Need help solving linker error in C++ engine/framework construction

Question

I came here as a last resort as I need help with this asap for an assignment due tomorrow.

I'm putting together a simple engine in C++ that handles nodes, texture/asset loading and a state system. I'd like to try and move on to coding the asset related stuff but in order to do that I need the state system to be working.

APPLICATION.h

#pragma once
#include "AppGSM\EGameStateManager.h"

class EGameStateManager;

class EApplication 
{
public:

    static void Init();
    static void RunApp(); 
    EGameStateManager* GetGameStateManager();


protected: 

    static int windowWidth;
    static int windowHeight;
    static bool fullScreen;
    static bool frameSync;
    static char* windowTitle;

};

Currently whenever I try and use the pointer seen above, in both my teststate class and my main.cpp, to the game state manager I receive linker errors. (seen below)

TEST STATE.cpp

#include "AppGSM\ETestState.h"
#include "AppGSM\EApplication.h"
#include <iostream>

ETestState::ETestState(EApplication* pApp){}

ETestState::~ETestState(){}

void ETestState::Update(float deltaTime)
{
    //if(INPUT::GetKey(KEY_T))
    //{
    //  cout << "Entered Test State" << endl;
    //}

    m_testTimer += deltaTime;

    if(m_testTimer > 3.0f)
    {
        m_pApp->GetGameStateManager()->ChangeState("Second TEST");
    }
}

void ETestState::Draw(){}

MAIN.cpp

#include "GL\glew.h"
#include "GL\glfw.h"
#include <conio.h>
#include "AppGSM\EApplication.h"
#include "AppGSM\ETestState.h"

void main()
{
    EApplication::Init();

    EApplication* pApp = new EApplication();

    pApp->GetGameStateManager()->SetState("TEST", new ETestState(pApp));

    EApplication::RunApp();
}

and this is the base game state class that holds the application pointer used in teststate:

BASEGAMESTATE.h

#pragma once 

class EApplication;
class EGameStateManager;

class EBaseGameState
{
public:

    EBaseGameState(){}
    EBaseGameState(EApplication* pApp);

    //always make the destructor virtual !!
    virtual ~EBaseGameState();

    //all game states must define update and draw
    virtual void Update(float deltaTime)    = 0;
    virtual void Draw()                     = 0;


protected:

    EApplication* m_pApp;


};

these are the linker errors:

Error   9   error LNK2019: unresolved external symbol "public: class EGameStateManager * __thiscall EApplication::GetGameStateManager(void)" (?GetGameStateManager@EApplication@@QAEPAVEGameStateManager@@XZ) referenced in function _main  D:\Engine\main.obj

Error   10  error LNK2001: unresolved external symbol "public: class EGameStateManager * __thiscall EApplication::GetGameStateManager(void)" (?GetGameStateManager@EApplication@@QAEPAVEGameStateManager@@XZ)   D:\Engine\ETestState.obj

Usually I'd put linker errors down to cyclical includes but I've written down a sequence diagram of sorts and nothing includes anything that includes itself. Its probably something obvious.. I'm just really stressed. Any help would be much appreciated.

Answer 1

The linker can't find the function. You need to implement the GetGameStateManager() function