179 lines
7.5 KiB
HTML
179 lines
7.5 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>ctime</title>
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<basefont size="3"> <a name="ctime"></a> <a name="tag_03_103"></a><!-- ctime -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_103_01"></a>NAME</h4>
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<blockquote>ctime, ctime_r - convert a time value to a date and time string</blockquote>
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<h4><a name="tag_03_103_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/time.h.html">time.h</a>><br>
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<br>
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char *ctime(const time_t *</tt><i>clock</i><tt>);<br>
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</tt></code></p>
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> char *ctime_r(const time_t *</tt><i>clock</i><tt>, char *</tt><i>buf</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_103_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>For <i>ctime</i>(): <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any
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conflict between the requirements described here and the ISO C standard is unintentional. This volume of
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IEEE Std 1003.1-2001 defers to the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></p>
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<p>The <i>ctime</i>() function shall convert the time pointed to by <i>clock</i>, representing time in seconds since the Epoch, to
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local time in the form of a string. It shall be equivalent to:</p>
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<pre>
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<tt>asctime(localtime(clock))
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</tt>
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</pre>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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<a href="../functions/asctime.html"><i>asctime</i>()</a>, <i>ctime</i>(), <a href="../functions/gmtime.html"><i>gmtime</i>()</a>,
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and <a href="../functions/localtime.html"><i>localtime</i>()</a> functions shall return values in one of two static objects: a
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broken-down time structure and an array of <b>char</b>. Execution of any of the functions may overwrite the information returned in
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either of these objects by any of the other functions.</p>
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<p>The <i>ctime</i>() function need not be reentrant. A function that is not required to be reentrant is not required to be
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thread-safe. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>ctime_r</i>() function shall convert the calendar time pointed to by <i>clock</i> to local time in exactly the same form as
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<i>ctime</i>() and put the string into the array pointed to by <i>buf</i> (which shall be at least 26 bytes in size) and return
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<i>buf</i>.</p>
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<p>Unlike <i>ctime</i>(), the thread-safe version <i>ctime_r</i>() is not required to set <i>tzname</i>. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_103_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>The <i>ctime</i>() function shall return the pointer returned by <a href="../functions/asctime.html"><i>asctime</i>()</a> with
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that broken-down time as an argument.</p>
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<p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Upon successful completion, <i>ctime_r</i>() shall return a pointer to the string pointed to by <i>buf</i>. When an error is
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encountered, a null pointer shall be returned. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_103_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_103_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_103_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>Values for the broken-down time structure can be obtained by calling <a href="../functions/gmtime.html"><i>gmtime</i>()</a> or
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<a href="../functions/localtime.html"><i>localtime</i>()</a>. The <i>ctime</i>() function is included for compatibility with older
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implementations, and does not support localized date and time formats. Applications should use the <a href=
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"../functions/strftime.html"><i>strftime</i>()</a> function to achieve maximum portability.</p>
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<p>The <i>ctime_r</i>() function is thread-safe and shall return values in a user-supplied buffer instead of possibly using a
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static data area that may be overwritten by each call.</p>
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</blockquote>
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<h4><a name="tag_03_103_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_103_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_103_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="asctime.html"><i>asctime</i>()</a> , <a href="clock.html"><i>clock</i>()</a> , <a href=
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"difftime.html"><i>difftime</i>()</a> , <a href="gmtime.html"><i>gmtime</i>()</a> , <a href="localtime.html"><i>localtime</i>()</a>
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, <a href="mktime.html"><i>mktime</i>()</a> , <a href="strftime.html"><i>strftime</i>()</a> , <a href=
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"strptime.html"><i>strptime</i>()</a> , <a href="time.html"><i>time</i>()</a> , <a href="utime.html"><i>utime</i>()</a> , the Base
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Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/time.h.html"><i><time.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_103_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_103_12"></a>Issue 5</h4>
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<blockquote>
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<p>Normative text previously in the APPLICATION USAGE section is moved to the DESCRIPTION.</p>
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<p>The <i>ctime_r</i>() function is included for alignment with the POSIX Threads Extension.</p>
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<p>A note indicating that the <i>ctime</i>() function need not be reentrant is added to the DESCRIPTION.</p>
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</blockquote>
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<h4><a name="tag_03_103_13"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.</p>
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<p>The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a
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static data area.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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