1TZFILE(5)                  Linux Programmer's Manual                 TZFILE(5)
2
3
4

NAME

6       tzfile - timezone information
7

SYNOPSIS

9       #include <tzfile.h>
10

DESCRIPTION

12       The  timezone  information  files used by tzset(3) begin with the magic
13       characters "TZif" to identify then as timezone information files,  fol‐
14       lowed  by  sixteen bytes reserved for future use, followed by six four-
15       byte values of type long, written in a "standard" byte order (the high-
16       order byte of the value is written first).  These values are, in order:
17
18       tzh_ttisgmtcnt
19              The number of UTC/local indicators stored in the file.
20
21       tzh_ttisstdcnt
22              The number of standard/wall indicators stored in the file.
23
24       tzh_leapcnt
25              The number of leap seconds for which data is stored in the file.
26
27       tzh_timecnt
28              The number of "transition times" for which data is stored in the
29              file.
30
31       tzh_typecnt
32              The number of "local time types" for which data is stored in the
33              file (must not be zero).
34
35       tzh_charcnt
36              The  number  of  characters  of  "timezone abbreviation strings"
37              stored in the file.
38
39       The above header is followed by tzh_timecnt four-byte  values  of  type
40       long,  sorted  in  ascending order.  These values are written in "stan‐
41       dard" byte order.  Each is used as a transition time  (as  returned  by
42       time(2)) at which the rules for computing local time change.  Next come
43       tzh_timecnt one-byte values of type unsigned char; each one tells which
44       of  the  different types of "local time" types described in the file is
45       associated with the same-indexed transition time.  These  values  serve
46       as  indices into an array of ttinfo structures that appears next in the
47       file; these structures are defined as follows:
48
49           struct ttinfo {
50               long         tt_gmtoff;
51               int          tt_isdst;
52               unsigned int tt_abbrind;
53           };
54
55       Each structure is written as a four-byte value for  tt_gmtoff  of  type
56       long,  in  a  standard  byte  order,  followed  by a one-byte value for
57       tt_isdst and a one-byte  value  for  tt_abbrind.   In  each  structure,
58       tt_gmtoff  gives  the  number  of  seconds to be added to UTC, tt_isdst
59       tells whether tm_isdst should be set by  localtime(3),  and  tt_abbrind
60       serves  as  an index into the array of timezone abbreviation characters
61       that follow the ttinfo structure(s) in the file.
62
63       Then there are tzh_leapcnt pairs of four-byte values, written in  stan‐
64       dard  byte  order;  the  first  value  of  each pair gives the time (as
65       returned by time(2)) at which a leap second occurs;  the  second  gives
66       the  total  number  of leap seconds to be applied after the given time.
67       The pairs of values are sorted in ascending order by time.
68
69       Then there are tzh_ttisstdcnt standard/wall indicators, each stored  as
70       a  one-byte  value;  they  tell whether the transition times associated
71       with local time types were specified as standard  time  or  wall  clock
72       time, and are used when a timezone file is used in handling POSIX-style
73       timezone environment variables.
74
75       Finally, there are tzh_ttisgmtcnt UTC/local indicators, each stored  as
76       a  one-byte  value;  they  tell whether the transition times associated
77       with local time types were specified as UTC or local time, and are used
78       when  a timezone file is used in handling POSIX-style timezone environ‐
79       ment variables.
80
81       Localtime uses the first standard-time ttinfo structure in the file (or
82       simply  the  first  ttinfo  structure in the absence of a standard-time
83       structure) if either tzh_timecnt is zero or the time argument  is  less
84       than the first transition time recorded in the file.
85

COLOPHON

87       This  page  is  part of release 3.25 of the Linux man-pages project.  A
88       description of the project, and information about reporting  bugs,  can
89       be found at http://www.kernel.org/doc/man-pages/.
90
91
92
93                                  1996-06-05                         TZFILE(5)
Impressum