Massive Headache with Templates...

I've got a really annoying unresolved symbol linker error in code I've written that uses a templatized State Design Pattern.

It starts like this...

Code:

---


#ifndef __ISTATE_H__
#define __ISTATE_H__

template <typename T>
class IState
{
        public:
                virtual void Enter(T* ) = 0;
                virtual void Execute(T* ) = 0;
                virtual void Exit(T* ) = 0;
};

#endif

#ifndef __ENGINE_STATE_H__
#define __ENGINE_STATE_H__

#include "State.h"

template <typename T>
class IEngineState: public IState<T>
{
        public:
                virtual bool KeyboardEvent(irr::SEvent& , T* ) = 0;
                virtual bool MouseEvent(irr::SEvent& , T* ) = 0;
                virtual bool MouseGUIEvent(irr::SEvent& , T* ) = 0;
};

#endif

#ifndef __STATE_MACHINE_H__
#define __STATE_MACHINE_H__

#include "State.h"

template <typename T>
class StateMachine
{
        public:

                StateMachine(T* pOwner);
                ~StateMachine();

                void Update();

                IState<T>* GetCurrentState() const;
                IState<T>* GetGlobalState() const;
                IState<T>* GetPreviousState() const;

                bool IsInState(IState<T>* s) const;

                void ChangeState(IState<T>* pNewState);
                void RevertToPreviousState();

                void SetCurrentState(IState<T>* s);
                void SetPreviousState(IState<T>* s);
                void SetGlobalState(IState<T>* s);

        private:
                T* m_pOwner;

                IState<T>* m_pCurrentState;
                IState<T>* m_pPreviousState;
                IState<T>* m_pGlobalState;
};

#endif



#ifndef __GAME_ENGINE_H__
#define __GAME_ENGINE_H__

class CGameEngine
{
        public:

                StateMachine<CGameEngine>* GetFSM();

        private:
                StateMachine<CGameEngine>* m_pStateMachine;
};

#endif

---

The offending code occurs in the game constructor- when I create the StateMachine to hold a reference to the owning GameEngine object...

Code:

---

CGameEngine::CGameEngine() :       
        m_pStateMachine(NULL), m_pIrrDev(NULL), m_pIrrSceneMan(NULL), m_pIrrGuiEnv(NULL)
{
        m_pStateMachine = new StateMachine<CGameEngine>(this);
}

---

1>GameEngine.obj : error LNK2019: unresolved external symbol "public: __thiscall StateMachine<class CGameEngine>::StateMachine<class CGameEngine>(class CGameEngine *)" referenced in function "public: __thiscall CGameEngine::CGameEngine(void)"

It's saying the constructor is undefined in the StateMachine class... but I've declared it like so...

Code:

---

template <typename T>
StateMachine<T>::StateMachine(T* pOwner):
        m_pOwner(pOwner), m_pCurrentState(NULL), m_pPreviousState(NULL), m_pGlobalState(NULL)
{

}

---

I can't figure it out and I've been looking at it all day... Any help is REALLY appreciated.

Thanks.

where did you implement this constructor? Template code needs to be implemented in the header file for most, maybe all, compilers.

Souldog- you are a champion!

Something as simple as putting template files in a source file causes linker problems. I've scratched my head all day trying to figure out what could possibly have caused this problem

Thanks again buddy!