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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>localtime</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="localtime"></a> <a name="tag_03_341"></a><!-- localtime --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_341_01"></a>NAME</h4><blockquote>localtime, localtime_r - convert a time value to a broken-down local time</blockquote><h4><a name="tag_03_341_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/time.h.html">time.h</a>><br><br> struct tm *localtime(const time_t *</tt><i>timer</i><tt>);<br></tt></code></p><div class="box"><code><tt><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> struct tm *localtime_r(const time_t *restrict</tt> <i>timer</i><tt>,<br> struct tm *restrict</tt> <i>result</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_341_03"></a>DESCRIPTION</h4><blockquote><p>For <i>localtime</i>(): <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The functionality described on this reference page is aligned with the ISO C standard. Anyconflict between the requirements described here and the ISO C standard is unintentional. This volume ofIEEE Std 1003.1-2001 defers to the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p><p>The <i>localtime</i>() function shall convert the time in seconds since the Epoch pointed to by <i>timer</i> into a broken-downtime, expressed as a local time. The function corrects for the timezone and any seasonal time adjustments. <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Local timezoneinformation is used as though <i>localtime</i>() calls <a href="../functions/tzset.html"><i>tzset</i>()</a>.</p><p>The relationship between a time in seconds since the Epoch used as an argument to <i>localtime</i>() and the <b>tm</b> structure(defined in the <a href="../basedefs/time.h.html"><i><time.h></i></a> header) is that the result shall be as specified in theexpression given in the definition of seconds since the Epoch (see the Base Definitions volume of IEEE Std 1003.1-2001,<a href="../basedefs/xbd_chap04.html#tag_04_14">Section 4.14, Seconds Since the Epoch</a>) corrected for timezone and any seasonaltime adjustments, where the names in the structure and in the expression correspond. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p><p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The same relationship shall apply for <i>localtime_r</i>(). <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p><p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The<i>localtime</i>() function need not be reentrant. A function that is not required to be reentrant is not required to bethread-safe.</p><p>The <a href="../functions/asctime.html"><i>asctime</i>()</a>, <a href="../functions/ctime.html"><i>ctime</i>()</a>, <a href="../functions/gmtime.html"><i>gmtime</i>()</a>, and <i>localtime</i>() functions shall return values in one of two static objects:a broken-down time structure and an array of type <b>char</b>. Execution of any of the functions may overwrite the informationreturned in either of these objects by any of the other functions. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p><p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The <i>localtime_r</i>() function shall convert the time in seconds since the Epoch pointed to by <i>timer</i> into a broken-downtime stored in the structure to which <i>result</i> points. The <i>localtime_r</i>() function shall also return a pointer to thatsame structure.</p><p>Unlike <i>localtime</i>(), the reentrant version is not required to set <i>tzname</i>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_341_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, the <i>localtime</i>() function shall return a pointer to the broken-down time structure. If anerror is detected, <i>localtime</i>() shall return a null pointer <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <imgsrc="../images/opt-start.gif" alt="[Option Start]" border="0"> and set <i>errno</i> to indicate the error. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p><p><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Upon successful completion, <i>localtime_r</i>() shall return a pointer to the structure pointed to by the argument <i>result</i>.<img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_341_05"></a>ERRORS</h4><blockquote><p>The <i>localtime</i>() function shall fail if:</p><dl compact><dt>[EOVERFLOW]</dt><dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The result cannot be represented. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_341_06"></a>EXAMPLES</h4><blockquote><h5><a name="tag_03_341_06_01"></a>Getting the Local Date and Time</h5><p>The following example uses the <a href="../functions/time.html"><i>time</i>()</a> function to calculate the time elapsed, inseconds, since January 1, 1970 0:00 UTC (the Epoch), <i>localtime</i>() to convert that value to a broken-down time, and <a href="../functions/asctime.html"><i>asctime</i>()</a> to convert the broken-down time values into a printable string.</p><pre><tt>#include <stdio.h>#include <time.h><br>int main(void){ time_t result;<br> result = time(NULL); printf("%s%ju secs since the Epoch\n", asctime(localtime(&result)), (uintmax_t)result); return(0);}</tt></pre><p>This example writes the current time to <i>stdout</i> in a form like this:</p><pre><tt>Wed Jun 26 10:32:15 1996835810335 secs since the Epoch</tt></pre><h5><a name="tag_03_341_06_02"></a>Getting the Modification Time for a File</h5><p>The following example gets the modification time for a file. The <i>localtime</i>() function converts the <b>time_t</b> value ofthe last modification date, obtained by a previous call to <a href="../functions/stat.html"><i>stat</i>()</a>, into a <b>tm</b>structure that contains the year, month, day, and so on.</p><pre><tt>#include <time.h>...struct stat statbuf;...tm = localtime(&statbuf.st_mtime);...</tt></pre><h5><a name="tag_03_341_06_03"></a>Timing an Event</h5><p>The following example gets the current time, converts it to a string using <i>localtime</i>() and <a href="../functions/asctime.html"><i>asctime</i>()</a>, and prints it to standard output using <a href="../functions/fputs.html"><i>fputs</i>()</a>. It then prints the number of minutes to an event being timed.</p><pre><tt>#include <time.h>#include <stdio.h>...time_t now;int minutes_to_event;...time(&now);printf("The time is ");fputs(asctime(localtime(&now)), stdout);printf("There are still %d minutes to the event.\n", minutes_to_event);...</tt></pre></blockquote><h4><a name="tag_03_341_07"></a>APPLICATION USAGE</h4><blockquote><p>The <i>localtime_r</i>() function is thread-safe and returns values in a user-supplied buffer instead of possibly using a staticdata area that may be overwritten by each call.</p></blockquote><h4><a name="tag_03_341_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_341_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_341_10"></a>SEE ALSO</h4><blockquote><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>, <a href="difftime.html"><i>difftime</i>()</a> , <a href="getdate.html"><i>getdate</i>()</a> , <a href="gmtime.html"><i>gmtime</i>()</a> , <a href="mktime.html"><i>mktime</i>()</a> , <a href="strftime.html"><i>strftime</i>()</a> , <ahref="strptime.html"><i>strptime</i>()</a> , <a href="time.html"><i>time</i>()</a> , <a href="utime.html"><i>utime</i>()</a> , theBase Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/time.h.html"><i><time.h></i></a></p></blockquote><h4><a name="tag_03_341_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><h4><a name="tag_03_341_12"></a>Issue 5</h4><blockquote><p>A note indicating that the <i>localtime</i>() function need not be reentrant is added to the DESCRIPTION.</p><p>The <i>localtime_r</i>() function is included for alignment with the POSIX Threads Extension.</p></blockquote><h4><a name="tag_03_341_13"></a>Issue 6</h4><blockquote><p>The <i>localtime_r</i>() function is marked as part of the Thread-Safe Functions option.</p><p>Extensions beyond the ISO C standard are marked.</p><p>The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using astatic data area.</p><p>The <b>restrict</b> keyword is added to the <i>localtime_r</i>() prototype for alignment with the ISO/IEC 9899:1999standard.</p><p>Examples are added.</p><p>IEEE Std 1003.1-2001/Cor 1-2002, itemm XSH/TC1/D6/32 is applied, adding the [EOVERFLOW] error.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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