if(!$this->session->userdata('userid') || $this->session->userdata('userid') == '')
{
echo "<script language=\"javascript\">alert('请登录后操作!')</script>";
redirect('');
}
if($this->session->userdata('roleid') < 10) //或者其他条件
{
echo "<script language=\"javascript\">alert('您无权限进行此操作!')</script>";
}