Converting double to string return strange value in objective c

Question

I have an NSDictionary which consist of multiple key/pair values. One of them consist double value.

NSNumber *goalValue = [info objectForKey:@"goalValue"];

I put breakpoint and I found that goalValue store the normal value that I need.

and just below I convert it to NSSting like

NSString *stringValue=[goalValue stringValue];

and this stringValue store very strange value.

Guys please help me. I am totally puzzled, I did goggle but nothing change. Please help me. Thanks in advance.

Answer 1

The method stringValue will convert the NSNumber to string by internally calling descriptionWithLocale: with locale as nil and this method in turn will call initWithFormat:locale: ,

From Apple docs,

To obtain the string representation, this method invokes NSString's initWithFormat:locale: method, supplying the format based on the type the NSNumber object was created with:

So format specifier used for double is %0.16g (ie 16 digit precision) hence the value 98.09999999999999

I'd suggest using NSNumberFormatter ,

NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
[numberFormatter setMaximumFractionDigits:2]; //2 decimal places, change this as required.
NSString *string = [numberFormatter stringFromNumber:goalValue];

Hope that helps!

Answer 2

To prevent this behavior, I suggest using NSDecimalNumber (also this is from my experience best format when dealing with very precise amounts)

NSDecimalNumber *doubleDecimal = [[NSDecimalNumber alloc] initWithDouble:[info objectForKey:@"goalValue"]];

for two digits formatting, use numberFormatter

NSNumberFormatter * nf = [[NSNumberFormatter alloc] init];
 [nf setMinimumFractionDigits:2];
 [nf setMaximumFractionDigits:2];
NSString *stringValue  = [nf stringFromNumber:doubleDecimal]

Answer 3

Its showing the rounded value so you can round the value to single digit using NSNumberFormatter .

 NSNumberFormatter *fomatter = [[NSNumberFormatter alloc] init];
    [fomatter setMaximumSignificantDigits:2];

    NSString *stringValue=[fomatter stringFromNumber:goalValue];