String formatting of a Double [duplicate]

Answer 1

There's no way to do this using String interpolation.

You can find a good discussion about this on this Apple Dev Forum post.

You can use NSNumberFormatter or NSDateFormatter to format the output.

Alternatively, to use printf-like syntax, you can still use NSString:

var str = NSString(format: "Hello, world %.2f", 42.12312312313)

Answer 2

Unsure if there is a pure Swift-way but you can always use NSStrings +stringWithFormat::

let str = String(format: "%.2f", 1.23)