How can I use PDO in CodeIgniter 2?

I would like to use PDO instead of the built-in database-classes. But how can I do it? I tried to do the modifications suggested in a blog post. I commented out a part of system\database\DB.php and also added:

$DB = new PDO(
$params['dbdriver'].':host='.$params['hostname'].';dbname='.$params['database'],
$params['username'], $params['password']);

return $DB;

But now my PHP-code crashes if I do $this->load->database(); in a Controller. So how should I use PDO and execute database queries using PDO in CodeIgniter?

I have also tried to use this code in a Controller:

foreach($this->db->query('SELECT * FROM users') as $row) {
    开发者_高级运维print_r($row);
}

but it didn't work.

$stmt = $this->db->prepare("SELECT * FROM users");  
$stmt->execute();  
foreach ($stmt->fetch(PDO::FETCH_ASSOC) as $row) {
      print_r($row);
}

Or:

foreach ($this->db->query("SELECT * FROM users") as $row) {  
     print_r($row)."\n";
}    

Learn more about 3 PDO database calls here...

PDO Query
PDO Exec
PDO Prepare

EDIT: Also check your app/config/database.php file for the following settings:

$active_group = 'default';  
$active_record = FALSE;  

$db['default']['hostname'] = 'YOURHOSTNAME';  
$db['default']['username'] = 'YOURUSERNAME';  
$db['default']['password'] = 'YOURPASSWORD';  
$db['default']['database'] = 'YOURDATABASE';  
$db['default']['dbdriver'] = 'mysql';  
$db['default']['dbprefix'] = '';  
$db['default']['pconnect'] = TRUE;  
$db['default']['db_debug'] = TRUE;  
$db['default']['cache_on'] = FALSE;  
$db['default']['cachedir'] = '';  
$db['default']['char_set'] = 'utf8';  
$db['default']['dbcollat'] = 'utf8_general_ci';  
$db['default']['swap_pre'] = '';  
$db['default']['autoinit'] = TRUE;  
$db['default']['stricton'] = FALSE;