Redirecting with the help of a GET variable

[kreut]

Hello,

 

I'm having some problems with a redirect situation.  I start on a page called Create Assignment.  From this page I pass (using GET) the variable assignment_id to a page called Add_questions (the user can add questions to this specific assignment).  When a user wants to add a question, they hit a link which brings them to my Database Update script.  All works great so far!  After the update, however, I want to redirect them BACK to the Add_questions page while keeping the same Assignment number.  I've tried using:

header('Location: list_assignment_question.php?assignment_id');

but I get this error:

 

Warning: Cannot modify header information - headers already sent by (output started at /Applications/MAMP/htdocs/algebra_book/main_scripts/db_insert_assignment_question.php:6) in /Applications/MAMP/htdocs/algebra_book/main_scripts/db_insert_assignment_question.php on line 12

 

Any thoughts?  I'd be more than happy to provide more code as needed.

[KevinM1]

Look at our stickied thread at the top of this subforum: http://www.phpfreaks.com/forums/php-coding-help/header-errors-read-here-before-posting-them/

[kreut]

Thank you for the quick reply.  I took a look at the stick note.  And, from what I understand (please tell me if this is correct..), I can't put the header command down within my code, as I do here:

 

<?php
$errors = array();
require_once('library.php');
try {
require_once('db_definitions.php');
	echo $_GET['question_id'];
	echo isset($_GET['question_id']);
	if (isset($_GET['question_id'])) {
	$data = array('question_id' => $_GET['question_id'],
				  'assignment_id' => $_GET['assignment_id']);	  
	$inserted = $dbWrite->insert('assignments_questions',$data);
	$returnto = $_SERVER['HTTP_REFERER'];
	header('Location: $returnto');
exit;

	}
} catch (Exception $e) {
  echo $e->getMessage();
}

 

However, I only want the redirect if there is a successful insert.  I guess I'm not quite sure how to both:

1) Not put the header within the code

2) Be able to have a conditional redirect.

 

Any help to this php newbie would be appreciated.

 

 

[KevinM1]

You can't have anything sent to the screen before the redirect.  That's what the 'Headers already sent' message means - an echo is, ultimately, an HTTP response.  And, if you think about it, echoing output to the screen doesn't make much sense in this case because you're going to another page.

 

If you want to display a message, delay, then redirect the user, look into JavaScript which will allow you to use the browser for redirection rather than an HTTP header command.

[kreut]

I think that this is starting to make sense!

 

I actually just put the echo's in to test things out.  So...if I understand correctly, if I get rid of the echo, which is an ouput to the browser, then it should work??? 

[kreut]

Never mind!  Error gone.... 

 

Thanks so much.

[bglinkerman]

Just an FYI, I have solved this issue by placing "ob_start();" for the very first line, then you have your redirect statements anywhere because the page is executing on the server side completely (ob stands for output buffering) before ever sending data to the client. So if your page finds that half way down the page a condition exists where it needs to redirect it will do so without an error. I use this just yesterday on a page and it works fine.

[KevinM1]

From a design standpoint, the output buffer is still a bit sloppy.  The ideal design is to organize your scripts like so:

 

ALL PHP Proccessing

|

|

|

V

Output

 

When you process first, you gain many advantages - you separate logic from presentation, you avoid header errors, you can store generated results in variables, simplifying your presentation code a lot.

 

Even though PHP gives you the option to jump in and out of HTML on the fly, it's really not the ideal way to structure your code.  I can't tell you how many people I've seen have loops of PHP where they're writing entire forms in straight HTML, with inline JavaScript to boot, wonder why something is broken.  Separation of concerns is the way to go.