header problem

fimbria

hi,

im currently working on a session based page...that need a session to be set to view the page. each section of the page is set in blocks, where the variable "$system" is set to a certain value, a section of code is ouputted. The code of the whole page is as follows:--


<?php
//database link
include "db.php";

// check for valid user session
session_start();

if(!session_is_registered("uname")| !session_is_registered("pw"))
{
header("Location: fimbria.php");
exit;
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html>

<title>Admin </title>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<LINK REL=stylesheet TYPE="text/css" HREF="css/style_new.css">

<body>
<table align="center" width="750" border="1">

<tr>
<td colspan="2" valign="middle">stats<br /></td>
</tr>
<tr >
<td>
<a href="?system=add">Add</a></td>
<td rowspan="20" valign="top" width="700">

<div align="center" class="textnetscape">
<h1>Admin</h1>
<?php
if($system=="add"){
print"add<br>";
}
elseif($system=="remove"){
print"remove";
}
elseif($system=="change"){
print"change";
}
elseif($system=="acces"){
print"Acces";
}
elseif($system=="no"){
print"no";  

} 
elseif($system=="addnewuser"){
print"add new user";
}
elseif($system=="removeuser"){
print"remove user";
}
elseif($system=="web"){
print"webstats";
}
elseif($system=="check2"){
print"Check2";
}
elseif($system=="logout"){
session_destroy();
header("Location:fimbria.php");
}

?>  

</td>
</tr>
</table>
</body>
</html>

The problem that i have is that when "$system=logout"
the session is being destroyed, but i get the following error message about the header:

Warning: Cannot add header information - headers already sent by (output started at /home//docs/admin.php:27) in /home//docs/admin.php on line 122

What am i doing wrong???

thanks for any help in advance....

chrima

Hi there,

The default property of Zend Engine (PHP) is output buffering off. You
can turn on output buffering programmatically at the start of PHP page,
before even you try to send any HTML output by calling the function

ob_start()

If this is enabled, you may send HTTP headers even after HTML output
has been sent.

Cheers,
chrima

lanjoky

One problem I see is this :

if(!session_is_registered("uname")|| !session_is_registered("pw")) // should be two '|' not one
{ 
header("Location: fimbria.php"); 
exit; 
}

#2 need to start the session before you include the file!!

That should fix it 🙂

fimbria

thanks for the comments....

i used "ob_start" as you suggested and it works great. Just a little question is it good practice to enable output buffering?

also i notice the other comment about the session info....

thanks ....

Weedpacket

It slows down the script - nothing gets sent to the browser until the very end.

In your code, if you've got something in db.php that produces output (including blank lines), or if there are any blank lines at the top of your posted script, take them out, because they will be what's causing the trouble.

The basic reason is that session_start() inserts http headers into the response sent to the browser. It can't do that if you've already started sending the content of the response.

So chrima's comment

If this is enabled, you may send HTTP headers even after HTML output
has been sent.

is wrong: the HTML output is not send until after the headers. Until those have gone out, the HTML has to sit around in PHP twiddling its thumbs - meanwhile everything else that's waiting for it is also sitting around twiddling their thumbs.

Output buffering has its uses, but this is not one of them.

fimbria

so "weedpacket", you saying to check the file "db.php" for blank lines and also the top of the posted script??

whereabouts upto on the posted script??

thanks

Weedpacket

What I said: at the top of the script. Before the <?php.

If anything is output including (but not limited to) blank lines, then you can no longer send headers.