CI_Config::base_url PHP Method

    public function base_url($uri = '', $protocol = NULL)
    {
        $base_url = $this->slash_item('base_url');
        if (isset($protocol)) {
            // For protocol-relative links
            if ($protocol === '') {
                $base_url = substr($base_url, strpos($base_url, '//'));
            } else {
                $base_url = $protocol . substr($base_url, strpos($base_url, '://'));
            }
        }
        return $base_url . ltrim($this->_uri_string($uri), '/');
    }

 function base_url($uri = '')
 {
     $url = parent::base_url($uri);
     if ($_SERVER['SERVER_PORT'] == 443) {
         $url = str_replace('http://', 'https://', $url);
     }
     return $url;
 }