i need help implementing my event manager and engine system (SDL && C++) - c++

Question

i need help with my attempt at writing a reusable game engine. it's not the best engine, but i definitely think it will be reusable once i am done. i am not asking for code or to be spoonfed, but i am asking for some advice :-).
my current layout:
i have an engine class, a game class, and an event manager class. the engine class extends the event manager class, and the game class extends the engine class. here is my current code for these 3 classes (ignore the Graphics class--it is just a reusable class i use to avoid rewriting fullscreen, initialize, and resize screen functions).
ENGINE.HPP
#ifndef _ENGINE_HPP
#define _ENGINE_HPP
#pragma once
#include <SDL/SDL.h>
#include "event_manager.hpp"
enum
{
ENGINE_SUCCESS = 0,
ENGINE_INITIALIZATION_ERROR
};
class Engine : public EventManager
{
public:
Engine();
virtual ~Engine();
int exec();
void handle_event(SDL_Event *);
void update_engine();
virtual bool init();
virtual void render();
virtual void update();
virtual void clean();
bool running_;
};
ENGINE.CPP
#include "./engine.hpp"
Engine::Engine()
{
running_ = false;
}
Engine::~Engine()
{
}
int Engine::exec()
{
if (!init())
{
clean();
return ENGINE_INITIALIZATION_ERROR;
}
SDL_Event event;
while (running_)
{
while (SDL_PollEvent(&event))
handle_event(&event);
update();
render();
}
clean();
return ENGINE_SUCCESS;
}
void update_engine()
{
}
void handle_event(SDL_Event *event)
{
EventManager::handle_event(event);
}
bool init() {return true;}
void render() {}
void update() {}
void clean() {}
EVENT_MANAGER.HPP
#ifndef _EVENT_MANAGER_HPP
#define _EVENT_MANAGER_HPP
#pragma once
#include <SDL/SDL.h>
class EventManager
{
public:
EventManager();
virtual ~EventManager();
virtual void handle_event(SDL_Event *);
// events here
virtual void event_exit();
};
#endif
EVENT_MANAGER.CPP
#include "./event_manager.hpp"
EventManager::EventManager()
{
}
EventManager::~EventManager()
{
}
void EventManager::handle_event(SDL_Event *event)
{
switch (event->type)
{
case SDL_QUIT:
event_exit();
break;
}
}
void on_exit() {}
GAME.HPP
#ifndef _GAME_HPP
#define _GAME_HPP
#include "./engine.hpp"
#include "./entity.hpp"
#include "./graphics.hpp"
class Game : public Engine
{
public:
Game();
bool init();
void render();
void update();
void clean();
private:
Graphics g;
};
#endif
GAME.CPP
#include "./game.hpp"
int main(int argc, char **argv)
{
Engine engine;
return engine.exec();
}
Game::Game() {}
bool Game::init()
{
if (!g.init(800, 600, 32, g.screen_flags()))
{
return false;
}
SDL_WM_SetCaption("Title", NULL);
return true;
}
void Game::update()
{
Engine::update_engine();
}
void Game::clean()
{
SDL_FreeSurface(g.screen_);
SDL_Quit();
}
void Game::render()
{
SDL_Flip(g.screen_);
}
i am getting this error:
engine.cpp: In function ‘void handle_event(SDL_Event*)’:
engine.cpp:40: error: cannot call member function ‘virtual void
EventManager::handle_event(SDL_Event*)’ without object
why is this happening? shouldn't i be able to do EventManager:: if the I did
class Engine : public EventManager
???
that is the only error i get, i am sure it is something simple. now i need a little bit of advice.
instead of handling events like
void Engine::event_exit()
in the engine, i'd rather do it in the game class.
class Game : public Engine
void Game::event_exit()
if that doesn't make sense, notice how i made Engine extend EventManager, and my Game class extends Engine
class Engine : public EventManager
class Game : public Engine
would it work if i called the snippet above these ^ two snippets? i can't test it because i get that error.

Answer 1

Happens to the best of us, but I think it's just a matter of forgetting to specify namespaces. When you implement the functions in engine.cpp, you forgot to prepend Engine::, so the code should be:
void Engine::update_engine()
{
}
void Engine::handle_event(SDL_Event *event)
{
EventManager::handle_event(event);
}
It's a classic case of C++ error messages not really telling you the root of the error.
A short explanation, just in case:
The compiler tried to compile the function void handle_event(SDL_Event *event), and saw a call to a method EventManager::handle_event(event);. Since the compiler thought the function was not part of the Engine class, it would expect you to call the method of a particular instance of the EventManager class, i.e.
someEventManager->handle_event(event);
As soon as you specify that the implementation you wrote is that of a method, belonging to the class Engine, the compiler essentially deduces:
void Engine::handle_event(SDL_Event *event)
{
this->EventManager::handle_event(event);
}
And therefore is happy.