Precision String Format Specifier In Swift

Question

Below is how I would have previously truncated a float to two decimal places

NSLog(@\" %.02f %.02f %.02f\", r, g, b);

I checked the docs an

Answer 1

You can still use NSLog in Swift as in Objective-C just without the @ sign.

NSLog("%.02f %.02f %.02f", r, g, b)

Edit: After working with Swift since a while I would like to add also this variation

    var r=1.2
    var g=1.3
    var b=1.4
    NSLog("\(r) \(g) \(b)")

Output:

2014-12-07 21:00:42.128 MyApp[1626:60b] 1.2 1.3 1.4

Answer 2

a simple way is:

import Foundation // required for String(format: _, _)

print(String(format: "hex string: %X", 123456))
print(String(format: "a float number: %.5f", 1.0321))

Answer 3

This is a very fast and simple way who doesn't need complex solution.

let duration = String(format: "%.01f", 3.32323242)
// result = 3.3

Answer 4

extension Double {
  func formatWithDecimalPlaces(decimalPlaces: Int) -> Double {
     let formattedString = NSString(format: "%.\(decimalPlaces)f", self) as String
     return Double(formattedString)!
     }
 }

 1.3333.formatWithDecimalPlaces(2)

Answer 5

I found String.localizedStringWithFormat to work quite well:

Example:

let value: Float = 0.33333
let unit: String = "mph"

yourUILabel.text = String.localizedStringWithFormat("%.2f %@", value, unit)

Answer 6

A more elegant and generic solution is to rewrite ruby / python % operator:

// Updated for beta 5
func %(format:String, args:[CVarArgType]) -> String {
    return NSString(format:format, arguments:getVaList(args))
}

"Hello %@, This is pi : %.2f" % ["World", M_PI]