In C++, infinity is represented by 1.#INF. Indeterminate is represented by -1.#IND. The problem is how to test if a variable is infinite or indeterminate. Checking infinity is relatively straightforward: You find the infinity definition in your particular C++. For my case (VS2003), it is std::numeric_limits
Indeterminate is a little tricky, because you cannot compare an indeterminate value to some other value. Any comparison returns false. You can use this property to detect an indeterminate value by comparing it to itself. Let's say you have a double variable called aVal. Under normal conditions, aVal != aVal returns false. But if aVal is indeterminate, aIndVal != aIndVal returns true. This weird situation is not present for infinite values, i.e. aInfVal != aInfVal always returns false.
Here are two functions that can be used to check for indeterminate and infinite values:
Update Jan 04, 2009: I asked this question on Stackoverflow