trusty (3) localtime_r.3posix.gz

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 .