php输出xml属性的方法

<?php
$xml = simplexml_load_file("books.xml");
foreach($xml->book[0]->author->attributes() AS $a => $b) {
echo "$a = $b <br />";
}
?>

<library>
<book>
<title>A</title>
<author gender="female">B</author>
<description>C</description>
</book>
<book>
<title>C</title>
<author gender="male">D</author>
<description>E</description>
</book>
<book>
<title>F</title>
<author gender="male">G</author>
<description>H</description>
</book>
</library>