//获得系统菜单
CMenu *pMenu = GetSystemMenu(false);
//获得关闭按钮ID
UINT ID = pMenu->GetMenuItemID(pMenu->GetMenuItemCount()-1);
//使关闭按钮无效
pMenu->EnableMenuItem(ID,MF_GRAYED);

//获得系统菜单
CMenu *pMenu = GetSystemMenu(false);
//获得关闭按钮ID
UINT ID = pMenu->GetMenuItemID(pMenu->GetMenuItemCount()-1);
//使关闭按钮可用
pMenu->EnableMenuItem(ID,MF_ENABLED);

//禁用最小化按钮
void CMainFrame::OnMenudismin() 
{
        //获得窗口风格
        Style = ::GetWindowLong(m_hWnd,GWL_STYLE);
        //设置新的风格
        Style &= ~(WS_MINIMIZEBOX);
        ::SetWindowLong(m_hWnd,GWL_STYLE,Style);
        GetWindowRect(&Rect);
        //重画窗口边框
        ::SetWindowPos(m_hWnd,HWND_TOP,Rect.left,Rect.top,Rect.Width(),Rect.Height(),SWP_DRAWFRAME);
}
//使最小化按钮有效
void CMainFrame::OnMenuablemin() 
{
        //获得窗口风格
        Style = ::GetWindowLong(m_hWnd,GWL_STYLE);
        //设置新的风格
        Style |= WS_MINIMIZEBOX;
        ::SetWindowLong(m_hWnd,GWL_STYLE,Style);
        GetWindowRect(&Rect);
        //重画窗口边框
        ::SetWindowPos(m_hWnd,HWND_TOP,Rect.left,Rect.top,Rect.Width(),Rect.Height(),SWP_DRAWFRAME);
}


//禁用最大化按钮
void CMainFrame::OnMenudismax() 
{
        //获得窗口风格
        Style = ::GetWindowLong(m_hWnd,GWL_STYLE);
        //设置新的风格
        Style &= ~(WS_MAXIMIZEBOX);
        ::SetWindowLong(m_hWnd,GWL_STYLE,Style);
        GetWindowRect(&Rect);
        //重画窗口边框
        ::SetWindowPos(m_hWnd,HWND_TOP,Rect.left,Rect.top,Rect.Width(),Rect.Height(),SWP_DRAWFRAME);
}
//使最大化按钮有效
void CMainFrame::OnMenuablemax() 
{
        //获得窗口风格
        Style = ::GetWindowLong(m_hWnd,GWL_STYLE);
        //设置新的风格
        Style |= WS_MAXIMIZEBOX;
        ::SetWindowLong(m_hWnd,GWL_STYLE,Style);
        GetWindowRect(&Rect);
        //重画窗口边框
        ::SetWindowPos(m_hWnd,HWND_TOP,Rect.left,Rect.top,Rect.Width(),Rect.Height(),SWP_DRAWFRAME);
}