/**
 * 将xml转为array
 * @param string  $xml xml字符串或者xml文件名
 * @param bool   $isfile 传入的是否是xml文件名
 * @return array  转换得到的数组
 */
function xmlToArray($xml,$isfile=false){
  //禁止引用外部xml实体
  libxml_disable_entity_loader(true);
  if($isfile){
    if(!file_exists($xml)) return false;
    $xmlstr = file_get_contents($xml);
  }else{
    $xmlstr = $xml;
  }
  $result= json_decode(json_encode(simplexml_load_string($xmlstr, 'SimpleXMLElement', LIBXML_NOCDATA)), true);
  return $result;
}

$xmlDoc=<<<ETO
<books>
 <book>
 <author>Jack Herrington</author>
 <title>PHP Hacks</title>
 <publisher>O'Reilly</publisher>
 </book>
 <book>
 <author>Jack Herrington</author>
 <title>Podcasting Hacks</title>
 <publisher>O'Reilly</publisher>
 </book>
 <book>
 <author>XML格式化</author>
 <title>在线工具</title>
 <publisher>tools.jb51.net</publisher>
 </book>
</books>
ETO;
$relarr=xmlToArray($xmlDoc);
print_r($relarr);

Array
(
  [book] => Array
    (
      [0] => Array
        (
          [author] => Jack Herrington
          [title] => PHP Hacks
          [publisher] => O'Reilly
        )
      [1] => Array
        (
          [author] => Jack Herrington
          [title] => Podcasting Hacks
          [publisher] => O'Reilly
        )
      [2] => Array
        (
          [author] => XML格式化
          [title] => 在线工具
          [publisher] => tools.jb51.net
        )
    )
)

/**
 * 数组转xml字符
 * @param string  $xml xml字符串
**/
function arrayToXml($data){
  if(!is_array($data) || count($data) <= 0){
    return false;
  }
  $xml = "<xml>";
  foreach ($data as $key=>$val){
    if (is_numeric($val)){
      $xml.="<".$key.">".$val."</".$key.">";
    }else{
      $xml.="<".$key."><![CDATA[".$val."]]></".$key.">";
    }
  }
  $xml.="</xml>";
  return $xml;
}

$arrDoc= array("author"=>"XML格式化","title"=>"在线工具","publisher"=>"tools.jb51.net");
$xmlrel=arrayToXml($arrDoc);
//运行结果：<xml><author><![CDATA[XML格式化]]></author><title><![CDATA[在线工具]]></title><publisher><![CDATA[tools.jb51.net]]></publisher></xml>