students.xml

<pre name="code" class="html"><?xml version="1.0" encoding="utf-8"?>
<students>
	<student>
		<name>小明</name>
		<age>20</age>
		<introduce>来自广东</introduce>
	</student>
	<student>
		<name>小花</name>
		<age>21</age>
		<introduce>来自北京</introduce>
	</student>

</students>

stu_update_dom.PHP

<?PHP

$xmldoc = new DOMDocument();	//1.创建DOMDocument对象
$xmldoc->load("students.xml");	//2.加载xml文件

//更新一个学生信息
$root = $xmldoc->getElementsByTagName("students")->item(0);    //取出根节点

//找到所有student
$stus = $xmldoc->getElementsByTagName("student");
$stu = $stus->item(1);	//确定要更新的student编号
$stu_age = $xmldoc->getElementsByTagName("age")->item(0);	//定位好更新的Tag
$stu_age->nodeValue+=10;	//更新age数据


//如果save是源文件名，则会对文件做更新处理
//如果save是新文件名，则会按文件名创建文件并保存
$xmldoc->save("students.xml");
?>

<?xml version="1.0" encoding="utf-8"?>
<students>
	<student>
		<name>小明</name>
		<age>30</age>
		<introduce>来自广东</introduce>
	</student>
	<student>
		<name>小花</name>
		<age>21</age>
		<introduce>来自北京</introduce>
	</student>

</students>