# 2.11BSD#431 - /usr/man/cat3/timezone.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

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