ci3使用PDO连接数据库

$db['default'] = array(
    'dsn'    => "mysql:host=localhost;dbname=test;charset=utf8",//设置数据库连接字符串
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => 'root',
    'database' => 'test',
    'dbdriver' => 'pdo',            //修改数据库驱动
    'dbprefix' => 'c_',
    'pconnect' => FALSE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

function show()
    {
        $pdo = $this->db->connect();                //建立对数据库的连接。
        $pdo = $this->db->db_pconnect(true);        //建立对数据库的连接，使用持久连接
        $sql = "select * from c_news";
        $res = $pdo->query($sql);
        $lst = $res->fetchAll();
        p($lst);
    }