4.4BSD/usr/share/man/cat5/tzfile.0

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

NNAAMMEE
     ttzzffiillee - time zone information

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<ttzzffiillee..hh>>

DDEESSCCRRIIPPTTIIOONN
     The time zone information files used by tzset(3) begin with bytes re-
     served for future use, followed by four four-byte values of type _l_o_n_g,
     written in a ``standard'' byte order (the high-order byte of the value is
     written first).  These values are, in order:

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

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

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

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

     _t_z_h___c_h_a_r_c_n_t     The number of characters of "time zone abbreviation
                     strings" stored in the file.

     The above header is followed by _t_z_h___t_i_m_e_c_n_t four-byte values of type
     _l_o_n_g, sorted in ascending order.  These values are written in ``stan-
     dard'' byte order.  Each is used as a transition time (as returned by
     time(2))  at which the rules for computing local time change.  Next come
     _t_z_h___t_i_m_e_c_n_t one-byte values of type _u_n_s_i_g_n_e_d _c_h_a_r; 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 _t_t_i_n_f_o 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 _t_t___g_m_t_o_f_f of type
     _l_o_n_g, in a standard byte order, followed by a one-byte value for _t_t___i_s_d_s_t
     and a one-byte value for _t_t___a_b_b_r_i_n_d. In each structure, _t_t___g_m_t_o_f_f gives
     the number of seconds to be added to GMT, _t_t___i_s_d_s_t tells whether _t_m___i_s_d_s_t
     should be set by localtime(3) and _t_t___a_b_b_r_i_n_d serves as an index into the
     array of time zone abbreviation characters that follow the _t_t_i_n_f_o struc-
     ture(s) in the file.

     Then there are _t_z_h___l_e_a_p_c_n_t 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 _t_o_t_a_l num-
     ber of leap seconds to be applied after the given time.  The pairs of
     values are sorted in ascending order by time.

     Finally there are _t_z_h___t_t_i_s_s_t_d_c_n_t 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.


     _L_o_c_a_l_t_i_m_e uses the first standard-time _t_t_i_n_f_o structure in the file (or
     simply the first _t_t_i_n_f_o structure in the absence of a standard-time
     structure) if either _t_z_h___t_i_m_e_c_n_t is zero or the time argument is less
     than the first transition time recorded in the file.

SSEEEE AALLSSOO
     ctime(3)

HHIISSTTOORRYY
     The ttzzffiillee file format appeared in 4.3BSDtahoe.

4.4BSD                           June 8, 1993                                2