CI框架导出数据

public function excel_out(){    header("Content-type:text/html");    header("Content-Disposition:attachment;filename=123.xls");    $array=$this->db->get("city")->result_array();    $str="id\t"."name\t"."pid\n";    foreach($array as $val){        $str.=$val['id']."\t".$val['name']."\t".$val['pid']."\n";    }    echo $str;}