Calling a Derived Class method from a Void Pointer cast to a Base Object

Question

I want to call an overridden method in a derived class from a void pointer. This fails at runtime because the virtual Base::foo() method is invoked, rather than Derived::foo(). This is how the relevant code works:

Class Base  
{  
public:  
    Base();  
    virtual void foo() = 0;
}

Class Derived: public Base
{
public:
    Derived();
    void foo();
}

int main()
{
    Derived* dv = new Derived();
    void* ptr = dv;

    static_cast<Base*>(ptr)->foo();
}

Answer 1

There's no way this can work other than by luck. Since this is a static_cast, the conversion must be known at compile time. But because the pointer is a void *, there's no way the compiler can know how the pointer needs to converted to point to the instance of the base inside the derived.