Link Errors in Simple SDL Engine - c++

Question

I am trying to build a simple game engine with C++ and SDL. I am going through and trying to take the things that I know work in one big .cpp file, and organizing them into more logical patterns. For example, having a Game class, that contains a Screen or Engine class, a Logic class, an Entities class, etc. Obviously doesn't need to be super advanced as I'm just trying to get a handle for the first time on setting up things logically. Unfortunately I get the linker errors:
1>game.obj : error LNK2019: unresolved external symbol "public: __thiscall Screen::~Screen(void)" (??1Screen##QAE#XZ) referenced in function "public: __thiscall Game::Game(void)" (??0Game##QAE#XZ)
1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall Game::~Game(void)" (??1Game##QAE#XZ) referenced in function _SDL_main
And the SDL is definitely set up properly, because the code executes just fine when everything is in one big file.
So far I have a Game class, and a Screen class.
game.h
#ifndef GAME_H
#define GAME_H
// Includes
#include "screen.h"
// SDL specific includes
#include "SDL.h"
class Game
{
private:
Screen screen;
public:
Game();
~Game();
};
#endif
game.cpp
#include "game.h"
Game::Game()
{
Screen screen;
}
screen.h
#ifndef SCREEN_H
#define SCREEN_H
#include "SDL.h"
class Screen
{
private:
// Screen dimension variables
int SCREEN_WIDTH, SCREEN_HEIGHT;
// --SDL object variables--
// The window we'll be rendering to
SDL_Window * window;
// The surface contained by the window
SDL_Surface * screenSurface;
public:
Screen();
~Screen();
// Functions for calling SDL objects
SDL_Window *getSDLWindow( void );
SDL_Surface *getSDLSurface( void );
};
#endif
screen.cpp
#include "screen.h"
#include <stdio.h>
Screen::Screen()
{
// Initialize window and SDL surface to null
window = NULL;
screenSurface = NULL;
// Initialize screen dimensions
SCREEN_WIDTH = 800;
SCREEN_HEIGHT = 600;
// Initialize SDL
if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
{
printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError() );
}
else
{
// Create a window
window = SDL_CreateWindow( "The First Mover", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN );
if (window == NULL)
{
printf ("Window could not be created! SDL Error: %s\n", SDL_GetError() );
}
else
{
// Get window surface
screenSurface = SDL_GetWindowSurface( window );
// Fill the surface white
SDL_FillRect( screenSurface, NULL, SDL_MapRGB( screenSurface->format, 0xFF, 0xFF, 0xFF) );
}
}
}
Any assistance appreciated! Also, if anyone has any ideas on how to better organize what I'm trying to do, feel free to comment!

Answer 1

Since you have declared the destructors for Screen and Game you need to provide definitions for them too. Add this in the Game.cpp and Screen.cpp files:
Game::~Game(){
// what ever you need in the destructor
}
Screen::~Screen(){
// what ever you need in the destructor
}
If you hadn't declared the destructors the compiler would have generated an implicitly for you.