Question

#pragma once
#include "Player.h"

class Player;
//class SmallHealth;

const int kNumOfCards = 3; //for Player class also
const int kCardLimit = 3;

class Cards
{
private:
protected:
    int turnsInEffect;
    Player *owner;
public:
    Cards()
    {turnsInEffect = 1;}
    void AssignOwner(Player &player)
    {
        owner = &player;
    }
    virtual void PlayCard()
    {}
    virtual ~Cards(void)
    {}

};

class SmallHealth : public Cards
{
public:
    void PlayCard()
    {
        turnsInEffect = 1;
        owner->SetHealth(owner->GetHealth() + 5);

        //check if health goes over
        if(owner->GetHealth() > owner->GetHealthLimit())
        {
            owner->SetHealth(owner->GetHealthLimit());
        }
        turnsInEffect--;
    }
};

I thought by declaring class Player I wouldn’t get these errors:

error C2027: use of undefined type 'Player

see declaration of ‘Player’

error C2227: left of '->SetHealth' must point to ...

Checking on error 2027, seems I have to explicitly have the whole class before the Cards class, but I thought the forward class declaration would make it unnecessary. How I have it set up is that Cards class is created and assigned a subclass by the Player class and stored in the Player class. The subclasses that inherit the Cards class will call upon the functions of the Player class. I’m having a tough time making sure the 2 classes identify each others classes.

Answer 1

In that case, a forward declaration of a C++ class will just tell the compiler that the type you’re using is a class.

This is often useful for headers, as you only need to know that the type is a class. Including the class’ header would take more compile time.

But in the implementation, it’s different. With a forward class, the compiler will not know about its members, methods, etc.

For that, you need to include the header file of the class.

For instance, with only the forward class, you can’t do that:

owner->GetHealth();

As there is no way for the compiler to know the GetHealth method exists in your Player class, with just a forward class.

Note you may also have a problem in your AssignOwner method, as you implement it using your header. I’m a bit rusty on C++, as I’m doing C most of the time, but I think you should try declaring only the prototype in the class header, and implement the actual method in your implementation file, after having included the correct header file.