C++ SDL: Undefined reference to Game::Game()?

**DecoratorFawn82** · 09-24-2013

I'm reading the book SDL Game Development. And where going to do this step. And then I'm got stuck my compiler complained about that Game::Game() was undefined? And I'm not really sure what's wrong?

I know that I have both main.cpp and Game.h in the same directory so it cannot be that, that is wrong.

What does a "undefined reference" error even mean?

The main.cpp file

Code:

#include <iostream>
#include "SDL.h"
#include "Game.h"


using namespace std;


Game *g_game = 0;


int main(int argc, char* argv[])
{
    g_game = new Game();
    return 0;
}

The Game.h file

Code:

#ifndef GAME_H_INCLUDED
#define GAME_H_INCLUDED


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


        // Initialize
        void init() {m_bRunning = true;}




        void render() {}
        void update() {}
        void handleEvents() {}


        // To access the private running variable
        bool running() {return m_bRunning;}


    private:
        bool m_bRunning;
};


#endif // GAME_H_INCLUDED

**laserlight** · 09-24-2013

Where did you define the member functions of the Game class? Maybe it is that source file that was not included in the project, or otherwise compiled and linked.

**DecoratorFawn82** · 09-24-2013

In the main.cpp file. Is all of the member functions of the Game class. But I find that I don't have to use yet: g_game = new Game(); But however I have included the member functions in the main.cpp file. Should I create a Game.cpp file for the constructor and deconstructor? To initialize them?

**laserlight** · 09-24-2013

Originally Posted by DecoratorFawn82

In the main.cpp file. Is all of the member functions of the Game class.

Since you did not show that part of your main.cpp file, I find it plausible that you may be mistaken, e.g., you forgot to define the default constructor.

Originally Posted by DecoratorFawn82

But I find that I don't have to use yet: g_game = new Game();

What do you mean?

Originally Posted by DecoratorFawn82

Should I create a Game.cpp file for the constructor and deconstructor? To initialize them?

We say "define", not "initialize" here. Also, "destructor", not "deconstructor". Anyway, I would likely have a separate game.cpp file for all the member function definitions of the Game class (at least those member functions that were not defined inline in the class definition), not just the constructor and destructor.

**rogster001** · 09-24-2013

What does a "undefined reference" error even mean?

If you don't know what that might be telling you then i think you might be running before you can walk.

The definition of the constructor (or other functions) is the working code that defines what your function does - You could if you really wanted write it into the class without adding it to another source file, i would not do that very often personally but you do see this in tutorials about class basics for example. Also a constructor is special in that if you don't define one then a default is provided for you.

**DecoratorFawn82** · 09-24-2013

OK thanks! And sorry if I'm used wrong words or spelled any words wrong. But you got what I mean however

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