强制下载通常默认不会下载的文件，如图片和html网页文件。用法很简单，后面两个参数没有必要设定，前两个是文件和文件名。

<?php
function force_download ($data, $name, $mimetype='', $filesize=false) {
    // File size not set?
    if ($filesize == false OR !is_numeric($filesize)) {
        $filesize = strlen($data);
    }
 
    // Mimetype not set?
    if (empty($mimetype)) {
        $mimetype = 'application/octet-stream';
    }
 
    // Make sure there's not anything else left
    ob_clean_all();
 
    // Start sending headers
    header("Pragma: public"); // required
    header("Expires: 0");
    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
    header("Cache-Control: private",false); // required for certain browsers
    header("Content-Transfer-Encoding: binary");
    header("Content-Type: " . $mimetype);
    header("Content-Length: " . $filesize);
    header("Content-Disposition: attachment; filename=\"" . $name . "\";" );
 
    // Send data
    echo $data;
    die();
}
 
function ob_clean_all () {
    $ob_active = ob_get_length () !== false;
    while($ob_active) {
        ob_end_clean();
        $ob_active = ob_get_length () !== false;
    }
 
    return true;
}
?>