Como conectar o CodeIgniter no Oracle?

Coloque isso no arquivo: system/application/config/database.php

$active_group = “default”;
$active_record = TRUE;
$dbhost = “172.18.3.226”;    //host 
$dbport= “1521”;          //port default is 1521 
$dbname = “testing”;        //name of database   
$dbuser = “testuser”;      //db user with all priviliges
$dbpassword = “testuser”;    // password of user
$dbConnString = “(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = “. $dbhost .”)(PORT = “. $dbport .”))
)(CONNECT_DATA =(SERVICE_NAME = “. $dbname .”)))”;    // connection string for this we must create TNS entry for Oracle 
$db[‘default’][‘hostname’] = $dbConnString;
$db[‘default’][‘username’] = $dbuser;
$db[‘default’][‘password’] = $dbpassword;
$db[‘default’][‘database’] = “”;
$db[‘default’][‘dbdriver’] = “oci8”;
$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”;

Outra forma que deu certo:

$active_group = 'default';
$active_record = TRUE;

$tnsname = '(DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
(CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = XE)))';

$db['default']['hostname'] = $tnsname;
$db['default']['username'] = 'XXXXXX';
$db['default']['password'] = 'XXXXX';
$db['default']['database'] = '';
$db['default']['dbdriver'] = 'oci8';
$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;