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>