LNK2019 Error when calling methods of a static member in .cpp file

Question

I am getting these errors in my code, they are all related to one static member in my Game class.

Game.obj : error LNK2019: unresolved external symbol "public: class std::shared_ptr<class MainMenuScene> __thiscall SceneManager::AddScene<class MainMenuScene>(void)" (??$AddScene@VMainMenuScene@@@SceneManager@@QAE?AV?$shared_ptr@VMainMenuScene@@@std@@XZ) referenced in function "public: void __thiscall Game::init(char const *,int,int,bool)" (?init@Game@@QAEXPBDHH_N@Z)
Game.obj : error LNK2019: unresolved external symbol "public: class std::shared_ptr<class GameSelectScene> __thiscall SceneManager::AddScene<class GameSelectScene>(void)" (??$AddScene@VGameSelectScene@@@SceneManager@@QAE?AV?$shared_ptr@VGameSelectScene@@@std@@XZ) referenced in function "public: void __thiscall Game::init(char const *,int,int,bool)" (?init@Game@@QAEXPBDHH_N@Z)
Game.obj : error LNK2019: unresolved external symbol "public: class std::shared_ptr<class MainMenuScene> __thiscall SceneManager::ChangeScene<class MainMenuScene>(void)" (??$ChangeScene@VMainMenuScene@@@SceneManager@@QAE?AV?$shared_ptr@VMainMenuScene@@@std@@XZ) referenced in function "public: void __thiscall Game::init(char const *,int,int,bool)" (?init@Game@@QAEXPBDHH_N@Z)

In my game.h I have:

#pragma once

class SceneManager; 

using namespace std;

class Game {
public:
    Game();
    ~Game();

    void init(const char* title, int width, int height, bool fullscreen);
    void handleEvents();
    void update();
    void render();
    void clean();

    bool isRunning() { return running; }

    static SDL_Renderer * renderer; 
    static SceneManager * sceneManager; 
};

The errors are happening in my game.cpp file in the init() method and my game.cpp looks like:

#include "Game.h"

#include "SceneManager.h"

#include "GameSelectScene.h"
#include "MainMenuScene.h" 

SceneManager * Game::sceneManager = new SceneManager();

Game::Game() {}
Game::~Game() {}

void Game::init(const char* title, int width, int height, bool fullscreen) {
    // I do some stuff up here

    // Here is where I think errors are happening.
    sceneManager->AddScene<MainMenuScene>();
    sceneManager->AddScene<GameSelectScene>();

    sceneManager->ChangeScene<MainMenuScene>();
}

My GameSelectScene.h and MainMenuScene.h are both subclasses of my Scene.h and my SceneManager is where the AddScene and ChangeScene methods are defined

My SceneManager.h: #pragma once

#include "Game.h"
#include "Scene.h"
#include <map>
#include <string>
#include <typeindex>

using namespace std;

class SceneManager {
public:
    SceneManager();
    ~SceneManager();

    void init();
    void update();
    void render();

    template <typename T> std::shared_ptr<T> ChangeScene();
    template <typename T> std::shared_ptr<T> AddScene();

private:
    std::map<type_index, std::shared_ptr<Scene>> scenes;
    std::shared_ptr<Scene> currentScene;
};

SceneManager.cpp:

#include "SceneManager.h"

SceneManager::SceneManager() {}
SceneManager::~SceneManager() {}

// I define the init() update() and render()

template <typename T> std::shared_ptr<T> SceneManager::ChangeScene() {
    type_index index(typeid(T));
    currentScene = scenes[index];
    return static_pointer_cast<T>(scenes[index]);
}

template <typename T> std::shared_ptr<T> SceneManager::AddScene() {
    T scene = new T();    
    scenes[std::type_index(typeid(*scene))] = scene;
    return scene;
}

If I remove my AddScene and ChangeScene method calls in the game.cpp file everything compiles correctly and the update, init and render methods defined in the SceneManager run perfectly. I have been researching this issue and walked through all the problems described in MSDN LNK2019 Error

score 1 · Accepted Answer · answered Sep 02 '18 at 20:38

1

Template functions must be defined in header files, not cpp.

Why can templates only be implemented in the header file?

answered Sep 02 '18 at 20:38

user4035

22,508
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Thanks that fixed my problems. I was focused on the #includes or something. However, because I am fairly new to C++ I am trying to figure out what would be best with my map>. I want to call the methods of the object in the shared pointer which is a subclass of the component class. I have looked at a lot of answers and want to make sure I am going about it correctly. Would it be best to do and ptr.get() and then somehow cast it to the subtype so I can call specific methods.. or is there a way I could initialize my map as map> – Taylor Riccetti Sep 05 '18 at 19:52
@TaylorRiccetti Can you ask a separate question about it? It's hard for me to understand the idea. – user4035 Sep 06 '18 at 17:58

LNK2019 Error when calling methods of a static member in .cpp file

1 Answers1