mktime(3C)						   Standard C Library Functions 						mktime(3C)

NAME

       mktime - converts a tm structure to a calendar time

SYNOPSIS

       #include <time.h>

       time_t mktime(struct tm *timeptr);

DESCRIPTION

       The  mktime() function 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 contains the following members:

	 int  tm_sec;	  /* seconds after the minute [0, 60]  */
	 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() normalizes 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 restricted 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 tm_year member must be for year 1901 or later. Calendar times before 20:45:52 UTC, December 13, 1901 or after  03:14:07  UTC,   January
       19, 2038 cannot be represented. Portable applications should not try to create dates before 00:00:00 UTC, January 1, 1970 or after 00:00:00
       UTC, January 1, 2038.

       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  origi-
       nal  values  are  assumed  to  be  in  the  main timezone and are converted to the alternate timezone if the main timezone is not valid. If
       tm_isdst is negative, mktime() attempts to determine whether the alternate timezone is in effect for the specified time.

       Local timezone information is used as if mktime() had called tzset(). See ctime(3C).

RETURN VALUES

       If the calendar time can be represented in an object of type time_t, mktime() returns the specified calendar time without  changing  errno.
       If the calendar time cannot be represented, the function returns the value (time_t)-1 and sets errno to indicate the error.

ERRORS

       The mktime() function will fail if:

       EOVERFLOW    The  date  represented  by	the  input tm struct cannot be represented in a time_t.  Note that the errno setting may change if
		    future revisions to the standards specify a different value.

USAGE

       The  mktime() function is MT-Safe in multithreaded applications, as long as no user-defined function directly modifies one of the following
       variables: timezone, altzone, daylight, and tzname. See ctime(3C).

       Note  that  -1  can  be	a valid return value for the time that is one second before the Epoch.	The user should clear errno before calling
       mktime(). If mktime() then returns -1, the user should check errno to determine whether or not an error actually occurred.

       The  mktime() function assumes Gregorian dates. Times before the adoption of the Gregorian calendar will not match historial records.

EXAMPLES

       Example 1 Sample code using mktime().

       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
", wday[time_str.tm_wday]);

BUGS

       The zoneinfo timezone data files do not transition past Tue Jan 19 03:14:07 2038 UTC.  Therefore for  64-bit  applications  using  zoneinfo
       timezones, calculations beyond this date may not use the correct offset from standard time, and could return incorrect values. This affects
       the 64-bit version of mktime().

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe with exceptions	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ctime(3C), getenv(3C), TIMEZONE(4), attributes(5), standards(5)

SunOS 5.11							    1 Nov 2003								mktime(3C)