C++ Polymorphism, incomplete downcasting

Question

I have an array which holds references to a bland base type, let's call it Object.

I have derived Class1 from Object and Class2 from Class1.

#include <vector>

class Object {};
class Class1 : public Object {
public:
virtual std::string ToString() {return "it is 1";}
};
class Class2 : public Class1 {
public:
    virtual std::string ToString() {return "it is 2";}
};

int _tmain(int argc, _TCHAR* argv[])
{
    std::vector<Object *> myvec;
    myvec.push_back(new Class2());
    printf("%s", (static_cast<Class1*>(myvec[0]))->ToString().c_str());
    return 0;
}

I call ToString() by casting from Object * to Class1 * like so

    printf("%s", (static_cast<Class1*>(myvec[0]))->ToString().c_str());

My question is, will this output 1 or 2 when the object is in fact of Class2 but not down cast to that specifically? Is the virtual keyword having the intended effect?

Answer 1

I slightly misread your question when I first answered, regarding demons and your nostrils.

The virtual keyword will have it's intended effect. That is, You will see 2. Although you have casted to Class1, the vtable will work it's magic.

Answer 2

It should call Class2's virtual function, since the object is of that type.

Remember: the purpose of a virtual function is to call the actual class's function, not the function for the class the pointer/reference currently appears to be.

Answer 3

First, this is not a safe cast. But assuming that myvec[i] is a pointer the an object you are casting to, then it will call the appropriate method for that class.