劳而无功夺
程序很多时候，需要进行下载，那么如何使浏览器弹出窗口进行下载呢？
下面的代码详细的解释了：
header("Content-type:application/octet-stream");
header("Content-dispostion:attachment;filename:a.gif");
header("Content-Length:"filesize("a.gif"));
$file = 'monkey.gif';
if (file_exists($file)) {
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($file));
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($file));
ob_clean();
flush();
readfile($file);
exit;
}