iPhone:Find the current timezone offset in HOURS

Question

How to find out the current timezone offset on the device in HOURS ?

Answer 1

Swift 4 extension method that returns timezone offset as a string

//: Playground - noun: a place where people can play

import Foundation

extension TimeZone {
    func offsetFromGMT() -> String
    {
        let localTimeZoneFormatter = DateFormatter()
        localTimeZoneFormatter.timeZone = self
        localTimeZoneFormatter.dateFormat = "Z"
        return localTimeZoneFormatter.string(from: Date())
    }
}

// Test: Print all timezones
TimeZone.knownTimeZoneIdentifiers.forEach({ timeZoneIdentifier in
    if let timezone = TimeZone(identifier: timeZoneIdentifier)
    {
        print("\(timezone.identifier) \(timezone.offsetFromGMT())")
    }
})

Test Output:

Africa/Abidjan +0000
Africa/Accra +0000
Africa/Addis_Ababa +0300
Africa/Algiers +0100
Africa/Asmara +0300
Africa/Bamako +0000
Africa/Bangui +0100
Africa/Banjul +0000
Africa/Bissau +0000
Africa/Blantyre +0200
Africa/Brazzaville +0100
Africa/Bujumbura +0200
Africa/Cairo +0200
Africa/Casablanca +0100
Africa/Ceuta +0200
Africa/Conakry +0000
Africa/Dakar +0000
Africa/Dar_es_Salaam +0300
Africa/Djibouti +0300
Africa/Douala +0100
Africa/El_Aaiun +0100
Africa/Freetown +0000
Africa/Gaborone +0200
Africa/Harare +0200
Africa/Johannesburg +0200
Africa/Juba +0300
Africa/Kampala +0300
Africa/Khartoum +0200
Africa/Kigali +0200
Africa/Kinshasa +0100
Africa/Lagos +0100
Africa/Libreville +0100
Africa/Lome +0000
Africa/Luanda +0100
Africa/Lubumbashi +0200
Africa/Lusaka +0200
Africa/Malabo +0100
Africa/Maputo +0200
Africa/Maseru +0200
Africa/Mbabane +0200
Africa/Mogadishu +0300
Africa/Monrovia +0000
Africa/Nairobi +0300
Africa/Ndjamena +0100
Africa/Niamey +0100
Africa/Nouakchott +0000
Africa/Ouagadougou +0000
Africa/Porto-Novo +0100
Africa/Sao_Tome +0100
Africa/Tripoli +0200
Africa/Tunis +0100
Africa/Windhoek +0200
America/Adak -0900
America/Anchorage -0800
America/Anguilla -0400
America/Antigua -0400
America/Araguaina -0300
America/Argentina/Buenos_Aires -0300
America/Argentina/Catamarca -0300
America/Argentina/Cordoba -0300
America/Argentina/Jujuy -0300
America/Argentina/La_Rioja -0300
America/Argentina/Mendoza -0300
America/Argentina/Rio_Gallegos -0300
America/Argentina/Salta -0300
America/Argentina/San_Juan -0300
America/Argentina/San_Luis -0300
America/Argentina/Tucuman -0300
America/Argentina/Ushuaia -0300
America/Aruba -0400
America/Asuncion -0400
America/Atikokan -0500
America/Bahia -0300
America/Bahia_Banderas -0500
America/Barbados -0400
America/Belem -0300
America/Belize -0600
America/Blanc-Sablon -0400
America/Boa_Vista -0400
America/Bogota -0500
America/Boise -0600
America/Cambridge_Bay -0600
America/Campo_Grande -0400
America/Cancun -0500
America/Caracas -0400
America/Cayenne -0300
America/Cayman -0500
America/Chicago -0500
America/Chihuahua -0600
America/Costa_Rica -0600
America/Creston -0700
America/Cuiaba -0400
America/Curacao -0400
America/Danmarkshavn +0000
America/Dawson -0700
America/Dawson_Creek -0700
America/Denver -0600
America/Detroit -0400
America/Dominica -0400
America/Edmonton -0600
America/Eirunepe -0500
America/El_Salvador -0600
America/Fort_Nelson -0700
America/Fortaleza -0300
America/Glace_Bay -0300
America/Godthab -0200
America/Goose_Bay -0300
America/Grand_Turk -0400
America/Grenada -0400
America/Guadeloupe -0400
America/Guatemala -0600
America/Guayaquil -0500
America/Guyana -0400
America/Halifax -0300
America/Havana -0400
America/Hermosillo -0700
America/Indiana/Indianapolis -0400
America/Indiana/Knox -0500
America/Indiana/Marengo -0400
America/Indiana/Petersburg -0400
America/Indiana/Tell_City -0500
America/Indiana/Vevay -0400
America/Indiana/Vincennes -0400
America/Indiana/Winamac -0400
America/Inuvik -0600
America/Iqaluit -0400
America/Jamaica -0500
America/Juneau -0800
America/Kentucky/Louisville -0400
America/Kentucky/Monticello -0400
America/Kralendijk -0400
America/La_Paz -0400
America/Lima -0500
America/Los_Angeles -0700
America/Lower_Princes -0400
America/Maceio -0300
America/Managua -0600
America/Manaus -0400
America/Marigot -0400
America/Martinique -0400
America/Matamoros -0500
America/Mazatlan -0600
America/Menominee -0500
America/Merida -0500
America/Metlakatla -0800
America/Mexico_City -0500
America/Miquelon -0200
America/Moncton -0300
America/Monterrey -0500
America/Montevideo -0300
America/Montreal -0400
America/Montserrat -0400
America/Nassau -0400
America/New_York -0400
America/Nipigon -0400
America/Nome -0800
America/Noronha -0200
America/North_Dakota/Beulah -0500
America/North_Dakota/Center -0500
America/North_Dakota/New_Salem -0500
America/Ojinaga -0600
America/Panama -0500
America/Pangnirtung -0400
America/Paramaribo -0300
America/Phoenix -0700
America/Port-au-Prince -0400
America/Port_of_Spain -0400
America/Porto_Velho -0400
America/Puerto_Rico -0400
America/Punta_Arenas -0300
America/Rainy_River -0500
America/Rankin_Inlet -0500
America/Recife -0300
America/Regina -0600
America/Resolute -0500
America/Rio_Branco -0500
America/Santa_Isabel -0700
America/Santarem -0300
America/Santiago -0300
America/Santo_Domingo -0400
America/Sao_Paulo -0300
America/Scoresbysund +0000
America/Shiprock -0600
America/Sitka -0800
America/St_Barthelemy -0400
America/St_Johns -0230
America/St_Kitts -0400
America/St_Lucia -0400
America/St_Thomas -0400
America/St_Vincent -0400
America/Swift_Current -0600
America/Tegucigalpa -0600
America/Thule -0300
America/Thunder_Bay -0400
America/Tijuana -0700
America/Toronto -0400
America/Tortola -0400
America/Vancouver -0700
America/Whitehorse -0700
America/Winnipeg -0500
America/Yakutat -0800
America/Yellowknife -0600
Antarctica/Casey +1100
Antarctica/Davis +0700
Antarctica/DumontDUrville +1000
Antarctica/Macquarie +1100
Antarctica/Mawson +0500
Antarctica/McMurdo +1200
Antarctica/Palmer -0300
Antarctica/Rothera -0300
Antarctica/South_Pole +1200
Antarctica/Syowa +0300
Antarctica/Troll +0200
Antarctica/Vostok +0600
Arctic/Longyearbyen +0200
Asia/Aden +0300
Asia/Almaty +0600
Asia/Amman +0300
Asia/Anadyr +1200
Asia/Aqtau +0500
Asia/Aqtobe +0500
Asia/Ashgabat +0500
Asia/Atyrau +0500
Asia/Baghdad +0300
Asia/Bahrain +0300
Asia/Baku +0400
Asia/Bangkok +0700
Asia/Barnaul +0700
Asia/Beirut +0300
Asia/Bishkek +0600
Asia/Brunei +0800
Asia/Calcutta +0530
Asia/Chita +0900
Asia/Choibalsan +0800
Asia/Chongqing +0800
Asia/Colombo +0530
Asia/Damascus +0300
Asia/Dhaka +0600
Asia/Dili +0900
Asia/Dubai +0400
Asia/Dushanbe +0500
Asia/Famagusta +0300
Asia/Gaza +0300
Asia/Harbin +0800
Asia/Hebron +0300
Asia/Ho_Chi_Minh +0700
Asia/Hong_Kong +0800
Asia/Hovd +0700
Asia/Irkutsk +0800
Asia/Jakarta +0700
Asia/Jayapura +0900
Asia/Jerusalem +0300
Asia/Kabul +0430
Asia/Kamchatka +1200
Asia/Karachi +0500
Asia/Kashgar +0600
Asia/Kathmandu +0545
Asia/Katmandu +0545
Asia/Khandyga +0900
Asia/Krasnoyarsk +0700
Asia/Kuala_Lumpur +0800
Asia/Kuching +0800
Asia/Kuwait +0300
Asia/Macau +0800
Asia/Magadan +1100
Asia/Makassar +0800
Asia/Manila +0800
Asia/Muscat +0400
Asia/Nicosia +0300
Asia/Novokuznetsk +0700
Asia/Novosibirsk +0700
Asia/Omsk +0600
Asia/Oral +0500
Asia/Phnom_Penh +0700
Asia/Pontianak +0700
Asia/Pyongyang +0830
Asia/Qatar +0300
Asia/Qyzylorda +0600
Asia/Rangoon +0630
Asia/Riyadh +0300
Asia/Sakhalin +1100
Asia/Samarkand +0500
Asia/Seoul +0900
Asia/Shanghai +0800
Asia/Singapore +0800
Asia/Srednekolymsk +1100
Asia/Taipei +0800
Asia/Tashkent +0500
Asia/Tbilisi +0400
Asia/Tehran +0430
Asia/Thimphu +0600
Asia/Tokyo +0900
Asia/Tomsk +0700
Asia/Ulaanbaatar +0800
Asia/Urumqi +0600
Asia/Ust-Nera +1000
Asia/Vientiane +0700
Asia/Vladivostok +1000
Asia/Yakutsk +0900
Asia/Yangon +0630
Asia/Yekaterinburg +0500
Asia/Yerevan +0400
Atlantic/Azores +0000
Atlantic/Bermuda -0300
Atlantic/Canary +0100
Atlantic/Cape_Verde -0100
Atlantic/Faroe +0100
Atlantic/Madeira +0100
Atlantic/Reykjavik +0000
Atlantic/South_Georgia -0200
Atlantic/St_Helena +0000
Atlantic/Stanley -0300
Australia/Adelaide +0930
Australia/Brisbane +1000
Australia/Broken_Hill +0930
Australia/Currie +1000
Australia/Darwin +0930
Australia/Eucla +0845
Australia/Hobart +1000
Australia/Lindeman +1000
Australia/Lord_Howe +1030
Australia/Melbourne +1000
Australia/Perth +0800
Australia/Sydney +1000
Europe/Amsterdam +0200
Europe/Andorra +0200
Europe/Astrakhan +0400
Europe/Athens +0300
Europe/Belgrade +0200
Europe/Berlin +0200
Europe/Bratislava +0200
Europe/Brussels +0200
Europe/Bucharest +0300
Europe/Budapest +0200
Europe/Busingen +0200
Europe/Chisinau +0300
Europe/Copenhagen +0200
Europe/Dublin +0100
Europe/Gibraltar +0200
Europe/Guernsey +0100
Europe/Helsinki +0300
Europe/Isle_of_Man +0100
Europe/Istanbul +0300
Europe/Jersey +0100
Europe/Kaliningrad +0200
Europe/Kiev +0300
Europe/Kirov +0300
Europe/Lisbon +0100
Europe/Ljubljana +0200
Europe/London +0100
Europe/Luxembourg +0200
Europe/Madrid +0200
Europe/Malta +0200
Europe/Mariehamn +0300
Europe/Minsk +0300
Europe/Monaco +0200
Europe/Moscow +0300
Europe/Oslo +0200
Europe/Paris +0200
Europe/Podgorica +0200
Europe/Prague +0200
Europe/Riga +0300
Europe/Rome +0200
Europe/Samara +0400
Europe/San_Marino +0200
Europe/Sarajevo +0200
Europe/Saratov +0400
Europe/Simferopol +0300
Europe/Skopje +0200
Europe/Sofia +0300
Europe/Stockholm +0200
Europe/Tallinn +0300
Europe/Tirane +0200
Europe/Ulyanovsk +0400
Europe/Uzhgorod +0300
Europe/Vaduz +0200
Europe/Vatican +0200
Europe/Vienna +0200
Europe/Vilnius +0300
Europe/Volgograd +0300
Europe/Warsaw +0200
Europe/Zagreb +0200
Europe/Zaporozhye +0300
Europe/Zurich +0200
GMT +0000
Indian/Antananarivo +0300
Indian/Chagos +0600
Indian/Christmas +0700
Indian/Cocos +0630
Indian/Comoro +0300
Indian/Kerguelen +0500
Indian/Mahe +0400
Indian/Maldives +0500
Indian/Mauritius +0400
Indian/Mayotte +0300
Indian/Reunion +0400
Pacific/Apia +1300
Pacific/Auckland +1200
Pacific/Bougainville +1100
Pacific/Chatham +1245
Pacific/Chuuk +1000
Pacific/Easter -0500
Pacific/Efate +1100
Pacific/Enderbury +1300
Pacific/Fakaofo +1300
Pacific/Fiji +1200
Pacific/Funafuti +1200
Pacific/Galapagos -0600
Pacific/Gambier -0900
Pacific/Guadalcanal +1100
Pacific/Guam +1000
Pacific/Honolulu -1000
Pacific/Johnston -1000
Pacific/Kiritimati +1400
Pacific/Kosrae +1100
Pacific/Kwajalein +1200
Pacific/Majuro +1200
Pacific/Marquesas -0930
Pacific/Midway -1100
Pacific/Nauru +1200
Pacific/Niue -1100
Pacific/Norfolk +1100
Pacific/Noumea +1100
Pacific/Pago_Pago -1100
Pacific/Palau +0900
Pacific/Pitcairn -0800
Pacific/Pohnpei +1100
Pacific/Ponape +1100
Pacific/Port_Moresby +1000
Pacific/Rarotonga -1000
Pacific/Saipan +1000
Pacific/Tahiti -1000
Pacific/Tarawa +1200
Pacific/Tongatapu +1300
Pacific/Truk +1000
Pacific/Wake +1200
Pacific/Wallis +1200