我如何使用 function 返回成员数据的地址

Question

i have my Engine class that contains the SDL_renderer* and I've been trying to get its address by using a function getRenderer but it returns null beside the fact that i have already initialize it (renderer) in the Engine.cpp

class Engine
{
    public:
      SDL_Renderer* GetRenderer() { return m_renderer; } // null

      Engine() {}
      ~Engine() {}
private:
    bool m_Running = true;

   SDL_Window* m_window;
   SDL_Renderer* m_renderer;
 };


bool Engine::init()
{
   // initialize SDL
   if (SDL_Init(SDL_INIT_EVERYTHING) >= 0)
   {
      // if succeeded create our window
      m_window = SDL_CreateWindow("the title", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
          SDL_WIDTH, SDL_HEIGHT, false);

      Engine* engine = new Engine();
      std::cout << engine->GetRenderer() << std::endl;
      if (m_window != nullptr)
      {
          std::cout << "entering this";
          m_renderer = SDL_CreateRenderer(m_window, -1, 0);
      }
      else
      {
          return false; // sdl could not initialize
      }
      std::cout << m_renderer<< std::endl; // this is not null
      std::cout << engine->GetRenderer()<<std::endl; // this is null

      textureManager = new TextureManager();
      textureManager->Load("tree", "Assets/tree.png"); // tree for tree texture
      m_Running = true;
      return true;
  }
 }

Answer 1

Usually, when you run your C++ app in debug mode, it "clears" (set's to 0) all the uninitialized variables (not necessarily BTW). If you try to compile and run in release mode, you might get a non-zero value from the function. That's why it is always recommended and necessary to initialize your variables in the constructor. Even more, if you have a member raw pointer, you should be very careful, and consider having proper constructors and destructors.

Edit

In your case, at least, I would suggest to initialize the variables and set them to be nullptr in the constructors initializer-list and then call Init directly from the constructor.

Maybe, there's a better solution, but this can be considered as a quick fix.

Edit 2

Worths to be mentioned the comment below: DONT FORGET ABOUT COPY AND MOVE CONSTRUCTORS