NAME
localtime, localtime_r - convert a time value to a broken-down local
time
SYNOPSIS
#include <time.h>
struct tm *localtime(const time_t *timer);
struct tm *localtime_r(const time_t *restrict timer,
struct tm *restrict result);
DESCRIPTION
For localtime(): 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.
The localtime() function shall convert the time in seconds since the
Epoch pointed to by timer 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
localtime() calls tzset().
The relationship between a time in seconds since the Epoch used as an
argument to localtime() and the tm structure (defined in the <time.h>
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.
The same relationship shall apply for localtime_r().
The localtime() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
The asctime(), ctime(), gmtime(), and localtime() functions shall
return values in one of two static objects: a broken-down time
structure and an array of type char. Execution of any of the functions
may overwrite the information returned in either of these objects by
any of the other functions.
The localtime_r() function shall convert the time in seconds since the
Epoch pointed to by timer into a broken-down time stored in the
structure to which result points. The localtime_r() function shall also
return a pointer to that same structure.
Unlike localtime(), the reentrant version is not required to set
tzname.
RETURN VALUE
Upon successful completion, the localtime() function shall return a
pointer to the broken-down time structure. If an error is detected,
localtime() shall return a null pointer and set errno to indicate the
error.
Upon successful completion, localtime_r() shall return a pointer to the
structure pointed to by the argument result.
ERRORS
The localtime() function shall fail if:
EOVERFLOW
The result cannot be represented.
The following sections are informative.
EXAMPLES
Getting the Local Date and Time
The following example uses the time() function to calculate the time
elapsed, in seconds, since January 1, 1970 0:00 UTC (the Epoch),
localtime() to convert that value to a broken-down time, and asctime()
to convert the broken-down time values into a printable string.
#include <stdio.h>
#include <time.h>
int main(void)
{
time_t result;
result = time(NULL);
printf("%s%ju secs since the Epoch\n",
asctime(localtime(&result)),
(uintmax_t)result);
return(0);
}
This example writes the current time to stdout in a form like this:
Wed Jun 26 10:32:15 1996
835810335 secs since the Epoch
Getting the Modification Time for a File
The following example gets the modification time for a file. The
localtime() function converts the time_t value of the last modification
date, obtained by a previous call to stat(), into a tm structure that
contains the year, month, day, and so on.
#include <time.h>
...
struct stat statbuf;
...
tm = localtime(&statbuf.st_mtime);
...
Timing an Event
The following example gets the current time, converts it to a string
using localtime() and asctime(), and prints it to standard output using
fputs(). It then prints the number of minutes to an event being timed.
#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);
...
APPLICATION USAGE
The localtime_r() 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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
asctime() , clock() , ctime() , difftime() , getdate() , gmtime() ,
mktime() , strftime() , strptime() , time() , utime() , the Base
Definitions volume of IEEE Std 1003.1-2001, <time.h>
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 .