180 lines
8.0 KiB
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180 lines
8.0 KiB
HTML
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<title>gmtime</title>
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<basefont size="3"> <a name="gmtime"></a> <a name="tag_03_261"></a><!-- gmtime -->
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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_261_01"></a>NAME</h4>
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<blockquote>gmtime, gmtime_r - convert a time value to a broken-down UTC time</blockquote>
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<h4><a name="tag_03_261_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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struct tm *gmtime(const time_t *</tt><i>timer</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"> struct tm *gmtime_r(const time_t *restrict</tt> <i>timer</i><tt>,<br>
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struct tm *restrict</tt> <i>result</i><tt>); <img src="../images/opt-end.gif" alt=
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"[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_261_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>For <i>gmtime</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>gmtime</i>() function shall convert the time in seconds since the Epoch pointed to by <i>timer</i> into a broken-down
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time, expressed as Coordinated Universal Time (UTC).</p>
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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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relationship between a time in seconds since the Epoch used as an argument to <i>gmtime</i>() and the <b>tm</b> structure (defined
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in the <a href="../basedefs/time.h.html"><i><time.h></i></a> header) is that the result shall be as specified in the
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expression given in the definition of seconds since the Epoch (see the Base Definitions volume of IEEE Std 1003.1-2001,
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<a href="../basedefs/xbd_chap04.html#tag_04_14">Section 4.14, Seconds Since the Epoch</a>), where the names in the structure and in
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the expression correspond. <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 same relationship shall apply for <i>gmtime_r</i>(). <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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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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<i>gmtime</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.</p>
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<p>The <a href="../functions/asctime.html"><i>asctime</i>()</a>, <a href="../functions/ctime.html"><i>ctime</i>()</a>,
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<i>gmtime</i>(), and <a href="../functions/localtime.html"><i>localtime</i>()</a> functions shall return values in one of two
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static objects: a broken-down time structure and an array of type <b>char</b>. Execution of any of the functions may overwrite the
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information returned in either of these objects by any of the other functions. <img src="../images/opt-end.gif" alt="[Option End]"
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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>gmtime_r</i>() function shall convert the time in seconds since the Epoch pointed to by <i>timer</i> into a broken-down time
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expressed as Coordinated Universal Time (UTC). The broken-down time is stored in the structure referred to by <i>result</i>. The
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<i>gmtime_r</i>() function shall also return the address of the same structure. <img src="../images/opt-end.gif" alt="[Option End]"
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border="0"></p>
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</blockquote>
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<h4><a name="tag_03_261_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>The <i>gmtime</i>() function shall return a pointer to a <b>struct tm</b>.</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>gmtime_r</i>() shall return the address of the structure pointed to by the argument <i>result</i>.
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If an error is detected, or UTC is not available, <i>gmtime_r</i>() shall return a null pointer. <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_261_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_261_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_261_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>gmtime_r</i>() function is thread-safe and returns values in a user-supplied buffer instead of possibly using a static
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data area that may be overwritten by each call.</p>
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</blockquote>
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<h4><a name="tag_03_261_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_261_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_261_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="ctime.html"><i>ctime</i>()</a>
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, <a href="difftime.html"><i>difftime</i>()</a> , <a href="localtime.html"><i>localtime</i>()</a> , <a href=
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"mktime.html"><i>mktime</i>()</a> , <a href="strftime.html"><i>strftime</i>()</a> , <a href="strptime.html"><i>strptime</i>()</a> ,
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<a href="time.html"><i>time</i>()</a> , <a href="utime.html"><i>utime</i>()</a> , the Base Definitions volume of
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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_261_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_261_12"></a>Issue 5</h4>
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<blockquote>
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<p>A note indicating that the <i>gmtime</i>() function need not be reentrant is added to the DESCRIPTION.</p>
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<p>The <i>gmtime_r</i>() function is included for alignment with the POSIX Threads Extension.</p>
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</blockquote>
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<h4><a name="tag_03_261_13"></a>Issue 6</h4>
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<blockquote>
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<p>The <i>gmtime_r</i>() function is marked as part of the Thread-Safe Functions option.</p>
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<p>Extensions beyond the ISO C standard are marked.</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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<p>The <b>restrict</b> keyword is added to the <i>gmtime_r</i>() prototype for alignment with the ISO/IEC 9899:1999
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standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<center><font size="2"><!--footer start-->
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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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