PHP 强制性文件下载功能的函数代码(任意文件格式)

/******************** 
*@file - path to file 
*/ 
function force_download($file) 
{ 
if ((isset($file))&&(file_exists($file))) { 
header("Content-length: ".filesize($file)); 
header('Content-Type: application/octet-stream'); 
header('Content-Disposition: attachment; filename="' . $file . '"'); 
readfile("$file"); 
} else { 
echo "No file selected"; 
} 
}