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limits.h(0p) |
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limits.h − implementation-defined constants
#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.
Runtime
Invariant Values (Possibly Indeterminate)
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 . |
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 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}
Runtime
Increasable Values
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}
Maximum
Values
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}.
Minimum
Values
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
Numerical
Limits
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
Other
Invariant Values
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 .
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limits.h(0p) | |