CODEWITHSUNDEEP
c++stdmove-semanticsunique-ptr
Lea Hayes
Lea Hayes

Reputation: 64196

How to change ownership of pointer in C++'11?

I would like to store a pointer to my native window instance using unique_ptr<NativeWindow> so that it is guaranteed to be freed when Window object goes out of scope.

// This would be maintained by a window manager
unique_ptr<Window> window;

void Foo() {
    NativeWindow *pNativeWindow = createNativeWindow();
    window = new Window(pNativeWindow);
}

// ...

class Window {
private:
    unique_ptr<NativeWindow> _nativeWindow;
public:
    inline NativeWindow& GetNativeWindow() {
        return *_nativeWindow;
    }

// ...

Window::Window(NativeWindow&& nativeWindow)
    : _nativeWindow(std::move(nativeWindow))
{
}

I am having a hard time understanding the move semantics and would find it easier to learn from this example. If this were vanilla pointers I would be fine, but I am trying to understand the new way!

Upvotes: 0

Views: 621

Answers (1)

Praetorian
Praetorian

Reputation: 109119

The Window constructor should be taking a NativeWindow *, not NativeWindow&&. 

Window::Window(NativeWindow* nativeWindow)
    : _nativeWindow(nativeWindow)
{
}

That should work, but I suggest you change the parameter to unique_ptr<NativeWindow> instead. This makes it clear that the Window object is assuming ownership of the NativeWindow argument.

Window::Window(std::unique_ptr<NativeWindow> nativeWindow)
    : _nativeWindow(std::move(nativeWindow))
{
}

Upvotes: 2

Related Questions