php从数据库中读取文件并下载为txt格式

$con = mysql_connect('localhost','root','') or die('数据库连接失败!');
$db = mysql_select_db('test') or die('数据库选择失败!');
mysql_query('set names utf8');
$sql = 'select * from demo';
$f = fopen('info.txt','a+');
fwrite($f,'姓名|邮箱|手机号码'."\r\n");
$result = mysql_query($sql);
$str = '';
while($res = mysql_fetch_array($result)){
    $str .= $res['name'].'|'.$res['email'].'|'.$res['tel']."\r\n";
}
fwrite($f,$str);
fclose($f);
header("Content-Type:application/force-download"); //强制下载保存
header("Content-Disposition:attachment;filename=info.txt");//保存文件名
readfile("info.txt"); //输出
unlink('info.txt');//保证第二次再下载时，没有重复数据，删除已生成的文件