warning header("Location: file.php")

#1 (**permalink**) 07-16-2006

Why if I use warning header("Location: file.php") i had this warning?
Warning: Cannot modify header information - headers already sent by

#2 (**permalink**) 07-16-2006

Shearer wrote:
> Why if I use warning header("Location: file.php") i had this warning?
> Warning: Cannot modify header information - headers already sent by
>
>

There is a space/tab (whitespace) or something else that has been outputted
before you use your header(), it's not allowed to output anything before a
header().

--- example whitespace ---

<?PHP
header("Location: file.php");
?>
--- eof ---

--- example HTML output ---
<!DOCTYPE html PUBLIC "-//w3c//dtd html 4.0 transitional//en">
<?PHP
header("Location: file.php");
?>
--- eof ---

--- example echo to early ---
<?PHP
if(true) {
echo "Hello";
}
header("Location: file.php");
?>
--- eof ---

--- ok use of header ---
<?PHP
if(true) {
header("Location: file.php");
exit;
}
echo "Hello";
?>
--- eof ---

Only the last one will work.

//Aho

#3 (**permalink**) 07-16-2006

"J.O. Aho" <user@example.net> wrote in message news:4htondF18nnvU1@individual.net...

> --- example whitespace ---
>
> <?PHP
> header("Location: file.php");
> ?>
> --- eof ---
> Only the last one will work.
>
> //Aho

Unless of course output_buffering is not set to "off" in the php.ini.

-Lost

#4 (**permalink**) 07-16-2006

Shearer wrote:

> Why if I use warning header("Location: file.php") i had this warning?
> Warning: Cannot modify header information - headers already sent by

1) NOTHING must be output BEFORE a header() call.

2) I believe header('Location: URL') wants a complete absolute URL.
ie: http://www.example.com/file.php.

f.

#5 (**permalink**) 07-16-2006

"Cujo" <fra@despammed.com> wrote in message news:4hur18F19qr1U2@individual.net...

> 1) NOTHING must be output BEFORE a header() call.
>
> 2) I believe header('Location: URL') wants a complete absolute URL.
> ie: http://www.example.com/file.php.

Entirely untrue. If you utilize the output buffer directive, it eliminates this problem.
Also, header (location) can take any valid URL handle as an argument. Or more
appropriately/specifically:

"HTTP/1.1 requires an absolute URI as argument to » Location: including the scheme,
hostname and absolute path, but some clients accept relative URIs. You can usually use
$_SERVER['HTTP_HOST'], $_SERVER['PHP_SELF'] and dirname() to make an absolute URI from a
relative one yourself:"

And as far as I know *all* major browsers still support relative URIs. So, it is kind of
like the W3C war on standards. It is *supposed* to be one way, yet <insert a bunch of bad
ways> all still work just fine.

-Lost

#6 (**permalink**) 07-16-2006

-Lost wrote:

> "Cujo" <fra@despammed.com> wrote in message news:4hur18F19qr1U2@individual.net...
>
>> 1) NOTHING must be output BEFORE a header() call.
>>
>> 2) I believe header('Location: URL') wants a complete absolute URL.
>> ie: http://www.example.com/file.php.
>

> Entirely untrue. If you utilize the output buffer directive, it eliminates this problem.

It does not *eliminate* the problem, rather it works around it by
delaying output to the client. The client still *MUST* receive the
headers before anything else...

I prefer to code cleanly in the first place, rather than have my php
interpreter rearrange the output for me.

> And as far as I know *all* major browsers still support relative URIs. So, it is kind of
> like the W3C war on standards. It is *supposed* to be one way, yet <insert a bunch of bad
> ways> all still work just fine.

I *STILL* prefer to code following standards, rather than "what seems to
work". Especially when there is *NO REASON* to deviate from the
standards. Build absolute urls on the fly in you need, no big deal.

regards, f.

#7 (**permalink**) 07-16-2006

>> "Cujo" <fra@despammed.com> wrote in message news:4hur18F19qr1U2@individual.net...
>>
>>> 1) NOTHING must be output BEFORE a header() call.
>>>
>>> 2) I believe header('Location: URL') wants a complete absolute URL.
>>> ie: http://www.example.com/file.php.
>>
>> Entirely untrue. If you utilize the output buffer directive, it eliminates this
>> problem.

> It does not *eliminate* the problem, rather it works around it by delaying output to the
> client. The client still *MUST* receive the headers before anything else...

It eliminates the problem of "nothing must be output before a header() call".

Also, I am not entirely sure how the "must receive the headers before..." goes. With an
output buffer of xxxx (bytes) I could throw a wee bit of HTML and a Location header for
example into the document and as long as it is sent at the *same* time as the content, it
is just fine.

Do not forget, having the output buffer store some of this information is the same thing
as using ob_ functions. You are buffering output (and you can buffer headers!) and
headers are always delivered before the buffer.

Or is there something I am missing?

> I prefer to code cleanly in the first place, rather than have my php interpreter
> rearrange the output for me.

I could not agree with you more.

> I *STILL* prefer to code following standards, rather than "what seems to work".
> Especially when there is *NO REASON* to deviate from the standards. Build absolute urls
> on the fly in you need, no big deal.

I still gotta' agree with you.

I just wanted to state the facts about header(). Being that it does not *require* the
standard. The standard requires absolute URIs and URL handles.

Be well.

-Lost

#8 (**permalink**) 07-16-2006

On Sun, 16 Jul 2006 14:51:00 +0200, Cujo <fra@despammed.com> wrote:

>Shearer wrote:
>
>> Why if I use warning header("Location: file.php") i had this warning?
>> Warning: Cannot modify header information - headers already sent by
>
>1) NOTHING must be output BEFORE a header() call.
>
>2) I believe header('Location: URL') wants a complete absolute URL.
> ie: http://www.example.com/file.php.

The URL simply needs to be valid. You can do something like:
header("Location:index.html");. It will treat the link as localhost.

>f.

David

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode