1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. 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.roff% 10.\" 11.\" @(#)tzfile.5 8.1 (Berkeley) 06/08/93 12.\" 13.Dd 14.Dt TZFILE 5 15.Os 16.Sh NAME 17.Nm tzfile 18.Nd time zone information 19.Sh SYNOPSIS 20.Fd #include <tzfile.h> 21.Sh DESCRIPTION 22The time zone information files used by 23.Xr tzset 3 24begin with bytes reserved for future use, 25followed by four four-byte values of type 26.Em long , 27written in a ``standard'' byte order 28(the high-order byte of the value is written first). 29These values are, 30in order: 31.Bl -tag -width tzh_ttisstdcnt 32.It Fa tzh_ttisstdcnt 33The number of standard/wall indicators stored in the file. 34.It Fa tzh_leapcnt 35The number of leap seconds for which data is stored in the file. 36.It Fa tzh_timecnt 37The number of "transition times" for which data is stored 38in the file. 39.It Fa tzh_typecnt 40The number of "local time types" for which data is stored 41in the file (must not be zero). 42.It Fa tzh_charcnt 43The number of characters of "time zone abbreviation strings" 44stored in the file. 45.El 46.Pp 47The above header is followed by 48.Fa tzh_timecnt 49four-byte values of type 50.Em long , 51sorted in ascending order. 52These values are written in ``standard'' byte order. 53Each is used as a transition time (as returned by 54.Xr time 2 ) 55at which the rules for computing local time change. 56Next come 57.Fa tzh_timecnt 58one-byte values of type 59.Fa unsigned char ; 60each one tells which of the different types of ``local time'' types 61described in the file is associated with the same-indexed transition time. 62These values serve as indices into an array of 63.Fa ttinfo 64structures that appears next in the file; 65these structures are defined as follows: 66.Bd -literal -offset indent 67struct ttinfo { 68 long tt_gmtoff; 69 int tt_isdst; 70 unsigned int tt_abbrind; 71}; 72.Ed 73.Pp 74Each structure is written as a four-byte value for 75.Fa tt_gmtoff 76of type 77.Em long , 78in a standard byte order, followed by a one-byte value for 79.Fa tt_isdst 80and a one-byte value for 81.Fa tt_abbrind . 82In each structure, 83.Fa tt_gmtoff 84gives the number of seconds to be added to 85.Tn GMT , 86.Fa tt_isdst 87tells whether 88.Fa tm_isdst 89should be set by 90.Xr localtime 3 91and 92.Fa tt_abbrind 93serves as an index into the array of time zone abbreviation characters 94that follow the 95.Fa ttinfo 96structure(s) in the file. 97.Pp 98Then there are 99.Fa tzh_leapcnt 100pairs of four-byte values, written in standard byte order; 101the first value of each pair gives the time 102(as returned by 103.Xr time 2 ) 104at which a leap second occurs; 105the second gives the 106.Em total 107number of leap seconds to be applied after the given time. 108The pairs of values are sorted in ascending order by time. 109.Pp 110Finally there are 111.Fa tzh_ttisstdcnt 112standard/wall indicators, each stored as a one-byte value; 113they tell whether the transition times associated with local time types 114were specified as standard time or wall clock time, 115and are used when a time zone file is used in handling 116.Tn POSIX Ns -style 117time zone environment variables. 118.Pp 119.Fa Localtime 120uses the first standard-time 121.Fa ttinfo 122structure in the file 123(or simply the first 124.Fa ttinfo 125structure in the absence of a standard-time structure) 126if either 127.Fa tzh_timecnt 128is zero or the time argument is less than the first transition time recorded 129in the file. 130.Sh SEE ALSO 131.Xr ctime 3 132.Sh HISTORY 133The 134.Nm tzfile 135file format appeared in 136.Bx 4.3 tahoe. 137