path: root/man3p/localtime.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "LOCALTIME" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" localtime 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
localtime, localtime_r \- convert a time value to a broken-down local
time
.SH SYNOPSIS
.LP
\fB#include <time.h>
.br
.sp
struct tm *localtime(const time_t *\fP\fItimer\fP\fB);
.br
\fP
.LP
\fBstruct tm *localtime_r(const time_t *restrict\fP \fItimer\fP\fB,
.br
\ \ \ \ \ \  struct tm *restrict\fP \fIresult\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
For \fIlocaltime\fP():   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. 
.LP
The \fIlocaltime\fP() function shall convert the time in seconds since
the Epoch pointed to by \fItimer\fP into a broken-down
time, expressed as a local time. The function corrects for the timezone
and any seasonal time adjustments.   \ Local timezone
information is used as though \fIlocaltime\fP() calls \fItzset\fP().
.LP
The relationship between a time in seconds since the Epoch used as
an argument to \fIlocaltime\fP() and the \fBtm\fP structure
(defined in the \fI<time.h>\fP 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,
Section 4.14, Seconds Since the Epoch) corrected for timezone and
any seasonal
time adjustments, where the names in the structure and in the expression
correspond. 
.LP
The same relationship shall apply for \fIlocaltime_r\fP(). 
.LP
The
\fIlocaltime\fP() function need not be reentrant. A function that
is not required to be reentrant is not required to be
thread-safe.
.LP
The \fIasctime\fP(), \fIctime\fP(), \fIgmtime\fP(), and \fIlocaltime\fP()
functions shall return values in one of two static objects:
a broken-down time structure and an array of type \fBchar\fP. Execution
of any of the functions may overwrite the information
returned in either of these objects by any of the other functions.
.LP
The \fIlocaltime_r\fP() function shall convert the time in seconds
since the Epoch pointed to by \fItimer\fP into a broken-down
time stored in the structure to which \fIresult\fP points. The \fIlocaltime_r\fP()
function shall also return a pointer to that
same structure.
.LP
Unlike \fIlocaltime\fP(), the reentrant version is not required to
set \fItzname\fP. 
.SH RETURN VALUE
.LP
Upon successful completion, the \fIlocaltime\fP() function shall return
a pointer to the broken-down time structure. If an
error is detected, \fIlocaltime\fP() shall return a null pointer 
\ and set \fIerrno\fP to indicate the error. 
.LP
Upon successful completion, \fIlocaltime_r\fP() shall return a pointer
to the structure pointed to by the argument \fIresult\fP.
.SH ERRORS
.LP
The \fIlocaltime\fP() function shall fail if:
.TP 7
.B EOVERFLOW
The result cannot be represented. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Getting the Local Date and Time
.LP
The following example uses the \fItime\fP() function to calculate
the time elapsed, in
seconds, since January 1, 1970 0:00 UTC (the Epoch), \fIlocaltime\fP()
to convert that value to a broken-down time, and \fIasctime\fP() to
convert the broken-down time values into a printable string.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <time.h>
.sp

int main(void)
{
    time_t result;
.sp

    result = time(NULL);
    printf("%s%ju secs since the Epoch\\n",
        asctime(localtime(&result)),
            (uintmax_t)result);
    return(0);
}
\fP
.fi
.RE
.LP
This example writes the current time to \fIstdout\fP in a form like
this:
.sp
.RS
.nf

\fBWed Jun 26 10:32:15 1996
835810335 secs since the Epoch
\fP
.fi
.RE
.SS Getting the Modification Time for a File
.LP
The following example gets the modification time for a file. The \fIlocaltime\fP()
function converts the \fBtime_t\fP value of
the last modification date, obtained by a previous call to \fIstat\fP(),
into a \fBtm\fP
structure that contains the year, month, day, and so on.
.sp
.RS
.nf

\fB#include <time.h>
\&...
struct stat statbuf;
\&...
tm = localtime(&statbuf.st_mtime);
\&...
\fP
.fi
.RE
.SS Timing an Event
.LP
The following example gets the current time, converts it to a string
using \fIlocaltime\fP() and \fIasctime\fP(), and prints it to standard
output using \fIfputs\fP(). It then prints the number of minutes to
an event being timed.
.sp
.RS
.nf

\fB#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);
\&...
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
The \fIlocaltime_r\fP() 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.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIasctime\fP(), \fIclock\fP(), \fIctime\fP()
, \fIdifftime\fP(), \fIgetdate\fP(), \fIgmtime\fP(), \fImktime\fP()
, \fIstrftime\fP(), \fIstrptime\fP(), \fItime\fP(), \fIutime\fP()
, the
Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<time.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .