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tzfile(4)
NAME
  tzfile - Time zone information

SYNOPSIS
  #include <tzfile.h>

DESCRIPTION
  The time zone information file used by tzset begins with bytes reserved for
  future use, followed by three 4-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_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.

  This header is followed by tzh_timecnt 4-byte values sorted in ascending
  order.  These values are written in ``standard'' byte order.	Each is used
  as a transition time (as returned by the time at which the rules for
  computing local time change).	 Next come the tzh_timecnt 1-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 indexes 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 4-byte value for tt_gmtoff of type long, in
  a standard byte order, followed by a 1-byte value for tt_isdst and a 1-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, and tt_abbrind serves as an index into the array of time zone
  abbreviation characters that follows the ttinfo structure or structures in
  the file.

  The localtime 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)