localtime(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 time

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.1‐2017 defers to the ISO C

       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.1‐2017, Section 4.16,
       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() sets tzname, it shall also set
       daylight and timezone.  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 error.

       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 string.

           #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

           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.1‐2017, Section 4.16,
       Seconds Since the Epoch, time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                     LOCALTIME(3P)

Pages that refer to this page: time.h(0p)asctime(3p)clock(3p)ctime(3p)difftime(3p)getdate(3p)gmtime(3p)mktime(3p)strftime(3p)time(3p)tzset(3p)