title: Fatal error: Call to undefined method Upload::do_upload()
body: <p>I get this error when trying to upload file.</p>
  
  <p>This is my code </p>
  
  <pre>
  
  class Upload extends CI_Controller {
  
      function __construct() {
          parent::__construct();
  
          $this->load->model(array(
                                    'm_campaign' 
                                    ,'m_upload'
                                  )
                              );
  
          $this->load->helper(array(
                                     'form' 
                                     ,'url'
                                  )
                              );
  
      }
  
      public function index()
      {
          $data = array(
                          'select_campaign'   => $this->select_campaign(),
                          'view'              => 'upload',
                          'js'                => 'script_upload'
                      );
  
          $this->load->view('admin/template', $data);
      }
  
      function select_campaign(){
          $select_campaign = $this->m_upload->table_campaign();
          return $select_campaign;
      }
  
      function start_upload(){
  
          if (!empty($_FILES)) {
              $config = array(
                                  'allowed_types' => 'jpg|xls|xlsx' 
                                  ,'upload_path'  =>  base_url('assets/media/excel/')
                                  ,'max_size'     =>  1000000
                                  ,'max_width'    =>  4024
                                  ,'max_height'   =>  1768
                                  ,'overwrite'    =>  true
                              );
              $this->load->library('upload', $config);
  
              $this->upload->do_upload();
          }
          redirect('admin/upload');
      } }
  }
  
  </pre>
  
  <p>I've trying to search but still confuse. </p>
  
  <p>Thank you for everyone here</p>