php通过正则表达式记取数据来读取xml的方法

<?xml version="1.0 encoding="UTF-8"?>
<humans>
<zhangying>
<name>张映</name>
<sex>男</sex>
<old>28</old>
</zhangying>
<tank>
<name>tank</name>
<sex>男</sex>
<old>28</old>
</tank>
</humans>

<?php
$xml = "";
$f = fopen('person.xml', 'r');
while($data = fread($f,4096)){
$xml .= $data;
}
fclose( $f );
// 上面读取数据
preg_match_all("/<humans>(.*?)</humans>/s",$xml,$humans);
//匹配最外层标签里面的内容
foreach( $humans[1] as $k=>$human )
{
preg_match_all("/<name>(.*?)</name>/",$human,$name);
//匹配出名字
preg_match_all("/<sex>(.*?)</sex>/",$human,$sex);
//匹配出性别
preg_match_all("/<old>(.*?)</old>/",$human,$old);
//匹配出年龄
}
foreach($name[1] as $key=>$val){
echo $val." - ".$sex[$key][1]." - ".$old[$key][1]."<br>" ;
}
?>