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Linux 2.6 - man page for localtime (linux section 3posix)

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

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  stan-
       dard 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  local-
       time()  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  local-
       time_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 con-
       verts  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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				     LOCALTIME(P)


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