings, respectively, do or do not have - state-dependent encodings. -8 If s is not a null pointer, the wctomb_s function stores into the int pointed to by - status either n or -1 if wc, respectively, does or does not correspond to a valid - multibyte character. -9 In no case will the int pointed to by status be set to a value greater than the - MB_CUR_MAX macro. - Returns -10 The wctomb_s function returns zero if successful, and a nonzero value if there was a - runtime-constraint violation or wc did not correspond to a valid multibyte character. - K.3.6.5 Multibyte/wide string conversion functions -1 The behavior of the multibyte string functions is affected by the LC_CTYPE category of - the current locale. - K.3.6.5.1 The mbstowcs_s function - Synopsis -1 #include <stdlib.h> - errno_t mbstowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char * restrict src, rsize_t len); - Runtime-constraints -2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then - neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, - then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal - zero. If dst is not a null pointer and len is not less than dstmax, then a null character - shall occur within the first dstmax multibyte characters of the array pointed to by src. -3 If there is a runtime-constraint violation, then mbstowcs_s does the following. If - retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If - dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then mbstowcs_s sets dst[0] to the null wide character. - Description -4 The mbstowcs_s function converts a sequence of multibyte characters that begins in - the initial shift state from the array pointed to by src into a sequence of corresponding - wide characters. If dst is not a null pointer, the converted characters are stored into the - array pointed to by dst. Conversion continues up to and including a terminating null - character, which is also stored. Conversion stops earlier in two cases: when a sequence of -[page 607] (Contents) - - bytes is encountered that does not form a valid multibyte character, or (if dst is not a - null pointer) when len wide characters have been stored into the array pointed to by - dst.400) If dst is not a null pointer and no null wide character was stored into the array - pointed to by dst, then dst[len] is set to the null wide character. Each conversion - takes place as if by a call to the mbrtowc function. -5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - sequence of bytes that do not form a valid multibyte character, an encoding error occurs: - the mbstowcs_s function stores the value (size_t)(-1) into *retval. - Otherwise, the mbstowcs_s function stores into *retval the number of multibyte - characters successfully converted, not including the terminating null character (if any). -6 All elements following the terminating null wide character (if any) written by - mbstowcs_s in the array of dstmax wide characters pointed to by dst take - unspecified values when mbstowcs_s returns.401) -7 If copying takes place between objects that overlap, the objects take on unspecified - values. - Returns -8 The mbstowcs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.6.5.2 The wcstombs_s function - Synopsis -1 #include <stdlib.h> - errno_t wcstombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t * restrict src, rsize_t len); - Runtime-constraints -2 Neither retval nor src shall be a null pointer. If dst is not a null pointer, then - neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer, - then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal - zero. If dst is not a null pointer and len is not less than dstmax, then the conversion - shall have been stopped (see below) because a terminating null wide character was - reached or because an encoding error occurred. - - - - - 400) Thus, the value of len is ignored if dst is a null pointer. - 401) This allows an implementation to attempt converting the multibyte string before discovering a - terminating null character did not occur where required. - -[page 608] (Contents) - -3 If there is a runtime-constraint violation, then wcstombs_s does the following. If - retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If - dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then wcstombs_s sets dst[0] to the null character. - Description -4 The wcstombs_s function converts a sequence of wide characters from the array - pointed to by src into a sequence of corresponding multibyte characters that begins in - the initial shift state. If dst is not a null pointer, the converted characters are then stored - into the array pointed to by dst. Conversion continues up to and including a terminating - null wide character, which is also stored. Conversion stops earlier in two cases: - -- when a wide character is reached that does not correspond to a valid multibyte - character; - -- (if dst is not a null pointer) when the next multibyte character would exceed the - limit of n total bytes to be stored into the array pointed to by dst. If the wide - character being converted is the null wide character, then n is the lesser of len or - dstmax. Otherwise, n is the lesser of len or dstmax-1. - If the conversion stops without converting a null wide character and dst is not a null - pointer, then a null character is stored into the array pointed to by dst immediately - following any multibyte characters already stored. Each conversion takes place as if by a - call to the wcrtomb function.402) -5 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - wide character that does not correspond to a valid multibyte character, an encoding error - occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval. - Otherwise, the wcstombs_s function stores into *retval the number of bytes in the - resulting multibyte character sequence, not including the terminating null character (if - any). -6 All elements following the terminating null character (if any) written by wcstombs_s - in the array of dstmax elements pointed to by dst take unspecified values when - wcstombs_s returns.403) -7 If copying takes place between objects that overlap, the objects take on unspecified - values. - - - 402) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. However, if - the conversion stops before a terminating null wide character has been reached, the result will be null - terminated, but might not end in the initial shift state. - 403) When len is not less than dstmax, the implementation might fill the array before discovering a - runtime-constraint violation. - -[page 609] (Contents) - - Returns -8 The wcstombs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.7 String handling <string.h> -1 The header <string.h> defines two types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. - K.3.7.1 Copying functions - K.3.7.1.1 The memcpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t memcpy_s(void * restrict s1, rsize_t s1max, - const void * restrict s2, rsize_t n); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between - objects that overlap. -3 If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first - s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is - not greater than RSIZE_MAX. - Description -4 The memcpy_s function copies n characters from the object pointed to by s2 into the - object pointed to by s1. - Returns -5 The memcpy_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - -[page 610] (Contents) - - K.3.7.1.2 The memmove_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t memmove_s(void *s1, rsize_t s1max, - const void *s2, rsize_t n); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. -3 If there is a runtime-constraint violation, the memmove_s function stores zeros in the - first s1max characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. - Description -4 The memmove_s function copies n characters from the object pointed to by s2 into the - object pointed to by s1. This copying takes place as if the n characters from the object - pointed to by s2 are first copied into a temporary array of n characters that does not - overlap the objects pointed to by s1 or s2, and then the n characters from the temporary - array are copied into the object pointed to by s1. - Returns -5 The memmove_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.1.3 The strcpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t strcpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max). - Copying shall not take place between objects that overlap. -3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the - null character. - -[page 611] (Contents) - - Description -4 The strcpy_s function copies the string pointed to by s2 (including the terminating - null character) into the array pointed to by s1. -5 All elements following the terminating null character (if any) written by strcpy_s in - the array of s1max characters pointed to by s1 take unspecified values when - strcpy_s returns.404) - Returns -6 The strcpy_s function returns zero405) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.1.4 The strncpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t strncpy_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max - shall be greater than strnlen_s(s2, s1max). Copying shall not take place between - objects that overlap. -3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the - null character. - Description -4 The strncpy_s function copies not more than n successive characters (characters that - follow a null character are not copied) from the array pointed to by s2 to the array - pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null - character. - - - 404) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 405) A zero return value implies that all of the requested characters from the string pointed to by s2 fit - within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 612] (Contents) - -5 All elements following the terminating null character (if any) written by strncpy_s in - the array of s1max characters pointed to by s1 take unspecified values when - strncpy_s returns.406) - Returns -6 The strncpy_s function returns zero407) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -7 EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result - will not be null terminated or that characters will be written past the end of the destination array. - #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - /* ... */ - char src1[100] = "hello"; - char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'}; - char dst1[6], dst2[5], dst3[5]; - int r1, r2, r3; - r1 = strncpy_s(dst1, 6, src1, 100); - r2 = strncpy_s(dst2, 5, src2, 7); - r3 = strncpy_s(dst3, 5, src2, 4); - The first call will assign to r1 the value zero and to dst1 the sequence hello\0. - The second call will assign to r2 a nonzero value and to dst2 the sequence \0. - The third call will assign to r3 the value zero and to dst3 the sequence good\0. - - K.3.7.2 Concatenation functions - K.3.7.2.1 The strcat_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t strcat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2); - Runtime-constraints -2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to - strcat_s. - - - - - 406) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 407) A zero return value implies that all of the requested characters from the string pointed to by s2 fit - within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 613] (Contents) - -3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. m shall not equal zero.408) m shall be greater than - strnlen_s(s2, m). Copying shall not take place between objects that overlap. -4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the - null character. - Description -5 The strcat_s function appends a copy of the string pointed to by s2 (including the - terminating null character) to the end of the string pointed to by s1. The initial character - from s2 overwrites the null character at the end of s1. -6 All elements following the terminating null character (if any) written by strcat_s in - the array of s1max characters pointed to by s1 take unspecified values when - strcat_s returns.409) - Returns -7 The strcat_s function returns zero410) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.2.2 The strncat_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t strncat_s(char * restrict s1, - rsize_t s1max, - const char * restrict s2, - rsize_t n); - Runtime-constraints -2 Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to - strncat_s. -3 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.411) If n is not less - - - 408) Zero means that s1 was not null terminated upon entry to strcat_s. - 409) This allows an implementation to append characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 410) A zero return value implies that all of the requested characters from the string pointed to by s2 were - appended to the string pointed to by s1 and that the result in s1 is null terminated. - -[page 614] (Contents) - - than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take - place between objects that overlap. -4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the - null character. - Description -5 The strncat_s function appends not more than n successive characters (characters - that follow a null character are not copied) from the array pointed to by s2 to the end of - the string pointed to by s1. The initial character from s2 overwrites the null character at - the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to - a null character. -6 All elements following the terminating null character (if any) written by strncat_s in - the array of s1max characters pointed to by s1 take unspecified values when - strncat_s returns.412) - Returns -7 The strncat_s function returns zero413) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -8 EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result - will not be null terminated or that characters will be written past the end of the destination array. - #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - /* ... */ - char s1[100] = "good"; - char s2[6] = "hello"; - char s3[6] = "hello"; - char s4[7] = "abc"; - char s5[1000] = "bye"; - int r1, r2, r3, r4; - r1 = strncat_s(s1, 100, s5, 1000); - r2 = strncat_s(s2, 6, "", 1); - r3 = strncat_s(s3, 6, "X", 2); - r4 = strncat_s(s4, 7, "defghijklmn", 3); - After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0. - - - - 411) Zero means that s1 was not null terminated upon entry to strncat_s. - 412) This allows an implementation to append characters from s2 to s1 while simultaneously checking if - any of those characters are null. Such an approach might write a character to every element of s1 - before discovering that the first element should be set to the null character. - 413) A zero return value implies that all of the requested characters from the string pointed to by s2 were - appended to the string pointed to by s1 and that the result in s1 is null terminated. - -[page 615] (Contents) - - After the second call r2 will have the value zero and s2 will contain the sequence hello\0. - After the third call r3 will have a nonzero value and s3 will contain the sequence \0. - After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0. - - K.3.7.3 Search functions - K.3.7.3.1 The strtok_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - char *strtok_s(char * restrict s1, - rsize_t * restrict s1max, - const char * restrict s2, - char ** restrict ptr); - Runtime-constraints -2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr - shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. - The end of the token found shall occur within the first *s1max characters of s1 for the - first call, and shall occur within the first *s1max characters of where searching resumes - on subsequent calls. -3 If there is a runtime-constraint violation, the strtok_s function does not indirect - through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. - Description -4 A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a - sequence of tokens, each of which is delimited by a character from the string pointed to - by s2. The fourth argument points to a caller-provided char pointer into which the - strtok_s function stores information necessary for it to continue scanning the same - string. -5 The first call in a sequence has a non-null first argument and s1max points to an object - whose value is the number of elements in the character array pointed to by the first - argument. The first call stores an initial value in the object pointed to by ptr and - updates the value pointed to by s1max to reflect the number of elements that remain in - relation to ptr. Subsequent calls in the sequence have a null first argument and the - objects pointed to by s1max and ptr are required to have the values stored by the - previous call in the sequence, which are then updated. The separator string pointed to by - s2 may be different from call to call. -6 The first call in the sequence searches the string pointed to by s1 for the first character - that is not contained in the current separator string pointed to by s2. If no such character - is found, then there are no tokens in the string pointed to by s1 and the strtok_s - function returns a null pointer. If such a character is found, it is the start of the first token. -[page 616] (Contents) - -7 The strtok_s function then searches from there for the first character in s1 that is - contained in the current separator string. If no such character is found, the current token - extends to the end of the string pointed to by s1, and subsequent searches in the same - string for a token return a null pointer. If such a character is found, it is overwritten by a - null character, which terminates the current token. -8 In all cases, the strtok_s function stores sufficient information in the pointer pointed - to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null character - (if any). - Returns -9 The strtok_s function returns a pointer to the first character of a token, or a null - pointer if there is no token or there is a runtime-constraint violation. -10 EXAMPLE - #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - static char str1[] = "?a???b,,,#c"; - static char str2[] = "\t \t"; - char *t, *ptr1, *ptr2; - rsize_t max1 = sizeof(str1); - rsize_t max2 = sizeof(str2); - t = strtok_s(str1, &max1, "?", &ptr1); // t points to the token "a" - t = strtok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b" - t = strtok_s(str2, &max2, " \t", &ptr2); // t is a null pointer - t = strtok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c" - t = strtok_s(NULL, &max1, "?", &ptr1); // t is a null pointer - - K.3.7.4 Miscellaneous functions - K.3.7.4.1 The memset_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n) - Runtime-constraints -2 s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n - shall not be greater than smax. -3 If there is a runtime-constraint violation, then if s is not a null pointer and smax is not - greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an - unsigned char) into each of the first smax characters of the object pointed to by s. - - - -[page 617] (Contents) - - Description -4 The memset_s function copies the value of c (converted to an unsigned char) into - each of the first n characters of the object pointed to by s. Unlike memset, any call to - the memset_s function shall be evaluated strictly according to the rules of the abstract - machine as described in (5.1.2.3). That is, any call to the memset_s function shall - assume that the memory indicated by s and n may be accessible in the future and thus - must contain the values indicated by c. - Returns -5 The memset_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.7.4.2 The strerror_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - errno_t strerror_s(char *s, rsize_t maxsize, - errno_t errnum); - Runtime-constraints -2 s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX. - maxsize shall not equal zero. -3 If there is a runtime-constraint violation, then the array (if any) pointed to by s is not - modified. - Description -4 The strerror_s function maps the number in errnum to a locale-specific message - string. Typically, the values for errnum come from errno, but strerror_s shall - map any value of type int to a message. -5 If the length of the desired string is less than maxsize, then the string is copied to the - array pointed to by s. -6 Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied - from the string to the array pointed to by s and then s[maxsize-1] is set to the null - character. Then, if maxsize is greater than 3, then s[maxsize-2], - s[maxsize-3], and s[maxsize-4] are set to the character period (.). - Returns -7 The strerror_s function returns zero if the length of the desired string was less than - maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s - function returns a nonzero value. - -[page 618] (Contents) - - K.3.7.4.3 The strerrorlen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - size_t strerrorlen_s(errno_t errnum); - Description -2 The strerrorlen_s function calculates the length of the (untruncated) locale-specific - message string that the strerror_s function maps to errnum. - Returns -3 The strerrorlen_s function returns the number of characters (not including the null - character) in the full message string. - K.3.7.4.4 The strnlen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <string.h> - size_t strnlen_s(const char *s, size_t maxsize); - Description -2 The strnlen_s function computes the length of the string pointed to by s. - Returns -3 If s is a null pointer,414) then the strnlen_s function returns zero. -4 Otherwise, the strnlen_s function returns the number of characters that precede the - terminating null character. If there is no null character in the first maxsize characters of - s then strnlen_s returns maxsize. At most the first maxsize characters of s shall - be accessed by strnlen_s. - - - - - 414) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints - along with the values returned for a null pointer or an unterminated string argument make - strnlen_s useful in algorithms that gracefully handle such exceptional data. - -[page 619] (Contents) - - K.3.8 Date and time <time.h> -1 The header <time.h> defines two types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. - K.3.8.1 Components of time -1 A broken-down time is normalized if the values of the members of the tm structure are in - their normal rages.415) - K.3.8.2 Time conversion functions -1 Like the strftime function, the asctime_s and ctime_s functions do not return a - pointer to a static object, and other library functions are permitted to call them. - K.3.8.2.1 The asctime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <time.h> - errno_t asctime_s(char *s, rsize_t maxsize, - const struct tm *timeptr); - Runtime-constraints -2 Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and - shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr - shall be normalized. The calendar year represented by the broken-down time pointed to - by timeptr shall not be less than calendar year 0 and shall not be greater than calendar - year 9999. -3 If there is a runtime-constraint violation, there is no attempt to convert the time, and - s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is - not greater than RSIZE_MAX. - Description -4 The asctime_s function converts the normalized broken-down time in the structure - pointed to by timeptr into a 26 character (including the null character) string in the - - - 415) The normal ranges are defined in 7.26.1. - -[page 620] (Contents) - - form - Sun Sep 16 01:03:52 1973\n\0 - The fields making up this string are (in order): - 1. The name of the day of the week represented by timeptr->tm_wday using the - following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat. - 2. The character space. - 3. The name of the month represented by timeptr->tm_mon using the following - three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, - Nov, and Dec. - 4. The character space. - 5. The value of timeptr->tm_mday as if printed using the fprintf format - "%2d". - 6. The character space. - 7. The value of timeptr->tm_hour as if printed using the fprintf format - "%.2d". - 8. The character colon. - 9. The value of timeptr->tm_min as if printed using the fprintf format - "%.2d". - 10. The character colon. - 11. The value of timeptr->tm_sec as if printed using the fprintf format - "%.2d". - 12. The character space. - 13. The value of timeptr->tm_year + 1900 as if printed using the fprintf - format "%4d". - 14. The character new line. - 15. The null character. - Recommended practice - The strftime function allows more flexible formatting and supports locale-specific - behavior. If you do not require the exact form of the result string produced by the - asctime_s function, consider using the strftime function instead. - Returns -5 The asctime_s function returns zero if the time was successfully converted and stored - into the array pointed to by s. Otherwise, it returns a nonzero value. -[page 621] (Contents) - - K.3.8.2.2 The ctime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <time.h> - errno_t ctime_s(char *s, rsize_t maxsize, - const time_t *timer); - Runtime-constraints -2 Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and - shall not be greater than RSIZE_MAX. -3 If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null - pointer and maxsize is not equal zero and is not greater than RSIZE_MAX. - Description -4 The ctime_s function converts the calendar time pointed to by timer to local time in - the form of a string. It is equivalent to - asctime_s(s, maxsize, localtime_s(timer)) - Recommended practice - The strftime function allows more flexible formatting and supports locale-specific - behavior. If you do not require the exact form of the result string produced by the - ctime_s function, consider using the strftime function instead. - Returns -5 The ctime_s function returns zero if the time was successfully converted and stored - into the array pointed to by s. Otherwise, it returns a nonzero value. - K.3.8.2.3 The gmtime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <time.h> - struct tm *gmtime_s(const time_t * restrict timer, - struct tm * restrict result); - Runtime-constraints -2 Neither timer nor result shall be a null pointer. -3 If there is a runtime-constraint violation, there is no attempt to convert the time. - Description -4 The gmtime_s function converts the calendar time pointed to by timer into a broken- - down time, expressed as UTC. The broken-down time is stored in the structure pointed -[page 622] (Contents) - - to by result. - Returns -5 The gmtime_s function returns result, or a null pointer if the specified time cannot - be converted to UTC or there is a runtime-constraint violation. - K.3.8.2.4 The localtime_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <time.h> - struct tm *localtime_s(const time_t * restrict timer, - struct tm * restrict result); - Runtime-constraints -2 Neither timer nor result shall be a null pointer. -3 If there is a runtime-constraint violation, there is no attempt to convert the time. - Description -4 The localtime_s function converts the calendar time pointed to by timer into a - broken-down time, expressed as local time. The broken-down time is stored in the - structure pointed to by result. - Returns -5 The localtime_s function returns result, or a null pointer if the specified time - cannot be converted to local time or there is a runtime-constraint violation. - K.3.9 Extended multibyte and wide character utilities <wchar.h> -1 The header <wchar.h> defines two types. -2 The types are - errno_t - which is type int; and - rsize_t - which is the type size_t. -3 Unless explicitly stated otherwise, if the execution of a function described in this - subclause causes copying to take place between objects that overlap, the objects take on - unspecified values. - - - - -[page 623] (Contents) - - K.3.9.1 Formatted wide character input/output functions - K.3.9.1.1 The fwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - int fwprintf_s(FILE * restrict stream, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier416) (modified or - not by flags, field width, or precision) shall not appear in the wide string pointed to by - format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a - null pointer. -3 If there is a runtime-constraint violation, the fwprintf_s function does not attempt to - produce further output, and it is unspecified to what extent fwprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The fwprintf_s function is equivalent to the fwprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The fwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.9.1.2 The fwscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdio.h> - #include <wchar.h> - int fwscanf_s(FILE * restrict stream, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. - - - 416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 624] (Contents) - -3 If there is a runtime-constraint violation, the fwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent fwscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The fwscanf_s function is equivalent to fwscanf except that the c, s, and [ - conversion specifiers apply to a pair of arguments (unless assignment suppression is - indicated by a *). The first of these arguments is the same as for fwscanf. That - argument is immediately followed in the argument list by the second argument, which has - type size_t and gives the number of elements in the array pointed to by the first - argument of the pair. If the first argument points to a scalar object, it is considered to be - an array of one element.417) -5 A matching failure occurs if the number of elements in a receiving object is insufficient to - hold the converted input (including any trailing null character). - Returns -6 The fwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - fwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.3 The snwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - int snwprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier418) (modified or not by flags, field width, or - - 417) If the format is known at translation time, an implementation may issue a diagnostic for any argument - used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an - argument of a type compatible with rsize_t. A limited amount of checking may be done if even if - the format is not known at translation time. For example, an implementation may issue a diagnostic - for each argument after format that has of type pointer to one of char, signed char, - unsigned char, or void that is not followed by an argument of a type compatible with - rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier - using the hh length modifier, a length argument must follow the pointer argument. Another useful - diagnostic could flag any non-pointer argument following format that did not have a type - compatible with rsize_t. - -[page 625] (Contents) - - precision) shall not appear in the wide string pointed to by format. Any argument to - snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding - error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the - null wide character. - Description -4 The snwprintf_s function is equivalent to the swprintf function except for the - explicit runtime-constraints listed above. -5 The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within - the array pointed to by s. - Returns -6 The snwprintf_s function returns the number of wide characters that would have - been written had n been sufficiently large, not counting the terminating wide null - character, or a negative value if a runtime-constraint violation occurred. Thus, the null- - terminated output has been completely written if and only if the returned value is - nonnegative and less than n. - K.3.9.1.4 The swprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - int swprintf_s(wchar_t * restrict s, rsize_t n, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of wide characters (including the trailing null) required - for the result to be written to the array pointed to by s shall not be greater than n. The %n - specifier419) (modified or not by flags, field width, or precision) shall not appear in the - wide string pointed to by format. Any argument to swprintf_s corresponding to a - %s specifier shall not be a null pointer. No encoding error shall occur. - - - 418) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - 419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 626] (Contents) - -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the - null wide character. - Description -4 The swprintf_s function is equivalent to the swprintf function except for the - explicit runtime-constraints listed above. -5 The swprintf_s function, unlike snwprintf_s, treats a result too big for the array - pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the swprintf_s function returns the - number of wide characters written in the array, not counting the terminating null wide - character. If an encoding error occurred or if n or more wide characters are requested to - be written, swprintf_s returns a negative value. If any other runtime-constraint - violation occurred, swprintf_s returns zero. - K.3.9.1.5 The swscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - int swscanf_s(const wchar_t * restrict s, - const wchar_t * restrict format, ...); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the swscanf_s function does not attempt to - perform further input, and it is unspecified to what extent swscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The swscanf_s function is equivalent to fwscanf_s, except that the argument s - specifies a wide string from which the input is to be obtained, rather than from a stream. - Reaching the end of the wide string is equivalent to encountering end-of-file for the - fwscanf_s function. - Returns -5 The swscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - swscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. -[page 627] (Contents) - - K.3.9.1.6 The vfwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - #include <wchar.h> - int vfwprintf_s(FILE * restrict stream, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither stream nor format shall be a null pointer. The %n specifier420) (modified or - not by flags, field width, or precision) shall not appear in the wide string pointed to by - format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be - a null pointer. -3 If there is a runtime-constraint violation, the vfwprintf_s function does not attempt - to produce further output, and it is unspecified to what extent vfwprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The vfwprintf_s function is equivalent to the vfwprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The vfwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.9.1.7 The vfwscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <stdio.h> - #include <wchar.h> - int vfwscanf_s(FILE * restrict stream, - const wchar_t * restrict format, va_list arg); - - - - 420) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 628] (Contents) - - Runtime-constraints -2 Neither stream nor format shall be a null pointer. Any argument indirected though in - order to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vfwscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument - list replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the - va_end macro.421) - Returns -5 The vfwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vfwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.8 The vsnwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <wchar.h> - int vsnwprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The %n specifier422) (modified or not by flags, field width, or - precision) shall not appear in the wide string pointed to by format. Any argument to - vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No - encoding error shall occur. - - 421) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - 422) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 629] (Contents) - -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to - the null wide character. - Description -4 The vsnwprintf_s function is equivalent to the vswprintf function except for the - explicit runtime-constraints listed above. -5 The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit - within the array pointed to by s. - Returns -6 The vsnwprintf_s function returns the number of wide characters that would have - been written had n been sufficiently large, not counting the terminating null character, or - a negative value if a runtime-constraint violation occurred. Thus, the null-terminated - output has been completely written if and only if the returned value is nonnegative and - less than n. - K.3.9.1.9 The vswprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <wchar.h> - int vswprintf_s(wchar_t * restrict s, - rsize_t n, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater - than RSIZE_MAX. The number of wide characters (including the trailing null) required - for the result to be written to the array pointed to by s shall not be greater than n. The %n - specifier423) (modified or not by flags, field width, or precision) shall not appear in the - wide string pointed to by format. Any argument to vswprintf_s corresponding to a - %s specifier shall not be a null pointer. No encoding error shall occur. -3 If there is a runtime-constraint violation, then if s is not a null pointer and n is greater - than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the - null wide character. - - 423) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 630] (Contents) - - Description -4 The vswprintf_s function is equivalent to the vswprintf function except for the - explicit runtime-constraints listed above. -5 The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the - array pointed to by s as a runtime-constraint violation. - Returns -6 If no runtime-constraint violation occurred, the vswprintf_s function returns the - number of wide characters written in the array, not counting the terminating null wide - character. If an encoding error occurred or if n or more wide characters are requested to - be written, vswprintf_s returns a negative value. If any other runtime-constraint - violation occurred, vswprintf_s returns zero. - K.3.9.1.10 The vswscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <wchar.h> - int vswscanf_s(const wchar_t * restrict s, - const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 Neither s nor format shall be a null pointer. Any argument indirected though in order - to store converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vswscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vswscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vswscanf_s function is equivalent to swscanf_s, with the variable argument - list replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vswscanf_s function does not invoke the - va_end macro.424) - - - - - 424) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - -[page 631] (Contents) - - Returns -5 The vswscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vswscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.11 The vwprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <wchar.h> - int vwprintf_s(const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier425) (modified or not by flags, field - width, or precision) shall not appear in the wide string pointed to by format. Any - argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the vwprintf_s function does not attempt to - produce further output, and it is unspecified to what extent vwprintf_s produced - output before discovering the runtime-constraint violation. - Description -4 The vwprintf_s function is equivalent to the vwprintf function except for the - explicit runtime-constraints listed above. - Returns -5 The vwprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - - - - - 425) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 632] (Contents) - - K.3.9.1.12 The vwscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <stdarg.h> - #include <wchar.h> - int vwscanf_s(const wchar_t * restrict format, - va_list arg); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the vwscanf_s function does not attempt to - perform further input, and it is unspecified to what extent vwscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The vwscanf_s function is equivalent to wscanf_s, with the variable argument list - replaced by arg, which shall have been initialized by the va_start macro (and - possibly subsequent va_arg calls). The vwscanf_s function does not invoke the - va_end macro.426) - Returns -5 The vwscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - vwscanf_s function returns the number of input items assigned, which can be fewer - than provided for, or even zero, in the event of an early matching failure. - K.3.9.1.13 The wprintf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - int wprintf_s(const wchar_t * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. The %n specifier427) (modified or not by flags, field - - 426) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the - value of arg after the return is indeterminate. - 427) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide - string pointed at by format when those wide characters are not a interpreted as a %n specifier. For - example, if the entire format string was L"%%n". - -[page 633] (Contents) - - width, or precision) shall not appear in the wide string pointed to by format. Any - argument to wprintf_s corresponding to a %s specifier shall not be a null pointer. -3 If there is a runtime-constraint violation, the wprintf_s function does not attempt to - produce further output, and it is unspecified to what extent wprintf_s produced output - before discovering the runtime-constraint violation. - Description -4 The wprintf_s function is equivalent to the wprintf function except for the explicit - runtime-constraints listed above. - Returns -5 The wprintf_s function returns the number of wide characters transmitted, or a - negative value if an output error, encoding error, or runtime-constraint violation occurred. - K.3.9.1.14 The wscanf_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - int wscanf_s(const wchar_t * restrict format, ...); - Runtime-constraints -2 format shall not be a null pointer. Any argument indirected though in order to store - converted input shall not be a null pointer. -3 If there is a runtime-constraint violation, the wscanf_s function does not attempt to - perform further input, and it is unspecified to what extent wscanf_s performed input - before discovering the runtime-constraint violation. - Description -4 The wscanf_s function is equivalent to fwscanf_s with the argument stdin - interposed before the arguments to wscanf_s. - Returns -5 The wscanf_s function returns the value of the macro EOF if an input failure occurs - before any conversion or if there is a runtime-constraint violation. Otherwise, the - wscanf_s function returns the number of input items assigned, which can be fewer than - provided for, or even zero, in the event of an early matching failure. - - - - -[page 634] (Contents) - - K.3.9.2 General wide string utilities - K.3.9.2.1 Wide string copying functions - K.3.9.2.1.1 The wcscpy_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - errno_t wcscpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - Runtime-constraints -2 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max). - Copying shall not take place between objects that overlap. -3 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the - null wide character. - Description -4 The wcscpy_s function copies the wide string pointed to by s2 (including the - terminating null wide character) into the array pointed to by s1. -5 All elements following the terminating null wide character (if any) written by - wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcscpy_s returns.428) - Returns -6 The wcscpy_s function returns zero429) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - - 428) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking - if any of those wide characters are null. Such an approach might write a wide character to every - element of s1 before discovering that the first element should be set to the null wide character. - 429) A zero return value implies that all of the requested wide characters from the string pointed to by s2 - fit within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 635] (Contents) - - K.3.9.2.1.2 The wcsncpy_s function - Synopsis -7 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - errno_t wcsncpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - Runtime-constraints -8 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max - shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between - objects that overlap. -9 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the - null wide character. - Description -10 The wcsncpy_s function copies not more than n successive wide characters (wide - characters that follow a null wide character are not copied) from the array pointed to by - s2 to the array pointed to by s1. If no null wide character was copied from s2, then - s1[n] is set to a null wide character. -11 All elements following the terminating null wide character (if any) written by - wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcsncpy_s returns.430) - Returns -12 The wcsncpy_s function returns zero431) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -13 EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the - result will not be null terminated or that wide characters will be written past the end of the destination - array. - - - - - 430) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking - if any of those wide characters are null. Such an approach might write a wide character to every - element of s1 before discovering that the first element should be set to the null wide character. - 431) A zero return value implies that all of the requested wide characters from the string pointed to by s2 - fit within the array pointed to by s1 and that the result in s1 is null terminated. - -[page 636] (Contents) - - #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - /* ... */ - wchar_t src1[100] = L"hello"; - wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'}; - wchar_t dst1[6], dst2[5], dst3[5]; - int r1, r2, r3; - r1 = wcsncpy_s(dst1, 6, src1, 100); - r2 = wcsncpy_s(dst2, 5, src2, 7); - r3 = wcsncpy_s(dst3, 5, src2, 4); - The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0. - The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0. - The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0. - - K.3.9.2.1.3 The wmemcpy_s function - Synopsis -14 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - errno_t wmemcpy_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - Runtime-constraints -15 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between - objects that overlap. -16 If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the - first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. - Description -17 The wmemcpy_s function copies n successive wide characters from the object pointed - to by s2 into the object pointed to by s1. - Returns -18 The wmemcpy_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - - - - -[page 637] (Contents) - - K.3.9.2.1.4 The wmemmove_s function - Synopsis -19 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - errno_t wmemmove_s(wchar_t *s1, rsize_t s1max, - const wchar_t *s2, rsize_t n); - Runtime-constraints -20 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. n shall not be greater than s1max. -21 If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the - first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and - s1max is not greater than RSIZE_MAX. - Description -22 The wmemmove_s function copies n successive wide characters from the object pointed - to by s2 into the object pointed to by s1. This copying takes place as if the n wide - characters from the object pointed to by s2 are first copied into a temporary array of n - wide characters that does not overlap the objects pointed to by s1 or s2, and then the n - wide characters from the temporary array are copied into the object pointed to by s1. - Returns -23 The wmemmove_s function returns zero if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.9.2.2 Wide string concatenation functions - K.3.9.2.2.1 The wcscat_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - errno_t wcscat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2); - Runtime-constraints -2 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to - wcscat_s. -3 Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX. - s1max shall not equal zero. m shall not equal zero.432) m shall be greater than - wcsnlen_s(s2, m). Copying shall not take place between objects that overlap. - -[page 638] (Contents) - -4 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the - null wide character. - Description -5 The wcscat_s function appends a copy of the wide string pointed to by s2 (including - the terminating null wide character) to the end of the wide string pointed to by s1. The - initial wide character from s2 overwrites the null wide character at the end of s1. -6 All elements following the terminating null wide character (if any) written by - wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcscat_s returns.433) - Returns -7 The wcscat_s function returns zero434) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. - K.3.9.2.2.2 The wcsncat_s function - Synopsis -8 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - errno_t wcsncat_s(wchar_t * restrict s1, - rsize_t s1max, - const wchar_t * restrict s2, - rsize_t n); - Runtime-constraints -9 Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to - wcsncat_s. -10 Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than - RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.435) If n is not less - than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take - place between objects that overlap. - - - 432) Zero means that s1 was not null terminated upon entry to wcscat_s. - 433) This allows an implementation to append wide characters from s2 to s1 while simultaneously - checking if any of those wide characters are null. Such an approach might write a wide character to - every element of s1 before discovering that the first element should be set to the null wide character. - 434) A zero return value implies that all of the requested wide characters from the wide string pointed to by - s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. - 435) Zero means that s1 was not null terminated upon entry to wcsncat_s. - -[page 639] (Contents) - -11 If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is - greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the - null wide character. - Description -12 The wcsncat_s function appends not more than n successive wide characters (wide - characters that follow a null wide character are not copied) from the array pointed to by - s2 to the end of the wide string pointed to by s1. The initial wide character from s2 - overwrites the null wide character at the end of s1. If no null wide character was copied - from s2, then s1[s1max-m+n] is set to a null wide character. -13 All elements following the terminating null wide character (if any) written by - wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified - values when wcsncat_s returns.436) - Returns -14 The wcsncat_s function returns zero437) if there was no runtime-constraint violation. - Otherwise, a nonzero value is returned. -15 EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the - result will not be null terminated or that wide characters will be written past the end of the destination - array. - #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - /* ... */ - wchar_t s1[100] = L"good"; - wchar_t s2[6] = L"hello"; - wchar_t s3[6] = L"hello"; - wchar_t s4[7] = L"abc"; - wchar_t s5[1000] = L"bye"; - int r1, r2, r3, r4; - r1 = wcsncat_s(s1, 100, s5, 1000); - r2 = wcsncat_s(s2, 6, L"", 1); - r3 = wcsncat_s(s3, 6, L"X", 2); - r4 = wcsncat_s(s4, 7, L"defghijklmn", 3); - After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0. - After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0. - After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0. - After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0. - - - - - 436) This allows an implementation to append wide characters from s2 to s1 while simultaneously - checking if any of those wide characters are null. Such an approach might write a wide character to - every element of s1 before discovering that the first element should be set to the null wide character. - 437) A zero return value implies that all of the requested wide characters from the wide string pointed to by - s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated. - -[page 640] (Contents) - - K.3.9.2.3 Wide string search functions - K.3.9.2.3.1 The wcstok_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - wchar_t *wcstok_s(wchar_t * restrict s1, - rsize_t * restrict s1max, - const wchar_t * restrict s2, - wchar_t ** restrict ptr); - Runtime-constraints -2 None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr - shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX. - The end of the token found shall occur within the first *s1max wide characters of s1 for - the first call, and shall occur within the first *s1max wide characters of where searching - resumes on subsequent calls. -3 If there is a runtime-constraint violation, the wcstok_s function does not indirect - through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr. - Description -4 A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1 - into a sequence of tokens, each of which is delimited by a wide character from the wide - string pointed to by s2. The fourth argument points to a caller-provided wchar_t - pointer into which the wcstok_s function stores information necessary for it to - continue scanning the same wide string. -5 The first call in a sequence has a non-null first argument and s1max points to an object - whose value is the number of elements in the wide character array pointed to by the first - argument. The first call stores an initial value in the object pointed to by ptr and - updates the value pointed to by s1max to reflect the number of elements that remain in - relation to ptr. Subsequent calls in the sequence have a null first argument and the - objects pointed to by s1max and ptr are required to have the values stored by the - previous call in the sequence, which are then updated. The separator wide string pointed - to by s2 may be different from call to call. -6 The first call in the sequence searches the wide string pointed to by s1 for the first wide - character that is not contained in the current separator wide string pointed to by s2. If no - such wide character is found, then there are no tokens in the wide string pointed to by s1 - and the wcstok_s function returns a null pointer. If such a wide character is found, it is - the start of the first token. - - -[page 641] (Contents) - -7 The wcstok_s function then searches from there for the first wide character in s1 that - is contained in the current separator wide string. If no such wide character is found, the - current token extends to the end of the wide string pointed to by s1, and subsequent - searches in the same wide string for a token return a null pointer. If such a wide character - is found, it is overwritten by a null wide character, which terminates the current token. -8 In all cases, the wcstok_s function stores sufficient information in the pointer pointed - to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer - value for ptr, shall start searching just past the element overwritten by a null wide - character (if any). - Returns -9 The wcstok_s function returns a pointer to the first wide character of a token, or a null - pointer if there is no token or there is a runtime-constraint violation. -10 EXAMPLE - #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - static wchar_t str1[] = L"?a???b,,,#c"; - static wchar_t str2[] = L"\t \t"; - wchar_t *t, *ptr1, *ptr2; - rsize_t max1 = wcslen(str1)+1; - rsize_t max2 = wcslen(str2)+1; - t = wcstok_s(str1, &max1, "?", &ptr1); // t points to the token "a" - t = wcstok_s(NULL, &max1, ",", &ptr1); // t points to the token "??b" - t = wcstok_s(str2, &max2, " \t", &ptr2); // t is a null pointer - t = wcstok_s(NULL, &max1, "#,", &ptr1); // t points to the token "c" - t = wcstok_s(NULL, &max1, "?", &ptr1); // t is a null pointer - - K.3.9.2.4 Miscellaneous functions - K.3.9.2.4.1 The wcsnlen_s function - Synopsis -1 #define __STDC_WANT_LIB_EXT1__ 1 - #include <wchar.h> - size_t wcsnlen_s(const wchar_t *s, size_t maxsize); - Description -2 The wcsnlen_s function computes the length of the wide string pointed to by s. - Returns -3 If s is a null pointer,438) then the wcsnlen_s function returns zero. -4 Otherwise, the wcsnlen_s function returns the number of wide characters that precede - the terminating null wide character. If there is no null wide character in the first - maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first - -[page 642] (Contents) - - maxsize wide characters of s shall be accessed by wcsnlen_s. - K.3.9.3 Extended multibyte/wide character conversion utilities - K.3.9.3.1 Restartable multibyte/wide character conversion functions -1 Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the - conversion state) to be a null pointer. - K.3.9.3.1.1 The wcrtomb_s function - Synopsis -2 #include <wchar.h> - errno_t wcrtomb_s(size_t * restrict retval, - char * restrict s, rsize_t smax, - wchar_t wc, mbstate_t * restrict ps); - Runtime-constraints -3 Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax - shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer, - then smax shall be not be less than the number of bytes to be stored in the array pointed - to by s. If s is a null pointer, then smax shall equal zero. -4 If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is - not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then - wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then - wcrtomb_s sets *retval to (size_t)(-1). - Description -5 If s is a null pointer, the wcrtomb_s function is equivalent to the call - wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps) - where retval and buf are internal variables of the appropriate types, and the size of - buf is greater than MB_CUR_MAX. -6 If s is not a null pointer, the wcrtomb_s function determines the number of bytes - needed to represent the multibyte character that corresponds to the wide character given - by wc (including any shift sequences), and stores the multibyte character representation - in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are - stored. If wc is a null wide character, a null byte is stored, preceded by any shift - sequence needed to restore the initial shift state; the resulting state described is the initial - conversion state. - - 438) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints - along with the values returned for a null pointer or an unterminated wide string argument make - wcsnlen_s useful in algorithms that gracefully handle such exceptional data. - -[page 643] (Contents) - -7 If wc does not correspond to a valid multibyte character, an encoding error occurs: the - wcrtomb_s function stores the value (size_t)(-1) into *retval and the - conversion state is unspecified. Otherwise, the wcrtomb_s function stores into - *retval the number of bytes (including any shift sequences) stored in the array pointed - to by s. - Returns -8 The wcrtomb_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.9.3.2 Restartable multibyte/wide string conversion functions -1 Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not - permit the ps parameter (the pointer to the conversion state) to be a null pointer. - K.3.9.3.2.1 The mbsrtowcs_s function - Synopsis -2 #include <wchar.h> - errno_t mbsrtowcs_s(size_t * restrict retval, - wchar_t * restrict dst, rsize_t dstmax, - const char ** restrict src, rsize_t len, - mbstate_t * restrict ps); - Runtime-constraints -3 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, - then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null - pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall - not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null - character shall occur within the first dstmax multibyte characters of the array pointed to - by *src. -4 If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If - retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1). - If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then mbsrtowcs_s sets dst[0] to the null wide character. - Description -5 The mbsrtowcs_s function converts a sequence of multibyte characters that begins in - the conversion state described by the object pointed to by ps, from the array indirectly - pointed to by src into a sequence of corresponding wide characters. If dst is not a null - pointer, the converted characters are stored into the array pointed to by dst. Conversion - continues up to and including a terminating null character, which is also stored. - Conversion stops earlier in two cases: when a sequence of bytes is encountered that does - not form a valid multibyte character, or (if dst is not a null pointer) when len wide -[page 644] (Contents) - - characters have been stored into the array pointed to by dst.439) If dst is not a null - pointer and no null wide character was stored into the array pointed to by dst, then - dst[len] is set to the null wide character. Each conversion takes place as if by a call - to the mbrtowc function. -6 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null character) or the address - just past the last multibyte character converted (if any). If conversion stopped due to - reaching a terminating null character and if dst is not a null pointer, the resulting state - described is the initial conversion state. -7 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - sequence of bytes that do not form a valid multibyte character, an encoding error occurs: - the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the - conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into - *retval the number of multibyte characters successfully converted, not including the - terminating null character (if any). -8 All elements following the terminating null wide character (if any) written by - mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take - unspecified values when mbsrtowcs_s returns.440) -9 If copying takes place between objects that overlap, the objects take on unspecified - values. - Returns -10 The mbsrtowcs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - K.3.9.3.2.2 The wcsrtombs_s function - Synopsis -11 #include <wchar.h> - errno_t wcsrtombs_s(size_t * restrict retval, - char * restrict dst, rsize_t dstmax, - const wchar_t ** restrict src, rsize_t len, - mbstate_t * restrict ps); - - - - - 439) Thus, the value of len is ignored if dst is a null pointer. - 440) This allows an implementation to attempt converting the multibyte string before discovering a - terminating null character did not occur where required. - -[page 645] (Contents) - - Runtime-constraints -12 None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, - then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null - pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall - not equal zero. If dst is not a null pointer and len is not less than dstmax, then the - conversion shall have been stopped (see below) because a terminating null wide character - was reached or because an encoding error occurred. -13 If there is a runtime-constraint violation, then wcsrtombs_s does the following. If - retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1). - If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, - then wcsrtombs_s sets dst[0] to the null character. - Description -14 The wcsrtombs_s function converts a sequence of wide characters from the array - indirectly pointed to by src into a sequence of corresponding multibyte characters that - begins in the conversion state described by the object pointed to by ps. If dst is not a - null pointer, the converted characters are then stored into the array pointed to by dst. - Conversion continues up to and including a terminating null wide character, which is also - stored. Conversion stops earlier in two cases: - -- when a wide character is reached that does not correspond to a valid multibyte - character; - -- (if dst is not a null pointer) when the next multibyte character would exceed the - limit of n total bytes to be stored into the array pointed to by dst. If the wide - character being converted is the null wide character, then n is the lesser of len or - dstmax. Otherwise, n is the lesser of len or dstmax-1. - If the conversion stops without converting a null wide character and dst is not a null - pointer, then a null character is stored into the array pointed to by dst immediately - following any multibyte characters already stored. Each conversion takes place as if by a - call to the wcrtomb function.441) -15 If dst is not a null pointer, the pointer object pointed to by src is assigned either a null - pointer (if conversion stopped due to reaching a terminating null wide character) or the - address just past the last wide character converted (if any). If conversion stopped due to - reaching a terminating null wide character, the resulting state described is the initial - conversion state. - - - 441) If conversion stops because a terminating null wide character has been reached, the bytes stored - include those necessary to reach the initial shift state immediately before the null byte. However, if - the conversion stops before a terminating null wide character has been reached, the result will be null - terminated, but might not end in the initial shift state. - -[page 646] (Contents) - -16 Regardless of whether dst is or is not a null pointer, if the input conversion encounters a - wide character that does not correspond to a valid multibyte character, an encoding error - occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval - and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores - into *retval the number of bytes in the resulting multibyte character sequence, not - including the terminating null character (if any). -17 All elements following the terminating null character (if any) written by wcsrtombs_s - in the array of dstmax elements pointed to by dst take unspecified values when - wcsrtombs_s returns.442) -18 If copying takes place between objects that overlap, the objects take on unspecified - values. - Returns -19 The wcsrtombs_s function returns zero if no runtime-constraint violation and no - encoding error occurred. Otherwise, a nonzero value is returned. - - - - - 442) When len is not less than dstmax, the implementation might fill the array before discovering a - runtime-constraint violation. - -[page 647] (Contents) - - Annex L - (normative) - Analyzability - L.1 Scope -1 This annex specifies optional behavior that can aid in the analyzability of C programs. -2 An implementation that defines __STDC_ANALYZABLE__ shall conform to the - specifications in this annex.443) - L.2 Definitions - L.2.1 -1 out-of-bounds store - an (attempted) access (3.1) that, at run time, for a given computational state, would - modify (or, for an object declared volatile, fetch) one or more bytes that lie outside - the bounds permitted by this Standard. - L.2.2 -1 bounded undefined behavior - undefined behavior (3.4.3) that does not perform an out-of-bounds store. -2 NOTE 1 The behavior might perform a trap. - -3 NOTE 2 Any values produced or stored might be indeterminate values. - - L.2.3 -1 critical undefined behavior - undefined behavior that is not bounded undefined behavior. -2 NOTE The behavior might perform an out-of-bounds store or perform a trap. - - - - - 443) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these - specifications. - -[page 648] (Contents) - - L.3 Requirements -1 If the program performs a trap (3.19.5), the implementation is permitted to invoke a - runtime-constraint handler. Any such semantics are implementation-defined. -2 All undefined behavior shall be limited to bounded undefined behavior, except for the - following which are permitted to result in critical undefined behavior: - -- An object is referred to outside of its lifetime (6.2.4). - -- An lvalue does not designate an object when evaluated (6.3.2.1). - -- A pointer is used to call a function whose type is not compatible with the referenced - type (6.3.2.3). - -- The operand of the unary * operator has an invalid value (6.5.3.2). - -- Addition or subtraction of a pointer into, or just beyond, an array object and an - integer type produces a result that points just beyond the array object and is used as - the operand of a unary * operator that is evaluated (6.5.6). - -- An argument to a library function has an invalid value or a type not expected by a - function with variable number of arguments (7.1.4). - -- The value of a pointer that refers to space deallocated by a call to the free or realloc - function is used (7.22.3). - -- A string or wide string utility function is instructed to access an array beyond the end - of an object (7.23.1, 7.28.4). - - - - -[page 649] (Contents) - - - Bibliography - 1. ''The C Reference Manual'' by Dennis M. Ritchie, a version of which was - published in The C Programming Language by Brian W. Kernighan and Dennis - M. Ritchie, Prentice-Hall, Inc., (1978). Copyright owned by AT&T. - 2. 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara, - California, USA, November 1984. - 3. ANSI X3/TR-1-82 (1982), American National Dictionary for Information - Processing Systems, Information Processing Systems Technical Report. - 4. ANSI/IEEE 754-1985, American National Standard for Binary Floating-Point - Arithmetic. - 5. ANSI/IEEE 854-1988, American National Standard for Radix-Independent - Floating-Point Arithmetic. - 6. IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems, - second edition (previously designated IEC 559:1989). - 7. ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and - symbols for use in the physical sciences and technology. - 8. ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for - information interchange. - 9. ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: - Fundamental terms. - 10. ISO 4217:1995, Codes for the representation of currencies and funds. - 11. ISO 8601:1988, Data elements and interchange formats -- Information - interchange -- Representation of dates and times. - 12. ISO/IEC 9899:1990, Programming languages -- C. - 13. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1. - 14. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2. - 15. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC 9899:1990 C Integrity. - 16. ISO/IEC 9899:1999, Programming languages -- C. - 17. ISO/IEC 9899:1999/Cor.1:2001, Technical Corrigendum 1. - 18. ISO/IEC 9899:1999/Cor.2:2004, Technical Corrigendum 2. - 19. ISO/IEC 9899:1999/Cor.3:2007, Technical Corrigendum 3. - - - -[page 650] (Contents) - - 20. ISO/IEC 9945-2:1993, Information technology -- Portable Operating System - Interface (POSIX) -- Part 2: Shell and Utilities. - 21. ISO/IEC TR 10176:1998, Information technology -- Guidelines for the - preparation of programming language standards. - 22. ISO/IEC 10646-1:1993, Information technology -- Universal Multiple-Octet - Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane. - 23. ISO/IEC 10646-1/COR1:1996, Technical Corrigendum 1 to - ISO/IEC 10646-1:1993. - 24. ISO/IEC 10646-1/COR2:1998, Technical Corrigendum 2 to - ISO/IEC 10646-1:1993. - 25. ISO/IEC 10646-1/AMD1:1996, Amendment 1 to ISO/IEC 10646-1:1993 - Transformation Format for 16 planes of group 00 (UTF-16). - 26. ISO/IEC 10646-1/AMD2:1996, Amendment 2 to ISO/IEC 10646-1:1993 UCS - Transformation Format 8 (UTF-8). - 27. ISO/IEC 10646-1/AMD3:1996, Amendment 3 to ISO/IEC 10646-1:1993. - 28. ISO/IEC 10646-1/AMD4:1996, Amendment 4 to ISO/IEC 10646-1:1993. - 29. ISO/IEC 10646-1/AMD5:1998, Amendment 5 to ISO/IEC 10646-1:1993 Hangul - syllables. - 30. ISO/IEC 10646-1/AMD6:1997, Amendment 6 to ISO/IEC 10646-1:1993 - Tibetan. - 31. ISO/IEC 10646-1/AMD7:1997, Amendment 7 to ISO/IEC 10646-1:1993 33 - additional characters. - 32. ISO/IEC 10646-1/AMD8:1997, Amendment 8 to ISO/IEC 10646-1:1993. - 33. ISO/IEC 10646-1/AMD9:1997, Amendment 9 to ISO/IEC 10646-1:1993 - Identifiers for characters. - 34. ISO/IEC 10646-1/AMD10:1998, Amendment 10 to ISO/IEC 10646-1:1993 - Ethiopic. - 35. ISO/IEC 10646-1/AMD11:1998, Amendment 11 to ISO/IEC 10646-1:1993 - Unified Canadian Aboriginal Syllabics. - 36. ISO/IEC 10646-1/AMD12:1998, Amendment 12 to ISO/IEC 10646-1:1993 - Cherokee. - 37. ISO/IEC 10967-1:1994, Information technology -- Language independent - arithmetic -- Part 1: Integer and floating point arithmetic. - - -[page 651] (Contents) - - 38. ISO/IEC TR 19769:2004, Information technology -- Programming languages, - their environments and system software interfaces -- Extensions for the - programming language C to support new character data types. - 39. ISO/IEC TR 24731-1:2007, Information technology -- Programming languages, - their environments and system software interfaces -- Extensions to the C library - -- Part 1: Bounds-checking interfaces. - - - - -[page 652] (Contents) - - -Index -[^ x ^], 3.20 , (comma operator), 5.1.2.4, 6.5.17 - , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, -[_ x _], 3.21 6.7.2.3, 6.7.9 -! (logical negation operator), 6.5.3.3 - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2 -!= (inequality operator), 6.5.9 - (unary minus operator), 6.5.3.3, F.3 -# operator, 6.10.3.2 -- (postfix decrement operator), 6.3.2.1, 6.5.2.4 -# preprocessing directive, 6.10.7 -- (prefix decrement operator), 6.3.2.1, 6.5.3.1 -# punctuator, 6.10 -= (subtraction assignment operator), 6.5.16.2 -## operator, 6.10.3.3 -> (structure/union pointer operator), 6.5.2.3 -#define preprocessing directive, 6.10.3 . (structure/union member operator), 6.3.2.1, -#elif preprocessing directive, 6.10.1 6.5.2.3 -#else preprocessing directive, 6.10.1 . punctuator, 6.7.9 -#endif preprocessing directive, 6.10.1 ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3 -#error preprocessing directive, 4, 6.10.5 / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1 -#if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, /* */ (comment delimiters), 6.4.9 - 6.10.1, 7.1.4 // (comment delimiter), 6.4.9 -#ifdef preprocessing directive, 6.10.1 /= (division assignment operator), 6.5.16.2 -#ifndef preprocessing directive, 6.10.1 : (colon punctuator), 6.7.2.1 -#include preprocessing directive, 5.1.1.2, :> (alternative spelling of ]), 6.4.6 - 6.10.2 ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3, -#line preprocessing directive, 6.10.4 6.8.5, 6.8.6 -#pragma preprocessing directive, 6.10.6 < (less-than operator), 6.5.8 -#undef preprocessing directive, 6.10.3.5, 7.1.3, <% (alternative spelling of {), 6.4.6 - 7.1.4 <: (alternative spelling of [), 6.4.6 -% (remainder operator), 6.2.6.2, 6.5.5 << (left-shift operator), 6.2.6.2, 6.5.7 -%: (alternative spelling of #), 6.4.6 <<= (left-shift assignment operator), 6.5.16.2 -%:%: (alternative spelling of ##), 6.4.6 <= (less-than-or-equal-to operator), 6.5.8 -%= (remainder assignment operator), 6.5.16.2 <assert.h> header, 7.2 -%> (alternative spelling of }), 6.4.6 <complex.h> header, 5.2.4.2.2, 6.10.8.3, 7.1.2, -& (address operator), 6.3.2.1, 6.5.3.2 7.3, 7.24, 7.30.1, G.6, J.5.17 -& (bitwise AND operator), 6.2.6.2, 6.5.10 <ctype.h> header, 7.4, 7.30.2 -&& (logical AND operator), 5.1.2.4, 6.5.13 <errno.h> header, 7.5, 7.30.3, K.3.2 -&= (bitwise AND assignment operator), 6.5.16.2 <fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, -' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, H - 7.4.1.10, 7.29.2.1.3 <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3, -( ) (cast operator), 6.5.4 7.28.4.1.1 -( ) (function-call operator), 6.5.2.2 <inttypes.h> header, 7.8, 7.30.4 -( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5 <iso646.h> header, 4, 7.9 -( ){ } (compound-literal operator), 6.5.2.5 <limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10 -* (asterisk punctuator), 6.7.6.1, 6.7.6.2 <locale.h> header, 7.11, 7.30.5 -* (indirection operator), 6.5.2.1, 6.5.3.2 <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, -* (multiplication operator), 6.2.6.2, 6.5.5, F.3, F.10, J.5.17 - G.5.1 <setjmp.h> header, 7.13 -*= (multiplication assignment operator), 6.5.16.2 <signal.h> header, 7.14, 7.30.6 -+ (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2, <stdalign.h> header, 4, 7.15 - 6.5.6, F.3, G.5.2 <stdarg.h> header, 4, 6.7.6.3, 7.16 -+ (unary plus operator), 6.5.3.3 <stdatomic.h> header, 6.10.8.3, 7.1.2, 7.17 -++ (postfix increment operator), 6.3.2.1, 6.5.2.4 <stdbool.h> header, 4, 7.18, 7.30.7, H -++ (prefix increment operator), 6.3.2.1, 6.5.3.1 <stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, -+= (addition assignment operator), 6.5.16.2 -[page 653] (Contents) - - 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 \x hexadecimal digits (hexadecimal-character -<stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8, escape sequence), 6.4.4.4 - 7.20, 7.30.8, K.3.3, K.3.4 ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11 -<stdio.h> header, 5.2.4.2.2, 7.21, 7.30.9, F, ^= (bitwise exclusive OR assignment operator), - K.3.5 6.5.16.2 -<stdlib.h> header, 5.2.4.2.2, 7.22, 7.30.10, F, __alignas_is_defined macro, 7.15 - K.3.1.4, K.3.6 __bool_true_false_are_defined -<string.h> header, 7.23, 7.30.11, K.3.7 macro, 7.18 -<tgmath.h> header, 7.24, G.7 __cplusplus macro, 6.10.8 -<threads.h> header, 6.10.8.3, 7.1.2, 7.25 __DATE__ macro, 6.10.8.1 -<time.h> header, 7.26, K.3.8 __FILE__ macro, 6.10.8.1, 7.2.1.1 -<uchar.h> header, 6.4.4.4, 6.4.5, 7.27 __func__ identifier, 6.4.2.2, 7.2.1.1 -<wchar.h> header, 5.2.4.2.2, 7.21.1, 7.28, __LINE__ macro, 6.10.8.1, 7.2.1.1 - 7.30.12, F, K.3.9 __STDC_, 6.11.9 -<wctype.h> header, 7.29, 7.30.13 __STDC__ macro, 6.10.8.1 -= (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9 __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1 -= (simple assignment operator), 6.5.16.1 __STDC_HOSTED__ macro, 6.10.8.1 -== (equality operator), 6.5.9 __STDC_IEC_559__ macro, 6.10.8.3, F.1 -> (greater-than operator), 6.5.8 __STDC_IEC_559_COMPLEX__ macro, ->= (greater-than-or-equal-to operator), 6.5.8 6.10.8.3, G.1 ->> (right-shift operator), 6.2.6.2, 6.5.7 __STDC_ISO_10646__ macro, 6.10.8.2 ->>= (right-shift assignment operator), 6.5.16.2 __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2 -? : (conditional operator), 5.1.2.4, 6.5.15 __STDC_MB_MIGHT_NEQ_WC__ macro, -?? (trigraph sequences), 5.2.1.1 6.10.8.2, 7.19 -[ ] (array subscript operator), 6.5.2.1, 6.5.3.2 __STDC_NO_COMPLEX__ macro, 6.10.8.3, -[ ] (brackets punctuator), 6.7.6.2, 6.7.9 7.3.1 -\ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4 __STDC_NO_THREADS__ macro, 6.10.8.3, -\ (escape character), 6.4.4.4 7.17.1, 7.25.1 -\" (double-quote escape sequence), 6.4.4.4, __STDC_NO_VLA__ macro, 6.10.8.3 - 6.4.5, 6.10.9 __STDC_UTF_16__ macro, 6.10.8.2 -\\ (backslash escape sequence), 6.4.4.4, 6.10.9 __STDC_UTF_32__ macro, 6.10.8.2 -\' (single-quote escape sequence), 6.4.4.4, 6.4.5 __STDC_VERSION__ macro, 6.10.8.1 -\0 (null character), 5.2.1, 6.4.4.4, 6.4.5 __STDC_WANT_LIB_EXT1__ macro, K.3.1.1 - padding of binary stream, 7.21.2 __TIME__ macro, 6.10.8.1 -\? (question-mark escape sequence), 6.4.4.4 __VA_ARGS__ identifier, 6.10.3, 6.10.3.1 -\a (alert escape sequence), 5.2.2, 6.4.4.4 _Alignas, 6.7.5 -\b (backspace escape sequence), 5.2.2, 6.4.4.4 _Atomic type qualifier, 6.7.3 -\f (form-feed escape sequence), 5.2.2, 6.4.4.4, _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1, - 7.4.1.10 F.4 -\n (new-line escape sequence), 5.2.2, 6.4.4.4, _Bool type conversions, 6.3.1.2 - 7.4.1.10 _Complex types, 6.2.5, 6.7.2, 7.3.1, G -\octal digits (octal-character escape sequence), _Complex_I macro, 7.3.1 - 6.4.4.4 _Exit function, 7.22.4.5, 7.22.4.7 -\r (carriage-return escape sequence), 5.2.2, _Imaginary keyword, G.2 - 6.4.4.4, 7.4.1.10 _Imaginary types, 7.3.1, G -\t (horizontal-tab escape sequence), 5.2.2, _Imaginary_I macro, 7.3.1, G.6 - 6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3 _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 -\U (universal character names), 6.4.3 _IOLBF macro, 7.21.1, 7.21.5.6 -\u (universal character names), 6.4.3 _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 -\v (vertical-tab escape sequence), 5.2.2, 6.4.4.4, _Noreturn, 6.7.4 - 7.4.1.10 _Pragma operator, 5.1.1.2, 6.10.9 - -[page 654] (Contents) - -_Static_assert, 6.7.10, 7.2 allocated storage, order and contiguity, 7.22.3 -_Thread_local storage-class specifier, 6.2.4, and macro, 7.9 - 6.7.1 AND operators -{ } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9, bitwise (&), 6.2.6.2, 6.5.10 - 6.8.2 bitwise assignment (&=), 6.5.16.2 -{ } (compound-literal operator), 6.5.2.5 logical (&&), 5.1.2.4, 6.5.13 -| (bitwise inclusive OR operator), 6.2.6.2, 6.5.12 and_eq macro, 7.9 -|= (bitwise inclusive OR assignment operator), anonymous structure, 6.7.2.1 - 6.5.16.2 anonymous union, 6.7.2.1 -|| (logical OR operator), 5.1.2.4, 6.5.14 ANSI/IEEE 754, F.1 -~ (bitwise complement operator), 6.2.6.2, 6.5.3.3 ANSI/IEEE 854, F.1 - argc (main function parameter), 5.1.2.2.1 -abort function, 7.2.1.1, 7.14.1.1, 7.21.3, argument, 3.3 - 7.22.4.1, 7.25.3.6, K.3.6.1.2 array, 6.9.1 -abort_handler_s function, K.3.6.1.2 default promotions, 6.5.2.2 -abs function, 7.22.6.1 function, 6.5.2.2, 6.9.1 -absolute-value functions macro, substitution, 6.10.3.1 - complex, 7.3.8, G.6.4 argument, complex, 7.3.9.1 - integer, 7.8.2.1, 7.22.6.1 argv (main function parameter), 5.1.2.2.1 - real, 7.12.7, F.10.4 arithmetic constant expression, 6.6 -abstract declarator, 6.7.7 arithmetic conversions, usual, see usual arithmetic -abstract machine, 5.1.2.3 conversions -access, 3.1, 6.7.3, L.2.1 arithmetic operators -accuracy, see floating-point accuracy additive, 6.2.6.2, 6.5.6, G.5.2 -acos functions, 7.12.4.1, F.10.1.1 bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12 -acos type-generic macro, 7.24 increment and decrement, 6.5.2.4, 6.5.3.1 -acosh functions, 7.12.5.1, F.10.2.1 multiplicative, 6.2.6.2, 6.5.5, G.5.1 -acosh type-generic macro, 7.24 shift, 6.2.6.2, 6.5.7 -acquire fence, 7.17.4 unary, 6.5.3.3 -acquire operation, 5.1.2.4 arithmetic types, 6.2.5 -active position, 5.2.2 arithmetic, pointer, 6.5.6 -actual argument, 3.3 array -actual parameter (deprecated), 3.3 argument, 6.9.1 -addition assignment operator (+=), 6.5.16.2 declarator, 6.7.6.2 -addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2, initialization, 6.7.9 - 6.5.6, F.3, G.5.2 multidimensional, 6.5.2.1 -additive expressions, 6.5.6, G.5.2 parameter, 6.9.1 -address constant, 6.6 storage order, 6.5.2.1 -address operator (&), 6.3.2.1, 6.5.3.2 subscript operator ([ ]), 6.5.2.1, 6.5.3.2 -address-free, 7.17.5 subscripting, 6.5.2.1 -aggregate initialization, 6.7.9 type, 6.2.5 -aggregate types, 6.2.5 type conversion, 6.3.2.1 -alert escape sequence (\a), 5.2.2, 6.4.4.4 variable length, 6.7.6, 6.7.6.2, 6.10.8.3 -aliasing, 6.5 arrow operator (->), 6.5.2.3 -alignas macro, 7.15 as-if rule, 5.1.2.3 -aligned_alloc function, 7.22.3, 7.22.3.1 ASCII code set, 5.2.1.1 -alignment, 3.2, 6.2.8, 7.22.3.1 asctime function, 7.26.3.1 - pointer, 6.2.5, 6.3.2.3 asctime_s function, K.3.8.2, K.3.8.2.1 - structure/union member, 6.7.2.1 asin functions, 7.12.4.2, F.10.1.2 -alignment specifier, 6.7.5 asin type-generic macro, 7.24, G.7 -alignof operator, 6.5.3, 6.5.3.4 asinh functions, 7.12.5.2, F.10.2.2 - -[page 655] (Contents) - -asinh type-generic macro, 7.24, G.7 atomic_is_lock_free generic function, -asm keyword, J.5.10 7.17.5.1 -assert macro, 7.2.1.1 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1 -assert.h header, 7.2 atomic_load generic functions, 7.17.7.2 -assignment ATOMIC_LONG_LOCK_FREE macro, 7.17.1 - compound, 6.5.16.2 ATOMIC_SHORT_LOCK_FREE macro, 7.17.1 - conversion, 6.5.16.1 atomic_signal_fence function, 7.17.4.2 - expression, 6.5.16 atomic_store generic functions, 7.17.7.1 - operators, 6.3.2.1, 6.5.16 atomic_thread_fence function, 7.17.4.1 - simple, 6.5.16.1 ATOMIC_VAR_INIT macro, 7.17.2.1 -associativity of operators, 6.5 ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1 -asterisk punctuator (*), 6.7.6.1, 6.7.6.2 atomics header, 7.17 -at_quick_exit function, 7.22.4.2, 7.22.4.3, auto storage-class specifier, 6.7.1, 6.9 - 7.22.4.4, 7.22.4.5, 7.22.4.7 automatic storage duration, 5.2.3, 6.2.4 -atan functions, 7.12.4.3, F.10.1.3 -atan type-generic macro, 7.24, G.7 backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4 -atan2 functions, 7.12.4.4, F.10.1.4 backslash escape sequence (\\), 6.4.4.4, 6.10.9 -atan2 type-generic macro, 7.24 backspace escape sequence (\b), 5.2.2, 6.4.4.4 -atanh functions, 7.12.5.3, F.10.2.3 basic character set, 3.6, 3.7.2, 5.2.1 -atanh type-generic macro, 7.24, G.7 basic types, 6.2.5 -atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4, behavior, 3.4 - 7.22.4.5, 7.22.4.7, J.5.13 binary streams, 7.21.2, 7.21.7.10, 7.21.9.2, -atof function, 7.22.1, 7.22.1.1 7.21.9.4 -atoi function, 7.22.1, 7.22.1.2 bit, 3.5 -atol function, 7.22.1, 7.22.1.2 high order, 3.6 -atoll function, 7.22.1, 7.22.1.2 low order, 3.6 -atomic lock-free macros, 7.17.1, 7.17.5 bit-field, 6.7.2.1 -atomic operations, 5.1.2.4 bitand macro, 7.9 -atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, bitor macro, 7.9 - 6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, bitwise operators, 6.5 - 7.17.6 AND, 6.2.6.2, 6.5.10 -atomic_address type, 7.17.1, 7.17.6 AND assignment (&=), 6.5.16.2 -ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1 complement (~), 6.2.6.2, 6.5.3.3 -atomic_bool type, 7.17.1, 7.17.6 exclusive OR, 6.2.6.2, 6.5.11 -ATOMIC_CHAR16_T_LOCK_FREE macro, exclusive OR assignment (^=), 6.5.16.2 - 7.17.1 inclusive OR, 6.2.6.2, 6.5.12 -ATOMIC_CHAR32_T_LOCK_FREE macro, inclusive OR assignment (|=), 6.5.16.2 - 7.17.1 shift, 6.2.6.2, 6.5.7 -ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 blank character, 7.4.1.3 -atomic_compare_exchange generic block, 6.8, 6.8.2, 6.8.4, 6.8.5 - functions, 7.17.7.4 block scope, 6.2.1 -atomic_exchange generic functions, 7.17.7.3 block structure, 6.2.1 -atomic_fetch and modify generic functions, bold type convention, 6.1 - 7.17.7.5 bool macro, 7.18 -atomic_flag type, 7.17.1, 7.17.8 boolean type, 6.3.1.2 -atomic_flag_clear functions, 7.17.8.2 boolean type conversion, 6.3.1.1, 6.3.1.2 -ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8 bounded undefined behavior, L.2.2 -atomic_flag_test_and_set functions, braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9, - 7.17.8.1 6.8.2 -atomic_init generic function, 7.17.2.2 brackets operator ([ ]), 6.5.2.1, 6.5.3.2 -ATOMIC_INT_LOCK_FREE macro, 7.17.1 brackets punctuator ([ ]), 6.7.6.2, 6.7.9 - -[page 656] (Contents) - -branch cuts, 7.3.3 type-generic macro for, 7.24 -break statement, 6.8.6.3 ccosh functions, 7.3.6.4, G.6.2.4 -broken-down time, 7.26.1, 7.26.2.3, 7.26.3, type-generic macro for, 7.24 - 7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5, ceil functions, 7.12.9.1, F.10.6.1 - K.3.8.2.1, K.3.8.2.3, K.3.8.2.4 ceil type-generic macro, 7.24 -bsearch function, 7.22.5, 7.22.5.1 cerf function, 7.30.1 -bsearch_s function, K.3.6.3, K.3.6.3.1 cerfc function, 7.30.1 -btowc function, 7.28.6.1.1 cexp functions, 7.3.7.1, G.6.3.1 -BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5 type-generic macro for, 7.24 -byte, 3.6, 6.5.3.4 cexp2 function, 7.30.1 -byte input/output functions, 7.21.1 cexpm1 function, 7.30.1 -byte-oriented stream, 7.21.2 char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2, - K.3.9.1.2 -C program, 5.1.1.1 char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, -c16rtomb function, 7.27.1.2 6.3.1.8 -c32rtomb function, 7.27.1.4 char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27 -cabs functions, 7.3.8.1, G.6 char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27 - type-generic macro for, 7.24 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1 -cacos functions, 7.3.5.1, G.6.1.1 CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1 - type-generic macro for, 7.24 CHAR_MIN macro, 5.2.4.2.1 -cacosh functions, 7.3.6.1, G.6.2.1 character, 3.7, 3.7.1 - type-generic macro for, 7.24 character array initialization, 6.7.9 -calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, character case mapping functions, 7.4.2 - 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, wide character, 7.29.3.1 - K.3.8.2.3, K.3.8.2.4 extensible, 7.29.3.2 -call by value, 6.5.2.2 character classification functions, 7.4.1 -call_once function, 7.25.1, 7.25.2.1 wide character, 7.29.2.1 -calloc function, 7.22.3, 7.22.3.2 extensible, 7.29.2.2 -carg functions, 7.3.9.1, G.6 character constant, 5.1.1.2, 5.2.1, 6.4.4.4 -carg type-generic macro, 7.24, G.7 character display semantics, 5.2.2 -carriage-return escape sequence (\r), 5.2.2, character handling header, 7.4, 7.11.1.1 - 6.4.4.4, 7.4.1.10 character input/output functions, 7.21.7, K.3.5.4 -carries a dependency, 5.1.2.4 wide character, 7.28.3 -case label, 6.8.1, 6.8.4.2 character sets, 5.2.1 -case mapping functions character string literal, see string literal - character, 7.4.2 character type conversion, 6.3.1.1 - wide character, 7.29.3.1 character types, 6.2.5, 6.7.9 - extensible, 7.29.3.2 cimag functions, 7.3.9.2, 7.3.9.5, G.6 -casin functions, 7.3.5.2, G.6 cimag type-generic macro, 7.24, G.7 - type-generic macro for, 7.24 cis function, G.6 -casinh functions, 7.3.6.2, G.6.2.2 classification functions - type-generic macro for, 7.24 character, 7.4.1 -cast expression, 6.5.4 floating-point, 7.12.3 -cast operator (( )), 6.5.4 wide character, 7.29.2.1 -catan functions, 7.3.5.3, G.6 extensible, 7.29.2.2 - type-generic macro for, 7.24 clearerr function, 7.21.10.1 -catanh functions, 7.3.6.3, G.6.2.3 clgamma function, 7.30.1 - type-generic macro for, 7.24 clock function, 7.26.2.1 -cbrt functions, 7.12.7.1, F.10.4.1 clock_t type, 7.26.1, 7.26.2.1 -cbrt type-generic macro, 7.24 CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1 -ccos functions, 7.3.5.4, G.6 clog functions, 7.3.7.2, G.6.3.2 - -[page 657] (Contents) - - type-generic macro for, 7.24 string, 7.23.3, K.3.7.2 -clog10 function, 7.30.1 wide string, 7.28.4.3, K.3.9.2.2 -clog1p function, 7.30.1 concatenation, preprocessing, see preprocessing -clog2 function, 7.30.1 concatenation -CMPLX macros, 7.3.9.3 conceptual models, 5.1 -cnd_broadcast function, 7.25.3.1, 7.25.3.5, conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3, - 7.25.3.6 7.1.2, F.1, G.1, K.2, L.1 -cnd_destroy function, 7.25.3.2 conditional inclusion, 6.10.1 -cnd_init function, 7.25.3.3 conditional operator (? :), 5.1.2.4, 6.5.15 -cnd_signal function, 7.25.3.4, 7.25.3.5, conflict, 5.1.2.4 - 7.25.3.6 conformance, 4 -cnd_t type, 7.25.1 conj functions, 7.3.9.4, G.6 -cnd_timedwait function, 7.25.3.5 conj type-generic macro, 7.24 -cnd_wait function, 7.25.3.3, 7.25.3.6 const type qualifier, 6.7.3 -collating sequences, 5.2.1 const-qualified type, 6.2.5, 6.3.2.1, 6.7.3 -colon punctuator (:), 6.7.2.1 constant expression, 6.6, F.8.4 -comma operator (,), 5.1.2.4, 6.5.17 constants, 6.4.4 -comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, as primary expression, 6.5.1 - 6.7.2.3, 6.7.9 character, 6.4.4.4 -command processor, 7.22.4.8 enumeration, 6.2.1, 6.4.4.3 -comment delimiters (/* */ and //), 6.4.9 floating, 6.4.4.2 -comments, 5.1.1.2, 6.4, 6.4.9 hexadecimal, 6.4.4.1 -common extensions, J.5 integer, 6.4.4.1 -common initial sequence, 6.5.2.3 octal, 6.4.4.1 -common real type, 6.3.1.8 constraint, 3.8, 4 -common warnings, I constraint_handler_t type, K.3.6 -comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2, consume operation, 5.1.2.4 - K.3.6.3, K.3.6.3.1, K.3.6.3.2 content of structure/union/enumeration, 6.7.2.3 - string, 7.23.4 contiguity of allocated storage, 7.22.3 - wide string, 7.28.4.4 continue statement, 6.8.6.2 -comparison macros, 7.12.14 contracted expression, 6.5, 7.12.2, F.7 -comparison, pointer, 6.5.8 control character, 5.2.1, 7.4 -compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6 control wide character, 7.29.2 -compl macro, 7.9 conversion, 6.3 -complement operator (~), 6.2.6.2, 6.5.3.3 arithmetic operands, 6.3.1 -complete type, 6.2.5 array argument, 6.9.1 -complex macro, 7.3.1 array parameter, 6.9.1 -complex numbers, 6.2.5, G arrays, 6.3.2.1 -complex type conversion, 6.3.1.6, 6.3.1.7 boolean, 6.3.1.2 -complex type domain, 6.2.5 boolean, characters, and integers, 6.3.1.1 -complex types, 6.2.5, 6.7.2, 6.10.8.3, G by assignment, 6.5.16.1 -complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2, by return statement, 6.8.6.4 - 7.3, 7.24, 7.30.1, G.6, J.5.17 complex types, 6.3.1.6 -compliance, see conformance explicit, 6.3 -components of time, 7.26.1, K.3.8.1 function, 6.3.2.1 -composite type, 6.2.7 function argument, 6.5.2.2, 6.9.1 -compound assignment, 6.5.16.2 function designators, 6.3.2.1 -compound literals, 6.5.2.5 function parameter, 6.9.1 -compound statement, 6.8.2 imaginary, G.4.1 -compound-literal operator (( ){ }), 6.5.2.5 imaginary and complex, G.4.3 -concatenation functions implicit, 6.3 - -[page 658] (Contents) - - lvalues, 6.3.2.1 csinh functions, 7.3.6.5, G.6.2.5 - pointer, 6.3.2.1, 6.3.2.3 type-generic macro for, 7.24 - real and complex, 6.3.1.7 csqrt functions, 7.3.8.3, G.6.4.2 - real and imaginary, G.4.2 type-generic macro for, 7.24 - real floating and integer, 6.3.1.4, F.3, F.4 ctan functions, 7.3.5.6, G.6 - real floating types, 6.3.1.5, F.3 type-generic macro for, 7.24 - signed and unsigned integers, 6.3.1.3 ctanh functions, 7.3.6.6, G.6.2.6 - usual arithmetic, see usual arithmetic type-generic macro for, 7.24 - conversions ctgamma function, 7.30.1 - void type, 6.3.2.2 ctime function, 7.26.3.2 -conversion functions ctime_s function, K.3.8.2, K.3.8.2.2 - multibyte/wide character, 7.22.7, K.3.6.4 ctype.h header, 7.4, 7.30.2 - extended, 7.28.6, K.3.9.3 current object, 6.7.9 - restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4 - multibyte/wide string, 7.22.8, K.3.6.5 - restartable, 7.28.6.4, K.3.9.3.2 data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6, - numeric, 7.8.2.3, 7.22.1 7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3, - wide string, 7.8.2.4, 7.28.4.1 7.28.6.4 - single byte/wide character, 7.28.6.1 data stream, see streams - time, 7.26.3, K.3.8.2 date and time header, 7.26, K.3.8 - wide character, 7.28.5 Daylight Saving Time, 7.26.1 -conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, DBL_DECIMAL_DIG macro, 5.2.4.2.2 - 7.28.2.2 DBL_DIG macro, 5.2.4.2.2 -conversion state, 7.22.7, 7.27.1, 7.27.1.1, DBL_EPSILON macro, 5.2.4.2.2 - 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6, DBL_HAS_SUBNORM macro, 5.2.4.2.2 - 7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3, DBL_MANT_DIG macro, 5.2.4.2.2 - 7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4, DBL_MAX macro, 5.2.4.2.2 - K.3.9.3.1, K.3.9.3.1.1, K.3.9.3.2, K.3.9.3.2.1, DBL_MAX_10_EXP macro, 5.2.4.2.2 - K.3.9.3.2.2 DBL_MAX_EXP macro, 5.2.4.2.2 -conversion state functions, 7.28.6.2 DBL_MIN macro, 5.2.4.2.2 -copying functions DBL_MIN_10_EXP macro, 5.2.4.2.2 - string, 7.23.2, K.3.7.1 DBL_MIN_EXP macro, 5.2.4.2.2 - wide string, 7.28.4.2, K.3.9.2.1 DBL_TRUE_MIN macro, 5.2.4.2.2 -copysign functions, 7.3.9.5, 7.12.11.1, F.3, decimal constant, 6.4.4.1 - F.10.8.1 decimal digit, 5.2.1 -copysign type-generic macro, 7.24 decimal-point character, 7.1.1, 7.11.2.1 -correctly rounded result, 3.9 DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1, -corresponding real type, 6.2.5 7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5 -cos functions, 7.12.4.5, F.10.1.5 declaration specifiers, 6.7 -cos type-generic macro, 7.24, G.7 declarations, 6.7 -cosh functions, 7.12.5.4, F.10.2.4 function, 6.7.6.3 -cosh type-generic macro, 7.24, G.7 pointer, 6.7.6.1 -cpow functions, 7.3.8.2, G.6.4.1 structure/union, 6.7.2.1 - type-generic macro for, 7.24 typedef, 6.7.8 -cproj functions, 7.3.9.5, G.6 declarator, 6.7.6 -cproj type-generic macro, 7.24 abstract, 6.7.7 -creal functions, 7.3.9.6, G.6 declarator type derivation, 6.2.5, 6.7.6 -creal type-generic macro, 7.24, G.7 decrement operators, see arithmetic operators, -critical undefined behavior, L.2.3 increment and decrement -csin functions, 7.3.5.5, G.6 default argument promotions, 6.5.2.2 - type-generic macro for, 7.24 default initialization, 6.7.9 - -[page 659] (Contents) - -default label, 6.8.1, 6.8.4.2 elif preprocessing directive, 6.10.1 -define preprocessing directive, 6.10.3 ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3 -defined operator, 6.10.1, 6.10.8 else preprocessing directive, 6.10.1 -definition, 6.7 else statement, 6.8.4.1 - function, 6.9.1 empty statement, 6.8.3 -dependency-ordered before, 5.1.2.4 encoding error, 7.21.3, 7.27.1.1, 7.27.1.2, -derived declarator types, 6.2.5 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, -derived types, 6.2.5 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, -designated initializer, 6.7.9 K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1, -destringizing, 6.10.9 K.3.9.3.2.2 -device input/output, 5.1.2.3 end-of-file, 7.28.1 -diagnostic message, 3.10, 5.1.1.3 end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1, -diagnostics, 5.1.1.3 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2, -diagnostics header, 7.2 7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1, -difftime function, 7.26.2.2 7.28.3.10 -digit, 5.2.1, 7.4 end-of-file macro, see EOF macro -digraphs, 6.4.6 end-of-line indicator, 5.2.1 -direct input/output functions, 7.21.8 endif preprocessing directive, 6.10.1 -display device, 5.2.2 enum type, 6.2.5, 6.7.2, 6.7.2.2 -div function, 7.22.6.2 enumerated type, 6.2.5 -div_t type, 7.22 enumeration, 6.2.5, 6.7.2.2 -division assignment operator (/=), 6.5.16.2 enumeration constant, 6.2.1, 6.4.4.3 -division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1 enumeration content, 6.7.2.3 -do statement, 6.8.5.2 enumeration members, 6.7.2.2 -documentation of implementation, 4 enumeration specifiers, 6.7.2.2 -domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4, enumeration tag, 6.2.3, 6.7.2.3 - 7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7, enumerator, 6.7.2.2 - 7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11, environment, 5 - 7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5, environment functions, 7.22.4, K.3.6.2 - 7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3 environment list, 7.22.4.6, K.3.6.2.1 -dot operator (.), 6.5.2.3 environmental considerations, 5.2 -double _Complex type, 6.2.5 environmental limits, 5.2.4, 7.13.1.1, 7.21.2, -double _Complex type conversion, 6.3.1.6, 7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2, - 6.3.1.7, 6.3.1.8 7.22.4.3, 7.28.2.1, K.3.5.1.2 -double _Imaginary type, G.2 EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2, -double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2, 7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11, - 7.28.2.2, F.2 7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4, -double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9, - 6.3.1.8 7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4, -double-precision arithmetic, 5.1.2.3 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12, -double-quote escape sequence (\"), 6.4.4.4, 7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7, - 6.4.5, 6.10.9 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, -double_t type, 7.12, J.5.6 K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, - K.3.9.1.14 -EDOM macro, 7.5, 7.12.1, see also domain error equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9 -effective type, 6.5 equal-to operator, see equality operator -EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2, equality expressions, 6.5.9 - 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, equality operator (==), 6.5.9 - 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1, - see also encoding error 7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see -element type, 6.2.5 also range error, pole error - -[page 660] (Contents) - -erf functions, 7.12.8.1, F.10.5.1 exp2 functions, 7.12.6.2, F.10.3.2 -erf type-generic macro, 7.24 exp2 type-generic macro, 7.24 -erfc functions, 7.12.8.2, F.10.5.2 explicit conversion, 6.3 -erfc type-generic macro, 7.24 expm1 functions, 7.12.6.3, F.10.3.3 -errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4, expm1 type-generic macro, 7.24 - 7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4, exponent part, 6.4.4.2 - 7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1, exponential functions - 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1, complex, 7.3.7, G.6.3 - 7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2, real, 7.12.6, F.10.3 - 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17, expression, 6.5 - K.3.1.3, K.3.7.4.2 assignment, 6.5.16 -errno.h header, 7.5, 7.30.3, K.3.2 cast, 6.5.4 -errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1, constant, 6.6 - K.3.7, K.3.8, K.3.9 evaluation, 5.1.2.3 -error full, 6.8 - domain, see domain error order of evaluation, see order of evaluation - encoding, see encoding error parenthesized, 6.5.1 - pole, see pole error primary, 6.5.1 - range, see range error unary, 6.5.3 -error conditions, 7.12.1 expression statement, 6.8.3 -error functions, 7.12.8, F.10.5 extended alignment, 6.2.8 -error indicator, 7.21.1, 7.21.5.3, 7.21.7.1, extended character set, 3.7.2, 5.2.1, 5.2.1.2 - 7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7, extended characters, 5.2.1 - 7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3, extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1, - 7.28.3.1, 7.28.3.3 7.20 -error preprocessing directive, 4, 6.10.5 extended multibyte/wide character conversion -error-handling functions, 7.21.10, 7.23.6.2, utilities, 7.28.6, K.3.9.3 - K.3.7.4.2, K.3.7.4.3 extensible wide character case mapping functions, -escape character (\), 6.4.4.4 7.29.3.2 -escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4 extensible wide character classification functions, -evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12 7.29.2.2 -evaluation method, 5.2.4.2.2, 6.5, F.8.5 extern storage-class specifier, 6.2.2, 6.7.1 -evaluation of expression, 5.1.2.3 external definition, 6.9 -evaluation order, see order of evaluation external identifiers, underscore, 7.1.3 -exceptional condition, 6.5 external linkage, 6.2.2 -excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external name, 6.4.2.1 -excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external object definitions, 6.9.2 -exclusive OR operators - bitwise (^), 6.2.6.2, 6.5.11 fabs functions, 7.12.7.2, F.3, F.10.4.2 - bitwise assignment (^=), 6.5.16.2 fabs type-generic macro, 7.24, G.7 -executable program, 5.1.1.1 false macro, 7.18 -execution character set, 5.2.1 fclose function, 7.21.5.1 -execution environment, 5, 5.1.2, see also fdim functions, 7.12.12.1, F.10.9.1 - environmental limits fdim type-generic macro, 7.24 -execution sequence, 5.1.2.3, 6.8 FE_ALL_EXCEPT macro, 7.6 -exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4, FE_DFL_ENV macro, 7.6 - 7.22.4.5, 7.22.4.7 FE_DIVBYZERO macro, 7.6, 7.12, F.3 -EXIT_FAILURE macro, 7.22, 7.22.4.4 FE_DOWNWARD macro, 7.6, F.3 -EXIT_SUCCESS macro, 7.22, 7.22.4.4 FE_INEXACT macro, 7.6, F.3 -exp functions, 7.12.6.1, F.10.3.1 FE_INVALID macro, 7.6, 7.12, F.3 -exp type-generic macro, 7.24 FE_OVERFLOW macro, 7.6, 7.12, F.3 - -[page 661] (Contents) - -FE_TONEAREST macro, 7.6, F.3 float _Complex type conversion, 6.3.1.6, -FE_TOWARDZERO macro, 7.6, F.3 6.3.1.7, 6.3.1.8 -FE_UNDERFLOW macro, 7.6, F.3 float _Imaginary type, G.2 -FE_UPWARD macro, 7.6, F.3 float type, 6.2.5, 6.4.4.2, 6.7.2, F.2 -feclearexcept function, 7.6.2, 7.6.2.1, F.3 float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, -fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3 6.3.1.8 -fegetexceptflag function, 7.6.2, 7.6.2.2, F.3 float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3, -fegetround function, 7.6, 7.6.3.1, F.3 7.28.4.1.1 -feholdexcept function, 7.6.4.2, 7.6.4.3, float_t type, 7.12, J.5.6 - 7.6.4.4, F.3 floating constant, 6.4.4.2 -fence, 5.1.2.4 floating suffix, f or F, 6.4.4.2 -fences, 7.17.4 floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, -fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H F.3, F.4 -FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9, floating types, 6.2.5, 6.11.1 - F.10 floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5, -fenv_t type, 7.6 7.22.1.3, F.5, see also contracted expression -feof function, 7.21.10.2 floating-point arithmetic functions, 7.12, F.10 -feraiseexcept function, 7.6.2, 7.6.2.3, F.3 floating-point classification functions, 7.12.3 -ferror function, 7.21.10.3 floating-point control mode, 7.6, F.8.6 -fesetenv function, 7.6.4.3, F.3 floating-point environment, 7.6, F.8, F.8.6 -fesetexceptflag function, 7.6.2, 7.6.2.4, F.3 floating-point exception, 7.6, 7.6.2, F.10 -fesetround function, 7.6, 7.6.3.2, F.3 floating-point number, 5.2.4.2.2, 6.2.5 -fetestexcept function, 7.6.2, 7.6.2.5, F.3 floating-point rounding mode, 5.2.4.2.2 -feupdateenv function, 7.6.4.2, 7.6.4.4, F.3 floating-point status flag, 7.6, F.8.6 -fexcept_t type, 7.6, F.3 floor functions, 7.12.9.2, F.10.6.2 -fflush function, 7.21.5.2, 7.21.5.3 floor type-generic macro, 7.24 -fgetc function, 7.21.1, 7.21.3, 7.21.7.1, FLT_DECIMAL_DIG macro, 5.2.4.2.2 - 7.21.7.5, 7.21.8.1 FLT_DIG macro, 5.2.4.2.2 -fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3 FLT_EPSILON macro, 5.2.4.2.2 -fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1 FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12, -fgetwc function, 7.21.1, 7.21.3, 7.28.3.1, F.10.11 - 7.28.3.6 FLT_HAS_SUBNORM macro, 5.2.4.2.2 -fgetws function, 7.21.1, 7.28.3.2 FLT_MANT_DIG macro, 5.2.4.2.2 -field width, 7.21.6.1, 7.28.2.1 FLT_MAX macro, 5.2.4.2.2 -file, 7.21.3 FLT_MAX_10_EXP macro, 5.2.4.2.2 - access functions, 7.21.5, K.3.5.2 FLT_MAX_EXP macro, 5.2.4.2.2 - name, 7.21.3 FLT_MIN macro, 5.2.4.2.2 - operations, 7.21.4, K.3.5.1 FLT_MIN_10_EXP macro, 5.2.4.2.2 - position indicator, 7.21.1, 7.21.2, 7.21.3, FLT_MIN_EXP macro, 5.2.4.2.2 - 7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10, FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3, - 7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2, 7.28.2.1, 7.28.4.1.1 - 7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1, FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3 - 7.28.3.3, 7.28.3.10 FLT_TRUE_MIN macro, 5.2.4.2.2 - positioning functions, 7.21.9 fma functions, 7.12, 7.12.13.1, F.10.10.1 -file scope, 6.2.1, 6.9 fma type-generic macro, 7.24 -FILE type, 7.21.1, 7.21.3 fmax functions, 7.12.12.2, F.10.9.2 -FILENAME_MAX macro, 7.21.1 fmax type-generic macro, 7.24 -flags, 7.21.6.1, 7.28.2.1, see also floating-point fmin functions, 7.12.12.3, F.10.9.3 - status flag fmin type-generic macro, 7.24 -flexible array member, 6.7.2.1 fmod functions, 7.12.10.1, F.10.7.1 -float _Complex type, 6.2.5 fmod type-generic macro, 7.24 - -[page 662] (Contents) - -fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1 K.3.5.3.7, K.3.5.3.9 -FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3, fseek function, 7.21.1, 7.21.5.3, 7.21.7.10, - K.3.5.1.1 7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10 -fopen_s function, K.3.5.1.1, K.3.5.2.1, fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10, - K.3.5.2.2 7.21.9.1, 7.21.9.3, 7.28.3.10 -for statement, 6.8.5, 6.8.5.3 ftell function, 7.21.9.2, 7.21.9.4 -form-feed character, 5.2.1, 6.4 full declarator, 6.7.6 -form-feed escape sequence (\f), 5.2.2, 6.4.4.4, full expression, 6.8 - 7.4.1.10 fully buffered stream, 7.21.3 -formal argument (deprecated), 3.16 function -formal parameter, 3.16 argument, 6.5.2.2, 6.9.1 -formatted input/output functions, 7.11.1.1, 7.21.6, body, 6.9.1 - K.3.5.3 call, 6.5.2.2 - wide character, 7.28.2, K.3.9.1 library, 7.1.4 -fortran keyword, J.5.9 declarator, 6.7.6.3, 6.11.6 -forward reference, 3.11 definition, 6.7.6.3, 6.9.1, 6.11.7 -FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see designator, 6.3.2.1 - also contracted expression image, 5.2.3 -FP_FAST_FMA macro, 7.12 inline, 6.7.4 -FP_FAST_FMAF macro, 7.12 library, 5.1.1.1, 7.1.4 -FP_FAST_FMAL macro, 7.12 name length, 5.2.4.1, 6.4.2.1, 6.11.3 -FP_ILOGB0 macro, 7.12, 7.12.6.5 no-return, 6.7.4 -FP_ILOGBNAN macro, 7.12, 7.12.6.5 parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1 -FP_INFINITE macro, 7.12, F.3 prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7, -FP_NAN macro, 7.12, F.3 6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12 -FP_NORMAL macro, 7.12, F.3 prototype scope, 6.2.1, 6.7.6.2 -FP_SUBNORMAL macro, 7.12, F.3 recursive call, 6.5.2.2 -FP_ZERO macro, 7.12, F.3 return, 6.8.6.4, F.6 -fpclassify macro, 7.12.3.1, F.3 scope, 6.2.1 -fpos_t type, 7.21.1, 7.21.2 type, 6.2.5 -fprintf function, 7.8.1, 7.21.1, 7.21.6.1, type conversion, 6.3.2.1 - 7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6, function specifiers, 6.7.4 - 7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1 function type, 6.2.5 -fprintf_s function, K.3.5.3.1 function-call operator (( )), 6.5.2.2 -fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3, function-like macro, 6.10.3 - 7.21.7.7, 7.21.8.2 fundamental alignment, 6.2.8 -fputs function, 7.21.1, 7.21.7.4 future directions -fputwc function, 7.21.1, 7.21.3, 7.28.3.3, language, 6.11 - 7.28.3.8 library, 7.30 -fputws function, 7.21.1, 7.28.3.4 fwide function, 7.21.2, 7.28.3.5 -fread function, 7.21.1, 7.21.8.1 fwprintf function, 7.8.1, 7.21.1, 7.21.6.2, -free function, 7.22.3.3, 7.22.3.5 7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5, -freestanding execution environment, 4, 5.1.2, 7.28.2.11, K.3.9.1.1 - 5.1.2.1 fwprintf_s function, K.3.9.1.1 -freopen function, 7.21.2, 7.21.5.4 fwrite function, 7.21.1, 7.21.8.2 -freopen_s function, K.3.5.2.2 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2, -frexp functions, 7.12.6.4, F.10.3.4 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10, -frexp type-generic macro, 7.24 K.3.9.1.2 -fscanf function, 7.8.1, 7.21.1, 7.21.6.2, fwscanf_s function, K.3.9.1.2, K.3.9.1.5, - 7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2 K.3.9.1.7, K.3.9.1.14 -fscanf_s function, K.3.5.3.2, K.3.5.3.4, - -[page 663] (Contents) - -gamma functions, 7.12.8, F.10.5 name spaces, 6.2.3 -general utilities, 7.22, K.3.6 reserved, 6.4.1, 7.1.3, K.3.1.2 - wide string, 7.28.4, K.3.9.2 scope, 6.2.1 -general wide string utilities, 7.28.4, K.3.9.2 type, 6.2.5 -generic parameters, 7.24 identifier list, 6.7.6 -generic selection, 6.5.1.1 identifier nondigit, 6.4.2.1 -getc function, 7.21.1, 7.21.7.5, 7.21.7.6 IEC 559, F.1 -getchar function, 7.21.1, 7.21.7.6 IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8.3, 7.3.3, -getenv function, 7.22.4.6 7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G, -getenv_s function, K.3.6.2.1 H.1 -gets function, K.3.5.4.1 IEEE 754, F.1 -gets_s function, K.3.5.4.1 IEEE 854, F.1 -getwc function, 7.21.1, 7.28.3.6, 7.28.3.7 IEEE floating-point arithmetic standard, see -getwchar function, 7.21.1, 7.28.3.7 IEC 60559, ANSI/IEEE 754, -gmtime function, 7.26.3.3 ANSI/IEEE 854 -gmtime_s function, K.3.8.2.3 if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, -goto statement, 6.2.1, 6.8.1, 6.8.6.1 6.10.1, 7.1.4 -graphic characters, 5.2.1 if statement, 6.8.4.1 -greater-than operator (>), 6.5.8 ifdef preprocessing directive, 6.10.1 -greater-than-or-equal-to operator (>=), 6.5.8 ifndef preprocessing directive, 6.10.1 - ignore_handler_s function, K.3.6.1.3 -happens before, 5.1.2.4 ilogb functions, 7.12, 7.12.6.5, F.10.3.5 -header, 5.1.1.1, 7.1.2, see also standard headers ilogb type-generic macro, 7.24 -header names, 6.4, 6.4.7, 6.10.2 imaginary macro, 7.3.1, G.6 -hexadecimal constant, 6.4.4.1 imaginary numbers, G -hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4 imaginary type domain, G.2 -hexadecimal prefix, 6.4.4.1 imaginary types, G -hexadecimal-character escape sequence imaxabs function, 7.8.2.1 - (\x hexadecimal digits), 6.4.4.4 imaxdiv function, 7.8, 7.8.2.2 -high-order bit, 3.6 imaxdiv_t type, 7.8 -horizontal-tab character, 5.2.1, 6.4 implementation, 3.12 -horizontal-tab escape sequence (\r), 7.29.2.1.3 implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1, -horizontal-tab escape sequence (\t), 5.2.2, 6.7.6, 6.8.4.2, E, see also environmental - 6.4.4.4, 7.4.1.3, 7.4.1.10 limits -hosted execution environment, 4, 5.1.2, 5.1.2.2 implementation-defined behavior, 3.4.1, 4, J.3 -HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3, implementation-defined value, 3.19.1 - 7.28.4.1.1, F.10 implicit conversion, 6.3 -HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3, implicit initialization, 6.7.9 - 7.28.4.1.1, F.10 include preprocessing directive, 5.1.1.2, 6.10.2 -HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3, inclusive OR operators - 7.28.4.1.1, F.10 bitwise (|), 6.2.6.2, 6.5.12 -hyperbolic functions bitwise assignment (|=), 6.5.16.2 - complex, 7.3.6, G.6.2 incomplete type, 6.2.5 - real, 7.12.5, F.10.2 increment operators, see arithmetic operators, -hypot functions, 7.12.7.3, F.10.4.3 increment and decrement -hypot type-generic macro, 7.24 indeterminate value, 3.19.2 - indeterminately sequenced, 5.1.2.3, 6.5.2.2, -I macro, 7.3.1, 7.3.9.5, G.6 6.5.2.4, 6.5.16.2, see also sequenced before, -identifier, 6.4.2.1, 6.5.1 unsequenced - linkage, see linkage indirection operator (*), 6.5.2.1, 6.5.3.2 - maximum length, 6.4.2.1 inequality operator (!=), 6.5.9 - -[page 664] (Contents) - -infinitary, 7.12.1 extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20 -INFINITY macro, 7.3.9.5, 7.12, F.2.1 inter-thread happens before, 5.1.2.4 -initial position, 5.2.2 interactive device, 5.1.2.3, 7.21.3, 7.21.5.3 -initial shift state, 5.2.1.2 internal linkage, 6.2.2 -initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9, internal name, 6.4.2.1 - F.8.5 interrupt, 5.2.3 - in blocks, 6.8 INTMAX_C macro, 7.20.4.2 -initializer, 6.7.9 INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 - permitted form, 6.6 INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 - string literal, 6.3.2.1 intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, -inline, 6.7.4 7.28.2.1, 7.28.2.2 -inner scope, 6.2.1 INTN_C macros, 7.20.4.1 -input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, INTN_MAX macros, 7.20.2.1 - K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9, INTN_MIN macros, 7.20.2.1 - K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5, intN_t types, 7.20.1.1 - K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14 INTPTR_MAX macro, 7.20.2.4 -input/output functions INTPTR_MIN macro, 7.20.2.4 - character, 7.21.7, K.3.5.4 intptr_t type, 7.20.1.4 - direct, 7.21.8 inttypes.h header, 7.8, 7.30.4 - formatted, 7.21.6, K.3.5.3 isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10 - wide character, 7.28.2, K.3.9.1 isalpha function, 7.4.1.1, 7.4.1.2 - wide character, 7.28.3 isblank function, 7.4.1.3 - formatted, 7.28.2, K.3.9.1 iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7, -input/output header, 7.21, K.3.5 7.4.1.11 -input/output, device, 5.1.2.3 isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5, -int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2 7.4.1.7, 7.4.1.11, 7.11.1.1 -int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, isfinite macro, 7.12.3.2, F.3 - 6.3.1.8 isgraph function, 7.4.1.6 -INT_FASTN_MAX macros, 7.20.2.3 isgreater macro, 7.12.14.1, F.3 -INT_FASTN_MIN macros, 7.20.2.3 isgreaterequal macro, 7.12.14.2, F.3 -int_fastN_t types, 7.20.1.3 isinf macro, 7.12.3.3 -INT_LEASTN_MAX macros, 7.20.2.2 isless macro, 7.12.14.3, F.3 -INT_LEASTN_MIN macros, 7.20.2.2 islessequal macro, 7.12.14.4, F.3 -int_leastN_t types, 7.20.1.2 islessgreater macro, 7.12.14.5, F.3 -INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5 islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1, -INT_MIN macro, 5.2.4.2.1, 7.12 7.4.2.2 -integer arithmetic functions, 7.8.2.1, 7.8.2.2, isnan macro, 7.12.3.4, F.3 - 7.22.6 isnormal macro, 7.12.3.5 -integer character constant, 6.4.4.4 ISO 31-11, 2, 3 -integer constant, 6.4.4.1 ISO 4217, 2, 7.11.2.1 -integer constant expression, 6.3.2.3, 6.6, 6.7.2.1, ISO 8601, 2, 7.26.3.5 - 6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1, ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2 - 7.1.4 ISO/IEC 10976-1, H.1 -integer conversion rank, 6.3.1.1 ISO/IEC 2382-1, 2, 3 -integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1, ISO/IEC 646, 2, 5.2.1.1 - 6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3, ISO/IEC 9945-2, 7.11 - 7.21.6.1, 7.28.2.1 iso646.h header, 4, 7.9 * -integer suffix, 6.4.4.1 isprint function, 5.2.2, 7.4.1.8 -integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9, - F.3, F.4 7.4.1.11 -integer types, 6.2.5, 7.20 isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9, - -[page 665] (Contents) - - 7.4.1.10, 7.4.1.11, 7.21.6.2, 7.22.1.3, LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1 - 7.22.1.4, 7.28.2.2 LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3, -isunordered macro, 7.12.14.6, F.3 7.28.4.4.2 -isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1, LC_CTYPE macro, 7.11, 7.11.1.1, 7.22, 7.22.7, - 7.4.2.2 7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2, -iswalnum function, 7.29.2.1.1, 7.29.2.1.9, 7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5 - 7.29.2.1.10, 7.29.2.2.1 LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1 -iswalpha function, 7.29.2.1.1, 7.29.2.1.2, LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1 - 7.29.2.2.1 LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5 -iswblank function, 7.29.2.1.3, 7.29.2.2.1 lconv structure type, 7.11 -iswcntrl function, 7.29.2.1.2, 7.29.2.1.4, LDBL_DECIMAL_DIG macro, 5.2.4.2.2 - 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_DIG macro, 5.2.4.2.2 -iswctype function, 7.29.2.2.1, 7.29.2.2.2 LDBL_EPSILON macro, 5.2.4.2.2 -iswdigit function, 7.29.2.1.1, 7.29.2.1.2, LDBL_HAS_SUBNORM macro, 5.2.4.2.2 - 7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_MANT_DIG macro, 5.2.4.2.2 -iswgraph function, 7.29.2.1, 7.29.2.1.6, LDBL_MAX macro, 5.2.4.2.2 - 7.29.2.1.10, 7.29.2.2.1 LDBL_MAX_10_EXP macro, 5.2.4.2.2 -iswlower function, 7.29.2.1.2, 7.29.2.1.7, LDBL_MAX_EXP macro, 5.2.4.2.2 - 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 LDBL_MIN macro, 5.2.4.2.2 -iswprint function, 7.29.2.1.6, 7.29.2.1.8, LDBL_MIN_10_EXP macro, 5.2.4.2.2 - 7.29.2.2.1 LDBL_MIN_EXP macro, 5.2.4.2.2 -iswpunct function, 7.29.2.1, 7.29.2.1.2, LDBL_TRUE_MIN macro, 5.2.4.2.2 - 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, ldexp functions, 7.12.6.6, F.10.3.6 - 7.29.2.1.11, 7.29.2.2.1 ldexp type-generic macro, 7.24 -iswspace function, 7.21.6.2, 7.28.2.2, ldiv function, 7.22.6.2 - 7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6, ldiv_t type, 7.22 - 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, leading underscore in identifiers, 7.1.3 - 7.29.2.1.11, 7.29.2.2.1 left-shift assignment operator (<<=), 6.5.16.2 -iswupper function, 7.29.2.1.2, 7.29.2.1.11, left-shift operator (<<), 6.2.6.2, 6.5.7 - 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 length -iswxdigit function, 7.29.2.1.12, 7.29.2.2.1 external name, 5.2.4.1, 6.4.2.1, 6.11.3 -isxdigit function, 7.4.1.12, 7.11.1.1 function name, 5.2.4.1, 6.4.2.1, 6.11.3 -italic type convention, 3, 6.1 identifier, 6.4.2.1 -iteration statements, 6.8.5 internal name, 5.2.4.1, 6.4.2.1 - length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1, -jmp_buf type, 7.13 7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1 -jump statements, 6.8.6 length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, - 7.28.2.2 -keywords, 6.4.1, G.2, J.5.9, J.5.10 less-than operator (<), 6.5.8 -kill_dependency macro, 5.1.2.4, 7.17.3.1 less-than-or-equal-to operator (<=), 6.5.8 -known constant size, 6.2.5 letter, 5.2.1, 7.4 - lexical elements, 5.1.1.2, 6.4 -L_tmpnam macro, 7.21.1, 7.21.4.4 lgamma functions, 7.12.8.3, F.10.5.3 -L_tmpnam_s macro, K.3.5, K.3.5.1.2 lgamma type-generic macro, 7.24 -label name, 6.2.1, 6.2.3 library, 5.1.1.1, 7, K.3 -labeled statement, 6.8.1 future directions, 7.30 -labs function, 7.22.6.1 summary, B -language, 6 terms, 7.1.1 - future directions, 6.11 use of functions, 7.1.4 - syntax summary, A lifetime, 6.2.4 -Latin alphabet, 5.2.1, 6.4.2.1 limits - -[page 666] (Contents) - - environmental, see environmental limits 6.3.1.6, 6.3.1.7, 6.3.1.8 - implementation, see implementation limits long double _Imaginary type, G.2 - numerical, see numerical limits long double suffix, l or L, 6.4.4.2 - translation, see translation limits long double type, 6.2.5, 6.4.4.2, 6.7.2, -limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2 -line buffered stream, 7.21.3 long double type conversion, 6.3.1.4, 6.3.1.5, -line number, 6.10.4, 6.10.8.1 6.3.1.7, 6.3.1.8 -line preprocessing directive, 6.10.4 long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, -lines, 5.1.1.2, 7.21.2 7.21.6.2, 7.28.2.1, 7.28.2.2 - preprocessing directive, 6.10 long int type conversion, 6.3.1.1, 6.3.1.3, -linkage, 6.2.2, 6.7, 6.7.4, 6.7.6.2, 6.9, 6.9.2, 6.3.1.4, 6.3.1.8 - 6.11.2 long integer suffix, l or L, 6.4.4.1 -llabs function, 7.22.6.1 long long int type, 6.2.5, 6.3.1.1, 6.7.2, -lldiv function, 7.22.6.2 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2 -lldiv_t type, 7.22 long long int type conversion, 6.3.1.1, -LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.3.1.3, 6.3.1.4, 6.3.1.8 - 7.28.4.1.2 long long integer suffix, ll or LL, 6.4.4.1 -LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4, LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2 - 7.28.4.1.2 LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2 -llrint functions, 7.12.9.5, F.3, F.10.6.5 longjmp function, 7.13.1.1, 7.13.2.1, 7.22.4.4, -llrint type-generic macro, 7.24 7.22.4.7 -llround functions, 7.12.9.7, F.10.6.7 loop body, 6.8.5 -llround type-generic macro, 7.24 low-order bit, 3.6 -local time, 7.26.1 lowercase letter, 5.2.1 -locale, 3.4.2 lrint functions, 7.12.9.5, F.3, F.10.6.5 -locale-specific behavior, 3.4.2, J.4 lrint type-generic macro, 7.24 -locale.h header, 7.11, 7.30.5 lround functions, 7.12.9.7, F.10.6.7 -localeconv function, 7.11.1.1, 7.11.2.1 lround type-generic macro, 7.24 -localization, 7.11 lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16, -localtime function, 7.26.3.4 6.7.2.4 -localtime_s function, K.3.8.2.4 lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1, -log functions, 7.12.6.7, F.10.3.7 6.5.16.2 -log type-generic macro, 7.24 -log10 functions, 7.12.6.8, F.10.3.8 macro argument substitution, 6.10.3.1 -log10 type-generic macro, 7.24 macro definition -log1p functions, 7.12.6.9, F.10.3.9 library function, 7.1.4 -log1p type-generic macro, 7.24 macro invocation, 6.10.3 -log2 functions, 7.12.6.10, F.10.3.10 macro name, 6.10.3 -log2 type-generic macro, 7.24 length, 5.2.4.1 -logarithmic functions predefined, 6.10.8, 6.11.9 - complex, 7.3.7, G.6.3 redefinition, 6.10.3 - real, 7.12.6, F.10.3 scope, 6.10.3.5 -logb functions, 7.12.6.11, F.3, F.10.3.11 macro parameter, 6.10.3 -logb type-generic macro, 7.24 macro preprocessor, 6.10 -logical operators macro replacement, 6.10.3 - AND (&&), 5.1.2.4, 6.5.13 magnitude, complex, 7.3.8.1 - negation (!), 6.5.3.3 main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4, - OR (||), 5.1.2.4, 6.5.14 7.21.3 -logical source lines, 5.1.1.2 malloc function, 7.22.3, 7.22.3.4, 7.22.3.5 -long double _Complex type, 6.2.5 manipulation functions -long double _Complex type conversion, complex, 7.3.9 - -[page 667] (Contents) - - real, 7.12.11, F.10.8 modf functions, 7.12.6.12, F.10.3.12 -matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, modifiable lvalue, 6.3.2.1 - K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 modification order, 5.1.2.4 -math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, modulus functions, 7.12.6.12 - F.10, J.5.17 modulus, complex, 7.3.8.1 -MATH_ERREXCEPT macro, 7.12, F.10 mtx_destroy function, 7.25.4.1 -math_errhandling macro, 7.1.3, 7.12, F.10 mtx_init function, 7.25.1, 7.25.4.2 -MATH_ERRNO macro, 7.12 mtx_lock function, 7.25.4.3 -max_align_t type, 7.19 mtx_t type, 7.25.1 -maximum functions, 7.12.12, F.10.9 mtx_timedlock function, 7.25.4.4 -MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2, mtx_trylock function, 7.25.4.5 - 7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3, mtx_unlock function, 7.25.4.3, 7.25.4.4, - K.3.6.4.1, K.3.9.3.1.1 7.25.4.5, 7.25.4.6 -MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.22 multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4 -mblen function, 7.22.7.1, 7.28.6.3 multibyte conversion functions -mbrlen function, 7.28.6.3.1 wide character, 7.22.7, K.3.6.4 -mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1 extended, 7.28.6, K.3.9.3 -mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 -mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2, wide string, 7.22.8, K.3.6.5 - 7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2, restartable, 7.28.6.4, K.3.9.3.2 - 7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1 multibyte string, 7.1.1 -mbsinit function, 7.28.6.2.1 multibyte/wide character conversion functions, -mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2 7.22.7, K.3.6.4 -mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1 extended, 7.28.6, K.3.9.3 -mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1, restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 - 7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1, multibyte/wide string conversion functions, - 7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3, 7.22.8, K.3.6.5 - 7.28.6.3.1, 7.28.6.4 restartable, 7.28.6.4, K.3.9.3.2 -mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4 multidimensional array, 6.5.2.1 -mbstowcs_s function, K.3.6.5.1 multiplication assignment operator (*=), 6.5.16.2 -mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2, multiplication operator (*), 6.2.6.2, 6.5.5, F.3, - 7.22.8.1, 7.28.6.3 G.5.1 -member access operators (. and ->), 6.5.2.3 multiplicative expressions, 6.5.5, G.5.1 -member alignment, 6.7.2.1 -memchr function, 7.23.5.1 n-char sequence, 7.22.1.3 -memcmp function, 7.23.4, 7.23.4.1 n-wchar sequence, 7.28.4.1.1 -memcpy function, 7.23.2.1 name -memcpy_s function, K.3.7.1.1 external, 5.2.4.1, 6.4.2.1, 6.11.3 -memmove function, 7.23.2.2 file, 7.21.3 -memmove_s function, K.3.7.1.2 internal, 5.2.4.1, 6.4.2.1 -memory location, 3.14 label, 6.2.3 -memory management functions, 7.22.3 structure/union member, 6.2.3 -memory_order type, 7.17.1, 7.17.3 name spaces, 6.2.3 -memset function, 7.23.6.1, K.3.7.4.1 named label, 6.8.1 -memset_s function, K.3.7.4.1 NaN, 5.2.4.2.2 -minimum functions, 7.12.12, F.10.9 nan functions, 7.12.11.2, F.2.1, F.10.8.2 -minus operator, unary, 6.5.3.3 NAN macro, 7.12, F.2.1 -miscellaneous functions NDEBUG macro, 7.2 - string, 7.23.6, K.3.7.4 nearbyint functions, 7.12.9.3, 7.12.9.4, F.3, - wide string, 7.28.4.6, K.3.9.2.4 F.10.6.3 -mktime function, 7.26.2.3 nearbyint type-generic macro, 7.24 - -[page 668] (Contents) - -nearest integer functions, 7.12.9, F.10.6 operating system, 5.1.2.1, 7.22.4.8 -negation operator (!), 6.5.3.3 operations on files, 7.21.4, K.3.5.1 -negative zero, 6.2.6.2, 7.12.11.1 operator, 6.4.6 -new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4 operators, 6.5 -new-line escape sequence (\n), 5.2.2, 6.4.4.4, additive, 6.2.6.2, 6.5.6 - 7.4.1.10 alignof, 6.5.3.4 -nextafter functions, 7.12.11.3, 7.12.11.4, F.3, assignment, 6.5.16 - F.10.8.3 associativity, 6.5 -nextafter type-generic macro, 7.24 equality, 6.5.9 -nexttoward functions, 7.12.11.4, F.3, F.10.8.4 multiplicative, 6.2.6.2, 6.5.5, G.5.1 -nexttoward type-generic macro, 7.24 postfix, 6.5.2 -no linkage, 6.2.2 precedence, 6.5 -no-return function, 6.7.4 preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9 -non-stop floating-point control mode, 7.6.4.2 relational, 6.5.8 -nongraphic characters, 5.2.2, 6.4.4.4 shift, 6.5.7 -nonlocal jumps header, 7.13 sizeof, 6.5.3.4 -norm, complex, 7.3.8.1 unary, 6.5.3 -normalized broken-down time, K.3.8.1, K.3.8.2.1 unary arithmetic, 6.5.3.3 -not macro, 7.9 optional features, see conditional features -not-equal-to operator, see inequality operator or macro, 7.9 -not_eq macro, 7.9 OR operators -null character (\0), 5.2.1, 6.4.4.4, 6.4.5 bitwise exclusive (^), 6.2.6.2, 6.5.11 - padding of binary stream, 7.21.2 bitwise exclusive assignment (^=), 6.5.16.2 -NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1, bitwise inclusive (|), 6.2.6.2, 6.5.12 - 7.26.1, 7.28.1 bitwise inclusive assignment (|=), 6.5.16.2 -null pointer, 6.3.2.3 logical (||), 5.1.2.4, 6.5.14 -null pointer constant, 6.3.2.3 or_eq macro, 7.9 -null preprocessing directive, 6.10.7 order of allocated storage, 7.22.3 -null statement, 6.8.3 order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3, -null wide character, 7.1.1 see also sequence points -number classification macros, 7.12, 7.12.3.1 ordinary identifier name space, 6.2.3 -numeric conversion functions, 7.8.2.3, 7.22.1 orientation of stream, 7.21.2, 7.28.3.5 - wide string, 7.8.2.4, 7.28.4.1 out-of-bounds store, L.2.1 -numerical limits, 5.2.4.2 outer scope, 6.2.1 - over-aligned, 6.2.8 -object, 3.15 -object representation, 6.2.6.1 padding -object type, 6.2.5 binary stream, 7.21.2 -object-like macro, 6.10.3 bits, 6.2.6.2, 7.20.1.1 -observable behavior, 5.1.2.3 structure/union, 6.2.6.1, 6.7.2.1 -obsolescence, 6.11, 7.30 parameter, 3.16 -octal constant, 6.4.4.1 array, 6.9.1 -octal digit, 6.4.4.1, 6.4.4.4 ellipsis, 6.7.6.3, 6.10.3 -octal-character escape sequence (\octal digits), function, 6.5.2.2, 6.7, 6.9.1 - 6.4.4.4 macro, 6.10.3 -offsetof macro, 7.19 main function, 5.1.2.2.1 -on-off switch, 6.10.6 program, 5.1.2.2.1 -once_flag type, 7.25.1 parameter type list, 6.7.6.3 -ONCE_FLAG_INIT macro, 7.25.1 parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5 -ones' complement, 6.2.6.2 parenthesized expression, 6.5.1 -operand, 6.4.6, 6.5 parse state, 7.21.2 - -[page 669] (Contents) - -perform a trap, 3.19.5 preprocessor, 6.10 -permitted form of initializer, 6.6 PRIcFASTN macros, 7.8.1 -perror function, 7.21.10.4 PRIcLEASTN macros, 7.8.1 -phase angle, complex, 7.3.9.1 PRIcMAX macros, 7.8.1 -physical source lines, 5.1.1.2 PRIcN macros, 7.8.1 -placemarker, 6.10.3.3 PRIcPTR macros, 7.8.1 -plus operator, unary, 6.5.3.3 primary expression, 6.5.1 -pointer arithmetic, 6.5.6 printf function, 7.21.1, 7.21.6.3, 7.21.6.10, -pointer comparison, 6.5.8 K.3.5.3.3 -pointer declarator, 6.7.6.1 printf_s function, K.3.5.3.3 -pointer operator (->), 6.5.2.3 printing character, 5.2.2, 7.4, 7.4.1.8 -pointer to function, 6.5.2.2 printing wide character, 7.29.2 -pointer type, 6.2.5 program diagnostics, 7.2.1 -pointer type conversion, 6.3.2.1, 6.3.2.3 program execution, 5.1.2.2.2, 5.1.2.3 -pointer, null, 6.3.2.3 program file, 5.1.1.1 -pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8, program image, 5.1.1.2 - 7.12.6.9, 7.12.6.10, 7.12.6.11, 7.12.7.4, program name (argv[0]), 5.1.2.2.1 - 7.12.8.3, 7.12.8.4 program parameters, 5.1.2.2.1 -portability, 4, J program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1 -position indicator, file, see file position indicator program structure, 5.1.1.1 -positive difference, 7.12.12.1 program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3, -positive difference functions, 7.12.12, F.10.9 5.1.2.3 -postfix decrement operator (--), 6.3.2.1, 6.5.2.4 program, conforming, 4 -postfix expressions, 6.5.2 program, strictly conforming, 4 -postfix increment operator (++), 6.3.2.1, 6.5.2.4 promotions -pow functions, 7.12.7.4, F.10.4.4 default argument, 6.5.2.2 -pow type-generic macro, 7.24 integer, 5.1.2.3, 6.3.1.1 -power functions prototype, see function prototype - complex, 7.3.8, G.6.4 pseudo-random sequence functions, 7.22.2 - real, 7.12.7, F.10.4 PTRDIFF_MAX macro, 7.20.3 -pp-number, 6.4.8 PTRDIFF_MIN macro, 7.20.3 -pragma operator, 6.10.9 ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1, -pragma preprocessing directive, 6.10.6, 6.11.8 7.21.6.2, 7.28.2.1, 7.28.2.2 -precedence of operators, 6.5 punctuators, 6.4.6 -precedence of syntax rules, 5.1.1.2 putc function, 7.21.1, 7.21.7.7, 7.21.7.8 -precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1 putchar function, 7.21.1, 7.21.7.8 - excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 puts function, 7.21.1, 7.21.7.9 -predefined macro names, 6.10.8, 6.11.9 putwc function, 7.21.1, 7.28.3.8, 7.28.3.9 -prefix decrement operator (--), 6.3.2.1, 6.5.3.1 putwchar function, 7.21.1, 7.28.3.9 -prefix increment operator (++), 6.3.2.1, 6.5.3.1 -preprocessing concatenation, 6.10.3.3 qsort function, 7.22.5, 7.22.5.2 -preprocessing directives, 5.1.1.2, 6.10 qsort_s function, K.3.6.3, K.3.6.3.2 -preprocessing file, 5.1.1.1, 6.10 qualified types, 6.2.5 -preprocessing numbers, 6.4, 6.4.8 qualified version of type, 6.2.5 -preprocessing operators question-mark escape sequence (\?), 6.4.4.4 - #, 6.10.3.2 quick_exit function, 7.22.4.3, 7.22.4.4, - ##, 6.10.3.3 7.22.4.7 - _Pragma, 5.1.1.2, 6.10.9 quiet NaN, 5.2.4.2.2 - defined, 6.10.1 -preprocessing tokens, 5.1.1.2, 6.4, 6.10 raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1 -preprocessing translation unit, 5.1.1.1 rand function, 7.22, 7.22.2.1, 7.22.2.2 - -[page 670] (Contents) - -RAND_MAX macro, 7.22, 7.22.2.1 restrict-qualified type, 6.2.5, 6.7.3 -range return statement, 6.8.6.4, F.6 - excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5, -range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1, 7.28.3.10 - 7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6, right-shift assignment operator (>>=), 6.5.16.2 - 7.12.6.13, 7.12.7.3, 7.12.7.4, 7.12.8.2, right-shift operator (>>), 6.2.6.2, 6.5.7 - 7.12.8.3, 7.12.8.4, 7.12.9.5, 7.12.9.7, rint functions, 7.12.9.4, F.3, F.10.6.4 - 7.12.11.3, 7.12.12.1, 7.12.13.1 rint type-generic macro, 7.24 -rank, see integer conversion rank round functions, 7.12.9.6, F.10.6.6 -read-modify-write operations, 5.1.2.4 round type-generic macro, 7.24 -real floating type conversion, 6.3.1.4, 6.3.1.5, rounding mode, floating point, 5.2.4.2.2 - 6.3.1.7, F.3, F.4 RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2, -real floating types, 6.2.5 K.3.5.3.5, K.3.5.3.6, K.3.5.3.12, K.3.5.3.13, -real type domain, 6.2.5 K.3.5.4.1, K.3.6.2.1, K.3.6.3.1, K.3.6.3.2, -real types, 6.2.5 K.3.6.4.1, K.3.6.5.1, K.3.6.5.2, K.3.7.1.1, -real-floating, 7.12.3 K.3.7.1.2, K.3.7.1.3, K.3.7.1.4, K.3.7.2.1, -realloc function, 7.22.3, 7.22.3.5 K.3.7.2.2, K.3.7.3.1, K.3.7.4.1, K.3.7.4.2, -recommended practice, 3.17 K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4, -recursion, 6.5.2.2 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2, -recursive function call, 6.5.2.2 K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1, -redefinition of macro, 6.10.3 K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1, -reentrancy, 5.1.2.3, 5.2.3 K.3.9.3.2.1, K.3.9.3.2.2 - library functions, 7.1.4 rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2, -referenced type, 6.2.5 K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 -register storage-class specifier, 6.7.1, 6.9 runtime-constraint, 3.18 -relational expressions, 6.5.8 Runtime-constraint handling functions, K.3.6.1 -relaxed atomic operations, 5.1.2.4 rvalue, 6.3.2.1 -release fence, 7.17.4 -release operation, 5.1.2.4 same scope, 6.2.1 -release sequence, 5.1.2.4 save calling environment function, 7.13.1 -reliability of data, interrupted, 5.1.2.3 scalar types, 6.2.5 -remainder assignment operator (%=), 6.5.16.2 scalbln function, 7.12.6.13, F.3, F.10.3.13 -remainder functions, 7.12.10, F.10.7 scalbln type-generic macro, 7.24 -remainder functions, 7.12.10.2, 7.12.10.3, F.3, scalbn function, 7.12.6.13, F.3, F.10.3.13 - F.10.7.2 scalbn type-generic macro, 7.24 -remainder operator (%), 6.2.6.2, 6.5.5 scanf function, 7.21.1, 7.21.6.4, 7.21.6.11 -remainder type-generic macro, 7.24 scanf_s function, K.3.5.3.4, K.3.5.3.11 -remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2 scanlist, 7.21.6.2, 7.28.2.2 -remquo functions, 7.12.10.3, F.3, F.10.7.3 scanset, 7.21.6.2, 7.28.2.2 -remquo type-generic macro, 7.24 SCHAR_MAX macro, 5.2.4.2.1 -rename function, 7.21.4.2 SCHAR_MIN macro, 5.2.4.2.1 -representations of types, 6.2.6 SCNcFASTN macros, 7.8.1 - pointer, 6.2.5 SCNcLEASTN macros, 7.8.1 -rescanning and replacement, 6.10.3.4 SCNcMAX macros, 7.8.1 -reserved identifiers, 6.4.1, 7.1.3, K.3.1.2 SCNcN macros, 7.8.1 -restartable multibyte/wide character conversion SCNcPTR macros, 7.8.1 - functions, 7.27.1, 7.28.6.3, K.3.9.3.1 scope of identifier, 6.2.1, 6.9.2 -restartable multibyte/wide string conversion search functions - functions, 7.28.6.4, K.3.9.3.2 string, 7.23.5, K.3.7.3 -restore calling environment function, 7.13.2 utility, 7.22.5, K.3.6.3 -restrict type qualifier, 6.7.3, 6.7.3.1 wide string, 7.28.4.5, K.3.9.2.3 - -[page 671] (Contents) - -SEEK_CUR macro, 7.21.1, 7.21.9.2 sign and magnitude, 6.2.6.2 -SEEK_END macro, 7.21.1, 7.21.9.2 sign bit, 6.2.6.2 -SEEK_SET macro, 7.21.1, 7.21.9.2 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7 -selection statements, 6.8.4 signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1 -self-referential structure, 6.7.2.3 signal handling functions, 7.14.1 -semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3, signal.h header, 7.14, 7.30.6 - 6.8.5, 6.8.6 signaling NaN, 5.2.4.2.2, F.2.1 -separate compilation, 5.1.1.1 signals, 5.1.2.3, 5.2.3, 7.14.1 -separate translation, 5.1.1.1 signbit macro, 7.12.3.6, F.3 -sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14, signed char type, 6.2.5, 7.21.6.1, 7.21.6.2, - 6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8, 7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2 - 7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3 signed character, 6.3.1.1 -sequenced after, see sequenced before signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1 -sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4, signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, - 6.5.16, see also indeterminately sequenced, 6.3.1.8 - unsequenced signed types, 6.2.5, 6.7.2 -sequencing of statements, 6.8 significand part, 6.4.4.2 -set_constraint_handler_s function, SIGSEGV macro, 7.14, 7.14.1.1 - K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3 SIGTERM macro, 7.14 -setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5 simple assignment operator (=), 6.5.16.1 -setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1 sin functions, 7.12.4.6, F.10.1.6 -setjmp.h header, 7.13 sin type-generic macro, 7.24, G.7 -setlocale function, 7.11.1.1, 7.11.2.1 single-byte character, 3.7.1, 5.2.1.2 -setvbuf function, 7.21.1, 7.21.3, 7.21.5.1, single-byte/wide character conversion functions, - 7.21.5.5, 7.21.5.6 7.28.6.1 -shall, 4 single-precision arithmetic, 5.1.2.3 -shift expressions, 6.5.7 single-quote escape sequence (\'), 6.4.4.4, 6.4.5 -shift sequence, 7.1.1 singularity, 7.12.1 -shift states, 5.2.1.2 sinh functions, 7.12.5.5, F.10.2.5 -short identifier, character, 5.2.4.1, 6.4.3 sinh type-generic macro, 7.24, G.7 -short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, SIZE_MAX macro, 7.20.3 - 7.21.6.2, 7.28.2.1, 7.28.2.2 size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1, -short int type conversion, 6.3.1.1, 6.3.1.3, 7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27, - 6.3.1.4, 6.3.1.8 7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4, -SHRT_MAX macro, 5.2.4.2.1 K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 -SHRT_MIN macro, 5.2.4.2.1 sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4 -side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4, snprintf function, 7.21.6.5, 7.21.6.12, - 6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5, K.3.5.3.5 - 7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1, snprintf_s function, K.3.5.3.5, K.3.5.3.6 - F.9.3 snwprintf_s function, K.3.9.1.3, K.3.9.1.4 -SIG_ATOMIC_MAX macro, 7.20.3 sorting utility functions, 7.22.5, K.3.6.3 -SIG_ATOMIC_MIN macro, 7.20.3 source character set, 5.1.1.2, 5.2.1 -sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1, source file, 5.1.1.1 - 7.20.3 name, 6.10.4, 6.10.8.1 -SIG_DFL macro, 7.14, 7.14.1.1 source file inclusion, 6.10.2 -SIG_ERR macro, 7.14, 7.14.1.1 source lines, 5.1.1.2 -SIG_IGN macro, 7.14, 7.14.1.1 source text, 5.1.1.2 -SIGABRT macro, 7.14, 7.22.4.1 space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, -SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17 7.4.1.10, 7.29.2.1.3 -SIGILL macro, 7.14, 7.14.1.1 sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6 -SIGINT macro, 7.14 sprintf_s function, K.3.5.3.5, K.3.5.3.6 - -[page 672] (Contents) - -sqrt functions, 7.12.7.5, F.3, F.10.4.5 do, 6.8.5.2 -sqrt type-generic macro, 7.24 else, 6.8.4.1 -srand function, 7.22.2.2 expression, 6.8.3 -sscanf function, 7.21.6.7, 7.21.6.14 for, 6.8.5.3 -sscanf_s function, K.3.5.3.7, K.3.5.3.14 goto, 6.8.6.1 -standard error stream, 7.21.1, 7.21.3, 7.21.10.4 if, 6.8.4.1 -standard headers, 4, 7.1.2 iteration, 6.8.5 - <assert.h>, 7.2 jump, 6.8.6 - <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3, labeled, 6.8.1 - 7.24, 7.30.1, G.6, J.5.17 null, 6.8.3 - <ctype.h>, 7.4, 7.30.2 return, 6.8.6.4, F.6 - <errno.h>, 7.5, 7.30.3, K.3.2 selection, 6.8.4 - <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H sequencing, 6.8 - <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3, switch, 6.8.4.2 - 7.28.4.1.1 while, 6.8.5.1 - <inttypes.h>, 7.8, 7.30.4 static assertions, 6.7.10 - <iso646.h>, 4, 7.9 static storage duration, 6.2.4 - <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10 static storage-class specifier, 6.2.2, 6.2.4, 6.7.1 - <locale.h>, 7.11, 7.30.5 static, in array declarators, 6.7.6.2, 6.7.6.3 - <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10, static_assert declaration, 6.7.10 - J.5.17 static_assert macro, 7.2 - <setjmp.h>, 7.13 stdalign.h header, 4, 7.15 - <signal.h>, 7.14, 7.30.6 stdarg.h header, 4, 6.7.6.3, 7.16 - <stdalign.h>, 4, 7.15 stdatomic.h header, 6.10.8.3, 7.1.2, 7.17 - <stdarg.h>, 4, 6.7.6.3, 7.16 stdbool.h header, 4, 7.18, 7.30.7, H - <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17 STDC, 6.10.6, 6.11.8 - <stdbool.h>, 4, 7.18, 7.30.7, H stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, - <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 - 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 stderr macro, 7.21.1, 7.21.2, 7.21.3 - <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4, - 7.30.8, K.3.3, K.3.4 7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4, - <stdio.h>, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 K.3.5.4.1, K.3.9.1.14 - <stdlib.h>, 5.2.4.2.2, 7.22, 7.30.10, F, stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, - K.3.1.4, K.3.6 7.30.8, K.3.3, K.3.4 - <string.h>, 7.23, 7.30.11, K.3.7 stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 - <tgmath.h>, 7.24, G.7 stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F, - <threads.h>, 6.10.8.3, 7.1.2, 7.25 K.3.1.4, K.3.6 - <time.h>, 7.26, K.3.8 stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3, - <uchar.h>, 6.4.4.4, 6.4.5, 7.27 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9 - <wchar.h>, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, storage duration, 6.2.4 - F, K.3.9 storage order of array, 6.5.2.1 - <wctype.h>, 7.29, 7.30.13 storage unit (bit-field), 6.2.6.1, 6.7.2.1 -standard input stream, 7.21.1, 7.21.3 storage-class specifiers, 6.7.1, 6.11.5 -standard integer types, 6.2.5 strcat function, 7.23.3.1 -standard output stream, 7.21.1, 7.21.3 strcat_s function, K.3.7.2.1 -standard signed integer types, 6.2.5 strchr function, 7.23.5.2 -state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4 strcmp function, 7.23.4, 7.23.4.2 -statements, 6.8 strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5 - break, 6.8.6.3 strcpy function, 7.23.2.3 - compound, 6.8.2 strcpy_s function, K.3.7.1.3 - continue, 6.8.6.2 strcspn function, 7.23.5.3 - -[page 673] (Contents) - -streams, 7.21.2, 7.22.4.4 7.22.1.4, 7.28.2.2 - fully buffered, 7.21.3 strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4 - line buffered, 7.21.3 strtoumax function, 7.8.2.3 - orientation, 7.21.2 struct hack, see flexible array member - standard error, 7.21.1, 7.21.3 struct lconv, 7.11 - standard input, 7.21.1, 7.21.3 struct tm, 7.26.1 - standard output, 7.21.1, 7.21.3 structure - unbuffered, 7.21.3 arrow operator (->), 6.5.2.3 -strerror function, 7.21.10.4, 7.23.6.2 content, 6.7.2.3 -strerror_s function, K.3.7.4.2, K.3.7.4.3 dot operator (.), 6.5.2.3 -strerrorlen_s function, K.3.7.4.3 initialization, 6.7.9 -strftime function, 7.11.1.1, 7.26.3, 7.26.3.5, member alignment, 6.7.2.1 - 7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2 member name space, 6.2.3 -stricter, 6.2.8 member operator (.), 6.3.2.1, 6.5.2.3 -strictly conforming program, 4 pointer operator (->), 6.5.2.3 -string, 7.1.1 specifier, 6.7.2.1 - comparison functions, 7.23.4 tag, 6.2.3, 6.7.2.3 - concatenation functions, 7.23.3, K.3.7.2 type, 6.2.5, 6.7.2.1 - conversion functions, 7.11.1.1 strxfrm function, 7.11.1.1, 7.23.4.5 - copying functions, 7.23.2, K.3.7.1 subnormal floating-point numbers, 5.2.4.2.2 - library function conventions, 7.23.1 subscripting, 6.5.2.1 - literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9 subtraction assignment operator (-=), 6.5.16.2 - miscellaneous functions, 7.23.6, K.3.7.4 subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2 - numeric conversion functions, 7.8.2.3, 7.22.1 suffix - search functions, 7.23.5, K.3.7.3 floating constant, 6.4.4.2 -string handling header, 7.23, K.3.7 integer constant, 6.4.4.1 -string.h header, 7.23, 7.30.11, K.3.7 switch body, 6.8.4.2 -stringizing, 6.10.3.2, 6.10.9 switch case label, 6.8.1, 6.8.4.2 -strlen function, 7.23.6.3 switch default label, 6.8.1, 6.8.4.2 -strncat function, 7.23.3.2 switch statement, 6.8.1, 6.8.4.2 -strncat_s function, K.3.7.2.2 swprintf function, 7.28.2.3, 7.28.2.7, -strncmp function, 7.23.4, 7.23.4.4 K.3.9.1.3, K.3.9.1.4 -strncpy function, 7.23.2.4 swprintf_s function, K.3.9.1.3, K.3.9.1.4 -strncpy_s function, K.3.7.1.4 swscanf function, 7.28.2.4, 7.28.2.8 -strnlen_s function, K.3.7.4.4 swscanf_s function, K.3.9.1.5, K.3.9.1.10 -stronger, 6.2.8 symbols, 3 -strpbrk function, 7.23.5.4 synchronization operation, 5.1.2.4 -strrchr function, 7.23.5.5 synchronize with, 5.1.2.4 -strspn function, 7.23.5.6 syntactic categories, 6.1 -strstr function, 7.23.5.7 syntax notation, 6.1 -strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3, syntax rule precedence, 5.1.1.2 - 7.28.2.2, F.3 syntax summary, language, A -strtof function, 7.12.11.2, 7.22.1.3, F.3 system function, 7.22.4.8 -strtoimax function, 7.8.2.3 -strtok function, 7.23.5.8 tab characters, 5.2.1, 6.4 -strtok_s function, K.3.7.3.1 tag compatibility, 6.2.7 -strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tag name space, 6.2.3 - 7.22.1.4, 7.28.2.2 tags, 6.7.2.3 -strtold function, 7.12.11.2, 7.22.1.3, F.3 tan functions, 7.12.4.7, F.10.1.7 -strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4 tan type-generic macro, 7.24, G.7 -strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tanh functions, 7.12.5.6, F.10.2.6 - -[page 674] (Contents) - -tanh type-generic macro, 7.24, G.7 toupper function, 7.4.2.2 -temporary lifetime, 6.2.4 towctrans function, 7.29.3.2.1, 7.29.3.2.2 -tentative definition, 6.9.2 towlower function, 7.29.3.1.1, 7.29.3.2.1 -terms, 3 towupper function, 7.29.3.1.2, 7.29.3.2.1 -text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4 translation environment, 5, 5.1.1 -tgamma functions, 7.12.8.4, F.10.5.4 translation limits, 5.2.4.1 -tgamma type-generic macro, 7.24 translation phases, 5.1.1.2 -tgmath.h header, 7.24, G.7 translation unit, 5.1.1.1, 6.9 -thrd_create function, 7.25.1, 7.25.5.1 trap, see perform a trap -thrd_current function, 7.25.5.2 trap representation, 3.19.4, 6.2.6.1, 6.2.6.2, -thrd_detach function, 7.25.5.3 6.3.2.3, 6.5.2.3 -thrd_equal function, 7.25.5.4 trigonometric functions -thrd_exit function, 7.25.5.5 complex, 7.3.5, G.6.1 -thrd_join function, 7.25.5.6 real, 7.12.4, F.10.1 -thrd_sleep function, 7.25.5.7 trigraph sequences, 5.1.1.2, 5.2.1.1 -thrd_start_t type, 7.25.1 true macro, 7.18 -thrd_t type, 7.25.1 trunc functions, 7.12.9.8, F.10.6.8 -thrd_yield function, 7.25.5.8 trunc type-generic macro, 7.24 -thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6 truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3 -thread storage duration, 6.2.4, 7.6 truncation toward zero, 6.5.5 -threads header, 7.25 tss_create function, 7.25.6.1 -threads.h header, 6.10.8.3, 7.1.2, 7.25 tss_delete function, 7.25.6.2 -time TSS_DTOR_ITERATIONS macro, 7.25.1 - broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1, tss_dtor_t type, 7.25.1 - 7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1, tss_get function, 7.25.6.3 - K.3.8.2.3, K.3.8.2.4 tss_set function, 7.25.6.4 - calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, tss_t type, 7.25.1 - 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, two's complement, 6.2.6.2, 7.20.1.1 - K.3.8.2.3, K.3.8.2.4 type category, 6.2.5 - components, 7.26.1, K.3.8.1 type conversion, 6.3 - conversion functions, 7.26.3, K.3.8.2 type definitions, 6.7.8 - wide character, 7.28.5 type domain, 6.2.5, G.2 - local, 7.26.1 type names, 6.7.7 - manipulation functions, 7.26.2 type punning, 6.5.2.3 - normalized broken down, K.3.8.1, K.3.8.2.1 type qualifiers, 6.7.3 -time function, 7.26.2.4 type specifiers, 6.7.2 -time.h header, 7.26, K.3.8 type-generic macro, 7.24, G.7 -time_t type, 7.26.1 typedef declaration, 6.7.8 -TIME_UTC macro, 7.25.7.1 typedef storage-class specifier, 6.7.1, 6.7.8 -tm structure type, 7.26.1, 7.28.1, K.3.8.1 types, 6.2.5 -TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4 atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3, -TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6 -tmpfile function, 7.21.4.3, 7.22.4.4 character, 6.7.9 -tmpfile_s function, K.3.5.1.1, K.3.5.1.2 compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6 -tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4, complex, 6.2.5, G - K.3.5.1.2 composite, 6.2.7 -tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2 const qualified, 6.7.3 -token, 5.1.1.2, 6.4, see also preprocessing tokens conversions, 6.3 -token concatenation, 6.10.3.3 imaginary, G -token pasting, 6.10.3.3 restrict qualified, 6.7.3 -tolower function, 7.4.2.1 volatile qualified, 6.7.3 - -[page 675] (Contents) - -uchar.h header, 6.4.4.4, 6.4.5, 7.27 universal character name, 6.4.3 -UCHAR_MAX macro, 5.2.4.2.1 unnormalized floating-point numbers, 5.2.4.2.2 -UINT_FASTN_MAX macros, 7.20.2.3 unqualified type, 6.2.5 -uint_fastN_t types, 7.20.1.3 unqualified version of type, 6.2.5 -uint_least16_t type, 7.27 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also -uint_least32_t type, 7.27 indeterminately sequenced, sequenced -UINT_LEASTN_MAX macros, 7.20.2.2 before -uint_leastN_t types, 7.20.1.2 unsigned char type, K.3.5.3.2, K.3.9.1.2 -UINT_MAX macro, 5.2.4.2.1 unsigned integer suffix, u or U, 6.4.4.1 -UINTMAX_C macro, 7.20.4.2 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1 -UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 unsigned type conversion, 6.3.1.1, 6.3.1.3, -uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, 6.3.1.4, 6.3.1.8 - 7.28.2.1, 7.28.2.2 unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2, -UINTN_C macros, 7.20.4.1 7.28.2.1, 7.28.2.2 -UINTN_MAX macros, 7.20.2.1 unspecified behavior, 3.4.4, 4, J.1 -uintN_t types, 7.20.1.1 unspecified value, 3.19.3 -UINTPTR_MAX macro, 7.20.2.4 uppercase letter, 5.2.1 -uintptr_t type, 7.20.1.4 use of library functions, 7.1.4 -ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, USHRT_MAX macro, 5.2.4.2.1 - 7.28.4.1.2 usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6, -ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15 - 7.28.4.1.2 UTF-16, 6.10.8.2 -unary arithmetic operators, 6.5.3.3 UTF-32, 6.10.8.2 -unary expression, 6.5.3 UTF-8 string literal, see string literal -unary minus operator (-), 6.5.3.3, F.3 utilities, general, 7.22, K.3.6 -unary operators, 6.5.3 wide string, 7.28.4, K.3.9.2 -unary plus operator (+), 6.5.3.3 -unbuffered stream, 7.21.3 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2, -undef preprocessing directive, 6.10.3.5, 7.1.3, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, - 7.1.4 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, -undefined behavior, 3.4.3, 4, J.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, -underscore character, 6.4.2.1 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11, -underscore, leading, in identifier, 7.1.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 -ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2, va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1, - 7.21.9.3 7.16.1.2, 7.16.1.3 -ungetwc function, 7.21.1, 7.28.3.10 va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3, -Unicode, 7.27, see also char16_t type, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, - char32_t type, wchar_t type 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, -Unicode required set, 6.10.8.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, -union 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11, - arrow operator (->), 6.5.2.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 - content, 6.7.2.3 va_list type, 7.16, 7.16.1.3 - dot operator (.), 6.5.2.3 va_start macro, 7.16, 7.16.1, 7.16.1.1, - initialization, 6.7.9 7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8, - member alignment, 6.7.2.1 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, - member name space, 6.2.3 7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6, - member operator (.), 6.3.2.1, 6.5.2.3 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10, - pointer operator (->), 6.5.2.3 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7, - specifier, 6.7.2.1 K.3.9.1.10, K.3.9.1.12 - tag, 6.2.3, 6.7.2.3 value, 3.19 - type, 6.2.5, 6.7.2.1 value bits, 6.2.6.2 - -[page 676] (Contents) - -variable arguments, 6.10.3, 7.16 vswscanf function, 7.28.2.8 -variable arguments header, 7.16 vswscanf_s function, K.3.9.1.10 -variable length array, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11 -variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf_s function, K.3.9.1.11 -vertical-tab character, 5.2.1, 6.4 vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10 -vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4, vwscanf_s function, K.3.9.1.12 - 7.4.1.10 -vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8 warnings, I -vfprintf_s function, K.3.5.3.8, K.3.5.3.9, wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, - K.3.5.3.11, K.3.5.3.14 F, K.3.9 -vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9 WCHAR_MAX macro, 7.20.3, 7.28.1 -vfscanf_s function, K.3.5.3.9, K.3.5.3.11, WCHAR_MIN macro, 7.20.3, 7.28.1 - K.3.5.3.14 wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19, -vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6 7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1, -vfwprintf_s function, K.3.9.1.6 7.28.2.1, 7.28.2.2 -vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10 wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2, -vfwscanf_s function, K.3.9.1.7 7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1, -visibility of identifier, 6.2.1 K.3.9.3.2.2 -visible sequence of side effects, 5.1.2.4 wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1 -visible side effect, 5.1.2.4 wcscat function, 7.28.4.3.1 -VLA, see variable length array wcscat_s function, K.3.9.2.2.1 -void expression, 6.3.2.2 wcschr function, 7.28.4.5.1 -void function parameter, 6.7.6.3 wcscmp function, 7.28.4.4.1, 7.28.4.4.4 -void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2, wcscoll function, 7.28.4.4.2, 7.28.4.4.4 - K.3.9.1.2 wcscpy function, 7.28.4.2.1 -void type conversion, 6.3.2.2 wcscpy_s function, K.3.9.2.1.1 -volatile storage, 5.1.2.3 wcscspn function, 7.28.4.5.2 -volatile type qualifier, 6.7.3 wcsftime function, 7.11.1.1, 7.28.5.1 -volatile-qualified type, 6.2.5, 6.7.3 wcslen function, 7.28.4.6.1 -vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10, wcsncat function, 7.28.4.3.2 - K.3.5.3.10 wcsncat_s function, K.3.9.2.2.2 -vprintf_s function, K.3.5.3.9, K.3.5.3.10, wcsncmp function, 7.28.4.4.3 - K.3.5.3.11, K.3.5.3.14 wcsncpy function, 7.28.4.2.2 -vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11 wcsncpy_s function, K.3.9.2.1.2 -vscanf_s function, K.3.5.3.9, K.3.5.3.11, wcsnlen_s function, K.3.9.2.4.1 - K.3.5.3.14 wcspbrk function, 7.28.4.5.3 -vsnprintf function, 7.21.6.8, 7.21.6.12, wcsrchr function, 7.28.4.5.4 - K.3.5.3.12 wcsrtombs function, 7.28.6.4.2, K.3.9.3.2 -vsnprintf_s function, K.3.5.3.9, K.3.5.3.11, wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2 - K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcsspn function, 7.28.4.5.5 -vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9 wcsstr function, 7.28.4.5.6 -vsprintf function, 7.21.6.8, 7.21.6.13, wcstod function, 7.21.6.2, 7.28.2.2 - K.3.5.3.13 wcstod function, 7.28.4.1.1 -vsprintf_s function, K.3.5.3.9, K.3.5.3.11, wcstof function, 7.28.4.1.1 - K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcstoimax function, 7.8.2.4 -vsscanf function, 7.21.6.8, 7.21.6.14 wcstok function, 7.28.4.5.7 -vsscanf_s function, K.3.5.3.9, K.3.5.3.11, wcstok_s function, K.3.9.2.3.1 - K.3.5.3.14 wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2, -vswprintf function, 7.28.2.7, K.3.9.1.8, 7.28.4.1.2 - K.3.9.1.9 wcstold function, 7.28.4.1.1 -vswprintf_s function, K.3.9.1.8, K.3.9.1.9 wcstoll function, 7.8.2.4, 7.28.4.1.2 - -[page 677] (Contents) - -wcstombs function, 7.22.8.2, 7.28.6.4 7.29.1 -wcstombs_s function, K.3.6.5.2 wmemchr function, 7.28.4.5.8 -wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2, wmemcmp function, 7.28.4.4.5 - 7.28.4.1.2 wmemcpy function, 7.28.4.2.3 -wcstoull function, 7.8.2.4, 7.28.4.1.2 wmemcpy_s function, K.3.9.2.1.3 -wcstoumax function, 7.8.2.4 wmemmove function, 7.28.4.2.4 -wcsxfrm function, 7.28.4.4.4 wmemmove_s function, K.3.9.2.1.4 -wctob function, 7.28.6.1.2, 7.29.2.1 wmemset function, 7.28.4.6.2 -wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3 wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11, -wctomb_s function, K.3.6.4.1 K.3.9.1.13 -wctrans function, 7.29.3.2.1, 7.29.3.2.2 wprintf_s function, K.3.9.1.13 -wctrans_t type, 7.29.1, 7.29.3.2.2 wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12, -wctype function, 7.29.2.2.1, 7.29.2.2.2 7.28.3.10 -wctype.h header, 7.29, 7.30.13 wscanf_s function, K.3.9.1.12, K.3.9.1.14 -wctype_t type, 7.29.1, 7.29.2.2.2 -weaker, 6.2.8 xor macro, 7.9 -WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6, xor_eq macro, 7.9 - 7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10, xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7, - 7.28.6.1.1, 7.29.1 7.25.7.1 -while statement, 6.8.5.1 xtime_get function, 7.25.7.1 -white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10, - 7.29.2.1.10 -white-space characters, 6.4 -wide character, 3.7.3 - case mapping functions, 7.29.3.1 - extensible, 7.29.3.2 - classification functions, 7.29.2.1 - extensible, 7.29.2.2 - constant, 6.4.4.4 - formatted input/output functions, 7.28.2, - K.3.9.1 - input functions, 7.21.1 - input/output functions, 7.21.1, 7.28.3 - output functions, 7.21.1 - single-byte conversion functions, 7.28.6.1 -wide string, 7.1.1 -wide string comparison functions, 7.28.4.4 -wide string concatenation functions, 7.28.4.3, - K.3.9.2.2 -wide string copying functions, 7.28.4.2, K.3.9.2.1 -wide string literal, see string literal -wide string miscellaneous functions, 7.28.4.6, - K.3.9.2.4 -wide string numeric conversion functions, 7.8.2.4, - 7.28.4.1 -wide string search functions, 7.28.4.5, K.3.9.2.3 -wide-oriented stream, 7.21.2 -width, 6.2.6.2 -WINT_MAX macro, 7.20.3 -WINT_MIN macro, 7.20.3 -wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1, - -[page 678] (Contents) -+ + Runtime-constraints +
+ None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, + then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null + pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall + not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null + character shall occur within the first dstmax multibyte characters of the array pointed to + by *src. +
+ If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If + retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1). + If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, + then mbsrtowcs_s sets dst[0] to the null wide character. +
+ The mbsrtowcs_s function converts a sequence of multibyte characters that begins in + the conversion state described by the object pointed to by ps, from the array indirectly + pointed to by src into a sequence of corresponding wide characters. If dst is not a null + pointer, the converted characters are stored into the array pointed to by dst. Conversion + continues up to and including a terminating null character, which is also stored. + Conversion stops earlier in two cases: when a sequence of bytes is encountered that does + not form a valid multibyte character, or (if dst is not a null pointer) when len wide + + characters have been stored into the array pointed to by dst.439) If dst is not a null + pointer and no null wide character was stored into the array pointed to by dst, then + dst[len] is set to the null wide character. Each conversion takes place as if by a call + to the mbrtowc function. +
+ If dst is not a null pointer, the pointer object pointed to by src is assigned either a null + pointer (if conversion stopped due to reaching a terminating null character) or the address + just past the last multibyte character converted (if any). If conversion stopped due to + reaching a terminating null character and if dst is not a null pointer, the resulting state + described is the initial conversion state. +
+ Regardless of whether dst is or is not a null pointer, if the input conversion encounters a + sequence of bytes that do not form a valid multibyte character, an encoding error occurs: + the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the + conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into + *retval the number of multibyte characters successfully converted, not including the + terminating null character (if any). +
+ All elements following the terminating null wide character (if any) written by + mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take + unspecified values when mbsrtowcs_s returns.440) +
+ If copying takes place between objects that overlap, the objects take on unspecified + values. +
+ The mbsrtowcs_s function returns zero if no runtime-constraint violation and no + encoding error occurred. Otherwise, a nonzero value is returned. + +
439) Thus, the value of len is ignored if dst is a null pointer. + +
440) This allows an implementation to attempt converting the multibyte string before discovering a + terminating null character did not occur where required. + + +
+
+ #include <wchar.h> + errno_t wcsrtombs_s(size_t * restrict retval, + char * restrict dst, rsize_t dstmax, + const wchar_t ** restrict src, rsize_t len, + mbstate_t * restrict ps); ++ + + + + + Runtime-constraints +
+ None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer, + then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null + pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall + not equal zero. If dst is not a null pointer and len is not less than dstmax, then the + conversion shall have been stopped (see below) because a terminating null wide character + was reached or because an encoding error occurred. +
+ If there is a runtime-constraint violation, then wcsrtombs_s does the following. If + retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1). + If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX, + then wcsrtombs_s sets dst[0] to the null character. +
+ The wcsrtombs_s function converts a sequence of wide characters from the array + indirectly pointed to by src into a sequence of corresponding multibyte characters that + begins in the conversion state described by the object pointed to by ps. If dst is not a + null pointer, the converted characters are then stored into the array pointed to by dst. + Conversion continues up to and including a terminating null wide character, which is also + stored. Conversion stops earlier in two cases: +
+ If dst is not a null pointer, the pointer object pointed to by src is assigned either a null + pointer (if conversion stopped due to reaching a terminating null wide character) or the + address just past the last wide character converted (if any). If conversion stopped due to + reaching a terminating null wide character, the resulting state described is the initial + conversion state. + + + +
+ Regardless of whether dst is or is not a null pointer, if the input conversion encounters a + wide character that does not correspond to a valid multibyte character, an encoding error + occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval + and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores + into *retval the number of bytes in the resulting multibyte character sequence, not + including the terminating null character (if any). +
+ All elements following the terminating null character (if any) written by wcsrtombs_s + in the array of dstmax elements pointed to by dst take unspecified values when + wcsrtombs_s returns.442) +
+ If copying takes place between objects that overlap, the objects take on unspecified + values. +
+ The wcsrtombs_s function returns zero if no runtime-constraint violation and no + encoding error occurred. Otherwise, a nonzero value is returned. + + + + + + +
441) If conversion stops because a terminating null wide character has been reached, the bytes stored + include those necessary to reach the initial shift state immediately before the null byte. However, if + the conversion stops before a terminating null wide character has been reached, the result will be null + terminated, but might not end in the initial shift state. + +
442) When len is not less than dstmax, the implementation might fill the array before discovering a + runtime-constraint violation. + + +
+ (normative) + Analyzability ++ +
+ This annex specifies optional behavior that can aid in the analyzability of C programs. +
+ An implementation that defines __STDC_ANALYZABLE__ shall conform to the + specifications in this annex.443) + +
443) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these + specifications. + + +
+ out-of-bounds store + an (attempted) access (3.1) that, at run time, for a given computational state, would + modify (or, for an object declared volatile, fetch) one or more bytes that lie outside + the bounds permitted by this Standard. + +
+ bounded undefined behavior + undefined behavior (3.4.3) that does not perform an out-of-bounds store. +
+ NOTE 1 The behavior might perform a trap. + +
+ NOTE 2 Any values produced or stored might be indeterminate values. + + +
+ critical undefined behavior + undefined behavior that is not bounded undefined behavior. +
+ NOTE The behavior might perform an out-of-bounds store or perform a trap. + + + + + + +
+ If the program performs a trap (3.19.5), the implementation is permitted to invoke a + runtime-constraint handler. Any such semantics are implementation-defined. +
+ All undefined behavior shall be limited to bounded undefined behavior, except for the + following which are permitted to result in critical undefined behavior: +
+ [^ x ^], 3.20 , (comma operator), 5.1.2.4, 6.5.17 + , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, + [_ x _], 3.21 6.7.2.3, 6.7.9 + ! (logical negation operator), 6.5.3.3 - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2 + != (inequality operator), 6.5.9 - (unary minus operator), 6.5.3.3, F.3 + # operator, 6.10.3.2 -- (postfix decrement operator), 6.3.2.1, 6.5.2.4 + # preprocessing directive, 6.10.7 -- (prefix decrement operator), 6.3.2.1, 6.5.3.1 + # punctuator, 6.10 -= (subtraction assignment operator), 6.5.16.2 + ## operator, 6.10.3.3 -> (structure/union pointer operator), 6.5.2.3 + #define preprocessing directive, 6.10.3 . (structure/union member operator), 6.3.2.1, + #elif preprocessing directive, 6.10.1 6.5.2.3 + #else preprocessing directive, 6.10.1 . punctuator, 6.7.9 + #endif preprocessing directive, 6.10.1 ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3 + #error preprocessing directive, 4, 6.10.5 / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1 + #if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, /* */ (comment delimiters), 6.4.9 + 6.10.1, 7.1.4 // (comment delimiter), 6.4.9 + #ifdef preprocessing directive, 6.10.1 /= (division assignment operator), 6.5.16.2 + #ifndef preprocessing directive, 6.10.1 : (colon punctuator), 6.7.2.1 + #include preprocessing directive, 5.1.1.2, :> (alternative spelling of ]), 6.4.6 + 6.10.2 ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3, + #line preprocessing directive, 6.10.4 6.8.5, 6.8.6 + #pragma preprocessing directive, 6.10.6 < (less-than operator), 6.5.8 + #undef preprocessing directive, 6.10.3.5, 7.1.3, <% (alternative spelling of {), 6.4.6 + 7.1.4 <: (alternative spelling of [), 6.4.6 + % (remainder operator), 6.2.6.2, 6.5.5 << (left-shift operator), 6.2.6.2, 6.5.7 + %: (alternative spelling of #), 6.4.6 <<= (left-shift assignment operator), 6.5.16.2 + %:%: (alternative spelling of ##), 6.4.6 <= (less-than-or-equal-to operator), 6.5.8 + %= (remainder assignment operator), 6.5.16.2 <assert.h> header, 7.2 + %> (alternative spelling of }), 6.4.6 <complex.h> header, 5.2.4.2.2, 6.10.8.3, 7.1.2, + & (address operator), 6.3.2.1, 6.5.3.2 7.3, 7.24, 7.30.1, G.6, J.5.17 + & (bitwise AND operator), 6.2.6.2, 6.5.10 <ctype.h> header, 7.4, 7.30.2 + && (logical AND operator), 5.1.2.4, 6.5.13 <errno.h> header, 7.5, 7.30.3, K.3.2 + &= (bitwise AND assignment operator), 6.5.16.2 <fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, + ' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, H + 7.4.1.10, 7.29.2.1.3 <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3, + ( ) (cast operator), 6.5.4 7.28.4.1.1 + ( ) (function-call operator), 6.5.2.2 <inttypes.h> header, 7.8, 7.30.4 + ( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5 <iso646.h> header, 4, 7.9 + ( ){ } (compound-literal operator), 6.5.2.5 <limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10 + * (asterisk punctuator), 6.7.6.1, 6.7.6.2 <locale.h> header, 7.11, 7.30.5 + * (indirection operator), 6.5.2.1, 6.5.3.2 <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, + * (multiplication operator), 6.2.6.2, 6.5.5, F.3, F.10, J.5.17 + G.5.1 <setjmp.h> header, 7.13 + *= (multiplication assignment operator), 6.5.16.2 <signal.h> header, 7.14, 7.30.6 + + (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2, <stdalign.h> header, 4, 7.15 + 6.5.6, F.3, G.5.2 <stdarg.h> header, 4, 6.7.6.3, 7.16 + + (unary plus operator), 6.5.3.3 <stdatomic.h> header, 6.10.8.3, 7.1.2, 7.17 + ++ (postfix increment operator), 6.3.2.1, 6.5.2.4 <stdbool.h> header, 4, 7.18, 7.30.7, H + ++ (prefix increment operator), 6.3.2.1, 6.5.3.1 <stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, + += (addition assignment operator), 6.5.16.2 + + 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 \x hexadecimal digits (hexadecimal-character + <stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8, escape sequence), 6.4.4.4 + 7.20, 7.30.8, K.3.3, K.3.4 ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11 + <stdio.h> header, 5.2.4.2.2, 7.21, 7.30.9, F, ^= (bitwise exclusive OR assignment operator), + K.3.5 6.5.16.2 + <stdlib.h> header, 5.2.4.2.2, 7.22, 7.30.10, F, __alignas_is_defined macro, 7.15 + K.3.1.4, K.3.6 __bool_true_false_are_defined + <string.h> header, 7.23, 7.30.11, K.3.7 macro, 7.18 + <tgmath.h> header, 7.24, G.7 __cplusplus macro, 6.10.8 + <threads.h> header, 6.10.8.3, 7.1.2, 7.25 __DATE__ macro, 6.10.8.1 + <time.h> header, 7.26, K.3.8 __FILE__ macro, 6.10.8.1, 7.2.1.1 + <uchar.h> header, 6.4.4.4, 6.4.5, 7.27 __func__ identifier, 6.4.2.2, 7.2.1.1 + <wchar.h> header, 5.2.4.2.2, 7.21.1, 7.28, __LINE__ macro, 6.10.8.1, 7.2.1.1 + 7.30.12, F, K.3.9 __STDC_, 6.11.9 + <wctype.h> header, 7.29, 7.30.13 __STDC__ macro, 6.10.8.1 + = (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9 __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1 + = (simple assignment operator), 6.5.16.1 __STDC_HOSTED__ macro, 6.10.8.1 + == (equality operator), 6.5.9 __STDC_IEC_559__ macro, 6.10.8.3, F.1 + > (greater-than operator), 6.5.8 __STDC_IEC_559_COMPLEX__ macro, + >= (greater-than-or-equal-to operator), 6.5.8 6.10.8.3, G.1 + >> (right-shift operator), 6.2.6.2, 6.5.7 __STDC_ISO_10646__ macro, 6.10.8.2 + >>= (right-shift assignment operator), 6.5.16.2 __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2 + ? : (conditional operator), 5.1.2.4, 6.5.15 __STDC_MB_MIGHT_NEQ_WC__ macro, + ?? (trigraph sequences), 5.2.1.1 6.10.8.2, 7.19 + [ ] (array subscript operator), 6.5.2.1, 6.5.3.2 __STDC_NO_COMPLEX__ macro, 6.10.8.3, + [ ] (brackets punctuator), 6.7.6.2, 6.7.9 7.3.1 + \ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4 __STDC_NO_THREADS__ macro, 6.10.8.3, + \ (escape character), 6.4.4.4 7.17.1, 7.25.1 + \" (double-quote escape sequence), 6.4.4.4, __STDC_NO_VLA__ macro, 6.10.8.3 + 6.4.5, 6.10.9 __STDC_UTF_16__ macro, 6.10.8.2 + \\ (backslash escape sequence), 6.4.4.4, 6.10.9 __STDC_UTF_32__ macro, 6.10.8.2 + \' (single-quote escape sequence), 6.4.4.4, 6.4.5 __STDC_VERSION__ macro, 6.10.8.1 + \0 (null character), 5.2.1, 6.4.4.4, 6.4.5 __STDC_WANT_LIB_EXT1__ macro, K.3.1.1 + padding of binary stream, 7.21.2 __TIME__ macro, 6.10.8.1 + \? (question-mark escape sequence), 6.4.4.4 __VA_ARGS__ identifier, 6.10.3, 6.10.3.1 + \a (alert escape sequence), 5.2.2, 6.4.4.4 _Alignas, 6.7.5 + \b (backspace escape sequence), 5.2.2, 6.4.4.4 _Atomic type qualifier, 6.7.3 + \f (form-feed escape sequence), 5.2.2, 6.4.4.4, _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1, + 7.4.1.10 F.4 + \n (new-line escape sequence), 5.2.2, 6.4.4.4, _Bool type conversions, 6.3.1.2 + 7.4.1.10 _Complex types, 6.2.5, 6.7.2, 7.3.1, G + \octal digits (octal-character escape sequence), _Complex_I macro, 7.3.1 + 6.4.4.4 _Exit function, 7.22.4.5, 7.22.4.7 + \r (carriage-return escape sequence), 5.2.2, _Imaginary keyword, G.2 + 6.4.4.4, 7.4.1.10 _Imaginary types, 7.3.1, G + \t (horizontal-tab escape sequence), 5.2.2, _Imaginary_I macro, 7.3.1, G.6 + 6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3 _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 + \U (universal character names), 6.4.3 _IOLBF macro, 7.21.1, 7.21.5.6 + \u (universal character names), 6.4.3 _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6 + \v (vertical-tab escape sequence), 5.2.2, 6.4.4.4, _Noreturn, 6.7.4 + 7.4.1.10 _Pragma operator, 5.1.1.2, 6.10.9 + + _Static_assert, 6.7.10, 7.2 allocated storage, order and contiguity, 7.22.3 + _Thread_local storage-class specifier, 6.2.4, and macro, 7.9 + 6.7.1 AND operators + { } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9, bitwise (&), 6.2.6.2, 6.5.10 + 6.8.2 bitwise assignment (&=), 6.5.16.2 + { } (compound-literal operator), 6.5.2.5 logical (&&), 5.1.2.4, 6.5.13 + | (bitwise inclusive OR operator), 6.2.6.2, 6.5.12 and_eq macro, 7.9 + |= (bitwise inclusive OR assignment operator), anonymous structure, 6.7.2.1 + 6.5.16.2 anonymous union, 6.7.2.1 + || (logical OR operator), 5.1.2.4, 6.5.14 ANSI/IEEE 754, F.1 + ~ (bitwise complement operator), 6.2.6.2, 6.5.3.3 ANSI/IEEE 854, F.1 + argc (main function parameter), 5.1.2.2.1 + abort function, 7.2.1.1, 7.14.1.1, 7.21.3, argument, 3.3 + 7.22.4.1, 7.25.3.6, K.3.6.1.2 array, 6.9.1 + abort_handler_s function, K.3.6.1.2 default promotions, 6.5.2.2 + abs function, 7.22.6.1 function, 6.5.2.2, 6.9.1 + absolute-value functions macro, substitution, 6.10.3.1 + complex, 7.3.8, G.6.4 argument, complex, 7.3.9.1 + integer, 7.8.2.1, 7.22.6.1 argv (main function parameter), 5.1.2.2.1 + real, 7.12.7, F.10.4 arithmetic constant expression, 6.6 + abstract declarator, 6.7.7 arithmetic conversions, usual, see usual arithmetic + abstract machine, 5.1.2.3 conversions + access, 3.1, 6.7.3, L.2.1 arithmetic operators + accuracy, see floating-point accuracy additive, 6.2.6.2, 6.5.6, G.5.2 + acos functions, 7.12.4.1, F.10.1.1 bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12 + acos type-generic macro, 7.24 increment and decrement, 6.5.2.4, 6.5.3.1 + acosh functions, 7.12.5.1, F.10.2.1 multiplicative, 6.2.6.2, 6.5.5, G.5.1 + acosh type-generic macro, 7.24 shift, 6.2.6.2, 6.5.7 + acquire fence, 7.17.4 unary, 6.5.3.3 + acquire operation, 5.1.2.4 arithmetic types, 6.2.5 + active position, 5.2.2 arithmetic, pointer, 6.5.6 + actual argument, 3.3 array + actual parameter (deprecated), 3.3 argument, 6.9.1 + addition assignment operator (+=), 6.5.16.2 declarator, 6.7.6.2 + addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2, initialization, 6.7.9 + 6.5.6, F.3, G.5.2 multidimensional, 6.5.2.1 + additive expressions, 6.5.6, G.5.2 parameter, 6.9.1 + address constant, 6.6 storage order, 6.5.2.1 + address operator (&), 6.3.2.1, 6.5.3.2 subscript operator ([ ]), 6.5.2.1, 6.5.3.2 + address-free, 7.17.5 subscripting, 6.5.2.1 + aggregate initialization, 6.7.9 type, 6.2.5 + aggregate types, 6.2.5 type conversion, 6.3.2.1 + alert escape sequence (\a), 5.2.2, 6.4.4.4 variable length, 6.7.6, 6.7.6.2, 6.10.8.3 + aliasing, 6.5 arrow operator (->), 6.5.2.3 + alignas macro, 7.15 as-if rule, 5.1.2.3 + aligned_alloc function, 7.22.3, 7.22.3.1 ASCII code set, 5.2.1.1 + alignment, 3.2, 6.2.8, 7.22.3.1 asctime function, 7.26.3.1 + pointer, 6.2.5, 6.3.2.3 asctime_s function, K.3.8.2, K.3.8.2.1 + structure/union member, 6.7.2.1 asin functions, 7.12.4.2, F.10.1.2 + alignment specifier, 6.7.5 asin type-generic macro, 7.24, G.7 + alignof operator, 6.5.3, 6.5.3.4 asinh functions, 7.12.5.2, F.10.2.2 + + asinh type-generic macro, 7.24, G.7 atomic_is_lock_free generic function, + asm keyword, J.5.10 7.17.5.1 + assert macro, 7.2.1.1 ATOMIC_LLONG_LOCK_FREE macro, 7.17.1 + assert.h header, 7.2 atomic_load generic functions, 7.17.7.2 + assignment ATOMIC_LONG_LOCK_FREE macro, 7.17.1 + compound, 6.5.16.2 ATOMIC_SHORT_LOCK_FREE macro, 7.17.1 + conversion, 6.5.16.1 atomic_signal_fence function, 7.17.4.2 + expression, 6.5.16 atomic_store generic functions, 7.17.7.1 + operators, 6.3.2.1, 6.5.16 atomic_thread_fence function, 7.17.4.1 + simple, 6.5.16.1 ATOMIC_VAR_INIT macro, 7.17.2.1 + associativity of operators, 6.5 ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1 + asterisk punctuator (*), 6.7.6.1, 6.7.6.2 atomics header, 7.17 + at_quick_exit function, 7.22.4.2, 7.22.4.3, auto storage-class specifier, 6.7.1, 6.9 + 7.22.4.4, 7.22.4.5, 7.22.4.7 automatic storage duration, 5.2.3, 6.2.4 + atan functions, 7.12.4.3, F.10.1.3 + atan type-generic macro, 7.24, G.7 backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4 + atan2 functions, 7.12.4.4, F.10.1.4 backslash escape sequence (\\), 6.4.4.4, 6.10.9 + atan2 type-generic macro, 7.24 backspace escape sequence (\b), 5.2.2, 6.4.4.4 + atanh functions, 7.12.5.3, F.10.2.3 basic character set, 3.6, 3.7.2, 5.2.1 + atanh type-generic macro, 7.24, G.7 basic types, 6.2.5 + atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4, behavior, 3.4 + 7.22.4.5, 7.22.4.7, J.5.13 binary streams, 7.21.2, 7.21.7.10, 7.21.9.2, + atof function, 7.22.1, 7.22.1.1 7.21.9.4 + atoi function, 7.22.1, 7.22.1.2 bit, 3.5 + atol function, 7.22.1, 7.22.1.2 high order, 3.6 + atoll function, 7.22.1, 7.22.1.2 low order, 3.6 + atomic lock-free macros, 7.17.1, 7.17.5 bit-field, 6.7.2.1 + atomic operations, 5.1.2.4 bitand macro, 7.9 + atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, bitor macro, 7.9 + 6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, bitwise operators, 6.5 + 7.17.6 AND, 6.2.6.2, 6.5.10 + atomic_address type, 7.17.1, 7.17.6 AND assignment (&=), 6.5.16.2 + ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1 complement (~), 6.2.6.2, 6.5.3.3 + atomic_bool type, 7.17.1, 7.17.6 exclusive OR, 6.2.6.2, 6.5.11 + ATOMIC_CHAR16_T_LOCK_FREE macro, exclusive OR assignment (^=), 6.5.16.2 + 7.17.1 inclusive OR, 6.2.6.2, 6.5.12 + ATOMIC_CHAR32_T_LOCK_FREE macro, inclusive OR assignment (|=), 6.5.16.2 + 7.17.1 shift, 6.2.6.2, 6.5.7 + ATOMIC_CHAR_LOCK_FREE macro, 7.17.1 blank character, 7.4.1.3 + atomic_compare_exchange generic block, 6.8, 6.8.2, 6.8.4, 6.8.5 + functions, 7.17.7.4 block scope, 6.2.1 + atomic_exchange generic functions, 7.17.7.3 block structure, 6.2.1 + atomic_fetch and modify generic functions, bold type convention, 6.1 + 7.17.7.5 bool macro, 7.18 + atomic_flag type, 7.17.1, 7.17.8 boolean type, 6.3.1.2 + atomic_flag_clear functions, 7.17.8.2 boolean type conversion, 6.3.1.1, 6.3.1.2 + ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8 bounded undefined behavior, L.2.2 + atomic_flag_test_and_set functions, braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9, + 7.17.8.1 6.8.2 + atomic_init generic function, 7.17.2.2 brackets operator ([ ]), 6.5.2.1, 6.5.3.2 + ATOMIC_INT_LOCK_FREE macro, 7.17.1 brackets punctuator ([ ]), 6.7.6.2, 6.7.9 + + branch cuts, 7.3.3 type-generic macro for, 7.24 + break statement, 6.8.6.3 ccosh functions, 7.3.6.4, G.6.2.4 + broken-down time, 7.26.1, 7.26.2.3, 7.26.3, type-generic macro for, 7.24 + 7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5, ceil functions, 7.12.9.1, F.10.6.1 + K.3.8.2.1, K.3.8.2.3, K.3.8.2.4 ceil type-generic macro, 7.24 + bsearch function, 7.22.5, 7.22.5.1 cerf function, 7.30.1 + bsearch_s function, K.3.6.3, K.3.6.3.1 cerfc function, 7.30.1 + btowc function, 7.28.6.1.1 cexp functions, 7.3.7.1, G.6.3.1 + BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5 type-generic macro for, 7.24 + byte, 3.6, 6.5.3.4 cexp2 function, 7.30.1 + byte input/output functions, 7.21.1 cexpm1 function, 7.30.1 + byte-oriented stream, 7.21.2 char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2, + K.3.9.1.2 + C program, 5.1.1.1 char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, + c16rtomb function, 7.27.1.2 6.3.1.8 + c32rtomb function, 7.27.1.4 char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27 + cabs functions, 7.3.8.1, G.6 char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27 + type-generic macro for, 7.24 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1 + cacos functions, 7.3.5.1, G.6.1.1 CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1 + type-generic macro for, 7.24 CHAR_MIN macro, 5.2.4.2.1 + cacosh functions, 7.3.6.1, G.6.2.1 character, 3.7, 3.7.1 + type-generic macro for, 7.24 character array initialization, 6.7.9 + calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, character case mapping functions, 7.4.2 + 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, wide character, 7.29.3.1 + K.3.8.2.3, K.3.8.2.4 extensible, 7.29.3.2 + call by value, 6.5.2.2 character classification functions, 7.4.1 + call_once function, 7.25.1, 7.25.2.1 wide character, 7.29.2.1 + calloc function, 7.22.3, 7.22.3.2 extensible, 7.29.2.2 + carg functions, 7.3.9.1, G.6 character constant, 5.1.1.2, 5.2.1, 6.4.4.4 + carg type-generic macro, 7.24, G.7 character display semantics, 5.2.2 + carriage-return escape sequence (\r), 5.2.2, character handling header, 7.4, 7.11.1.1 + 6.4.4.4, 7.4.1.10 character input/output functions, 7.21.7, K.3.5.4 + carries a dependency, 5.1.2.4 wide character, 7.28.3 + case label, 6.8.1, 6.8.4.2 character sets, 5.2.1 + case mapping functions character string literal, see string literal + character, 7.4.2 character type conversion, 6.3.1.1 + wide character, 7.29.3.1 character types, 6.2.5, 6.7.9 + extensible, 7.29.3.2 cimag functions, 7.3.9.2, 7.3.9.5, G.6 + casin functions, 7.3.5.2, G.6 cimag type-generic macro, 7.24, G.7 + type-generic macro for, 7.24 cis function, G.6 + casinh functions, 7.3.6.2, G.6.2.2 classification functions + type-generic macro for, 7.24 character, 7.4.1 + cast expression, 6.5.4 floating-point, 7.12.3 + cast operator (( )), 6.5.4 wide character, 7.29.2.1 + catan functions, 7.3.5.3, G.6 extensible, 7.29.2.2 + type-generic macro for, 7.24 clearerr function, 7.21.10.1 + catanh functions, 7.3.6.3, G.6.2.3 clgamma function, 7.30.1 + type-generic macro for, 7.24 clock function, 7.26.2.1 + cbrt functions, 7.12.7.1, F.10.4.1 clock_t type, 7.26.1, 7.26.2.1 + cbrt type-generic macro, 7.24 CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1 + ccos functions, 7.3.5.4, G.6 clog functions, 7.3.7.2, G.6.3.2 + + type-generic macro for, 7.24 string, 7.23.3, K.3.7.2 + clog10 function, 7.30.1 wide string, 7.28.4.3, K.3.9.2.2 + clog1p function, 7.30.1 concatenation, preprocessing, see preprocessing + clog2 function, 7.30.1 concatenation + CMPLX macros, 7.3.9.3 conceptual models, 5.1 + cnd_broadcast function, 7.25.3.1, 7.25.3.5, conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3, + 7.25.3.6 7.1.2, F.1, G.1, K.2, L.1 + cnd_destroy function, 7.25.3.2 conditional inclusion, 6.10.1 + cnd_init function, 7.25.3.3 conditional operator (? :), 5.1.2.4, 6.5.15 + cnd_signal function, 7.25.3.4, 7.25.3.5, conflict, 5.1.2.4 + 7.25.3.6 conformance, 4 + cnd_t type, 7.25.1 conj functions, 7.3.9.4, G.6 + cnd_timedwait function, 7.25.3.5 conj type-generic macro, 7.24 + cnd_wait function, 7.25.3.3, 7.25.3.6 const type qualifier, 6.7.3 + collating sequences, 5.2.1 const-qualified type, 6.2.5, 6.3.2.1, 6.7.3 + colon punctuator (:), 6.7.2.1 constant expression, 6.6, F.8.4 + comma operator (,), 5.1.2.4, 6.5.17 constants, 6.4.4 + comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, as primary expression, 6.5.1 + 6.7.2.3, 6.7.9 character, 6.4.4.4 + command processor, 7.22.4.8 enumeration, 6.2.1, 6.4.4.3 + comment delimiters (/* */ and //), 6.4.9 floating, 6.4.4.2 + comments, 5.1.1.2, 6.4, 6.4.9 hexadecimal, 6.4.4.1 + common extensions, J.5 integer, 6.4.4.1 + common initial sequence, 6.5.2.3 octal, 6.4.4.1 + common real type, 6.3.1.8 constraint, 3.8, 4 + common warnings, I constraint_handler_t type, K.3.6 + comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2, consume operation, 5.1.2.4 + K.3.6.3, K.3.6.3.1, K.3.6.3.2 content of structure/union/enumeration, 6.7.2.3 + string, 7.23.4 contiguity of allocated storage, 7.22.3 + wide string, 7.28.4.4 continue statement, 6.8.6.2 + comparison macros, 7.12.14 contracted expression, 6.5, 7.12.2, F.7 + comparison, pointer, 6.5.8 control character, 5.2.1, 7.4 + compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6 control wide character, 7.29.2 + compl macro, 7.9 conversion, 6.3 + complement operator (~), 6.2.6.2, 6.5.3.3 arithmetic operands, 6.3.1 + complete type, 6.2.5 array argument, 6.9.1 + complex macro, 7.3.1 array parameter, 6.9.1 + complex numbers, 6.2.5, G arrays, 6.3.2.1 + complex type conversion, 6.3.1.6, 6.3.1.7 boolean, 6.3.1.2 + complex type domain, 6.2.5 boolean, characters, and integers, 6.3.1.1 + complex types, 6.2.5, 6.7.2, 6.10.8.3, G by assignment, 6.5.16.1 + complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2, by return statement, 6.8.6.4 + 7.3, 7.24, 7.30.1, G.6, J.5.17 complex types, 6.3.1.6 + compliance, see conformance explicit, 6.3 + components of time, 7.26.1, K.3.8.1 function, 6.3.2.1 + composite type, 6.2.7 function argument, 6.5.2.2, 6.9.1 + compound assignment, 6.5.16.2 function designators, 6.3.2.1 + compound literals, 6.5.2.5 function parameter, 6.9.1 + compound statement, 6.8.2 imaginary, G.4.1 + compound-literal operator (( ){ }), 6.5.2.5 imaginary and complex, G.4.3 + concatenation functions implicit, 6.3 + + lvalues, 6.3.2.1 csinh functions, 7.3.6.5, G.6.2.5 + pointer, 6.3.2.1, 6.3.2.3 type-generic macro for, 7.24 + real and complex, 6.3.1.7 csqrt functions, 7.3.8.3, G.6.4.2 + real and imaginary, G.4.2 type-generic macro for, 7.24 + real floating and integer, 6.3.1.4, F.3, F.4 ctan functions, 7.3.5.6, G.6 + real floating types, 6.3.1.5, F.3 type-generic macro for, 7.24 + signed and unsigned integers, 6.3.1.3 ctanh functions, 7.3.6.6, G.6.2.6 + usual arithmetic, see usual arithmetic type-generic macro for, 7.24 + conversions ctgamma function, 7.30.1 + void type, 6.3.2.2 ctime function, 7.26.3.2 + conversion functions ctime_s function, K.3.8.2, K.3.8.2.2 + multibyte/wide character, 7.22.7, K.3.6.4 ctype.h header, 7.4, 7.30.2 + extended, 7.28.6, K.3.9.3 current object, 6.7.9 + restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4 + multibyte/wide string, 7.22.8, K.3.6.5 + restartable, 7.28.6.4, K.3.9.3.2 data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6, + numeric, 7.8.2.3, 7.22.1 7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3, + wide string, 7.8.2.4, 7.28.4.1 7.28.6.4 + single byte/wide character, 7.28.6.1 data stream, see streams + time, 7.26.3, K.3.8.2 date and time header, 7.26, K.3.8 + wide character, 7.28.5 Daylight Saving Time, 7.26.1 + conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, DBL_DECIMAL_DIG macro, 5.2.4.2.2 + 7.28.2.2 DBL_DIG macro, 5.2.4.2.2 + conversion state, 7.22.7, 7.27.1, 7.27.1.1, DBL_EPSILON macro, 5.2.4.2.2 + 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6, DBL_HAS_SUBNORM macro, 5.2.4.2.2 + 7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3, DBL_MANT_DIG macro, 5.2.4.2.2 + 7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4, DBL_MAX macro, 5.2.4.2.2 + K.3.9.3.1, K.3.9.3.1.1, K.3.9.3.2, K.3.9.3.2.1, DBL_MAX_10_EXP macro, 5.2.4.2.2 + K.3.9.3.2.2 DBL_MAX_EXP macro, 5.2.4.2.2 + conversion state functions, 7.28.6.2 DBL_MIN macro, 5.2.4.2.2 + copying functions DBL_MIN_10_EXP macro, 5.2.4.2.2 + string, 7.23.2, K.3.7.1 DBL_MIN_EXP macro, 5.2.4.2.2 + wide string, 7.28.4.2, K.3.9.2.1 DBL_TRUE_MIN macro, 5.2.4.2.2 + copysign functions, 7.3.9.5, 7.12.11.1, F.3, decimal constant, 6.4.4.1 + F.10.8.1 decimal digit, 5.2.1 + copysign type-generic macro, 7.24 decimal-point character, 7.1.1, 7.11.2.1 + correctly rounded result, 3.9 DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1, + corresponding real type, 6.2.5 7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5 + cos functions, 7.12.4.5, F.10.1.5 declaration specifiers, 6.7 + cos type-generic macro, 7.24, G.7 declarations, 6.7 + cosh functions, 7.12.5.4, F.10.2.4 function, 6.7.6.3 + cosh type-generic macro, 7.24, G.7 pointer, 6.7.6.1 + cpow functions, 7.3.8.2, G.6.4.1 structure/union, 6.7.2.1 + type-generic macro for, 7.24 typedef, 6.7.8 + cproj functions, 7.3.9.5, G.6 declarator, 6.7.6 + cproj type-generic macro, 7.24 abstract, 6.7.7 + creal functions, 7.3.9.6, G.6 declarator type derivation, 6.2.5, 6.7.6 + creal type-generic macro, 7.24, G.7 decrement operators, see arithmetic operators, + critical undefined behavior, L.2.3 increment and decrement + csin functions, 7.3.5.5, G.6 default argument promotions, 6.5.2.2 + type-generic macro for, 7.24 default initialization, 6.7.9 + + default label, 6.8.1, 6.8.4.2 elif preprocessing directive, 6.10.1 + define preprocessing directive, 6.10.3 ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3 + defined operator, 6.10.1, 6.10.8 else preprocessing directive, 6.10.1 + definition, 6.7 else statement, 6.8.4.1 + function, 6.9.1 empty statement, 6.8.3 + dependency-ordered before, 5.1.2.4 encoding error, 7.21.3, 7.27.1.1, 7.27.1.2, + derived declarator types, 6.2.5 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, + derived types, 6.2.5 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, + designated initializer, 6.7.9 K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1, + destringizing, 6.10.9 K.3.9.3.2.2 + device input/output, 5.1.2.3 end-of-file, 7.28.1 + diagnostic message, 3.10, 5.1.1.3 end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1, + diagnostics, 5.1.1.3 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2, + diagnostics header, 7.2 7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1, + difftime function, 7.26.2.2 7.28.3.10 + digit, 5.2.1, 7.4 end-of-file macro, see EOF macro + digraphs, 6.4.6 end-of-line indicator, 5.2.1 + direct input/output functions, 7.21.8 endif preprocessing directive, 6.10.1 + display device, 5.2.2 enum type, 6.2.5, 6.7.2, 6.7.2.2 + div function, 7.22.6.2 enumerated type, 6.2.5 + div_t type, 7.22 enumeration, 6.2.5, 6.7.2.2 + division assignment operator (/=), 6.5.16.2 enumeration constant, 6.2.1, 6.4.4.3 + division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1 enumeration content, 6.7.2.3 + do statement, 6.8.5.2 enumeration members, 6.7.2.2 + documentation of implementation, 4 enumeration specifiers, 6.7.2.2 + domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4, enumeration tag, 6.2.3, 6.7.2.3 + 7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7, enumerator, 6.7.2.2 + 7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11, environment, 5 + 7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5, environment functions, 7.22.4, K.3.6.2 + 7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3 environment list, 7.22.4.6, K.3.6.2.1 + dot operator (.), 6.5.2.3 environmental considerations, 5.2 + double _Complex type, 6.2.5 environmental limits, 5.2.4, 7.13.1.1, 7.21.2, + double _Complex type conversion, 6.3.1.6, 7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2, + 6.3.1.7, 6.3.1.8 7.22.4.3, 7.28.2.1, K.3.5.1.2 + double _Imaginary type, G.2 EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2, + double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2, 7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11, + 7.28.2.2, F.2 7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4, + double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9, + 6.3.1.8 7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4, + double-precision arithmetic, 5.1.2.3 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12, + double-quote escape sequence (\"), 6.4.4.4, 7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7, + 6.4.5, 6.10.9 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, + double_t type, 7.12, J.5.6 K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, + K.3.9.1.14 + EDOM macro, 7.5, 7.12.1, see also domain error equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9 + effective type, 6.5 equal-to operator, see equality operator + EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2, equality expressions, 6.5.9 + 7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3, equality operator (==), 6.5.9 + 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1, + see also encoding error 7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see + element type, 6.2.5 also range error, pole error + + erf functions, 7.12.8.1, F.10.5.1 exp2 functions, 7.12.6.2, F.10.3.2 + erf type-generic macro, 7.24 exp2 type-generic macro, 7.24 + erfc functions, 7.12.8.2, F.10.5.2 explicit conversion, 6.3 + erfc type-generic macro, 7.24 expm1 functions, 7.12.6.3, F.10.3.3 + errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4, expm1 type-generic macro, 7.24 + 7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4, exponent part, 6.4.4.2 + 7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1, exponential functions + 7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1, complex, 7.3.7, G.6.3 + 7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2, real, 7.12.6, F.10.3 + 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17, expression, 6.5 + K.3.1.3, K.3.7.4.2 assignment, 6.5.16 + errno.h header, 7.5, 7.30.3, K.3.2 cast, 6.5.4 + errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1, constant, 6.6 + K.3.7, K.3.8, K.3.9 evaluation, 5.1.2.3 + error full, 6.8 + domain, see domain error order of evaluation, see order of evaluation + encoding, see encoding error parenthesized, 6.5.1 + pole, see pole error primary, 6.5.1 + range, see range error unary, 6.5.3 + error conditions, 7.12.1 expression statement, 6.8.3 + error functions, 7.12.8, F.10.5 extended alignment, 6.2.8 + error indicator, 7.21.1, 7.21.5.3, 7.21.7.1, extended character set, 3.7.2, 5.2.1, 5.2.1.2 + 7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7, extended characters, 5.2.1 + 7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3, extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1, + 7.28.3.1, 7.28.3.3 7.20 + error preprocessing directive, 4, 6.10.5 extended multibyte/wide character conversion + error-handling functions, 7.21.10, 7.23.6.2, utilities, 7.28.6, K.3.9.3 + K.3.7.4.2, K.3.7.4.3 extensible wide character case mapping functions, + escape character (\), 6.4.4.4 7.29.3.2 + escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4 extensible wide character classification functions, + evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12 7.29.2.2 + evaluation method, 5.2.4.2.2, 6.5, F.8.5 extern storage-class specifier, 6.2.2, 6.7.1 + evaluation of expression, 5.1.2.3 external definition, 6.9 + evaluation order, see order of evaluation external identifiers, underscore, 7.1.3 + exceptional condition, 6.5 external linkage, 6.2.2 + excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external name, 6.4.2.1 + excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 external object definitions, 6.9.2 + exclusive OR operators + bitwise (^), 6.2.6.2, 6.5.11 fabs functions, 7.12.7.2, F.3, F.10.4.2 + bitwise assignment (^=), 6.5.16.2 fabs type-generic macro, 7.24, G.7 + executable program, 5.1.1.1 false macro, 7.18 + execution character set, 5.2.1 fclose function, 7.21.5.1 + execution environment, 5, 5.1.2, see also fdim functions, 7.12.12.1, F.10.9.1 + environmental limits fdim type-generic macro, 7.24 + execution sequence, 5.1.2.3, 6.8 FE_ALL_EXCEPT macro, 7.6 + exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4, FE_DFL_ENV macro, 7.6 + 7.22.4.5, 7.22.4.7 FE_DIVBYZERO macro, 7.6, 7.12, F.3 + EXIT_FAILURE macro, 7.22, 7.22.4.4 FE_DOWNWARD macro, 7.6, F.3 + EXIT_SUCCESS macro, 7.22, 7.22.4.4 FE_INEXACT macro, 7.6, F.3 + exp functions, 7.12.6.1, F.10.3.1 FE_INVALID macro, 7.6, 7.12, F.3 + exp type-generic macro, 7.24 FE_OVERFLOW macro, 7.6, 7.12, F.3 + + FE_TONEAREST macro, 7.6, F.3 float _Complex type conversion, 6.3.1.6, + FE_TOWARDZERO macro, 7.6, F.3 6.3.1.7, 6.3.1.8 + FE_UNDERFLOW macro, 7.6, F.3 float _Imaginary type, G.2 + FE_UPWARD macro, 7.6, F.3 float type, 6.2.5, 6.4.4.2, 6.7.2, F.2 + feclearexcept function, 7.6.2, 7.6.2.1, F.3 float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, + fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3 6.3.1.8 + fegetexceptflag function, 7.6.2, 7.6.2.2, F.3 float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3, + fegetround function, 7.6, 7.6.3.1, F.3 7.28.4.1.1 + feholdexcept function, 7.6.4.2, 7.6.4.3, float_t type, 7.12, J.5.6 + 7.6.4.4, F.3 floating constant, 6.4.4.2 + fence, 5.1.2.4 floating suffix, f or F, 6.4.4.2 + fences, 7.17.4 floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, + fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H F.3, F.4 + FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9, floating types, 6.2.5, 6.11.1 + F.10 floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5, + fenv_t type, 7.6 7.22.1.3, F.5, see also contracted expression + feof function, 7.21.10.2 floating-point arithmetic functions, 7.12, F.10 + feraiseexcept function, 7.6.2, 7.6.2.3, F.3 floating-point classification functions, 7.12.3 + ferror function, 7.21.10.3 floating-point control mode, 7.6, F.8.6 + fesetenv function, 7.6.4.3, F.3 floating-point environment, 7.6, F.8, F.8.6 + fesetexceptflag function, 7.6.2, 7.6.2.4, F.3 floating-point exception, 7.6, 7.6.2, F.10 + fesetround function, 7.6, 7.6.3.2, F.3 floating-point number, 5.2.4.2.2, 6.2.5 + fetestexcept function, 7.6.2, 7.6.2.5, F.3 floating-point rounding mode, 5.2.4.2.2 + feupdateenv function, 7.6.4.2, 7.6.4.4, F.3 floating-point status flag, 7.6, F.8.6 + fexcept_t type, 7.6, F.3 floor functions, 7.12.9.2, F.10.6.2 + fflush function, 7.21.5.2, 7.21.5.3 floor type-generic macro, 7.24 + fgetc function, 7.21.1, 7.21.3, 7.21.7.1, FLT_DECIMAL_DIG macro, 5.2.4.2.2 + 7.21.7.5, 7.21.8.1 FLT_DIG macro, 5.2.4.2.2 + fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3 FLT_EPSILON macro, 5.2.4.2.2 + fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1 FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12, + fgetwc function, 7.21.1, 7.21.3, 7.28.3.1, F.10.11 + 7.28.3.6 FLT_HAS_SUBNORM macro, 5.2.4.2.2 + fgetws function, 7.21.1, 7.28.3.2 FLT_MANT_DIG macro, 5.2.4.2.2 + field width, 7.21.6.1, 7.28.2.1 FLT_MAX macro, 5.2.4.2.2 + file, 7.21.3 FLT_MAX_10_EXP macro, 5.2.4.2.2 + access functions, 7.21.5, K.3.5.2 FLT_MAX_EXP macro, 5.2.4.2.2 + name, 7.21.3 FLT_MIN macro, 5.2.4.2.2 + operations, 7.21.4, K.3.5.1 FLT_MIN_10_EXP macro, 5.2.4.2.2 + position indicator, 7.21.1, 7.21.2, 7.21.3, FLT_MIN_EXP macro, 5.2.4.2.2 + 7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10, FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3, + 7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2, 7.28.2.1, 7.28.4.1.1 + 7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1, FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3 + 7.28.3.3, 7.28.3.10 FLT_TRUE_MIN macro, 5.2.4.2.2 + positioning functions, 7.21.9 fma functions, 7.12, 7.12.13.1, F.10.10.1 + file scope, 6.2.1, 6.9 fma type-generic macro, 7.24 + FILE type, 7.21.1, 7.21.3 fmax functions, 7.12.12.2, F.10.9.2 + FILENAME_MAX macro, 7.21.1 fmax type-generic macro, 7.24 + flags, 7.21.6.1, 7.28.2.1, see also floating-point fmin functions, 7.12.12.3, F.10.9.3 + status flag fmin type-generic macro, 7.24 + flexible array member, 6.7.2.1 fmod functions, 7.12.10.1, F.10.7.1 + float _Complex type, 6.2.5 fmod type-generic macro, 7.24 + + fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1 K.3.5.3.7, K.3.5.3.9 + FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3, fseek function, 7.21.1, 7.21.5.3, 7.21.7.10, + K.3.5.1.1 7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10 + fopen_s function, K.3.5.1.1, K.3.5.2.1, fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10, + K.3.5.2.2 7.21.9.1, 7.21.9.3, 7.28.3.10 + for statement, 6.8.5, 6.8.5.3 ftell function, 7.21.9.2, 7.21.9.4 + form-feed character, 5.2.1, 6.4 full declarator, 6.7.6 + form-feed escape sequence (\f), 5.2.2, 6.4.4.4, full expression, 6.8 + 7.4.1.10 fully buffered stream, 7.21.3 + formal argument (deprecated), 3.16 function + formal parameter, 3.16 argument, 6.5.2.2, 6.9.1 + formatted input/output functions, 7.11.1.1, 7.21.6, body, 6.9.1 + K.3.5.3 call, 6.5.2.2 + wide character, 7.28.2, K.3.9.1 library, 7.1.4 + fortran keyword, J.5.9 declarator, 6.7.6.3, 6.11.6 + forward reference, 3.11 definition, 6.7.6.3, 6.9.1, 6.11.7 + FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see designator, 6.3.2.1 + also contracted expression image, 5.2.3 + FP_FAST_FMA macro, 7.12 inline, 6.7.4 + FP_FAST_FMAF macro, 7.12 library, 5.1.1.1, 7.1.4 + FP_FAST_FMAL macro, 7.12 name length, 5.2.4.1, 6.4.2.1, 6.11.3 + FP_ILOGB0 macro, 7.12, 7.12.6.5 no-return, 6.7.4 + FP_ILOGBNAN macro, 7.12, 7.12.6.5 parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1 + FP_INFINITE macro, 7.12, F.3 prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7, + FP_NAN macro, 7.12, F.3 6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12 + FP_NORMAL macro, 7.12, F.3 prototype scope, 6.2.1, 6.7.6.2 + FP_SUBNORMAL macro, 7.12, F.3 recursive call, 6.5.2.2 + FP_ZERO macro, 7.12, F.3 return, 6.8.6.4, F.6 + fpclassify macro, 7.12.3.1, F.3 scope, 6.2.1 + fpos_t type, 7.21.1, 7.21.2 type, 6.2.5 + fprintf function, 7.8.1, 7.21.1, 7.21.6.1, type conversion, 6.3.2.1 + 7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6, function specifiers, 6.7.4 + 7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1 function type, 6.2.5 + fprintf_s function, K.3.5.3.1 function-call operator (( )), 6.5.2.2 + fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3, function-like macro, 6.10.3 + 7.21.7.7, 7.21.8.2 fundamental alignment, 6.2.8 + fputs function, 7.21.1, 7.21.7.4 future directions + fputwc function, 7.21.1, 7.21.3, 7.28.3.3, language, 6.11 + 7.28.3.8 library, 7.30 + fputws function, 7.21.1, 7.28.3.4 fwide function, 7.21.2, 7.28.3.5 + fread function, 7.21.1, 7.21.8.1 fwprintf function, 7.8.1, 7.21.1, 7.21.6.2, + free function, 7.22.3.3, 7.22.3.5 7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5, + freestanding execution environment, 4, 5.1.2, 7.28.2.11, K.3.9.1.1 + 5.1.2.1 fwprintf_s function, K.3.9.1.1 + freopen function, 7.21.2, 7.21.5.4 fwrite function, 7.21.1, 7.21.8.2 + freopen_s function, K.3.5.2.2 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2, + frexp functions, 7.12.6.4, F.10.3.4 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10, + frexp type-generic macro, 7.24 K.3.9.1.2 + fscanf function, 7.8.1, 7.21.1, 7.21.6.2, fwscanf_s function, K.3.9.1.2, K.3.9.1.5, + 7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2 K.3.9.1.7, K.3.9.1.14 + fscanf_s function, K.3.5.3.2, K.3.5.3.4, + + gamma functions, 7.12.8, F.10.5 name spaces, 6.2.3 + general utilities, 7.22, K.3.6 reserved, 6.4.1, 7.1.3, K.3.1.2 + wide string, 7.28.4, K.3.9.2 scope, 6.2.1 + general wide string utilities, 7.28.4, K.3.9.2 type, 6.2.5 + generic parameters, 7.24 identifier list, 6.7.6 + generic selection, 6.5.1.1 identifier nondigit, 6.4.2.1 + getc function, 7.21.1, 7.21.7.5, 7.21.7.6 IEC 559, F.1 + getchar function, 7.21.1, 7.21.7.6 IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8.3, 7.3.3, + getenv function, 7.22.4.6 7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G, + getenv_s function, K.3.6.2.1 H.1 + gets function, K.3.5.4.1 IEEE 754, F.1 + gets_s function, K.3.5.4.1 IEEE 854, F.1 + getwc function, 7.21.1, 7.28.3.6, 7.28.3.7 IEEE floating-point arithmetic standard, see + getwchar function, 7.21.1, 7.28.3.7 IEC 60559, ANSI/IEEE 754, + gmtime function, 7.26.3.3 ANSI/IEEE 854 + gmtime_s function, K.3.8.2.3 if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, + goto statement, 6.2.1, 6.8.1, 6.8.6.1 6.10.1, 7.1.4 + graphic characters, 5.2.1 if statement, 6.8.4.1 + greater-than operator (>), 6.5.8 ifdef preprocessing directive, 6.10.1 + greater-than-or-equal-to operator (>=), 6.5.8 ifndef preprocessing directive, 6.10.1 + ignore_handler_s function, K.3.6.1.3 + happens before, 5.1.2.4 ilogb functions, 7.12, 7.12.6.5, F.10.3.5 + header, 5.1.1.1, 7.1.2, see also standard headers ilogb type-generic macro, 7.24 + header names, 6.4, 6.4.7, 6.10.2 imaginary macro, 7.3.1, G.6 + hexadecimal constant, 6.4.4.1 imaginary numbers, G + hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4 imaginary type domain, G.2 + hexadecimal prefix, 6.4.4.1 imaginary types, G + hexadecimal-character escape sequence imaxabs function, 7.8.2.1 + (\x hexadecimal digits), 6.4.4.4 imaxdiv function, 7.8, 7.8.2.2 + high-order bit, 3.6 imaxdiv_t type, 7.8 + horizontal-tab character, 5.2.1, 6.4 implementation, 3.12 + horizontal-tab escape sequence (\r), 7.29.2.1.3 implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1, + horizontal-tab escape sequence (\t), 5.2.2, 6.7.6, 6.8.4.2, E, see also environmental + 6.4.4.4, 7.4.1.3, 7.4.1.10 limits + hosted execution environment, 4, 5.1.2, 5.1.2.2 implementation-defined behavior, 3.4.1, 4, J.3 + HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3, implementation-defined value, 3.19.1 + 7.28.4.1.1, F.10 implicit conversion, 6.3 + HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3, implicit initialization, 6.7.9 + 7.28.4.1.1, F.10 include preprocessing directive, 5.1.1.2, 6.10.2 + HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3, inclusive OR operators + 7.28.4.1.1, F.10 bitwise (|), 6.2.6.2, 6.5.12 + hyperbolic functions bitwise assignment (|=), 6.5.16.2 + complex, 7.3.6, G.6.2 incomplete type, 6.2.5 + real, 7.12.5, F.10.2 increment operators, see arithmetic operators, + hypot functions, 7.12.7.3, F.10.4.3 increment and decrement + hypot type-generic macro, 7.24 indeterminate value, 3.19.2 + indeterminately sequenced, 5.1.2.3, 6.5.2.2, + I macro, 7.3.1, 7.3.9.5, G.6 6.5.2.4, 6.5.16.2, see also sequenced before, + identifier, 6.4.2.1, 6.5.1 unsequenced + linkage, see linkage indirection operator (*), 6.5.2.1, 6.5.3.2 + maximum length, 6.4.2.1 inequality operator (!=), 6.5.9 + + infinitary, 7.12.1 extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20 + INFINITY macro, 7.3.9.5, 7.12, F.2.1 inter-thread happens before, 5.1.2.4 + initial position, 5.2.2 interactive device, 5.1.2.3, 7.21.3, 7.21.5.3 + initial shift state, 5.2.1.2 internal linkage, 6.2.2 + initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9, internal name, 6.4.2.1 + F.8.5 interrupt, 5.2.3 + in blocks, 6.8 INTMAX_C macro, 7.20.4.2 + initializer, 6.7.9 INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 + permitted form, 6.6 INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 + string literal, 6.3.2.1 intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, + inline, 6.7.4 7.28.2.1, 7.28.2.2 + inner scope, 6.2.1 INTN_C macros, 7.20.4.1 + input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, INTN_MAX macros, 7.20.2.1 + K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9, INTN_MIN macros, 7.20.2.1 + K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5, intN_t types, 7.20.1.1 + K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14 INTPTR_MAX macro, 7.20.2.4 + input/output functions INTPTR_MIN macro, 7.20.2.4 + character, 7.21.7, K.3.5.4 intptr_t type, 7.20.1.4 + direct, 7.21.8 inttypes.h header, 7.8, 7.30.4 + formatted, 7.21.6, K.3.5.3 isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10 + wide character, 7.28.2, K.3.9.1 isalpha function, 7.4.1.1, 7.4.1.2 + wide character, 7.28.3 isblank function, 7.4.1.3 + formatted, 7.28.2, K.3.9.1 iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7, + input/output header, 7.21, K.3.5 7.4.1.11 + input/output, device, 5.1.2.3 isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5, + int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2 7.4.1.7, 7.4.1.11, 7.11.1.1 + int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, isfinite macro, 7.12.3.2, F.3 + 6.3.1.8 isgraph function, 7.4.1.6 + INT_FASTN_MAX macros, 7.20.2.3 isgreater macro, 7.12.14.1, F.3 + INT_FASTN_MIN macros, 7.20.2.3 isgreaterequal macro, 7.12.14.2, F.3 + int_fastN_t types, 7.20.1.3 isinf macro, 7.12.3.3 + INT_LEASTN_MAX macros, 7.20.2.2 isless macro, 7.12.14.3, F.3 + INT_LEASTN_MIN macros, 7.20.2.2 islessequal macro, 7.12.14.4, F.3 + int_leastN_t types, 7.20.1.2 islessgreater macro, 7.12.14.5, F.3 + INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5 islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1, + INT_MIN macro, 5.2.4.2.1, 7.12 7.4.2.2 + integer arithmetic functions, 7.8.2.1, 7.8.2.2, isnan macro, 7.12.3.4, F.3 + 7.22.6 isnormal macro, 7.12.3.5 + integer character constant, 6.4.4.4 ISO 31-11, 2, 3 + integer constant, 6.4.4.1 ISO 4217, 2, 7.11.2.1 + integer constant expression, 6.3.2.3, 6.6, 6.7.2.1, ISO 8601, 2, 7.26.3.5 + 6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1, ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2 + 7.1.4 ISO/IEC 10976-1, H.1 + integer conversion rank, 6.3.1.1 ISO/IEC 2382-1, 2, 3 + integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1, ISO/IEC 646, 2, 5.2.1.1 + 6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3, ISO/IEC 9945-2, 7.11 + 7.21.6.1, 7.28.2.1 iso646.h header, 4, 7.9 * + integer suffix, 6.4.4.1 isprint function, 5.2.2, 7.4.1.8 + integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9, + F.3, F.4 7.4.1.11 + integer types, 6.2.5, 7.20 isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9, + + 7.4.1.10, 7.4.1.11, 7.21.6.2, 7.22.1.3, LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1 + 7.22.1.4, 7.28.2.2 LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3, + isunordered macro, 7.12.14.6, F.3 7.28.4.4.2 + isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1, LC_CTYPE macro, 7.11, 7.11.1.1, 7.22, 7.22.7, + 7.4.2.2 7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2, + iswalnum function, 7.29.2.1.1, 7.29.2.1.9, 7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5 + 7.29.2.1.10, 7.29.2.2.1 LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1 + iswalpha function, 7.29.2.1.1, 7.29.2.1.2, LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1 + 7.29.2.2.1 LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5 + iswblank function, 7.29.2.1.3, 7.29.2.2.1 lconv structure type, 7.11 + iswcntrl function, 7.29.2.1.2, 7.29.2.1.4, LDBL_DECIMAL_DIG macro, 5.2.4.2.2 + 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_DIG macro, 5.2.4.2.2 + iswctype function, 7.29.2.2.1, 7.29.2.2.2 LDBL_EPSILON macro, 5.2.4.2.2 + iswdigit function, 7.29.2.1.1, 7.29.2.1.2, LDBL_HAS_SUBNORM macro, 5.2.4.2.2 + 7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1 LDBL_MANT_DIG macro, 5.2.4.2.2 + iswgraph function, 7.29.2.1, 7.29.2.1.6, LDBL_MAX macro, 5.2.4.2.2 + 7.29.2.1.10, 7.29.2.2.1 LDBL_MAX_10_EXP macro, 5.2.4.2.2 + iswlower function, 7.29.2.1.2, 7.29.2.1.7, LDBL_MAX_EXP macro, 5.2.4.2.2 + 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 LDBL_MIN macro, 5.2.4.2.2 + iswprint function, 7.29.2.1.6, 7.29.2.1.8, LDBL_MIN_10_EXP macro, 5.2.4.2.2 + 7.29.2.2.1 LDBL_MIN_EXP macro, 5.2.4.2.2 + iswpunct function, 7.29.2.1, 7.29.2.1.2, LDBL_TRUE_MIN macro, 5.2.4.2.2 + 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, ldexp functions, 7.12.6.6, F.10.3.6 + 7.29.2.1.11, 7.29.2.2.1 ldexp type-generic macro, 7.24 + iswspace function, 7.21.6.2, 7.28.2.2, ldiv function, 7.22.6.2 + 7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6, ldiv_t type, 7.22 + 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, leading underscore in identifiers, 7.1.3 + 7.29.2.1.11, 7.29.2.2.1 left-shift assignment operator (<<=), 6.5.16.2 + iswupper function, 7.29.2.1.2, 7.29.2.1.11, left-shift operator (<<), 6.2.6.2, 6.5.7 + 7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2 length + iswxdigit function, 7.29.2.1.12, 7.29.2.2.1 external name, 5.2.4.1, 6.4.2.1, 6.11.3 + isxdigit function, 7.4.1.12, 7.11.1.1 function name, 5.2.4.1, 6.4.2.1, 6.11.3 + italic type convention, 3, 6.1 identifier, 6.4.2.1 + iteration statements, 6.8.5 internal name, 5.2.4.1, 6.4.2.1 + length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1, + jmp_buf type, 7.13 7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1 + jump statements, 6.8.6 length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1, + 7.28.2.2 + keywords, 6.4.1, G.2, J.5.9, J.5.10 less-than operator (<), 6.5.8 + kill_dependency macro, 5.1.2.4, 7.17.3.1 less-than-or-equal-to operator (<=), 6.5.8 + known constant size, 6.2.5 letter, 5.2.1, 7.4 + lexical elements, 5.1.1.2, 6.4 + L_tmpnam macro, 7.21.1, 7.21.4.4 lgamma functions, 7.12.8.3, F.10.5.3 + L_tmpnam_s macro, K.3.5, K.3.5.1.2 lgamma type-generic macro, 7.24 + label name, 6.2.1, 6.2.3 library, 5.1.1.1, 7, K.3 + labeled statement, 6.8.1 future directions, 7.30 + labs function, 7.22.6.1 summary, B + language, 6 terms, 7.1.1 + future directions, 6.11 use of functions, 7.1.4 + syntax summary, A lifetime, 6.2.4 + Latin alphabet, 5.2.1, 6.4.2.1 limits + + environmental, see environmental limits 6.3.1.6, 6.3.1.7, 6.3.1.8 + implementation, see implementation limits long double _Imaginary type, G.2 + numerical, see numerical limits long double suffix, l or L, 6.4.4.2 + translation, see translation limits long double type, 6.2.5, 6.4.4.2, 6.7.2, + limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2 + line buffered stream, 7.21.3 long double type conversion, 6.3.1.4, 6.3.1.5, + line number, 6.10.4, 6.10.8.1 6.3.1.7, 6.3.1.8 + line preprocessing directive, 6.10.4 long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, + lines, 5.1.1.2, 7.21.2 7.21.6.2, 7.28.2.1, 7.28.2.2 + preprocessing directive, 6.10 long int type conversion, 6.3.1.1, 6.3.1.3, + linkage, 6.2.2, 6.7, 6.7.4, 6.7.6.2, 6.9, 6.9.2, 6.3.1.4, 6.3.1.8 + 6.11.2 long integer suffix, l or L, 6.4.4.1 + llabs function, 7.22.6.1 long long int type, 6.2.5, 6.3.1.1, 6.7.2, + lldiv function, 7.22.6.2 7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2 + lldiv_t type, 7.22 long long int type conversion, 6.3.1.1, + LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.3.1.3, 6.3.1.4, 6.3.1.8 + 7.28.4.1.2 long long integer suffix, ll or LL, 6.4.4.1 + LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4, LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2 + 7.28.4.1.2 LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2 + llrint functions, 7.12.9.5, F.3, F.10.6.5 longjmp function, 7.13.1.1, 7.13.2.1, 7.22.4.4, + llrint type-generic macro, 7.24 7.22.4.7 + llround functions, 7.12.9.7, F.10.6.7 loop body, 6.8.5 + llround type-generic macro, 7.24 low-order bit, 3.6 + local time, 7.26.1 lowercase letter, 5.2.1 + locale, 3.4.2 lrint functions, 7.12.9.5, F.3, F.10.6.5 + locale-specific behavior, 3.4.2, J.4 lrint type-generic macro, 7.24 + locale.h header, 7.11, 7.30.5 lround functions, 7.12.9.7, F.10.6.7 + localeconv function, 7.11.1.1, 7.11.2.1 lround type-generic macro, 7.24 + localization, 7.11 lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16, + localtime function, 7.26.3.4 6.7.2.4 + localtime_s function, K.3.8.2.4 lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1, + log functions, 7.12.6.7, F.10.3.7 6.5.16.2 + log type-generic macro, 7.24 + log10 functions, 7.12.6.8, F.10.3.8 macro argument substitution, 6.10.3.1 + log10 type-generic macro, 7.24 macro definition + log1p functions, 7.12.6.9, F.10.3.9 library function, 7.1.4 + log1p type-generic macro, 7.24 macro invocation, 6.10.3 + log2 functions, 7.12.6.10, F.10.3.10 macro name, 6.10.3 + log2 type-generic macro, 7.24 length, 5.2.4.1 + logarithmic functions predefined, 6.10.8, 6.11.9 + complex, 7.3.7, G.6.3 redefinition, 6.10.3 + real, 7.12.6, F.10.3 scope, 6.10.3.5 + logb functions, 7.12.6.11, F.3, F.10.3.11 macro parameter, 6.10.3 + logb type-generic macro, 7.24 macro preprocessor, 6.10 + logical operators macro replacement, 6.10.3 + AND (&&), 5.1.2.4, 6.5.13 magnitude, complex, 7.3.8.1 + negation (!), 6.5.3.3 main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4, + OR (||), 5.1.2.4, 6.5.14 7.21.3 + logical source lines, 5.1.1.2 malloc function, 7.22.3, 7.22.3.4, 7.22.3.5 + long double _Complex type, 6.2.5 manipulation functions + long double _Complex type conversion, complex, 7.3.9 + + real, 7.12.11, F.10.8 modf functions, 7.12.6.12, F.10.3.12 + matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10, modifiable lvalue, 6.3.2.1 + K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 modification order, 5.1.2.4 + math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F, modulus functions, 7.12.6.12 + F.10, J.5.17 modulus, complex, 7.3.8.1 + MATH_ERREXCEPT macro, 7.12, F.10 mtx_destroy function, 7.25.4.1 + math_errhandling macro, 7.1.3, 7.12, F.10 mtx_init function, 7.25.1, 7.25.4.2 + MATH_ERRNO macro, 7.12 mtx_lock function, 7.25.4.3 + max_align_t type, 7.19 mtx_t type, 7.25.1 + maximum functions, 7.12.12, F.10.9 mtx_timedlock function, 7.25.4.4 + MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2, mtx_trylock function, 7.25.4.5 + 7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3, mtx_unlock function, 7.25.4.3, 7.25.4.4, + K.3.6.4.1, K.3.9.3.1.1 7.25.4.5, 7.25.4.6 + MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.22 multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4 + mblen function, 7.22.7.1, 7.28.6.3 multibyte conversion functions + mbrlen function, 7.28.6.3.1 wide character, 7.22.7, K.3.6.4 + mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1 extended, 7.28.6, K.3.9.3 + mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3 restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 + mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2, wide string, 7.22.8, K.3.6.5 + 7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2, restartable, 7.28.6.4, K.3.9.3.2 + 7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1 multibyte string, 7.1.1 + mbsinit function, 7.28.6.2.1 multibyte/wide character conversion functions, + mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2 7.22.7, K.3.6.4 + mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1 extended, 7.28.6, K.3.9.3 + mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1, restartable, 7.27.1, 7.28.6.3, K.3.9.3.1 + 7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1, multibyte/wide string conversion functions, + 7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3, 7.22.8, K.3.6.5 + 7.28.6.3.1, 7.28.6.4 restartable, 7.28.6.4, K.3.9.3.2 + mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4 multidimensional array, 6.5.2.1 + mbstowcs_s function, K.3.6.5.1 multiplication assignment operator (*=), 6.5.16.2 + mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2, multiplication operator (*), 6.2.6.2, 6.5.5, F.3, + 7.22.8.1, 7.28.6.3 G.5.1 + member access operators (. and ->), 6.5.2.3 multiplicative expressions, 6.5.5, G.5.1 + member alignment, 6.7.2.1 + memchr function, 7.23.5.1 n-char sequence, 7.22.1.3 + memcmp function, 7.23.4, 7.23.4.1 n-wchar sequence, 7.28.4.1.1 + memcpy function, 7.23.2.1 name + memcpy_s function, K.3.7.1.1 external, 5.2.4.1, 6.4.2.1, 6.11.3 + memmove function, 7.23.2.2 file, 7.21.3 + memmove_s function, K.3.7.1.2 internal, 5.2.4.1, 6.4.2.1 + memory location, 3.14 label, 6.2.3 + memory management functions, 7.22.3 structure/union member, 6.2.3 + memory_order type, 7.17.1, 7.17.3 name spaces, 6.2.3 + memset function, 7.23.6.1, K.3.7.4.1 named label, 6.8.1 + memset_s function, K.3.7.4.1 NaN, 5.2.4.2.2 + minimum functions, 7.12.12, F.10.9 nan functions, 7.12.11.2, F.2.1, F.10.8.2 + minus operator, unary, 6.5.3.3 NAN macro, 7.12, F.2.1 + miscellaneous functions NDEBUG macro, 7.2 + string, 7.23.6, K.3.7.4 nearbyint functions, 7.12.9.3, 7.12.9.4, F.3, + wide string, 7.28.4.6, K.3.9.2.4 F.10.6.3 + mktime function, 7.26.2.3 nearbyint type-generic macro, 7.24 + + nearest integer functions, 7.12.9, F.10.6 operating system, 5.1.2.1, 7.22.4.8 + negation operator (!), 6.5.3.3 operations on files, 7.21.4, K.3.5.1 + negative zero, 6.2.6.2, 7.12.11.1 operator, 6.4.6 + new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4 operators, 6.5 + new-line escape sequence (\n), 5.2.2, 6.4.4.4, additive, 6.2.6.2, 6.5.6 + 7.4.1.10 alignof, 6.5.3.4 + nextafter functions, 7.12.11.3, 7.12.11.4, F.3, assignment, 6.5.16 + F.10.8.3 associativity, 6.5 + nextafter type-generic macro, 7.24 equality, 6.5.9 + nexttoward functions, 7.12.11.4, F.3, F.10.8.4 multiplicative, 6.2.6.2, 6.5.5, G.5.1 + nexttoward type-generic macro, 7.24 postfix, 6.5.2 + no linkage, 6.2.2 precedence, 6.5 + no-return function, 6.7.4 preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9 + non-stop floating-point control mode, 7.6.4.2 relational, 6.5.8 + nongraphic characters, 5.2.2, 6.4.4.4 shift, 6.5.7 + nonlocal jumps header, 7.13 sizeof, 6.5.3.4 + norm, complex, 7.3.8.1 unary, 6.5.3 + normalized broken-down time, K.3.8.1, K.3.8.2.1 unary arithmetic, 6.5.3.3 + not macro, 7.9 optional features, see conditional features + not-equal-to operator, see inequality operator or macro, 7.9 + not_eq macro, 7.9 OR operators + null character (\0), 5.2.1, 6.4.4.4, 6.4.5 bitwise exclusive (^), 6.2.6.2, 6.5.11 + padding of binary stream, 7.21.2 bitwise exclusive assignment (^=), 6.5.16.2 + NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1, bitwise inclusive (|), 6.2.6.2, 6.5.12 + 7.26.1, 7.28.1 bitwise inclusive assignment (|=), 6.5.16.2 + null pointer, 6.3.2.3 logical (||), 5.1.2.4, 6.5.14 + null pointer constant, 6.3.2.3 or_eq macro, 7.9 + null preprocessing directive, 6.10.7 order of allocated storage, 7.22.3 + null statement, 6.8.3 order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3, + null wide character, 7.1.1 see also sequence points + number classification macros, 7.12, 7.12.3.1 ordinary identifier name space, 6.2.3 + numeric conversion functions, 7.8.2.3, 7.22.1 orientation of stream, 7.21.2, 7.28.3.5 + wide string, 7.8.2.4, 7.28.4.1 out-of-bounds store, L.2.1 + numerical limits, 5.2.4.2 outer scope, 6.2.1 + over-aligned, 6.2.8 + object, 3.15 + object representation, 6.2.6.1 padding + object type, 6.2.5 binary stream, 7.21.2 + object-like macro, 6.10.3 bits, 6.2.6.2, 7.20.1.1 + observable behavior, 5.1.2.3 structure/union, 6.2.6.1, 6.7.2.1 + obsolescence, 6.11, 7.30 parameter, 3.16 + octal constant, 6.4.4.1 array, 6.9.1 + octal digit, 6.4.4.1, 6.4.4.4 ellipsis, 6.7.6.3, 6.10.3 + octal-character escape sequence (\octal digits), function, 6.5.2.2, 6.7, 6.9.1 + 6.4.4.4 macro, 6.10.3 + offsetof macro, 7.19 main function, 5.1.2.2.1 + on-off switch, 6.10.6 program, 5.1.2.2.1 + once_flag type, 7.25.1 parameter type list, 6.7.6.3 + ONCE_FLAG_INIT macro, 7.25.1 parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5 + ones' complement, 6.2.6.2 parenthesized expression, 6.5.1 + operand, 6.4.6, 6.5 parse state, 7.21.2 + + perform a trap, 3.19.5 preprocessor, 6.10 + permitted form of initializer, 6.6 PRIcFASTN macros, 7.8.1 + perror function, 7.21.10.4 PRIcLEASTN macros, 7.8.1 + phase angle, complex, 7.3.9.1 PRIcMAX macros, 7.8.1 + physical source lines, 5.1.1.2 PRIcN macros, 7.8.1 + placemarker, 6.10.3.3 PRIcPTR macros, 7.8.1 + plus operator, unary, 6.5.3.3 primary expression, 6.5.1 + pointer arithmetic, 6.5.6 printf function, 7.21.1, 7.21.6.3, 7.21.6.10, + pointer comparison, 6.5.8 K.3.5.3.3 + pointer declarator, 6.7.6.1 printf_s function, K.3.5.3.3 + pointer operator (->), 6.5.2.3 printing character, 5.2.2, 7.4, 7.4.1.8 + pointer to function, 6.5.2.2 printing wide character, 7.29.2 + pointer type, 6.2.5 program diagnostics, 7.2.1 + pointer type conversion, 6.3.2.1, 6.3.2.3 program execution, 5.1.2.2.2, 5.1.2.3 + pointer, null, 6.3.2.3 program file, 5.1.1.1 + pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8, program image, 5.1.1.2 + 7.12.6.9, 7.12.6.10, 7.12.6.11, 7.12.7.4, program name (argv[0]), 5.1.2.2.1 + 7.12.8.3, 7.12.8.4 program parameters, 5.1.2.2.1 + portability, 4, J program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1 + position indicator, file, see file position indicator program structure, 5.1.1.1 + positive difference, 7.12.12.1 program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3, + positive difference functions, 7.12.12, F.10.9 5.1.2.3 + postfix decrement operator (--), 6.3.2.1, 6.5.2.4 program, conforming, 4 + postfix expressions, 6.5.2 program, strictly conforming, 4 + postfix increment operator (++), 6.3.2.1, 6.5.2.4 promotions + pow functions, 7.12.7.4, F.10.4.4 default argument, 6.5.2.2 + pow type-generic macro, 7.24 integer, 5.1.2.3, 6.3.1.1 + power functions prototype, see function prototype + complex, 7.3.8, G.6.4 pseudo-random sequence functions, 7.22.2 + real, 7.12.7, F.10.4 PTRDIFF_MAX macro, 7.20.3 + pp-number, 6.4.8 PTRDIFF_MIN macro, 7.20.3 + pragma operator, 6.10.9 ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1, + pragma preprocessing directive, 6.10.6, 6.11.8 7.21.6.2, 7.28.2.1, 7.28.2.2 + precedence of operators, 6.5 punctuators, 6.4.6 + precedence of syntax rules, 5.1.1.2 putc function, 7.21.1, 7.21.7.7, 7.21.7.8 + precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1 putchar function, 7.21.1, 7.21.7.8 + excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 puts function, 7.21.1, 7.21.7.9 + predefined macro names, 6.10.8, 6.11.9 putwc function, 7.21.1, 7.28.3.8, 7.28.3.9 + prefix decrement operator (--), 6.3.2.1, 6.5.3.1 putwchar function, 7.21.1, 7.28.3.9 + prefix increment operator (++), 6.3.2.1, 6.5.3.1 + preprocessing concatenation, 6.10.3.3 qsort function, 7.22.5, 7.22.5.2 + preprocessing directives, 5.1.1.2, 6.10 qsort_s function, K.3.6.3, K.3.6.3.2 + preprocessing file, 5.1.1.1, 6.10 qualified types, 6.2.5 + preprocessing numbers, 6.4, 6.4.8 qualified version of type, 6.2.5 + preprocessing operators question-mark escape sequence (\?), 6.4.4.4 + #, 6.10.3.2 quick_exit function, 7.22.4.3, 7.22.4.4, + ##, 6.10.3.3 7.22.4.7 + _Pragma, 5.1.1.2, 6.10.9 quiet NaN, 5.2.4.2.2 + defined, 6.10.1 + preprocessing tokens, 5.1.1.2, 6.4, 6.10 raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1 + preprocessing translation unit, 5.1.1.1 rand function, 7.22, 7.22.2.1, 7.22.2.2 + + RAND_MAX macro, 7.22, 7.22.2.1 restrict-qualified type, 6.2.5, 6.7.3 + range return statement, 6.8.6.4, F.6 + excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4 rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5, + range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1, 7.28.3.10 + 7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6, right-shift assignment operator (>>=), 6.5.16.2 + 7.12.6.13, 7.12.7.3, 7.12.7.4, 7.12.8.2, right-shift operator (>>), 6.2.6.2, 6.5.7 + 7.12.8.3, 7.12.8.4, 7.12.9.5, 7.12.9.7, rint functions, 7.12.9.4, F.3, F.10.6.4 + 7.12.11.3, 7.12.12.1, 7.12.13.1 rint type-generic macro, 7.24 + rank, see integer conversion rank round functions, 7.12.9.6, F.10.6.6 + read-modify-write operations, 5.1.2.4 round type-generic macro, 7.24 + real floating type conversion, 6.3.1.4, 6.3.1.5, rounding mode, floating point, 5.2.4.2.2 + 6.3.1.7, F.3, F.4 RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2, + real floating types, 6.2.5 K.3.5.3.5, K.3.5.3.6, K.3.5.3.12, K.3.5.3.13, + real type domain, 6.2.5 K.3.5.4.1, K.3.6.2.1, K.3.6.3.1, K.3.6.3.2, + real types, 6.2.5 K.3.6.4.1, K.3.6.5.1, K.3.6.5.2, K.3.7.1.1, + real-floating, 7.12.3 K.3.7.1.2, K.3.7.1.3, K.3.7.1.4, K.3.7.2.1, + realloc function, 7.22.3, 7.22.3.5 K.3.7.2.2, K.3.7.3.1, K.3.7.4.1, K.3.7.4.2, + recommended practice, 3.17 K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4, + recursion, 6.5.2.2 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2, + recursive function call, 6.5.2.2 K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1, + redefinition of macro, 6.10.3 K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1, + reentrancy, 5.1.2.3, 5.2.3 K.3.9.3.2.1, K.3.9.3.2.2 + library functions, 7.1.4 rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2, + referenced type, 6.2.5 K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 + register storage-class specifier, 6.7.1, 6.9 runtime-constraint, 3.18 + relational expressions, 6.5.8 Runtime-constraint handling functions, K.3.6.1 + relaxed atomic operations, 5.1.2.4 rvalue, 6.3.2.1 + release fence, 7.17.4 + release operation, 5.1.2.4 same scope, 6.2.1 + release sequence, 5.1.2.4 save calling environment function, 7.13.1 + reliability of data, interrupted, 5.1.2.3 scalar types, 6.2.5 + remainder assignment operator (%=), 6.5.16.2 scalbln function, 7.12.6.13, F.3, F.10.3.13 + remainder functions, 7.12.10, F.10.7 scalbln type-generic macro, 7.24 + remainder functions, 7.12.10.2, 7.12.10.3, F.3, scalbn function, 7.12.6.13, F.3, F.10.3.13 + F.10.7.2 scalbn type-generic macro, 7.24 + remainder operator (%), 6.2.6.2, 6.5.5 scanf function, 7.21.1, 7.21.6.4, 7.21.6.11 + remainder type-generic macro, 7.24 scanf_s function, K.3.5.3.4, K.3.5.3.11 + remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2 scanlist, 7.21.6.2, 7.28.2.2 + remquo functions, 7.12.10.3, F.3, F.10.7.3 scanset, 7.21.6.2, 7.28.2.2 + remquo type-generic macro, 7.24 SCHAR_MAX macro, 5.2.4.2.1 + rename function, 7.21.4.2 SCHAR_MIN macro, 5.2.4.2.1 + representations of types, 6.2.6 SCNcFASTN macros, 7.8.1 + pointer, 6.2.5 SCNcLEASTN macros, 7.8.1 + rescanning and replacement, 6.10.3.4 SCNcMAX macros, 7.8.1 + reserved identifiers, 6.4.1, 7.1.3, K.3.1.2 SCNcN macros, 7.8.1 + restartable multibyte/wide character conversion SCNcPTR macros, 7.8.1 + functions, 7.27.1, 7.28.6.3, K.3.9.3.1 scope of identifier, 6.2.1, 6.9.2 + restartable multibyte/wide string conversion search functions + functions, 7.28.6.4, K.3.9.3.2 string, 7.23.5, K.3.7.3 + restore calling environment function, 7.13.2 utility, 7.22.5, K.3.6.3 + restrict type qualifier, 6.7.3, 6.7.3.1 wide string, 7.28.4.5, K.3.9.2.3 + + SEEK_CUR macro, 7.21.1, 7.21.9.2 sign and magnitude, 6.2.6.2 + SEEK_END macro, 7.21.1, 7.21.9.2 sign bit, 6.2.6.2 + SEEK_SET macro, 7.21.1, 7.21.9.2 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7 + selection statements, 6.8.4 signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1 + self-referential structure, 6.7.2.3 signal handling functions, 7.14.1 + semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3, signal.h header, 7.14, 7.30.6 + 6.8.5, 6.8.6 signaling NaN, 5.2.4.2.2, F.2.1 + separate compilation, 5.1.1.1 signals, 5.1.2.3, 5.2.3, 7.14.1 + separate translation, 5.1.1.1 signbit macro, 7.12.3.6, F.3 + sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14, signed char type, 6.2.5, 7.21.6.1, 7.21.6.2, + 6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8, 7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2 + 7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3 signed character, 6.3.1.1 + sequenced after, see sequenced before signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1 + sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4, signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, + 6.5.16, see also indeterminately sequenced, 6.3.1.8 + unsequenced signed types, 6.2.5, 6.7.2 + sequencing of statements, 6.8 significand part, 6.4.4.2 + set_constraint_handler_s function, SIGSEGV macro, 7.14, 7.14.1.1 + K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3 SIGTERM macro, 7.14 + setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5 simple assignment operator (=), 6.5.16.1 + setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1 sin functions, 7.12.4.6, F.10.1.6 + setjmp.h header, 7.13 sin type-generic macro, 7.24, G.7 + setlocale function, 7.11.1.1, 7.11.2.1 single-byte character, 3.7.1, 5.2.1.2 + setvbuf function, 7.21.1, 7.21.3, 7.21.5.1, single-byte/wide character conversion functions, + 7.21.5.5, 7.21.5.6 7.28.6.1 + shall, 4 single-precision arithmetic, 5.1.2.3 + shift expressions, 6.5.7 single-quote escape sequence (\'), 6.4.4.4, 6.4.5 + shift sequence, 7.1.1 singularity, 7.12.1 + shift states, 5.2.1.2 sinh functions, 7.12.5.5, F.10.2.5 + short identifier, character, 5.2.4.1, 6.4.3 sinh type-generic macro, 7.24, G.7 + short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1, SIZE_MAX macro, 7.20.3 + 7.21.6.2, 7.28.2.1, 7.28.2.2 size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1, + short int type conversion, 6.3.1.1, 6.3.1.3, 7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27, + 6.3.1.4, 6.3.1.8 7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4, + SHRT_MAX macro, 5.2.4.2.1 K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2 + SHRT_MIN macro, 5.2.4.2.1 sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4 + side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4, snprintf function, 7.21.6.5, 7.21.6.12, + 6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5, K.3.5.3.5 + 7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1, snprintf_s function, K.3.5.3.5, K.3.5.3.6 + F.9.3 snwprintf_s function, K.3.9.1.3, K.3.9.1.4 + SIG_ATOMIC_MAX macro, 7.20.3 sorting utility functions, 7.22.5, K.3.6.3 + SIG_ATOMIC_MIN macro, 7.20.3 source character set, 5.1.1.2, 5.2.1 + sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1, source file, 5.1.1.1 + 7.20.3 name, 6.10.4, 6.10.8.1 + SIG_DFL macro, 7.14, 7.14.1.1 source file inclusion, 6.10.2 + SIG_ERR macro, 7.14, 7.14.1.1 source lines, 5.1.1.2 + SIG_IGN macro, 7.14, 7.14.1.1 source text, 5.1.1.2 + SIGABRT macro, 7.14, 7.22.4.1 space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3, + SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17 7.4.1.10, 7.29.2.1.3 + SIGILL macro, 7.14, 7.14.1.1 sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6 + SIGINT macro, 7.14 sprintf_s function, K.3.5.3.5, K.3.5.3.6 + + sqrt functions, 7.12.7.5, F.3, F.10.4.5 do, 6.8.5.2 + sqrt type-generic macro, 7.24 else, 6.8.4.1 + srand function, 7.22.2.2 expression, 6.8.3 + sscanf function, 7.21.6.7, 7.21.6.14 for, 6.8.5.3 + sscanf_s function, K.3.5.3.7, K.3.5.3.14 goto, 6.8.6.1 + standard error stream, 7.21.1, 7.21.3, 7.21.10.4 if, 6.8.4.1 + standard headers, 4, 7.1.2 iteration, 6.8.5 + <assert.h>, 7.2 jump, 6.8.6 + <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3, labeled, 6.8.1 + 7.24, 7.30.1, G.6, J.5.17 null, 6.8.3 + <ctype.h>, 7.4, 7.30.2 return, 6.8.6.4, F.6 + <errno.h>, 7.5, 7.30.3, K.3.2 selection, 6.8.4 + <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H sequencing, 6.8 + <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3, switch, 6.8.4.2 + 7.28.4.1.1 while, 6.8.5.1 + <inttypes.h>, 7.8, 7.30.4 static assertions, 6.7.10 + <iso646.h>, 4, 7.9 static storage duration, 6.2.4 + <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10 static storage-class specifier, 6.2.2, 6.2.4, 6.7.1 + <locale.h>, 7.11, 7.30.5 static, in array declarators, 6.7.6.2, 6.7.6.3 + <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10, static_assert declaration, 6.7.10 + J.5.17 static_assert macro, 7.2 + <setjmp.h>, 7.13 stdalign.h header, 4, 7.15 + <signal.h>, 7.14, 7.30.6 stdarg.h header, 4, 6.7.6.3, 7.16 + <stdalign.h>, 4, 7.15 stdatomic.h header, 6.10.8.3, 7.1.2, 7.17 + <stdarg.h>, 4, 6.7.6.3, 7.16 stdbool.h header, 4, 7.18, 7.30.7, H + <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17 STDC, 6.10.6, 6.11.8 + <stdbool.h>, 4, 7.18, 7.30.7, H stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, + <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 + 6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3 stderr macro, 7.21.1, 7.21.2, 7.21.3 + <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4, + 7.30.8, K.3.3, K.3.4 7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4, + <stdio.h>, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 K.3.5.4.1, K.3.9.1.14 + <stdlib.h>, 5.2.4.2.2, 7.22, 7.30.10, F, stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20, + K.3.1.4, K.3.6 7.30.8, K.3.3, K.3.4 + <string.h>, 7.23, 7.30.11, K.3.7 stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5 + <tgmath.h>, 7.24, G.7 stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F, + <threads.h>, 6.10.8.3, 7.1.2, 7.25 K.3.1.4, K.3.6 + <time.h>, 7.26, K.3.8 stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3, + <uchar.h>, 6.4.4.4, 6.4.5, 7.27 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9 + <wchar.h>, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, storage duration, 6.2.4 + F, K.3.9 storage order of array, 6.5.2.1 + <wctype.h>, 7.29, 7.30.13 storage unit (bit-field), 6.2.6.1, 6.7.2.1 + standard input stream, 7.21.1, 7.21.3 storage-class specifiers, 6.7.1, 6.11.5 + standard integer types, 6.2.5 strcat function, 7.23.3.1 + standard output stream, 7.21.1, 7.21.3 strcat_s function, K.3.7.2.1 + standard signed integer types, 6.2.5 strchr function, 7.23.5.2 + state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4 strcmp function, 7.23.4, 7.23.4.2 + statements, 6.8 strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5 + break, 6.8.6.3 strcpy function, 7.23.2.3 + compound, 6.8.2 strcpy_s function, K.3.7.1.3 + continue, 6.8.6.2 strcspn function, 7.23.5.3 + + streams, 7.21.2, 7.22.4.4 7.22.1.4, 7.28.2.2 + fully buffered, 7.21.3 strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4 + line buffered, 7.21.3 strtoumax function, 7.8.2.3 + orientation, 7.21.2 struct hack, see flexible array member + standard error, 7.21.1, 7.21.3 struct lconv, 7.11 + standard input, 7.21.1, 7.21.3 struct tm, 7.26.1 + standard output, 7.21.1, 7.21.3 structure + unbuffered, 7.21.3 arrow operator (->), 6.5.2.3 + strerror function, 7.21.10.4, 7.23.6.2 content, 6.7.2.3 + strerror_s function, K.3.7.4.2, K.3.7.4.3 dot operator (.), 6.5.2.3 + strerrorlen_s function, K.3.7.4.3 initialization, 6.7.9 + strftime function, 7.11.1.1, 7.26.3, 7.26.3.5, member alignment, 6.7.2.1 + 7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2 member name space, 6.2.3 + stricter, 6.2.8 member operator (.), 6.3.2.1, 6.5.2.3 + strictly conforming program, 4 pointer operator (->), 6.5.2.3 + string, 7.1.1 specifier, 6.7.2.1 + comparison functions, 7.23.4 tag, 6.2.3, 6.7.2.3 + concatenation functions, 7.23.3, K.3.7.2 type, 6.2.5, 6.7.2.1 + conversion functions, 7.11.1.1 strxfrm function, 7.11.1.1, 7.23.4.5 + copying functions, 7.23.2, K.3.7.1 subnormal floating-point numbers, 5.2.4.2.2 + library function conventions, 7.23.1 subscripting, 6.5.2.1 + literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9 subtraction assignment operator (-=), 6.5.16.2 + miscellaneous functions, 7.23.6, K.3.7.4 subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2 + numeric conversion functions, 7.8.2.3, 7.22.1 suffix + search functions, 7.23.5, K.3.7.3 floating constant, 6.4.4.2 + string handling header, 7.23, K.3.7 integer constant, 6.4.4.1 + string.h header, 7.23, 7.30.11, K.3.7 switch body, 6.8.4.2 + stringizing, 6.10.3.2, 6.10.9 switch case label, 6.8.1, 6.8.4.2 + strlen function, 7.23.6.3 switch default label, 6.8.1, 6.8.4.2 + strncat function, 7.23.3.2 switch statement, 6.8.1, 6.8.4.2 + strncat_s function, K.3.7.2.2 swprintf function, 7.28.2.3, 7.28.2.7, + strncmp function, 7.23.4, 7.23.4.4 K.3.9.1.3, K.3.9.1.4 + strncpy function, 7.23.2.4 swprintf_s function, K.3.9.1.3, K.3.9.1.4 + strncpy_s function, K.3.7.1.4 swscanf function, 7.28.2.4, 7.28.2.8 + strnlen_s function, K.3.7.4.4 swscanf_s function, K.3.9.1.5, K.3.9.1.10 + stronger, 6.2.8 symbols, 3 + strpbrk function, 7.23.5.4 synchronization operation, 5.1.2.4 + strrchr function, 7.23.5.5 synchronize with, 5.1.2.4 + strspn function, 7.23.5.6 syntactic categories, 6.1 + strstr function, 7.23.5.7 syntax notation, 6.1 + strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3, syntax rule precedence, 5.1.1.2 + 7.28.2.2, F.3 syntax summary, language, A + strtof function, 7.12.11.2, 7.22.1.3, F.3 system function, 7.22.4.8 + strtoimax function, 7.8.2.3 + strtok function, 7.23.5.8 tab characters, 5.2.1, 6.4 + strtok_s function, K.3.7.3.1 tag compatibility, 6.2.7 + strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tag name space, 6.2.3 + 7.22.1.4, 7.28.2.2 tags, 6.7.2.3 + strtold function, 7.12.11.2, 7.22.1.3, F.3 tan functions, 7.12.4.7, F.10.1.7 + strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4 tan type-generic macro, 7.24, G.7 + strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2, tanh functions, 7.12.5.6, F.10.2.6 + + tanh type-generic macro, 7.24, G.7 toupper function, 7.4.2.2 + temporary lifetime, 6.2.4 towctrans function, 7.29.3.2.1, 7.29.3.2.2 + tentative definition, 6.9.2 towlower function, 7.29.3.1.1, 7.29.3.2.1 + terms, 3 towupper function, 7.29.3.1.2, 7.29.3.2.1 + text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4 translation environment, 5, 5.1.1 + tgamma functions, 7.12.8.4, F.10.5.4 translation limits, 5.2.4.1 + tgamma type-generic macro, 7.24 translation phases, 5.1.1.2 + tgmath.h header, 7.24, G.7 translation unit, 5.1.1.1, 6.9 + thrd_create function, 7.25.1, 7.25.5.1 trap, see perform a trap + thrd_current function, 7.25.5.2 trap representation, 3.19.4, 6.2.6.1, 6.2.6.2, + thrd_detach function, 7.25.5.3 6.3.2.3, 6.5.2.3 + thrd_equal function, 7.25.5.4 trigonometric functions + thrd_exit function, 7.25.5.5 complex, 7.3.5, G.6.1 + thrd_join function, 7.25.5.6 real, 7.12.4, F.10.1 + thrd_sleep function, 7.25.5.7 trigraph sequences, 5.1.1.2, 5.2.1.1 + thrd_start_t type, 7.25.1 true macro, 7.18 + thrd_t type, 7.25.1 trunc functions, 7.12.9.8, F.10.6.8 + thrd_yield function, 7.25.5.8 trunc type-generic macro, 7.24 + thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6 truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3 + thread storage duration, 6.2.4, 7.6 truncation toward zero, 6.5.5 + threads header, 7.25 tss_create function, 7.25.6.1 + threads.h header, 6.10.8.3, 7.1.2, 7.25 tss_delete function, 7.25.6.2 + time TSS_DTOR_ITERATIONS macro, 7.25.1 + broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1, tss_dtor_t type, 7.25.1 + 7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1, tss_get function, 7.25.6.3 + K.3.8.2.3, K.3.8.2.4 tss_set function, 7.25.6.4 + calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4, tss_t type, 7.25.1 + 7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2, two's complement, 6.2.6.2, 7.20.1.1 + K.3.8.2.3, K.3.8.2.4 type category, 6.2.5 + components, 7.26.1, K.3.8.1 type conversion, 6.3 + conversion functions, 7.26.3, K.3.8.2 type definitions, 6.7.8 + wide character, 7.28.5 type domain, 6.2.5, G.2 + local, 7.26.1 type names, 6.7.7 + manipulation functions, 7.26.2 type punning, 6.5.2.3 + normalized broken down, K.3.8.1, K.3.8.2.1 type qualifiers, 6.7.3 + time function, 7.26.2.4 type specifiers, 6.7.2 + time.h header, 7.26, K.3.8 type-generic macro, 7.24, G.7 + time_t type, 7.26.1 typedef declaration, 6.7.8 + TIME_UTC macro, 7.25.7.1 typedef storage-class specifier, 6.7.1, 6.7.8 + tm structure type, 7.26.1, 7.28.1, K.3.8.1 types, 6.2.5 + TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4 atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3, + TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6 + tmpfile function, 7.21.4.3, 7.22.4.4 character, 6.7.9 + tmpfile_s function, K.3.5.1.1, K.3.5.1.2 compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6 + tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4, complex, 6.2.5, G + K.3.5.1.2 composite, 6.2.7 + tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2 const qualified, 6.7.3 + token, 5.1.1.2, 6.4, see also preprocessing tokens conversions, 6.3 + token concatenation, 6.10.3.3 imaginary, G + token pasting, 6.10.3.3 restrict qualified, 6.7.3 + tolower function, 7.4.2.1 volatile qualified, 6.7.3 + + uchar.h header, 6.4.4.4, 6.4.5, 7.27 universal character name, 6.4.3 + UCHAR_MAX macro, 5.2.4.2.1 unnormalized floating-point numbers, 5.2.4.2.2 + UINT_FASTN_MAX macros, 7.20.2.3 unqualified type, 6.2.5 + uint_fastN_t types, 7.20.1.3 unqualified version of type, 6.2.5 + uint_least16_t type, 7.27 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also + uint_least32_t type, 7.27 indeterminately sequenced, sequenced + UINT_LEASTN_MAX macros, 7.20.2.2 before + uint_leastN_t types, 7.20.1.2 unsigned char type, K.3.5.3.2, K.3.9.1.2 + UINT_MAX macro, 5.2.4.2.1 unsigned integer suffix, u or U, 6.4.4.1 + UINTMAX_C macro, 7.20.4.2 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1 + UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5 unsigned type conversion, 6.3.1.1, 6.3.1.3, + uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2, 6.3.1.4, 6.3.1.8 + 7.28.2.1, 7.28.2.2 unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2, + UINTN_C macros, 7.20.4.1 7.28.2.1, 7.28.2.2 + UINTN_MAX macros, 7.20.2.1 unspecified behavior, 3.4.4, 4, J.1 + uintN_t types, 7.20.1.1 unspecified value, 3.19.3 + UINTPTR_MAX macro, 7.20.2.4 uppercase letter, 5.2.1 + uintptr_t type, 7.20.1.4 use of library functions, 7.1.4 + ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4, USHRT_MAX macro, 5.2.4.2.1 + 7.28.4.1.2 usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6, + ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15 + 7.28.4.1.2 UTF-16, 6.10.8.2 + unary arithmetic operators, 6.5.3.3 UTF-32, 6.10.8.2 + unary expression, 6.5.3 UTF-8 string literal, see string literal + unary minus operator (-), 6.5.3.3, F.3 utilities, general, 7.22, K.3.6 + unary operators, 6.5.3 wide string, 7.28.4, K.3.9.2 + unary plus operator (+), 6.5.3.3 + unbuffered stream, 7.21.3 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2, + undef preprocessing directive, 6.10.3.5, 7.1.3, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, + 7.1.4 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, + undefined behavior, 3.4.3, 4, J.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, + underscore character, 6.4.2.1 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11, + underscore, leading, in identifier, 7.1.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 + ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2, va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1, + 7.21.9.3 7.16.1.2, 7.16.1.3 + ungetwc function, 7.21.1, 7.28.3.10 va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3, + Unicode, 7.27, see also char16_t type, 7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10, + char32_t type, wchar_t type 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14, + Unicode required set, 6.10.8.2 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, + union 7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11, + arrow operator (->), 6.5.2.3 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12 + content, 6.7.2.3 va_list type, 7.16, 7.16.1.3 + dot operator (.), 6.5.2.3 va_start macro, 7.16, 7.16.1, 7.16.1.1, + initialization, 6.7.9 7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8, + member alignment, 6.7.2.1 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, + member name space, 6.2.3 7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6, + member operator (.), 6.3.2.1, 6.5.2.3 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10, + pointer operator (->), 6.5.2.3 K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7, + specifier, 6.7.2.1 K.3.9.1.10, K.3.9.1.12 + tag, 6.2.3, 6.7.2.3 value, 3.19 + type, 6.2.5, 6.7.2.1 value bits, 6.2.6.2 + + variable arguments, 6.10.3, 7.16 vswscanf function, 7.28.2.8 + variable arguments header, 7.16 vswscanf_s function, K.3.9.1.10 + variable length array, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11 + variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3 vwprintf_s function, K.3.9.1.11 + vertical-tab character, 5.2.1, 6.4 vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10 + vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4, vwscanf_s function, K.3.9.1.12 + 7.4.1.10 + vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8 warnings, I + vfprintf_s function, K.3.5.3.8, K.3.5.3.9, wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12, + K.3.5.3.11, K.3.5.3.14 F, K.3.9 + vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9 WCHAR_MAX macro, 7.20.3, 7.28.1 + vfscanf_s function, K.3.5.3.9, K.3.5.3.11, WCHAR_MIN macro, 7.20.3, 7.28.1 + K.3.5.3.14 wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19, + vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6 7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1, + vfwprintf_s function, K.3.9.1.6 7.28.2.1, 7.28.2.2 + vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10 wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2, + vfwscanf_s function, K.3.9.1.7 7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1, + visibility of identifier, 6.2.1 K.3.9.3.2.2 + visible sequence of side effects, 5.1.2.4 wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1 + visible side effect, 5.1.2.4 wcscat function, 7.28.4.3.1 + VLA, see variable length array wcscat_s function, K.3.9.2.2.1 + void expression, 6.3.2.2 wcschr function, 7.28.4.5.1 + void function parameter, 6.7.6.3 wcscmp function, 7.28.4.4.1, 7.28.4.4.4 + void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2, wcscoll function, 7.28.4.4.2, 7.28.4.4.4 + K.3.9.1.2 wcscpy function, 7.28.4.2.1 + void type conversion, 6.3.2.2 wcscpy_s function, K.3.9.2.1.1 + volatile storage, 5.1.2.3 wcscspn function, 7.28.4.5.2 + volatile type qualifier, 6.7.3 wcsftime function, 7.11.1.1, 7.28.5.1 + volatile-qualified type, 6.2.5, 6.7.3 wcslen function, 7.28.4.6.1 + vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10, wcsncat function, 7.28.4.3.2 + K.3.5.3.10 wcsncat_s function, K.3.9.2.2.2 + vprintf_s function, K.3.5.3.9, K.3.5.3.10, wcsncmp function, 7.28.4.4.3 + K.3.5.3.11, K.3.5.3.14 wcsncpy function, 7.28.4.2.2 + vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11 wcsncpy_s function, K.3.9.2.1.2 + vscanf_s function, K.3.5.3.9, K.3.5.3.11, wcsnlen_s function, K.3.9.2.4.1 + K.3.5.3.14 wcspbrk function, 7.28.4.5.3 + vsnprintf function, 7.21.6.8, 7.21.6.12, wcsrchr function, 7.28.4.5.4 + K.3.5.3.12 wcsrtombs function, 7.28.6.4.2, K.3.9.3.2 + vsnprintf_s function, K.3.5.3.9, K.3.5.3.11, wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2 + K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcsspn function, 7.28.4.5.5 + vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9 wcsstr function, 7.28.4.5.6 + vsprintf function, 7.21.6.8, 7.21.6.13, wcstod function, 7.21.6.2, 7.28.2.2 + K.3.5.3.13 wcstod function, 7.28.4.1.1 + vsprintf_s function, K.3.5.3.9, K.3.5.3.11, wcstof function, 7.28.4.1.1 + K.3.5.3.12, K.3.5.3.13, K.3.5.3.14 wcstoimax function, 7.8.2.4 + vsscanf function, 7.21.6.8, 7.21.6.14 wcstok function, 7.28.4.5.7 + vsscanf_s function, K.3.5.3.9, K.3.5.3.11, wcstok_s function, K.3.9.2.3.1 + K.3.5.3.14 wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2, + vswprintf function, 7.28.2.7, K.3.9.1.8, 7.28.4.1.2 + K.3.9.1.9 wcstold function, 7.28.4.1.1 + vswprintf_s function, K.3.9.1.8, K.3.9.1.9 wcstoll function, 7.8.2.4, 7.28.4.1.2 + + wcstombs function, 7.22.8.2, 7.28.6.4 7.29.1 + wcstombs_s function, K.3.6.5.2 wmemchr function, 7.28.4.5.8 + wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2, wmemcmp function, 7.28.4.4.5 + 7.28.4.1.2 wmemcpy function, 7.28.4.2.3 + wcstoull function, 7.8.2.4, 7.28.4.1.2 wmemcpy_s function, K.3.9.2.1.3 + wcstoumax function, 7.8.2.4 wmemmove function, 7.28.4.2.4 + wcsxfrm function, 7.28.4.4.4 wmemmove_s function, K.3.9.2.1.4 + wctob function, 7.28.6.1.2, 7.29.2.1 wmemset function, 7.28.4.6.2 + wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3 wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11, + wctomb_s function, K.3.6.4.1 K.3.9.1.13 + wctrans function, 7.29.3.2.1, 7.29.3.2.2 wprintf_s function, K.3.9.1.13 + wctrans_t type, 7.29.1, 7.29.3.2.2 wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12, + wctype function, 7.29.2.2.1, 7.29.2.2.2 7.28.3.10 + wctype.h header, 7.29, 7.30.13 wscanf_s function, K.3.9.1.12, K.3.9.1.14 + wctype_t type, 7.29.1, 7.29.2.2.2 + weaker, 6.2.8 xor macro, 7.9 + WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6, xor_eq macro, 7.9 + 7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10, xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7, + 7.28.6.1.1, 7.29.1 7.25.7.1 + while statement, 6.8.5.1 xtime_get function, 7.25.7.1 + white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10, + 7.29.2.1.10 + white-space characters, 6.4 + wide character, 3.7.3 + case mapping functions, 7.29.3.1 + extensible, 7.29.3.2 + classification functions, 7.29.2.1 + extensible, 7.29.2.2 + constant, 6.4.4.4 + formatted input/output functions, 7.28.2, + K.3.9.1 + input functions, 7.21.1 + input/output functions, 7.21.1, 7.28.3 + output functions, 7.21.1 + single-byte conversion functions, 7.28.6.1 + wide string, 7.1.1 + wide string comparison functions, 7.28.4.4 + wide string concatenation functions, 7.28.4.3, + K.3.9.2.2 + wide string copying functions, 7.28.4.2, K.3.9.2.1 + wide string literal, see string literal + wide string miscellaneous functions, 7.28.4.6, + K.3.9.2.4 + wide string numeric conversion functions, 7.8.2.4, + 7.28.4.1 + wide string search functions, 7.28.4.5, K.3.9.2.3 + wide-oriented stream, 7.21.2 + width, 6.2.6.2 + WINT_MAX macro, 7.20.3 + WINT_MIN macro, 7.20.3 + wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1, ++