Limiting both the fractional and total number of digits when formatting a float for display

Question

I need to print a float value in area of limited width most efficiently. I\'m using an NSNumberFormatter, and I set two numbers after the decimal point as the d

Answer 1

You're looking for a combination of "maximum significant digits" and "maximum fraction digits", along with particular rounding behavior. NSNumberFormatter is equal to the task:

float twofortythreetwentyfive = 234.25;
float onetwothreefourtwentyfive = 1234.25;
float eleventwothreefourtwentyfive = 11234.25;

NSNumberFormatter * formatter =  [[NSNumberFormatter alloc] init];
[formatter setUsesSignificantDigits:YES];
[formatter setMaximumSignificantDigits:5];
[formatter setMaximumFractionDigits:2];
[formatter setRoundingMode:NSNumberFormatterRoundCeiling];

NSLog(@"%@", [formatter stringFromNumber:[NSNumber numberWithFloat:twofortythreetwentyfive]]);
NSLog(@"%@", [formatter stringFromNumber:[NSNumber numberWithFloat:onetwothreefourtwentyfive]]);
NSLog(@"%@", [formatter stringFromNumber:[NSNumber numberWithFloat:eleventwothreefourtwentyfive]]);

Result:

2012-04-26 16:32:04.481 SignificantDigits[11565:707] 234.25
2012-04-26 16:32:04.482 SignificantDigits[11565:707] 1234.3
2012-04-26 16:32:04.483 SignificantDigits[11565:707] 11235