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1871769f1f
The stdtime sources were moved from lib/libc to contrib/tzcode, and tzfile.h is not an installed header, so the man page refers to its location in the source tree. The documentation could be more clear about the internal nature of the header, but those changes should go through upstream tzcode. PR: docs/176864 Approved by: hrs (mentor)
153 lines
4.3 KiB
Groff
153 lines
4.3 KiB
Groff
.\" $FreeBSD$
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.Dd September 13, 1994
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.Dt TZFILE 5
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.Os
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.Sh NAME
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.Nm tzfile
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.Nd timezone information
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.Sh SYNOPSIS
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.Fd #include \&"/usr/src/contrib/tzcode/stdtime/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 the magic characters
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.Dq Li TZif
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to identify them as
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time zone information files,
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followed by a character identifying the version of the file's format
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(as of 2005, either an ASCII NUL or a '2')
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followed by fifteen bytes containing zeroes reserved for future use,
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followed by four four-byte values
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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 Va tzh_ttisgmtcnt
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The number of UTC/local indicators stored in the file.
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.It Va tzh_ttisstdcnt
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The number of standard/wall indicators stored in the file.
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.It Va tzh_leapcnt
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The number of leap seconds for which data is stored in the file.
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.It Va 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 Va 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 Va 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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.Va 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 3 )
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at which the rules for computing local time change.
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Next come
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.Va 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 (with
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.Fa tzh_typecnt
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entries) 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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.Va 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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.Va tt_isdst
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and a one-byte value for
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.Va tt_abbrind .
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In each structure,
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.Va tt_gmtoff
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gives the number of seconds to be added to UTC,
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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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.Va 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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.Va 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 3 )
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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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Then there are
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.Va 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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Finally there are
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.Va tzh_ttisgmtcnt
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UTC/local 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 UTC or local 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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.Pp
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For version-2-format time zone files,
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the above header and data is followed by a second header and data,
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identical in format except that eight bytes are used for each
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transition time or leap second time.
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After the second header and data comes a newline-enclosed,
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POSIX-TZ-environment-variable-style string for use in handling instants
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after the last transition time stored in the file
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(with nothing between the newlines if there is no POSIX representation for
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such instants).
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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 8.3
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.\" This file is in the public domain, so clarified as of
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.\" 1996-06-05 by Arthur David Olson.
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