使用_remap（）函数。这允许您对404错误执行一些非常强大的操作，这些操作超出了通常内置的范围，例如

• Different 404 messages depending if the user is logged in or not!
• Extra logging of 404 errors - you can now see what the referring person was to the 404, thus helping track down errors. This includes seeing if it was a bot (such as Google bot) - or if it was a logged in user, which user caused the 404 (so you can contact them for more information - or ban them if they are trying to guess admin routes or something)
• Ignore certain 404 errors (such as a precomposed.png error for iPhone users).
• Allow certain controllers to handle their own 404 errors different if you have a specific need (i.e. allow a blog controller to reroute to the latest blog for example)

让您的所有控制器扩展MY_Controller：

class MY_Controller extends CI_Controller
{
    // Remap the 404 error functions
    public function _remap($method, $params = array())
    {
        // Check if the requested route exists
        if (method_exists($this, $method))
        {
            // Method exists - so just continue as normal
            return call_user_func_array(array($this, $method), $params);
        }

        //*** If you reach here you have a 404 error - do whatever you want! ***//

        // Set status header to a 404 for SEO
        $this->output->set_status_header( 404 );


        // ignore 404 errors for -precomposed.png errors to save my logs and
        // stop baby jesus crying
        if ( ! (strpos($_SERVER[ REQUEST_URI ],  -precomposed.png )))
        {
            // This custom 404 log error records as much information as possible
            // about the 404. This gives us alot of information to help fix it in
            // the future. You can change this as required for your needs   
            log_message( error ,  404:  ***METHOD:  .var_export($method, TRUE).   ***PARAMS:  .var_export($params, TRUE).   ***SERVER:  .var_export($_SERVER, TRUE).  ***SESSION:  .var_export($this->session->all_userdata(), TRUE));
        }

        // Check if user is logged in or not
        if ($this->ion_auth->logged_in())
        {
            // Show 404 page for logged in users
            $this->load->view( 404_logged_in );
        }
        else
        {
            // Show 404 page for people not logged in
            $this->load->view( 404_normal );
        }
   }

然后在routes.php中将404设置为主控制器，设置为不存在的函数，即。

$route[ 404 ]             = "welcome/my_404";
$route[ 404_override ]    =  welcome/my_404 ;

但是welcome中有否my_404（）函数-这意味着你的所有404都将通过_remap

如果你在逻辑中使用show_404（）或只是redirect（my_404），这取决于你。如果你使用show_404（），那么只需修改Exceptions类即可重定向

class MY_Exceptions extends CI_Exceptions
{
    function show_404($page =   , $log_error = TRUE)
    {
         redirect( my_404 );
    }
}