PHP导出CSV表格文件的方法

<?php
$ret = '';
$arrs = array(array(1,'test1'),
             array(2,'test2'),
             array(3,'test3'),
             array(4,'test4'),
             array(5,'test5'),
             array(6,'test6'),
             array(7,'test7')
            );
foreach($arrs as $k=>$arr){
    $ret .= $arr[0].",".$arr[1]." n";
}
//$ret = @mb_convert_encoding ($ret, 'GBK','UTF-8');
header("Content-Disposition: attachment; filename=xxxx.csv");
header("Content-Type:APPLICATION/OCTET-STREAM");
echo $ret;