1.cpp

//Variable declaration in the class
static std::unique_ptr<SDL_Window, void (*)(SDL_Window*)> mWindow;

//Assignment of a value to the variable
//I create a unique pointer of the same type with the data I want and then swap it with the member variable
std::unique_ptr<SDL_Window, void (*)(SDL_Window*)> win(SDL_CreateWindow(title.c_str(), 100, 100, 
	SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE), SDL_DestroyWindow);
std::swap(win, mWindow);