mktime(3C)							    mktime(3C)

NAME    [Toc]    [Back]

     mktime - converts a tm structure to a calendar time

SYNOPSIS    [Toc]    [Back]

     #include <time.h>

     time_t mktime (struct tm *timeptr);

DESCRIPTION    [Toc]    [Back]

     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	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 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 tm_isdst is negative, the
     correct timezone is determined and	the components are not adjusted.






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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 (time_t)-1.

EXAMPLE    [Toc]    [Back]

     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    [Toc]    [Back]

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

NOTES    [Toc]    [Back]

     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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