CTIME(3)                  OpenBSD Programmer's Manual                 CTIME(3)

NAME
     asctime, ctime, gmtime, localtime, mktime - convert date and time to
     ASCII



SYNOPSIS
     #include <sys/types.h>
     #include <time.h>

     extern char *tzname[2]; void
     tzset(void);

     char *
     ctime(time_t *clock);

     double
     difftime(time_t time1, time_t time0);

     char *
     asctime(const struct tm *tm);

     struct tm *
     localtime(const time_t *clock);

     struct tm *
     gmtime(const time_t *clock);

     time_t
     mktime(struct tm *tm);

DESCRIPTION
     ctime() converts a time_t , pointed to by clock , representing the time
     in seconds since 00:00:00 UTC, 1970-01-01, and returns a pointer to a
     26-character string of the form

           Thu Nov 24 18:22:48 198600

     All the fields have constant width.

     localtime() and gmtime() return pointers to tm structures, described be-
     low.  localtime() corrects for the time zone and any time zone adjust-
     ments (such as Daylight Saving Time in the U.S.A.).  After filling in the
     tm structure, localtime() sets the tm_isdst element of tzname to a point-
     er to an ASCII string that's the time zone abbreviation to be used with
     the return value of localtime().

     gmtime() converts to Coordinated Universal Time.

     asctime() converts a time value contained in a tm structure to a 26-char-
     acter string, as shown in the above example, and returns a pointer to the
     string.

     mktime() converts the broken-down time, expressed as local time, in the
     structure pointed to by tm into a calendar time value with the same en-
     coding as that of the values returned by the time() function.  The origi-
     nal values of the tm_wday and tm_yday components of the structure are ig-
     nored, and the original values of the other components are not restricted
     to their normal ranges.  (A positive or zero value for tm_isdst causes
     mktime() to presume initially that summer time (for example, Daylight
     Saving Time in the U.S.A.)  respectively, is or is not in effect for the
     specified time.  A negative value for tm_isdst causes the mktime() func-
     tion to attempt to divine whether summer time is in effect for the speci-
     fied time.)  On successful completion, the values of the tm_wday and
     tm_yday components of the structure are set appropriately, and the other
     components are set to represent the specified calendar time, but with
     their values forced to their normal ranges; the final value of tm_mday is
     not set until tm_mon and tm_year are determined.  mktime() returns the
     specified calendar time; If the calendar time cannot be represented, it
     returns -1.

     difftime() returns the difference between two calendar times, ( time1 -
     time0 ), expressed in seconds.

     Declarations of all the functions and externals, and the tm structure,
     are in the <time.h> header file.  The structure (of type) struct tm in-
     cludes the following fields:

                   int tm_sec;     /* seconds (0 - 60) */
                   int tm_min;     /* minutes (0 - 59) */
                   int tm_hour;    /* hours (0 - 23) */
                   int tm_mday;    /* day of month (1 - 31) */
                   int tm_mon;     /* month of year (0 - 11) */
                   int tm_year;    /* year - 1900 */
                   int tm_wday;    /* day of week (Sunday = 0) */
                   int tm_yday;    /* day of year (0 - 365) */
                   int tm_isdst;   /* is summer time in effect? */
                   char *tm_zone;  /* abbreviation of timezone name */
                   long tm_gmtoff; /* offset from UTC in seconds */

     The tm_zone and tm_gmtoff fields exist, and are filled in, only if ar-
     rangements to do so were made when the library containing these functions
     was created.  There is no guarantee that these fields will continue to
     exist in this form in future releases of this code.

     tm_isdst is non-zero if summer time is in effect.

     tm_gmtoff is the offset (in seconds) of the time represented from UTC,
     with positive values indicating east of the Prime Meridian.

FILES
     /usr/share/zoneinfo             time zone information directory

     /etc/localtime                  local time zone file

     /usr/share/zoneinfo/posixrules  used with POSIX-style TZ's

     /usr/share/zoneinfo/GMT         for UTC leap seconds

     If /usr/share/zoneinfo/GMT is absent, UTC leap seconds are loaded from
     /usr/share/zoneinfo/posixrules.

SEE ALSO
     getenv(3),  strftime(3),  time(3),  tzset(3),  tzfil(5)

NOTES
     The return values point to static data; the data is overwritten by each
     call.  The tm_zone field of a returned struct tm points to a static array
     of characters, which will also be overwritten at the next call (and by
     calls to tzset() ).

     Avoid using out-of-range values with mktime() when setting up lunch with
     promptness sticklers in Riyadh.

OpenBSD 2.6                    February 16, 1999                             2