Codeigniter with Oracle 12c

hi all,

I am new to Codeigniter, start learning because of one of our customer want the conversion of their some Oracle Forms to web app and I found it is much easier to use CI framework of PHP but one thing I can't connect / work with their Oracle database 12c Release 2. I have a VM with Win 8, Oracle DB 12c and WAMP ( latest downloaded on 10-Nov-2018 ). I searched for it and found various solution (not any of 12c), tried some but still I failed to even load data from a table.
can somebody help me, I can upload my project files if here is option and I can.
I have modified php.ini file in Apache to un-remark for line extension=oci8_12c and have entry in database.php ( 2 entries are there first for Mysql and another one for Oracle )

$active_group = 'default';  // MYSQL entry
$query_builder = TRUE;

$db['default'] = array(
    'dsn'   => '',
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => '',
    'database' => 'mydb01',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    '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
);

$active_group = 'oracle';  // Oracle entry
$query_builder = TRUE;

$db['oracle'] = array(
    'dsn'   => '',
    'hostname' => 'localhost/orclpdb',
    'username' => 'hr',
    'password' => 'hr',
    'database' => 'orclpdb',
    'dbdriver' => 'oci8',
    'dbprefix' => '',
    '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
);

more entries i tried, will show here if someone want ( or can upload files )

Please help in this matter.
regards