大侠进来帮忙看看！

在下面是WndProc数中的语句，((LPCREATESTRUCT) lParam)->hInstance据说是返回子窗口的hInstance,这句是怎么实现的啊！
源代码：
for (i = 0 ; i < NUM ; i++)
               hwndButton[i] = CreateWindow ( TEXT("button"), 
                                   button[i].szText,
                                   WS_CHILD | WS_VISIBLE | button[i].iStyle,
                                   cxChar, cyChar * (1 + 2 * i),
                                   20 * cxChar, 7 * cyChar / 4,
                                   hwnd, (HMENU) i,
                                   ((LPCREATESTRUCT) lParam)->hInstance, NULL) ;
          return 0 ;