generatesDecimalNumbers for NumberFormatter does not work

Question

My function is converting a string to Decimal

func getDecimalFromString(_ strValue: String) -> NSDecimalNumber {
    let formatter = NumberFormatter()
            


        

Answer 1

That seems to be a bug, compare

• NSDecimalNumbers from NSNumberFormatter are affected by binary approximation error

Even with generatesDecimalNumbers set to true, the formatter produces a binary floating point number internally, and that cannot represent decimal fractions like 8.2 precisely.

Note also that (contrary to the documentation), the maximumFractionDigits property has no effect when parsing a string into a number.

There is a simple solution: Use

NSDecimalNumber(string: strValue) // or
NSDecimalNumber(string: strValue, locale: Locale.current)

instead, depending on whether the string is localized or not.

Or with the Swift 3 Decimal type:

Decimal(string: strValue) // or
Decimal(string: strValue, locale: .current)

Example:

if let d = Decimal(string: "8.2") {
    print(d) // 8.2
}