You need not to change anything from files inside CODEIGNITER system folder. Codeigniter allows developer to extend their feature. You can create a file named as MY_Router.php.
<?php
class MY_Router extends CI_Router {
protected function _set_default_controller() {
if (empty($this->default_controller)) {
show_error('Unable to determine what should be displayed. A default route has not been specified in the routing file.');
}
if (sscanf($this->default_controller, '%[^/]/%s', $class, $method) !== 2) {
$method = 'index';
}
if( is_dir(APPPATH.'controllers/'.$class) ) {
$this->set_directory($class);
$class = $method;
if (sscanf($method, '%[^/]/%s', $class, $method) !== 2) {
$method = 'index';
}
}
if ( ! file_exists(APPPATH.'controllers/'.$this->directory.ucfirst($class).'.php')) {
return;
}
$this->set_class($class);
$this->set_method($method);
$this->uri->rsegments = array(
1 => $class,
2 => $method
);
log_message('debug', 'No URI present. Default controller set.');
}
}
Note: Do not change the file name.