php 輸出file,要使用header

header("Content-type: application/download"); //這三步只是輸出回應標頭
header("Content-Disposition: attachment; filename=" . $b_name);
header("Content-Transfer-Encoding: binary");
$fp = fopen($b_path, 'r'); //這兩步才是輸出檔案的內容
fpassthru($fp);