93 lines
3.7 KiB
Text
93 lines
3.7 KiB
Text
NAME
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tzfile - time zone information
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SYNOPSIS
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#include <tzfile.h>
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DESCRIPTION
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The time zone information files used by tzset(3) begin with
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the magic characters "TZif" to identify then as time zone
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information files, followed by sixteen bytes reserved for
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future use, followed by six four-byte values of type long,
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written in a ``standard'' byte order (the high-order byte of
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the value is written first). These values are, in order:
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tzh_ttisgmtcnt
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The number of UTC/local indicators stored in the file.
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tzh_ttisstdcnt
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The number of standard/wall indicators stored in the
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file.
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tzh_leapcnt
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The number of leap seconds for which data is stored in
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the file.
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tzh_timecnt
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The number of "transition times" for which data is
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stored in the file.
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tzh_typecnt
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The number of "local time types" for which data is
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stored in the file (must not be zero).
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tzh_charcnt
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The number of characters of "time zone abbreviation
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strings" stored in the file.
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The above header is followed by tzh_timecnt four-byte values
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of type long, sorted in ascending order. These values are
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written in ``standard'' byte order. Each is used as a
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transition time (as returned by time(2)) at which the rules
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for computing local time change. Next come tzh_timecnt
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one-byte values of type unsigned char; each one tells which
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of the different types of ``local time'' types described in
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the file is associated with the same-indexed transition
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time. These values serve as indices into an array of ttinfo
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structures that appears next in the file; these structures
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are defined as follows:
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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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Each structure is written as a four-byte value for tt_gmtoff
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of type long, in a standard byte order, followed by a one-
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byte value for tt_isdst and a one-byte value for tt_abbrind.
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In each structure, tt_gmtoff gives the number of seconds to
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be added to UTC, tt_isdst tells whether tm_isdst should be
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set by localtime (3) and tt_abbrind serves as an index into
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the array of time zone abbreviation characters that follow
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the ttinfo structure(s) in the file.
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Then there are tzh_leapcnt pairs of four-byte values,
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written in standard byte order; the first value of each pair
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gives the time (as returned by time(2)) at which a leap
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second occurs; the second gives the total number of leap
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seconds to be applied after the given time. The pairs of
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values are sorted in ascending order by time.
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Then there are tzh_ttisstdcnt standard/wall indicators, each
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stored as a one-byte value; they tell whether the transition
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times associated with local time types were specified as
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standard time or wall clock time, and are used when a time
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zone file is used in handling POSIX-style time zone
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environment variables.
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Finally there are tzh_ttisgmtcnt UTC/local indicators, each
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stored as a one-byte value; they tell whether the transition
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times associated with local time types were specified as UTC
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or local time, and are used when a time zone file is used in
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handling POSIX-style time zone environment variables.
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Localtime uses the first standard-time ttinfo structure in
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the file (or simply the first ttinfo structure in the
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absence of a standard-time structure) if either tzh_timecnt
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is zero or the time argument is less than the first
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transition time recorded in the file.
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SEE ALSO
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newctime(3)
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