MKTIME(3C-SVR4)     RISC/os Reference Manual      MKTIME(3C-SVR4)



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  tm_sec;   /* seconds after the minute [0, 61]  */
               int  tm_min;   /* minutes after the hour [0, 59] */
               int  tm_hour;  /* hour since midnight [0, 23] */
               int  tm_mday;  /* day of the month [1, 31] */
               int  tm_mon;   /* months since January [0, 11] */
               int  tm_year;  /* years since 1900 */
               int  tm_wday;  /* days since Sunday [0, 6] */
               int  tm_yday;  /* days since January 1 [0, 365] */
               int  tm_isdst; /* flag for daylight savings time */
          };

     In addition to computing the calendar time, mktime normal-
     izes the supplied tm structure.  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 res-
     tricted to the ranges indicated in the definition of the
     structure.  On successful completion, the values of the
     tm_wday and tm_yday 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 tm_mday is not set
     until tm_mon and tm_year are determined.

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

     If tm_isdst 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 tm_isdst 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



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MKTIME(3C-SVR4)     RISC/os Reference Manual      MKTIME(3C-SVR4)



     tm_isdst is negative, the correct timezone is determined 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
     (time_t)-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 time_str;
          /*...*/
          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)
              time_str.tm_wday=7;
          printf("%s\n", wday[time_str.tm_wday]);


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

NOTES
     tm_year 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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