codeigniter文件上传而不使用数组

I have used codeigniter file uploading ,single and multiple both. but if the file names are not in an array how to upload files. ex:- if form1 has file1,file2 and file3 file-inputs, and user only providing file1 and file3. then how to identify if file2 is not given. if i use the array format, it is not possible to find which particular field is given and which is not.

I have tried array based uploading but, any file missing will give me a wrongly indexed array. I need to have a proper $_POST where non selected form members are clearly given.

It will post only $_FILES which have value.

HTML

<input type="file" name="mass_consume_upload[]" />
<input type="file" name="mass_consume_upload[]" />
<input type="file" name="mass_consume_upload[]" />

PHP (Codeigniter)

        $this->load->library('upload');

        $tempfiles = $_FILES;
        //print_r($tempfiles);
        foreach ($tempfiles as $files) {
            $_FILES['mass_consume_upload'] = $files;

            $this->upload->initialize(array(
                'upload_path' => $path,
                'allowed_types' => 'pdf',
                'overwrite' => FALSE
            ));
            if (!$this->upload->do_upload('mass_consume_upload')) {
                $uploadArr['error'][] = array(
                    'filename' => $_FILES['mass_consume_upload']['name'],
                    'msg' => $this->upload->display_errors('', '')
                );
            } else {
                $uploadArr['success'][] = array('filename' => $_FILES['mass_consume_upload']['name']);
            }
        }