limits.h.html

IEEE 1003.1-2003, Single Unix Specification v3

<dd>
Maximum length of terminal device name.<br>
Minimum Acceptable Value: {_POSIX_TTY_NAME_MAX}</dd>

<dt>{TZNAME_MAX}</dt>

<dd>
Maximum number of bytes supported for the name of a timezone (not of the <i>TZ</i> variable).<br>
Minimum Acceptable Value: {_POSIX_TZNAME_MAX}</dd>
</dl>

<basefont size="2"> 

<dl>
<dt><b>Note:</b></dt>

<dd>The length given by {TZNAME_MAX} does not include the quoting characters mentioned in <a href=
"xbd_chap08.html#tag_08_03"><i>Other Environment Variables</i></a> .</dd>
</dl>

<basefont size="3"> 

<h5><a name="tag_13_24_03_02"></a>Pathname Variable Values</h5>

<p>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.</p>

<p>A definition of one of the values shall be omitted from the <i>&lt;limits.h&gt;</i> 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 <a href=
"../functions/pathconf.html"><i>pathconf</i>()</a> function.</p>

<dl compact>
<dt>{FILESIZEBITS}</dt>

<dd>
Minimum number of bits needed to represent, as a signed integer value, the maximum size of a regular file allowed in the specified
directory.<br>
Minimum Acceptable Value: 32</dd>

<dt>{LINK_MAX}</dt>

<dd>
Maximum number of links to a single file.<br>
Minimum Acceptable Value: {_POSIX_LINK_MAX}</dd>

<dt>{MAX_CANON}</dt>

<dd>
Maximum number of bytes in a terminal canonical input line.<br>
Minimum Acceptable Value: {_POSIX_MAX_CANON}</dd>

<dt>{MAX_INPUT}</dt>

<dd>
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.<br>
Minimum Acceptable Value: {_POSIX_MAX_INPUT}</dd>

<dt>{NAME_MAX}</dt>

<dd>
Maximum number of bytes in a filename (not including terminating null).<br>
Minimum Acceptable Value: {_POSIX_NAME_MAX}<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Minimum Acceptable Value: {_XOPEN_NAME_MAX} <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{PATH_MAX}</dt>

<dd>
Maximum number of bytes in a pathname, including the terminating null character.<br>
Minimum Acceptable Value: {_POSIX_PATH_MAX}<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
Minimum Acceptable Value: {_XOPEN_PATH_MAX} <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{PIPE_BUF}</dt>

<dd>
Maximum number of bytes that is guaranteed to be atomic when writing to a pipe.<br>
Minimum Acceptable Value: {_POSIX_PIPE_BUF}</dd>

<dt>{POSIX_ALLOC_SIZE_MIN}</dt>

<dd><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
Minimum number of bytes of storage actually allocated for any portion of a file.<br>
Minimum Acceptable Value: Not specified. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{POSIX_REC_INCR_XFER_SIZE}</dt>

<dd><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
Recommended increment for file transfer sizes between the {POSIX_REC_MIN_XFER_SIZE} and {POSIX_REC_MAX_XFER_SIZE} values.<br>
Minimum Acceptable Value: Not specified. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{POSIX_REC_MAX_XFER_SIZE}</dt>

<dd><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
Maximum recommended file transfer size.<br>
Minimum Acceptable Value: Not specified. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{POSIX_REC_MIN_XFER_SIZE}</dt>

<dd><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
Minimum recommended file transfer size.<br>
Minimum Acceptable Value: Not specified. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{POSIX_REC_XFER_ALIGN}</dt>

<dd><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
Recommended file transfer buffer alignment.<br>
Minimum Acceptable Value: Not specified. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{SYMLINK_MAX}</dt>

<dd>
Maximum number of bytes in a symbolic link.<br>
Minimum Acceptable Value: {_POSIX_SYMLINK_MAX}</dd>
</dl>

<h5><a name="tag_13_24_03_03"></a>Runtime Increasable Values</h5>

<p>The magnitude limitations in the following list shall be fixed by specific implementations. An application should assume that
the value supplied by <i>&lt;limits.h&gt;</i> 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
<i>&lt;limits.h&gt;</i> for that implementation. The actual value supported by a specific instance shall be provided by the <a
href="../functions/sysconf.html"><i>sysconf</i>()</a> function.</p>

<dl compact>
<dt>{BC_BASE_MAX}</dt>

<dd>
Maximum <i>obase</i> values allowed by the <a href="../utilities/bc.html"><i>bc</i></a> utility.<br>
Minimum Acceptable Value: {_POSIX2_BC_BASE_MAX}</dd>

<dt>{BC_DIM_MAX}</dt>

<dd>
Maximum number of elements permitted in an array by the <a href="../utilities/bc.html"><i>bc</i></a> utility.<br>
Minimum Acceptable Value: {_POSIX2_BC_DIM_MAX}</dd>

<dt>{BC_SCALE_MAX}</dt>

<dd>
Maximum <i>scale</i> value allowed by the <a href="../utilities/bc.html"><i>bc</i></a> utility.<br>
Minimum Acceptable Value: {_POSIX2_BC_SCALE_MAX}</dd>

<dt>{BC_STRING_MAX}</dt>

<dd>
Maximum length of a string constant accepted by the <a href="../utilities/bc.html"><i>bc</i></a> utility.<br>
Minimum Acceptable Value: {_POSIX2_BC_STRING_MAX}</dd>

<dt>{CHARCLASS_NAME_MAX}</dt>

<dd>
Maximum number of bytes in a character class name.<br>
Minimum Acceptable Value: {_POSIX2_CHARCLASS_NAME_MAX}</dd>

<dt>{COLL_WEIGHTS_MAX}</dt>

<dd>
Maximum number of weights that can be assigned to an entry of the <i>LC_COLLATE</i> <b>order</b> keyword in the locale definition
file; see <a href="xbd_chap07.html#tag_07"><i>Locale</i></a> .<br>
Minimum Acceptable Value: {_POSIX2_COLL_WEIGHTS_MAX}</dd>

<dt>{EXPR_NEST_MAX}</dt>

<dd>
Maximum number of expressions that can be nested within parentheses by the <a href="../utilities/expr.html"><i>expr</i></a>
utility.<br>
Minimum Acceptable Value: {_POSIX2_EXPR_NEST_MAX}</dd>

<dt>{LINE_MAX}</dt>

<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 &lt;newline&gt;.<br>
Minimum Acceptable Value: {_POSIX2_LINE_MAX}</dd>

<dt>{NGROUPS_MAX}</dt>

<dd>
Maximum number of simultaneous supplementary group IDs per process.<br>
Minimum Acceptable Value: {_POSIX_NGROUPS_MAX}</dd>

<dt>{RE_DUP_MAX}</dt>

<dd>
Maximum number of repeated occurrences of a regular expression permitted when using the interval notation \{<i>m</i>,<i>n</i>\};
see <a href="xbd_chap09.html#tag_09"><i>Regular Expressions</i></a> .<br>
Minimum Acceptable Value: {_POSIX2_RE_DUP_MAX}</dd>
</dl>

<h5><a name="tag_13_24_03_04"></a>Maximum Values</h5>

<p><sup>[<a href="javascript:open_code('TMR')">TMR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
The symbolic constants in the following list shall be defined in <i>&lt;limits.h&gt;</i> 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. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>

<dl compact>
<dt>{_POSIX_CLOCKRES_MIN}</dt>

<dd><sup>[<a href="javascript:open_code('TMR')">TMR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The resolution of the CLOCK_REALTIME clock, in nanoseconds.<br>
Value: 20 000 000 <img src="../images/opt-end.gif" alt="[Option End]" border="0"> 

<p><sup>[<a href="javascript:open_code('MON')">MON</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
If the Monotonic Clock option is supported, the resolution of the CLOCK_MONOTONIC clock, in nanoseconds, is represented by
{_POSIX_CLOCKRES_MIN}. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
</dd>
</dl>

<h5><a name="tag_13_24_03_05"></a>Minimum Values</h5>

<p>The symbolic constants in the following list shall be defined in <i>&lt;limits.h&gt;</i> 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&nbsp;Std&nbsp;1003.1-2001. Related symbolic constants are defined elsewhere in this volume of IEEE&nbsp;Std&nbsp;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.</p>

<dl compact>
<dt>{_POSIX_AIO_LISTIO_MAX}</dt>

<dd><sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The number of I/O operations that can be specified in a list I/O call.<br>
Value: 2 <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{_POSIX_AIO_MAX}</dt>

<dd><sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The number of outstanding asynchronous I/O operations.<br>
Value: 1 <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{_POSIX_ARG_MAX}</dt>

<dd>
Maximum length of argument to the <i>exec</i> functions including environment data.<br>
Value: 4 096</dd>

<dt>{_POSIX_CHILD_MAX}</dt>

<dd>
Maximum number of simultaneous processes per real user ID.<br>
Value: 25</dd>

<dt>{_POSIX_DELAYTIMER_MAX}</dt>

<dd><sup>[<a href="javascript:open_code('TMR')">TMR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The number of timer expiration overruns.<br>
Value: 32 <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{_POSIX_HOST_NAME_MAX}</dt>

<dd>
Maximum length of a host name (not including the terminating null) as returned from the <a href=
"../functions/gethostname.html"><i>gethostname</i>()</a> function.<br>
Value: 255</dd>

<dt>{_POSIX_LINK_MAX}</dt>

<dd>
Maximum number of links to a single file.<br>
Value: 8</dd>

<dt>{_POSIX_LOGIN_NAME_MAX}</dt>

<dd>
The size of the storage required for a login name, in bytes, including the terminating null.<br>
Value: 9</dd>

<dt>{_POSIX_MAX_CANON}</dt>

<dd>
Maximum number of bytes in a terminal canonical input queue.<br>
Value: 255</dd>

<dt>{_POSIX_MAX_INPUT}</dt>

<dd>
Maximum number of bytes allowed in a terminal input queue.<br>
Value: 255</dd>

<dt>{_POSIX_MQ_OPEN_MAX}</dt>

<dd><sup>[<a href="javascript:open_code('MSG')">MSG</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The number of message queues that can be open for a single process.<br>
Value: 8 <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{_POSIX_MQ_PRIO_MAX}</dt>

<dd><sup>[<a href="javascript:open_code('MSG')">MSG</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The maximum number of message priorities supported by the implementation.<br>
Value: 32 <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>

<dt>{_POSIX_NAME_MAX}</dt>

<dd>
Maximum number of bytes in a filename (not including terminating null).<br>
Value: 14</dd>