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

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

       mktime - convert broken-down time into time since the Epoch

       #include <time.h>

       time_t mktime(struct tm *timeptr);

       The  mktime() function shall convert the broken-down time, expressed as local time, in the
       structure pointed to by timeptr, into a time since the Epoch value with the same  encoding
       as  that  of the values returned by time(). The original values of the tm_wday and tm_yday
       components of the structure are ignored, and the original values of the	other  components
       are not restricted to the ranges described in <time.h>.

       A positive or 0 value for tm_isdst shall cause mktime() to presume initially that Daylight
       Savings Time, respectively, is or is not in effect for  the  specified  time.  A  negative
       value  for  tm_isdst shall cause mktime() to attempt to determine whether Daylight Savings
       Time is in effect for the specified time.

       Local timezone information shall be set as though mktime() called tzset().

       The relationship between the tm structure (defined in the <time.h> header) and the time in
       seconds	since  the Epoch 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 cor-

       Upon successful completion, the values of the tm_wday and tm_yday components of the struc-
       ture shall be set appropriately, and the other components are set to represent the  speci-
       fied  time  since  the  Epoch, but with their values forced to the ranges indicated in the
       <time.h> entry; the final value of tm_mday shall not be set until tm_mon and  tm_year  are

       The  mktime()  function shall return the specified time since the Epoch encoded as a value
       of type time_t. If the time since the Epoch cannot  be  represented,  the  function  shall
       return the value (time_t)-1.

       No errors are defined.

       The following sections are informative.

       What day of the week is July 4, 2001?

	      #include <stdio.h>
	      #include <time.h>

	      struct tm time_str;

	      char daybuf[20];

	      int main(void)
		  time_str.tm_year = 2001 - 1900;
		  time_str.tm_mon = 7 - 1;
		  time_str.tm_mday = 4;
		  time_str.tm_hour = 0;
		  time_str.tm_min = 0;
		  time_str.tm_sec = 1;
		  time_str.tm_isdst = -1;
		  if (mktime(&time_str) == -1)
		  else {
		      (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
		  return 0;




       asctime()  ,  clock() , ctime() , difftime() , gmtime() , localtime() , strftime() , strp-
       time() , time() , utime() , the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>

       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					MKTIME(P)

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