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file format change

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SCCS-file: tzfile.5
SCCS-SID: 1.5
This commit is contained in:
Arthur David Olson
1986-03-02 22:03:34 -05:00
committed by Paul Eggert
parent 73a47de4fe
commit 0dcdfce628
1 changed files with 71 additions and 47 deletions
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118
tzfile.5
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@@ -9,74 +9,98 @@ The time zone information files used by
.IR settz (3)
and
.IR newlocaltime (3)
have the format of the
begin with a
.I tzinfo
structure described in the include file
structure (as defined in the include file
.B
"tzfile.h":
"tzfile.h"\c
):
.sp
.nf
.in +.5i
struct tzinfo {
int tz_timecnt;
long tz_times[TZ_MAX_TIMES];
char tz_types[TZ_MAX_TIMES];
struct dsinfo {
long ds_gmtoff;
char ds_abbr[TZ_ABBR_LEN+1];
char ds_isdst;
} tz_dsinfo[TZ_MAX_TYPES];
.ta .5i +\w'unsigned short 'u
struct tzhead {
char tzh_reserved[14];
unsigned short tzh_timecnt;
unsigned short tzh_typecnt;
unsigned short tzh_charcnt;
};
.in -.5i
.fi
.PP
The
.B tz_timecnt
field tells how many of the
.B tz_times
and
.B tz_types
stored in the file are meaningful.
Each of the meaningful
.B tz_times
entries is a starting time (as returned by
.IR time (2));
the same-indexed
.B tz_types
entry is the index of the
.B tz_dsinfo
array element that tells about how "local time" is generated starting at that
time.
For a file to be used by
.IR settz ,
its
.B tz_times
entries must be sorted in ascending order.
.B tzh_reserved
element is currently unused.
The
.B tzh_timecnt
element gives the number of "transition times" for which data is stored
in the file;
the
.B tzh_typecnt
(which must not be zero)
element gives the number of "local time types" for which data is stored
in the file;
and the
.B tzh_charcnt
element gives the number of characters of "time zone abbreviation strings"
stored in the file.
.PP
In the
.B tz_dsinfo
structures,
.B ds_gmtoff
gives the number of seconds that should be added to GMT;
.B ds_abbr
is the ASCII-NUL-terminated string used as the time zone abbreviation;
and
The above header is followed by
.B tzh_timecnt
values of type
.BR long ;
each is used as a transition time (as returned by
.IR time (2))
at which the rules for computing local time change.
Next come
.B tzh_timecnt
values of type
.BR "unsigned char" ;
each one tells which of the different types of "local time" described in the
file is associated with the same-indexed transition time.
These values serve as indices into an array of
.B ttinfo
structures that appears next in the file;
these structures are defined as follows:
.in +.5i
.sp
.nf
.ta .5i +\w'unsigned short 'u
struct ttinfo {
long tt_gmtoff;
int tt_isdst;
unsigned int tt_abbrind;
};
.in -.5i
.fi
.sp
In each structure,
.B tt_gmtoff
gives the number of seconds to be added to GMT,
.B
ds_isdst
tt_isdst
tells whether
.B
tm_isdst
should be set by
.IR newlocaltime (3).
.IR newlocaltime (3),
and
.B tt_abbrind
serves as an index into the array of time zone abbreviation chaaracters
that follow the
.B ttinfo
structure(s) in the file.
.PP
.I Newlocaltime
uses the first element of
.B tz_dsinfo
uses the first
.B ttinfo
structure in the file
if either
.B tz_timecnt
.B tzh_timecnt
is zero or
.IR newlocaltime 's
argument is less than
.BR tz_times[0] .
the first transition time recorded in the file.
.SH SEE ALSO
settz(3)
.. %W%