252 lines
10 KiB
HTML
252 lines
10 KiB
HTML
<!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 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 1003.1-2001<br>
|
|
Copyright © 2001 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. Any
|
|
conflict between the requirements described here and the ISO C standard is unintentional. This volume of
|
|
IEEE 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-down
|
|
time, 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 timezone
|
|
information 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 the
|
|
expression 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 seasonal
|
|
time 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 be
|
|
thread-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 information
|
|
returned 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-down
|
|
time stored in the structure to which <i>result</i> points. The <i>localtime_r</i>() function shall also return a pointer to that
|
|
same 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>The <i>localtime</i>() function shall return a pointer to the broken-down time structure.</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>No errors are defined.</p>
|
|
</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, in
|
|
seconds, 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 1996
|
|
835810335 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 of
|
|
the 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 static
|
|
data 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> , <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
|
|
Base 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 a
|
|
static data area.</p>
|
|
|
|
<p>The <b>restrict</b> keyword is added to the <i>localtime_r</i>() prototype for alignment with the ISO/IEC 9899:1999
|
|
standard.</p>
|
|
|
|
<p>Examples are added.</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>
|
|
|