[Win32 API] DefWindowProc Function

Calls the default window procedure to provide default processing for any window messages that an application does not process. This function ensures that every message is processed. DefWindowproc is called with the same parameters recieved by the window procedure.

Syntax

LRESULT WINAPI DefWindowProc(
  __in  HWND hWnd,
  __in  UINT Msg,
  __in  WPARAM wParam,
  __in  LPARAM lParam
);

Parameters

Same as WindowProc Function.

Return Value

The return value is the result of the message processing and depends on the message.

Reference : http://msdn.microsoft.com/en-us/library/ms633572(VS.85).aspx