1.\" $FreeBSD: src/lib/libc/stdtime/tzfile.5,v 1.8.2.2 2001/08/17 15:42:43 ru Exp $ 2.\" $DragonFly: src/lib/libc/stdtime/tzfile.5,v 1.3 2008/05/02 02:05:04 swildner Exp $ 3.Dd September 13, 1994 4.Dt TZFILE 5 5.Os 6.Sh NAME 7.Nm tzfile 8.Nd timezone information 9.Sh SYNOPSIS 10.Fd #include \&"/usr/src/lib/libc/stdtime/tzfile.h\&" 11.Sh DESCRIPTION 12The time zone information files used by 13.Xr tzset 3 14begin with the magic characters 15.Dq Li TZif 16to identify them as 17time zone information files, 18followed by sixteen bytes reserved for future use, 19followed by four four-byte values 20written in a ``standard'' byte order 21(the high-order byte of the value is written first). 22These values are, 23in order: 24.Pp 25.Bl -tag -compact -width tzh_ttisstdcnt 26.It Va tzh_ttisgmtcnt 27The number of UTC/local indicators stored in the file. 28.It Va tzh_ttisstdcnt 29The number of standard/wall indicators stored in the file. 30.It Va tzh_leapcnt 31The number of leap seconds for which data is stored in the file. 32.It Va tzh_timecnt 33The number of ``transition times'' for which data is stored 34in the file. 35.It Va tzh_typecnt 36The number of ``local time types'' for which data is stored 37in the file (must not be zero). 38.It Va tzh_charcnt 39The number of characters of ``time zone abbreviation strings'' 40stored in the file. 41.El 42.Pp 43The above header is followed by 44.Va tzh_timecnt 45four-byte values of type 46.Fa long , 47sorted in ascending order. 48These values are written in ``standard'' byte order. 49Each is used as a transition time (as returned by 50.Xr time 3 ) 51at which the rules for computing local time change. 52Next come 53.Va tzh_timecnt 54one-byte values of type 55.Fa "unsigned char" ; 56each one tells which of the different types of ``local time'' types 57described in the file is associated with the same-indexed transition time. 58These values serve as indices into an array of 59.Fa ttinfo 60structures that appears next in the file; 61these structures are defined as follows: 62.Bd -literal -offset indent 63struct ttinfo { 64 long tt_gmtoff; 65 int tt_isdst; 66 unsigned int tt_abbrind; 67}; 68.Ed 69.Pp 70Each structure is written as a four-byte value for 71.Va tt_gmtoff 72of type 73.Fa long , 74in a standard byte order, followed by a one-byte value for 75.Va tt_isdst 76and a one-byte value for 77.Va tt_abbrind . 78In each structure, 79.Va tt_gmtoff 80gives the number of seconds to be added to UTC, 81.Li tt_isdst 82tells whether 83.Li tm_isdst 84should be set by 85.Xr localtime 3 86and 87.Va tt_abbrind 88serves as an index into the array of time zone abbreviation characters 89that follow the 90.Li ttinfo 91structure(s) in the file. 92.Pp 93Then there are 94.Va tzh_leapcnt 95pairs of four-byte values, written in standard byte order; 96the first value of each pair gives the time 97(as returned by 98.Xr time 3 ) 99at which a leap second occurs; 100the second gives the 101.Em total 102number of leap seconds to be applied after the given time. 103The pairs of values are sorted in ascending order by time. 104.Pp 105Then there are 106.Va tzh_ttisstdcnt 107standard/wall indicators, each stored as a one-byte value; 108they tell whether the transition times associated with local time types 109were specified as standard time or wall clock time, 110and are used when a time zone file is used in handling POSIX-style 111time zone environment variables. 112.Pp 113Finally there are 114.Va tzh_ttisgmtcnt 115UTC/local indicators, each stored as a one-byte value; 116they tell whether the transition times associated with local time types 117were specified as UTC or local time, 118and are used when a time zone file is used in handling POSIX-style 119time zone environment variables. 120.Pp 121.Nm localtime 122uses the first standard-time 123.Li ttinfo 124structure in the file 125(or simply the first 126.Li ttinfo 127structure in the absence of a standard-time structure) 128if either 129.Li tzh_timecnt 130is zero or the time argument is less than the first transition time recorded 131in the file. 132.Sh SEE ALSO 133.Xr ctime 3 , 134.Xr time2posix 3 , 135.Xr zic 8 136.\" @(#)tzfile.5 7.2 137.\" This file is in the public domain, so clarified as of 138.\" 1996-06-05 by Arthur David Olson (arthur_david_olson@nih.gov). 139