NAME | SYNOPSIS | DESCRIPTION | COLOPHON
TZFILE(5) Linux Programmer's Manual TZFILE(5)
tzfile - timezone information
#include <tzfile.h>
The timezone information files used by tzset(3) begin with the magic
characters "TZif" to identify then as timezone information files, followed by
sixteen bytes reserved for future use, followed by six 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_ttisgmtcnt
The number of UTC/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
(must not be zero).
tzh_charcnt
The number of characters of "timezone 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 UTC, tt_isdst tells whether tm_isdst should be set by
localtime(3), and tt_abbrind serves as an index into the array of timezone
abbreviation characters that follow the ttinfo structure(s) in the file.
Then 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.
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
timezone file is used in handling POSIX-style timezone environment variables.
Finally, there are tzh_ttisgmtcnt UTC/local indicators, each stored as a one-
byte value; they tell whether the transition times associated with local time
types were specified as UTC or local time, and are used when a timezone file
is used in handling POSIX-style timezone environment variables.
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.
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
1996-06-05 TZFILE(5)