localtime_r(3p) — Linux manual page


LOCALTIME(3P)             POSIX Programmer's Manual            LOCALTIME(3P)

PROLOG         top

       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.

NAME         top

       localtime, localtime_r — convert a time value to a broken-down local

SYNOPSIS         top

       #include <time.h>

       struct tm *localtime(const time_t *timer);
       struct tm *localtime_r(const time_t *restrict timer,
           struct tm *restrict result);

DESCRIPTION         top

       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 POSIX.1‐2008 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 POSIX.1‐2008, Section 4.15, 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 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 localtime_r() function is not required to set
       tzname.  If localtime_r() does not set tzname, it shall not set
       daylight and shall not set timezone.

RETURN VALUE         top

       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

       Upon successful completion, localtime_r() shall return a pointer to
       the structure pointed to by the argument result.  If an error is
       detected, localtime_r() shall return a null pointer and set errno to
       indicate the error.

ERRORS         top

       The localtime() and localtime_r() functions shall fail if:

              The result cannot be represented.

       The following sections are informative.

EXAMPLES         top

   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

           #include <stdio.h>
           #include <time.h>

           int main(void)
               time_t result;

               result = time(NULL);
               printf("%s%ju secs since the Epoch\n",

       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 prints the last data modification timestamp in
       the local timezone for a given file.

           #include <stdio.h>
           #include <time.h>
           #include <sys/stat.h>

           print_file_time(const char *pathname)
               struct stat statbuf;
               struct tm *tm;
               char timestr[BUFSIZ];

               if(stat(pathname, &statbuf) == −1)
                   return −1;
               if((tm = localtime(&statbuf.st_mtime)) == NULL)
                   return −1;
               if(strftime(timestr, sizeof(timestr), "%Y-%m-%d %H:%M:%S", tm) == 0)
                   return −1;
               printf("%s: %s.%09ld\n", pathname, timestr, statbuf.st_mtim.tv_nsec);
               return 0;

   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;
           printf("The time is ");
           fputs(asctime(localtime(&now)), stdout);
           printf("There are still %d minutes to the event.\n",


       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         top




SEE ALSO         top

       asctime(3p), clock(3p), ctime(3p), difftime(3p), getdate(3p),
       gmtime(3p), mktime(3p), strftime(3p), strptime(3p), time(3p),
       tzset(3p), utime(3p)

       The Base Definitions volume of POSIX.1‐2008, Section 4.15, Seconds
       Since the Epoch, time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                       LOCALTIME(3P)