$main_url = $rs['host'];     if(!strcmp(long2ip(sprintf('%u', ip2long($main_url))), $main_url)) {         return $main_url;     } else {         $arr = explode('.', $main_url);         $count = count($arr);         $endArr = array('com', 'net', 'org'); //com.cn net.cn 等情况         if (in_array($arr[$count - 2], $endArr)){             $domain = $arr[$count - 3] . '.' . $arr[$count - 2] . '.' . $arr[$count - 1];         } else {             $domain = $arr[$count - 2] . '.' . $arr[$count - 1];         return $domain;

参考： http://blog.csdn.net/hanjinchun2009/article/details/4757520