PHP讀寫xml

use SimpleXMLElement;
public function abc(){
            $xmlTag = array(
                'starttime',
                'endtime',
                'school'
            );
  $study = array();
            $xml = simplexml_load_file('write_sim.xml');
            foreach($xml->children() as $period) {
                $study[] = get_object_vars($period);//獲取對象全部屬性，返回數組
            }
echo '<pre>';
            print_r($study);
        }
 public function save_xml(){
            $a=[
                [
                    'starttime'=>2000,
                    'endtime'=>2001,
                    'school'=>'hao',
                    ],  [
                    'starttime'=>2002,
                    'endtime'=>2001,
                    'school'=>'hao',
                ],  [
                    'starttime'=>2003,
                    'endtime'=>2001,
                    'school'=>'hao',
                ]
            ];
//XML標籤配置
            $xmlTag = array(
                'starttime',
                'endtime',
                'school'
            );
$xml = new SimpleXMLElement('<?xml version="1.0" encoding="UTF-8"?><studentcareer />');
            foreach($a as $s) {
                $period = $xml->addChild('period');
 foreach($xmlTag as $x) {
                    $period->addChild($x, $s[$x]);
                }
            }
$xml->asXml('write_sim.xml');//輸出XML文件（沒有格式化）
            echo 'success';
        }