Originální popis anglicky:
limits.h - implementation-defined constants
Návod, kniha: POSIX Programmer's Manual
#include <limits.h>
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 IEEE Std 1003.1-2001,
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.
The
<limits.h> header shall define various symbolic names.
Different categories of names are described below.
The names represent various limits on resources that the implementation imposes
on applications.
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 symbolic names 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.
A definition of one of the symbolic names 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}
- Maximum number of files that one process can have open at
any one time.
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}
- {RE_DUP_MAX}
- The number of repeated occurrences of a BRE permitted by
the regexec() and regcomp() functions when using the
interval notation {\( m,n\}; see BREs Matching Multiple
Characters .
Minimum Acceptable Value: {_POSIX2_RE_DUP_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}
- The 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.
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.
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 Other Environment Variables .
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 values 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
terminating null).
Minimum Acceptable Value: {_POSIX_NAME_MAX}
Minimum Acceptable Value: {_XOPEN_NAME_MAX}
- {PATH_MAX}
- Maximum number of bytes in a pathname, including the
terminating null character.
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}
The magnitude limitations in the following list shall be fixed by specific
implementations. An application should assume that the value supplied 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 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 regular
expression permitted when using the interval notation \{
m,n\}; see Regular Expressions .
Minimum Acceptable Value: {_POSIX2_RE_DUP_MAX}
The symbolic constants in the following list shall be defined in
<limits.h> with the values shown. These are symbolic names for
the most restrictive value for certain features on an implementation
supporting the Timers option. 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}.
The symbolic constants in the following list shall be defined in
<limits.h> with the values shown. These are symbolic names for
the most restrictive value for certain features on an implementation
conforming to this volume of IEEE Std 1003.1-2001. Related
symbolic constants are defined elsewhere in this volume of
IEEE Std 1003.1-2001 which reflect the actual implementation and
which need not be as restrictive. A conforming implementation shall provide
values at least this large. 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
terminating null).
Value: 14
- {_POSIX_NGROUPS_MAX}
- Maximum number of simultaneous supplementary group IDs per
process.
Value: 8
- {_POSIX_OPEN_MAX}
- Maximum number of files that one process can have open at
any one time.
Value: 20
- {_POSIX_PATH_MAX}
- 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}
- The number of repeated occurrences of a BRE permitted by
the regexec() and regcomp() functions when using the
interval notation {\( m,n\}; see BREs 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_STREAM_MAX}
- The number of streams that one process can have open at one
time.
Value: 8
- {_POSIX_SS_REPL_MAX}
-
The number of replenishment operations that may be simultaneously pending
for a particular sporadic server scheduler.
Value: 4
- {_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.
Value: 30
- {_POSIX_TRACE_NAME_MAX}
-
The length in bytes of a trace generation version string or a trace stream
name.
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 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 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 regular
expression permitted when using the interval notation \{
m,n\}; see Regular Expressions .
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).
Value: 255
- {_XOPEN_PATH_MAX}
-
Maximum number of bytes in a pathname.
Value: 1024
The values in the following lists shall be defined in
<limits.h>
and are constant expressions suitable for use in
#if preprocessing
directives. Moreover, except for {CHAR_BIT}, {DBL_DIG}, {DBL_MAX}, {FLT_DIG},
{FLT_MAX}, {LONG_BIT}, {WORD_BIT}, and {MB_LEN_MAX}, the symbolic names are
defined as expressions of the correct type.
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 of type char.
Value: {UCHAR_MAX} or {SCHAR_MAX}
- {CHAR_MIN}
- Minimum value of type char.
Value: {SCHAR_MIN} or 0
- {INT_MAX}
- Maximum value of an int.
Minimum Acceptable Value: 2 147 483 647
- {LONG_BIT}
-
Number of bits in a long.
Minimum Acceptable Value: 32
- {LONG_MAX}
- Maximum value of a long.
Minimum 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 of type signed char.
Value: +127
- {SHRT_MAX}
- Maximum value of type short.
Minimum Acceptable Value: +32 767
- {SSIZE_MAX}
- Maximum value of an object of type ssize_t.
Minimum Acceptable Value: {_POSIX_SSIZE_MAX}
- {UCHAR_MAX}
- Maximum value of type unsigned char.
Value: 255
- {UINT_MAX}
- Maximum value of type unsigned.
Minimum Acceptable Value: 4 294 967 295
- {ULONG_MAX}
- Maximum value of type unsigned long.
Minimum Acceptable Value: 4 294 967 295
- {USHRT_MAX}
- Maximum value for a type unsigned short.
Minimum Acceptable Value: 65 535
- {WORD_BIT}
-
Number of bits in a word or type int.
Minimum Acceptable Value: 16
- {INT_MIN}
- Minimum value of type int.
Maximum Acceptable Value: -2 147 483 647
- {LONG_MIN}
- Minimum value of type long.
Maximum Acceptable Value: -2 147 483 647
- {SCHAR_MIN}
- Minimum value of type signed char.
Value: -128
- {SHRT_MIN}
- Minimum value of type short.
Maximum Acceptable Value: -32 767
- {LLONG_MIN}
- Minimum value of type long long.
Maximum Acceptable Value: -9223372036854775807
- {LLONG_MAX}
- Maximum value of type long long.
Minimum Acceptable Value: +9223372036854775807
- {ULLONG_MAX}
- Maximum value of type unsigned long long.
Minimum Acceptable Value: 18446744073709551615
The following constants shall be defined on all implementations in
<limits.h>:
- {CHARCLASS_NAME_MAX}
-
Maximum number of bytes in a character class name.
Minimum Acceptable Value: 14
- {NL_ARGMAX}
-
Maximum value of digit in calls to the printf() and
scanf() 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_NMAX}
-
Maximum number of bytes in an N-to-1 collation mapping.
Minimum Acceptable Value: No guaranteed value across all conforming
implementations.
- {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.
None.
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 writers 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
filenames 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}.
None.
The System Interfaces volume of IEEE Std 1003.1-2001,
fpathconf(),
pathconf(),
sysconf()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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
.
