2.11BSD#431 - /usr/man/cat3/localtime.0

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


NAME
     ctime, localtime, gmtime, asctime, timezone, tzset -  con-
     vert date and time to ASCII

SYNOPSIS
     void tzset()

     char *ctime(clock)
     time_t *clock;

     #include <time.h>

     char *asctime(tm)
     struct tm *tm;

     struct tm *localtime(clock)
     time_t *clock;

     struct tm *gmtime(clock)
     time_t *clock;

     char *timezone(zone, dst)

DESCRIPTION
     Tzset uses the value of the environment variable TZ to set
     up the time conversion information used by localtime.

     If TZ does not appear in the environment, the TZDEFAULT file
     (as defined in tzfile.h) is used by localtime.  If this file
     fails for any reason, the GMT offset as provided by the ker-
     nel is used.  In this case, DST is ignored, resulting in the
     time being incorrect by some amount if DST is currently in
     effect.  If this fails for any reason, GMT is used.

     If TZ appears in the environment but its value is a null
     string, Greenwich Mean Time is used; if TZ appears and
     begins with a slash, it is used as the absolute pathname of
     the tzfile(5)-format file from which to read the time
     conversion information; if TZ appears and begins with a
     character other than a slash, it's used as a pathname rela-
     tive to the system time conversion information directory,
     defined as TZDIR in the include file tzfile.h.  If this file
     fails for any reason, GMT is used.

     Programs that always wish to use local wall clock time
     should explicitly remove the environmental variable TZ with
     unsetenv(3).

     Ctime converts a long integer, pointed to by clock, such as
     returned by time(2) into ASCII and returns a pointer to a
     26-character string in the following form.  All the fields
     have constant width.


Printed 11/26/99	November 27, 1996			1


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


	 Sun Sep 16 01:03:52 1973\n

     Localtime and gmtime return pointers to structures contain-
     ing the broken-down time.	Localtime corrects for the time
     zone and possible daylight savings time; gmtime converts
     directly to GMT, which is the time UNIX uses.  Asctime con-
     verts a broken-down time to ASCII and returns a pointer to a
     26-character string.

     The structure declaration from the include file is:

	  struct tm {
	       int tm_sec;    /* 0-59  seconds */
	       int tm_min;    /* 0-59  minutes */
	       int tm_hour;   /* 0-23  hour */
	       int tm_mday;   /* 1-31  day of month */
	       int tm_mon;    /* 0-11  month */
	       int tm_year;   /* 0-    year - 1900 */
	       int tm_wday;   /* 0-6   day of week (Sunday = 0) */
	       int tm_yday;   /* 0-365 day of year */
	       int tm_isdst;  /* flag: daylight savings time in effect */
	       char **tm_zone;	       /* abbreviation of timezone name */
	       long tm_gmtoff;	       /* offset from GMT in seconds */
	  };

     Tm_isdst is non-zero if a time zone adjustment such as Day-
     light Savings time is in effect.

     Tm_gmtoff is the offset (in seconds) of the time represented
     from GMT, with positive values indicating East of Greenwich.

     Timezone remains for compatibility reasons only; it's impos-
     sible to reliably map timezone's arguments (zone, a "minutes
     west of GMT" value and dst, a "daylight saving time in
     effect" flag) to a time zone abbreviation.

     If the environmental string TZNAME exists, timezone returns
     its value, unless it consists of two comma separated
     strings, in which case the second string is returned if dst
     is non-zero, else the first string.  If TZNAME doesn't
     exist, zone is checked for equality with a built-in table of
     values, in which case timezone returns the time zone or day-
     light time zone abbreviation associated with that value.  If
     the requested zone does not appear in the table, the differ-
     ence from GMT is returned; e.g. in Afghanistan, timezone(-
     (60*4+30), 0) is appropriate because it is 4:30 ahead of
     GMT, and the string GMT+4:30 is returned.	Programs that in
     the past used the timezone function should return the zone
     name as set by localtime to assure correctness.

FILES
     /usr/share/zoneinfotime zone information directory


Printed 11/26/99	November 27, 1996			2


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


     /etc/localtime	local time zone file

SEE ALSO
     gettimeofday(2), getenv(3), time(3), tzfile(5), environ(7)

NOTE
     The return values point to static data whose content 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).


Printed 11/26/99	November 27, 1996			3