文件路径名表示问题

[steel06]

$file_dir = "d:\\homework\\".$tit."\\";
$tit是一字符窜变量

请问这种表示正确吗？

[steel06]

急……！！！

[foolfish]

可以的

正确.

[steel06]

我写的是一个文件下载的程序：
<?
$w=strtok($title,".");
$tit=$w;
echo $tit;
echo $title;
$file_name ="$title";
$file_dir = "d:\homework\\";
$file_dir=$file_dir.$tit."\\";

echo $file_dir;
$file_dir=addslashes($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;}
?>
错误信息如下：
Warning: Cannot add header information - headers already sent by (output started at c:\apache\htdocs\ide\data\download.php:4) in c:\apache\htdocs\ide\data\download.php on line 18

Warning: Cannot add header information - headers already sent by (output started at c:\apache\htdocs\ide\data\download.php:4) in c:\apache\htdocs\ide\data\download.php on line 19

Warning: Cannot add header information - headers already sent by (output started at c:\apache\htdocs\ide\data\download.php:4) in c:\apache\htdocs\ide\data\download.php on line 20

Warning: Cannot add header information - headers already sent by (output started at c:\apache\htdocs\ide\data\download.php:4) in c:\apache\htdocs\ide\data\download.php on line 21
请问这是什么错误了？

[darzui]

在header之前有一句echo $file_dir;把它去掉
使用header的时候，应该保证之前页面上没有输出任何内容（包括空行）

[benjamin9]

另外,在使用header的时候，应该保证前面没有任何HTML标记元素的存在.