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RedHat 9 (Linux i386) - man page for tzfile (redhat section 5)

TZFILE(5)										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 ``standard'' 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)


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