So as the title states im receiving some odd errors with a couple of class that im working on. Im trying to implement the Entity Component System example from Game Programming Gems 6 and im getting a lot of issues with it from just doing test compiles every once in a while to check for syntax errors and such.

These classes are without definitions yet but I don't think that would be an issue.

#pragma once
#include <string>
#include <map>
#include "Component.h"

class GameObject
{
public:
	GameObject(const std::string GameObjectID);
	virtual ~GameObject()=0;

	const std::string GetID();
	void ClearComponents();

private:
	std::string mGameObjectID;
	std::map<const std::string, Component*> ComponentTable;
};

#pragma once
#include <string>
#include "GameObject.h"

class Component
{
public:
	Component();
	virtual ~Component()=0;

	virtual const std::string componentID() const = 0;

	virtual void Update();

	void SetOwner(GameObject* go);
	GameObject* GetOwner() const;

private:
	GameObject* mOwner;
};

Warning	4	warning C4183: 'GetOwner': missing return type; assumed to be a member function returning 'int'	c:\users\\code\c++\engine\engine\component.h	16	1	Engine
Error	3	error C4430: missing type specifier - int assumed. Note: C++ does not support default-int	c:\users\\code\c++\engine\engine\component.h	16	1	Engine
Error	6	error C4430: missing type specifier - int assumed. Note: C++ does not support default-int	c:\users\\code\c++\engine\engine\component.h	19	1	Engine
Error	9	error C2143: syntax error : missing ';' before '}'	c:\users\\code\c++\engine\engine\gameobject.h	18	1	Engine
Error	11	error C2143: syntax error : missing ';' before '}'	c:\users\\code\c++\engine\engine\component.h	20	1	Engine
Error	12	error C2143: syntax error : missing ';' before '}'	c:\users\\code\c++\engine\engine\component.cpp	12	1	Engine
Error	10	error C2143: syntax error : missing ';' before '{'	c:\users\\code\c++\engine\engine\component.h	6	1	Engine
Error	2	error C2143: syntax error : missing ';' before '*'	c:\users\\code\c++\engine\engine\component.h	16	1	Engine
Error	5	error C2143: syntax error : missing ';' before '*'	c:\users\\code\c++\engine\engine\component.h	19	1	Engine
Error	7	error C2065: 'Component' : undeclared identifier	c:\users\\code\c++\engine\engine\gameobject.h	17	1	Engine
Error	1	error C2061: syntax error : identifier 'GameObject'	c:\users\\code\c++\engine\engine\component.h	15	1	Engine
Error	8	error C2059: syntax error : '>'	c:\users\\code\c++\engine\engine\gameobject.h	17	1	Engine
Error	13	error C1004: unexpected end-of-file found	c:\users\\code\c++\engine\engine\component.cpp	12	1	Engine

You've got circular inclusions for GameObject and Component.

Since you seem to only use pointers to each other remove the "#include "GameObject.h" from Component.h and vice versa. Add a forward declaration to each header.

...
class GameObject;
 
class Component
{
  ...

GameObject.h

...
class Component;
 
class GameObject
{
  ...

Seems to have done the trick and has given me one more C++ topic to research. Thank you.

You've got circular inclusions for GameObject and Component.

Since you seem to only use pointers to each other remove the "#include "GameObject.h" from Component.h and vice versa. Add a forward declaration to each header.

...
class GameObject;
 
class Component
{
  ...

GameObject.h

...
class Component;
 
class GameObject
{
  ...

Seems to have done the trick and has given me one more C++ topic to research. Thank you.

GameDev.net published this really nice article about this and other C/C++ code organization problems. A very good read.