Why am I getting Warning: Cannot modify header information - headers already sent by (output started at ...)?

Question

I'm reusing a search PHP script, but I get this error:

Warning: Cannot modify header information - headers already sent by (output started at /Volumes/Work/MAMP/PC Flag/php_scripts/conection.php:2) in /Volumes/Work/MAMP/PC Flag/includes/search.php on line 63

line #2 conection.php:

$con = mysqli_connect("localhost", "root", "root", "cms");

line #63 search.php:

header('Location: search-page.php?keywords=' . urlencode($keywords));

What is the problem?

Also I need to mention that the script doesn't redirect me anymore to search-page.php as it should.

Did you echo anything before putting the `header()` ? – Kunal Gupta Oct 03 '14 at 15:50 — Kunal Gupta, Oct 03 '14 at 15:50

Alex Quintero · Accepted Answer · 2014-10-03T16:19:38.433

3

When you use header() it shouldn't be any output before, not even a space, you have two solution:

Dirty one

Use ob_clean() before the header to clean the output buffer

ob_clean();
header('Location: search-page.php?keywords=' . urlencode($keywords));

Correct one

Search in your script and your request route for any output, content before <?php, echoes, HTML code, prints or spaces after the ?> are usually the cause of this ;)

Debug

This snippet may help you to find out where is the output in your code:

var_dump(ob_get_contents());die()

Put this before line 63

Javascript workaround

In the case that everything fails, you have another option, use javascript to redirect, although I recommend you to keep trying without get to this point :)

Replace the header(...) with this:

echo '<script>window.location.href="search-page.php?keywords=' . urlencode($keywords)) . '";</script>';

edited Oct 03 '14 at 16:19

answered Oct 03 '14 at 15:52

Alex Quintero

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That's a good one, same as mine answer but better explained IMO – Szymon Toda Oct 03 '14 at 15:53
@Ultra the UTF-8 BOM that you mention is also an important point – Alex Quintero Oct 03 '14 at 15:56
I`ve deleted some space in conection.php and now I get the same error for header.php line 22. In header I don`t have any php code nor spaces. Also ob_clean() doesn`t do the trick. When I put var_dump() it displays bool(false). – Bogdan Constantin Oct 03 '14 at 16:11
1

Try to convert all your files to **UTF-8 without BOM**, Notepad++ and Sublime Text are great tools for this, in the worst case you can use javascript to redirect ;) – Alex Quintero Oct 03 '14 at 16:14
Thanks a lot for your support! I wish there are more persons like you in the comunity! – Bogdan Constantin Oct 03 '14 at 16:33

score 1 · Answer 2 · edited May 23 '17 at 10:26

You have send a header already as error states. Please investigate when and how headers are sent.

That usually happens when something is printed before that line to output buffer.

Make sure that you are using UTF-8 without BOM document encoding - BOM sign is invisible in most text editors yet can be interpreted as content which forces sending HTTP headers.

You can debug your output with Output Control function

score 0 · Answer 3 · answered Oct 03 '14 at 15:51

0

It's happening because output has been sent already. You can't edit Header Information when you have echo'd anything!

answered Oct 03 '14 at 15:51

Frederik Spang

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I agree, although. I am not sure OP does though. I'd say that the error message, was pretty selfexplaining. – Frederik Spang Oct 03 '14 at 15:57

score 0 · Answer 4 · edited May 23 '17 at 10:33

0

It seems like the error you're getting is because an output have been occured.you can fix it with this code :

if (headers_sent()) {
    ob_clean();
}

Just found this detailed answer.

edited May 23 '17 at 10:33

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