Question

I have this sample code:

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
NSString *numberString = @"9.2";
NSNumber *number = [formatter numberFromString:numberString];
NSLog(@"String: %@, Number: %@", numberString, number);

The printed result is:

String: 9.2, Number: 9.199999999999999

I don’t understand why this would happen. Am I missing a setting?

Answer 1

According to this reference, an NSNumber can store any ordinary C numeric type. Since this is obtained by parsing a non-integer, the two types to choose from are float and double, and by the displayed value, the chosen representation is double.

Since decimal fractions like 9.2 aren’t exactly representable as doubles, you get the closest representable number. That is displayed to default precision, which is about 16 decimal places.