NAME¶
DateTime::TimeZone::SystemV - System V and POSIX timezone strings
SYNOPSIS¶
use DateTime::TimeZone::SystemV;
$tz = DateTime::TimeZone::SystemV->new("EST5EDT");
if($tz->is_floating) { ...
if($tz->is_utc) { ...
if($tz->is_olson) { ...
$category = $tz->category;
$tz_string = $tz->name;
if($tz->has_dst_changes) { ...
if($tz->is_dst_for_datetime($dt)) { ...
$offset = $tz->offset_for_datetime($dt);
$abbrev = $tz->short_name_for_datetime($dt);
$offset = $tz->offset_for_local_datetime($dt);
DESCRIPTION¶
An instance of this class represents a timezone that was specified by means of a
System V timezone string or the POSIX extended form of the same syntax. These
can express a plain offset from Universal Time, or a system of two offsets
(standard and daylight saving time) switching on a yearly cycle according to
certain types of rule.
This class implements the DateTime::TimeZone interface, so that its instances
can be used with DateTime objects.
SYSTEM V TIMEZONE SYNTAX¶
In the POSIX extended form of the System V timezone syntax, a timezone may be
specified that has a fixed offset by the syntax "
aaaooo", or a timezone with DST by the syntax "
aaa
oooaaa[
ooo]
,rrr,rrr".
"
aaa" gives an abbreviation by which an offset is known,
"
ooo" specifies the offset, and "
rrr" is a
rule for when DST starts or ends. For backward compatibility, the rules part
may also be omitted from a DST-using timezone, in which case some built-in
default rules are used; don't rely on those rules being useful.
An abbreviation must be a string of three or more characters from ASCII
alphanumerics, "
+", and "
-". If it contains
only ASCII alphabetic characters then the abbreviation specification "
aaa" may be simply the abbreviation. Otherwise "
aaa" must consist of the abbreviation wrapped in angle brackets
("
<...
>"). The angle bracket form is always
allowed.
An offset (from Universal Time), "
ooo", is given in hours, or
hours and minutes, or hours and minutes and seconds, with an optional
preceding sign. The maximum magnitude permitted is 24:59:59. The sign in the
specification is the opposite of the sign of the actual offset. If no sign is
given then the default is "
+", meaning a timezone that is
behind UT. If no DST offset is specified, it defaults to one hour ahead of the
standard offset.
A DST-using timezone has one change to DST and one change to standard time in
each Gregorian year. The changes may be in either order within the year. If
the changes are in different orders from year to year then the behaviour is
undefined; don't rely on it remaining the same in future versions.
A change rule "
rrr" takes the form
"
ddd[
/ttt]", where "
ddd" is
the rule giving the day on which the change takes place and "
ttt" is the time of day at which the change takes place. The time
may be given in hours, or hours and minutes, or hours and minutes and seconds,
and if not stated then it defaults to 02:00:00. The time for the change to DST
is interpreted according to the standard offset, and the time for the change
to standard time is interpreted according to the DST offset. (Thus normally
the change time is interpreted according to the offset that prevailed
immediately before the change.)
A day rule "
ddd" may take three forms. Firstly,
"
Jnnn" means the month-day date that is the
nnnth day of a non-leap year. Thus "
J59" means the
February 28 and "
J60" means March 1 (even in a leap year).
February 29 cannot be specified this way.
Secondly, if "
ddd" is just a decimal number, it means the
(1+
ddd)th day of the year. February 29 counts in this case, and it is
not possible to specify December 31 of a leap year.
Thirdly, "
ddd" may have the form
"
Mm. w.d" means day
d of the
wth week of the
mth month. The day is given as a
single digit, with "
0" meaning Sunday and
"
6" meaning Saturday. The first week contains days 1 to 7 of
the month, the second week contains days 8 to 14, and so on. If "
w" is "
5" then the last week of the month
(containing its last seven days) is used, rather than the fifth week (which is
incomplete).
Examples:
- MUT-4
- Mauritius time, since 1907: 4 hours ahead of UT all
year.
- EST5EDT,M3.2.0,M11.1.0
- US Eastern timezone with DST, from 2007 onwards. 5 hours
behind UT in winter and 4 hours behind in summer. Changes on the second
Sunday in March and the first Sunday in November, in each case at 02:00
local time.
- NST3:30NDT,M3.2.0/0:01,M11.1.0/0:01
- Newfoundland timezone with DST, from 2007 onwards. 3.5
hours behind UT in winter and 2.5 hours behind in summer. Changes on the
second Sunday in March and the first Sunday in November, in each case at
00:01 local time.
- GMT0BST,M3.5.0/1,M10.5.0
- UK civil time, from 1996 onwards. On UT during the winter,
calling it "GMT", and 1 hour ahead of UT during the summer,
called "BST". Changes on the last Sunday in March and the last
Sunday in October, in each case at 01:00 UT.
- EST-10EST,M10.5.0,M3.5.0/3
- Australian Eastern timezone, from 2007 onwards. 10 hours
ahead of UT in the southern winter (the middle of the calendar year), and
11 hours ahead in the southern summer. Changes to DST on the last Sunday
in October, and back on the last Sunday in March, in each case at 02:00
standard time (16:00 UT of the preceding day).
CONSTRUCTOR¶
- DateTime::TimeZone::SystemV->new(TZ_STRING)
- TZ_STRING must be a timezone specification as
described in "SYSTEM V TIMEZONE SYNTAX". Constructs and returns
a DateTime-compatible timezone object that implements the timezone
specified by TZ_STRING.
METHODS¶
These methods are all part of the DateTime::TimeZone interface. See that class
for the general meaning of these methods; the documentation below only
comments on the specific behaviour of this class.
Identification¶
- $tz->is_floating
- Returns false.
- $tz->is_utc
- Returns false.
- $tz->is_olson
- Returns false.
- $tz->category
- Returns "undef", because the category concept
doesn't properly apply to these timezones.
- $tz->name
- Returns the TZ_STRING that was supplied to the
constructor.
Offsets¶
- $tz->has_dst_changes
- Returns a boolean indicating whether the timezone includes
a DST offset.
- $tz->is_dst_for_datetime(DT)
- DT must be a DateTime-compatible object
(specifically, it must implement the "utc_rd_values" method).
Returns a boolean indicating whether the timezone is on DST at the instant
represented by DT.
- $tz->offset_for_datetime(DT)
- DT must be a DateTime-compatible object
(specifically, it must implement the "utc_rd_values" method).
Returns the offset from UT that is in effect at the instant represented by
DT, in seconds.
- $tz->short_name_for_datetime(DT)
- DT must be a DateTime-compatible object
(specifically, it must implement the "utc_rd_values" method).
Returns the time scale abbreviation for the offset that is in effect at
the instant represented by DT.
- $tz->offset_for_local_datetime(DT)
- DT must be a DateTime-compatible object
(specifically, it must implement the "local_rd_values" method).
Takes the local time represented by DT (regardless of what absolute
time it also represents), and interprets that as a local time in the
timezone of the timezone object (not the timezone used in DT).
Returns the offset from UT that is in effect at that local time, in
seconds.
If the local time given is ambiguous due to a nearby offset change, the
numerically lower offset (usually the standard one) is returned with no
warning of the situation. If the local time given does not exist due to a
nearby offset change, the method "die"s saying so.
SEE ALSO¶
DateTime, DateTime::TimeZone
AUTHOR¶
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT¶
Copyright (C) 2007, 2009 Andrew Main (Zefram) <zefram@fysh.org>
LICENSE¶
This module is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.