a040910f9b
4.4. The code is almost identical to the 4.4 versions, but this organization should make it easier to merge new versions in the future.
123 lines
3.1 KiB
Groff
123 lines
3.1 KiB
Groff
.Dd September 13, 1994
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.Dt TZFILE 5
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.Os FreeBSD 2.0
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.Sh NAME
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.Nm tzfile
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.Nd time zone information
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.Sh SYNOPSIS
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.Fd #include <tzfile.h>
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.Sh DESCRIPTION
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The time zone information files used by
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.Xr tzset 3
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begin with bytes reserved for future use,
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followed by four four-byte values of type
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.Fa long ,
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written in a ``standard'' byte order
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(the high-order byte of the value is written first).
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These values are,
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in order:
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.Pp
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.Bl -tag -compact -width tzh_ttisstdcnt
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.It Li tzh_ttisstdcnt
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The number of standard/wall indicators stored in the file.
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.It Li tzh_leapcnt
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The number of leap seconds for which data is stored in the file.
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.It Li tzh_timecnt
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The number of ``transition times'' for which data is stored
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in the file.
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.It Li tzh_typecnt
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The number of ``local time types'' for which data is stored
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in the file (must not be zero).
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.It Li tzh_charcnt
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The number of characters of ``time zone abbreviation strings''
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stored in the file.
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.El
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.Pp
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The above header is followed by
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.Li tzh_timecnt
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four-byte values of type
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.Fa long ,
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sorted in ascending order.
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These values are written in ``standard'' byte order.
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Each is used as a transition time (as returned by
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.Xr time 2 )
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at which the rules for computing local time change.
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Next come
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.Li tzh_timecnt
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one-byte values of type
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.Fa "unsigned char" ;
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each one tells which of the different types of ``local time'' types
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described in the file is associated with the same-indexed transition time.
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These values serve as indices into an array of
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.Fa ttinfo
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structures that appears next in the file;
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these structures are defined as follows:
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.Pp
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.Bd -literal -offset indent
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struct ttinfo {
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long tt_gmtoff;
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int tt_isdst;
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unsigned int tt_abbrind;
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};
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.Ed
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.Pp
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Each structure is written as a four-byte value for
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.Li tt_gmtoff
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of type
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.Fa long ,
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in a standard byte order, followed by a one-byte value for
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.Li tt_isdst
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and a one-byte value for
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.Li tt_abbrind .
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In each structure,
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.Li tt_gmtoff
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gives the number of seconds to be added to GMT,
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.Li tt_isdst
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tells whether
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.Li tm_isdst
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should be set by
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.Xr localtime 3
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and
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.Li tt_abbrind
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serves as an index into the array of time zone abbreviation characters
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that follow the
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.Li ttinfo
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structure(s) in the file.
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.Pp
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Then there are
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.Li tzh_leapcnt
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pairs of four-byte values, written in standard byte order;
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the first value of each pair gives the time
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(as returned by
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.Xr time 2 )
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at which a leap second occurs;
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the second gives the
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.Em total
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number of leap seconds to be applied after the given time.
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The pairs of values are sorted in ascending order by time.
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.Pp
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Finally there are
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.Li tzh_ttisstdcnt
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standard/wall indicators, each stored as a one-byte value;
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they tell whether the transition times associated with local time types
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were specified as standard time or wall clock time,
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and are used when a time zone file is used in handling POSIX-style
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time zone environment variables.
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.Pp
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.Nm localtime
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uses the first standard-time
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.Li ttinfo
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structure in the file
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(or simply the first
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.Li ttinfo
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structure in the absence of a standard-time structure)
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if either
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.Li tzh_timecnt
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is zero or the time argument is less than the first transition time recorded
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in the file.
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.Sh SEE ALSO
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.Xr ctime 3 ,
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.Xr time2posix 3 ,
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.Xr zic 8
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.\" @(#)tzfile.5 7.2
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