phpexcel next column prev column letter

gistfile1.txt

     /**
     * Next letter for excel
     *
     * @param string $current_letter
     *
     * @return string
     * @throws \PhpOffice\PhpSpreadsheet\Exception
     */
    function excel_next_letter($current_letter = 'A')
    {
        $columnAlpha_index = \PhpOffice\PhpSpreadsheet\Cell\Coordinate::columnIndexFromString($current_letter);
        $letter = \PhpOffice\PhpSpreadsheet\Cell\Coordinate::stringFromColumnIndex($columnAlpha_index + 1);

        return $letter;
    }//end excel_next_letter

    /**
     * Previous letter for excel
     *
     * @param string $current_letter
     *
     * @return string
     * @throws \PhpOffice\PhpSpreadsheet\Exception
     */
    function excel_prev_letter($current_letter = 'A')
    {
        $columnAlpha_index = \PhpOffice\PhpSpreadsheet\Cell\Coordinate::columnIndexFromString($current_letter);
        $letter = \PhpOffice\PhpSpreadsheet\Cell\Coordinate::stringFromColumnIndex($columnAlpha_index - 1);

        return $letter;
    }//end excel_prev_letter