2.11BSD/src/man/man5/tzfile.5

.\"	@(#)tzfile.5	1.2 (Berkeley) 3/11/87
.\"
.TH TZFILE 5
.AT 5
.SH NAME
tzfile \- time zone information
.SH SYNOPSIS
.B
#include <tzfile.h>
.SH DESCRIPTION
The time zone information files used by
.IR tzset (3)
begin with bytes reserved for future use,
followed by three four-byte values of type
.BR long ,
written in a ``standard'' byte order
(the high-order byte of the value is written first).
These values are,
in order:
.TP
.I tzh_timecnt
The number of "transition times" for which data is stored
in the file.
.TP
.I tzh_typecnt
The number of "local time types" for which data is stored
in the file (must not be zero).
.TP
.I tzh_charcnt
The number of characters of "time zone abbreviation strings"
stored in the file.
.PP
The above header is followed by
.I tzh_timecnt
four-byte values of type
.BR long ,
sorted in ascending order.
These values are written in ``standard'' byte order.
Each is used as a transition time (as returned by
.IR time (2))
at which the rules for computing local time change.
Next come
.I tzh_timecnt
one-byte values of type
.BR "unsigned char" ;
each one tells which of the different types of ``local time'' types
described in the file is associated with the same-indexed transition time.
These values serve as indices into an array of
.I ttinfo
structures that appears next in the file; 
these structures are defined as follows:
.in +.5i
.sp
.nf
.ta .5i +\w'unsigned int\0\0'u
struct ttinfo {	
	long	tt_gmtoff;
	int	tt_isdst;
	unsigned int	tt_abbrind;
};
.in -.5i
.fi
.sp
Each structure is written as a four-byte value for
.I tt_gmtoff
of type
.BR long ,
in a standard byte order, followed by a one-byte value for
.I tt_isdst
and a one-byte value for
.IR tt_abbrind .
In each structure,
.I tt_gmtoff
gives the number of seconds to be added to GMT,
.I tt_isdst
tells whether
.I tm_isdst
should be set by
.I localtime (3)
and
.I tt_abbrind
serves as an index into the array of time zone abbreviation characters
that follow the
.I ttinfo
structure(s) in the file.
.PP
.I Localtime
uses the first standard-time
.I ttinfo
structure in the file
(or simply the first
.I ttinfo
structure in the absence of a standard-time structure)
if either
.I tzh_timecnt
is zero or the time argument is less than the first transition time recorded
in the file.
.SH SEE ALSO
ctime(3)