Passing objects as parameters by another object visual c++ - object

Question

I'm trying to pass an object by reference in c++. I get these errors:
Error 1 error C2061: syntax error : identifier 'Common' graphics.h 6 1 SDLGameDev
Error 2 error C2511: 'void Graphics::CreateWindow(Common &)' : overloaded member function not found in 'Graphics' 4 1 SDLGameDev
I found answers about this area, but not any that covers how to do this:
object1.someFunction(object2);
Here is my code:
//Common.h
#ifndef COMMON_H
#define COMMON_H
#include "SDL.h"
#include "iostream"
class Common{
public:
void Init();
bool GetGameRunState(){ return GameRunState; }
void SetGameRunState(bool x){ GameRunState = x; }
private:
bool GameRunState;
};
#endif
//Commmon.cpp
#include "Common.h"
void Common::Init()
{
if (SDL_Init(SDL_INIT_EVERYTHING) == 0)
{
SetGameRunState(true);
}
else
{
SetGameRunState(false);
}
}
//Graphics.h
#ifndef GRAPHICS_H
#define GRAPHICS_H
class Graphics{
public:
void CreateWindow(Common & co);
};
#endif
//Graphics.cpp
#include "Graphics.h"
#include "Common.h"
void Graphics::CreateWindow(Common & co)
{
if (co.GetGameRunState() == true)
{
std::cout << "TEST for CreateWindow()\n";
}
}
//main.cpp
#include "Common.h"
#include "Graphics.h"
Common co;
Graphics go;
int main(int argc, char * args[])
{
co.Init();
go.CreateWindow(co);
while (co.GetGameRunState() == true)
{
std::cout << "Game is running\n";
SDL_Delay(2000);
break;
}
return 0;
}

Answer 1

You haven't included Common.h in the file Graphics.h so it doesn't know about the class.
#ifndef GRAPHICS_H
#define GRAPHICS_H
#include "Common.h" // You need this line
class Graphics {
public:
void CreateWindow(Common & co);
};
#endif

Answer 2

I would recommend using singletons and put the initialisation of sdl, creation of the renderer and window etc all together in one class. Your question has already been answered.