C++ doesnt find type definitions? - c++

Question

So, i started learning C++ about a year ago, i learned Java C# and VB.NET before it.
As it is now, i would consider myself a advanced C++ coder. However, theres one thing i dont quite get. The linking process. And heres the problem.
Right now, im coding a XNA-like library for Game development, with a basic Component System -
but i get Compiler errors when building it, C++ pretending it doesnt know a specific type, in this case, the GameComponent class doesnt know the ComponentSelector class (and vice versa), although its correctly included and typed. Im gonna show you my two header files, hopefully you can help me out.
ComponentSelector.hpp:
#ifndef COMPONENTSELECTOR_HPP
#define COMPONENTSELECTOR_HPP
#include<sem/System/Types.hpp>
#include<sem/System/GameComponent.hpp>
#include<vector>
namespace sem
{
class ComponentSelector
{
public:
GameComponent* getComponent1(); //GameComponent does not name a type
GameComponent* getComponent2(); //GameComponent does not name a type
GameComponent* getComponent3(); //GameComponent does not name a type
void addComponent(GameComponent* item); //GameComponent does not name a type
void removeComponent1();
void removeComponent2();
void removeComponent3();
void clearList();
private:
std::vector<GameComponent*> m_Components;
protected:
};
}
#endif // COMPONENTSELECTOR_HPP
GameComponent.hpp:
#ifndef GAMECOMPONENT_HPP
#define GAMECOMPONENT_HPP
#include<sem/System/ComponentSelector.hpp>
#include <sem/System/Types.hpp>
namespace sem
{
class GameComponent
{
public:
virtual void load() = 0;
virtual void unload() = 0;
virtual void update() = 0;
virtual void draw() = 0;
ComponentSelector* m_Selector; //ComponentSelector does not name a type
SEMlong getID();
SEMstring getName();
SEMstring getType();
private:
SEMlong m_ComponentID;
SEMstring m_ComponentName;
SEMstring m_ComponentType;
protected:
};
}
#endif // GAMECOMPONENT_HPP
Any solution and tips would be greatly appreciated.

Answer 1

You need a forward declaration for class ComponentSelector in your GameComponent class declaration:
// Remove this: #include<sem/System/ComponentSelector.hpp>
#include <sem/System/Types.hpp>
namespace sem
{
class ComponentSelector; // Note the forward declaration added!
class GameComponent
{
// ...
ComponentSelector* m_Selector; // Compiles now!
// ...
I'd recommend to do the same in the ComponentSelector declaration header vice versa. Include the full class declarations then, where you are going to use any members (this is in the compilation units i.e. .cpp-files usually).