tzfile(4)						     Kernel Interfaces Manual							 tzfile(4)

NAME

       tzfile - Time zone information

SYNOPSIS

       #include <tzfile.h>

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: The  number  of  GMT/local
       indicators  stored  in  the file.  The number of standard/wall indicators stored in the file.  The number of leap seconds for which data is
       stored in the file.  The number of transition times for which data is stored in the file.  The number of local time types for which data is
       stored in the file.  (This value must not be zero.)  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 variables.

       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) delim off

																	 tzfile(4)