怎么通过ip获取域名？

function getContent($url){  
    $content=file_get_contents($url);  
    return $content;  
}  
 
function getResult($ip){  
    $pagesize=10;  
    $page=1;  
    $url="http://cn.bing.com/search?q=ip%3A$ip&first=$page";  
    $result=array();  
    do 
    {  
        $url="http://cn.bing.com/search?q=ip%3A$ip&first=$page";  
        $content=getContent($url);  
        $pattern="/([a-zA-Z0-9\.]*)(?:\/.*)?<\/cite>/isU";  
        preg_match_all($pattern, $content, $matches);  
        $result=array_merge($result,$matches[1]);  
        $nextpage=strpos($content, "下一页");  
        $page=$page+$pagesize;  
    }while($nextpage);  
      
    $result=array_values(array_unique($result));  
      
    return $result;  
}  
 
// 调用方法
$result=getResult("220.181.111.85");
//$result=getResult("117.79.93.222");//csdn
echo "
";
print_r($result);