localtime

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



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.

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
       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, 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
       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
       The localtime() and localtime_r() functions 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 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;
           }

   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(), tzset(), utime()

       The Base Definitions volume of POSIX.1‐2017, Section 4.16, Seconds Since
       the Epoch, <time.h>

COPYRIGHT
       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)