trusty (3) mktime.3posix.gz

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 .