include 和 header()

[feinst]

各位大侠，我在redhat7中遇到一个问题, include和header()中似乎有问题，代码如下：
　　
<? // file name login.php

include ("getmysql.inc");
$dbhand=mysql_connect("feinst","root","");
mysql_select_db("mall",$dbhand);
header("location:account.php");
?>　

而这个getmysql.inc文件中没有任何内容。一执行login.php,就出现：
　　Warning: Cannot add header information - headers already sent by (output started at getmysql.inc:20) in /var/www/html/mall/php/login.php on line 6

　　请问各位，这是怎么回事，多谢了！！！