TZFILE(5)                                           Linux Programmer's Manual                                          TZFILE(5)



NAME
       tzfile - timezone information

SYNOPSIS
       #include <tzfile.h>

DESCRIPTION
       The  timezone  information  files  used  by  tzset(3) begin with the magic characters "TZif" to identify then as timezone
       information files, followed by sixteen bytes reserved for future use, followed by six  four-byte  values  of  type  long,
       written in a "standard" byte order (the high-order byte of the value is written first).  These values are, in order:

       tzh_ttisgmtcnt
              The number of UTC/local indicators stored in the file.

       tzh_ttisstdcnt
              The number of standard/wall indicators stored in the file.

       tzh_leapcnt
              The number of leap seconds for which data is stored in the file.

       tzh_timecnt
              The number of "transition times" for which data is stored in the file.

       tzh_typecnt
              The number of "local time types" for which data is stored in the file (must not be zero).

       tzh_charcnt
              The number of characters of "timezone abbreviation strings" stored in the file.

       The  above  header is followed by tzh_timecnt four-byte values of type long, sorted in ascending order.  These values are
       written in "standard" byte order.  Each is used as a transition time (as returned by time(2)) at which the rules for com-
       puting  local time change.  Next come tzh_timecnt one-byte values of type unsigned char; each one tells which of the dif-
       ferent types of "local time" types described in the file is associated with the same-indexed transition time.  These val-
       ues  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 UTC, tt_isdst tells whether tm_isdst should be set by localtime(3), and tt_abbrind serves as  an  index  into
       the array of timezone abbreviation characters that follow the ttinfo structure(s) in the file.

       Then  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(2)) 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  timezone
       file is used in handling POSIX-style timezone environment variables.

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

       Localtime  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.

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                                           1996-06-05                                                  TZFILE(5)