The  TZ environment variable is used to establish the local time zone.  The
value of the variable is used by various time functions to compute times
relative to Coordinated Universal Time (UTC) (formerly known as Greenwich
Mean Time (GMT)).

The time on the computer should be set to the local time.  Use the DOS time
command and the DOS date command if the time is not automatically maintained
by the computer hardware.

The  TZ environment variable can be set (before the program is executed) by
using the DOS set command as follows:


         SET TZ=PST8PDT

or (during the program execution) by using the  setenv or  putenv library
functions:


         setenv( "TZ", "PST8PDT", 1 );
         putenv( "TZ=PST8PDT" );

The value of the variable can be obtained by using the  getenv function:


         char *tzvalue;
          . . .
         tzvalue = getenv( "TZ" );

The  tzset function processes the  TZ environment variable and sets the
global variables  daylight (indicates if daylight saving time is supported
in the locale),  timezone (contains the number of seconds of time difference
between the local time zone and Coordinated Universal Time (UTC)), and
 tzname (a vector of two pointers to character strings containing the
standard and daylight time-zone names).

The value of the  TZ environment variable should be set as follows (spaces
are for clarity only):

std offset dst offset , rule

The expanded format is as follows:

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

std, dst
    three or more letters that are the designation for the standard (std) or
    summer (dst) time zone.  Only std is required.  If dst is omitted, then
    summer time does not apply in this locale.  Upper- and lowercase letters
    are allowed.  Any characters except for a leading colon (:), digits,
    comma (,), minus (-), plus (+), and ASCII NUL (\0) are allowed.

offset
    indicates the value one must add to the local time to arrive at
    Coordinated Universal Time (UTC).  The offset has the form:

    hh[:mm[:ss]]

    The minutes (mm) and seconds (ss) are optional.  The hour (hh) is
    required and may be a single digit.  The offset following std is
    required.  If no offset follows dst, summer time is assumed to be one
    hour ahead of standard time.  One or more digits may be used; the value
    is always interpreted as a decimal number.  The hour may be between 0
    and 24, and the minutes (and seconds) - if present - between 0 and 59.
     If preceded by a "-", the time zone will be east of the  Prime Meridian
    ; otherwise it will be west (which may be indicated by an optional
    preceding "+").

rule
    indicates when to change to and back from summer time.  The rule has the
    form:

    date/time,date/time

    where the first date describes when the change from standard to summer
    time occurs and the second date describes when the change back happens.
     Each time field describes when, in current local time, the change to
    the other time is made.

    The format of date may be one of the following:

    Jn
        The Julian day n (1 <= n <= 365).  Leap days are not counted.  That
        is, in all years - including leap years - February 28 is day 59 and
        March 1 is day 60.  It is impossible to explicitly refer to the
        occasional February 29.

    n
        The zero-based Julian day (0 <= n <= 365).  Leap years are counted,
        and it is possible to refer to February 29.

    Mm.n.d
        The d'th day (0 <= d <= 6) of week n of month m of the year (1 <= n
        <= 5, 1 <= m <= 12, where week 5 means "the last d day in month m"
        which may occur in the fourth or fifth week).  Week 1 is the first
        week in which the d'th day occurs.  Day zero is Sunday.

    The time has the same format as offset except that no leading sign ("+"
    or "-") is allowed.  The default, if time is omitted, is 02:00:00.

Whenever  ctime,  _ctime,  localtime,  _localtime or  mktime is called, the
time zone names contained in the external variable  tzname will be set as if
the  tzset function had been called.  The same is true if the %Z directive
of  strftime is used.

Some examples are:

TZ=EST5EDT
    Eastern Standard Time is 5 hours earlier than Coordinated Universal Time
    (UTC).  Standard time and daylight saving time both apply to this
    locale.  By default, Eastern Daylight Time (EDT) is one hour ahead of
    standard time (i.e., EDT4).  Since it is not specified, daylight saving
    time starts on the first Sunday of April at 2:00 A.M.  and ends on the
    last Sunday of October at 2:00 A.M.  This is the default when the  TZ
    variable is not set.

TZ=EST5EDT4,M4.1.0/02:00:00,M10.5.0/02:00:00
    This is the full specification for the default when the  TZ variable is
    not set.  Eastern Standard Time is 5 hours earlier than Coordinated
    Universal Time (UTC).  Standard time and daylight saving time both apply
    to this locale.  Eastern Daylight Time (EDT) is one hour ahead of
    standard time.  Daylight saving time starts on the first (1) Sunday (0)
    of April (4) at 2:00 A.M.  and ends on the last (5) Sunday (0) of
    October (10) at 2:00 A.M.

TZ=PST8PDT
    Pacific Standard Time is 8 hours earlier than Coordinated Universal Time
    (UTC).  Standard time and daylight saving time both apply to this
    locale.  By default, Pacific Daylight Time is one hour ahead of standard
    time (i.e., PDT7).  Since it is not specified, daylight saving time
    starts on the first Sunday of April at 2:00 A.M.  and ends on the last
    Sunday of October at 2:00 A.M.

TZ=NST3:30NDT1:30
    Newfoundland Standard Time is 3 and 1/2 hours earlier than Coordinated
    Universal Time (UTC).  Standard time and daylight saving time both apply
    to this locale.  Newfoundland Daylight Time is 1 and 1/2 hours earlier
    than Coordinated Universal Time (UTC).

TZ=Central Europe Time-2:00
    Central European Time is 2 hours later than Coordinated Universal Time
    (UTC).  Daylight saving time does not apply in this locale.