1 .\" $FreeBSD: src/lib/libc/stdtime/tzfile.5,v 1.8.2.2 2001/08/17 15:42:43 ru Exp $
2 .\" $DragonFly: src/lib/libc/stdtime/tzfile.5,v 1.4 2008/10/19 20:15:58 swildner Exp $
8 .Nd timezone information
10 .Fd #include \&"/usr/src/lib/libc/stdtime/tzfile.h\&"
12 The time zone information files used by
14 begin with the magic characters
17 time zone information files,
18 followed by a character identifying the version of the file's format
19 (as of 2005, either an ASCII
23 followed by fifteen bytes containing zeroes reserved for future use,
24 followed by six four-byte values of type
29 (the high-order byte of the value is written first).
33 .Bl -tag -compact -width tzh_ttisstdcnt
35 The number of UTC/local indicators stored in the file.
37 The number of standard/wall indicators stored in the file.
39 The number of leap seconds for which data is stored in the file.
43 for which data is stored
48 for which data is stored
49 in the file (must not be zero).
51 The number of characters of
52 .Dq time zone abbreviation strings
56 The above header is followed by
58 four-byte values of type
60 sorted in ascending order.
61 These values are written in
64 Each is used as a transition time (as returned by
66 at which the rules for computing local time change.
69 one-byte values of type
71 each one tells which of the different types of
74 described in the file is associated with the same-indexed transition time.
75 These values serve as indices into an array of
79 entries) that appears next in the file;
80 these structures are defined as follows:
81 .Bd -literal -offset indent
85 unsigned int tt_abbrind;
89 Each structure is written as a four-byte value for
93 in a standard byte order, followed by a one-byte value for
95 and a one-byte value for
99 gives the number of seconds to be added to UTC,
107 serves as an index into the array of time zone abbreviation characters
110 structure(s) in the file.
114 pairs of four-byte values, written in standard byte order;
115 the first value of each pair gives the time
118 at which a leap second occurs;
121 number of leap seconds to be applied after the given time.
122 The pairs of values are sorted in ascending order by time.
126 standard/wall indicators, each stored as a one-byte value;
127 they tell whether the transition times associated with local time types
128 were specified as standard time or wall clock time,
129 and are used when a time zone file is used in handling POSIX-style
130 time zone environment variables.
134 UTC/local indicators, each stored as a one-byte value;
135 they tell whether the transition times associated with local time types
136 were specified as UTC or local time,
137 and are used when a time zone file is used in handling POSIX-style
138 time zone environment variables.
141 uses the first standard-time
143 structure in the file
146 structure in the absence of a standard-time structure)
149 is zero or the time argument is less than the first transition time recorded
152 For version-2-format time zone files,
153 the above header and data is followed by a second header and data,
154 identical in format except that
155 eight bytes are used for each transition time or leap second time.
156 After the second header and data comes a newline-enclosed,
157 POSIX-TZ-environment-variable-style string for use in handling instants
158 after the last transition time stored in the file
159 (with nothing between the newlines if there is no POSIX representation for
166 .\" This file is in the public domain, so clarified as of
167 .\" 1996-06-05 by Arthur David Olson.