TZFILE(5)							File Formats Manual							 TZFILE(5)

NAME

       tzfile - time zone information

SYNOPSIS

       #include <tzfile.h>

DESCRIPTION

       The  time  zone	information files used by tzset(3) begin with the magic characters "TZif" to identify then as time zone information files,
       followed by sixteen bytes reserved for future use, followed by six four-byte values of type long, written in a ``standard'' byte order (the
       high-order byte of the value is written first).	These values are, in order:

       tzh_ttisgmtcnt
	      The number of UTC/local indicators stored in the file.

       tzh_ttisstdcnt
	      The number of standard/wall indicators stored in the file.

       tzh_leapcnt
	      The number of leap seconds for which data is stored in the file.

       tzh_timecnt
	      The number of "transition times" for which data is stored in the file.

       tzh_typecnt
	      The number of "local time types" for which data is stored in the file (must not be zero).

       tzh_charcnt
	      The number of characters of "time zone abbreviation strings" stored in the file.

       The  above header is followed by tzh_timecnt four-byte values of type long, sorted in ascending order.  These values are written in ``stan-
       dard'' byte order.  Each is used as a transition time (as returned by time(2)) at which the rules for computing local  time  change.   Next
       come  tzh_timecnt  one-byte  values of type unsigned char; each one tells which of the different types of ``local time'' types described in
       the file is associated with the same-indexed transition time.  These values serve as indices  into  an  array  of  ttinfo  structures  that
       appears next in the file; these structures are defined as follows:

	    struct ttinfo {
		 long	       tt_gmtoff;
		 int	       tt_isdst;
		 unsigned int  tt_abbrind;
	    };

       Each  structure	is  written  as  a  four-byte value for tt_gmtoff of type long, in a standard byte order, followed by a one-byte value for
       tt_isdst and a one-byte value for tt_abbrind.  In each structure, tt_gmtoff gives the number of seconds to be added to UTC, tt_isdst  tells
       whether	tm_isdst should be set by localtime(3), and tt_abbrind serves as an index into the array of time zone abbreviation characters that
       follow the ttinfo structure(s) in the file.

       Then there are tzh_leapcnt pairs of four-byte values, written in standard byte order; the first value of  each  pair  gives  the  time  (as
       returned  by  time(2)) at which a leap second occurs; the second gives the total number of leap seconds to be applied after the given time.
       The pairs of values are sorted in ascending order by time.

       Then there are tzh_ttisstdcnt standard/wall indicators, each stored as a one-byte value; they tell whether the transition times	associated
       with  local  time  types  were specified as standard time or wall clock time, and are used when a time zone file is used in handling POSIX-
       style time zone environment variables.

       Finally, there are tzh_ttisgmtcnt UTC/local indicators, each stored as a one-byte value; they tell whether the transition times	associated
       with  local  time  types  were specified as UTC or local time, and are used when a time zone file is used in handling POSIX-style time zone
       environment variables.

       Localtime uses the first standard-time ttinfo structure in the file (or simply the first ttinfo structure in the absence of a standard-time
       structure) if either tzh_timecnt is zero or the time argument is less than the first transition time recorded in the file.

																	 TZFILE(5)