Convert iOS localTimeZone to a knownTimeZone

Question

Using NSTimeZone the list of knownTimeZoneNames does not match the timezone retrieved by localTimeZone. How can I convert a timezone from localTimeZone to a time zone from knownTimeZoneNames. More specifically, the timezone .name return value must match a timezone in this list of timezones.

(lldb) po [NSTimeZone localTimeZone]
Local Time Zone (US/Pacific (PST) offset -28800)

(lldb) po [[NSTimeZone localTimeZone] name]
US/Pacific

(lldb) po [NSTimeZone knownTimeZoneNames]
<__NSCFArray 0x10ab5c00>(
Africa/Abidjan,
Africa/Accra,
Africa/Addis_Ababa,
Africa/Algiers,
Africa/Asmara,
Africa/Bamako,
Africa/Bangui,
Africa/Banjul,
Africa/Bissau,
Africa/Blantyre,
Africa/Brazzaville,
Africa/Bujumbura,
Africa/Cairo,
Africa/Casablanca,
Africa/Ceuta,
Africa/Conakry,
Africa/Dakar,
Africa/Dar_es_Salaam,
Africa/Djibouti,
Africa/Douala,
Africa/El_Aaiun,
Africa/Freetown,
Africa/Gaborone,
Africa/Harare,
Africa/Johannesburg,
Africa/Juba,
Africa/Kampala,
Africa/Khartoum,
Africa/Kigali,
Africa/Kinshasa,
Africa/Lagos,
Africa/Libreville,
Africa/Lome,
Africa/Luanda,
Africa/Lubumbashi,
Africa/Lusaka,
Africa/Malabo,
Africa/Maputo,
Africa/Maseru,
Africa/Mbabane,
Africa/Mogadishu,
Africa/Monrovia,
Africa/Nairobi,
Africa/Ndjamena,
Africa/Niamey,
Africa/Nouakchott,
Africa/Ouagadougou,
Africa/Porto-Novo,
Africa/Sao_Tome,
Africa/Tripoli,
Africa/Tunis,
Africa/Windhoek,
America/Adak,
America/Anchorage,
America/Anguilla,
America/Antigua,
America/Araguaina,
America/Argentina/Buenos_Aires,
America/Argentina/Catamarca,
America/Argentina/Cordoba,
America/Argentina/Jujuy,
America/Argentina/La_Rioja,
America/Argentina/Mendoza,
America/Argentina/Rio_Gallegos,
America/Argentina/Salta,
America/Argentina/San_Juan,
America/Argentina/San_Luis,
America/Argentina/Tucuman,
America/Argentina/Ushuaia,
America/Aruba,
America/Asuncion,
America/Atikokan,
America/Bahia,
America/Bahia_Banderas,
America/Barbados,
America/Belem,
America/Belize,
America/Blanc-Sablon,
America/Boa_Vista,
America/Bogota,
America/Boise,
America/Cambridge_Bay,
America/Campo_Grande,
America/Cancun,
America/Caracas,
America/Cayenne,
America/Cayman,
America/Chicago,
America/Chihuahua,
America/Costa_Rica,
America/Creston,
America/Cuiaba,
America/Curacao,
America/Danmarkshavn,
America/Dawson,
America/Dawson_Creek,
America/Denver,
America/Detroit,
America/Dominica,
America/Edmonton,
America/Eirunepe,
America/El_Salvador,
America/Fortaleza,
America/Glace_Bay,
America/Godthab,
America/Goose_Bay,
America/Grand_Turk,
America/Grenada,
America/Guadeloupe,
America/Guatemala,
America/Guayaquil,
America/Guyana,
America/Halifax,
America/Havana,
America/Hermosillo,
America/Indiana/Indianapolis,
America/Indiana/Knox,
America/Indiana/Marengo,
America/Indiana/Petersburg,
America/Indiana/Tell_City,
America/Indiana/Vevay,
America/Indiana/Vincennes,
America/Indiana/Winamac,
America/Inuvik,
America/Iqaluit,
America/Jamaica,
America/Juneau,
America/Kentucky/Louisville,
America/Kentucky/Monticello,
America/Kralendijk,
America/La_Paz,
America/Lima,
America/Los_Angeles,
America/Lower_Princes,
America/Maceio,
America/Managua,
America/Manaus,
America/Marigot,
America/Martinique,
America/Matamoros,
America/Mazatlan,
America/Menominee,
America/Merida,
America/Metlakatla,
America/Mexico_City,
America/Miquelon,
America/Moncton,
America/Monterrey,
America/Montevideo,
America/Montreal,
America/Montserrat,
America/Nassau,
America/New_York,
America/Nipigon,
America/Nome,
America/Noronha,
America/North_Dakota/Beulah,
America/North_Dakota/Center,
America/North_Dakota/New_Salem,
America/Ojinaga,
America/Panama,
America/Pangnirtung,
America/Paramaribo,
America/Phoenix,
America/Port-au-Prince,
America/Port_of_Spain,
America/Porto_Velho,
America/Puerto_Rico,
America/Rainy_River,
America/Rankin_Inlet,
America/Recife,
America/Regina,
America/Resolute,
America/Rio_Branco,
America/Santa_Isabel,
America/Santarem,
America/Santiago,
America/Santo_Domingo,
America/Sao_Paulo,
America/Scoresbysund,
America/Shiprock,
America/Sitka,
America/St_Barthelemy,
America/St_Johns,
America/St_Kitts,
America/St_Lucia,
America/St_Thomas,
America/St_Vincent,
America/Swift_Current,
America/Tegucigalpa,
America/Thule,
America/Thunder_Bay,
America/Tijuana,
America/Toronto,
America/Tortola,
America/Vancouver,
America/Whitehorse,
America/Winnipeg,
America/Yakutat,
America/Yellowknife,
Antarctica/Casey,
Antarctica/Davis,
Antarctica/DumontDUrville,
Antarctica/Macquarie,
Antarctica/Mawson,
Antarctica/McMurdo,
Antarctica/Palmer,
Antarctica/Rothera,
Antarctica/South_Pole,
Antarctica/Syowa,
Antarctica/Vostok,
Arctic/Longyearbyen,
Asia/Aden,
Asia/Almaty,
Asia/Amman,
Asia/Anadyr,
Asia/Aqtau,
Asia/Aqtobe,
Asia/Ashgabat,
Asia/Baghdad,
Asia/Bahrain,
Asia/Baku,
Asia/Bangkok,
Asia/Beirut,
Asia/Bishkek,
Asia/Brunei,
Asia/Choibalsan,
Asia/Chongqing,
Asia/Colombo,
Asia/Damascus,
Asia/Dhaka,
Asia/Dili,
Asia/Dubai,
Asia/Dushanbe,
Asia/Gaza,
Asia/Harbin,
Asia/Hebron,
Asia/Ho_Chi_Minh,
Asia/Hong_Kong,
Asia/Hovd,
Asia/Irkutsk,
Asia/Jakarta,
Asia/Jayapura,
Asia/Jerusalem,
Asia/Kabul,
Asia/Kamchatka,
Asia/Karachi,
Asia/Kashgar,
Asia/Kathmandu,
Asia/Katmandu,
Asia/Khandyga,
Asia/Kolkata,
Asia/Krasnoyarsk,
Asia/Kuala_Lumpur,
Asia/Kuching,
Asia/Kuwait,
Asia/Macau,
Asia/Magadan,
Asia/Makassar,
Asia/Manila,
Asia/Muscat,
Asia/Nicosia,
Asia/Novokuznetsk,
Asia/Novosibirsk,
Asia/Omsk,
Asia/Oral,
Asia/Phnom_Penh,
Asia/Pontianak,
Asia/Pyongyang,
Asia/Qatar,
Asia/Qyzylorda,
Asia/Rangoon,
Asia/Riyadh,
Asia/Sakhalin,
Asia/Samarkand,
Asia/Seoul,
Asia/Shanghai,
Asia/Singapore,
Asia/Taipei,
Asia/Tashkent,
Asia/Tbilisi,
Asia/Tehran,
Asia/Thimphu,
Asia/Tokyo,
Asia/Ulaanbaatar,
Asia/Urumqi,
Asia/Ust-Nera,
Asia/Vientiane,
Asia/Vladivostok,
Asia/Yakutsk,
Asia/Yekaterinburg,
Asia/Yerevan,
Atlantic/Azores,
Atlantic/Bermuda,
Atlantic/Canary,
Atlantic/Cape_Verde,
Atlantic/Faroe,
Atlantic/Madeira,
Atlantic/Reykjavik,
Atlantic/South_Georgia,
Atlantic/St_Helena,
Atlantic/Stanley,
Australia/Adelaide,
Australia/Brisbane,
Australia/Broken_Hill,
Australia/Currie,
Australia/Darwin,
Australia/Eucla,
Australia/Hobart,
Australia/Lindeman,
Australia/Lord_Howe,
Australia/Melbourne,
Australia/Perth,
Australia/Sydney,
Europe/Amsterdam,
Europe/Andorra,
Europe/Athens,
Europe/Belgrade,
Europe/Berlin,
Europe/Bratislava,
Europe/Brussels,
Europe/Bucharest,
Europe/Budapest,
Europe/Busingen,
Europe/Chisinau,
Europe/Copenhagen,
Europe/Dublin,
Europe/Gibraltar,
Europe/Guernsey,
Europe/Helsinki,
Europe/Isle_of_Man,
Europe/Istanbul,
Europe/Jersey,
Europe/Kaliningrad,
Europe/Kiev,
Europe/Lisbon,
Europe/Ljubljana,
Europe/London,
Europe/Luxembourg,
Europe/Madrid,
Europe/Malta,
Europe/Mariehamn,
Europe/Minsk,
Europe/Monaco,
Europe/Moscow,
Europe/Oslo,
Europe/Paris,
Europe/Podgorica,
Europe/Prague,
Europe/Riga,
Europe/Rome,
Europe/Samara,
Europe/San_Marino,
Europe/Sarajevo,
Europe/Simferopol,
Europe/Skopje,
Europe/Sofia,
Europe/Stockholm,
Europe/Tallinn,
Europe/Tirane,
Europe/Uzhgorod,
Europe/Vaduz,
Europe/Vatican,
Europe/Vienna,
Europe/Vilnius,
Europe/Volgograd,
Europe/Warsaw,
Europe/Zagreb,
Europe/Zaporozhye,
Europe/Zurich,
GMT,
Indian/Antananarivo,
Indian/Chagos,
Indian/Christmas,
Indian/Cocos,
Indian/Comoro,
Indian/Kerguelen,
Indian/Mahe,
Indian/Maldives,
Indian/Mauritius,
Indian/Mayotte,
Indian/Reunion,
Pacific/Apia,
Pacific/Auckland,
Pacific/Chatham,
Pacific/Chuuk,
Pacific/Easter,
Pacific/Efate,
Pacific/Enderbury,
Pacific/Fakaofo,
Pacific/Fiji,
Pacific/Funafuti,
Pacific/Galapagos,
Pacific/Gambier,
Pacific/Guadalcanal,
Pacific/Guam,
Pacific/Honolulu,
Pacific/Johnston,
Pacific/Kiritimati,
Pacific/Kosrae,
Pacific/Kwajalein,
Pacific/Majuro,
Pacific/Marquesas,
Pacific/Midway,
Pacific/Nauru,
Pacific/Niue,
Pacific/Norfolk,
Pacific/Noumea,
Pacific/Pago_Pago,
Pacific/Palau,
Pacific/Pitcairn,
Pacific/Pohnpei,
Pacific/Ponape,
Pacific/Port_Moresby,
Pacific/Rarotonga,
Pacific/Saipan,
Pacific/Tahiti,
Pacific/Tarawa,
Pacific/Tongatapu,
Pacific/Truk,
Pacific/Wake,
Pacific/Wallis
)

Answer 1

The reason localTimeZone is not included in the list is that your local time zone is showing an older name that's only supported for backward compatibility. The semi-official list of time zones is maintained by IANA. Their format is generally Continent/City but they support older names for compatibility.

Unlike API calls, older names are not in any sense deprecated. They're not current, but still completely valid.

If your local time zone is US/Pacific, the current official name for the zone is America/Los_Angeles, which does appear in the list. Based on your results it would appear that knownTimeZoneNames only lists current names. Why iOS is giving you an older name isn't something I can answer, but I do know that it's common.

To match them up, you have a couple of options:

• Run through known time zones and exhaustively compare the zone data attribute to find one that's equivalent. Yeah, ugly.
• Get the IANA data. It includes a file called backward that maps old names to new names. Include that file in your project. Then, if you get a zone name not found in the "known" list, consult the backward compatibility list to get the current name.

I wouldn't recommend @eipipuz's approach. It seems to work, but the problem with abbreviations is that they're not globally unique. Known abbreviations may vary depending on the user's locale (for example, more than one place as "EST" for its Eastern time zone). As a result some "common" abbreviations may have different definitions in different places, or simply have no definition.

Answer 2

You can use the dictionary described in this question: GMT timezone conversion in objective c. Makes it pretty simple since you have the key.

Hold on a second, the problem is that you are going to have multiple entries that apply given only the code. What you have is not enough information.

This question is pretty close: iPhone NSTimeZone: localTimeZone confusion to your observation.

Answer 3

I think the answer is:

NSString *known = @"US/Pacific"
NSString *abbr = [[NSTimeZone timeZoneWithName:known] abbreviation];
NSString *expected = [[NSTimeZone abbreviationDictionary] objectForKey:abbr];