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tzfile(4)

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NAME    [Toc]    [Back]

       tzfile - Time zone information

SYNOPSIS    [Toc]    [Back]

       #include <tzfile.h>

DESCRIPTION    [Toc]    [Back]

       The  time  zone  information  files used by tzset(3) begin
       with bytes reserved for future use, followed by six  fourbyte
  values,  written  in a standard byte order (that is,
       with the high-order byte  of  the  value  written  first).
       These  values are, in order: The number of GMT/local indicators
 stored in the file.  The  number  of  standard/wall
       indicators stored in the file.  The number of leap seconds
       for which data is stored in the file.  The number of transition
  times  for  which data is stored in the file.  The
       number of local time types for which data is stored in the
       file.  (This value must not be zero.)  The number of characters
 of time zone abbreviation  strings  stored  in  the
       file.

       The above header is followed by tzh_timecnt four-byte values,
 sorted in ascending order.  These values are  written
       in standard byte order.  Each is used as a transition time
       (as returned by time(3)) at which the rules for  computing
       local  time change.  Next come tzh_timecnt one-byte values
       of type unsigned char.  Each value tells which of the different
  local  time types described in the file is associated
 with the same-indexed transition time.  These  values
       serve  as  indices into an array of ttinfo structures that
       appears next in the file.  These structures are defined as
       follows:

       struct ttinfo {
        long          tt_gmtoff;
        int           tt_isdst;
        unsigned int  tt_abbrind; };

       Each  structure  is  written  as  a  four-byte  value  for
       tt_gmtoff of type long, in a standard byte order, followed
       by  a one-byte value for tt_isdst and a one-byte value for
       tt_abbrind.  In each structure, tt_gmtoff gives the number
       of  seconds  to  be  added  to GMT, tt_isdst tells whether
       tm_isdst should be  set  by  localtime(3)  and  tt_abbrind
       serves  as  an index into the array of time zone abbreviation
 characters that follow the ttinfo structure(s) in the
       file.

       Next,  there  are  tzh_leapcnt  pairs of four-byte values,
       written in standard byte order.  The first value  of  each
       pair  gives  the time (as returned by  time(3)) at which a
       leap second occurs.  The second gives the total number  of
       leap  seconds  to  be  applied  after the given time.  The
       pairs of values are sorted in ascending order by time.

       Then there are  tzh_ttisstdcnt  standard/wall  indicators,
       each  stored  as  a one-byte value.  They tell whether the
       transition times associated with  local  time  types  were
       specified  as  standard  time  or wall clock time, and are
       used when a time zone file is used in handling POSIX-style
       time zone environment variables.

       Fnally,  there  are  tzh_ttisgmtcnt  GMT/local indicators,
       each stored as a one-byte value;  they  tell  whether  the
       transition  times  associated  with  local time types were
       specified as GMT or local time, and are used when  a  time
       zone  file is used in handling POSIX-style time zone environment
 variables.

       The localtime(3) call uses the first standard-time  ttinfo
       structure  in  the file (or simply the first ttinfo structure,
 in the absence  of  a  standard-time  structure)  if
       either  tzh_timecnt  is  zero or the time argument is less
       than the first transition time recorded in the file.

RELATED INFORMATION    [Toc]    [Back]

       ctime(3) delim off



                                                        tzfile(4)
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