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TZFILE(5) Linux Programmer's Manual TZFILE(5)
NAME
tzfile - time zone information
SYNOPSIS
#include <tzfile.h>
DESCRIPTION
This page describes the structure of timezone files as commonly found in /usr/lib/zoneinfo
or /usr/share/zoneinfo.
The time zone information files used by tzset(3) begin with the magic characters "TZif" to
identify then as time zone 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 "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 UTC, 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.
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 time zone file is used in handling
POSIX-style time zone 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 time zone file is used in handling POSIX-style time
zone 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.
NOTES
This manual page documents <tzfile.h> in the glibc source archive, see timezone/tzfile.h.
It seems that timezone uses tzfile internally, but glibc refuses to expose it to
userspace. This is most likely because the standardised functions are more useful and
portable, and actually documented by glibc. It may only be in glibc just to support the
non-glibc-maintained timezone data (which is maintained by some other entity).
SEE ALSO
time(3), gettimeofday(3), tzset(3), ctime(3)
COLOPHON
This page is part of release 3.05 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at http://www.ker-
nel.org/doc/man-pages/.
1996-06-05 TZFILE(5)
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On Apache
Under GNU General Public License
2012-05-26 04:17 @38.107.179.240 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)