代码执行错误

$mysqli=new mysqli("localhost","root","","test4");
var_dump($mysqli);

Warning: Unterminated comment starting line 16 in D:\phpStudy\WWW\MYSQL2\1.php on line 16

Warning: mysqli::__construct(): (HY000/1045): Access denied for user 'root'@'localhost' (using password: NO) in D:\phpStudy\WWW\MYSQL2\1.php on line 12

Warning: var_dump(): Property access is not allowed yet in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Property access is not allowed yet in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Property access is not allowed yet in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Property access is not allowed yet in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13

Warning: var_dump(): Couldn't fetch mysqli in D:\phpStudy\WWW\MYSQL2\1.php on line 13
object(mysqli)#1 (19) { ["affected_rows"]=> NULL ["client_info"]=> NULL ["client_version"]=> int(50012) ["connect_errno"]=> int(1045) ["connect_error"]=> string(62) "Access denied for user 'root'@'localhost' (using password: NO)" ["errno"]=> NULL ["error"]=> NULL ["error_list"]=> NULL ["field_count"]=> NULL ["host_info"]=> NULL ["info"]=> NULL ["insert_id"]=> NULL ["server_info"]=> NULL ["server_version"]=> NULL ["stat"]=> NULL ["sqlstate"]=> NULL ["protocol_version"]=> NULL ["thread_id"]=> NULL ["warning_count"]=> NULL }

D:\phpStudy>mysql -uroot -p

Enter password: ******

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 3

Server version: 5.5.53 MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its

affiliates. Other names may be trademarks of their respective

owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use test4;

Database changed

mysql>

数据库也打开了 还是不行

望解决