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 1.2 2003/06/17 04:26:46 dillon 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.Pp 63.Bd -literal -offset indent 64struct ttinfo { 65 long tt_gmtoff; 66 int tt_isdst; 67 unsigned int tt_abbrind; 68}; 69.Ed 70.Pp 71Each structure is written as a four-byte value for 72.Va tt_gmtoff 73of type 74.Fa long , 75in a standard byte order, followed by a one-byte value for 76.Va tt_isdst 77and a one-byte value for 78.Va tt_abbrind . 79In each structure, 80.Va tt_gmtoff 81gives the number of seconds to be added to UTC, 82.Li tt_isdst 83tells whether 84.Li tm_isdst 85should be set by 86.Xr localtime 3 87and 88.Va tt_abbrind 89serves as an index into the array of time zone abbreviation characters 90that follow the 91.Li ttinfo 92structure(s) in the file. 93.Pp 94Then there are 95.Va tzh_leapcnt 96pairs of four-byte values, written in standard byte order; 97the first value of each pair gives the time 98(as returned by 99.Xr time 3 ) 100at which a leap second occurs; 101the second gives the 102.Em total 103number of leap seconds to be applied after the given time. 104The pairs of values are sorted in ascending order by time. 105.Pp 106Then there are 107.Va tzh_ttisstdcnt 108standard/wall indicators, each stored as a one-byte value; 109they tell whether the transition times associated with local time types 110were specified as standard time or wall clock time, 111and are used when a time zone file is used in handling POSIX-style 112time zone environment variables. 113.Pp 114Finally there are 115.Va tzh_ttisgmtcnt 116UTC/local indicators, each stored as a one-byte value; 117they tell whether the transition times associated with local time types 118were specified as UTC or local time, 119and are used when a time zone file is used in handling POSIX-style 120time zone environment variables. 121.Pp 122.Nm localtime 123uses the first standard-time 124.Li ttinfo 125structure in the file 126(or simply the first 127.Li ttinfo 128structure in the absence of a standard-time structure) 129if either 130.Li tzh_timecnt 131is zero or the time argument is less than the first transition time recorded 132in the file. 133.Sh SEE ALSO 134.Xr ctime 3 , 135.Xr time2posix 3 , 136.Xr zic 8 137.\" @(#)tzfile.5 7.2 138.\" This file is in the public domain, so clarified as of 139.\" 1996-06-05 by Arthur David Olson (arthur_david_olson@nih.gov). 140