Implementation of the replacing game scene in C++ - c++

Question

I have about 10 scene classes in my C++ game. It's something like a regular game screen (menu screen, game screen, leaderboard, options, etc). So I need some technique to replace one scene to another. I've read all comments you posted me in this thread and tried to implement it. Now I have following code:
// -----[ main.cpp ]----- //
#include "SceneManager.h"
#include "Scene.h"
int main( int argc, const char * argv[] ) {
SceneManager *sceneManager = new SceneManager();
sceneManager->changeScene( 0 );
delete sceneManager;
return 0;
}
// -----[ Scene.h ]----- //
class SceneManager;
class Scene {
public:
SceneManager *sceneManager;
void start( SceneManager *sceneManager );
};
// -----[ SceneManager.h ]----- //
#include "Scene.h"
#include "MenuScene.h"
#include "GameScene.h"
class Scene;
class MenuScene;
class GameScene;
class SceneManager {
public:
Scene* scene;
void changeScene( short id ) {
if ( scene != NULL ) {
delete scene; // to prevent a memory leak
}
if ( id == 0 ) {
scene = new MenuScene();
} else if ( id == 1 ) {
scene = new GameScene();
}
if (scene) {
scene->start( this );
}
}
};
// -----[ MenuScene.h ]----- //
class MenuScene: public Scene {
public:
void start( SceneManager *sceneManager ) {
this->sceneManager = sceneManager;
}
};
// -----[ GameScene.h ]----- //
class GameScene: public Scene {
public:
void start( SceneManager *sceneManager ) {
this->sceneManager = sceneManager;
}
};
It doesn't work because of error (XCode 4.6, MacOS X):
Apple Match-O Linker (id) Error
Undefined symbols for architecture x86_64:
"Scene::start(SceneManager*)", referenced from:
SceneManager::changeScene(short) in main.o
ld: symbol(s) not found for architecture x86_64
What do i do wrong? How to fix it? Maybe someone knows about some popular issues on this subject?

Answer 1

As mentioned in the comments, I believe your design conceptually needs another class. Here is a rough example.
class Scene {
public:
virtual void start() = 0;
};
class SceneManager {
public:
void changeScene( short id ) {
Scene* scene = NULL;
if ( id == 0 ) {
scene = new MenuScene(); // undeclared yet
} else if ( id == 1 ) {
scene = new GameScene(); // undeclared yet
}
if (scene) {
// TODO: make the scene visible.
scene->start();
}
}
};
class MenuScene: public Scene {
public:
virtual void start() {
// Draw menu stuff
}
};
class GameScene: public Scene {
public:
void start() {
// Draw game stuff
}
};
It's hard to be more specific than that without knowing more context about your particular environment.