limits.h.html

unix 下的C开发手册,还用详细的例程。

Maximum number of simultaneous processes per real user ID.

Value: 6

<dt>_POSIX_DELAYTIMER_MAX<dd>

The number of timer expiration overruns.

Value: 32

<dt>_POSIX_LINK_MAX<dd>

Maximum number of links to a single file.

Value: 8

<dt>_POSIX_LOGIN_NAME_MAX<dd>

The size of the storage required for a login name, in bytes,
including the terminating null.

Value: 9

<dt>_POSIX_MAX_CANON<dd>

Maximum number of bytes in a terminal canonical input queue.

Value: 255

<dt>_POSIX_MAX_INPUT<dd>

Maximum number of bytes allowed in a terminal input queue.

Value: 255

<dt>_POSIX_MQ_OPEN_MAX<dd>

The number of message queues that can be open for a single process.

Value: 8

<dt>_POSIX_MQ_PRIO_MAX<dd>

The maximum number of message priorities supported by the implementation.

Value: 32

<dt>_POSIX_NAME_MAX<dd>

Maximum number of bytes in a filename (not including terminating null).

Value: 14

<dt>_POSIX_NGROUPS_MAX<dd>

Maximum number of simultaneous supplementary group IDs per process.

Value: 0

<dt>_POSIX_OPEN_MAX<dd>

Maximum number of files that one process can have open at any one time.

Value: 16

<dt>_POSIX_PATH_MAX<dd>

Maximum number of bytes in a pathname.

Value: 255

<dt>_POSIX_PIPE_BUF<dd>

Maximum number of bytes that is guaranteed to be atomic when writing to
a pipe.

Value: 512

<dt>_POSIX_RTSIG_MAX<dd>

The number of realtime signal numbers reserved for application use.

Value: 8

<dt>_POSIX_SEM_NSEMS_MAX<dd>

The number of semaphores that a process may have.

Value: 256

<dt>_POSIX_SEM_VALUE_MAX<dd>

The maximum value a semaphore may have.

Value: 32 767

<dt>_POSIX_SIGQUEUE_MAX<dd>

The number of queued signals that a process may send and have pending
at the receiver(s) at any time.

Value: 32

<dt>_POSIX_SSIZE_MAX<dd>

The value that can be stored in an object of type <b>ssize_t</b>.

Value: 32 767

<dt>_POSIX_STREAM_MAX<dd>

The number of streams that one process can have open at one time.

Value: 8

<dt>_POSIX_THREAD_DESTRUCTOR_ITERATIONS<dd>

The number of attempts made to destroy a thread's thread-specific data
values on thread exit.

Value: 4

<dt>_POSIX_THREAD_KEYS_MAX<dd>

The number of data keys per process.

Value: 128

<dt>_POSIX_THREAD_THREADS_MAX<dd>

The number of threads per process.

Value: 64

<dt>_POSIX_TIMER_MAX<dd>

The per process number of timers.

Value: 32

<dt>_POSIX_TTY_NAME_MAX<dd>

The size of the storage required for a terminal device name, in bytes,
including the terminating null.

Value: 9

<dt>_POSIX_TZNAME_MAX<dd>

Maximum number of bytes supported for the name of a time zone (not of TZ
variable).

Value: 3

<dt>_POSIX2_BC_BASE_MAX<dd>

Maximum
<i>obase</i>
values allowed by the
<i><a href="../xcu/bc.html">bc</a></i>
utility.

Value: 99

<dt>_POSIX2_BC_DIM_MAX<dd>

Maximum number of elements permitted in an array by the <i>bc</i> utility.

Value: 2 048

<dt>_POSIX2_BC_SCALE_MAX<dd>

Maximum
<i>scale</i>
value allowed by the
<i><a href="../xcu/bc.html">bc</a></i>
utility.

Value: 99

<dt>_POSIX2_BC_STRING_MAX<dd>

Maximum length of a string constant accepted by the <i>bc</i> utility.

Value: 1 000

<dt>_POSIX2_COLL_WEIGHTS_MAX<dd>

Maximum number of weights that can be assigned to an entry of
the LC_COLLATE <b>order</b> keyword in the locale definition file;
see the <b>XBD</b> specification, <a href="../xbd/locale.html"><b>Locale</b>&nbsp;</a>.

Value: 2

<dt>_POSIX2_EXPR_NEST_MAX<dd>

Maximum number of expressions that can be nested within parentheses by the
<i><a href="../xcu/expr.html">expr</a></i>
utility.

Value: 32

<dt>_POSIX2_LINE_MAX<dd>

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

<dt>_POSIX2_RE_DUP_MAX<dd>

Maximum number of repeated occurrences of a regular expression permitted
when using the interval notation \{<i>m</i>,<i>n</i>\};
see the <b>XBD</b> specification, <a href="../xbd/re.html"><b>Regular Expressions</b>&nbsp;</a>.

Value: 255

<dt>_XOPEN_IOV_MAX<dd>

Maximum number of <b>iovec</b> structures that one process has available
for use with
<i><a href="readv.html">readv()</a></i>
or
<i><a href="writev.html">writev()</a></i>.

Value: 16

</dl>
<h5><a name = "tag_000_007_349_006">&nbsp;</a>Numerical Limits</h5>
<p>
The values in the following lists are defined in
<i>&lt;limits.h&gt;</i>
and will be constant expressions suitable for use in
<b>#if</b>
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 will be defined as expressions of the correct type.
<p>
If the value of an object of type
<b>char</b>
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.
<dl compact>

<dt>CHAR_BIT<dd>

Number of bits in a type <b>char</b>.

Minimum Acceptable Value: 8

<dt>CHAR_MAX<dd>

Maximum value of a type <b>char</b>.

Minimum Acceptable Value: UCHAR_MAX or SCHAR_MAX

<dt>DBL_DIG<dd>

Digits of precision of a type <b>double</b>.  (<b>LEGACY</b>)

Minimum Acceptable Value: 10

<dt>DBL_MAX<dd>

Maximum value of a type <b>double</b>.  (<b>LEGACY</b>)

Minimum Acceptable Value: 1E +37

<dt>FLT_DIG<dd>

Digits of precision of a type <b>float</b>.  (<b>LEGACY</b>)

Minimum Acceptable Value: 6

<dt>FLT_MAX<dd>

Maximum value of a <b>float</b>.  (<b>LEGACY</b>)

Minimum Acceptable Value: 1E+37

<dt>INT_MAX<dd>

Maximum value of an <b>int</b>.

Minimum Acceptable Value: 2 147 483 647

<dt>LONG_BIT<dd>

Number of bits in a <b>long int</b>.

Minimum Acceptable Value: 32

<dt>LONG_MAX<dd>

Maximum value of a <b>long int</b>.

Minimum Acceptable Value: [phone]

<dt>MB_LEN_MAX<dd>

Maximum number of bytes in a character, for any supported locale.

Minimum Acceptable Value: 1

<dt>SCHAR_MAX<dd>

Maximum value of a type signed <b> char</b>.

Minimum Acceptable Value: +127

<dt>SHRT_MAX<dd>

Maximum value of a type <b>short</b>.

Minimum Acceptable Value: +32 767

<dt>SSIZE_MAX<dd>

Maximum value of an object of type <b>ssize_t</b>.

Minimum Acceptable Value: _POSIX_SSIZE_MAX

<dt>UCHAR_MAX<dd>

Maximum value of a type <b>unsigned char</b>.

Minimum Acceptable Value: 255

<dt>UINT_MAX<dd>

Maximum value of a type <b>unsigned int</b>.

Minimum Acceptable Value: 4 294 967 295

<dt>ULONG_MAX<dd>

Maximum value of a type <b>unsigned long int</b>.

Minimum Acceptable Value: 4 294 967 295

<dt>USHRT_MAX<dd>

Maximum value for a type <b>unsigned short int</b>.

Minimum Acceptable Value: 65 535

<dt>WORD_BIT<dd>

Number of bits in a word or type <b>int</b>.

Minimum Acceptable Value: 16

<dt>CHAR_MIN<dd>

Minimum value of a type <b>char</b>.

Maximum Acceptable Value: SCHAR_MIN or 0

<dt>INT_MIN<dd>

Minimum value of a type <b>int</b>.

Maximum Acceptable Value: -2 147 483 647

<dt>LONG_MIN<dd>

Minimum value of a type <b>long int</b>.

Maximum Acceptable Value: -2 147 483 647

<dt>SCHAR_MIN<dd>

Minimum value of a type <b>signed char</b>.

Maximum Acceptable Value: -127

<dt>SHRT_MIN<dd>

Minimum value of a type <b>short</b>.

Maximum Acceptable Value: -32 767

</dl>
<h5><a name = "tag_000_007_349_007">&nbsp;</a>Other Invariant Values</h5>
<p>
The following constants are defined on all systems in
<i>&lt;limits.h&gt;</i>.
<dl compact>

<dt>CHARCLASS_NAME_MAX<dd>

Maximum number of bytes in a character class name.

Minimum Acceptable Value: 14

<dt>NL_ARGMAX<dd>

Maximum value of <i>digit</i> in calls to the
<i><a href="printf.html">printf()</a></i>
and
<i><a href="scanf.html">scanf()</a></i>
functions.

Minimum Acceptable Value: 9

<dt>NL_LANGMAX<dd>

Maximum number of bytes in a <i>LANG</i> name.

Minimum Acceptable Value: 14

<dt>NL_MSGMAX<dd>

Maximum message number.

Minimum Acceptable Value: 32 767

<dt>NL_NMAX<dd>

Maximum number of bytes in an N-to-1 collation mapping.

Minimum Acceptable Value: *

<dt>NL_SETMAX<dd>

Maximum set number.

Minimum Acceptable Value: 255

<dt>NL_TEXTMAX<dd>

Maximum number of bytes in a message string.

Minimum Acceptable Value: _POSIX2_LINE_MAX

<dt>NZERO<dd>

Default process priority.

Minimum Acceptable Value: 20

<dt>TMP_MAX<dd>

Minimum number of unique pathnames generated by
<i><a href="tmpnam.html">tmpnam()</a></i>.
Maximum number of times an application can call
<i><a href="tmpnam.html">tmpnam()</a></i>
reliably.  (<b>LEGACY</b>)

Minimum Acceptable Value: 10 000

</dl>
</blockquote><h4><a name = "tag_000_007_350">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_351">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_007_352">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="fpathconf.html">fpathconf()</a></i>,
<i><a href="pathconf.html">pathconf()</a></i>,
<i><a href="sysconf.html">sysconf()</a></i>.
</blockquote><hr size=2 noshade>
<center><font size=2>
UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
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