mktime(3C)             UNIX System V(C Development Set)              mktime(3C)


NAME
      mktime - converts a tm structure to a calendar time

SYNOPSIS
      #include <time.h>

      timet mktime (struct tm *timeptr);

DESCRIPTION
      mktime converts the time represented by the tm structure pointed to by
      timeptr into a calendar time (the number of seconds since 00:00:00 UTC,
      January 1, 1970).

      The tm structure has the following format.

            struct      tm {
                  int   tmsec;     /* seconds after the minute [0, 61]  */
                  int   tmmin;     /* minutes after the hour [0, 59] */
                  int   tmhour;    /* hour since midnight [0, 23] */
                  int   tmmday;    /* day of the month [1, 31] */
                  int   tmmon;     /* months since January [0, 11] */
                  int   tmyear;    /* years since 1900 */
                  int   tmwday;    /* days since Sunday [0, 6] */
                  int   tmyday;    /* days since January 1 [0, 365] */
                  int   tmisdst;   /* flag for daylight savings time */
            };

      In addition to computing the calendar time, mktime normalizes the
      supplied tm structure.  The original values of the tmwday and tmyday
      components of the structure are ignored, and the original values of the
      other components are not restricted to the ranges indicated in the
      definition of the structure.  On successful completion, the values of the
      tmwday and tmyday components are set appropriately, and the other
      components are set to represent the specified calendar time, but with
      their values forced to be within the appropriate ranges.  The final value
      of tmmday is not set until tmmon and tmyear are determined.

      The original values of the components may be either greater than or less
      than the specified range.  For example, a tmhour of -1 means 1 hour
      before midnight, tmmday of 0 means the day preceding the current month,
      and tmmon of -2 means 2 months before January of tmyear.

      If tmisdst is positive, the original values are assumed to be in the
      alternate timezone.  If it turns out that the alternate timezone is not
      valid for the computed calendar time, then the components are adjusted to
      the main timezone.  Likewise, if tmisdst is zero, the original values
      are assumed to be in the main timezone and are converted to the alternate
      timezone if the main timezone is not valid.  If tmisdst is negative, the
      correct timezone is determined and the components are not adjusted.





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mktime(3C)             UNIX System V(C Development Set)              mktime(3C)


      Local timezone information is used as if mktime had called tzset.

      mktime returns the specified calendar time.  If the calendar time cannot
      be represented, the function returns the value (timet)-1.

EXAMPLE
      What day of the week is July 4, 2001?

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

            static char *const wday[] = {
                  "Sunday", "Monday", "Tuesday", "Wednesday",
                  "Thursday", "Friday", "Saturday", "-unknown-"
            };
            struct tm timestr;
            /*...*/
            timestr.tmyear  = 2001 - 1900;
            timestr.tmmon   = 7 - 1;
            timestr.tmmday  = 4;
            timestr.tmhour  = 0;
            timestr.tmmin   = 0;
            timestr.tmsec         = 1;
            timestr.tmisdst = -1;
            if (mktime(&timestr)== -1)
                timestr.tmwday=7;
            printf("%s\n", wday[timestr.tmwday]);


SEE ALSO
      ctime(3C), getenv(3C), timezone(4).

NOTES
      tmyear of the tm structure must be for year 1970 or later.  Calendar
      times before 00:00:00 UTC, January 1, 1970 or after 03:14:07 UTC, January
      19, 2038 cannot be represented.


















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