NAME

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

SYNOPSIS

       #include <time.h>

       time_t mktime(struct tm *timeptr);

DESCRIPTION

       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
       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.

ERRORS

       No errors are defined.

       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() , 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 .