根据链接地址获取域名

	// 根据链接地址获取域名
	public static function getRootDomain($url) {
		$ohurl = $ohip = array ();
		$url = $url . "/";
		preg_match ( "/((\w*):\/\/)?\w*\.?([\w|-]*\.(com.cn|net.cn|gov.cn|org.cn|com|net|cn|org|asia|tel|mobi|me|tv|biz|cc|name|info))\//i", $url, $ohurl );
		if (! isset ( $ohurl [3] ) || $ohurl [3] == '') {
			preg_match ( "/((\d+\.){3}\d+)\//", $url, $ohip );
			return isset ( $ohip [1] ) ? $ohip [1] : '';
		}
		return $ohurl [3];
	}