I've been struggling with this error for a while now.
To start with, I just thought it was white space, but after further research I think it might be a problem similar to this:
Look for any statements that could send output to the user before this header statement. If you find one or more, change your code to move the header statement before them. Complex conditional statements may complicate the issue, but they may also help solve the problem. Consider a conditional expression at the top of the PHP script that determines the header value as early as possible and sets it there.
I'm guessing the include header is causing the problem along with the header(), but I'm not sure how to rearrange the code to get rid of this error.
How do I remove the error?
<?php
$username = $password = $token = $fName = "";
include_once 'header.php';
if (isset($_POST['username']) && isset($_POST['password']))
$username = sanitizeString($_POST['username']);
$password = sanitizeString($_POST['password']); //Set temporary username and password variables
$token = md5("$password"); //Encrypt temporary password
if ($username != 'admin')
{
header("Location:summary.php");
}
elseif($username == 'admin')
{
header("Location:admin.php");
}
elseif($username == '')
{
header("Location:index.php");
}
else
die ("<body><div class='container'><p class='error'>Invalid username or password.</p></div></body>");
if ($username == "" || $token == "")
{
echo "<body><div class='container'><p class='error'>Please enter your username and password</p></div></body>";
}
else
{
$query = "SELECT * FROM members WHERE username='$username'AND password = '$token'"; //Look in table for username entered
$result = mysql_query($query);
if (!$result)
die ("Database access failed: " . mysql_error());
elseif (mysql_num_rows($result) > 0)
{
$row = mysql_fetch_row($result);
$_SESSION['username'] = $username; //Set session variables
$_SESSION['password'] = $token;
$fName = $row[0];
}
}
?>
Lines 45-47:
?>
<?php
That's sending a couple of newlines as output, so the headers are already dispatched. Just remove those 3 lines (it's all one big PHP block after all, no need to end PHP parsing and then start it again), as well as the similar block on lines 60-62, and it'll work.
Notice that the error message you got actually gives you a lot of information to help you find this yourself:
Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\speedycms\deleteclient.php:47) in C:\xampp\htdocs\speedycms\deleteclient.php on line 106
The two bolded sections tell you where the item is that sent output before the headers (line 47) and where the item is that was trying to send a header after output (line 106).
There are some problems with your header() calls, one of which might be causing problems
exit() after each of the header("Location: calls otherwise code execution will continue: so it reads "Location: http://foo"Location header, you should form an absolute URL like http://www.mysite.com/some/path.phpCheck something with echo, print() or printr() in the include file, header.php.
It might be that this is the problem OR if any MVC file, then check the number of spaces after ?>. This could also make a problem.
You are trying to send headers information after outputing content.
If you want to do this, look for output buffering.
Therefore, look to use ob_start();
Those blank lines between your ?> and <?php tags are being sent to the client.
When the first one of those is sent, it causes your headers to be sent first.
Once that happens, you can't modify the headers any more.
Remove those unnecessary tags, have it all in one big <?php block.
This typically occurs when there is unintended output from the script before you start the session. With your current code, you could try to use output buffering to solve it.
try adding a call to the ob_start(); function at the very top of your script and ob_end_flush(); at the very end of the document.
Check the document encoding.
I had this same problem. I develop on Windows XP using Notepad++ and WampServer to run Apache locally and all was fine. After uploading to hosting provider that uses Apache on Unix I got this error. I had no extra PHP tags or white-space from extra lines after the closing tag.
For me this was caused by the encoding of the text documents. I used the "Convert to UTF-8 without BOM" option in Notepad++(under Encoding tab) and reloaded to the web server. Problem fixed, no code/editing changes required.
There is likely whitespace outside of your php tags.
Source: Stackoverflow.com