Basic Excel Generator PHP

PHP_excel_maker.php

<?php
/**
 *  Basic Excel Generator
 *
 *  Usage:
    $data = array(  
        array( 'cell_1_1', 'cell_1_2'),
        array( 'cell_2_1', 'cell_2_2')
    );
    $excel = new ExcelMaker( $data ) ;
    file_put_contents( 'output.xls',  $excel->getContents()) ;
*/
class ExcelMaker{
    private $data = array();
    /**
     *  
     * @param Array $data  
     */
    public function __construct(  $data  ) {
        $this->data = $data ;
    }
    /**
     * 
     * @return String Contents of Excel file
     */
    private function getContents(    ) {
        $contents = $this->xlsBOF(); 
        $tr1 = 0;
        foreach($this->data as $k => $v ) {
            $nn1 = 0;
            foreach($v as $k1 => $v1 ) {
                $contents .= $this->xlsWriteLabel( $tr1, $nn1, $v1 );
                $nn1++;
            }
            $tr1++;
        }
        $contents .= $this->xlsEOF(); 
        return $contents;
    }
    private function xlsBOF() {
        return pack("ssssss", 0x809, 0x8, 0x0, 0x10, 0x0, 0x0);
    }
    function xlsEOF() {
        return pack("ss", 0x0A, 0x00);
    }
    private function xlsWriteNumber($row, $col, $value) {
        return pack("sssss", 0x203, 14, $row, $col, 0x0).pack("d", $value);
    }
    function xlsWriteLabel($row, $col, $value ) {
        $l = strlen($value);
        return pack("ssssss", 0x204, 8 + $l, $row, $col, 0x0, $l). $value;
    }
}