Why use !! when converting int to bool?

Question

What can be a reason for converting an integer to a boolean in this way?

bool booleanValue = !!integerValue;

instead of just

Answer 1

I've never like this technique of converting to a bool data type - it smells wrong!

Instead, we're using a handy template called boolean_cast found here. It's a flexible solution that's more explicit in what it's doing and can used as follows:

bool IsWindow = boolean_cast< bool >(::IsWindow(hWnd));