Why NSString's doubleValue differ from the original string?

Question

NSString is @"16.240" it's doubleValue is 16.239999999999998

What happened behind the scenes?

the code is simple, just `self.price = text.doubleValue` in textDidChange method. @Anbu.Karthik — Gon, Jul 19 '16 at 09:13
if you are convert from double to string , it round the value — Anbu.Karthik, Jul 19 '16 at 09:21
The ultimate, underlying issue is that the closest IEEE 754 64-bit binary float to 16.24 is 16.239999999999998436805981327779591083526611328125. The value you see depends on how many digits are preserved by the conversion to decimal. — Patricia Shanahan, Jul 19 '16 at 15:03

score 0 · Answer 1 · edited Apr 12 '17 at 07:31

0

Because of floating point rounding errors.

Long-story-short; not every number can be represented using floating point types.

References: #1, #2, #3.

edited Apr 12 '17 at 07:31

Community

answered Jul 19 '16 at 09:20

Droppy

score 0 · Answer 2 · answered Jul 19 '16 at 09:46

If it is value for price (or money in general) better to use NSDecimalNumber because it is save each part of float value as is.

NSDecimalNumber *price = [NSDecimalNumber decimalNumberWithString:@"16.240"];
NSLog(price); //16.24

2 Answers2