Title: Cannot modify header information
Last modified: August 19, 2016

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# Cannot modify header information

 *  [michaelthulin](https://wordpress.org/support/users/michaelthulin/)
 * (@michaelthulin)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/)
 * I have recently installed WordPress v. 2.9.1.
 * Then I decided to create a plug-in myself,
    to handle a top navigation and some
   pages.
 * At first hand sight it looked like working, but
    then I tried to update one of
   my pages (the original wordpress page) and I recievede following errormessage:
 * `Warning: Cannot modify header information - headers already sent by (output 
   started at /domains/www.xxx.xx/wp-content/plugins/topmenu/topmenu.php:1) in /
   domains/www.xxx.xx/wp-includes/pluggable.php on line 868`
 * I have tried searching the web for any solutions but they all referred to the
   wordpress-topic which says that you have to be sure no extra spaces are included.
   I therefore opened the pages told in a text-editor
    but no help it was.
 * I have tried to install another plug-in to see if it was my own code that provoked
   the error, but anyway it still gave me that ugly error.
 * Can anyone help me to fix this error?
    or shall I program a menu beside wordpress?
 * Kind Regards
    Michael Thulin

Viewing 9 replies - 1 through 9 (of 9 total)

 *  [vtxyzzy](https://wordpress.org/support/users/vtxyzzy/)
 * (@vtxyzzy)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340113)
 * Looks like you have some non-php text (maybe a blank line, or a space at the 
   start of the line) as the first line of topmenu.php. The first line must start
   with `<?php`.
 *  Thread Starter [michaelthulin](https://wordpress.org/support/users/michaelthulin/)
 * (@michaelthulin)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340131)
 * I am aware of that.
 * But as I said – even when I copy one of the other existing plugins,
    the problem
   is still there.
 *  [vtxyzzy](https://wordpress.org/support/users/vtxyzzy/)
 * (@vtxyzzy)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340219)
 * I’m sorry, I don’t understand what you mean by ‘copy one of the other plugins’.
   Did you mean copying a different plugin and naming it topmenu.php, or deleting
   topmenu.php and using a plugin with a different name?
 * How about pasting the first 5 lines of topmenu.php in a reply? May not help, 
   but won’t hurt either.
 *  Thread Starter [michaelthulin](https://wordpress.org/support/users/michaelthulin/)
 * (@michaelthulin)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340238)
 *     ```
       <?php
       /*
       Plugin Name: test
       Plugin URI: http://xxx.xx
       Description: Test description
       Version: 1.0
       Author: Michael Thulin
       Author URI: http://xxx.xx
       */
       if (!class_exists("testclass")) {
           class testclass {
               function testfunction() {
       			function addHeaderCode() {
                   ?>
       <!-- thulin Was Here -->
                   <?php
   
       			}
               }
           }
       }
   
       if (class_exists("testclass")) {
           $dl_pluginSeries = new testclass();
       }
   
       if (isset($dl_pluginSeries)) {
           add_action('wp_head', array(&$dl_pluginSeries, 'addHeaderCode'), 1);
       }
       ?>
       ```
   
 *  [vtxyzzy](https://wordpress.org/support/users/vtxyzzy/)
 * (@vtxyzzy)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340241)
 * OK, just to clarify, when you installed another plugin and it still gave you 
   an error, did it still say topmenu.php in the error message?
 *  [s_ha_dum](https://wordpress.org/support/users/apljdi/)
 * (@apljdi)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340242)
 * I copied your code into my plugins directory and I don’t get the ‘headers sent’
   error. I do get this:
 *     ```
       Warning:  call_user_func_array() [<a href='function.call-user-func-array'>function.call-user-func-array</a>]: First argument is expected to be a valid callback, 'testclass::addHeaderCode' was given in /usr/local/apache/htdocs/wordpress/ysmagazine/wp-includes/plugin.php on line 339
       ```
   
 * `addHeaderCode` is nested inside `testfunction` so it isn’t being found.
 * The original error states that the headers were sent by topmenu.php. That’s were
   I’d look for the problem.
 *  [Mark / t31os](https://wordpress.org/support/users/t31os_/)
 * (@t31os_)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340246)
 * The key is right here in the message..
 * > **output** started at /domains/www.xxx.xx/wp-content/**plugins/topmenu**
 * “Output” ie. something has been output, before the headers were sent.. (you cant
   output before sending headers).
 * Disable or fix whichever plugin that is..
 *  Thread Starter [michaelthulin](https://wordpress.org/support/users/michaelthulin/)
 * (@michaelthulin)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340252)
 * was trying out some code for a plug-in tutorial.
    I have tried to copy Akismet
   into the topmenu.php and I still get the same error therefore I thought that 
   it actually was a problem.
 * But even tho I installed a plugin with following comment:
 *     ```
       /*
       Plugin Name: test
       Plugin URI: http://xxx.xx
       Description: Test description
       Version: 1.0
       Author: Michael Thulin
       Author URI: http://xxx.xx
       */
       ```
   
 * (nothing more)
 * and the same error still appeared – why’s that?
 *  [Shane G.](https://wordpress.org/support/users/shane-g-1/)
 * (@shane-g-1)
 * [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340254)
 * Hi,
 * It is usually due to spaces, new lines, or other garbage at opening/closing PHP
   file <?php tag or after a closing ?> tag in wp-config.php. It can be other file
   too so need to check error message as it may list file name where the error occurred.
 * One can either upload error file from the backup or edit erroneous file. To edit
   the file one need to check below mentioned points:
 * 1. Download the file mentioned in the error message.
    2. Open that file in a 
   plain text editor 3. Check that the very first characters are <?php 4. Check 
   that the very last characters are ?> 5. Place the cursor between the ? and > 
   6. Now press the DELETE key on your computer and keep that key pressed for at
   least 15 seconds. 7. Now type > and 8. Save without pressing any other key at
   all.
 * That’s it!
 * Thanks,
 * Shane G.

Viewing 9 replies - 1 through 9 (of 9 total)

The topic ‘Cannot modify header information’ is closed to new replies.

## Tags

 * [modify header information](https://wordpress.org/support/topic-tag/modify-header-information/)

 * In: [Fixing WordPress](https://wordpress.org/support/forum/how-to-and-troubleshooting/)
 * 9 replies
 * 5 participants
 * Last reply from: [Shane G.](https://wordpress.org/support/users/shane-g-1/)
 * Last activity: [16 years, 5 months ago](https://wordpress.org/support/topic/cannot-modify-header-information-30/#post-1340254)
 * Status: not resolved

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