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TZSET
!!!TZSET
NAME
SYNOPSIS
DESCRIPTION
FILES
CONFORMING TO
SEE ALSO
----
!!NAME


tzset - initialize time conversion information
!!SYNOPSIS


__#include
__''tzname''__[[2]
__
!!DESCRIPTION


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 ''localtime'' found in the
system timezone directory (see below). (One also often sees
''/etc/localtime'' used here, a symlink to the right file
in the system timezone directory.)


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
format 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
time:


''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 following formats:


J''n''


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.


M''m''.''w''.''d''


This specifies day ''d'' (0 ''d''
''w'' (1 ''w'' ''m''
(1 ''m''
''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:


:[[filespec]


If the file specification ''filespec'' is omitted, the
time zone information is read from the file ''localtime''
in the system timezone directory, which nowadays usually is
''/usr/share/zoneinfo''. This file is in tzfile(5)
format. If ''filespec'' is given, it specifies another
tzfile(5)-format file to read the time zone
information from. If ''filespec'' does not begin with a
`/', the file specification is relative to the system
timezone directory.
!!FILES


The system time zone directory used depends on the (g)libc
version. Libc4 and libc5 use ''/usr/lib/zoneinfo'', and,
since libc-5.4.6, when this doesn't work, will try
''/usr/share/zoneinfo''. Glibc2 will use the environment
variable TZDIR, when that exists. Its default depends on how
it was installed, but normally is
''/usr/share/zoneinfo''.


This timezone directory contains the files


localtime      local time zone file
posixrules     rules for POSIX-style TZ's
Often ''/etc/localtime'' is a symlink to the file ''localtime'' or to the correct time zone file in the system time zone directory.
!!CONFORMING TO


SVID 3, POSIX, BSD 4.3
!!SEE ALSO


date(1), gettimeofday(2), time(2),
ctime(3), getenv(3),
tzfile(5)
----
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Last edited on Tuesday, June 4, 2002 12:24:39 am by "perry"
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