minix/commands/zoneinfo/tzfile.5.txt

94 lines
3.7 KiB
Text
Raw Normal View History

NAME
tzfile - 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 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.
SEE ALSO
newctime(3)