1limits.h(3HEAD) Headers limits.h(3HEAD)
2
6 limits.h, limits - implementation-defined constants
7
9 #include <limits.h>
10
13 The <limits.h> header defines various symbolic names. Different cate‐
14 gories of names are described below.
15 The names represent various limits on resources that the implementation
18 imposes on applications. Symbolic constant names beginning with _POSIX
19 can be found in unistd.h(3HEAD).
20 Applications should not assume any particular value for a limit. An
23 application wishing to avail itself of the full amount of a resource
24 available on an implementation can make use of the value given in lim‐
25 its.h on that particular implementation by using the symbolic names
26 listed below. Many of the listed limits are not invariant, and at run‐
27 time, the value of the limit might differ from those given in this
28 header, for the following reasons:
29 o The limit is pathname-dependent.
31 o The limit differs between the compile and runtime machines.
33 For these reasons, an application can use the fpathconf(2), path‐
36 conf(2), and sysconf(3C) functions to determine the actual value of a
37 limit at runtime.
38 Runtime Invariant Values (Possibly Indeterminate)
40 AIO_LISTIO_MAX
41 Maximum number of I/O operations in a single list I/O call sup‐
43 ported by the implementation.
44 AIO_MAX
47 Maximum number of outstanding asynchronous I/O operations supported
49 by the implementation.
50 AIO_PRIO_DELTA_MAX
53 The maximum amount by which a process can decrease its asynchronous
55 I/O priority level from its own scheduling priority.
56 ARG_MAX
59 Maximum length of argument to the exec(2) functions including envi‐
61 ronment data.
62 ATEXIT_MAX
65 Maximum number of functions that can be registered with atexit(3C).
67 CHILD_MAX
70 Maximum number of simultaneous processes per real user ID.
72 CLK_TCK
75 Number of clock ticks per second returned by the times(2) function.
77 DELAYTIMER_MAX
80 Maximum number of timer expiration overruns.
82 HOST_NAME_MAX
85 Maximum length of a host name (not including the terminating null)
87 as returned from the gethostname(3C) function.
88 IOV_MAX
91 Maximum number of iovec structures that one process has available
93 for use with read(2) or write(2).
94 LOGIN_NAME_MAX
97 Maximum length of a login name.
99 MQ_OPEN_MAX
102 The maximum number of open message queue descriptors a process is
104 allowed to hold.
105 LOGIN_NAME_MAX
108 Maximum length of a login name.
110 MQ_OPEN_MAX
113 The maximum number of open message queue descriptors a process is
115 allowed to hold.
116 MQ_PRIO_MAX
119 The maximum number of message priorities supported by the implemen‐
121 tation.
122 OPEN_MAX
125 Maximum number of files that one process can have open at any one
127 time.
128 PAGESIZE
131 Size in bytes of a page.
133 PAGE_SIZE
136 Equivalent to PAGESIZE. If either PAGESIZE or PAGE_SIZE is defined,
138 the other is defined with the same value.
139 PASS_MAX
142 The maximum number of significant bytes in a password, not includ‐
144 ing the terminating null.
145 PTHREAD_DESTRUCTOR_ITERATIONS
148 Maximum number of attempts made to destroy a thread's thread-spe‐
150 cific data values on thread exit.
151 PTHREAD_KEYS_MAX
154 Maximum number of data keys that can be created by a process.
156 PTHREAD_STACK_MIN
159 Minimum size in bytes of thread stack storage.
161 PTHREAD_THREADS_MAX
164 Maximum number of threads that can be created per process.
166 RE_DUP_MAX
169 The number of repeated occurrences of a BRE permitted by the
171 regexec(3C) and regcomp(3C) functions when using the interval nota‐
172 tion {\(m,n\}.
173 RTSIG_MAX
176 Maximum number of realtime signals reserved for application use in
178 this implementation.
179 SEM_NSEMS_MAX
182 Maximum number of semaphores that a process can have.
184 SEM_VALUE_MAX
187 The maximum value a semaphore can have.
189 SIGQUEUE_MAX
192 Maximum number of queued signals that a process can send and have
194 pending at the receiver(s) at any time.
195 SS_REPL_MAX
198 The maximum number of replenishment operations that may be simulta‐
200 neously pending for a particular sporadic server scheduler.
201 STREAM_MAX
204 The number of streams that one process can have open at one time.
206 If defined, it has the same value as FOPEN_MAX.
207 SYMLOOP_MAX
210 Maximum number of symbolic links that can be reliably traversed in
212 the resolution of a pathname in the absence of a loop.
213 TIMER_MAX
216 Maximum number of timers per process supported by the implementa‐
218 tion.
219 TRACE_EVENT_NAME_MAX
222 Maximum length of the trace event name.
224 TRACE_NAME_MAX
227 Maximum length of the trace generation version string or of the
229 trace stream name.
230 TRACE_SYS_MAX
233 Maximum number of trace streams that may simultaneously exist in
235 the system.
236 TRACE_USER_EVENT_MAX
239 Maximum number of user trace event type identifiers that may simul‐
241 taneously exist in a traced process, including the predefined user
242 trace event POSIX_TRACE_UNNAMED_USER_EVENT.
243 TTY_NAME_MAX
246 Maximum length of terminal device name.
248 TZNAME_MAX
251 Maximum number of bytes supported for the name of a timezone (not
253 of the TZ variable).
254 Pathname Variable Values
257 The values in the following list can be constants within an implementa‐
258 tion or can vary from one pathname to another. For example, file sys‐
259 tems or directories can have different characteristics. The value sup‐
260 ported for a specific pathname is provided by the pathconf(2) function.
261 FILESIZEBITS Minimum number of bits needed to represent,
263 as a signed integer value, the maximum size
264 of a regular file allowed in the specified
265 directory.
266 LINK_MAX Maximum number of links to a single file.
269 MAX_CANON Maximum number of bytes in a terminal
272 canonical input line.
273 MAX_INPUT Minimum number of bytes for which space is
276 available in a terminal input queue; there‐
277 fore, the maximum number of bytes a con‐
278 forming application may require to be typed
279 as input before reading them.
280 NAME_MAX Maximum number of bytes in a filename (not
283 including terminating null).
284 PATH_MAX Maximum number of bytes in a pathname,
287 including the terminating null character.
288 PIPE_BUF Maximum number of bytes that is guaranteed
291 to be atomic when writing to a pipe.
292 POSIX_ALLOC_SIZE_MIN Minimum number of bytes of storage actually
295 allocated for any portion of a file.
296 POSIX_REC_INCR_XFER_SIZE Recommended increment for file transfer
299 sizes between the POSIX_REC_MIN_XFER_SIZE
300 and POSIX_REC_MAX_XFER_SIZE values.
301 POSIX_REC_MAX_XFER_SIZE Maximum recommended file transfer size.
304 POSIX_REC_MIN_XFER_SIZE Minimum recommended file transfer size.
307 POSIX_REC_XFER_ALIGN Recommended file transfer buffer alignment.
310 SYMLINK_MAX Maximum number of bytes in a symbolic link.
313 Runtime Increasable Values
316 The magnitude limitations in the following list are fixed by specific
317 implementations. An application should assume that the value supplied
318 by <limits.h> in a specific implementation is the minimum that pertains
319 whenever the application is run under that implementation. A specific
320 instance of a specific implementation can increase the value relative
321 to that supplied by <limits.h> for that implementation. The actual
322 value supported by a specific instance is provided by the sysconf(3C)
323 function.
324 BC_BASE_MAX Maximum obase values allowed by the bc(1) util‐
326 ity.
327 BC_DIM_MAX Maximum number of elements permitted in an array
330 by the bc utility.
331 BC_SCALE_MAX Maximum scale value allowed by the bc utility.
334 BC_STRING_MAX Maximum length of a string constant accepted by
337 the bc utility.
338 CHARCLASS_NAME_MAX Maximum number of bytes in a character class
341 name.
342 COLL_WEIGHTS_MAX Maximum number of weights that can be assigned to
345 an entry of the LC_COLLATE order keyword in the
346 locale definition file.
347 EXPR_NEST_MAX Maximum number of expressions that can be nested
350 within parentheses by the expr(1) utility.
351 EXPR_NEST_MAX Maximum number of expressions that can be nested
354 within parentheses by the expr utility.
355 LINE_MAX Unless otherwise noted, the maximum length, in
358 bytes, of a utility's input line (either standard
359 input or another file), when the utility is
360 described as processing text files. The length
361 includes room for the trailing <newline>.
362 NGROUPS_MAX Maximum number of simultaneous supplementary
365 group IDs per process.
366 RE_DUP_MAX Maximum number of repeated occurrences of a regu‐
369 lar expression permitted when using the interval
370 notation \{m,n\}.
371 Maximum Values
374 The symbolic constants in the following list are symbolic names for the
375 most restrictive value for certain features on an implementation sup‐
376 porting the POSIX Timers option.
377 _POSIX_CLOCKRES_MIN The resolution of the CLOCK_REALTIME clock, in
379 nanoseconds.
380 Minimum Values
383 The symbolic constants in the following list are symbolic names for the
384 most restrictive value for certain features on an implementation con‐
385 forming to various POSIX and Single Unix Specification requirements.
386 See standards(5).
387 _POSIX_AIO_LISTIO_MAX
389 The number of I/O operations that can be specified in a list I/O
391 call.
392 _POSIX_AIO_MAX
395 The number of outstanding asynchronous I/O operations.
397 _POSIX_ARG_MAX
400 Maximum length of argument to the exec(2) functions including envi‐
402 ronment data.
403 _POSIX_CHILD_MAX
406 Maximum number of simultaneous processes per real user ID.
408 _POSIX_DELAYTIMER_MAX
411 The number of timer expiration overruns.
413 _POSIX_HOST_NAME_MAX
416 Maximum length of a host name (not including the terminating null)
418 as returned from the gethostname(3C) function.
419 _POSIX_LINK_MAX
422 Maximum number of links to a single file.
424 _POSIX_LOGIN_NAME_MAX
427 The size of the storage required for a login name, in bytes,
429 including the terminating null.
430 _POSIX_MAX_CANON
433 Maximum number of bytes in a terminal canonical input queue.
435 _POSIX_MAX_INPUT
438 Maximum number of bytes allowed in a terminal input queue.
440 _POSIX_MQ_OPEN_MAX
443 The number of message queues that can be open for a single process.
445 _POSIX_MQ_PRIO_MAX
448 The maximum number of message priorities supported by the implemen‐
450 tation.
451 _POSIX_NAME_MAX
454 Maximum number of bytes in a filename (not including terminating
456 null).
457 _POSIX_NGROUPS_MAX
460 Maximum number of simultaneous supplementary group IDs per process.
462 _POSIX_OPEN_MAX
465 Maximum number of files that one process can have open at any one
467 time.
468 _POSIX_PATH_MAX
471 Maximum number of bytes in a pathname.
473 _POSIX_PIPE_BUF
476 Maximum number of bytes that is guaranteed to be atomic when writ‐
478 ing to a pipe.
479 _POSIX_RE_DUP_MAX
482 The number of repeated occurrences of a BRE permitted by the
484 regexec() and regcomp() functions when using the interval notation
485 {\(m,n\}
486 _POSIX_RTSIG_MAX
489 The number of realtime signal numbers reserved for application use.
491 _POSIX_SEM_NSEMS_MAX
494 The number of semaphores that a process can have.
496 _POSIX_SEM_VALUE_MAX
499 The maximum value a semaphore can have.
501 _POSIX_SIGQUEUE_MAX
504 The number of queued signals that a process can send and have pend‐
506 ing at the receiver(s) at any time.
507 _POSIX_SSIZE_MAX
510 The value that can be stored in an object of type ssize_t.
512 _POSIX_STREAM_MAX
515 The number of streams that one process can have open at one time.
517 _POSIX_SS_REPL_MAX
520 The number of replenishment operations that can be simultaneously
522 pending for a particular sporadic server scheduler.
523 _POSIX_SYMLINK_MAX
526 The number of bytes in a symbolic link.
528 _POSIX_SYMLOOP_MAX
531 The number of symbolic links that can be traversed in the resolu‐
533 tion of a pathname in the absence of a loop.
534 _POSIX_THREAD_DESTRUCTOR_ITERATIONS
537 The number of attempts made to destroy a thread's thread-specific
539 data values on thread exit.
540 _POSIX_THREAD_KEYS_MAX
543 The number of data keys per process.
545 _POSIX_THREAD_THREADS_MAX
548 The number of threads per process.
550 _POSIX_TIMER_MAX
553 The per-process number of timers.
555 _POSIX_TRACE_EVENT_NAME_MAX
558 The length in bytes of a trace event name.
560 _POSIX_TRACE_NAME_MAX
563 The length in bytes of a trace generation version string or a trace
565 stream name.
566 _POSIX_TRACE_SYS_MAX
569 The number of trace streams that can simultaneously exist in the
571 system.
572 _POSIX_TRACE_USER_EVENT_MAX
575 The number of user trace event type identifiers that may simultane‐
577 ously exist in a traced process, including the predefined user
578 trace event POSIX_TRACE_UNNAMED_USER_EVENT.
579 _POSIX_TTY_NAME_MAX
582 The size of the storage required for a terminal device name, in
584 bytes, including the terminating null.
585 _POSIX_TZNAME_MAX
588 Maximum number of bytes supported for the name of a timezone (not
590 of the TZ variable).
591 _POSIX2_BC_BASE_MAX
594 Maximum obase values allowed by the bc utility.
596 _POSIX2_BC_DIM_MAX
599 Maximum number of elements permitted in an array by the bc utility.
601 _POSIX2_BC_SCALE_MAX
604 Maximum scale value allowed by the bc utility.
606 _POSIX2_BC_STRING_MAX
609 Maximum length of a string constant accepted by the bc utility.
611 _POSIX2_CHARCLASS_NAME_MAX
614 Maximum number of bytes in a character class name.
616 _POSIX2_COLL_WEIGHTS_MAX
619 Maximum number of weights that can be assigned to an entry of the
621 LC_COLLATE order keyword in the locale definition file.
622 _POSIX2_EXPR_NEST_MAX
625 Maximum number of expressions that can be nested within parentheses
627 by the expr utility.
628 _POSIX2_LINE_MAX
631 Unless otherwise noted, the maximum length, in bytes, of a util‐
633 ity's input line (either standard input or another file), when the
634 utility is described as processing text files. The length includes
635 room for the trailing <newline>.
636 _POSIX2_RE_DUP_MAX
639 Maximum number of repeated occurrences of a regular expression per‐
641 mitted when using the interval notation \{m,n\}.
642 _XOPEN_IOV_MAX
645 Maximum number of iovec structures that one process has available
647 for use with read(2) or write(2).
648 _XOPEN_NAME_MAX
651 Maximum number of bytes in a filename (not including the terminat‐
653 ing null).
654 _XOPEN_PATH_MAX
657 Maximum number of bytes in a pathname.
659 Numerical Limits
662 The values in the following lists shall be defined in <limits.h> and
663 are constant expressions suitable for use in #if preprocessing direc‐
664 tives. Moreover, except for CHAR_BIT, DBL_DIG, DBL_MAX, FLT_DIG,
665 FLT_MAX, LONG_BIT, WORD_BIT, and MB_LEN_MAX, the symbolic names are
666 defined as expressions of the correct type.
667 If the value of an object of type char is treated as a signed integer
670 when used in an expression, the value of CHAR_MIN is the same as that
671 of SCHAR_MIN and the value of CHAR_MAX is the same as that of
672 SCHAR_MAX. Otherwise, the value of CHAR_MIN is 0 and the value of
673 CHAR_MAX is the same as that of UCHAR_MAX.
674 CHAR_BIT Number of bits in a type char.
676 CHAR_MAX Maximum value of type char.
679 CHAR_MIN Minimum value of type char.
682 DBL_DIG Digits of precision of type double.
685 DBL_MAX Maximum decimal value of a double.
688 DBL_MIN Minimum decimal value of a double.
691 FLT_DIG Digits of precision of type float.
694 FLT_MAX Maximum decimal value of a float.
697 FLT_MIN Minimum decimal value of a float.
700 INT_MIN Minimum value of type int.
703 INT_MAX Maximum value of an int.
706 LLONG_MIN Minimum value of type long long.
709 LLONG_MAX Maximum value of type long long.
712 LONG_BIT Number of bits in a long.
715 LONG_MIN Minimum value of type long.
718 LONG_MAX Maximum value of a long.
721 MB_LEN_MAX Maximum number of bytes in a character, for any supported
724 locale.
725 SCHAR_MIN Minimum value of type signed char.
728 SCHAR_MAX Maximum value of type signed char.
731 SHRT_MIN Minimum value of type short.
734 SHRT_MAX Maximum value of type short.
737 SSIZE_MAX Maximum value of an object of type ssize_t.
740 TMP_MAX Minimum number of unique filename generated by tmp‐
743 nam(3C). Maximum number of times an application can call
744 tmpnam() reliably.
745 UCHAR_MAX Maximum value of type unsigned char.
748 UINT_MAX Maximum value of type unsigned.
751 ULLONG_MAX Maximum value of type unsigned long long.
754 ULONG_MAX Maximum value of type unsigned long.
757 USHRT_MAX Maximum value for a type unsigned short.
760 WORD_BIT Number of bits in a word or type int.
763 Other Invariant Values
766 The following constants are defined in <limits.h>.
767 CHARCLASS_NAME_MAX Maximum number of bytes in a character class
769 name.
770 LOGNAME_MAX The maximum number of bytes supported in a user's
773 login name.
774 NL_ARGMAX Maximum value of digit in calls to the printf(3C)
777 and scanf(3C) functions.
778 NL_LANGMAX Maximum number of bytes in a LANG name.
781 NL_MSGMAX Maximum message number.
784 NL_NMAX Maximum number of bytes in an N-to-1 collation
787 mapping.
788 NL_SETMAX Maximum set number.
791 NL_TEXTMAX Maximum number of bytes in a message string.
794 NZERO Default process priority.
797
800 fpathconf(2), pathconf(2), sysconf(3C), standards(5)
801SunOS 5.11 8 April 2004 limits.h(3HEAD)