Question

The Math “pow” function returns -1.#IND. What kind of error value is -1.#IND and how do I detect the error in an if-statement?

Answer 1

-1.#IND is the textual representation of NaN on Windows.

You can check if a float value is NaN with this small function:

// NaN never compares equal, not even to itself
bool is_nan(double d){ return d != d; }

(As @chris notes, if you have a C++11 compliant stdlib, you get std::isnan in <cmath>.)

In normal program flow, you shouldn’t need to worry about NaN as long as you sanity-check your math inputs. Of course, you can also go the other way and just do your math calculations and check against NaN afterwards. 🙂