tzset - initialize time conversion information


     #include <time.h>

     void tzset (void);

     extern char *tzname[2]


     The tzset() function initializes the  tzname  variable  from
     the TZ environment variable.  This function is automatically
     called by the other time conversion functions that depend on
     the time zone.

     If the TZ variable does not appear in the  environment,  the
     tzname  variable  is initialized with the best approximation
     of local wall clock time, as  specified  by  the  tzfile(5)-
     format file /usr/lib/zoneinfo/localtime.

     If the TZ variable does appear in the  environment  but  its
     value  is  NULL or its value cannot be interpreted using any
     of the formats specified below, Coordinated  Universal  Time
     (UTC) is used.

     The value of TZ can be one of three formats.  The first for-
     mat  is  used  when  there is no daylight saving time in the
     local time zone:

          std offset

     The std string specifies the name of the time zone and  must
     be  three  or more alphabetic characters.  The offset string
     immediately follows std and specifies the time value  to  be
     added  to  the  local time to get Coordinated Universal Time
     (UTC).  The offset is positive if the  local  time  zone  is
     west  of the Prime Meridian and negative if it is east.  The
     hour must be between 0 and 24, and the minutes and seconds 0
     and 59.

     The second format is used  when  there  is  daylight  saving

          std offset dst [offset],start[/time],end[/time]

     There are no spaces in the specification.  The  initial  std
     and  offset  specify  the  standard  time zone, as described
     above.  The dst string  and  offset  specify  the  name  and
     offset for the corresponding daylight savings time zone.  If
     the offset is omitted, it defaults  to  one  hour  ahead  of
     standard time.
     The start field specifies when daylight  savings  time  goes
     into  effect  and the end field specifies when the change is
     made back to standard time.  These fields may have the  fol-
     lowing formats:

     Jn   This specifies the Julian day with n between 1 and 365.
          February 29 is never counted even in leap years.

     n    This specifies the Julian day with n between 1 and 365.
          February 29 is counted in leap years.

          This specifies day d (0 <= d <= 6) of week w (1 <= w <=
          5) of month m (1 <= m <= 12).  Week 1 is the first week
          in which day d occurs and week 5 is the  last  week  in
          which day d occurs.  Day 0 is a Sunday.

     The time fields specify when, in the local time currently in
     effect,  the  change  to the other time occurs.  If omitted,
     the default is 02:00:00.

     The third format specifies that the  time  zone  information
     should be read from a file:


     If the file specification filespec is omitted, the time zone
     information  is  read from /usr/lib/zoneinfo/localtime which
     is in tzfile(5) format.  If filespec is given, it  specifies
     another tzfile(5)-format file to read the time zone informa-
     tion from.  If filespec does not begin with a `/', the  file
     specification  is  relative  to  the  system time conversion
     information directory /usr/lib/zoneinfo.


     /usr/lib/zoneinfo                system time zone directory
     /usr/lib/zoneinfo/localtime      local time zone file
     /usr/lib/zoneinfo/posixrules     rules for POSIX-style TZ's


     SVID 3, POSIX, BSD 4.3


     date(1), gettimeofday(2), time(2), getenv(3), tzfile(5)