mktime(3C)                                                       mktime(3C)

NAME
     mktime - convert 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;     /* hours 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 deter-
     mined.

     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.




Page 1                       Reliant UNIX 5.44                Printed 11/98

mktime(3C)                                                       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]);

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).



















Page 2                       Reliant UNIX 5.44                Printed 11/98