新手发个php修改XML的问题

$dom=new DOMDocument('1.0');$dom->load('ceshi.xml');$root=$dom->getElementsByTagName('online');$root=$root->item(0);$userid=$root->getElementsByTagName('userid');foreach($userid as $b){  foreach($b->attributes as $attr){ $value=$attr->nodeValue;$name[].=$attr->nodeName;{if($value=="xiao"){     print_r($name);   } }}}$dom->save('ceshi.xml');

<?xml version="1.0"?><online> <userid time="2007-06-13 11:20:08" ip="wangqile" label="wang">xiaxin</userid> <userid time="2007-06-13 13:22:15" pp="dasdsa" label="xiao" ip="dasdsa">rwet</userid> <userid time="2007-06-13 17:17:00" ip="dasdsa" label="ji"> gaoji</userid> </online>

$dom=new DOMDocument('1.0');$dom->load('ceshi.xml');$root=$dom->getElementsByTagName('online');$root=$root->item(0);$userid=$root->getElementsByTagName('userid');foreach($userid as $b) {  if($b->attributes->getNamedItem('label')->nodeValue == 'xiao') {    foreach($b->attributes as $attr){      $res[$attr->nodeName] = $attr->nodeValue;    }    print_r($res);  }}