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TZFILE(5)		    BSD	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 them	as time	zone information files,	fol-
     lowed by a	character identifying the version of the file's	format (as of
     2005, either an ASCII NUL or a '2') followed by fifteen bytes containing
     zeroes 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 "standard"
     byte order.  Each is used as a transition time (as	returned by time(3))
     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 as-
     sociated with the same-indexed transition time.  These values serve as
     indices into an array of ttinfo structures	(with tzh_typecnt entries)
     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 struc-
     ture(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(3)) 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(3) 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.

     For version-2-format time zone files, the above header and	data is	fol-
     lowed by a	second header and data,	identical in format except that	eight
     bytes are used for	each transition	time or	leap second time.  After the
     second header and data comes a newline-enclosed, POSIX-TZ-environment-
     variable-style string for use in handling instants	after the last transi-
     tion time stored in the file (with	nothing	between	the newlines if	there
     is	no POSIX representation	for such instants).

SEE ALSO
     ctime(3), localtime(3), time(3)

BSD			      September	16, 2001			   BSD

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO

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