mktime(3C)              LIBRARY FUNCTIONS              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 struc-
     ture 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  normal-
     izes  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 res-
     tricted 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



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mktime(3C)              LIBRARY FUNCTIONS              mktime(3C)



     the components are not adjusted.

     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]);


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.

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















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