Thread: class schema implementation doubt

If A contains an instance of B, it must know all about B. Therefore B must come first (or included from a header).

B however doesn't contain an instance of A (it couldn't). Instead it just has to know that a class by the name A exists, so it can declare pointers to it. For that forward declarations are used.

All in all the layout would be:

Code:

//forward declaration of A
class A;

//declaration of B
class B
{
    //...
};

//declaration of A
class A
{
    //we know all about B:
    B b;
    //...
};

//now we also know all about A and can implement the function in B
//that needs to know about A's member functions
void B::set_pointer(A* a) {...}

Other notes:
main() should have an explicit return type (C++ does not accept defaulting return types).

A little indentation wouldn't hurt.

Code:

A a= A();

This, of course, is the same as

Code:

A a;

except potentially calling one constructor and one destructor less.