Question

i’m looking for a way to represent a double value in a NSString meeting the following format requirements:

1.) no trailing zeros: x = 0.5000000 -> @”0.5″

2.) at least on decimal: x = 45 -> @”45.0″

3.) maximum 8 decimal characters (last one rounded): x = 0.000000005 -> @”0.00000001″

I tried with @”%.8f”, @”%g” or @”%.8g” but all fail for at least one of the requirements.

I think I could do with @”%.8f” and then loop the characters of the string beginning with the last character of string to the front deleting the “0” characters,

Or start with a “%.8g” and append a “.0” if the string does not contain a decimal point.

Is there any smarter solution available?

Answer 1

You can do this with a number formatter, but you need to create an NSNumber with your double first:

NSNumber *halfNumber            = [NSNumber numberWithDouble:0.5000000];    
NSNumber *wholeNumber           = [NSNumber numberWithDouble:45];           
NSNumber *longNumber            = [NSNumber numberWithDouble:0.000000005];  

NSNumberFormatter *formatter    = [NSNumberFormatter new];
formatter.numberStyle           = NSNumberFormatterDecimalStyle;
formatter.roundingMode          = NSNumberFormatterRoundHalfUp;
formatter.minimumFractionDigits = 1;
formatter.maximumFractionDigits = 8;

NSString *halfString            = [formatter stringFromNumber:halfNumber];
NSString *wholeString           = [formatter stringFromNumber:wholeNumber];
NSString *longString            = [formatter stringFromNumber:longNumber];

NSLog(@"%@", halfString);
NSLog(@"%@", wholeString);
NSLog(@"%@", longString);

// Output is:
// 2012-11-12 04:22:41.181 Testing App[48069:fb03] 0.5
// 2012-11-12 04:22:41.182 Testing App[48069:fb03] 45.0
// 2012-11-12 04:22:41.183 Testing App[48069:fb03] 0.00000001