Class reference to parent

Question

i'm pretty new at using C++ and I'm actually stopped at a problem.

I have some class A,B,C defined as follow (PSEUDOCODE)

class A
{
...
    DoSomething(B par1);
    DoSomething(C par1);
...
}

class B
{
   A parent;
...
}

class C
{
   A parent;
...
}

The problem is :

How to make this? If I simply do it (as I've always done in c#) it gives errors. I pretty much understand the reason of this. (A isn't already declared if I add the reference (include) of B and C into its own header)

Any way to go around this problem? (Using void* pointer is not the way to go imho)

Answer 1

Forward-declare B and C. This way compiler will know they exist before you reach the definition of class A.

class B;
class C;

// At this point, B and C are incomplete types:
// they exist, but their layout is not known.
// You can declare them as function parameters, return type
// and declare them as pointer and reference variables, but not normal variables.
class A
{
    ....
}

// Followed by the *definition* of B and C.

---

P. S.

Plus, one more tip unrelated to the question (seeing how you come from a C# background): it's better to pass by const reference than by value:

class A
{
...
    void DoSomething(const B& par1);
    void DoSomething(const C& par1);
...
}