Rounding doubles for use in NSString

Question

I have a situation where I have lots of different double values, for example 1.00, 0.25 and 2.50. I would like to round these doubles so that they become 1, 0.25 and 2.5; in other words I want to remove any trailing 0's. Is there a way to do this?

At the moment I have been using %.2f, and I'm wondering if I can make use of this but adapt it in some way. Please can someone help me out?

jscs · Accepted Answer · 2011-12-06T21:34:00.080

As long as you're talking only about display, this is quite easy. The format specifier you want is %g:

The double argument shall be converted in the style f or e (or in the style F or E in the case of a G conversion specifier), with the precision specifying the number of significant digits [...] Trailing zeros shall be removed from the fractional portion of the result[...]

double twopointfive = 2.500;
double onepointzero = 1.0;
double pointtwofive = .25000000000;
NSLog(@"%g %f", twopointfive, twopointfive);
NSLog(@"%g %f", onepointzero, onepointzero);
NSLog(@"%g %f", pointtwofive, pointtwofive);

2011-12-06 21:27:59.180 TrailingZeroes[39506:903] 2.5 2.500000
2011-12-06 21:27:59.184 TrailingZeroes[39506:903] 1 1.000000
2011-12-06 21:27:59.185 TrailingZeroes[39506:903] 0.25 0.250000

The same format specifier can be used with an NSNumberFormatter, which will also give you some control over significant digits.

The trailing zeroes can't be removed from the way the number is stored in memory, of course.

Mark Adams · Answer 2 · 2011-12-06T21:42:50.147

2

I believe you want the %g format specifier to redact trailing zeros.

edited Dec 06 '11 at 21:42

answered Dec 06 '11 at 21:23

Mark Adams

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Littlejon · Answer 3 · 2011-12-06T21:35:39.517

1

Not really rounding, but have you tried just %f it should only show the number of digits required rather then padding out the number.

My answer above is wrong, %g as others has stated is the right way to go.

The documentation for string formatters should help too. http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265

edited Dec 06 '11 at 21:35

answered Dec 06 '11 at 21:26

Littlejon

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score 1 · Answer 4 · answered Dec 13 '11 at 13:39

Here is a list of all the format specifiers that you can use...

%@     Object
%d, %i signed int
%u     unsigned int
%f     float/double

%x, %X hexadecimal int
%o     octal int
%zu    size_t
%p     pointer
%e     float/double (in scientific notation)
%g     float/double (as %f or %e, depending on value)
%s     C string (bytes)
%S     C string (unichar)
%.*s   Pascal string (requires two arguments, pass pstr[0] as the first, pstr+1 as the second)
%c     character
%C     unichar

%lld   long long
%llu   unsigned long long
%Lf    long double

Rounding doubles for use in NSString

4 Answers4