Why is “operator bool()” invoked when I cast to “long”?

Question

I have the following class:

class MyClass {
public:
   MyClass( char* what ) : controlled( what ) {}
   ~MyClass() { delete[] controlled; }
   operator char*() c         


        

Answer 1

It's one of the known pitfalls of using operator bool, that is a aftershock of C inheritance. You'd definitively benefit from reading about the Safe Bool Idiom.

In general, you didn't provide any other matchable casting operator, and bool (unfortunately) is treated as a good source for arithmetic casting.

Answer 2

You cannot implicitly cast a T* to long. But you can cast a bool to long.

So the operator bool is used.

You have to define a operator LPARAM.

Answer 3

operator bool is the best match, because char* and void* can't be converted to long without an explicit cast, unlike bool:

long L1 = (void*)instance; // error
long L2 = (char*)instance; // error
long L3 = (bool)instance; // ok