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1.1 root 1: .TH TZFILE 5
2: .SH NAME
3: tzfile \- time zone information
4: .SH SYNOPSIS
5: .B
6: #include <tzfile.h>
7: .SH DESCRIPTION
8: The time zone information files used by
9: .IR tzset (3)
10: begin with bytes reserved for future use,
11: followed by four four-byte values of type
12: .BR long ,
13: written in a ``standard'' byte order
14: (the high-order byte of the value is written first).
15: These values are,
16: in order:
17: .TP
18: .I tzh_ttisstdcnt
19: The number of standard/wall indicators stored in the file.
20: .TP
21: .I tzh_leapcnt
22: The number of leap seconds for which data is stored in the file.
23: .TP
24: .I tzh_timecnt
25: The number of "transition times" for which data is stored
26: in the file.
27: .TP
28: .I tzh_typecnt
29: The number of "local time types" for which data is stored
30: in the file (must not be zero).
31: .TP
32: .I tzh_charcnt
33: The number of characters of "time zone abbreviation strings"
34: stored in the file.
35: .PP
36: The above header is followed by
37: .I tzh_timecnt
38: four-byte values of type
39: .BR long ,
40: sorted in ascending order.
41: These values are written in ``standard'' byte order.
42: Each is used as a transition time (as returned by
43: .IR time (2))
44: at which the rules for computing local time change.
45: Next come
46: .I tzh_timecnt
47: one-byte values of type
48: .BR "unsigned char" ;
49: each one tells which of the different types of ``local time'' types
50: described in the file is associated with the same-indexed transition time.
51: These values serve as indices into an array of
52: .I ttinfo
53: structures that appears next in the file;
54: these structures are defined as follows:
55: .in +.5i
56: .sp
57: .nf
58: .ta .5i +\w'unsigned int\0\0'u
59: struct ttinfo {
60: long tt_gmtoff;
61: int tt_isdst;
62: unsigned int tt_abbrind;
63: };
64: .in -.5i
65: .fi
66: .sp
67: Each structure is written as a four-byte value for
68: .I tt_gmtoff
69: of type
70: .BR long ,
71: in a standard byte order, followed by a one-byte value for
72: .I tt_isdst
73: and a one-byte value for
74: .IR tt_abbrind .
75: In each structure,
76: .I tt_gmtoff
77: gives the number of seconds to be added to GMT,
78: .I tt_isdst
79: tells whether
80: .I tm_isdst
81: should be set by
82: .I localtime (3)
83: and
84: .I tt_abbrind
85: serves as an index into the array of time zone abbreviation characters
86: that follow the
87: .I ttinfo
88: structure(s) in the file.
89: .PP
90: Then there are
91: .I tzh_leapcnt
92: pairs of four-byte values, written in standard byte order;
93: the first value of each pair gives the time
94: (as returned by
95: .IR time(2))
96: at which a leap second occurs;
97: the second gives the
98: .I total
99: number of leap seconds to be applied after the given time.
100: The pairs of values are sorted in ascending order by time.
101: .PP
102: Finally there are
103: .I tzh_ttisstdcnt
104: standard/wall indicators, each stored as a one-byte value;
105: they tell whether the transition times associated with local time types
106: were specified as standard time or wall clock time,
107: and are used when a time zone file is used in handling POSIX-style
108: time zone environment variables.
109: .PP
110: .I Localtime
111: uses the first standard-time
112: .I ttinfo
113: structure in the file
114: (or simply the first
115: .I ttinfo
116: structure in the absence of a standard-time structure)
117: if either
118: .I tzh_timecnt
119: is zero or the time argument is less than the first transition time recorded
120: in the file.
121: .SH SEE ALSO
122: ctime(3)
123: .. @(#)tzfile.5 4.2
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