man0p/unistd.h.0p

   1 .\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
   2 .TH "<unistd.h>" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
   3 .\" <unistd.h>
   4 .SH NAME
   5 unistd.h \- standard symbolic constants and types
   6 .SH SYNOPSIS
   7 .LP
   8 \fB#include <unistd.h>\fP
   9 .SH DESCRIPTION
  10 .LP
  11 The \fI<unistd.h>\fP header defines miscellaneous symbolic constants
  12 and types, and declares miscellaneous functions. The
  13 actual values of the constants are unspecified except as shown. The
  14 contents of this header are shown below.
  15 .SS Version Test Macros
  16 .LP
  17 The following symbolic constants shall be defined:
  18 .TP 7
  19 _POSIX_VERSION
  20 Integer value indicating version of IEEE\ Std\ 1003.1 (C-language
  21 binding) to which the implementation conforms. For
  22 implementations conforming to IEEE\ Std\ 1003.1-2001, the value shall
  23 be 200112L.
  24 .TP 7
  25 _POSIX2_VERSION
  26 Integer value indicating version of the Shell and Utilities volume
  27 of IEEE\ Std\ 1003.1 to which the implementation
  28 conforms. For implementations conforming to IEEE\ Std\ 1003.1-2001,
  29 the value shall be 200112L.
  30 .sp
  31 .LP
  32 The following symbolic constant shall be defined only if the implementation
  33 supports the XSI option; see \fIXSI Conformance\fP .
  34 .TP 7
  35 _XOPEN_VERSION
  36 .sp
  37 Integer value indicating version of the X/Open Portability Guide to
  38 which the implementation conforms. The value shall be 600.
  39 .sp
  40 .SS Constants for Options and Option Groups
  41 .LP
  42 The following symbolic constants, if defined in \fI<unistd.h>\fP,
  43 shall have a value of -1, 0, or greater, unless
  44 otherwise specified below. If these are undefined, the \fIfpathconf\fP(),
  45 \fIpathconf\fP(), or \fIsysconf\fP() functions can be
  46 used to determine whether the option is provided for a particular
  47 invocation of the application.
  48 .LP
  49 If a symbolic constant is defined with the value -1, the option is
  50 not supported. Headers, data types, and function interfaces
  51 required only for the option need not be supplied. An application
  52 that attempts to use anything associated only with the option is
  53 considered to be requiring an extension.
  54 .LP
  55 If a symbolic constant is defined with a value greater than zero,
  56 the option shall always be supported when the application is
  57 executed. All headers, data types, and functions shall be present
  58 and shall operate as specified.
  59 .LP
  60 If a symbolic constant is defined with the value zero, all headers,
  61 data types, and functions shall be present. The application
  62 can check at runtime to see whether the option is supported by calling
  63 \fIfpathconf\fP(), \fIpathconf\fP(), or \fIsysconf\fP() with the indicated
  64 \fIname\fP parameter.
  65 .LP
  66 Unless explicitly specified otherwise, the behavior of functions associated
  67 with an unsupported option is unspecified, and an
  68 application that uses such functions without first checking \fIfpathconf\fP(),
  69 \fIpathconf\fP(), or \fIsysconf\fP() is considered to be
  70 requiring an extension.
  71 .LP
  72 For conformance requirements, refer to \fIConformance\fP .
  73 .TP 7
  74 _POSIX_ADVISORY_INFO
  75 .sp
  76 The implementation supports the Advisory Information option. If this
  77 symbol has a value other than -1 or 0, it shall have the value
  78 200112L.
  79 .TP 7
  80 _POSIX_ASYNCHRONOUS_IO
  81 .sp
  82 The implementation supports the Asynchronous Input and Output option.
  83 If this symbol has a value other than -1 or 0, it shall have
  84 the value 200112L.
  85 .TP 7
  86 _POSIX_BARRIERS
  87 .sp
  88 The implementation supports the Barriers option. If this symbol has
  89 a value other than -1 or 0, it shall have the value 200112L.
  90 .TP 7
  91 _POSIX_CHOWN_RESTRICTED
  92 The use of \fIchown\fP() and \fIfchown\fP() is
  93 restricted to a process with appropriate privileges, and to changing
  94 the group ID of a file only to the effective group ID of the
  95 process or to one of its supplementary group IDs. This symbol shall
  96 always be set to a value other than -1.
  97 .TP 7
  98 _POSIX_CLOCK_SELECTION
  99 .sp
 100 The implementation supports the Clock Selection option. If this symbol
 101 has a value other than -1 or 0, it shall have the value
 102 200112L.
 103 .TP 7
 104 _POSIX_CPUTIME
 105 .sp
 106 The implementation supports the Process CPU-Time Clocks option. If
 107 this symbol has a value other than -1 or 0, it shall have the
 108 value 200112L.
 109 .TP 7
 110 _POSIX_FSYNC
 111 .sp
 112 The implementation supports the File Synchronization option. If this
 113 symbol has a value other than -1 or 0, it shall have the value
 114 200112L.
 115 .TP 7
 116 _POSIX_IPV6
 117 The implementation supports the IPv6 option. If this symbol has a
 118 value other than -1 or 0, it shall have the value 200112L.
 119 .TP 7
 120 _POSIX_JOB_CONTROL
 121 The implementation supports job control. This symbol shall always
 122 be set to a value greater than zero.
 123 .TP 7
 124 _POSIX_MAPPED_FILES
 125 .sp
 126 The implementation supports the Memory Mapped Files option. If this
 127 symbol has a value other than -1 or 0, it shall have the value
 128 200112L.
 129 .TP 7
 130 _POSIX_MEMLOCK
 131 .sp
 132 The implementation supports the Process Memory Locking option. If
 133 this symbol has a value other than -1 or 0, it shall have the
 134 value 200112L.
 135 .TP 7
 136 _POSIX_MEMLOCK_RANGE
 137 .sp
 138 The implementation supports the Range Memory Locking option. If this
 139 symbol has a value other than -1 or 0, it shall have the value
 140 200112L.
 141 .TP 7
 142 _POSIX_MEMORY_PROTECTION
 143 .sp
 144 The implementation supports the Memory Protection option. If this
 145 symbol has a value other than -1 or 0, it shall have the value
 146 200112L.
 147 .TP 7
 148 _POSIX_MESSAGE_PASSING
 149 .sp
 150 The implementation supports the Message Passing option. If this symbol
 151 has a value other than -1 or 0, it shall have the value
 152 200112L.
 153 .TP 7
 154 _POSIX_MONOTONIC_CLOCK
 155 .sp
 156 The implementation supports the Monotonic Clock option. If this symbol
 157 has a value other than -1 or 0, it shall have the value
 158 200112L.
 159 .TP 7
 160 _POSIX_NO_TRUNC
 161 Pathname components longer than {NAME_MAX} generate an error. This
 162 symbol shall always be set to a value other than -1.
 163 .TP 7
 164 _POSIX_PRIORITIZED_IO
 165 .sp
 166 The implementation supports the Prioritized Input and Output option.
 167 If this symbol has a value other than -1 or 0, it shall have
 168 the value 200112L.
 169 .TP 7
 170 _POSIX_PRIORITY_SCHEDULING
 171 .sp
 172 The implementation supports the Process Scheduling option. If this
 173 symbol has a value other than -1 or 0, it shall have the value
 174 200112L.
 175 .TP 7
 176 _POSIX_RAW_SOCKETS
 177 .sp
 178 The implementation supports the Raw Sockets option. If this symbol
 179 has a value other than -1 or 0, it shall have the value 200112L.
 180 .TP 7
 181 _POSIX_READER_WRITER_LOCKS
 182 .sp
 183 The implementation supports the Read-Write Locks option. This is always
 184 set to a value greater than zero if the Threads option is
 185 supported. If this symbol has a value other than -1 or 0, it shall
 186 have the value 200112L.
 187 .TP 7
 188 _POSIX_REALTIME_SIGNALS
 189 .sp
 190 The implementation supports the Realtime Signals Extension option.
 191 If this symbol has a value other than -1 or 0, it shall have the
 192 value 200112L.
 193 .TP 7
 194 _POSIX_REGEXP
 195 The implementation supports the Regular Expression Handling option.
 196 This symbol shall always be set to a value greater than
 197 zero.
 198 .TP 7
 199 _POSIX_SAVED_IDS
 200 Each process has a saved set-user-ID and a saved set-group-ID. This
 201 symbol shall always be set to a value greater than zero.
 202 .TP 7
 203 _POSIX_SEMAPHORES
 204 .sp
 205 The implementation supports the Semaphores option. If this symbol
 206 has a value other than -1 or 0, it shall have the value 200112L.
 207 .TP 7
 208 _POSIX_SHARED_MEMORY_OBJECTS
 209 .sp
 210 The implementation supports the Shared Memory Objects option. If this
 211 symbol has a value other than -1 or 0, it shall have the
 212 value 200112L.
 213 .TP 7
 214 _POSIX_SHELL
 215 The implementation supports the POSIX shell. This symbol shall always
 216 be set to a value greater than zero.
 217 .TP 7
 218 _POSIX_SPAWN
 219 .sp
 220 The implementation supports the Spawn option. If this symbol has a
 221 value other than -1 or 0, it shall have the value 200112L.
 222 .TP 7
 223 _POSIX_SPIN_LOCKS
 224 .sp
 225 The implementation supports the Spin Locks option. If this symbol
 226 has a value other than -1 or 0, it shall have the value 200112L.
 227 .TP 7
 228 _POSIX_SPORADIC_SERVER
 229 .sp
 230 The implementation supports the Process Sporadic Server option. If
 231 this symbol has a value other than -1 or 0, it shall have the
 232 value 200112L.
 233 .TP 7
 234 _POSIX_SYNCHRONIZED_IO
 235 .sp
 236 The implementation supports the Synchronized Input and Output option.
 237 If this symbol has a value other than -1 or 0, it shall have
 238 the value 200112L.
 239 .TP 7
 240 _POSIX_THREAD_ATTR_STACKADDR
 241 .sp
 242 The implementation supports the Thread Stack Address Attribute option.
 243 If this symbol has a value other than -1 or 0, it shall have
 244 the value 200112L.
 245 .TP 7
 246 _POSIX_THREAD_ATTR_STACKSIZE
 247 .sp
 248 The implementation supports the Thread Stack Size Attribute option.
 249 If this symbol has a value other than -1 or 0, it shall have
 250 the value 200112L.
 251 .TP 7
 252 _POSIX_THREAD_CPUTIME
 253 .sp
 254 The implementation supports the Thread CPU-Time Clocks option. If
 255 this symbol has a value other than -1 or 0, it shall have the
 256 value 200112L.
 257 .TP 7
 258 _POSIX_THREAD_PRIO_INHERIT
 259 .sp
 260 The implementation supports the Thread Priority Inheritance option.
 261 If this symbol has a value other than -1 or 0, it shall have
 262 the value 200112L.
 263 .TP 7
 264 _POSIX_THREAD_PRIO_PROTECT
 265 .sp
 266 The implementation supports the Thread Priority Protection option.
 267 If this symbol has a value other than -1 or 0, it shall have the
 268 value 200112L.
 269 .TP 7
 270 _POSIX_THREAD_PRIORITY_SCHEDULING
 271 .sp
 272 The implementation supports the Thread Execution Scheduling option.
 273 If this symbol has a value other than -1 or 0, it shall have
 274 the value 200112L.
 275 .TP 7
 276 _POSIX_THREAD_PROCESS_SHARED
 277 .sp
 278 The implementation supports the Thread Process-Shared Synchronization
 279 option. If this symbol has a value other than -1 or 0, it
 280 shall have the value 200112L.
 281 .TP 7
 282 _POSIX_THREAD_SAFE_FUNCTIONS
 283 .sp
 284 The implementation supports the Thread-Safe Functions option. If this
 285 symbol has a value other than -1 or 0, it shall have the
 286 value 200112L.
 287 .TP 7
 288 _POSIX_THREAD_SPORADIC_SERVER
 289 .sp
 290 The implementation supports the Thread Sporadic Server option. If
 291 this symbol has a value other than -1 or 0, it shall have the
 292 value 200112L.
 293 .TP 7
 294 _POSIX_THREADS
 295 .sp
 296 The implementation supports the Threads option. If this symbol has
 297 a value other than -1 or 0, it shall have the value 200112L.
 298 .TP 7
 299 _POSIX_TIMEOUTS
 300 .sp
 301 The implementation supports the Timeouts option. If this symbol has
 302 a value other than -1 or 0, it shall have the value 200112L.
 303 .TP 7
 304 _POSIX_TIMERS
 305 .sp
 306 The implementation supports the Timers option. If this symbol has
 307 a value other than -1 or 0, it shall have the value 200112L.
 308 .TP 7
 309 _POSIX_TRACE
 310 .sp
 311 The implementation supports the Trace option. If this symbol has a
 312 value other than -1 or 0, it shall have the value 200112L.
 313 .TP 7
 314 _POSIX_TRACE_EVENT_FILTER
 315 .sp
 316 The implementation supports the Trace Event Filter option. If this
 317 symbol has a value other than -1 or 0, it shall have the value
 318 200112L.
 319 .TP 7
 320 _POSIX_TRACE_INHERIT
 321 .sp
 322 The implementation supports the Trace Inherit option. If this symbol
 323 has a value other than -1 or 0, it shall have the value
 324 200112L.
 325 .TP 7
 326 _POSIX_TRACE_LOG
 327 .sp
 328 The implementation supports the Trace Log option. If this symbol has
 329 a value other than -1 or 0, it shall have the value 200112L.
 330 .TP 7
 331 _POSIX_TYPED_MEMORY_OBJECTS
 332 .sp
 333 The implementation supports the Typed Memory Objects option. If this
 334 symbol has a value other than -1 or 0, it shall have the value
 335 200112L.
 336 .TP 7
 337 _POSIX_VDISABLE
 338 This symbol shall be defined to be the value of a character that shall
 339 disable terminal special character handling as described in
 340 \fI<termios.h>\fP . This symbol shall always be set to a value other
 341 than -1.
 342 .TP 7
 343 _POSIX2_C_BIND
 344 The implementation supports the C-Language Binding option. This symbol
 345 shall always have the value 200112L.
 346 .TP 7
 347 _POSIX2_C_DEV
 348 .sp
 349 The implementation supports the C-Language Development Utilities option.
 350 If this symbol has a value other than -1 or 0, it shall
 351 have the value 200112L.
 352 .TP 7
 353 _POSIX2_CHAR_TERM
 354 The implementation supports at least one terminal type.
 355 .TP 7
 356 _POSIX2_FORT_DEV
 357 .sp
 358 The implementation supports the FORTRAN Development Utilities option.
 359 If this symbol has a value other than -1 or 0, it shall have
 360 the value 200112L.
 361 .TP 7
 362 _POSIX2_FORT_RUN
 363 .sp
 364 The implementation supports the FORTRAN Runtime Utilities option.
 365 If this symbol has a value other than -1 or 0, it shall have the
 366 value 200112L.
 367 .TP 7
 368 _POSIX2_LOCALEDEF
 369 The implementation supports the creation of locales by the \fIlocaledef\fP
 370 utility. If
 371 this symbol has a value other than -1 or 0, it shall have the value
 372 200112L.
 373 .TP 7
 374 _POSIX2_PBS
 375 .sp
 376 The implementation supports the Batch Environment Services and Utilities
 377 option. If this symbol has a value other than -1 or 0, it
 378 shall have the value 200112L.
 379 .TP 7
 380 _POSIX2_PBS_ACCOUNTING
 381 .sp
 382 The implementation supports the Batch Accounting option. If this symbol
 383 has a value other than -1 or 0, it shall have the value
 384 200112L.
 385 .TP 7
 386 _POSIX2_PBS_CHECKPOINT
 387 .sp
 388 The implementation supports the Batch Checkpoint/Restart option. If
 389 this symbol has a value other than -1 or 0, it shall have the
 390 value 200112L.
 391 .TP 7
 392 _POSIX2_PBS_LOCATE
 393 .sp
 394 The implementation supports the Locate Batch Job Request option. If
 395 this symbol has a value other than -1 or 0, it shall have the
 396 value 200112L.
 397 .TP 7
 398 _POSIX2_PBS_MESSAGE
 399 .sp
 400 The implementation supports the Batch Job Message Request option.
 401 If this symbol has a value other than -1 or 0, it shall have the
 402 value 200112L.
 403 .TP 7
 404 _POSIX2_PBS_TRACK
 405 .sp
 406 The implementation supports the Track Batch Job Request option. If
 407 this symbol has a value other than -1 or 0, it shall have the
 408 value 200112L.
 409 .TP 7
 410 _POSIX2_SW_DEV
 411 .sp
 412 The implementation supports the Software Development Utilities option.
 413 If this symbol has a value other than -1 or 0, it shall have
 414 the value 200112L.
 415 .TP 7
 416 _POSIX2_UPE
 417 .sp
 418 The implementation supports the User Portability Utilities option.
 419 If this symbol has a value other than -1 or 0, it shall have the
 420 value 200112L.
 421 .TP 7
 422 _V6_ILP32_OFF32
 423 The implementation provides a C-language compilation environment with
 424 32-bit \fBint\fP, \fBlong\fP, \fBpointer\fP, and
 425 \fBoff_t\fP types.
 426 .TP 7
 427 _V6_ILP32_OFFBIG
 428 The implementation provides a C-language compilation environment with
 429 32-bit \fBint\fP, \fBlong\fP, and \fBpointer\fP types and
 430 an \fBoff_t\fP type using at least 64 bits.
 431 .TP 7
 432 _V6_LP64_OFF64
 433 The implementation provides a C-language compilation environment with
 434 32-bit \fBint\fP and 64-bit \fBlong\fP, \fBpointer\fP, and
 435 \fBoff_t\fP types.
 436 .TP 7
 437 _V6_LPBIG_OFFBIG
 438 The implementation provides a C-language compilation environment with
 439 an \fBint\fP type using at least 32 bits and \fBlong\fP,
 440 \fBpointer\fP, and \fBoff_t\fP types using at least 64 bits.
 441 .TP 7
 442 _XBS5_ILP32_OFF32 (\fBLEGACY\fP)
 443 .sp
 444 The implementation provides a C-language compilation environment with
 445 32-bit \fBint\fP, \fBlong\fP, \fBpointer\fP, and
 446 \fBoff_t\fP types.
 447 .TP 7
 448 _XBS5_ILP32_OFFBIG (\fBLEGACY\fP)
 449 .sp
 450 The implementation provides a C-language compilation environment with
 451 32-bit \fBint\fP, \fBlong\fP, and \fBpointer\fP types and
 452 an \fBoff_t\fP type using at least 64 bits.
 453 .TP 7
 454 _XBS5_LP64_OFF64 (\fBLEGACY\fP)
 455 .sp
 456 The implementation provides a C-language compilation environment with
 457 32-bit \fBint\fP and 64-bit \fBlong\fP, \fBpointer\fP, and
 458 \fBoff_t\fP types.
 459 .TP 7
 460 _XBS5_LPBIG_OFFBIG (\fBLEGACY\fP)
 461 .sp
 462 The implementation provides a C-language compilation environment with
 463 an \fBint\fP type using at least 32 bits and \fBlong\fP,
 464 \fBpointer\fP, and \fBoff_t\fP types using at least 64 bits.
 465 .TP 7
 466 _XOPEN_CRYPT
 467 .sp
 468 The implementation supports the X/Open Encryption Option Group.
 469 .TP 7
 470 _XOPEN_ENH_I18N
 471 The implementation supports the Issue 4, Version 2 Enhanced Internationalization
 472 Option Group. This symbol shall always be set to a
 473 value other than -1.
 474 .TP 7
 475 _XOPEN_LEGACY
 476 The implementation supports the Legacy Option Group.
 477 .TP 7
 478 _XOPEN_REALTIME
 479 The implementation supports the X/Open Realtime Option Group.
 480 .TP 7
 481 _XOPEN_REALTIME_THREADS
 482 The implementation supports the X/Open Realtime Threads Option Group.
 483 .TP 7
 484 _XOPEN_SHM
 485 The implementation supports the Issue 4, Version 2 Shared Memory Option
 486 Group. This symbol shall always be set to a value other
 487 than -1.
 488 .TP 7
 489 _XOPEN_STREAMS
 490 The implementation supports the XSI STREAMS Option Group.
 491 .TP 7
 492 _XOPEN_UNIX
 493 .sp
 494 The implementation supports the XSI extension.
 495 .sp
 496 .SS Execution-Time Symbolic Constants
 497 .LP
 498 If any of the following constants are not defined in the \fI<unistd.h>\fP
 499 header, the value shall vary depending on the
 500 file to which it is applied.
 501 .LP
 502 If any of the following constants are defined to have value -1 in
 503 the \fI<unistd.h>\fP header, the implementation shall
 504 not provide the option on any file; if any are defined to have a value
 505 other than -1 in the \fI<unistd.h>\fP header, the
 506 implementation shall provide the option on all applicable files.
 507 .LP
 508 All of the following constants, whether defined in \fI<unistd.h>\fP
 509 or not, may be queried with respect to a specific
 510 file using the \fIpathconf\fP() or \fIfpathconf\fP() functions:
 511 .TP 7
 512 _POSIX_ASYNC_IO
 513 Asynchronous input or output operations may be performed for the associated
 514 file.
 515 .TP 7
 516 _POSIX_PRIO_IO
 517 Prioritized input or output operations may be performed for the associated
 518 file.
 519 .TP 7
 520 _POSIX_SYNC_IO
 521 Synchronized input or output operations may be performed for the associated
 522 file.
 523 .sp
 524 .SS Constants for Functions
 525 .LP
 526 The following symbolic constant shall be defined:
 527 .TP 7
 528 NULL
 529 Null pointer
 530 .sp
 531 .LP
 532 The following symbolic constants shall be defined for the \fIaccess\fP()
 533 function:
 534 .TP 7
 535 F_OK
 536 Test for existence of file.
 537 .TP 7
 538 R_OK
 539 Test for read permission.
 540 .TP 7
 541 W_OK
 542 Test for write permission.
 543 .TP 7
 544 X_OK
 545 Test for execute (search) permission.
 546 .sp
 547 .LP
 548 The constants F_OK, R_OK, W_OK, and X_OK and the expressions \fIR_OK\fP|\fIW_OK\fP,
 549 \fIR_OK\fP|\fIX_OK\fP, and
 550 \fIR_OK\fP|\fIW_OK\fP|\fIX_OK\fP shall all have distinct values.
 551 .LP
 552 The following symbolic constants shall be defined for the \fIconfstr\fP()
 553 function:
 554 .TP 7
 555 _CS_PATH
 556 This is the value for the \fIPATH\fP environment variable that finds
 557 all standard utilities.
 558 .TP 7
 559 _CS_POSIX_V6_ILP32_OFF32_CFLAGS
 560 If \fIsysconf\fP(_SC_V6_ILP32_OFF32) returns -1, the meaning of this
 561 value is unspecified. Otherwise, this value is the set of
 562 initial options to be given to the \fIc99\fP utility to build an application
 563 using a
 564 programming model with 32-bit \fBint\fP, \fBlong\fP, \fBpointer\fP,
 565 and \fBoff_t\fP types.
 566 .TP 7
 567 _CS_POSIX_V6_ILP32_OFF32_LDFLAGS
 568 If \fIsysconf\fP(_SC_V6_ILP32_OFF32) returns -1, the meaning of this
 569 value is unspecified. Otherwise, this value is the set of
 570 final options to be given to the \fIc99\fP utility to build an application
 571 using a programming
 572 model with 32-bit \fBint\fP, \fBlong\fP, \fBpointer\fP, and \fBoff_t\fP
 573 types.
 574 .TP 7
 575 _CS_POSIX_V6_ILP32_OFF32_LIBS
 576 If \fIsysconf\fP(_SC_V6_ILP32_OFF32) returns -1, the meaning of this
 577 value is unspecified. Otherwise, this value is the set of
 578 libraries to be given to the \fIc99\fP utility to build an application
 579 using a programming
 580 model with 32-bit \fBint\fP, \fBlong\fP, \fBpointer\fP, and \fBoff_t\fP
 581 types.
 582 .TP 7
 583 _CS_POSIX_V6_ILP32_OFFBIG_CFLAGS
 584 If \fIsysconf\fP(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this
 585 value is unspecified. Otherwise, this value is the set of
 586 initial options to be given to the \fIc99\fP utility to build an application
 587 using a
 588 programming model with 32-bit \fBint\fP, \fBlong\fP, and \fBpointer\fP
 589 types, and an \fBoff_t\fP type using at least 64
 590 bits.
 591 .TP 7
 592 _CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS
 593 If \fIsysconf\fP(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this
 594 value is unspecified. Otherwise, this value is the set of
 595 final options to be given to the \fIc99\fP utility to build an application
 596 using a programming
 597 model with 32-bit \fBint\fP, \fBlong\fP, and \fBpointer\fP types,
 598 and an \fBoff_t\fP type using at least 64 bits.
 599 .TP 7
 600 _CS_POSIX_V6_ILP32_OFFBIG_LIBS
 601 If \fIsysconf\fP(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this
 602 value is unspecified. Otherwise, this value is the set of
 603 libraries to be given to the \fIc99\fP utility to build an application
 604 using a programming
 605 model with 32-bit \fBint\fP, \fBlong\fP, and \fBpointer\fP types,
 606 and an \fBoff_t\fP type using at least 64 bits.
 607 .TP 7
 608 _CS_POSIX_V6_LP64_OFF64_CFLAGS
 609 If \fIsysconf\fP(_SC_V6_LP64_OFF64) returns -1, the meaning of this
 610 value is unspecified. Otherwise, this value is the set of
 611 initial options to be given to the \fIc99\fP utility to build an application
 612 using a
 613 programming model with 32-bit \fBint\fP and 64-bit \fBlong\fP, \fBpointer\fP,
 614 and \fBoff_t\fP types.
 615 .TP 7
 616 _CS_POSIX_V6_LP64_OFF64_LDFLAGS
 617 If \fIsysconf\fP(_SC_V6_LP64_OFF64) returns -1, the meaning of this
 618 value is unspecified. Otherwise, this value is the set of
 619 final options to be given to the \fIc99\fP utility to build an application
 620 using a programming
 621 model with 32-bit \fBint\fP and 64-bit \fBlong\fP, \fBpointer\fP,
 622 and \fBoff_t\fP types.
 623 .TP 7
 624 _CS_POSIX_V6_LP64_OFF64_LIBS
 625 If \fIsysconf\fP(_SC_V6_LP64_OFF64) returns -1, the meaning of this
 626 value is unspecified. Otherwise, this value is the set of
 627 libraries to be given to the \fIc99\fP utility to build an application
 628 using a programming
 629 model with 32-bit \fBint\fP and 64-bit \fBlong\fP, \fBpointer\fP,
 630 and \fBoff_t\fP types.
 631 .TP 7
 632 _CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS
 633 If \fIsysconf\fP(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this
 634 value is unspecified. Otherwise, this value is the set of
 635 initial options to be given to the \fIc99\fP utility to build an application
 636 using a
 637 programming model with an \fBint\fP type using at least 32 bits and
 638 \fBlong\fP, \fBpointer\fP, and \fBoff_t\fP types using at
 639 least 64 bits.
 640 .TP 7
 641 _CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS
 642 If \fIsysconf\fP(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this
 643 value is unspecified. Otherwise, this value is the set of
 644 final options to be given to the \fIc99\fP utility to build an application
 645 using a programming
 646 model with an \fBint\fP type using at least 32 bits and \fBlong\fP,
 647 \fBpointer\fP, and \fBoff_t\fP types using at least 64
 648 bits.
 649 .TP 7
 650 _CS_POSIX_V6_LPBIG_OFFBIG_LIBS
 651 If \fIsysconf\fP(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this
 652 value is unspecified. Otherwise, this value is the set of
 653 libraries to be given to the \fIc99\fP utility to build an application
 654 using a programming
 655 model with an \fBint\fP type using at least 32 bits and \fBlong\fP,
 656 \fBpointer\fP, and \fBoff_t\fP types using at least 64
 657 bits.
 658 .TP 7
 659 _CS_POSIX_V6_WIDTH_RESTRICTED_ENVS
 660 This value is a <newline>-separated list of names of programming environments
 661 supported by the implementation in which the
 662 widths of the \fBblksize_t\fP, \fBcc_t\fP, \fBmode_t\fP, \fBnfds_t\fP,
 663 \fBpid_t\fP, \fBptrdiff_t\fP, \fBsize_t\fP,
 664 \fBspeed_t\fP, \fBssize_t\fP, \fBsuseconds_t\fP, \fBtcflag_t\fP, \fBuseconds_t\fP,
 665 \fBwchar_t\fP, and \fBwint_t\fP types are
 666 no greater than the width of type \fBlong\fP.
 667 .sp
 668 .LP
 669 The following symbolic constants are reserved for compatibility with
 670 Issue 5:
 671 .LP
 672 .sp
 673 _CS_XBS5_ILP32_OFF32_CFLAGS (\fBLEGACY\fP)
 674 .br
 675 _CS_XBS5_ILP32_OFF32_LDFLAGS (\fBLEGACY\fP)
 676 .br
 677 _CS_XBS5_ILP32_OFF32_LIBS (\fBLEGACY\fP)
 678 .br
 679 _CS_XBS5_ILP32_OFF32_LINTFLAGS (\fBLEGACY\fP)
 680 .br
 681 _CS_XBS5_ILP32_OFFBIG_CFLAGS (\fBLEGACY\fP)
 682 .br
 683 _CS_XBS5_ILP32_OFFBIG_LDFLAGS (\fBLEGACY\fP)
 684 .br
 685 _CS_XBS5_ILP32_OFFBIG_LIBS (\fBLEGACY\fP)
 686 .br
 687 _CS_XBS5_ILP32_OFFBIG_LINTFLAGS (\fBLEGACY\fP)
 688 .br
 689 _CS_XBS5_LP64_OFF64_CFLAGS (\fBLEGACY\fP)
 690 .br
 691 _CS_XBS5_LP64_OFF64_LDFLAGS (\fBLEGACY\fP)
 692 .br
 693 _CS_XBS5_LP64_OFF64_LIBS (\fBLEGACY\fP)
 694 .br
 695 _CS_XBS5_LP64_OFF64_LINTFLAGS (\fBLEGACY\fP)
 696 .br
 697 _CS_XBS5_LPBIG_OFFBIG_CFLAGS (\fBLEGACY\fP)
 698 .br
 699 _CS_XBS5_LPBIG_OFFBIG_LDFLAGS (\fBLEGACY\fP)
 700 .br
 701 _CS_XBS5_LPBIG_OFFBIG_LIBS (\fBLEGACY\fP)
 702 .br
 703 _CS_XBS5_LPBIG_OFFBIG_LINTFLAGS (\fBLEGACY\fP)
 704 .br
 705 .sp
 706 .LP
 707 The following symbolic constants shall be defined for the \fIlseek\fP()
 708 and \fIfcntl\fP() functions and shall have distinct values:
 709 .TP 7
 710 SEEK_CUR
 711 Set file offset to current plus \fIoffset\fP.
 712 .TP 7
 713 SEEK_END
 714 Set file offset to EOF plus \fIoffset\fP.
 715 .TP 7
 716 SEEK_SET
 717 Set file offset to \fIoffset\fP.
 718 .sp
 719 .LP
 720 The following symbolic constants shall be defined as possible values
 721 for the \fIfunction\fP argument to the \fIlockf\fP() function:
 722 .TP 7
 723 F_LOCK
 724 Lock a section for exclusive use.
 725 .TP 7
 726 F_TEST
 727 Test section for locks by other processes.
 728 .TP 7
 729 F_TLOCK
 730 Test and lock a section for exclusive use.
 731 .TP 7
 732 F_ULOCK
 733 Unlock locked sections.
 734 .sp
 735 .LP
 736 The following symbolic constants shall be defined for \fIpathconf\fP():
 737 .LP
 738 .sp
 739 _PC_ALLOC_SIZE_MIN
 740 .br
 741 _PC_ASYNC_IO
 742 .br
 743 _PC_CHOWN_RESTRICTED
 744 .br
 745 _PC_FILESIZEBITS
 746 .br
 747 _PC_LINK_MAX
 748 .br
 749 _PC_MAX_CANON
 750 .br
 751 _PC_MAX_INPUT
 752 .br
 753 _PC_NAME_MAX
 754 .br
 755 _PC_NO_TRUNC
 756 .br
 757 _PC_PATH_MAX
 758 .br
 759 _PC_PIPE_BUF
 760 .br
 761 _PC_PRIO_IO
 762 .br
 763 _PC_REC_INCR_XFER_SIZE
 764 .br
 765 _PC_REC_MIN_XFER_SIZE
 766 .br
 767 _PC_REC_XFER_ALIGN
 768 .br
 769 _PC_SYMLINK_MAX
 770 .br
 771 _PC_SYNC_IO
 772 .br
 773 _PC_VDISABLE
 774 .br
 775 .LP
 776 The following symbolic constants shall be defined for \fIsysconf\fP():
 777 .LP
 778 .sp
 779 _SC_2_C_BIND
 780 .br
 781 _SC_2_C_DEV
 782 .br
 783 _SC_2_C_VERSION
 784 .br
 785 _SC_2_CHAR_TERM
 786 .br
 787 _SC_2_FORT_DEV
 788 .br
 789 _SC_2_FORT_RUN
 790 .br
 791 _SC_2_LOCALEDEF
 792 .br
 793 _SC_2_PBS
 794 .br
 795 _SC_2_PBS_ACCOUNTING
 796 .br
 797 _SC_2_PBS_CHECKPOINT
 798 .br
 799 _SC_2_PBS_LOCATE
 800 .br
 801 _SC_2_PBS_MESSAGE
 802 .br
 803 _SC_2_PBS_TRACK
 804 .br
 805 _SC_2_SW_DEV
 806 .br
 807 _SC_2_UPE
 808 .br
 809 _SC_2_VERSION
 810 .br
 811 _SC_ADVISORY_INFO
 812 .br
 813 _SC_ARG_MAX
 814 .br
 815 _SC_AIO_LISTIO_MAX
 816 .br
 817 _SC_AIO_MAX
 818 .br
 819 _SC_AIO_PRIO_DELTA_MAX
 820 .br
 821 _SC_ASYNCHRONOUS_IO
 822 .br
 823 _SC_ATEXIT_MAX
 824 .br
 825 _SC_BARRIERS
 826 .br
 827 _SC_BC_BASE_MAX
 828 .br
 829 _SC_BC_DIM_MAX
 830 .br
 831 _SC_BC_SCALE_MAX
 832 .br
 833 _SC_BC_STRING_MAX
 834 .br
 835 _SC_CHILD_MAX
 836 .br
 837 _SC_CLK_TCK
 838 .br
 839 _SC_CLOCK_SELECTION
 840 .br
 841 _SC_COLL_WEIGHTS_MAX
 842 .br
 843 _SC_CPUTIME
 844 .br
 845 _SC_DELAYTIMER_MAX
 846 .br
 847 _SC_EXPR_NEST_MAX
 848 .br
 849 _SC_FILE_LOCKING
 850 .br
 851 _SC_FSYNC
 852 .br
 853 _SC_GETGR_R_SIZE_MAX
 854 .br
 855 _SC_GETPW_R_SIZE_MAX
 856 .br
 857 _SC_HOST_NAME_MAX
 858 .br
 859 _SC_IOV_MAX
 860 .br
 861 _SC_IPV6
 862 .br
 863 _SC_JOB_CONTROL
 864 .br
 865 _SC_LINE_MAX
 866 .br
 867 _SC_LOGIN_NAME_MAX
 868 .br
 869 _SC_MAPPED_FILES
 870 .br
 871 _SC_MEMLOCK
 872 .br
 873 _SC_MEMLOCK_RANGE
 874 .br
 875 _SC_MEMORY_PROTECTION
 876 .br
 877 _SC_MESSAGE_PASSING
 878 .br
 879 _SC_MONOTONIC_CLOCK
 880 .br
 881 _SC_MQ_OPEN_MAX
 882 .br
 883 _SC_MQ_PRIO_MAX
 884 .br
 885 _SC_NGROUPS_MAX
 886 .br
 887 _SC_OPEN_MAX
 888 .br
 889 _SC_PAGE_SIZE
 890 .br
 891 _SC_PAGESIZE
 892 .br
 893 _SC_PRIORITIZED_IO
 894 .br
 895 _SC_PRIORITY_SCHEDULING
 896 .br
 897 _SC_RAW_SOCKETS
 898 .br
 899 _SC_RE_DUP_MAX
 900 .br
 901 _SC_READER_WRITER_LOCKS
 902 .br
 903 _SC_REALTIME_SIGNALS
 904 .br
 905 _SC_REGEXP
 906 .br
 907 _SC_RTSIG_MAX
 908 .br
 909 _SC_SAVED_IDS
 910 .br
 911 _SC_SEMAPHORES
 912 .br
 913 _SC_SEM_NSEMS_MAX
 914 .br
 915 _SC_SEM_VALUE_MAX
 916 .br
 917 _SC_SHARED_MEMORY_OBJECTS
 918 .br
 919 _SC_SHELL
 920 .br
 921 _SC_SIGQUEUE_MAX
 922 .br
 923 _SC_SPAWN
 924 .br
 925 _SC_SPIN_LOCKS
 926 .br
 927 _SC_SPORADIC_SERVER
 928 .br
 929 _SC_STREAM_MAX
 930 .br
 931 _SC_SYMLOOP_MAX
 932 .br
 933 _SC_SYNCHRONIZED_IO
 934 .br
 935 _SC_THREAD_ATTR_STACKADDR
 936 .br
 937 _SC_THREAD_ATTR_STACKSIZE
 938 .br
 939 _SC_THREAD_CPUTIME
 940 .br
 941 _SC_THREAD_DESTRUCTOR_ITERATIONS
 942 .br
 943 _SC_THREAD_KEYS_MAX
 944 .br
 945 _SC_THREAD_PRIO_INHERIT
 946 .br
 947 _SC_THREAD_PRIO_PROTECT
 948 .br
 949 _SC_THREAD_PRIORITY_SCHEDULING
 950 .br
 951 _SC_THREAD_PROCESS_SHARED
 952 .br
 953 _SC_THREAD_SAFE_FUNCTIONS
 954 .br
 955 _SC_THREAD_SPORADIC_SERVER
 956 .br
 957 _SC_THREAD_STACK_MIN
 958 .br
 959 _SC_THREAD_THREADS_MAX
 960 .br
 961 _SC_TIMEOUTS
 962 .br
 963 _SC_THREADS
 964 .br
 965 _SC_TIMER_MAX
 966 .br
 967 _SC_TIMERS
 968 .br
 969 _SC_TRACE
 970 .br
 971 _SC_TRACE_EVENT_FILTER
 972 .br
 973 _SC_TRACE_INHERIT
 974 .br
 975 _SC_TRACE_LOG
 976 .br
 977 _SC_TTY_NAME_MAX
 978 .br
 979 _SC_TYPED_MEMORY_OBJECTS
 980 .br
 981 _SC_TZNAME_MAX
 982 .br
 983 _SC_V6_ILP32_OFF32
 984 .br
 985 _SC_V6_ILP32_OFFBIG
 986 .br
 987 _SC_V6_LP64_OFF64
 988 .br
 989 _SC_V6_LPBIG_OFFBIG
 990 .br
 991 _SC_VERSION
 992 .br
 993 _SC_XBS5_ILP32_OFF32 (\fBLEGACY\fP)
 994 .br
 995 _SC_XBS5_ILP32_OFFBIG (\fBLEGACY\fP)
 996 .br
 997 _SC_XBS5_LP64_OFF64 (\fBLEGACY\fP)
 998 .br
 999 _SC_XBS5_LPBIG_OFFBIG (\fBLEGACY\fP)
1000 .br
1001 _SC_XOPEN_CRYPT
1002 .br
1003 _SC_XOPEN_ENH_I18N
1004 .br
1005 _SC_XOPEN_LEGACY
1006 .br
1007 _SC_XOPEN_REALTIME
1008 .br
1009 _SC_XOPEN_REALTIME_THREADS
1010 .br
1011 _SC_XOPEN_SHM
1012 .br
1013 _SC_XOPEN_STREAMS
1014 .br
1015 _SC_XOPEN_UNIX
1016 .br
1017 _SC_XOPEN_VERSION
1018 .br
1019 _SC_XOPEN_XCU_VERSION
1020 .br
1021 .LP
1022 The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to
1023 have the same value.
1024 .LP
1025 The following symbolic constants shall be defined for file streams:
1026 .TP 7
1027 STDERR_FILENO
1028 File number of \fIstderr\fP; 2.
1029 .TP 7
1030 STDIN_FILENO
1031 File number of \fIstdin\fP; 0.
1032 .TP 7
1033 STDOUT_FILENO
1034 File number of \fIstdout\fP; 1.
1035 .sp
1036 .SS Type Definitions
1037 .LP
1038 The \fBsize_t\fP, \fBssize_t\fP, \fBuid_t\fP, \fBgid_t\fP, \fBoff_t\fP,
1039 \fBpid_t\fP, and \fBuseconds_t\fP types shall be
1040 defined as described in \fI<sys/types.h>\fP.
1041 .LP
1042 The \fBintptr_t\fP type shall be defined as described in \fI<inttypes.h>\fP.
1043 .SS Declarations
1044 .LP
1045 The following shall be declared as functions and may also be defined
1046 as macros. Function prototypes shall be provided.
1047 .sp
1048 .RS
1049 .nf
1050
1051 \fBint          access(const char *, int);
1052 unsigned     alarm(unsigned);
1053 int          chdir(const char *);
1054 int          chown(const char *, uid_t, gid_t);
1055 int          close(int);
1056 size_t       confstr(int, char *, size_t);
1057 .sp
1058
1059
1060 char        *crypt(const char *, const char *);
1061 char        *ctermid(char *);
1062
1063 int          dup(int);
1064 .sp
1065
1066 int          dup2(int, int);
1067
1068 void         encrypt(char[64], int);
1069
1070 int          execl(const char *, const char *, ...);
1071 int          execle(const char *, const char *, ...);
1072 int          execlp(const char *, const char *, ...);
1073 int          execv(const char *, char *const []);
1074 int          execve(const char *, char *const [], char *const []);
1075 int          execvp(const char *, char *const []);
1076 void        _exit(int);
1077 int          fchown(int, uid_t, gid_t);
1078
1079 int          fchdir(int);
1080
1081
1082 int          fdatasync(int);
1083
1084 pid_t        fork(void);
1085 long         fpathconf(int, int);
1086
1087 int          fsync(int);
1088
1089 int          ftruncate(int, off_t);
1090 char        *getcwd(char *, size_t);
1091 gid_t        getegid(void);
1092 uid_t        geteuid(void);
1093 gid_t        getgid(void);
1094 int          getgroups(int, gid_t []);
1095
1096 long         gethostid(void);
1097
1098 int          gethostname(char *, size_t);
1099 char        *getlogin(void);
1100 int          getlogin_r(char *, size_t);
1101 int          getopt(int, char * const [], const char *);
1102
1103 pid_t        getpgid(pid_t);
1104
1105 pid_t        getpgrp(void);
1106 pid_t        getpid(void);
1107 pid_t        getppid(void);
1108
1109 pid_t        getsid(pid_t);
1110
1111 uid_t        getuid(void);
1112
1113 char        *getwd(char *); (\fP\fBLEGACY\fP \fB)
1114
1115 int          isatty(int);
1116
1117 int          lchown(const char *, uid_t, gid_t);
1118
1119 int          link(const char *, const char *);
1120
1121 int          lockf(int, int, off_t);
1122
1123 off_t        lseek(int, off_t, int);
1124
1125 int          nice(int);
1126
1127 long         pathconf(const char *, int);
1128 int          pause(void);
1129 int          pipe(int [2]);
1130
1131 ssize_t      pread(int, void *, size_t, off_t);
1132 ssize_t      pwrite(int, const void *, size_t, off_t);
1133
1134 ssize_t      read(int, void *, size_t);
1135 ssize_t      readlink(const char *restrict, char *restrict, size_t);
1136 int          rmdir(const char *);
1137 int          setegid(gid_t);
1138 int          seteuid(uid_t);
1139 int          setgid(gid_t);
1140 .sp
1141
1142 int          setpgid(pid_t, pid_t);
1143
1144 pid_t        setpgrp(void);
1145 int          setregid(gid_t, gid_t);
1146 int          setreuid(uid_t, uid_t);
1147
1148 pid_t        setsid(void);
1149 int          setuid(uid_t);
1150 unsigned     sleep(unsigned);
1151
1152 void         swab(const void *restrict, void *restrict, ssize_t);
1153 int          symlink(const char *, const char *);
1154 void         sync(void);
1155
1156 long         sysconf(int);
1157 pid_t        tcgetpgrp(int);
1158 int          tcsetpgrp(int, pid_t);
1159
1160 int          truncate(const char *, off_t);
1161
1162 char        *ttyname(int);
1163 int          ttyname_r(int, char *, size_t);
1164
1165 useconds_t   ualarm(useconds_t, useconds_t);
1166
1167 int          unlink(const char *);
1168
1169 int          usleep(useconds_t);
1170 pid_t        vfork(void);
1171
1172 ssize_t      write(int, const void *, size_t);
1173 \fP
1174 .fi
1175 .RE
1176 .LP
1177 Implementations may also include the \fIpthread_atfork\fP() prototype
1178 as defined
1179 in \fI<pthread.h>\fP .
1180 .LP
1181 The following external variables shall be declared:
1182 .sp
1183 .RS
1184 .nf
1185
1186 \fBextern char  *optarg;
1187 extern int    optind, opterr, optopt;
1188 \fP
1189 .fi
1190 .RE
1191 .LP
1192 \fIThe following sections are informative.\fP
1193 .SH APPLICATION USAGE
1194 .LP
1195 IEEE\ Std\ 1003.1-2001 only describes the behavior of systems that
1196 claim conformance to it. However, application
1197 developers who want to write applications that adapt to other versions
1198 of IEEE\ Std\ 1003.1 (or to systems that do not
1199 conform to any POSIX standard) may find it useful to code them so
1200 as to conditionally compile different code depending on the value
1201 of _POSIX_VERSION, for example:
1202 .sp
1203 .RS
1204 .nf
1205
1206 \fB#if _POSIX_VERSION >= 200112L
1207 /* Use the newer function that copes with large files. */
1208 off_t pos=ftello(fp);
1209 #else
1210 /* Either this is an old version of POSIX, or _POSIX_VERSION is
1211    not even defined, so use the traditional function. */
1212 long pos=ftell(fp);
1213 #endif
1214 \fP
1215 .fi
1216 .RE
1217 .LP
1218 Earlier versions of IEEE\ Std\ 1003.1 and of the Single UNIX Specification
1219 can be identified by the following
1220 macros:
1221 .TP 7
1222 POSIX.1-1988 standard
1223 _POSIX_VERSION==198808L
1224 .TP 7
1225 POSIX.1-1990 standard
1226 _POSIX_VERSION==199009L
1227 .TP 7
1228 ISO\ POSIX-1:1996 standard
1229 _POSIX_VERSION==199506L
1230 .TP 7
1231 Single UNIX Specification, Version 1
1232 _XOPEN_UNIX and _XOPEN_VERSION==4
1233 .TP 7
1234 Single UNIX Specification, Version 2
1235 _XOPEN_UNIX and _XOPEN_VERSION==500
1236 .sp
1237 .LP
1238 IEEE\ Std\ 1003.1-2001 does not make any attempt to define application
1239 binary interaction with the underlying operating
1240 system. However, application developers may find it useful to query
1241 _SC_VERSION at runtime via \fIsysconf\fP() to determine whether the
1242 current version of the operating system supports the
1243 necessary functionality as in the following program fragment:
1244 .sp
1245 .RS
1246 .nf
1247
1248 \fBif (sysconf(_SC_VERSION) < 200112L) {
1249     fprintf(stderr, "POSIX.1-2001 system required, terminating \\n");
1250     exit(1);
1251 }
1252 \fP
1253 .fi
1254 .RE
1255 .LP
1256 New applications should not use _XOPEN_SHM or _XOPEN_ENH_I18N.
1257 .SH RATIONALE
1258 .LP
1259 As IEEE\ Std\ 1003.1-2001 evolved, certain options became sufficiently
1260 standardized that it was concluded that simply
1261 requiring one of the option choices was simpler than retaining the
1262 option. However, for backwards-compatibility, the option flags
1263 (with required constant values) are retained.
1264 .SS Version Test Macros
1265 .LP
1266 The standard developers considered altering the definition of _POSIX_VERSION
1267 and removing _SC_VERSION from the specification of
1268 \fIsysconf\fP() since the utility to an application was deemed by
1269 some to be minimal, and
1270 since the implementation of the functionality is potentially problematic.
1271 However, they recognized that support for existing
1272 application binaries is a concern to manufacturers, application developers,
1273 and the users of implementations conforming to
1274 IEEE\ Std\ 1003.1-2001.
1275 .LP
1276 While the example using _SC_VERSION in the APPLICATION USAGE section
1277 does not provide the greatest degree of imaginable utility
1278 to the application developer or user, it is arguably better than a
1279 \fBcore\fP file or some other equally obscure result. (It is
1280 also possible for implementations to encode and recognize application
1281 binaries compiled in various POSIX.1-conforming environments,
1282 and modify the semantics of the underlying system to conform to the
1283 expectations of the application.) For the reasons outlined in
1284 the preceding paragraphs and in the APPLICATION USAGE section, the
1285 standard developers elected to retain the _POSIX_VERSION and
1286 _SC_VERSION functionality.
1287 .SS Compile-Time Symbolic Constants for System-Wide Options
1288 .LP
1289 IEEE\ Std\ 1003.1-2001 now includes support in certain areas for the
1290 newly adopted policy governing options and
1291 stubs.
1292 .LP
1293 This policy provides flexibility for implementations in how they support
1294 options. It also specifies how conforming applications
1295 can adapt to different implementations that support different sets
1296 of options. It allows the following:
1297 .IP " 1." 4
1298 If an implementation has no interest in supporting an option, it does
1299 not have to provide anything associated with that option
1300 beyond the announcement that it does not support it.
1301 .LP
1302 .IP " 2." 4
1303 An implementation can support a partial or incompatible version of
1304 an option (as a non-standard extension) as long as it does
1305 not claim to support the option.
1306 .LP
1307 .IP " 3." 4
1308 An application can determine whether the option is supported. A strictly
1309 conforming application must check this announcement
1310 mechanism before first using anything associated with the option.
1311 .LP
1312 .LP
1313 There is an important implication of this policy. IEEE\ Std\ 1003.1-2001
1314 cannot dictate the behavior of interfaces
1315 associated with an option when the implementation does not claim to
1316 support the option. In particular, it cannot require that a
1317 function associated with an unsupported option will fail if it does
1318 not perform as specified. However, this policy does not prevent
1319 a standard from requiring certain functions to always be present,
1320 but that they shall always fail on some implementations. The \fIsetpgid\fP()
1321 function in the POSIX.1-1990 standard, for example, is considered
1322 appropriate.
1323 .LP
1324 The POSIX standards include various options, and the C-language binding
1325 support for an option implies that the implementation
1326 must supply data types and function interfaces. An application must
1327 be able to discover whether the implementation supports each
1328 option.
1329 .LP
1330 Any application must consider the following three cases for each option:
1331 .IP " 1." 4
1332 Option never supported.
1333 .LP
1334 The implementation advertises at compile time that the option will
1335 never be supported. In this case, it is not necessary for the
1336 implementation to supply any of the data types or function interfaces
1337 that are provided only as part of the option. The
1338 implementation might provide data types and functions that are similar
1339 to those defined by IEEE\ Std\ 1003.1-2001, but
1340 there is no guarantee for any particular behavior.
1341 .LP
1342 .IP " 2." 4
1343 Option always supported.
1344 .LP
1345 The implementation advertises at compile time that the option will
1346 always be supported. In this case, all data types and
1347 function interfaces shall be available and shall operate as specified.
1348 .LP
1349 .IP " 3." 4
1350 Option might or might not be supported.
1351 .LP
1352 Some implementations might not provide a mechanism to specify support
1353 of options at compile time. In addition, the
1354 implementation might be unable or unwilling to specify support or
1355 non-support at compile time. In either case, any application that
1356 might use the option at runtime must be able to compile and execute.
1357 The implementation must provide, at compile time, all data
1358 types and function interfaces that are necessary to allow this. In
1359 this situation, there must be a mechanism that allows the
1360 application to query, at runtime, whether the option is supported.
1361 If the application attempts to use the option when it is not
1362 supported, the result is unspecified unless explicitly specified otherwise
1363 in IEEE\ Std\ 1003.1-2001.
1364 .LP
1365 .SH FUTURE DIRECTIONS
1366 .LP
1367 None.
1368 .SH SEE ALSO
1369 .LP
1370 \fI<inttypes.h>\fP , \fI<limits.h>\fP , \fI<sys/socket.h>\fP , \fI<sys/types.h>\fP
1371 , \fI<termios.h>\fP , \fI<wctype.h>\fP , the System Interfaces volume
1372 of IEEE\ Std\ 1003.1-2001, \fIaccess\fP(), \fIalarm\fP(), \fIchdir\fP(),
1373 \fIchown\fP(), \fIclose\fP(), \fIcrypt\fP(), \fIctermid\fP(), \fIdup\fP(),
1374 \fIencrypt\fP(), \fIenviron\fP, \fIexec\fP, \fIexit\fP(), \fIfchdir\fP(),
1375 \fIfchown\fP(), \fIfcntl\fP(), \fIfork\fP(), \fIfpathconf\fP(), \fIfsync\fP(),
1376 \fIftruncate\fP(), \fIgetcwd\fP(), \fIgetegid\fP(), \fIgeteuid\fP(),
1377 \fIgetgid\fP(), \fIgetgroups\fP(), \fIgethostid\fP(), \fIgethostname\fP(),
1378 \fIgetlogin\fP(), \fIgetpgid\fP(), \fIgetpgrp\fP(), \fIgetpid\fP(),
1379 \fIgetppid\fP(), \fIgetsid\fP(), \fIgetuid\fP(), \fIisatty\fP(), \fIlchown\fP(),
1380 \fIlink\fP(), \fIlockf\fP(), \fIlseek\fP(), \fInice\fP(), \fIpathconf\fP(),
1381 \fIpause\fP(), \fIpipe\fP(), \fIread\fP(), \fIreadlink\fP(), \fIrmdir\fP(),
1382 \fIsetgid\fP(), \fIsetpgid\fP(), \fIsetpgrp\fP(), \fIsetregid\fP(),
1383 \fIsetreuid\fP(), \fIsetsid\fP(), \fIsetuid\fP(), \fIsleep\fP(), \fIswab\fP(),
1384 \fIsymlink\fP(), \fIsync\fP(), \fIsysconf\fP(), \fItcgetpgrp\fP(),
1385 \fItcsetpgrp\fP(), \fItruncate\fP(), \fIttyname\fP(), \fIualarm\fP(),
1386 \fIunlink\fP(), \fIusleep\fP(), \fIvfork\fP(), \fIwrite\fP()
1387 .SH COPYRIGHT
1388 Portions of this text are reprinted and reproduced in electronic form
1389 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
1390 -- Portable Operating System Interface (POSIX), The Open Group Base
1391 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
1392 Electrical and Electronics Engineers, Inc and The Open Group. In the
1393 event of any discrepancy between this version and the original IEEE and
1394 The Open Group Standard, the original IEEE and The Open Group Standard
1395 is the referee document. The original Standard can be obtained online at
1396 http://www.opengroup.org/unix/online.html .