161 lines
5.2 KiB
Groff
161 lines
5.2 KiB
Groff
.\" Copyright (c) 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Arthur David Olson of the National Cancer Institute.
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)tzfile.5 5.3 (Berkeley) 5/10/91
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.\"
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.Dd May 10, 1991
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.Dt TZFILE 5
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.Sh NAME
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.Nm tzfile
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.Nd time zone information
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.Sh SYNOPSIS
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.Fd #include <tzfile.h>
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.Sh DESCRIPTION
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The time zone information files used by
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.Xr tzset 3
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begin with bytes reserved for future use,
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followed by four four-byte values of type
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.Em long ,
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written in a ``standard'' byte order
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(the high-order byte of the value is written first).
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These values are,
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in order:
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.Bl -tag -width tzh_ttisstdcnt
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.It Fa tzh_ttisstdcnt
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The number of standard/wall indicators stored in the file.
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.It Fa tzh_leapcnt
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The number of leap seconds for which data is stored in the file.
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.It Fa tzh_timecnt
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The number of "transition times" for which data is stored
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in the file.
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.It Fa tzh_typecnt
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The number of "local time types" for which data is stored
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in the file (must not be zero).
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.It Fa tzh_charcnt
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The number of characters of "time zone abbreviation strings"
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stored in the file.
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.El
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.Pp
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The above header is followed by
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.Fa tzh_timecnt
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four-byte values of type
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.Em long ,
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sorted in ascending order.
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These values are written in ``standard'' byte order.
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Each is used as a transition time (as returned by
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.Xr time 2 )
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at which the rules for computing local time change.
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Next come
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.Fa tzh_timecnt
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one-byte values of type
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.Fa unsigned char ;
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each one tells which of the different types of ``local time'' types
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described in the file is associated with the same-indexed transition time.
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These values serve as indices into an array of
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.Fa ttinfo
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structures that appears next in the file;
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these structures are defined as follows:
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.Bd -literal -offset indent
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struct ttinfo {
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long tt_gmtoff;
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int tt_isdst;
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unsigned int tt_abbrind;
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};
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.Ed
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.Pp
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Each structure is written as a four-byte value for
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.Fa tt_gmtoff
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of type
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.Em long ,
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in a standard byte order, followed by a one-byte value for
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.Fa tt_isdst
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and a one-byte value for
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.Fa tt_abbrind .
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In each structure,
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.Fa tt_gmtoff
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gives the number of seconds to be added to GMT,
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.Fa tt_isdst
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tells whether
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.Fa tm_isdst
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should be set by
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.Xr localtime 3
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and
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.Fa tt_abbrind
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serves as an index into the array of time zone abbreviation characters
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that follow the
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.Fa ttinfo
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structure(s) in the file.
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.Pp
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Then there are
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.Fa tzh_leapcnt
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pairs of four-byte values, written in standard byte order;
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the first value of each pair gives the time
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(as returned by
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.Xr time 2 )
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at which a leap second occurs;
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the second gives the
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.Em total
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number of leap seconds to be applied after the given time.
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The pairs of values are sorted in ascending order by time.
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.Pp
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Finally there are
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.Fa tzh_ttisstdcnt
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standard/wall indicators, each stored as a one-byte value;
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they tell whether the transition times associated with local time types
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were specified as standard time or wall clock time,
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and are used when a time zone file is used in handling
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.Tn POSIX Ns -style
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time zone environment variables.
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.Pp
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.Fa Localtime
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uses the first standard-time
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.Fa ttinfo
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structure in the file
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(or simply the first
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.Fa ttinfo
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structure in the absence of a standard-time structure)
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if either
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.Fa tzh_timecnt
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is zero or the time argument is less than the first transition time recorded
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in the file.
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.Sh SEE ALSO
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.Xr ctime 3
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.Sh HISTORY
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The
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.Nm tzfile
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file format appeared in
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.Bx 4.3 tahoe.
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