TZFILE(5)                   BSD File Formats Manual                  TZFILE(5)

NAME
     tzfile -- timezone information

SYNOPSIS
     ##include ""/usr/src/lib/libc/stdtime/tzfile.h""

DESCRIPTION
     The time zone information files used by tzset(3) begin with the magic
     characters ``TZif'' to identify them as time zone information files, fol-
     lowed by sixteen bytes reserved for future use, followed by four four-
     byte values written in a ``standard'' byte order (the high-order byte of
     the value is written first).  These values are, in order:

     tzhttisgmtcnt  The number of UTC/local indicators stored in the file.
     tzhttisstdcnt  The number of standard/wall indicators stored in the
                     file.
     tzhleapcnt     The number of leap seconds for which data is stored in
                     the file.
     tzhtimecnt     The number of ``transition times'' for which data is
                     stored in the file.
     tzhtypecnt     The number of ``local time types'' for which data is
                     stored in the file (must not be zero).
     tzhcharcnt     The number of characters of ``time zone abbreviation
                     strings'' stored in the file.

     The above header is followed by tzhtimecnt four-byte values of type
     long, sorted in ascending order.  These values are written in ``stan-
     dard'' 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
     tzhtimecnt one-byte values of type unsigned char; each one tells which
     of the different types of ``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    ttgmtoff;
                   int     ttisdst;
                   unsigned int    ttabbrind;
           };

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

     Then there are tzhleapcnt 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 tzhttisstdcnt 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.

     Finally there are tzhttisgmtcnt 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
     time zone file is used in handling POSIX-style time zone 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 tzhtimecnt is zero or the time argument is less
     than the first transition time recorded in the file.

SEE ALSO
     ctime(3), time2posix(3), zic(8)

BSD                           September 13, 1994                           BSD