pass argument in index function of controller

you can add routing for it in your routes.php file, like:

$route['abc/(:any)'] = 'abc/index/$1';

doing this will route your url www.example.com/abc/argument to www.example.com/abc/index/argument

Are you looking for remapping ?

public function _remap($method, $params = array())
{
    if (method_exists($this, $method))
    {
       return call_user_func_array(array($this, $method), $params);
    } 
    else 
    {
       return $this->index($method);
    }
    show_404();
}

The only way to use it is to have a new controller.

In your case it should be name as argument that could make it work as you wish it to.

Unless you want to overwrite CI_Exceptions/ function show_404 which will provide unstable solution , you could try using another function d inside your class abc :

    function d (){
        $argument= $this -> uri -> segment(3);
        if ($argument) {
            //do something
        }
    }

and then you call it with this: www.example.com/abc/d/argument

You can create an init function in your controller class and then check if there any function named your first argument by function_exist() follow http://php.net/manual/en/function.function-exists.php, and then call your index function by $this->index() and pass the argument to the index function by $this->index($arg1).