Check did select file Or no, in input:file

How can know, if select(Choice Or Browse...) file in input:file run some code with php?

<form action="#" method="post" enctype="multipart/form-data">
    <input type="file" name="userfile[]" valign="baseline">
</form>


if(select file){
    run my code
}

Update:

I use of Multiple Uploads with JQuery and Code Igniter , when that i don't select file, output print_r($_FILES['userfile']); is:

Array ( [error] => 4 [name] => [size] => 0 [tmp_name] => [type] => [key] => userfile )

[error] => 4 is -> You did not select a file to upload.

If i select file, have following error in case i have in input:file this: name="userfile[]":

Message: Undefined index: userfile in here:print_r($_FILES['userfile']);

Update 2: I use from these Controller but if don't select a file, in the here if ( ! $files ) return is false and give error. i want if user did not select file does not get error with a if

class Upload extends Controller {
    function Upload()
    {
        parent::Controller();
        $this->load->helper(array('form', 'url'));
    }

    function index()
    {    
        $this->load->view('upload_form');
    }

    function do_upload()
    {
   if($_FILE('userfile')){
        $config['upload_path'] = './uploads/'; // server directory
        $config['allowed_types'] = 'gif|jpg|png'; // by extension, will check for whether it is an image

        $config['max_size']    = '1000'; // in kb
        $config['max_width']  = '1024';
        $config['max_height']  = '768';

        $this->load->library('upload', $config);
        $this->load->library('Multi_upload');

        $files = $this->multi_upload->go_upload();

        if ( ! $files )        
        {
            $error = array('error' => $this->upload->display_errors());
            开发者_StackOverflow$this->load->view('upload_form', $error);
        } else {
            $data = array('upload_data' => $files);
            $this->load->view('upload_success', $data);
        }
    }
 redirect('inse/show');
    }        
}

<?php
  if (isset($_FILES['my_file_input'])) {
    // your code
  }
?>

NOTE: you descripted a wrong input type if i get you right - file input should use this signature:

<input type="file" name="my_file_input" />

NOTE: the form the file input is located within should have its enctype set to "multipart-form-data" (or something like that).

UPD: i may be wrong, but here's come controller from the module you have specified:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Upload extends Controller {
    function Upload()
    {
        parent::Controller();
        $this->load->helper(array('form', 'url'));
    }

    function index()
    {    
        $this->load->view('upload_form');
    }

    function do_upload()
    {
        $config['upload_path'] = './uploads/'; // server directory
        $config['allowed_types'] = 'gif|jpg|png'; // by extension, will check for whether it is an image

        $config['max_size']    = '1000'; // in kb
        $config['max_width']  = '1024';
        $config['max_height']  = '768';

        $this->load->library('upload', $config);
        $this->load->library('Multi_upload');

        $files = $this->multi_upload->go_upload();

        if ( ! $files )        
        {
            $error = array('error' => $this->upload->display_errors());
            $this->load->view('upload_form', $error);
        } else {
            $data = array('upload_data' => $files);
            $this->load->view('upload_success', $data);
        }
    }    
}
?>

If you still do not get any satisfying results, try var_dump($_FILES); and find out how the files are stored.