$this->load->helper(array('text'));
$config['upload_path'] = './uploads/';
$config['allowed_types'] = 'xls|xlsx|xlsm';
$config['file_name'] = convert_accented_characters($_FILES['excel_file']['name']);
$this->load->library('upload', $config);
$is_uploaded = $this->upload->do_upload('excel_file');<?php echo form_open_multipart('/reader/update') ?>
<input type="file" name="excel_file">
<?php echo form_close() ?>