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102 lines
2.4 KiB
Groff
102 lines
2.4 KiB
Groff
.TH TZFILE 5
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.SH NAME
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tzfile \- time zone information
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.SH SYNOPSIS
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.B
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#include <tzfile.h>
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.SH DESCRIPTION
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The time zone information files used by
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.IR settz (3)
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and
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.IR newlocaltime (3)
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begin with bytes reserved for future use,
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followed by three four-byte values of type
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.BR long ,
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written in a ``standard'' byte order (the uppermost byte of the
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value is written first, followed by the lowermost byte). These values are,
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in order:
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.TP
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.I 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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.TP
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.I 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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.TP
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.I 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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.PP
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The above header is followed by
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.I tzh_timecnt
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four-byte values of type
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.BR long ,
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sorted in ascending order.
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These values are written in a ``standard'' byte order (the uppermost byte of
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the value is written first, followed by the next lower byte, and so forth).
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Each is used as a transition time (as returned by
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.IR 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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.I tzh_timecnt
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one-byte values of type
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.BR "unsigned char" ;
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each one tells which of the different types of ``local time'' described in the
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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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.I 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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.in +.5i
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.sp
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.nf
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.ta .5i +\w'unsigned short 'u
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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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.in -.5i
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.fi
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.sp
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Each structure is written as a four-byte value for
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.I tt_gmtoff
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of type
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.BR long ,
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in a standard byte order, followed by a one-byte value for
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.I tt_isdst
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and a one-byte value for
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.IR tt_abbrind .
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In each structure,
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.I tt_gmtoff
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gives the number of seconds to be added to GMT,
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.I tt_isdst
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tells whether
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.I tm_isdst
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should be set by
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.IR newlocaltime (3),
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and
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.I tt_abbrind
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serves as an index into the array of time zone abbreviation chaaracters
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that follow the
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.I ttinfo
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structure(s) in the file.
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.PP
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.I Newlocaltime
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uses the first standard-time
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.I ttinfo
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structure in the file
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(or simply the first
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.I ttinfo
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structure in the absence of a standard-time structure)
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if either
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.I tzh_timecnt
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is zero or
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.IR newlocaltime 's
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argument is less than
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the first transition time recorded in the file.
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.SH SEE ALSO
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settz(3)
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.. %W%
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