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

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

SYNOPSIS

       #include <time.h>

       time_t mktime(struct tm *timeptr);

DESCRIPTION

       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  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
       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 components of the
       structure shall be set appropriately, and the other components 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.

RETURN VALUE

       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.

ERRORS

       The mktime() function shall fail if:

       EOVERFLOW
              The result cannot be represented.

       The following sections are informative.

EXAMPLES

       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)
                   (void)puts("-unknown-");
               else {
                   (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
                   (void)puts(daybuf);
               }
               return 0;
           }

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       asctime(),  clock(),  ctime(),  difftime(), gmtime(), localtime(), strftime(), strptime(),
       time(), tzset(), utime()

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

COPYRIGHT

       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 Electrical 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 http://www.unix.org/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 .