tzfile — time zone information
#include <tzfile.h>
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_ttisgmtcntThe number of UTC/local indicators stored in the file.
tzh_ttisstdcntThe number of standard/wall indicators stored in the file.
tzh_leapcntThe number of leap seconds for which data is stored in the file.
tzh_timecntThe number of "transition times" for which data is stored in the file.
tzh_typecntThe number of "local time types" for which data is stored in the file (must not be zero).
tzh_charcntThe 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.
This page is part of release 2.80 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/.
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(#)tzfile.5 7.11 This file is in the public domain, so clarified as of 1996-06-05 by Arthur David Olson <arthur_david_olsonnih.gov>. |