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

       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.

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

       #include <time.h>

       time_t mktime(struct tm *timeptr);

       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.1‐2008
       defers to the ISO C standard.

       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 com‐
       ponents are not restricted to the ranges described in <time.h>.

       A positive or 0 value for tm_isdst shall cause mktime() to presume ini‐
       tially 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

       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 sec‐
       onds since the Epoch (see the Base Definitions volume of	 POSIX.1‐2008,
       Section	4.15,  Seconds Since the Epoch) corrected for timezone and any
       seasonal time adjustments, where the names in the structure and in  the
       expression correspond.

       Upon  successful completion, the values of the tm_wday and tm_yday com‐
       ponents of the structure shall be set appropriately, and the other com‐
       ponents	are  set  to represent the specified 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 determined.

       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 and  set
       errno to indicate the error.

       The mktime() function shall fail if:

	      The result cannot be represented.

       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(), strf‐
       time(), strptime(), time(), tzset(), utime()

       The Base Definitions volume  of	POSIX.1‐2008,  Section	4.15,  Seconds
       Since the Epoch, <time.h>

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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 .

       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.ker‐ .

IEEE/The Open Group		     2013			    MKTIME(3P)

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