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DateTime-TimeZone-0.42
River stage four • 91 direct dependents • 3701 total dependents
20 ++
/ DateTime::TimeZone

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:

  • 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".

    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.

Object Methods

DateTime::TimeZone objects provide the following methods:

  • 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.

  • 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.

  • 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.

  • 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.

  • is_floating

    Returns a boolean indicating whether or not this object represents a floating time zone, as defined by RFC 2445.

  • is_utc

    Indicates whether or not this object represents the UTC (GMT) time zone.

  • has_dst_changes

    Indicates whether or not this zone ever has a change to and from DST.

  • is_olson

    Returns true if the time zone is a named time zone from the Olson database.

  • category

    Returns the part of the time zone name before the first slash. For example, the "America/Chicago" time zone would return "America".

Class Methods

This class provides one class method:

  • 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.

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.

Functions

This class also contains several functions, none of which are exported. Calling these as class methods will also work.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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 (:).

  • 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.

SUPPORT

Support for this module is provided via the datetime@perl.org email list. See http://lists.perl.org/ for more 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.

AUTHOR

Dave Rolsky <autarch@urth.org>

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.

COPYRIGHT

Copyright (c) 2003 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@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.