$conDB = mysqli_connect("localhost","user",'pass',"name");
 
 $forum_user =(explode(".",$_SERVER['HTTP_HOST']));
$user = $forum_user[0];
 
 $selectDB = $conDB->query("SELECT * FROM forums WHERE domain = '$user' ");
 $fetchDB = mysqli_fetch_assoc($selectDB);
 
    $sDB = $fetchDB['domaine']; 

    $oldDB = "forum_".$user; 

if($sDB == $user){
    $config['db']['name'] = $oldDB ;
    
}

$config['db']['server'] = 'localhost';
$config['db']['username'] = 'user';
$config['db']['password'] = 'pass';
$config['db']['prefix'] = 'pbb_';
$config['db']['dbtype'] = 'mysqli';