1.\" Copyright (c) 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Arthur David Olson of the National Cancer Institute. 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 9.\" %sccs.include.redist.man% 10.\" 11.\" @(#)tzfile.5 5.3 (Berkeley) 05/10/91 12.\" 13.Dd 14.Dt TZFILE 5 15.Sh NAME 16.Nm tzfile 17.Nd time zone information 18.Sh SYNOPSIS 19.Fd #include <tzfile.h> 20.Sh DESCRIPTION 21The time zone information files used by 22.Xr tzset 3 23begin with bytes reserved for future use, 24followed by four four-byte values of type 25.Em long , 26written in a ``standard'' byte order 27(the high-order byte of the value is written first). 28These values are, 29in order: 30.Bl -tag -width tzh_ttisstdcnt 31.It Fa tzh_ttisstdcnt 32The number of standard/wall indicators stored in the file. 33.It Fa tzh_leapcnt 34The number of leap seconds for which data is stored in the file. 35.It Fa tzh_timecnt 36The number of "transition times" for which data is stored 37in the file. 38.It Fa tzh_typecnt 39The number of "local time types" for which data is stored 40in the file (must not be zero). 41.It Fa tzh_charcnt 42The number of characters of "time zone abbreviation strings" 43stored in the file. 44.El 45.Pp 46The above header is followed by 47.Fa tzh_timecnt 48four-byte values of type 49.Em long , 50sorted in ascending order. 51These values are written in ``standard'' byte order. 52Each is used as a transition time (as returned by 53.Xr time 2 ) 54at which the rules for computing local time change. 55Next come 56.Fa tzh_timecnt 57one-byte values of type 58.Fa unsigned char ; 59each one tells which of the different types of ``local time'' types 60described in the file is associated with the same-indexed transition time. 61These values serve as indices into an array of 62.Fa ttinfo 63structures that appears next in the file; 64these structures are defined as follows: 65.Bd -literal -offset indent 66struct ttinfo { 67 long tt_gmtoff; 68 int tt_isdst; 69 unsigned int tt_abbrind; 70}; 71.Ed 72.Pp 73Each structure is written as a four-byte value for 74.Fa tt_gmtoff 75of type 76.Em long , 77in a standard byte order, followed by a one-byte value for 78.Fa tt_isdst 79and a one-byte value for 80.Fa tt_abbrind . 81In each structure, 82.Fa tt_gmtoff 83gives the number of seconds to be added to GMT, 84.Fa tt_isdst 85tells whether 86.Fa tm_isdst 87should be set by 88.Xr localtime 3 89and 90.Fa tt_abbrind 91serves as an index into the array of time zone abbreviation characters 92that follow the 93.Fa ttinfo 94structure(s) in the file. 95.Pp 96Then there are 97.Fa tzh_leapcnt 98pairs of four-byte values, written in standard byte order; 99the first value of each pair gives the time 100(as returned by 101.Xr time 2 ) 102at which a leap second occurs; 103the second gives the 104.Em total 105number of leap seconds to be applied after the given time. 106The pairs of values are sorted in ascending order by time. 107.Pp 108Finally there are 109.Fa tzh_ttisstdcnt 110standard/wall indicators, each stored as a one-byte value; 111they tell whether the transition times associated with local time types 112were specified as standard time or wall clock time, 113and are used when a time zone file is used in handling 114.Tn POSIX Ns -style 115time zone environment variables. 116.Pp 117.Fa Localtime 118uses the first standard-time 119.Fa ttinfo 120structure in the file 121(or simply the first 122.Fa ttinfo 123structure in the absence of a standard-time structure) 124if either 125.Fa tzh_timecnt 126is zero or the time argument is less than the first transition time recorded 127in the file. 128.Sh SEE ALSO 129.Xr ctime 3 130.Sh HISTORY 131The 132.Nm tzfile 133file format appeared in 134.Bx 4.3 tahoe. 135