mktime(3C)          (C Programming Language Utilities)           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


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   mktime(3C)          (C Programming Language Utilities)           mktime(3C)


         and 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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