HWND

An hWnd is a handle to a window in the Win32 API. In Windows programming, HWND is a typedef that represents a window object. An hWnd is an opaque, pointer-sized value that identifies a particular window within a thread's message queue. The handle is obtained when a window is created or found (for example, via CreateWindowEx, CreateWindow, or FindWindow). The operating system uses the hwnd to deliver events and messages to the window's window procedure (WndProc). The WndProc receives a parameter of type HWND, which identifies the window receiving the message.

A window's lifetime is managed by the system. It exists from creation until DestroyWindow or until its owning thread terminates and the window is destroyed. After destruction, the handle may be recycled for other windows, so it must not be assumed valid. Developers can test with IsWindow or store data with SetWindowLongPtr (GWLP_USERDATA) to help manage lifecycle and state.

Windows are associated with a thread; messages for a window are processed by that thread's message queue. Sending messages to windows on other threads is possible via SendMessage or PostMessage, but cross-thread SendMessage may block and requires careful synchronization. Generally, PostMessage is preferred when crossing threads to avoid deadlocks.

HWND is distinct from other Windows handles such as HINSTANCE, HMENU, or HBITMAP. It is not a direct pointer to an object in memory but an opaque identifier that the system uses to locate the window and dispatch messages.