Question

I am little bit confused on referencing a sub class inside a super class in C++.
For example, given Java :

public class Entity {


  protected ComplexEntity _ce;

  public Entity() {

  }

  public ComplexEntity getCentity() {
    return _ce;
  }
}

Where ComplexEntity extends the entity.It works.In the sub class I call getCentity() no errors.

Now ,in C++ when I write something like that:

 #pragma once

 #include "maininclude.h"
 #include "ExtendedEntity.h"
 using namespace std;

 class EntityBase
 {
 public:
    EntityBase(void);
    EntityBase(const string &name);

    ~EntityBase(void);

 protected:

    ExtendedEntity* _extc;
    string   _name;
 };

I am getting compiler error:

  error C2504: 'Entity' : base class undefined  

In the classes which inherit from this Entity.Why does that happen?

Is it completely unacceptable in C++?

May be Entity must be abstract ?
I would like to get suggestions on possible workarounds.

Answer 1

You may consider using CRTP, cut/paste from Wikipedia:

// The Curiously Recurring Template Pattern (CRTP)
template<class Derived>
class Base
{
    Derived* getDerived() { return static_cast<Derived*>(this); }
};

class Derived : public Base<Derived>
{
    // ...
};