WMQUIT

WMQUIT, more commonly known as WM_QUIT, is a Windows message code used to signal termination of a thread’s message loop. It is not a message sent to a window procedure; instead, it is posted to the thread’s message queue to indicate that the thread should exit.

The WM_QUIT value is 0x0012 (18 decimal). It is posted by the function PostQuitMessage, which takes an exit code that is stored in the thread’s message and becomes the wParam of the WM_QUIT message. When a program’s message loop retrieves WM_QUIT, GetMessage returns 0, and the loop typically ends. The lParam value is unused, and the exit code is available in the wParam field of the MSG structure.

Usage typically involves a message loop that runs until WM_QUIT is received. A common pattern is:

GetMessage(&msg, NULL, 0, 0) > 0, then TranslateMessage(&msg); DispatchMessage(&msg); After the loop exits, the program often returns (int)msg.wParam as its exit code.

A key distinction is that WM_QUIT is thread-level and not delivered to window procedures. It is one way for an application or a single thread to request termination of its own message loop. It differs from other signals such as WM_CLOSE or WM_DESTROY, which are window-specific. PostQuitMessage affects only the thread’s queue; other threads or the process as a whole may continue running until their own workflows terminate.

See also: WM_QUIT semantics, PostQuitMessage, GetMessage, message loops in Win32 programming.