The reason I would prefer !! (or != 0) is that there are far too many err, non-bool bools. Even if you know for sure it's the stdbool.h bool, the next reader mi

The reason I would prefer !! (or != 0) is that there are far too many err, non-bool bools. Even if you know for sure it's the stdbool.h bool, the next reader might not be aware -- presuming that when you do this you care about the distinction (otherwise I agree that the cast is fine).