1 .\" $FreeBSD: src/lib/libc/stdtime/tzfile.5,v 1.8.2.2 2001/08/17 15:42:43 ru Exp $
7 .Nd timezone information
9 .Fd #include \&"/usr/src/lib/libc/stdtime/tzfile.h\&"
11 The time zone information files used by
13 begin with the magic characters
16 time zone information files,
17 followed by a character identifying the version of the file's format
18 (as of 2005, either an ASCII
22 followed by fifteen bytes containing zeroes reserved for future use,
23 followed by six four-byte values of type
28 (the high-order byte of the value is written first).
32 .Bl -tag -compact -width tzh_ttisstdcnt
34 The number of UTC/local indicators stored in the file.
36 The number of standard/wall indicators stored in the file.
38 The number of leap seconds for which data is stored in the file.
42 for which data is stored
47 for which data is stored
48 in the file (must not be zero).
50 The number of characters of
51 .Dq time zone abbreviation strings
55 The above header is followed by
57 four-byte values of type
59 sorted in ascending order.
60 These values are written in
63 Each is used as a transition time (as returned by
65 at which the rules for computing local time change.
68 one-byte values of type
70 each one tells which of the different types of
73 described in the file is associated with the same-indexed transition time.
74 These values serve as indices into an array of
78 entries) that appears next in the file;
79 these structures are defined as follows:
80 .Bd -literal -offset indent
84 unsigned int tt_abbrind;
88 Each structure is written as a four-byte value for
92 in a standard byte order, followed by a one-byte value for
94 and a one-byte value for
98 gives the number of seconds to be added to UTC,
106 serves as an index into the array of time zone abbreviation characters
109 structure(s) in the file.
113 pairs of four-byte values, written in standard byte order;
114 the first value of each pair gives the time
117 at which a leap second occurs;
120 number of leap seconds to be applied after the given time.
121 The pairs of values are sorted in ascending order by time.
125 standard/wall indicators, each stored as a one-byte value;
126 they tell whether the transition times associated with local time types
127 were specified as standard time or wall clock time,
128 and are used when a time zone file is used in handling POSIX-style
129 time zone environment variables.
133 UTC/local indicators, each stored as a one-byte value;
134 they tell whether the transition times associated with local time types
135 were specified as UTC or local time,
136 and are used when a time zone file is used in handling POSIX-style
137 time zone environment variables.
140 uses the first standard-time
142 structure in the file
145 structure in the absence of a standard-time structure)
148 is zero or the time argument is less than the first transition time recorded
151 For version-2-format time zone files,
152 the above header and data are followed by a second header and data,
153 identical in format except that
154 eight bytes are used for each transition time or leap second time.
155 After the second header and data comes a newline-enclosed,
156 POSIX-TZ-environment-variable-style string for use in handling instants
157 after the last transition time stored in the file
158 (with nothing between the newlines if there is no POSIX representation for
164 .\" This file is in the public domain, so clarified as of
165 .\" 1996-06-05 by Arthur David Olson.