tzfile(4)tzfile(4)NAMEtzfile - 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 stan‐
dard 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 INFORMATIONctime(3) delim off
tzfile(4)
