Question about Headers

izbryte

I know this is probably a stupid question but I'm confused about the way headers work.
I'm using a template for my header so the beginning of my code starts with

include_once ('header.tpl');

This works fine until I want to change the location:

Header("Location: index.php")

then I get the error

Warning: Cannot modify header information - headers already sent by blah blah blah

How can I use the template and still change the location?

Again, sorry if this is dumb. :bemused:

cgraz

headers need to be called before you have outputted anything. That means

print "Test";

header("location: url.php")

Would cause a headers already sent error.

header("Location: url.php");

print "Test";

would not.

NogDog

If your include file has a linefeed after its closing ?> tag, that will cause text to be output, which means you can not call header(), setcookie(), etc. after you include it, so make sure there is absolutely nothing after the closing ?>.

Salkcin

as mentioned, no output to the browser is allowed before you use headers, not even a single litle space-char...

Anyway, a simple fix is to add ob_start() at the very beginning of your php file.

ex:

<?php
ob_start();

// rest of your code

?>

NogDog

Salkcin wrote:
as mentioned, no output to the browser is allowed before you use headers, not even a single litle space-char...

Anyway, a simple fix is to add ob_start() at the very beginning of your php file.

ex:
<?php
ob_start();

// rest of your code

?>

This will add a little overhead to your processing time. Probably for most applications it's not enough to worry about, but if you're in a situation where you want to save every millisecond possible, you may be better off just making sure your code does not output anything prior to doing anything that sends headers rather than using ob_start().

bradgrafelman

In addition to NogDog, using output buffering won't always fix a "header already sent" problem.

Plus, I would call slapping ob_start() at the beginning of your script a quick patch, not a quick fix. A fix to me would constitute understanding the logical flow of a script and altering it so that you can do validation and redirects before anything is outputted.