Question

I want to know what makes a float number nan in c++. I am using a large dataset and it is really hard to trace. I want to know the ways of changing a float number to nan to reduce bug possibilities.

I found the code that causes the nan problem. I found that s/m is nan in some cases. But I don’t know how to solve it.

float gp(float x){
float e = 2.71828183;
x *= -1;
float s = pow(e,x);
float m = (1 + pow(e,x)) * (1 + pow(e,x));  
return s / m;}

Answer 1

Taken from wikipedia -> special values -> nan

• 0/0
• ∞×0
• sqrt(−1)
• in general “invalid operations” (I am not sure wether there are not more than the three above)

Looking at you code: infinity times 0 is possible, is it?

edit:

• 0 <= s <= +inf

• 1 <= m <= +inf

s / m:

• +inf / +inf does indeed make minus NaN (I tested it)

I think that’s the only thing that makes a NaN.