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tzfile(4)							    tzfile(4)



NAME

  tzfile - Time	zone information

SYNOPSIS

  #include <&lt;tzfile.h>&gt;

DESCRIPTION

  The time zone	information files used by tzset(3) begin with bytes reserved
  for future use, followed by six four-byte values, written in a standard
  byte order (that is, with the	high-order byte	of the value written first).
  These	values are, in order:

  tzh_ttisgmtcnt
      The number of GMT/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.
      (This value 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,	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 value tells which of the	different 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 GMT,	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.


  Next,	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.

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

  The localtime(3) call	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.

RELATED	INFORMATION

  ctime(3)