TZFILE(5) OpenBSD Programmer's Manual TZFILE(5)NAMEtzfile - time zone information
SYNOPSIS
#include <tzfile.h>
DESCRIPTION
The time zone information files used by tzset(3) begin with the magic
characters "TZif" to identify themselves as time zone information files,
followed by a character identifying the version of the file's format (as
of 2005, either an ASCII NUL or a '2') followed by fifteen bytes
containing zeroes 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(3)) 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 (with tzh_typecnt
entries) 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(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.
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(3) 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.
For version-2-format time zone files, the above header and data is
followed by a second header and data, identical in format except that
eight bytes are used for each transition time or leap second time. After
the second header and data comes a newline-enclosed, POSIX-TZ-
environment-variable-style string for use in handling instants after the
last transition time stored in the file (with nothing between the
newlines if there is no POSIX representation for such instants).
SEE ALSOctime(3)OpenBSD 4.9 August 23, 2010 OpenBSD 4.9
