PHP提示Deprecated: mysql_connect(): The mysql extension is

function connectit () { 
global $CFG; 
mysql_connect($CFG['db_host'], $CFG['db_user'], $CFG['db_pass']) or die(mysql_error()); 
mysql_select_db($CFG['db_name']); 
} 

$dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass); 

$link = mysqli_connect( 
 'localhost', / The host to connect to 连接MySQL地址 /   
 'user',   / The user to connect as 连接MySQL用户名 /   
 'password', / The password to use 连接MySQL密码 /   
 'world');  / The default database to query 连接数据库名称/   

if (!$link) { 
  printf("Can't connect to MySQL Server. Errorcode: %s ", mysqli_connect_error()); 
  exit; 
}