NAME¶
DateTime::TimeZone - Time zone object base class and factory
VERSION¶
version 1.75
SYNOPSIS¶
use DateTime;
use DateTime::TimeZone;
my $tz = DateTime::TimeZone->new( name => 'America/Chicago' );
my $dt = DateTime->now();
my $offset = $tz->offset_for_datetime($dt);
DESCRIPTION¶
This class is the base class for all time zone objects. A time zone is
represented internally as a set of observances, each of which describes the
offset from GMT for a given time period.
Note that without the "DateTime.pm" module, this module does not do
much. It's primary interface is through a "DateTime" object, and
most users will not need to directly use "DateTime::TimeZone"
methods.
USAGE¶
This class has the following methods:
DateTime::TimeZone->new( name => $tz_name )¶
Given a valid time zone name, this method returns a new time zone blessed into
the appropriate subclass. Subclasses are named for the given time zone, so
that the time zone "America/Chicago" is the
DateTime::TimeZone::America::Chicago class.
If the name given is a "link" name in the Olson database, the object
created may have a different name. For example, there is a link from the old
"EST5EDT" name to "America/New_York".
When loading a time zone from the Olson database, the constructor checks the
version of the loaded class to make sure it matches the version of the current
DateTime::TimeZone installation. If they do not match it will issue a warning.
This is useful because time zone names may fall out of use, but you may have
an old module file installed for that time zone.
There are also several special values that can be given as names.
If the "name" parameter is "floating", then a
"DateTime::TimeZone::Floating" object is returned. A floating time
zone does have
any offset, and is always the same time. This is useful
for calendaring applications, which may need to specify that a given event
happens at the same
local time, regardless of where it occurs. See RFC
2445 for more details.
If the "name" parameter is "UTC", then a
"DateTime::TimeZone::UTC" object is returned.
If the "name" is an offset string, it is converted to a number, and a
"DateTime::TimeZone::OffsetOnly" object is returned.
The "local" time zone
If the "name" parameter is "local", then the module attempts
to determine the local time zone for the system.
The method for finding the local zone varies by operating system. See the
appropriate module for details of how we check for the local time zone.
- •
- DateTime::TimeZone::Local::Unix
- •
- DateTime::TimeZone::Local::Win32
- •
- DateTime::TimeZone::Local::VMS
If a local time zone is not found, then an exception will be thrown.
$tz->offset_for_datetime( $dt )¶
Given a "DateTime" object, this method returns the offset in seconds
for the given datetime. This takes into account historical time zone
information, as well as Daylight Saving Time. The offset is determined by
looking at the object's UTC Rata Die days and seconds.
$tz->offset_for_local_datetime( $dt )¶
Given a "DateTime" object, this method returns the offset in seconds
for the given datetime. Unlike the previous method, this method uses the local
time's Rata Die days and seconds. This should only be done when the
corresponding UTC time is not yet known, because local times can be ambiguous
due to Daylight Saving Time rules.
$tz->is_dst_for_datetime( $dt )¶
Given a "DateTime" object, this method returns true if the DateTime is
currently in Daylight Saving Time.
$tz->name¶
Returns the name of the time zone.
$tz->short_name_for_datetime( $dt )¶
Given a "DateTime" object, this method returns the "short
name" for the current observance and rule this datetime is in. These are
names like "EST", "GMT", etc.
It is
strongly recommended that you do not rely on these names for
anything other than display. These names are not official, and many of them
are simply the invention of the Olson database maintainers. Moreover, these
names are not unique. For example, there is an "EST" at both -0500
and +1000/+1100.
$tz->is_floating¶
Returns a boolean indicating whether or not this object represents a floating
time zone, as defined by RFC 2445.
$tz->is_utc¶
Indicates whether or not this object represents the UTC (GMT) time zone.
$tz->has_dst_changes¶
Indicates whether or not this zone has
ever had a change to and from DST,
either in the past or future.
$tz->is_olson¶
Returns true if the time zone is a named time zone from the Olson database.
$tz->category¶
Returns the part of the time zone name before the first slash. For example, the
"America/Chicago" time zone would return "America".
DateTime::TimeZone->is_valid_name($name)¶
Given a string, this method returns a boolean value indicating whether or not
the string is a valid time zone name. If you are using
"DateTime::TimeZone::Alias", any aliases you've created will be
valid.
DateTime::TimeZone->all_names¶
This returns a pre-sorted list of all the time zone names. This list does not
include link names. In scalar context, it returns an array reference, while in
list context it returns an array.
DateTime::TimeZone->categories¶
This returns a list of all time zone categories. In scalar context, it returns
an array reference, while in list context it returns an array.
DateTime::TimeZone->links¶
This returns a hash of all time zone links, where the keys are the old,
deprecated names, and the values are the new names. In scalar context, it
returns a hash reference, while in list context it returns a hash.
DateTime::TimeZone->names_in_category( $category )¶
Given a valid category, this method returns a list of the names in that
category, without the category portion. So the list for the
"America" category would include the strings "Chicago",
"Kentucky/Monticello", and "New_York". In scalar context,
it returns an array reference, while in list context it returns an array.
DateTime::TimeZone->countries()¶
Returns a sorted list of all the valid country codes (in lower-case) which can
be passed to "names_in_country()". In scalar context, it returns an
array reference, while in list context it returns an array.
If you need to convert country codes to names or vice versa you can use
"Locale::Country" to do so.
DateTime::TimeZone->names_in_country( $country_code )¶
Given a two-letter ISO3166 country code, this method returns a list of time
zones used in that country. The country code may be of any case. In scalar
context, it returns an array reference, while in list context it returns an
array.
This list is returned in an order vaguely based on geography and population. In
general, the least used zones come last, but there are not guarantees of a
specific order from one release to the next. This order is probably the best
option for presenting zones names to end users.
DateTime::TimeZone->offset_as_seconds( $offset )¶
Given an offset as a string, this returns the number of seconds represented by
the offset as a positive or negative number. Returns "undef" if
$offset is not in the range "-99:59:59" to "+99:59:59".
The offset is expected to match either
"/^([\+\-])?(\d\d?):(\d\d)(?::(\d\d))?$/" or
"/^([\+\-])?(\d\d)(\d\d)(\d\d)?$/". If it doesn't match either of
these, "undef" will be returned.
This means that if you want to specify hours as a single digit, then each
element of the offset must be separated by a colon (:).
DateTime::TimeZone->offset_as_string( $offset )¶
Given an offset as a number, this returns the offset as a string. Returns
"undef" if $offset is not in the range "-359999" to
359999.
Storable Hooks¶
This module provides freeze and thaw hooks for "Storable" so that the
huge data structures for Olson time zones are not actually stored in the
serialized structure.
If you subclass "DateTime::TimeZone", you will inherit its hooks,
which may not work for your module, so please test the interaction of your
module with Storable.
SUPPORT¶
Support for this module is provided via the datetime@perl.org email list. See
http://datetime.perl.org/wiki/datetime/page/Mailing_List for details.
Please submit bugs to the CPAN RT system at
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=datetime%3A%3Atimezone or via
email at bug-datetime-timezone@rt.cpan.org.
DONATIONS¶
If you'd like to thank me for the work I've done on this module, please consider
making a "donation" to me via PayPal. I spend a lot of free time
creating free software, and would appreciate any support you'd care to offer.
Please note that
I am not suggesting that you must do this in order for
me to continue working on this particular software. I will continue to do so,
inasmuch as I have in the past, for as long as it interests me.
Similarly, a donation made in this way will probably not make me work on this
software much more, unless I get so many donations that I can consider working
on free software full time, which seems unlikely at best.
To donate, log into PayPal and send money to autarch@urth.org or use the button
on this page: <
http://www.urth.org/~autarch/fs-donation.html>
CREDITS¶
This module was inspired by Jesse Vincent's work on Date::ICal::Timezone, and
written with much help from the datetime@perl.org list.
SEE ALSO¶
datetime@perl.org mailing list
http://datetime.perl.org/
The tools directory of the DateTime::TimeZone distribution includes two scripts
that may be of interest to some people. They are parse_olson and
tests_from_zdump. Please run them with the --help flag to see what they can be
used for.
AUTHOR¶
Dave Rolsky <autarch@urth.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2014 by Dave Rolsky.
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.