1.\" $NetBSD: tzfile.5,v 1.12 2003/04/16 13:34:58 wiz Exp $ 2.\" 3.\" @(#)tzfile.5 7.11 4.\" This file is in the public domain, so clarified as of 5.\" 1996-06-05 by Arthur David Olson (arthur_david_olson@nih.gov). 6.Dd September 16, 2001 7.Os 8.Dt TZFILE 5 9.Sh NAME 10.Nm tzfile 11.Nd time zone information 12.Sh SYNOPSIS 13.In tzfile.h 14.Sh DESCRIPTION 15The time zone information files used by 16.Xr tzset 3 17begin with the magic characters 18.Dq TZif 19to identify them as time zone information files, 20followed by sixteen bytes reserved for future use, 21followed by six four-byte values of type 22.Fa long , 23written in a 24.Dq standard 25byte order (the high-order byte of the value is written first). 26These values are, in order: 27.Bl -tag -width XXXXXX -compact 28.It Va tzh_ttisgmtcnt 29The number of UTC/local indicators stored in the file. 30.It Va tzh_ttisstdcnt 31The number of standard/wall indicators stored in the file. 32.It Va tzh_leapcnt 33The number of leap seconds for which data is stored in the file. 34.It Va tzh_timecnt 35The number of 36.Dq transition times 37for which data is stored in the file. 38.It Va tzh_typecnt 39The number of 40.Dq local time types 41for which data is stored in the file (must not be zero). 42.It Va 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.Va tzh_timecnt 49four-byte values of type 50.Fa long , 51sorted in ascending order. 52These values are written in 53.Dq standard 54byte order. 55Each is used as a transition time (as returned by 56.Xr time 3 ) 57at which the rules for computing local time change. 58Next come 59.Va tzh_timecnt 60one-byte values of type 61.Fa unsigned char ; 62each one tells which of the different types of 63.Dq local time 64types described in the file is associated with the same-indexed 65transition time. 66These values serve as indices into an array of 67.Fa ttinfo 68structures that appears next in the file; 69these structures are defined as follows: 70.Bd -literal 71struct ttinfo { 72 long tt_gmtoff; 73 int tt_isdst; 74 unsigned int tt_abbrind; 75}; 76.Ed 77Each structure is written as a four-byte value for 78.Va tt_gmtoff 79of type 80.Fa long , 81in a standard byte order, followed by a one-byte value for 82.Va tt_isdst 83and a one-byte value for 84.Va tt_abbrind . 85In each structure, 86.Va tt_gmtoff 87gives the number of seconds to be added to UTC, 88.Va tt_isdst 89tells whether 90.Va tm_isdst 91should be set by 92.Xr localtime 3 93and 94.Va tt_abbrind 95serves as an index into the array of time zone abbreviation characters 96that follow the 97.Va ttinfo 98structure(s) in the file. 99.Pp 100Then there are 101.Va tzh_leapcnt 102pairs of four-byte values, written in standard byte order; 103the first value of each pair gives the time 104(as returned by 105.Xr time 3 ) 106at which a leap second occurs; 107the second gives the 108.Em total 109number of leap seconds to be applied after the given time. 110The pairs of values are sorted in ascending order by time. 111.Pp 112Then there are 113.Va tzh_ttisstdcnt 114standard/wall indicators, each stored as a one-byte value; 115they tell whether the transition times associated with local time types 116were specified as standard time or wall clock time, 117and are used when a time zone file is used in handling POSIX-style 118time zone environment variables. 119.Pp 120Finally there are 121.Va tzh_ttisgmtcnt 122UTC/local indicators, each stored as a one-byte value; 123they tell whether the transition times associated with local time types 124were specified as UTC or local time, 125and are used when a time zone file is used in handling POSIX-style 126time zone environment variables. 127.Pp 128.Xr localtime 3 129uses the first standard-time 130.Fa ttinfo 131structure in the file 132(or simply the first 133.Fa ttinfo 134structure in the absence of a standard-time structure) 135if either 136.Va tzh_timecnt 137is zero or the time argument is less than the first transition time recorded 138in the file. 139.Sh SEE ALSO 140.Xr ctime 3 , 141.Xr localtime 3 , 142.Xr time 3 143