This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       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(3POSIX)

       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 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.1‐2017,
       Section4.16, SecondsSincetheEpoch) 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.

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

       EOVERFLOW
              The result cannot be represented.

       Thefollowingsectionsareinformative.

GettingtheLocalDateandTime
       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

   GettingtheModificationTimeforaFile
       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>

           int
           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;
           }

   TiminganEvent
       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);
           ...

       None.

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

       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.

       None.

       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.

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

       The Base Definitions volume of POSIX.1‐2017, Section4.16, SecondsSincetheEpoch, <time.h>

       #include <time.h>

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