limits.h(3)                POSIX Programmer's Manual               limits.h(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       limits.h -- implementation-defined constants

SYNOPSIS
       #include <limits.h>

DESCRIPTION
       Some of the functionality described on this reference page extends the
       ISO C standard. Applications shall define the appropriate feature test
       macro (see the System Interfaces volume of POSIX.1-2017, Section 2.2,
       The Compilation Environment) to enable the visibility of these symbols
       in this header.

       Many of the symbols listed here are not defined by the
       ISO/IEC 9899:1999 standard. Such symbols are not shown as CX shaded,
       except under the heading ``Numerical Limits''.

       The <limits.h> header shall define macros and symbolic constants for
       various limits.  Different categories of limits are described below,
       representing various limits on resources that the implementation
       imposes on applications.  All macros and symbolic constants defined in
       this header shall be suitable for use in #if preprocessing directives.

       Implementations may choose any appropriate value for each limit,
       provided it is not more restrictive than the Minimum Acceptable Values
       listed below. Symbolic constant names beginning with _POSIX may be
       found in <unistd.h>.

       Applications should not assume any particular value for a limit. To
       achieve maximum portability, an application should not require more
       resource than the Minimum Acceptable Value quantity. However, an
       application wishing to avail itself of the full amount of a resource
       available on an implementation may make use of the value given in
       <limits.h> on that particular implementation, by using the macros and
       symbolic constants listed below. It should be noted, however, that many
       of the listed limits are not invariant, and at runtime, the value of
       the limit may differ from those given in this header, for the following
       reasons:

        *  The limit is pathname-dependent.

        *  The limit differs between the compile and runtime machines.

       For these reasons, an application may use the fpathconf(), pathconf(),
       and sysconf() functions to determine the actual value of a limit at
       runtime.

       The items in the list ending in _MIN give the most negative values that
       the mathematical types are guaranteed to be capable of representing.
       Numbers of a more negative value may be supported on some
       implementations, as indicated by the <limits.h> header on the
       implementation, but applications requiring such numbers are not
       guaranteed to be portable to all implementations. For positive
       constants ending in _MIN, this indicates the minimum acceptable value.

   Runtime Invariant Values (Possibly Indeterminate)
       A definition of one of the symbolic constants in the following list
       shall be omitted from <limits.h> on specific implementations where the
       corresponding value is equal to or greater than the stated minimum, but
       is unspecified.

       This indetermination might depend on the amount of available memory
       space on a specific instance of a specific implementation. The actual
       value supported by a specific instance shall be provided by the
       sysconf() function.

       {AIO_LISTIO_MAX}
             Maximum number of I/O operations in a single list I/O call
             supported by the implementation.
             Minimum Acceptable Value: {_POSIX_AIO_LISTIO_MAX}

       {AIO_MAX}
             Maximum number of outstanding asynchronous I/O operations
             supported by the implementation.
             Minimum Acceptable Value: {_POSIX_AIO_MAX}

       {AIO_PRIO_DELTA_MAX}
             The maximum amount by which a process can decrease its
             asynchronous I/O priority level from its own scheduling priority.
             Minimum Acceptable Value: 0

       {ARG_MAX}
             Maximum length of argument to the exec functions including
             environment data.
             Minimum Acceptable Value: {_POSIX_ARG_MAX}

       {ATEXIT_MAX}
             Maximum number of functions that may be registered with atexit().
             Minimum Acceptable Value: 32

       {CHILD_MAX}
             Maximum number of simultaneous processes per real user ID.
             Minimum Acceptable Value: {_POSIX_CHILD_MAX}

       {DELAYTIMER_MAX}
             Maximum number of timer expiration overruns.
             Minimum Acceptable Value: {_POSIX_DELAYTIMER_MAX}

       {HOST_NAME_MAX}
             Maximum length of a host name (not including the terminating
             null) as returned from the gethostname() function.
             Minimum Acceptable Value: {_POSIX_HOST_NAME_MAX}

       {IOV_MAX}
             Maximum number of iovec structures that one process has available
             for use with readv() or writev().
             Minimum Acceptable Value: {_XOPEN_IOV_MAX}

       {LOGIN_NAME_MAX}
             Maximum length of a login name.
             Minimum Acceptable Value: {_POSIX_LOGIN_NAME_MAX}

       {MQ_OPEN_MAX}
             The maximum number of open message queue descriptors a process
             may hold.
             Minimum Acceptable Value: {_POSIX_MQ_OPEN_MAX}

       {MQ_PRIO_MAX}
             The maximum number of message priorities supported by the
             implementation.
             Minimum Acceptable Value: {_POSIX_MQ_PRIO_MAX}

       {OPEN_MAX}
             A value one greater than the maximum value that the system may
             assign to a newly-created file descriptor.
             Minimum Acceptable Value: {_POSIX_OPEN_MAX}

       {PAGESIZE}
             Size in bytes of a page.
             Minimum Acceptable Value: 1

       {PAGE_SIZE}
             Equivalent to {PAGESIZE}.  If either {PAGESIZE} or {PAGE_SIZE} is
             defined, the other is defined with the same value.

       {PTHREAD_DESTRUCTOR_ITERATIONS}
             Maximum number of attempts made to destroy a thread's thread-
             specific data values on thread exit.
             Minimum Acceptable Value: {_POSIX_THREAD_DESTRUCTOR_ITERATIONS}

       {PTHREAD_KEYS_MAX}
             Maximum number of data keys that can be created by a process.
             Minimum Acceptable Value: {_POSIX_THREAD_KEYS_MAX}

       {PTHREAD_STACK_MIN}
             Minimum size in bytes of thread stack storage.
             Minimum Acceptable Value: 0

       {PTHREAD_THREADS_MAX}
             Maximum number of threads that can be created per process.
             Minimum Acceptable Value: {_POSIX_THREAD_THREADS_MAX}

       {RTSIG_MAX}
             Maximum number of realtime signals reserved for application use
             in this implementation.
             Minimum Acceptable Value: {_POSIX_RTSIG_MAX}

       {SEM_NSEMS_MAX}
             Maximum number of semaphores that a process may have.
             Minimum Acceptable Value: {_POSIX_SEM_NSEMS_MAX}

       {SEM_VALUE_MAX}
             The maximum value a semaphore may have.
             Minimum Acceptable Value: {_POSIX_SEM_VALUE_MAX}

       {SIGQUEUE_MAX}
             Maximum number of queued signals that a process may send and have
             pending at the receiver(s) at any time.
             Minimum Acceptable Value: {_POSIX_SIGQUEUE_MAX}

       {SS_REPL_MAX}
             The maximum number of replenishment operations that may be
             simultaneously pending for a particular sporadic server
             scheduler.
             Minimum Acceptable Value: {_POSIX_SS_REPL_MAX}

       {STREAM_MAX}
             Maximum number of streams that one process can have open at one
             time.  If defined, it has the same value as {FOPEN_MAX} (see
             <stdio.h>).
             Minimum Acceptable Value: {_POSIX_STREAM_MAX}

       {SYMLOOP_MAX}
             Maximum number of symbolic links that can be reliably traversed
             in the resolution of a pathname in the absence of a loop.
             Minimum Acceptable Value: {_POSIX_SYMLOOP_MAX}

       {TIMER_MAX}
             Maximum number of timers per process supported by the
             implementation.
             Minimum Acceptable Value: {_POSIX_TIMER_MAX}

       {TRACE_EVENT_NAME_MAX}
             Maximum length of the trace event name (not including the
             terminating null).
             Minimum Acceptable Value: {_POSIX_TRACE_EVENT_NAME_MAX}

       {TRACE_NAME_MAX}
             Maximum length of the trace generation version string or of the
             trace stream name (not including the terminating null).
             Minimum Acceptable Value: {_POSIX_TRACE_NAME_MAX}

       {TRACE_SYS_MAX}
             Maximum number of trace streams that may simultaneously exist in
             the system.
             Minimum Acceptable Value: {_POSIX_TRACE_SYS_MAX}

       {TRACE_USER_EVENT_MAX}
             Maximum number of user trace event type identifiers that may
             simultaneously exist in a traced process, including the
             predefined user trace event POSIX_TRACE_UNNAMED_USER_EVENT.
             Minimum Acceptable Value: {_POSIX_TRACE_USER_EVENT_MAX}

       {TTY_NAME_MAX}
             Maximum length of terminal device name.
             Minimum Acceptable Value: {_POSIX_TTY_NAME_MAX}

       {TZNAME_MAX}
             Maximum number of bytes supported for the name of a timezone (not
             of the TZ variable).
             Minimum Acceptable Value: {_POSIX_TZNAME_MAX}

       Note:     The length given by {TZNAME_MAX} does not include the quoting
                 characters mentioned in Section 8.3, Other Environment
                 Variables.

   Pathname Variable Values
       The values in the following list may be constants within an
       implementation or may vary from one pathname to another. For example,
       file systems or directories may have different characteristics.

       A definition of one of the symbolic constants in the following list
       shall be omitted from the <limits.h> header on specific implementations
       where the corresponding value is equal to or greater than the stated
       minimum, but where the value can vary depending on the file to which it
       is applied. The actual value supported for a specific pathname shall be
       provided by the pathconf() function.

       {FILESIZEBITS}
             Minimum number of bits needed to represent, as a signed integer
             value, the maximum size of a regular file allowed in the
             specified directory.
             Minimum Acceptable Value: 32

       {LINK_MAX}
             Maximum number of links to a single file.
             Minimum Acceptable Value: {_POSIX_LINK_MAX}

       {MAX_CANON}
             Maximum number of bytes in a terminal canonical input line.
             Minimum Acceptable Value: {_POSIX_MAX_CANON}

       {MAX_INPUT}
             Minimum number of bytes for which space is available in a
             terminal input queue; therefore, the maximum number of bytes a
             conforming application may require to be typed as input before
             reading them.
             Minimum Acceptable Value: {_POSIX_MAX_INPUT}

       {NAME_MAX}
             Maximum number of bytes in a filename (not including the
             terminating null of a filename string).
             Minimum Acceptable Value: {_POSIX_NAME_MAX}
             Minimum Acceptable Value: {_XOPEN_NAME_MAX}

       {PATH_MAX}
             Maximum number of bytes the implementation will store as a
             pathname in a user-supplied buffer of unspecified size, including
             the terminating null character. Minimum number the implementation
             will accept as the maximum number of bytes in a pathname.
             Minimum Acceptable Value: {_POSIX_PATH_MAX}
             Minimum Acceptable Value: {_XOPEN_PATH_MAX}

       {PIPE_BUF}
             Maximum number of bytes that is guaranteed to be atomic when
             writing to a pipe.
             Minimum Acceptable Value: {_POSIX_PIPE_BUF}

       {POSIX_ALLOC_SIZE_MIN}
             Minimum number of bytes of storage actually allocated for any
             portion of a file.
             Minimum Acceptable Value: Not specified.

       {POSIX_REC_INCR_XFER_SIZE}
             Recommended increment for file transfer sizes between the
             {POSIX_REC_MIN_XFER_SIZE} and {POSIX_REC_MAX_XFER_SIZE} values.
             Minimum Acceptable Value: Not specified.

       {POSIX_REC_MAX_XFER_SIZE}
             Maximum recommended file transfer size.
             Minimum Acceptable Value: Not specified.

       {POSIX_REC_MIN_XFER_SIZE}
             Minimum recommended file transfer size.
             Minimum Acceptable Value: Not specified.

       {POSIX_REC_XFER_ALIGN}
             Recommended file transfer buffer alignment.
             Minimum Acceptable Value: Not specified.

       {SYMLINK_MAX}
             Maximum number of bytes in a symbolic link.
             Minimum Acceptable Value: {_POSIX_SYMLINK_MAX}

   Runtime Increasable Values
       The magnitude limitations in the following list shall be fixed by
       specific implementations. An application should assume that the value
       of the symbolic constant defined by <limits.h> in a specific
       implementation is the minimum that pertains whenever the application is
       run under that implementation. A specific instance of a specific
       implementation may increase the value relative to that supplied by
       <limits.h> for that implementation. The actual value supported by a
       specific instance shall be provided by the sysconf() function.

       {BC_BASE_MAX}
             Maximum obase values allowed by the bc utility.
             Minimum Acceptable Value: {_POSIX2_BC_BASE_MAX}

       {BC_DIM_MAX}
             Maximum number of elements permitted in an array by the bc
             utility.
             Minimum Acceptable Value: {_POSIX2_BC_DIM_MAX}

       {BC_SCALE_MAX}
             Maximum scale value allowed by the bc utility.
             Minimum Acceptable Value: {_POSIX2_BC_SCALE_MAX}

       {BC_STRING_MAX}
             Maximum length of a string constant accepted by the bc utility.
             Minimum Acceptable Value: {_POSIX2_BC_STRING_MAX}

       {CHARCLASS_NAME_MAX}
             Maximum number of bytes in a character class name.
             Minimum Acceptable Value: {_POSIX2_CHARCLASS_NAME_MAX}

       {COLL_WEIGHTS_MAX}
             Maximum number of weights that can be assigned to an entry of the
             LC__COLLATE order keyword in the locale definition file; see
             Chapter _7, Locale.
             Minimum Acceptable Value: {_POSIX2_COLL_WEIGHTS_MAX}

       {EXPR_NEST_MAX}
             Maximum number of expressions that can be nested within
             parentheses by the expr utility.
             Minimum Acceptable Value: {_POSIX2_EXPR_NEST_MAX}

       {LINE_MAX}
             Unless otherwise noted, the maximum length, in bytes, of a
             utility's input line (either standard input or another file),
             when the utility is described as processing text files. The
             length includes room for the trailing <newline>.
             Minimum Acceptable Value: {_POSIX2_LINE_MAX}

       {NGROUPS_MAX}
             Maximum number of simultaneous supplementary group IDs per
             process.
             Minimum Acceptable Value: {_POSIX_NGROUPS_MAX}

       {RE_DUP_MAX}
             Maximum number of repeated occurrences of a BRE or ERE interval
             expression; see Section 9.3.6, BREs Matching Multiple Characters
             and Section 9.4.6, EREs Matching Multiple Characters.
             Minimum Acceptable Value: {_POSIX_RE_DUP_MAX}

   Maximum Values
       The <limits.h> header shall define the following symbolic constants
       with the values shown. These are the most restrictive values for
       certain features on an implementation. A conforming implementation
       shall provide values no larger than these values. A conforming
       application must not require a smaller value for correct operation.

       {_POSIX_CLOCKRES_MIN}
             The resolution of the CLOCK_REALTIME clock, in nanoseconds.
             Value: 20 000 000

             If the Monotonic Clock option is supported, the resolution of the
             CLOCK_MONOTONIC clock, in nanoseconds, is represented by
             {_POSIX_CLOCKRES_MIN}.

   Minimum Values
       The <limits.h> header shall define the following symbolic constants
       with the values shown. These are the most restrictive values for
       certain features on an implementation conforming to this volume of
       POSIX.1-2017. Related symbolic constants are defined elsewhere in this
       volume of POSIX.1-2017 which reflect the actual implementation and
       which need not be as restrictive. For each of these limits, a
       conforming implementation shall provide a value at least this large or
       shall have no limit. A strictly conforming application must not require
       a larger value for correct operation.

       {_POSIX_AIO_LISTIO_MAX}
             The number of I/O operations that can be specified in a list I/O
             call.
             Value: 2

       {_POSIX_AIO_MAX}
             The number of outstanding asynchronous I/O operations.
             Value: 1

       {_POSIX_ARG_MAX}
             Maximum length of argument to the exec functions including
             environment data.
             Value: 4 096

       {_POSIX_CHILD_MAX}
             Maximum number of simultaneous processes per real user ID.
             Value: 25

       {_POSIX_DELAYTIMER_MAX}
             The number of timer expiration overruns.
             Value: 32

       {_POSIX_HOST_NAME_MAX}
             Maximum length of a host name (not including the terminating
             null) as returned from the gethostname() function.
             Value: 255

       {_POSIX_LINK_MAX}
             Maximum number of links to a single file.
             Value: 8

       {_POSIX_LOGIN_NAME_MAX}
             The size of the storage required for a login name, in bytes
             (including the terminating null).
             Value: 9

       {_POSIX_MAX_CANON}
             Maximum number of bytes in a terminal canonical input queue.
             Value: 255

       {_POSIX_MAX_INPUT}
             Maximum number of bytes allowed in a terminal input queue.
             Value: 255

       {_POSIX_MQ_OPEN_MAX}
             The number of message queues that can be open for a single
             process.
             Value: 8

       {_POSIX_MQ_PRIO_MAX}
             The maximum number of message priorities supported by the
             implementation.
             Value: 32

       {_POSIX_NAME_MAX}
             Maximum number of bytes in a filename (not including the
             terminating null of a filename string).
             Value: 14

       {_POSIX_NGROUPS_MAX}
             Maximum number of simultaneous supplementary group IDs per
             process.
             Value: 8

       {_POSIX_OPEN_MAX}
             A value one greater than the maximum value that the system may
             assign to a newly-created file descriptor.
             Value: 20

       {_POSIX_PATH_MAX}
             Minimum number the implementation will accept as the maximum
             number of bytes in a pathname.
             Value: 256

       {_POSIX_PIPE_BUF}
             Maximum number of bytes that is guaranteed to be atomic when
             writing to a pipe.
             Value: 512

       {_POSIX_RE_DUP_MAX}
             Maximum number of repeated occurrences of a BRE or ERE interval
             expression; see Section 9.3.6, BREs Matching Multiple Characters
             and Section 9.4.6, EREs Matching Multiple Characters.
             Value: 255

       {_POSIX_RTSIG_MAX}
             The number of realtime signal numbers reserved for application
             use.
             Value: 8

       {_POSIX_SEM_NSEMS_MAX}
             The number of semaphores that a process may have.
             Value: 256

       {_POSIX_SEM_VALUE_MAX}
             The maximum value a semaphore may have.
             Value: 32 767

       {_POSIX_SIGQUEUE_MAX}
             The number of queued signals that a process may send and have
             pending at the receiver(s) at any time.
             Value: 32

       {_POSIX_SSIZE_MAX}
             The value that can be stored in an object of type ssize_t.
             Value: 32 767

       {_POSIX_SS_REPL_MAX}
             The number of replenishment operations that may be simultaneously
             pending for a particular sporadic server scheduler.
             Value: 4

       {_POSIX_STREAM_MAX}
             The number of streams that one process can have open at one time.
             Value: 8

       {_POSIX_SYMLINK_MAX}
             The number of bytes in a symbolic link.
             Value: 255

       {_POSIX_SYMLOOP_MAX}
             The number of symbolic links that can be traversed in the
             resolution of a pathname in the absence of a loop.
             Value: 8

       {_POSIX_THREAD_DESTRUCTOR_ITERATIONS}
             The number of attempts made to destroy a thread's thread-specific
             data values on thread exit.
             Value: 4

       {_POSIX_THREAD_KEYS_MAX}
             The number of data keys per process.
             Value: 128

       {_POSIX_THREAD_THREADS_MAX}
             The number of threads per process.
             Value: 64

       {_POSIX_TIMER_MAX}
             The per-process number of timers.
             Value: 32

       {_POSIX_TRACE_EVENT_NAME_MAX}
             The length in bytes of a trace event name (not including the
             terminating null).
             Value: 30

       {_POSIX_TRACE_NAME_MAX}
             The length in bytes of a trace generation version string or a
             trace stream name (not including the terminating null).
             Value: 8

       {_POSIX_TRACE_SYS_MAX}
             The number of trace streams that may simultaneously exist in the
             system.
             Value: 8

       {_POSIX_TRACE_USER_EVENT_MAX}
             The number of user trace event type identifiers that may
             simultaneously exist in a traced process, including the
             predefined user trace event POSIX_TRACE_UNNAMED_USER_EVENT.
             Value: 32

       {_POSIX_TTY_NAME_MAX}
             The size of the storage required for a terminal device name, in
             bytes (including the terminating null).
             Value: 9

       {_POSIX_TZNAME_MAX}
             Maximum number of bytes supported for the name of a timezone (not
             of the TZ variable).
             Value: 6

             Note:     The length given by {_POSIX_TZNAME_MAX} does not
                       include the quoting characters mentioned in Section
                       8.3, Other Environment Variables.

       {_POSIX2_BC_BASE_MAX}
             Maximum obase values allowed by the bc utility.
             Value: 99

       {_POSIX2_BC_DIM_MAX}
             Maximum number of elements permitted in an array by the bc
             utility.
             Value: 2 048

       {_POSIX2_BC_SCALE_MAX}
             Maximum scale value allowed by the bc utility.
             Value: 99

       {_POSIX2_BC_STRING_MAX}
             Maximum length of a string constant accepted by the bc utility.
             Value: 1 000

       {_POSIX2_CHARCLASS_NAME_MAX}
             Maximum number of bytes in a character class name.
             Value: 14

       {_POSIX2_COLL_WEIGHTS_MAX}
             Maximum number of weights that can be assigned to an entry of the
             LC__COLLATE order keyword in the locale definition file; see
             Chapter _7, Locale.
             Value: 2

       {_POSIX2_EXPR_NEST_MAX}
             Maximum number of expressions that can be nested within
             parentheses by the expr utility.
             Value: 32

       {_POSIX2_LINE_MAX}
             Unless otherwise noted, the maximum length, in bytes, of a
             utility's input line (either standard input or another file),
             when the utility is described as processing text files. The
             length includes room for the trailing <newline>.
             Value: 2 048

       {_POSIX2_RE_DUP_MAX}
             Maximum number of repeated occurrences of a BRE or ERE interval
             expression; see Section 9.3.6, BREs Matching Multiple Characters
             and Section 9.4.6, EREs Matching Multiple Characters.
             Value: 255

       {_XOPEN_IOV_MAX}
             Maximum number of iovec structures that one process has available
             for use with readv() or writev().
             Value: 16

       {_XOPEN_NAME_MAX}
             Maximum number of bytes in a filename (not including the
             terminating null of a filename string).
             Value: 255

       {_XOPEN_PATH_MAX}
             Minimum number the implementation will accept as the maximum
             number of bytes in a pathname.
             Value: 1024

   Numerical Limits
       The <limits.h> header shall define the following macros and, except for
       {CHAR_BIT}, {LONG_BIT}, {MB_LEN_MAX}, and {WORD_BIT}, they shall be
       replaced by expressions that have the same type as would an expression
       that is an object of the corresponding type converted according to the
       integer promotions.

       If the value of an object of type char is treated as a signed integer
       when used in an expression, the value of {CHAR_MIN} is the same as that
       of {SCHAR_MIN} and the value of {CHAR_MAX} is the same as that of
       {SCHAR_MAX}.  Otherwise, the value of {CHAR_MIN} is 0 and the value of
       {CHAR_MAX} is the same as that of {UCHAR_MAX}.

       {CHAR_BIT}
             Number of bits in a type char.
             Value: 8

       {CHAR_MAX}
             Maximum value for an object of type char.
             Value: {UCHAR_MAX} or {SCHAR_MAX}

       {CHAR_MIN}
             Minimum value for an object of type char.
             Value: {SCHAR_MIN} or 0

       {INT_MAX}
             Maximum value for an object of type int.
             Minimum Acceptable Value: 2 147 483 647

       {INT_MIN}
             Minimum value for an object of type int.
             Maximum Acceptable Value: -2 147 483 647

       {LLONG_MAX}
             Maximum value for an object of type long long.
             Minimum Acceptable Value: +9223372036854775807

       {LLONG_MIN}
             Minimum value for an object of type long long.
             Maximum Acceptable Value: -9223372036854775807

       {LONG_BIT}
             Number of bits in an object of type long.
             Minimum Acceptable Value: 32

       {LONG_MAX}
             Maximum value for an object of type long.
             Minimum Acceptable Value: +2 147 483 647

       {LONG_MIN}
             Minimum value for an object of type long.
             Maximum Acceptable Value: -2 147 483 647

       {MB_LEN_MAX}
             Maximum number of bytes in a character, for any supported locale.
             Minimum Acceptable Value: 1

       {SCHAR_MAX}
             Maximum value for an object of type signed char.
             Value: +127

       {SCHAR_MIN}
             Minimum value for an object of type signed char.
             Value: -128

       {SHRT_MAX}
             Maximum value for an object of type short.
             Minimum Acceptable Value: +32 767

       {SHRT_MIN}
             Minimum value for an object of type short.
             Maximum Acceptable Value: -32 767

       {SSIZE_MAX}
             Maximum value for an object of type ssize_t.
             Minimum Acceptable Value: {_POSIX_SSIZE_MAX}

       {UCHAR_MAX}
             Maximum value for an object of type unsigned char.
             Value: 255

       {UINT_MAX}
             Maximum value for an object of type unsigned.
             Minimum Acceptable Value: 4 294 967 295

       {ULLONG_MAX}
             Maximum value for an object of type unsigned long long.
             Minimum Acceptable Value: 18446744073709551615

       {ULONG_MAX}
             Maximum value for an object of type unsigned long.
             Minimum Acceptable Value: 4 294 967 295

       {USHRT_MAX}
             Maximum value for an object of type unsigned short.
             Minimum Acceptable Value: 65 535

       {WORD_BIT}
             Number of bits in an object of type int.
             Minimum Acceptable Value: 32

   Other Invariant Values
       The <limits.h> header shall define the following symbolic constants:

       {NL_ARGMAX}
             Maximum value of _n in conversion specifications using the "%_n$"
             sequence in calls to the printf() and scanf() families of
             functions.
             Minimum Acceptable Value: 9

       {NL_LANGMAX}
             Maximum number of bytes in a LANG name.
             Minimum Acceptable Value: 14

       {NL_MSGMAX}
             Maximum message number.
             Minimum Acceptable Value: 32 767

       {NL_SETMAX}
             Maximum set number.
             Minimum Acceptable Value: 255

       {NL_TEXTMAX}
             Maximum number of bytes in a message string.
             Minimum Acceptable Value: {_POSIX2_LINE_MAX}

       {NZERO}
             Default process priority.
             Minimum Acceptable Value: 20

       The following sections are informative.

APPLICATION USAGE
       None.

RATIONALE
       A request was made to reduce the value of {_POSIX_LINK_MAX} from the
       value of 8 specified for it in the POSIX.1-1990 standard to 2. The
       standard developers decided to deny this request for several reasons:

        *  They wanted to avoid making any changes to the standard that could
           break conforming applications, and the requested change could have
           that effect.

        *  The use of multiple hard links to a file cannot always be replaced
           with use of symbolic links. Symbolic links are semantically
           different from hard links in that they associate a pathname with
           another pathname rather than a pathname with a file. This has
           implications for access control, file permanence, and transparency.

        *  The original standard developers had considered the issue of
           allowing for implementations that did not in general support hard
           links, and decided that this would reduce consensus on the
           standard.

       Systems that support historical versions of the development option of
       the ISO POSIX-2 standard retain the name {_POSIX2_RE_DUP_MAX} as an
       alias for {_POSIX_RE_DUP_MAX}.

       {PATH_MAX}
             IEEE PASC Interpretation 1003.1 #15 addressed the inconsistency
             in the standard with the definition of pathname and the
             description of {PATH_MAX}, allowing application developers to
             allocate either {PATH_MAX} or {PATH_MAX}+1 bytes. The
             inconsistency has been removed by correction to the {PATH_MAX}
             definition to include the null character. With this change,
             applications that previously allocated {PATH_MAX} bytes will
             continue to succeed.

       {SYMLINK_MAX}
             This symbol refers to space for data that is stored in the file
             system, as opposed to {PATH_MAX} which is the length of a name
             that can be passed to a function. In some existing
             implementations, the pathnames pointed to by symbolic links are
             stored in the inodes of the links, so it is important that
             {SYMLINK_MAX} not be constrained to be as large as {PATH_MAX}.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Chapter _7, Locale, <stdio.h>, <unistd.h>

       The System Interfaces volume of POSIX.1-2017, Section 2.2, The
       Compilation Environment, fpathconf(), sysconf()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          limits.h(3)
