How to convert Data to a String

Swift version: 5.10

Paul Hudson @twostraws May 16th 2024

If you know an instance of Data contains a String and you want to convert it, you can use the String(decoding:as:) initializer, like this:

let str = String(decoding: data, as: UTF8.self)

If the Data instance can’t be converted to a UTF-8 string, you’ll might be sent back an empty string, but Swift might replace any bad characters with the Unicode replacement character. You do need to know which format is used to store the string, but UTF-8 is usually the best to go with.

If you're unsure about whether the string can safely be converted or not, there's a failable initializer you should use instead:

if let str = String(data: data, encoding: .utf8) {
    print("Successfully decoded: \(str)")
}

Using this optional approach avoids any problems around decoding invalid strings – if it succeeds you can be sure the string that was loaded is intact and correct.