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DateTime::TimeZone(3pm) User Contributed Perl Documentation DateTime::TimeZone(3pm)
NAME
DateTime::TimeZone - Time zone object base class and factory
VERSION
version 2.38
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 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.
Special Case Platforms
If you are on the Win32 platform, you will want to also install
DateTime::TimeZone::Local::Win32. This will enable you to specify a time zone of 'local'
when creating a DateTime object.
If you are on HPUX, install DateTime::TimeZone::HPUX. This provides support for HPUX style
time zones like 'MET-1METDST'.
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 not 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
<https://www.ietf.org/rfc/rfc2445.txt> 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.
o DateTime::TimeZone::Local::Unix
o DateTime::TimeZone::Local::Android
o DateTime::TimeZone::Local::hpux
o DateTime::TimeZone::Local::Win32
o DateTime::TimeZone::Local::VMS
If a local time zone is not found, then an exception will be thrown. This exception will
always stringify to something containing the text "Cannot determine local time zone".
If you are writing code for users to run on systems you do not control, you should try to
account for the possibility that this exception may be thrown. Falling back to UTC might
be a reasonable alternative.
When writing tests for your modules that might be run on others' systems, you are strongly
encouraged to either not use "local" when creating DateTime objects or to set $ENV{TZ} to
a known value in your test code. All of the per-OS classes check this environment
variable.
$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 <https://www.ietf.org/rfc/rfc2445.txt>.
$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.
LOADING TIME ZONES IN A PRE-FORKING SYSTEM
If you are running an application that does pre-forking (for example with Starman), then
you should try to load all the time zones that you'll need in the parent process. Time
zones are loaded on-demand, so loading them once in each child will waste memory that
could otherwise be shared.
CREDITS
This module was inspired by Jesse Vincent's work on Date::ICal::Timezone, and written with
much help from the datetime AT perl.org list.
SEE ALSO
datetime AT 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.
SUPPORT
Support for this module is provided via the datetime AT 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 AT rt.org.
Bugs may be submitted at <https://github.com/houseabsolute/DateTime-TimeZone/issues>.
I am also usually active on IRC as 'autarch' on "irc://irc.perl.org".
SOURCE
The source code repository for DateTime-TimeZone can be found at
<https://github.com/houseabsolute/DateTime-TimeZone>.
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 (let's all have a chuckle at that together).
To donate, log into PayPal and send money to autarch AT urth.org, or use the button at
<http://www.urth.org/~autarch/fs-donation.html>.
AUTHOR
Dave Rolsky <autarch AT urth.org>
CONTRIBUTORS
o Alexey Molchanov <alexey.molchanov AT gmail.com>
o Alfie John <alfiej AT fastmail.fm>
o Andrew Paprocki <apaprocki AT bloomberg.net>
o Bron Gondwana <brong AT fastmail.fm>
o Daisuke Maki <dmaki AT cpan.org>
o David Pinkowitz <dave AT pinkowitz.com>
o Iain Truskett <deceased>
o Jakub Wilk <jwilk AT jwilk.net>
o James E Keenan <jkeenan AT cpan.org>
o Joshua Hoblitt <jhoblitt AT cpan.org>
o Karen Etheridge <ether AT cpan.org>
o karupanerura <karupa AT cpan.org>
o kclaggett <kclaggett AT proofpoint.com>
o Mohammad S Anwar <mohammad.anwar AT yahoo.com>
o Olaf Alders <olaf AT wundersolutions.com>
o Peter Rabbitson <ribasushi AT cpan.org>
o Tom Wyant <wyant AT cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2019 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.
The full text of the license can be found in the LICENSE file included with this
distribution.
perl v5.30.0 2019-11-16 DateTime::TimeZone(3pm)
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On Apache
Under GNU General Public License
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