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NAME

       tzfile - time zone information

SYNOPSIS

       #include <tzfile.h>

DESCRIPTION

       This  page  describes the structure of timezone files as commonly found
       in /usr/lib/zoneinfo or /usr/share/zoneinfo.

       The time zone information files used by tzset(3) begin with  the  magic
       characters  "TZif"  to  identify  then  as time zone 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 computing local time  change.   Next
       come  tzh_timecnt 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         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.

NOTES

       This manual page documents <tzfile.h> in the glibc source archive,  see
       timezone/tzfile.h.

       It  seems  that  timezone  uses tzfile internally, but glibc refuses to
       expose it to userspace.  This is most likely because  the  standardised
       functions  are  more  useful  and  portable, and actually documented by
       glibc.  It may  only  be  in  glibc  just  to  support  the  non-glibc-
       maintained timezone data (which is maintained by some other entity).

SEE ALSO

       time(3), gettimeofday(3), tzset(3), ctime(3)

COLOPHON

       This  page  is  part of release 3.15 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)