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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) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>asctime</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="asctime"></a> <a name="tag_03_22"></a><!-- asctime --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_22_01"></a>NAME</h4><blockquote>asctime, asctime_r - convert date and time to a string</blockquote><h4><a name="tag_03_22_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/time.h.html">time.h</a>><br><br> char *asctime(const struct tm *</tt><i>timeptr</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"> char *asctime_r(const struct tm *restrict</tt> <i>tm</i><tt>, char *restrict</tt> <i>buf</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_22_03"></a>DESCRIPTION</h4><blockquote><p>For <i>asctime</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>asctime</i>() function shall convert the broken-down time in the structure pointed to by <i>timeptr</i> into a string inthe form:</p><pre><tt>Sun Sep 16 01:03:52 1973\n\0</tt></pre><p>using the equivalent of the following algorithm:</p><pre><tt>char *asctime(const struct tm *timeptr){ static char wday_name[7][3] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" }; static char mon_name[12][3] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" }; static char result[26];<br> sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n", wday_name[timeptr->tm_wday], mon_name[timeptr->tm_mon], timeptr->tm_mday, timeptr->tm_hour, timeptr->tm_min, timeptr->tm_sec, 1900 + timeptr->tm_year); return result;}</tt></pre><p>The <b>tm</b> structure is defined in the <a href="../basedefs/time.h.html"><i><time.h></i></a> header.</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>asctime</i>(), <a href="../functions/ctime.html"><i>ctime</i>()</a>, <a href="../functions/gmtime.html"><i>gmtime</i>()</a>, and<a href="../functions/localtime.html"><i>localtime</i>()</a> functions shall return values in one of two static objects: abroken-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.</p><p>The <i>asctime</i>() function need not be reentrant. A function that is not required to be reentrant is not required to bethread-safe. <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>asctime_r</i>() function shall convert the broken-down time in the structure pointed to by <i>tm</i> into a string (of thesame form as that returned by <i>asctime</i>()) that is placed in the user-supplied buffer pointed to by <i>buf</i> (which shallcontain at least 26 bytes) and then return <i>buf</i>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_22_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>asctime</i>() shall return a pointer to the string. <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If thefunction is unsuccessful, it shall return NULL. <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>asctime_r</i>() shall return a pointer to a character string containing the date and time. Thisstring is pointed to by the argument <i>buf</i>. If the function is unsuccessful, it shall return NULL. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_22_05"></a>ERRORS</h4><blockquote><p>No errors are defined.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_22_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_22_07"></a>APPLICATION USAGE</h4><blockquote><p>Values for the broken-down time structure can be obtained by calling <a href="../functions/gmtime.html"><i>gmtime</i>()</a> or<a href="../functions/localtime.html"><i>localtime</i>()</a>. This function is included for compatibility with olderimplementations, and does not support localized date and time formats. Applications should use <a href="../functions/strftime.html"><i>strftime</i>()</a> to achieve maximum portability.</p><p>The <i>asctime_r</i>() function is thread-safe and shall return values in a user-supplied buffer instead of possibly using astatic data area that may be overwritten by each call.</p></blockquote><h4><a name="tag_03_22_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_22_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_22_10"></a>SEE ALSO</h4><blockquote><p><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="gmtime.html"><i>gmtime</i>()</a>, <a href="localtime.html"><i>localtime</i>()</a>, <a href="mktime.html"><i>mktime</i>()</a>, <a href="strftime.html"><i>strftime</i>()</a>, <a href="strptime.html"><i>strptime</i>()</a>, <a href="time.html"><i>time</i>()</a>, <a href="utime.html"><i>utime</i>()</a>, the BaseDefinitions 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_22_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_22_12"></a>Issue 5</h4><blockquote><p>Normative text previously in the APPLICATION USAGE section is moved to the DESCRIPTION.</p><p>The <i>asctime_r</i>() function is included for alignment with the POSIX Threads Extension.</p><p>A note indicating that the <i>asctime</i>() function need not be reentrant is added to the DESCRIPTION.</p></blockquote><h4><a name="tag_03_22_13"></a>Issue 6</h4><blockquote><p>The <i>asctime_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 DESCRIPTION of <i>asctime_r</i>() is updated to describe the format of the string returned.</p><p>The <b>restrict</b> keyword is added to the <i>asctime_r</i>() prototype for alignment with the ISO/IEC 9899:1999standard.</p><p>IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/17 is applied, adding the CX extension in the RETURN VALUEsection requiring that if the <i>asctime</i>() function is unsuccessful it returns NULL.</p></blockquote><div class="box"><em>End of informative text.</em></div><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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