为什么会出现这个异常

class db{? 

????????private $_link;

??????????

????????function __construct($dbhost='localhost',$dbuser='root',$dbpassword='',$dbname='test',$charset='utf-8') {? 

????????????$this->_link = mysql_connect($dbhost,$dbuser,$dbpassword,true);? 

????????????$this->_link or $this->errmsg('无法连接MYSQL服务器！');? 

????????????if ($this->version() > '4.1') {????????????????? 

????????????????$this->query('set names '.$charset);???????? 

????????????}? 

????????????

????????????mysql_select_db($dbname,$this->_link) or $this->errmsg('无法连接数据库！');? 

????????}? 

??????????

????????

????????public function query($sql) {?????????????????????????????????????????????????????????????? 

????????????$result = mysql_query($sql,$this->_link);? 

????????????$result or $this->errmsg('执行SQL语句错误！');? 

????????????return $result;? 

????????} 

???????????

????????

????????

????????

????????

????????public function fetch_array($result,$type = MYSQL_ASSOC) {

????????????return mysql_fetch_array($result,$type);???? 

????????} 

???????????

????????

????????public function fetch_object($result) {? 

????????????return mysql_fetch_object($result);? 

????????} 

???????????

????????

????????public function affected_rows() {? 

????????????return mysql_affected_rows($this->_link);? 

????????}? 

??????????

????????

????????public function free_result($result) {? 

????????????return mysql_free_result($result);?? 

????????}? 

??????????

????????

????????public function num_rows($result) {? 

????????????return mysql_num_rows($result);? 

????????}

????????????

????????

????????public function num_fields($result) {? 

????????????return mysql_num_fields($result);? 

????????}? 

??????????

????????

????????public function insert_id() {? 

????????????return mysql_insert_id($this->_link);? 

????????} 

???????????

????????

????????private function errmsg($msg) {? 

????????????$message? = '一个MySQL错误发生！
';? 

????????????$message .= '错误号：'. mysql_errno($this->_link) .'
';? 

????????????$message .= '错误描述：'. $msg . mysql_error($this->_link) .'
';? 

????????????$message .= '错误时间：'. date('Y-m-d H:i:s');? 

????????????exit($message);? 

????????} 

???????????

????????

????????public function link_id() {? 

????????????return $this->_link;? 

????????}

????????????

????????

????????public function version() {? 

????????????return mysql_get_server_info($this->_link);? 

????????}? 

??????????

????????

????????function getip() {? 

????????????if(getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown")) {? 

????????????????$ip = getenv("HTTP_CLIENT_IP");? 

????????????}elseif(getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown")) {?