$base_url = ((isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == "on") ? "https" : "http");
$base_url .= "://". @$_SERVER['HTTP_HOST'];
$base_url .= str_replace(basename($_SERVER['SCRIPT_NAME']),"",$_SERVER['SCRIPT_NAME']);
$config['base_url'] = $base_url;
defined('BASE_URL') OR define('BASE_URL', (is_https() ? 'https://' : 'http://') . $_SERVER['HTTP_HOST'] . dirname($_SERVER['SCRIPT_NAME']) . '/');
$config['base_url'] = BASE_URL;
$this->load->helper('url');
$config['base_url'] = "http://".$_SERVER['SERVER_NAME']."/project_name/";
this way you config you base_url , then won't worry about in hosting. both works in localhost and server.
$base_url = ((isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == "on") ? "https" : "http");
$base_url .= "://". @$_SERVER['HTTP_HOST'];
$base_url .= str_replace(basename($_SERVER['SCRIPT_NAME']),"",$_SERVER['SCRIPT_NAME']);
$config['base_url'] = $base_url;