Using Raw vs. Smart Pointers for SDL Resources

Yes, SDL_Window* is a raw C-style pointer. SDL is fundamentally a C library, and its API is designed around C idioms, which heavily rely on raw pointers for managing resources like windows, renderers, surfaces, textures, etc.

When you call SDL_CreateWindow(), SDL allocates memory and resources for the window and returns a raw pointer to the opaque SDL_Window structure that represents it. You, the programmer, are then responsible for managing the lifetime of this resource and ensuring SDL_DestroyWindow() is called with that pointer when the window is no longer needed.

1// Raw pointer management (as shown in the lesson)
2class Window {
3public:
4  Window() {
5    SDLWindow = SDL_CreateWindow(/* ... */);
6  }
7  
8  ~Window() {
9    if (SDLWindow) {
10      // Manual cleanup
11      SDL_DestroyWindow(SDLWindow); 
12    }
13  }
14  // Prevent copying (Rule of 3/5)
15  Window(const Window&) = delete;
16  Window& operator=(const Window&) = delete;
17  // Potentially handle moves too
18
19private:
20  // Raw pointer
21  SDL_Window* SDLWindow{nullptr}; 
22};

This manual management requires care:

• You must remember to call SDL_DestroyWindow().
• You must handle copying and moving correctly (Rule of Three/Five) to prevent double-frees or dangling pointers.
• You need to be careful about exceptions - if an exception occurs after resource acquisition but before the delete/SDL_DestroyWindow call, the resource might leak unless you use techniques like RAII.

Using Smart Pointers (std::unique_ptr)

Modern C++ strongly encourages the use of smart pointers (like std::unique_ptr and std::shared_ptr) to automate resource management through the RAII (Resource Acquisition Is Initialization) principle. Smart pointers automatically manage the lifetime of the resource they own, ensuring cleanup happens correctly, even in the presence of exceptions.

We can wrap the raw SDL_Window* in a std::unique_ptr with a custom deleter. std::unique_ptr guarantees exclusive ownership and automatically calls its deleter when it goes out of scope.

Here's how you could adapt the Window class:

1#include <SDL.h>
2#include <memory> // Required for std::unique_ptr
3
4// Define a custom deleter for SDL_Window*
5struct SDLWindowDeleter {                
6  void operator()(SDL_Window* window) const { 
7    if (window) {                       
8      SDL_DestroyWindow(window);        
9      // Optional: Log window destruction
10    }
11  }
12};
13
14// Alias for convenience
15using UniqueSDLWindow =
16  std::unique_ptr<SDL_Window, SDLWindowDeleter>; 
17
18class Window {
19public:
20  Window() {
21    // Create window and immediately
22    // transfer ownership to unique_ptr
23    SDL_Window* rawPtr{SDL_CreateWindow(
24      "Smart Pointer Window",
25      SDL_WINDOWPOS_UNDEFINED,
26      SDL_WINDOWPOS_UNDEFINED,
27      800, 600, 0
28    )};
29    if (!rawPtr) {
30      // Handle creation failure (e.g., throw exception)
31      // Log SDL_GetError()
32    }
33    // Store in smart pointer
34    SDLWindow = UniqueSDLWindow(rawPtr); 
35  }
36
37  // No explicit destructor needed! // <h>
38  // ~Window() is no longer required; unique_ptr handles cleanup.
39
40  // Rule of 0: If resource is managed by RAII wrapper,
41  // default special members often work or are implicitly deleted.
42  // unique_ptr is non-copyable by default, so copy operations
43  // are implicitly deleted. Move operations are defaulted.
44  // Window(const Window&) = delete; // Implicitly deleted
45  // Window& operator=(const Window&) = delete; // Implicitly deleted
46  // Window(Window&&) = default; // Implicitly defaulted
47  // Window& operator=(Window&&) = default; // Implicitly defaulted
48
49
50  // Need a way to get the raw pointer for other SDL functions
51  SDL_Window* GetRaw() const { 
52    return SDLWindow.get();
53  }
54
55private:
56  // Store the window resource in a unique_ptr
57  UniqueSDLWindow SDLWindow{nullptr};  // Smart pointer
58};

Advantages of std::unique_ptr****:

• Automatic Cleanup: No need for an explicit destructor to call SDL_DestroyWindow. The SDLWindowDeleter is called automatically when the Window object is destroyed.
• Exception Safety: If an exception occurs during the Window object's lifetime, the unique_ptr destructor still runs, ensuring the SDL_Window is cleaned up (stack unwinding).
• Clear Ownership: std::unique_ptr expresses exclusive ownership, making the code's intent clearer. Copying is prevented by default. Moving is allowed and correctly transfers ownership.
• Rule of Zero: Often, when all resources are managed by RAII objects like smart pointers, the class doesn't need any user-defined special member functions (destructor, copy/move operations), simplifying the class design.

Should you use them? Using smart pointers is generally considered best practice in modern C++. It makes resource management safer and often simpler. However, when learning SDL, which is a C library, you will encounter its C-style API directly. Seeing the raw pointer management first can help understand what SDL expects and why smart pointers are beneficial. This course may initially stick closer to the C API style before introducing C++ wrappers like smart pointers.