PHP to implement file download with code

We generally implement the download is to call the URL to download, but encountered IE can identify open files can not be used in this way, such as downloading a picture, HTML page, etc., then need to program to achieve, the following PHP code can be resolved:

<?
if( empty($_GET['FileName'])|| empty($_GET['FileDir'])|| empty($_GET['FileId'])){
　　echo'<script> alert("非法连接 !"); location.replace ("index.php") </script>'; exit();
}
$file_name=$_GET['FileName'];
$file_dir=$_GET['FileDir'];
$FileId=$_GET['FileId'];
$file_dir = $file_dir."/";
if　 (!file_exists($file_dir.$file_name))　 {　 //检查文件是否存在
　echo　 "文件找不到";
　exit;
　}　 else　 {
$file = fopen($file_dir . $file_name,"r"); // 打开文件
// 输入文件标签
Header("Content-type: application/octet-stream");
Header("Accept-Ranges: bytes");
Header("Accept-Length: ".filesize($file_dir . $file_name));
Header("Content-Disposition: attachment; filename=" . $file_name);
// 输出文件内容
echo fread($file,filesize($file_dir . $file_name));
fclose($file);
exit();
}
?>