Warning: Cannot modify header information

mjvbosox

I know this is a familiar error for many, usually caused by an include('somefile.php') or require_once('somefile.php') command, in which 'somefile.php' contains the header('Location: [url]http://.[/url].....') redirect. Normally, the error occurs if the redirect comes after the page has already written content, or especially if an extra blank space or line-break precedes <?php or follows ?> in either the included file or the main/parent file.

My issue is, I have the exact same code (see below) to begin several files within an admin section of a site where a password is required, however 3 of the files report the following error:

Warning: Cannot modify header information - headers already sent by (output started at /home/content/57/8312157/html/admin/filename.php:1) in /home/content/57/8312157/html/admin/check.php on line 1

and the other four do not, properly redirecting the user to the login page. Each file begins like this:

<?php require_once('check.php'); ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
(with no spaces or breaks before or after the <?php ... ?>)

where 'check.php' contains an if-then statement checking for a cookie. If the cookie exists, the page is displayed, if not, the user is redirected to the login page.

Since some of the pages do not return the error, I know 'check.php' is not the problem. After meticulously going over the first line of code in each file, making sure there are no blank spaces, I can not find any differences in the files that properly redirect to the login screen and the files that cause the error. I feel like I'm missing something really simple, but for the life of me, I can not figure it out.

Here's an example of the code working correctly:
http://www.calkain.com/admin/users.php redirects to the login screen.

I can not provide links to the problem files, as they contain sensitive client data. But I assure you, there IS NO DIFFERENCE in the first line of code in any of the files.

Has anyone ever had a similar problem? I've searched all over, and the only solutions I've come across are the "check for blank space" suggestions. I'd appreciate any help on this! Thanks very much.

bradgrafelman

One possibility is that the problematic files were saved in the UTF-8 encoding and have a BOM at the beginning of them.

mjvbosox;11007097 wrote:
But I assure you, there IS NO DIFFERENCE in the first line of code in any of the files.

And I can assure you that there is a difference, based upon the error message you posted. 🙂

How can you make such an assurance? Did you view the raw binary contents of the files (e.g. using a hex editor/viewer) and compare the first few bytes with other working files?

mjvbosox

Thanks for the response! I have explored the BOM possibility, viewing the file in every program I have, from Notepad to Dreamweaver, in ISO and UTF-8.. I have not, however, used a hex editor (that I am aware of anyway).. can you suggest a good one? Meanwhile, I will google around for one... Thanks again!

mjvbosox

That was it! I needed a hex editor (used Hexplorer), and there were 3 BOM characters at the beginning of the problematic files. All fixed. Thanks again!!

NogDog

Note that most decent code editors will have a configuraiton option where, if you select to save your file as UTF-8 (e.g. instead of ASCII), you can specify that it do so without the BOM.

mjvbosox

Good to know. Man, 11 years doing this and still learning... appreciate the help very much.

mattt2

Finally I got it! This error made me sick..

Thanks a lot guys, for asking my questions and answering it..