Question

How to correctly forward declare classes ?. If I try this it won’t compile:

#include<iostream>
#include<conio.h>

class B ;

class A
{
    public:
    B returnB()
    {
        return B() ;
    }
} ;

class B
{
    public:
    A returnA()
    {
        return A() ;
    }
} ;

int main(void)
{

    getch() ;
    return 0 ;
}

Answer 1

Sometimes there are scenarios where you must define your functions outside of the class:

class B;

class A
{
public:
    B returnB();
};

class B
{
public:
    A returnA();
};

B A::returnB()
{
    return B();
}

A B::returnA()
{
    return A();
}

Usually the definition (implementation) goes inside a separate *.cpp file. If it is in a header, then it has to be inline.