PHP Redirect not working

Hi
I had this code which worked one website. 
header('Location: tm_wufoo.php');

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So it redirected to the tm_wufoo page once certain conditions were met.
It doesn't work on the new site though. Instead I get the message:
Warning: Cannot modify header information - headers already sent by (output started at blah.org\tm_header.php:25) in blah.org\tm_login.php on line 31

What must I do to get rid of this warning?
Thanks
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jdhackettAsked:
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StingRaYCommented:
Try inserting "exit();" after redirect like this:

header('Location: tm_wufoo.php');
exit();

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Paul-BCommented:
You could get around this using javascript.... like 

<?php
function MyJavaScriptRedirection($url)
{?>
<script type=”text/javascript”>
<!–
window.location = “<?=$url?>”
//–>
</script>
<?}
print “do stuff”;
MyJavaScriptRedirection(“tm_wufoo.php”);

?>

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A better way is to put it all in one tag of possible though.
jdhackettAuthor Commented:
Stringray - added exit() but it made no difference. Are there PHP admin settings that could account for the difference in the way the code works?
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Dave BaldwinFixer of ProblemsCommented:
Any redirect with header('Location: tm_wufoo.php'); must come BEFORE any output to the browser.  Even a space ' ' will cause the other headers to be sent and block sending anymore.  There are no settings which can change that, it's part of the HTTP protocol.
Dave BaldwinFixer of ProblemsCommented:

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Paul-BCommented:
you might try changing the line to 

header('Refresh: 1; url=http://yoursite.com/PATHtoFILE/tm_wufoo.php');

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Ray PaseurCommented:
DaveBaldwin is correct.  If you add this line as the first line of your script, PHP will buffer the browser output until the end of the script.  It should get you past the issue of accidentally sending browser output before your script has completed the headers.

ob_start();
jdhackettAuthor Commented:
Thanks everyone. Ob_start solved the issue.
Is it considered "bad practice" that I had to do this?
Dave BaldwinFixer of ProblemsCommented:
No, that's what it's there for.
jrm213jrm213Commented:
I wouldn't say it is considered bad practice, but I also don't think the intended purpose of output buffering was so that people could redirect at any point when they had already started sending output.

The issue you are facing is that the headers have already been sent because of output that was started at line 25 of your tm_header.php file, so you can't change them, which is what your script is trying to do.

I think the best solution (if possible) would be for you to check for the redirect condition in your tm_header.php file before you start sending output.

Output buffering is going to write your output to a buffer in memory, so it is going to increase the memory usage on your server. If your pages are large you can exceed your script limit, or just cause a major slow down on your server (I have no idea what kind of server you are on, just wanted to mention it).
Ray PaseurCommented:
I generally agree with jrm213jrm213 about the logic that would begin producing browser output before it had completed all of the logic needed to build the page.  Life works better, your scripts are more maintainable that way, etc.

But in my experience the observed behavior of using ob_start is that it makes your scripts run faster.  Instead of connecting and sending several chunks of browser output, it saves all the chunks together in one big chunk until the script terminates, and then sends it all at once.  There is considerable overhead associated with sending each chunk of browser output, thus reducing the number of chunks can reduce the total overhead.
jdhackettAuthor Commented:
Thanks everyone for their help, very educational.
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