Codeigniter Rename file on upload

Question

I\'m trying to add time as the prefix of the image name along with the original name when uploading, But I couldn\'t figure it out. Please help me with the following code to

Answer 1

        /* Conf */
        $new_name                   = time().$_FILES["userfiles"]['name'];
        $config['file_name']        = $new_name;
        $config['upload_path']      = './upload/';
        $config['allowed_types']    = 'gif|jpg|png';
        $config['max_size']         = '';
        $config['max_width']        = '';
        $config['max_height']       = '';
        $config['file_ext_tolower'] = TRUE;

      /*  Load the upload library  */   
        $this->load->library('upload', $config);