TZFILE(5) BSD Reference Manual TZFILE(5)
tzfile - time zone information
#include <tzfile.h>
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 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(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 dif-
ferent 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 struc-
tures 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.
ctime(3)
MirBSD #10-current May 24, 1999 1