SetWindowLong的GWL_USERDATA


class CAsyncSocketExHelperWindow
{
public:
CAsyncSocketExHelperWindow()
{
//Create window
WNDCLASSEX wndclass;
wndclass.cbSize=sizeof wndclass;
wndclass.style=0;
wndclass.lpfnWndProc=WindowProc;
wndclass.cbClsExtra=0;
wndclass.cbWndExtra=0;
wndclass.hInstance=GetModuleHandle(0);
wndclass.hIcon=0;
wndclass.hCursor=0;
wndclass.hbrBackground=0;
wndclass.lpszMenuName=0;
wndclass.lpszClassName=_T("CAsyncSocketEx Helper Window");
wndclass.hIconSm=0; RegisterClassEx(&wndclass); m_hWnd=CreateWindow(_T("CAsyncSocketEx Helper Window"), _T("CAsyncSocketEx Helper Window"), 0, 0, 0, 0, 0, 0, 0, 0, GetModuleHandle(0));
ASSERT(m_hWnd);
SetWindowLong(m_hWnd, GWL_USERDATA, (LONG)this);  //这个意思是把this指向的对象藏在窗口地址里吗？
};
         //-------------------------------------------------------------------
static LRESULT CALLBACK WindowProc( HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam )
{
if (message>=WM_SOCKETEX_NOTIFY)
{
//Verify parameters
ASSERT(hWnd);
CAsyncSocketExHelperWindow *pWnd=(CAsyncSocketExHelperWindow *)GetWindowLong(hWnd, GWL_USERDATA);  //这里是把刚才藏在窗口里的那个对象取出来吗？？？？？？？
}