CTIME(3)						     Library Functions Manual							  CTIME(3)

NAME

       ctime, localtime, gmtime, asctime, timezone, tzset -  convert 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 kernel 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 relative 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.

	   Sun Sep 16 01:03:52 1973


       Localtime and gmtime return pointers to structures containing the broken-down time.  Localtime corrects for the time zone and possible day-
       light savings time; gmtime converts directly to GMT, which is the time UNIX uses.  Asctime converts 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 Daylight 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 impossible 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 daylight time zone  abbreviation  associated  with  that  value.   If  the
       requested zone does not appear in the table, the difference from GMT is returned; e.g. in Afghanistan, timezone(-(60*4+30), 0) is appropri-
       ate 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
       /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).

4th Berkeley Distribution					 November 27, 1996							  CTIME(3)