1limits.h(0P) POSIX Programmer's Manual limits.h(0P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 limits.h — implementation-defined constants
13
15 #include <limits.h>
16
18 Some of the functionality described on this reference page extends the
19 ISO C standard. Applications shall define the appropriate feature test
20 macro (see the System Interfaces volume of POSIX.1‐2017, Section 2.2,
21 The Compilation Environment) to enable the visibility of these symbols
22 in this header.
23 Many of the symbols listed here are not defined by the
25 ISO/IEC 9899:1999 standard. Such symbols are not shown as CX shaded,
26 except under the heading ``Numerical Limits''.
27 The <limits.h> header shall define macros and symbolic constants for
29 various limits. Different categories of limits are described below,
30 representing various limits on resources that the implementation
31 imposes on applications. All macros and symbolic constants defined in
32 this header shall be suitable for use in #if preprocessing directives.
33 Implementations may choose any appropriate value for each limit, pro‐
35 vided it is not more restrictive than the Minimum Acceptable Values
36 listed below. Symbolic constant names beginning with _POSIX may be
37 found in <unistd.h>.
38 Applications should not assume any particular value for a limit. To
40 achieve maximum portability, an application should not require more
41 resource than the Minimum Acceptable Value quantity. However, an appli‐
42 cation wishing to avail itself of the full amount of a resource avail‐
43 able on an implementation may make use of the value given in <limits.h>
44 on that particular implementation, by using the macros and symbolic
45 constants listed below. It should be noted, however, that many of the
46 listed limits are not invariant, and at runtime, the value of the limit
47 may differ from those given in this header, for the following reasons:
48 * The limit is pathname-dependent.
50 * The limit differs between the compile and runtime machines.
52 For these reasons, an application may use the fpathconf(), pathconf(),
54 and sysconf() functions to determine the actual value of a limit at
55 runtime.
56 The items in the list ending in _MIN give the most negative values that
58 the mathematical types are guaranteed to be capable of representing.
59 Numbers of a more negative value may be supported on some implementa‐
60 tions, as indicated by the <limits.h> header on the implementation, but
61 applications requiring such numbers are not guaranteed to be portable
62 to all implementations. For positive constants ending in _MIN, this
63 indicates the minimum acceptable value.
64 Runtime Invariant Values (Possibly Indeterminate)
66 A definition of one of the symbolic constants in the following list
67 shall be omitted from <limits.h> on specific implementations where the
68 corresponding value is equal to or greater than the stated minimum, but
69 is unspecified.
70 This indetermination might depend on the amount of available memory
72 space on a specific instance of a specific implementation. The actual
73 value supported by a specific instance shall be provided by the
74 sysconf() function.
75 {AIO_LISTIO_MAX}
77 Maximum number of I/O operations in a single list I/O call sup‐
78 ported by the implementation.
79 Minimum Acceptable Value: {_POSIX_AIO_LISTIO_MAX}
80 {AIO_MAX}
82 Maximum number of outstanding asynchronous I/O operations sup‐
83 ported by the implementation.
84 Minimum Acceptable Value: {_POSIX_AIO_MAX}
85 {AIO_PRIO_DELTA_MAX}
87 The maximum amount by which a process can decrease its asynchro‐
88 nous I/O priority level from its own scheduling priority.
89 Minimum Acceptable Value: 0
90 {ARG_MAX}
92 Maximum length of argument to the exec functions including envi‐
93 ronment data.
94 Minimum Acceptable Value: {_POSIX_ARG_MAX}
95 {ATEXIT_MAX}
97 Maximum number of functions that may be registered with atexit().
98 Minimum Acceptable Value: 32
99 {CHILD_MAX}
101 Maximum number of simultaneous processes per real user ID.
102 Minimum Acceptable Value: {_POSIX_CHILD_MAX}
103 {DELAYTIMER_MAX}
105 Maximum number of timer expiration overruns.
106 Minimum Acceptable Value: {_POSIX_DELAYTIMER_MAX}
107 {HOST_NAME_MAX}
109 Maximum length of a host name (not including the terminating
110 null) as returned from the gethostname() function.
111 Minimum Acceptable Value: {_POSIX_HOST_NAME_MAX}
112 {IOV_MAX}
114 Maximum number of iovec structures that one process has available
115 for use with readv() or writev().
116 Minimum Acceptable Value: {_XOPEN_IOV_MAX}
117 {LOGIN_NAME_MAX}
119 Maximum length of a login name.
120 Minimum Acceptable Value: {_POSIX_LOGIN_NAME_MAX}
121 {MQ_OPEN_MAX}
123 The maximum number of open message queue descriptors a process
124 may hold.
125 Minimum Acceptable Value: {_POSIX_MQ_OPEN_MAX}
126 {MQ_PRIO_MAX}
128 The maximum number of message priorities supported by the imple‐
129 mentation.
130 Minimum Acceptable Value: {_POSIX_MQ_PRIO_MAX}
131 {OPEN_MAX}
133 A value one greater than the maximum value that the system may
134 assign to a newly-created file descriptor.
135 Minimum Acceptable Value: {_POSIX_OPEN_MAX}
136 {PAGESIZE}
138 Size in bytes of a page.
139 Minimum Acceptable Value: 1
140 {PAGE_SIZE}
142 Equivalent to {PAGESIZE}. If either {PAGESIZE} or {PAGE_SIZE} is
143 defined, the other is defined with the same value.
144 {PTHREAD_DESTRUCTOR_ITERATIONS}
146 Maximum number of attempts made to destroy a thread's thread-spe‐
147 cific data values on thread exit.
148 Minimum Acceptable Value: {_POSIX_THREAD_DESTRUCTOR_ITERATIONS}
149 {PTHREAD_KEYS_MAX}
151 Maximum number of data keys that can be created by a process.
152 Minimum Acceptable Value: {_POSIX_THREAD_KEYS_MAX}
153 {PTHREAD_STACK_MIN}
155 Minimum size in bytes of thread stack storage.
156 Minimum Acceptable Value: 0
157 {PTHREAD_THREADS_MAX}
159 Maximum number of threads that can be created per process.
160 Minimum Acceptable Value: {_POSIX_THREAD_THREADS_MAX}
161 {RTSIG_MAX}
163 Maximum number of realtime signals reserved for application use
164 in this implementation.
165 Minimum Acceptable Value: {_POSIX_RTSIG_MAX}
166 {SEM_NSEMS_MAX}
168 Maximum number of semaphores that a process may have.
169 Minimum Acceptable Value: {_POSIX_SEM_NSEMS_MAX}
170 {SEM_VALUE_MAX}
172 The maximum value a semaphore may have.
173 Minimum Acceptable Value: {_POSIX_SEM_VALUE_MAX}
174 {SIGQUEUE_MAX}
176 Maximum number of queued signals that a process may send and have
177 pending at the receiver(s) at any time.
178 Minimum Acceptable Value: {_POSIX_SIGQUEUE_MAX}
179 {SS_REPL_MAX}
181 The maximum number of replenishment operations that may be simul‐
182 taneously pending for a particular sporadic server scheduler.
183 Minimum Acceptable Value: {_POSIX_SS_REPL_MAX}
184 {STREAM_MAX}
186 Maximum number of streams that one process can have open at one
187 time. If defined, it has the same value as {FOPEN_MAX} (see
188 <stdio.h>).
189 Minimum Acceptable Value: {_POSIX_STREAM_MAX}
190 {SYMLOOP_MAX}
192 Maximum number of symbolic links that can be reliably traversed
193 in the resolution of a pathname in the absence of a loop.
194 Minimum Acceptable Value: {_POSIX_SYMLOOP_MAX}
195 {TIMER_MAX}
197 Maximum number of timers per process supported by the implementa‐
198 tion.
199 Minimum Acceptable Value: {_POSIX_TIMER_MAX}
200 {TRACE_EVENT_NAME_MAX}
202 Maximum length of the trace event name (not including the termi‐
203 nating null).
204 Minimum Acceptable Value: {_POSIX_TRACE_EVENT_NAME_MAX}
205 {TRACE_NAME_MAX}
207 Maximum length of the trace generation version string or of the
208 trace stream name (not including the terminating null).
209 Minimum Acceptable Value: {_POSIX_TRACE_NAME_MAX}
210 {TRACE_SYS_MAX}
212 Maximum number of trace streams that may simultaneously exist in
213 the system.
214 Minimum Acceptable Value: {_POSIX_TRACE_SYS_MAX}
215 {TRACE_USER_EVENT_MAX}
217 Maximum number of user trace event type identifiers that may
218 simultaneously exist in a traced process, including the prede‐
219 fined user trace event POSIX_TRACE_UNNAMED_USER_EVENT.
220 Minimum Acceptable Value: {_POSIX_TRACE_USER_EVENT_MAX}
221 {TTY_NAME_MAX}
223 Maximum length of terminal device name.
224 Minimum Acceptable Value: {_POSIX_TTY_NAME_MAX}
225 {TZNAME_MAX}
227 Maximum number of bytes supported for the name of a timezone (not
228 of the TZ variable).
229 Minimum Acceptable Value: {_POSIX_TZNAME_MAX}
230 Note: The length given by {TZNAME_MAX} does not include the quoting
232 characters mentioned in Section 8.3, Other Environment Vari‐
233 ables.
234 Pathname Variable Values
236 The values in the following list may be constants within an implementa‐
237 tion or may vary from one pathname to another. For example, file sys‐
238 tems or directories may have different characteristics.
239 A definition of one of the symbolic constants in the following list
241 shall be omitted from the <limits.h> header on specific implementations
242 where the corresponding value is equal to or greater than the stated
243 minimum, but where the value can vary depending on the file to which it
244 is applied. The actual value supported for a specific pathname shall be
245 provided by the pathconf() function.
246 {FILESIZEBITS}
248 Minimum number of bits needed to represent, as a signed integer
249 value, the maximum size of a regular file allowed in the speci‐
250 fied directory.
251 Minimum Acceptable Value: 32
252 {LINK_MAX}
254 Maximum number of links to a single file.
255 Minimum Acceptable Value: {_POSIX_LINK_MAX}
256 {MAX_CANON}
258 Maximum number of bytes in a terminal canonical input line.
259 Minimum Acceptable Value: {_POSIX_MAX_CANON}
260 {MAX_INPUT}
262 Minimum number of bytes for which space is available in a termi‐
263 nal input queue; therefore, the maximum number of bytes a con‐
264 forming application may require to be typed as input before read‐
265 ing them.
266 Minimum Acceptable Value: {_POSIX_MAX_INPUT}
267 {NAME_MAX}
269 Maximum number of bytes in a filename (not including the termi‐
270 nating null of a filename string).
271 Minimum Acceptable Value: {_POSIX_NAME_MAX}
272 Minimum Acceptable Value: {_XOPEN_NAME_MAX}
273 {PATH_MAX}
275 Maximum number of bytes the implementation will store as a path‐
276 name in a user-supplied buffer of unspecified size, including the
277 terminating null character. Minimum number the implementation
278 will accept as the maximum number of bytes in a pathname.
279 Minimum Acceptable Value: {_POSIX_PATH_MAX}
280 Minimum Acceptable Value: {_XOPEN_PATH_MAX}
281 {PIPE_BUF}
283 Maximum number of bytes that is guaranteed to be atomic when
284 writing to a pipe.
285 Minimum Acceptable Value: {_POSIX_PIPE_BUF}
286 {POSIX_ALLOC_SIZE_MIN}
288 Minimum number of bytes of storage actually allocated for any
289 portion of a file.
290 Minimum Acceptable Value: Not specified.
291 {POSIX_REC_INCR_XFER_SIZE}
293 Recommended increment for file transfer sizes between the
294 {POSIX_REC_MIN_XFER_SIZE} and {POSIX_REC_MAX_XFER_SIZE} values.
295 Minimum Acceptable Value: Not specified.
296 {POSIX_REC_MAX_XFER_SIZE}
298 Maximum recommended file transfer size.
299 Minimum Acceptable Value: Not specified.
300 {POSIX_REC_MIN_XFER_SIZE}
302 Minimum recommended file transfer size.
303 Minimum Acceptable Value: Not specified.
304 {POSIX_REC_XFER_ALIGN}
306 Recommended file transfer buffer alignment.
307 Minimum Acceptable Value: Not specified.
308 {SYMLINK_MAX}
310 Maximum number of bytes in a symbolic link.
311 Minimum Acceptable Value: {_POSIX_SYMLINK_MAX}
312 Runtime Increasable Values
314 The magnitude limitations in the following list shall be fixed by spe‐
315 cific implementations. An application should assume that the value of
316 the symbolic constant defined by <limits.h> in a specific implementa‐
317 tion is the minimum that pertains whenever the application is run under
318 that implementation. A specific instance of a specific implementation
319 may increase the value relative to that supplied by <limits.h> for that
320 implementation. The actual value supported by a specific instance shall
321 be provided by the sysconf() function.
322 {BC_BASE_MAX}
324 Maximum obase values allowed by the bc utility.
325 Minimum Acceptable Value: {_POSIX2_BC_BASE_MAX}
326 {BC_DIM_MAX}
328 Maximum number of elements permitted in an array by the bc util‐
329 ity.
330 Minimum Acceptable Value: {_POSIX2_BC_DIM_MAX}
331 {BC_SCALE_MAX}
333 Maximum scale value allowed by the bc utility.
334 Minimum Acceptable Value: {_POSIX2_BC_SCALE_MAX}
335 {BC_STRING_MAX}
337 Maximum length of a string constant accepted by the bc utility.
338 Minimum Acceptable Value: {_POSIX2_BC_STRING_MAX}
339 {CHARCLASS_NAME_MAX}
341 Maximum number of bytes in a character class name.
342 Minimum Acceptable Value: {_POSIX2_CHARCLASS_NAME_MAX}
343 {COLL_WEIGHTS_MAX}
345 Maximum number of weights that can be assigned to an entry of the
346 LC_COLLATE order keyword in the locale definition file; see Chap‐
347 ter 7, Locale.
348 Minimum Acceptable Value: {_POSIX2_COLL_WEIGHTS_MAX}
349 {EXPR_NEST_MAX}
351 Maximum number of expressions that can be nested within parenthe‐
352 ses by the expr utility.
353 Minimum Acceptable Value: {_POSIX2_EXPR_NEST_MAX}
354 {LINE_MAX}
356 Unless otherwise noted, the maximum length, in bytes, of a util‐
357 ity's input line (either standard input or another file), when
358 the utility is described as processing text files. The length
359 includes room for the trailing <newline>.
360 Minimum Acceptable Value: {_POSIX2_LINE_MAX}
361 {NGROUPS_MAX}
363 Maximum number of simultaneous supplementary group IDs per
364 process.
365 Minimum Acceptable Value: {_POSIX_NGROUPS_MAX}
366 {RE_DUP_MAX}
368 Maximum number of repeated occurrences of a BRE or ERE interval
369 expression; see Section 9.3.6, BREs Matching Multiple Characters
370 and Section 9.4.6, EREs Matching Multiple Characters.
371 Minimum Acceptable Value: {_POSIX_RE_DUP_MAX}
372 Maximum Values
374 The <limits.h> header shall define the following symbolic constants
375 with the values shown. These are the most restrictive values for cer‐
376 tain features on an implementation. A conforming implementation shall
377 provide values no larger than these values. A conforming application
378 must not require a smaller value for correct operation.
379 {_POSIX_CLOCKRES_MIN}
381 The resolution of the CLOCK_REALTIME clock, in nanoseconds.
382 Value: 20 000 000
383 If the Monotonic Clock option is supported, the resolution of the
385 CLOCK_MONOTONIC clock, in nanoseconds, is represented by
386 {_POSIX_CLOCKRES_MIN}.
387 Minimum Values
389 The <limits.h> header shall define the following symbolic constants
390 with the values shown. These are the most restrictive values for cer‐
391 tain features on an implementation conforming to this volume of
392 POSIX.1‐2017. Related symbolic constants are defined elsewhere in this
393 volume of POSIX.1‐2017 which reflect the actual implementation and
394 which need not be as restrictive. For each of these limits, a conform‐
395 ing implementation shall provide a value at least this large or shall
396 have no limit. A strictly conforming application must not require a
397 larger value for correct operation.
398 {_POSIX_AIO_LISTIO_MAX}
400 The number of I/O operations that can be specified in a list I/O
401 call.
402 Value: 2
403 {_POSIX_AIO_MAX}
405 The number of outstanding asynchronous I/O operations.
406 Value: 1
407 {_POSIX_ARG_MAX}
409 Maximum length of argument to the exec functions including envi‐
410 ronment data.
411 Value: 4 096
412 {_POSIX_CHILD_MAX}
414 Maximum number of simultaneous processes per real user ID.
415 Value: 25
416 {_POSIX_DELAYTIMER_MAX}
418 The number of timer expiration overruns.
419 Value: 32
420 {_POSIX_HOST_NAME_MAX}
422 Maximum length of a host name (not including the terminating
423 null) as returned from the gethostname() function.
424 Value: 255
425 {_POSIX_LINK_MAX}
427 Maximum number of links to a single file.
428 Value: 8
429 {_POSIX_LOGIN_NAME_MAX}
431 The size of the storage required for a login name, in bytes
432 (including the terminating null).
433 Value: 9
434 {_POSIX_MAX_CANON}
436 Maximum number of bytes in a terminal canonical input queue.
437 Value: 255
438 {_POSIX_MAX_INPUT}
440 Maximum number of bytes allowed in a terminal input queue.
441 Value: 255
442 {_POSIX_MQ_OPEN_MAX}
444 The number of message queues that can be open for a single
445 process.
446 Value: 8
447 {_POSIX_MQ_PRIO_MAX}
449 The maximum number of message priorities supported by the imple‐
450 mentation.
451 Value: 32
452 {_POSIX_NAME_MAX}
454 Maximum number of bytes in a filename (not including the termi‐
455 nating null of a filename string).
456 Value: 14
457 {_POSIX_NGROUPS_MAX}
459 Maximum number of simultaneous supplementary group IDs per
460 process.
461 Value: 8
462 {_POSIX_OPEN_MAX}
464 A value one greater than the maximum value that the system may
465 assign to a newly-created file descriptor.
466 Value: 20
467 {_POSIX_PATH_MAX}
469 Minimum number the implementation will accept as the maximum num‐
470 ber of bytes in a pathname.
471 Value: 256
472 {_POSIX_PIPE_BUF}
474 Maximum number of bytes that is guaranteed to be atomic when
475 writing to a pipe.
476 Value: 512
477 {_POSIX_RE_DUP_MAX}
479 Maximum number of repeated occurrences of a BRE or ERE interval
480 expression; see Section 9.3.6, BREs Matching Multiple Characters
481 and Section 9.4.6, EREs Matching Multiple Characters.
482 Value: 255
483 {_POSIX_RTSIG_MAX}
485 The number of realtime signal numbers reserved for application
486 use.
487 Value: 8
488 {_POSIX_SEM_NSEMS_MAX}
490 The number of semaphores that a process may have.
491 Value: 256
492 {_POSIX_SEM_VALUE_MAX}
494 The maximum value a semaphore may have.
495 Value: 32 767
496 {_POSIX_SIGQUEUE_MAX}
498 The number of queued signals that a process may send and have
499 pending at the receiver(s) at any time.
500 Value: 32
501 {_POSIX_SSIZE_MAX}
503 The value that can be stored in an object of type ssize_t.
504 Value: 32 767
505 {_POSIX_SS_REPL_MAX}
507 The number of replenishment operations that may be simultaneously
508 pending for a particular sporadic server scheduler.
509 Value: 4
510 {_POSIX_STREAM_MAX}
512 The number of streams that one process can have open at one time.
513 Value: 8
514 {_POSIX_SYMLINK_MAX}
516 The number of bytes in a symbolic link.
517 Value: 255
518 {_POSIX_SYMLOOP_MAX}
520 The number of symbolic links that can be traversed in the resolu‐
521 tion of a pathname in the absence of a loop.
522 Value: 8
523 {_POSIX_THREAD_DESTRUCTOR_ITERATIONS}
525 The number of attempts made to destroy a thread's thread-specific
526 data values on thread exit.
527 Value: 4
528 {_POSIX_THREAD_KEYS_MAX}
530 The number of data keys per process.
531 Value: 128
532 {_POSIX_THREAD_THREADS_MAX}
534 The number of threads per process.
535 Value: 64
536 {_POSIX_TIMER_MAX}
538 The per-process number of timers.
539 Value: 32
540 {_POSIX_TRACE_EVENT_NAME_MAX}
542 The length in bytes of a trace event name (not including the ter‐
543 minating null).
544 Value: 30
545 {_POSIX_TRACE_NAME_MAX}
547 The length in bytes of a trace generation version string or a
548 trace stream name (not including the terminating null).
549 Value: 8
550 {_POSIX_TRACE_SYS_MAX}
552 The number of trace streams that may simultaneously exist in the
553 system.
554 Value: 8
555 {_POSIX_TRACE_USER_EVENT_MAX}
557 The number of user trace event type identifiers that may simulta‐
558 neously exist in a traced process, including the predefined user
559 trace event POSIX_TRACE_UNNAMED_USER_EVENT.
560 Value: 32
561 {_POSIX_TTY_NAME_MAX}
563 The size of the storage required for a terminal device name, in
564 bytes (including the terminating null).
565 Value: 9
566 {_POSIX_TZNAME_MAX}
568 Maximum number of bytes supported for the name of a timezone (not
569 of the TZ variable).
570 Value: 6
571 Note: The length given by {_POSIX_TZNAME_MAX} does not
573 include the quoting characters mentioned in Section
574 8.3, Other Environment Variables.
575 {_POSIX2_BC_BASE_MAX}
577 Maximum obase values allowed by the bc utility.
578 Value: 99
579 {_POSIX2_BC_DIM_MAX}
581 Maximum number of elements permitted in an array by the bc util‐
582 ity.
583 Value: 2 048
584 {_POSIX2_BC_SCALE_MAX}
586 Maximum scale value allowed by the bc utility.
587 Value: 99
588 {_POSIX2_BC_STRING_MAX}
590 Maximum length of a string constant accepted by the bc utility.
591 Value: 1 000
592 {_POSIX2_CHARCLASS_NAME_MAX}
594 Maximum number of bytes in a character class name.
595 Value: 14
596 {_POSIX2_COLL_WEIGHTS_MAX}
598 Maximum number of weights that can be assigned to an entry of the
599 LC_COLLATE order keyword in the locale definition file; see Chap‐
600 ter 7, Locale.
601 Value: 2
602 {_POSIX2_EXPR_NEST_MAX}
604 Maximum number of expressions that can be nested within parenthe‐
605 ses by the expr utility.
606 Value: 32
607 {_POSIX2_LINE_MAX}
609 Unless otherwise noted, the maximum length, in bytes, of a util‐
610 ity's input line (either standard input or another file), when
611 the utility is described as processing text files. The length
612 includes room for the trailing <newline>.
613 Value: 2 048
614 {_POSIX2_RE_DUP_MAX}
616 Maximum number of repeated occurrences of a BRE or ERE interval
617 expression; see Section 9.3.6, BREs Matching Multiple Characters
618 and Section 9.4.6, EREs Matching Multiple Characters.
619 Value: 255
620 {_XOPEN_IOV_MAX}
622 Maximum number of iovec structures that one process has available
623 for use with readv() or writev().
624 Value: 16
625 {_XOPEN_NAME_MAX}
627 Maximum number of bytes in a filename (not including the termi‐
628 nating null of a filename string).
629 Value: 255
630 {_XOPEN_PATH_MAX}
632 Minimum number the implementation will accept as the maximum num‐
633 ber of bytes in a pathname.
634 Value: 1024
635 Numerical Limits
637 The <limits.h> header shall define the following macros and, except for
638 {CHAR_BIT}, {LONG_BIT}, {MB_LEN_MAX}, and {WORD_BIT}, they shall be
639 replaced by expressions that have the same type as would an expression
640 that is an object of the corresponding type converted according to the
641 integer promotions.
642 If the value of an object of type char is treated as a signed integer
644 when used in an expression, the value of {CHAR_MIN} is the same as that
645 of {SCHAR_MIN} and the value of {CHAR_MAX} is the same as that of
646 {SCHAR_MAX}. Otherwise, the value of {CHAR_MIN} is 0 and the value of
647 {CHAR_MAX} is the same as that of {UCHAR_MAX}.
648 {CHAR_BIT}
650 Number of bits in a type char.
651 Value: 8
652 {CHAR_MAX}
654 Maximum value for an object of type char.
655 Value: {UCHAR_MAX} or {SCHAR_MAX}
656 {CHAR_MIN}
658 Minimum value for an object of type char.
659 Value: {SCHAR_MIN} or 0
660 {INT_MAX}
662 Maximum value for an object of type int.
663 Minimum Acceptable Value: 2 147 483 647
664 {INT_MIN}
666 Minimum value for an object of type int.
667 Maximum Acceptable Value: -2 147 483 647
668 {LLONG_MAX}
670 Maximum value for an object of type long long.
671 Minimum Acceptable Value: +9223372036854775807
672 {LLONG_MIN}
674 Minimum value for an object of type long long.
675 Maximum Acceptable Value: -9223372036854775807
676 {LONG_BIT}
678 Number of bits in an object of type long.
679 Minimum Acceptable Value: 32
680 {LONG_MAX}
682 Maximum value for an object of type long.
683 Minimum Acceptable Value: +2 147 483 647
684 {LONG_MIN}
686 Minimum value for an object of type long.
687 Maximum Acceptable Value: -2 147 483 647
688 {MB_LEN_MAX}
690 Maximum number of bytes in a character, for any supported locale.
691 Minimum Acceptable Value: 1
692 {SCHAR_MAX}
694 Maximum value for an object of type signed char.
695 Value: +127
696 {SCHAR_MIN}
698 Minimum value for an object of type signed char.
699 Value: -128
700 {SHRT_MAX}
702 Maximum value for an object of type short.
703 Minimum Acceptable Value: +32 767
704 {SHRT_MIN}
706 Minimum value for an object of type short.
707 Maximum Acceptable Value: -32 767
708 {SSIZE_MAX}
710 Maximum value for an object of type ssize_t.
711 Minimum Acceptable Value: {_POSIX_SSIZE_MAX}
712 {UCHAR_MAX}
714 Maximum value for an object of type unsigned char.
715 Value: 255
716 {UINT_MAX}
718 Maximum value for an object of type unsigned.
719 Minimum Acceptable Value: 4 294 967 295
720 {ULLONG_MAX}
722 Maximum value for an object of type unsigned long long.
723 Minimum Acceptable Value: 18446744073709551615
724 {ULONG_MAX}
726 Maximum value for an object of type unsigned long.
727 Minimum Acceptable Value: 4 294 967 295
728 {USHRT_MAX}
730 Maximum value for an object of type unsigned short.
731 Minimum Acceptable Value: 65 535
732 {WORD_BIT}
734 Number of bits in an object of type int.
735 Minimum Acceptable Value: 32
736 Other Invariant Values
738 The <limits.h> header shall define the following symbolic constants:
739 {NL_ARGMAX}
741 Maximum value of n in conversion specifications using the "%n$"
742 sequence in calls to the printf() and scanf() families of func‐
743 tions.
744 Minimum Acceptable Value: 9
745 {NL_LANGMAX}
747 Maximum number of bytes in a LANG name.
748 Minimum Acceptable Value: 14
749 {NL_MSGMAX}
751 Maximum message number.
752 Minimum Acceptable Value: 32 767
753 {NL_SETMAX}
755 Maximum set number.
756 Minimum Acceptable Value: 255
757 {NL_TEXTMAX}
759 Maximum number of bytes in a message string.
760 Minimum Acceptable Value: {_POSIX2_LINE_MAX}
761 {NZERO}
763 Default process priority.
764 Minimum Acceptable Value: 20
765 The following sections are informative.
767
769 None.
770
772 A request was made to reduce the value of {_POSIX_LINK_MAX} from the
773 value of 8 specified for it in the POSIX.1‐1990 standard to 2. The
774 standard developers decided to deny this request for several reasons:
775 * They wanted to avoid making any changes to the standard that could
777 break conforming applications, and the requested change could have
778 that effect.
779 * The use of multiple hard links to a file cannot always be replaced
781 with use of symbolic links. Symbolic links are semantically differ‐
782 ent from hard links in that they associate a pathname with another
783 pathname rather than a pathname with a file. This has implications
784 for access control, file permanence, and transparency.
785 * The original standard developers had considered the issue of allow‐
787 ing for implementations that did not in general support hard links,
788 and decided that this would reduce consensus on the standard.
789 Systems that support historical versions of the development option of
791 the ISO POSIX‐2 standard retain the name {_POSIX2_RE_DUP_MAX} as an
792 alias for {_POSIX_RE_DUP_MAX}.
793 {PATH_MAX}
795 IEEE PASC Interpretation 1003.1 #15 addressed the inconsistency
796 in the standard with the definition of pathname and the descrip‐
797 tion of {PATH_MAX}, allowing application developers to allocate
798 either {PATH_MAX} or {PATH_MAX}+1 bytes. The inconsistency has
799 been removed by correction to the {PATH_MAX} definition to
800 include the null character. With this change, applications that
801 previously allocated {PATH_MAX} bytes will continue to succeed.
802 {SYMLINK_MAX}
804 This symbol refers to space for data that is stored in the file
805 system, as opposed to {PATH_MAX} which is the length of a name
806 that can be passed to a function. In some existing implementa‐
807 tions, the pathnames pointed to by symbolic links are stored in
808 the inodes of the links, so it is important that {SYMLINK_MAX}
809 not be constrained to be as large as {PATH_MAX}.
810
812 None.
813
815 Chapter 7, Locale, <stdio.h>, <unistd.h>
816 The System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compila‐
818 tion Environment, fpathconf(), sysconf()
819
821 Portions of this text are reprinted and reproduced in electronic form
822 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
823 table Operating System Interface (POSIX), The Open Group Base Specifi‐
824 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
825 Electrical and Electronics Engineers, Inc and The Open Group. In the
826 event of any discrepancy between this version and the original IEEE and
827 The Open Group Standard, the original IEEE and The Open Group Standard
828 is the referee document. The original Standard can be obtained online
829 at http://www.opengroup.org/unix/online.html .
830 Any typographical or formatting errors that appear in this page are
832 most likely to have been introduced during the conversion of the source
833 files to man page format. To report such errors, see https://www.ker‐
834 nel.org/doc/man-pages/reporting_bugs.html .
835IEEE/The Open Group 2017 limits.h(0P)