NAME
tzfile - time zone information

SYNOPSIS
#include <tzfile.h>

DESCRIPTION
The time zone information files used by tzset (see ctime(3)) begin
with bytes reserved for future use, followed by four 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_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
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.

Finally, 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.

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.

SEE ALSO
ctime(3)