public function responseMsg()
{
 global $db;
 //get post data, May be due to the different environments
 $postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
 $postObj = simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
 writeover("msg.txt",$postStr."rn","a+");
 //。。。。。
}

<xml><ToUserName><![CDATA[gh_a64528aca3b]]></ToUserName>
<FromUserName><![CDATA[oSgH_jveTxJSlFK_6QSiGeVaSyk]]></FromUserName>
<CreateTime>1394705044</CreateTime>
<MsgType><![CDATA[text]]></MsgType>
<Content><![CDATA[ha]]></Content>
<MsgId>5990212551746www.phpfensi.com353512</MsgId>
</xml>

<xml><ToUserName><![CDATA[gh_a5218aca3b]]></ToUserName>
<FromUserName><![CDATA[oSgH_jveTxJSlFK_6QSiGeVyk]]></FromUserName>
<CreateTime>1394706271</CreateTime>
<MsgType><![CDATA[event]]></MsgType>
<Event><![CDATA[subscribe]]></Event>
<EventKey><![CDATA[]]></EventKey>
</xml>

function writeover2($filename,$data,$method="rb+",$iflock=1)
{
 @touch($filename);/*文件不存在则创建之.可以采用file_exists验证并其他创建文件函数代替.测试结果效率相当*/
 $handle=@fopen($filename,$method);
 if($iflock){
  flock($handle,LOCK_EX);
 }
 fwrite($handle,$data);
 if($method=="rb+") ftruncate($handle,strlen($data));
 fclose($handle);
}