Connect Codeigniter to Oracle 11g

In your config's database.php make the following changes

$active_group = 'default';$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;

change default to XE

$active_group = 'XE';$active_record = TRUE;$tnsname = '(DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))        (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = XE)))';$db['XE']['hostname'] = $tnsname;$db['XE']['username'] = 'XXXXXX';$db['XE']['password'] = 'XXXXX';$db['XE']['database'] = '';$db['XE']['dbdriver'] = 'oci8';$db['XE']['dbprefix'] = '';$db['XE']['pconnect'] = TRUE;$db['XE']['db_debug'] = TRUE;$db['XE']['cache_on'] = FALSE;$db['XE']['cachedir'] = '';$db['XE']['char_set'] = 'utf8';$db['XE']['dbcollat'] = 'utf8_general_ci';$db['XE']['swap_pre'] = '';$db['XE']['autoinit'] = TRUE;$db['XE']['stricton'] = FALSE;

try to do this changeschange the hostname to http://localhost:1521:orclyou are given database name as orcl , by default orcl is default instance id.try to create new user or database and change it in to the configuration database.