Comparison of floating point values

**spsen16** · 10-08-2010

//code

int testFunc(double value)

double test = 0.0;

if(val<=test)
std::cout<<"Both are Equal"<<std::endl;

///

The if loop may result to true if value ==0 but comparison of floating point values are not proper and violate the coding standard.
How can I carry out such a comparison??????????

Regards,
Sanjib

**GReaper** · 10-08-2010

Because of floating point rounding errors, you may never end up with a float, or a double, which is exactly 0.0 ( unless you set it yourself ). That is why i use the following technique:

Code:

if ((val-ROUNDING_ERROR) <= test && (val+ROUNDING_ERROR) >= test)

An alternative is the following:

Code:

if (fabs(val-test) <= ROUNDING_ERROR) // I'm not sure if that way works

Which one you'll choose to use is up to you. For performance sake, i suggest the second one, but for simplicity the first.

Code:

val            :: The first number you want to compare
test           :: The second number you want to compare
ROUNDING_ERROR :: typical float tolerance is 0.0000001f , for double tolerance i'm not sure 
                   ( You can even use your own tolerance by passing in to the function.

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