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

NAME
     asctime, asctime_r, ctime, ctime_r, difftime, gmtime, gmtime_r,
     localtime, localtime_r, mktime, timegm, timelocal - convert date and time
     to ASCII

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

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

     char *
     ctime(const time_t *clock);

     char *
     ctime_r(const time_t *clock, char *buf);

     double
     difftime(time_t time1, time_t time0);

     char *
     asctime(const struct tm *tm);

     char *
     asctime_r(const struct tm *tm, char *buf);

     struct tm *
     localtime(const time_t *clock);

     struct tm *
     localtime_r(const time_t *clock, struct tm *result);

     struct tm *
     gmtime(const time_t *clock);

     struct tm *
     gmtime_r(const time_t *clock, struct tm *result);

     time_t
     mktime(struct tm *tm);

     time_t
     timegm(struct tm *tm);

     time_t
     timelocal(struct tm *tm);

DESCRIPTION
     The ctime() function 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 1986\n

     All the fields have constant width.

     The ctime_r() function converts the calendar time pointed to by clock to
     local time in exactly the same way as ctime() and puts the string into
     the array pointed to by buf (which contains at least 26 bytes) and re-
     turns buf. Unlike ctime(), the thread-safe version ctime_r() is not re-
     quired to set tzname.

     The localtime() and gmtime() functions return pointers to tm structures,
     described below.  localtime() corrects for the time zone and any time
     zone adjustments (such as Daylight Saving Time in the U.S.A.).  After
     filling in the tm structure, localtime() sets the tm_isdst'th element of
     tzname to a pointer 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.

     The localtime_r() and gmtime_r() functions convert the calendar time
     pointed to by clock into a broken-down time in exactly the same was as
     their non-reentrant counterparts, localtime() and gmtime(), but instead
     store the result directly into the structure pointed to by result. Unlike
     localtime(), the reentrant version is not required to set tzname.

     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.  asctime_r() uses the buffer pointed to by buf (which should con-
     tain at least 26 bytes) and then returns buf.

     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.

     timelocal() is a deprecated interface that is equivalent to calling
     mktime() with a negative value for tm_isdst.

     timegm() is a deprecated interface that converts the broken-down time, as
     returned by gmtime(), into a calendar time value with the same encoding
     as that of the values returned by the time() function.

     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), tzfile(5), zic(8)

NOTES
     The return values of the non re-entrant functions 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()).

     The default system time zone may be set by running ``zic -l timezone'' as
     the superuser.

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

OpenBSD 3.1                    February 16, 1999                             3

NAME | SYNOPSIS | DESCRIPTION | FILES | SEE ALSO | NOTES

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