Problem when two classes use each other!

[nikosxatz]

In the following code class A has a method witch has a parameter an object of class B. Class B has also a method with a parameter an object of class A.
The program does not compile. The foreword declarations of the two classes didn't help! I understand the reason but I don't know how to solve it!
Any help is welcome. If you propose a solution, please give a working version of my code as well.

Thanks a lot!

#include <iostream>
using namespace std;

class A;
class B;

class A
{
public:
int A1;
void display(B objB)
{
cout<<objB.B1<<endl;
}

};

class B
{
public:
int B1;
void display(A objA)
{
cout<<objA.A1<<endl;
}

};

int main()
{
A Aobj;
B Bobj;
Aobj.A1=10;
Bobj.B1=20;
Aobj.display(Bobj);
Bobj.display(Aobj);
return 0;
}

[coder777]

put the functions that uses the forwarded class in another (.cpp) file where you can inlcude the whole class and hence can use the members

[bufige]

It should be something like this.

#include <iostream>



class A;
class B;

class A
{
public:
    int A1;
    void display(B b);
};

class B
{
public:
    int B1;
    void display(A a);
};

void A::display(B b)
{
    std::cout << "B:" <<b.B1 << std::endl;
}
void B::display(A a)
{
    std::cout << "A:"<< a.A1 << std::endl;
}


int main()
{
    A a;
    B b;

    a.A1 = 10;
    b.B1 = 20;

    a.display(b);
    b.display(a);

    return 0;
}

[giblit]

Forward declarations are incomplete types. So how can you call the public methods of an object without completing the type?

//Example 1:
class B;

class A
{
    public:
       int A1;
       void display( B objB ); //Okay you are just telling it what to expect
};


//Example 2:
class B;

class A
{
    public:
        int A1;
        void display( B objB ){ cout << objB.b1 << endl; } //not okay what is 
        //inside the class? All we know is  we are looking for type B
       //but there is no definition of it yet
};

[nikosxatz]

Thanks a LOT!