自身窗口句柄可用AfxGetMainWnd获取。系统中其他APP的窗口句柄可用FindWindow获取(用SPY帮一下忙)。AfxGetMainWnd获取自身窗口句柄。可用FindWindow获取系统中其他窗口句柄.

HWND hWnd = AfxGetMainWnd()->m_hWnd;
HWND hWnd =::FindWindow(NULL,"XXXXXX");

如：

HWND hBtnClose;
HWND hWnd=::FindWindow(NULL,"腾讯QQ系统广播");
if(hWnd)
{
    hBtnClose=GetDlgItem(hWnd,2);
    if(hBtnClose)
        PostMessage(hBtnClose,BM_CLICK,NULL,NULL);
}

比如查看 Internet选项 窗口是否正打开着：

hwndParent=::FindWindow("#32770","Internet属性");//(for winme)
hwndParent=::FindWindow("#32770","Internet选项");//(for winXP