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Cannot modify header information - headers already sent by

P: 1
Cannot modify header information - headers already sent by
Mar 2 '07 #1
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6 Replies


ronverdonk
Expert 2.5K+
P: 4,258
Good for you!

What is your problem and question?

moderator
Mar 2 '07 #2

P: 24
Cannot modify header information - headers already sent by
Dear
Really your question is very very short. Please write something so that anyone can understand.
Your problem is due to header after output to browser.
You are trying to send header info (header('....')) after some output is already sent. That output can be a blank line or any html text.
If you did not get then write ob_start(); at top of the page.
Mar 3 '07 #3

ronverdonk
Expert 2.5K+
P: 4,258
I will show the text of an article by wildteen88, june 2006, who can explain this a lot better then I can.

The reason why you are getting this message is because you have may have/be:
  • Whitespace before the opening php tag <?php
  • Outputting something to the browser before you use session_start, header, setcookie etc
session_start, setcookie, header and a few other functions write header information to the web server/browser what to do. Such as when you use session_start it requests the browser to create a cookie which stores the PHPSESSID.

If you have output before you use these functions then they are unable to send new header information as it has already been sent in the form text/html, and so you get the headers already sent error message.

You can easily find the source of the problem by looking at the error message. As the answer is actully in there, but most people dont notice it as they may not understand what the error means. So lets take this error message as an example:

Warning: Cannot modify header information - headers already sent by (output started at C:\server\www\test.php:6) in C:\server\www\test.php on line 8
Now PHP has given us a clue here as it has told use where the output has started! Have look where it says output started at and it gives you the full path to the file and the line number. Now the line number that it stats is not usually where the output has started but where the output has ended, becuase the output could be above that line.
So lets look at test.php:
Expand|Select|Wrap|Line Numbers
  1.  1 <html>
  2.  2 <head>
  3.  3 <title>Header test</title>
  4.  4 </head>
  5.  5 <body>
  6.  6 <?php
  7.  7
  8.  8 header("Location: http://www.google.com");
  9.  9
  10. 10 ?>
  11. 11 </body>
  12. 12 </html>
As you can see line 6 is the opening PHP tag (< ?php) this isn't the output but look above that line you'll notice it has some HTML code. This html code is the cause of the error!

So when you get this error message again look for the clue where it says output started at and goto the file and line number it says. Look above the line number and find where your output is located to.

Hope that helps you understand why your are getting this error message. (Thanks to wildteen88)

Ronald :cool:
Mar 3 '07 #4

P: 1
I will show the text of an article by wildteen88, june 2006, who can explain this a lot better then I can.

The reason why you are getting this message is because you have may have/be:
  • Whitespace before the opening php tag <?php
  • Outputting something to the browser before you use session_start, header, setcookie etc
session_start, setcookie, header and a few other functions write header information to the web server/browser what to do. Such as when you use session_start it requests the browser to create a cookie which stores the PHPSESSID.

If you have output before you use these functions then they are unable to send new header information as it has already been sent in the form text/html, and so you get the headers already sent error message.

You can easily find the source of the problem by looking at the error message. As the answer is actully in there, but most people dont notice it as they may not understand what the error means. So lets take this error message as an example:


Now PHP has given us a clue here as it has told use where the output has started! Have look where it says output started at and it gives you the full path to the file and the line number. Now the line number that it stats is not usually where the output has started but where the output has ended, becuase the output could be above that line.
So lets look at test.php:
Expand|Select|Wrap|Line Numbers
  1.  1 <html>
  2.  2 <head>
  3.  3 <title>Header test</title>
  4.  4 </head>
  5.  5 <body>
  6.  6 <?php
  7.  7
  8.  8 header("Location: http://www.google.com");
  9.  9
  10. 10 ?>
  11. 11 </body>
  12. 12 </html>
As you can see line 6 is the opening PHP tag (< ?php) this isn't the output but look above that line you'll notice it has some HTML code. This html code is the cause of the error!

So when you get this error message again look for the clue where it says output started at and goto the file and line number it says. Look above the line number and find where your output is located to.

Hope that helps you understand why your are getting this error message. (Thanks to wildteen88)

Ronald :cool:

Thanks a lot we have been trying to remove this error for th elast 1 day
The explaanation given here has not only removed our error but also cleared our
concepts about session management , output buffering , headers and cookies
Apr 2 '07 #5

ronverdonk
Expert 2.5K+
P: 4,258
You are welcome any time.

Ronald :cool:
Apr 2 '07 #6

P: n/a
thanks thanks thanks..
Oct 21 '10 #7

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