tzfile.5

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH tzfile 5
.SH Name
tzfile \- time zone information
.SH Syntax
.B #include <tzfile.h>
.SH Description
The time zone information files used by
.PN tzset
begin with bytes reserved for future use,
followed by three 4-byte values of type
``long'', written in a ``standard'' byte order
(the high-order byte of the value is written first).
These values are,
in order:
.IP tzh_timecnt 15
The number of transition times for which data is stored
in the file.
.IP tzh_typecnt
The number of local time types for which data is stored
in the file (must not be zero).
.IP tzh_charcnt
The number of characters of ``time zone abbreviation strings''
stored in the file.
.IP
This header is followed by
.PN tzh_timecnt
4-byte values of type ``long'',
sorted in ascending order.
These values are written in ``standard'' byte order.
Each is used as a transition time (as returned by
.PN time
at which the rules for computing local time change).
Next come
.PN tzh_timecnt
1-byte values of type ``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:
.EX
struct ttinfo {	
	long          tt_gmtoff;
	int           tt_isdst;
	unsigned int  tt_abbrind;
};
.EE
Each structure is written as a 4-byte value for
.PN tt_gmtoff
of type ``long'',
in a standard byte order, followed by a 1-byte value for
.PN tt_isdst
and a 1-byte value for
.PN tt_abbrind .
In each structure,
.PN tt_gmtoff
gives the number of seconds to be added to GMT,
.PN tt_isdst
tells whether
.PN tm_isdst
should be set by
.PN localtime
and
.PN tt_abbrind
serves as an index into the array of time zone abbreviation characters
that follows the
.PN ttinfo
structure or structures in the file.
.PP
The
.PN localtime
call uses the first standard-time
.PN ttinfo
structure in the file
(or simply the first
.PN ttinfo
structure, in the absence of a standard-time structure)
if either
.PN tzh_timecnt
is zero or the time argument is less than the first transition time recorded
in the file.
.SH See Also
ctime(3)