Thread: C++ Polymorphism

I'm trying to get along with C++ and polymorpism. Therefore I created the following code example. When try to compile i'm getting the following error message. Actually the code sample was Java exam and and now i try to translate it to C++.

Code:

$ g++ main.cpp -o main
main.cpp: In member function `void A::func5(C*)':
main.cpp:18: Fehler: invalid use of undefined type `struct C'
main.cpp:6: Fehler: forward declaration of `struct C'

Can anyone help me what's wrong with the example below. I guess it's related to forward declaration but don't know what's wrong. Any code improvements are appreciated as well.

Code:

#include <iostream>


using namespace std;


class C; // forward declaration


class A
{
    public:
        A()                  { cout << "A::A()"  << endl; }
        virtual ~A()         { cout << "A::~A()" << endl; }


        virtual void func1() { cout << "A::func1()"  << endl; }
        virtual void func2() { cout << "A::func2()"  << endl; }
        virtual void func3() { cout << "A::func3()"  << endl; }
        void func4(A* pA)    { cout << "A::func4()"  << endl; pA->func1(); }
        void func5(C* pC)    { cout << "A::func5()"  << endl; pC->func1(); }
};


class B : public A
{
    public:
        B()                 { cout << "B::B()"     << endl; }
        ~B()                { cout << "B::~C()"    << endl; }
        void func1()        { cout << "B::func1()" << endl; }
        void func2(int* pI) { cout << "B::func2"   << endl; }
};


class C : public B
{
    public:
        C()                  { cout << "C::C()"  << endl; }
        ~C()                 { cout << "C::~B()" << endl; }


        virtual void func1() { cout << "C::func1()"  << endl; }
        virtual void func2() { cout << "C::func2()"  << endl; }
        virtual void func3() { cout << "C::func3()"  << endl; }
        void func4()         { cout << "C::func4()"  << endl; }
};


int main()
{
    A* ap = new C();


    cout << endl;


    ap->func1();
    ap->func2();
    ap->func3();
    ap->func4(ap);
    ((C*)ap)->func4();
    // static_cast<B*>(ap)->p()


    cout << endl;


    delete ap;


    return 0;
}

Commenting out the line "void func5(C* pC) ..." and the program works...

Code:

A::A()
B::B()
C::C()


C::func1()
C::func2()
C::func3()
A::func4()
C::func1()
C::func4()


C::~B()
B::~C()
A::~A()