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DateTime::TimeZone(3pm) User Contributed Perl Documentation DateTime::TimeZone(3pm)
NAME
DateTime::TimeZone - Time zone object base class and factory
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.
First it checks $ENV for keys named "TZ", "SYS$TIMEZONE_RULE", "SYS$TIMEZONE_NAME",
"UCX$TZ", or "TCPIP$TZC" (the last 4 are for VMS). If this is defined, and it is not the
string "local", then it is treated as any other valid name (including "floating"), and the
constructor tries to create a time zone based on that name.
Next, it checks for the existence of a symlink at /etc/localtime. It follows this link to
the real file and figures out what the file's name is. It then tries to turn this name
into a valid time zone. For example, if this file is linked to
/usr/share/zoneinfo/US/Central, it will end up trying "US/Central", which will then be
converted to "America/Chicago" internally.
Some systems just copy the relevant file to /etc/localtime instead of making a symlink.
In this case, we look in /usr/share/zoneinfo for a file that has the same size and content
as /etc/localtime to determine the local time zone.
Then it checks for a file called /etc/timezone or /etc/TIMEZONE. If one of these exists,
it is read and it tries to create a time zone with the name contained in the file.
Finally, it checks for a file called /etc/sysconfig/clock. If this file exists, it looks
for a line inside the file matching "/^(?:TIME)?ZONE="([^"]+)"/". If this line exists, it
tries the value as a time zone name.
If none of these methods work, it gives up and dies.
$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->name
Returns the name of the time zone. If this value is passed to the "new()" method, it is
guaranteed to create the same object.
$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.
The list is returned in order of population by zone, which should mean that this order
will be the best to use for most UIs.
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 ISO3066 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.
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 AT perl.org email list. See
http://datetime.perl.org/?MailingList 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.
AUTHOR
Dave Rolsky <autarch AT urth.org>
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.
COPYRIGHT
Copyright (c) 2003-2008 David Rolsky. All rights reserved. This program is free
software; you can redistribute it and/or modify it under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included with this module.
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.
perl v5.10.0 2008-06-04 DateTime::TimeZone(3pm)
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