CODEWITHSUNDEEP
objective-cioscocoa-touch
Cpu86
Cpu86

Reputation: 123

NSNumberFormatter iOS big double value

I have a problem formatting big numbers.

I first format a string to a number and since i need to save a string, i get the stringValue from it:

formatter = [[NSNumberFormatter alloc] init];
[formatter setLocale:[NSLocale currentLocale]];
[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
[formatter setUsesSignificantDigits:NO];
[formatter setMaximumFractionDigits:6];
[formatter setMinimumFractionDigits:0];
[formatter setGroupingSeparator:@""];
value = [formatter numberFromString:textField.text];
label = [value stringValue]

and everything is ok, i.e. if i enter 123456745678592.6, i'll get 123456745678592.6.

Then i've to format the string because of different locale:

numberFormatter = [[NSNumberFormatter alloc] init];
[numberFormatter setLocale:[NSLocale currentLocale]];
[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
[numberFormatter setGroupingSeparator:@""];
[numberFormatter setUsesSignificantDigits:NO];
[numberFormatter setMinimumFractionDigits:0];
[numberFormatter setMaximumFractionDigits:6];
tempString = myNumberString;
NSLog(@"number: %@",[NSNumber numberWithDouble:[tempString doubleValue]]);
tempString = [numberFormatter stringFromNumber:[NSNumber numberWithDouble:[tempString doubleValue]]];
NSLog(@"string translated: %@",tempString);

and i get this: "number: 123456745678592.6" "string translated: 123456745678593"

This rounding happens when the significative digits are greater than 15.

Let's say i enter: 12345674567859.2 i then get the right number, i.e. "number: 12345674567859.2" "string translated: 12345674567859.2"

with: 12345674567859.23 i get: "number: 12345674567859.23" "string translated: 12345674567859.2"

but with: 1234567456785921 i get this: "number: 1234567456785921" "string translated: 1234567456785920"

Is this an intrinsic limit of the nsnumberformatter, because the documentation says nothing about this, or i'm doing something wrong?

Upvotes: 3

Views: 3624

Answers (2)

Sulthan
Sulthan

Reputation: 130072

Could you check what is the actual class of the number? Is it NSNumber or NSDecimalNumber?

A NSNumber is backed up by a double and cannot hold more than 15 significant decimal digits. On the other hand, NSDecimalNumber uses decimal arithmetics and can hold up to 32 significant digits.

I have already learned that NSDecimalFormatter cannot format NSDecimalNumbers correctly (see iOS: formatting decimal numbers). But maybe it can create a NSDecimalNumber correctly from a string.

Upvotes: 1

Antonio MG
Antonio MG

Reputation: 20410

I think the problem is not in the limit of the NSNumberFormatter, it´s in the limit of the double itself.

The max value of a double in Objective-C is 15 digits, I think that is a good clue about what is going on in your program.

I think that when you are doing this¨

[NSNumber numberWithDouble:[tempString doubleValue]]];

You are limiting the value of the NSNumber, because doubleValue is going to have a limit!

Upvotes: 0

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