How to get timezone offset between UTC and iPhone - Swift 4.2?

Question

I'm on Swift 4.2. I'm struggling trying to get the offset time between UTC and the one from my iPhone.

---

I have this code

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

---

func getCurrentTimeZone() -> String{
    return String (TimeZone.current.identifier)
}


var tzOffset = ""
let currentTimeZone = getCurrentTimeZone()
TimeZone.knownTimeZoneIdentifiers.forEach({ timeZoneIdentifier in
    if let timezone = TimeZone(identifier: timeZoneIdentifier)
    {
        //print("\(timezone.identifier) \(timezone.offsetFromGMT())")
    
        if(timezone.identifier == currentTimeZone){
            tzOffset = timezone.offsetFromGMT()
        }
    }
})

---

Result

If I do

print(tzOffset)

I got

-0500

Should it be -5 since my currentTimeZone is America/Montreal ?

Can someone please give me a hints ?

Answer 1

You can get the current timezone, get the number of seconds from GMT and divide it by 3600.

TimeZone.current.secondsFromGMT() / 3600    // -3 hs America/Sao_Paulo (current) Brazil

If you need more precision like fraction of hour as well just convert it to double before dividing it.

Answer 2

it should be -0500.

From the Wikipedia page

The reason why it has 4 digits instead of one is because it is in a 24 hour format, and some time zones are measured in a half-hour distance from UTC