You should not compare floating point numbers for equality in most
cases. This is true of any language on any platform.
Indeed, some floating-point numbers (such as the one represented by
the integer 0x7fc00000) will compare as not equal to themselves:
I think what the OP really wanted to know (and I'm interested in
the answer too) is whether going out to the stringValue and back to
the doubleValue is guaranteed to yield a float that is bitwise
identical to the original float, or whether there is "drift" in the
least significant bit or two due to the changes in representation.
Anyway, even if that's not the OP meant, that's what I'd like to
ask. :->
My original intent was to store a representation of the float in a
string so I can load it back again. In the meanwhile I found that
using the %a format along with NSScanner's scanHexDouble does the
trick (since I don't need that string to be human readable a hex
representation is ok for me)
double a=pi;
double b;
[[NSScanner scannerWithString:[NSString stringWithFormat:@"%a",a]]
scanHexDouble:&b];
if (a==b)
NSLog(@"Success");
else
NSLog(@"Failure");
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