2.在系统菜单中添加菜单项
int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
{ .
  .
  .
   CMenu *pMenu=GetSystem(FALSE);//获得一个指向系统菜单的指针
   pMenu->AppendMenu(MF_SEPARATOR);//添加分隔线
   pMenu->AppendMenu(MF_STRING,ID_SYSMENU_ABOUT,"About");//添加系统菜单项
    return 0;
}


3.消息处理，对应的是WM_SYSCOMMAND消息
 (1)在CMAINFRAME的头文件中添加
   protected:
//{{AFX_MSG(CMainFrame)
     afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct);
     afx_msg void OnSysCommand(UINT nID,LPARAM lParam);//要添加的代码
 (2)添加消息映射
    BEGIN_MESSAGE_MAP(CMainFrame, CFrameWnd)
   //{{AFX_MSG_MAP(CMainFrame)
   // NOTE - the ClassWizard will add and remove mapping macros here.
   //  DO NOT EDIT what you see in these blocks of generated code !
ON_WM_CREATE()
ON_WM_SYSCOMMAND()//添加的代码
   /