WordPress 2.6: register_activation_hook Cannot See Global Variables

September 3rd, 2008

I have recently been trying to update an old plugin I created for WordPress 2.3.2 so that it would be compatible with the latest version : 2.6.

I am currently having an issue where the register_activation_hook function (and this may not be limited to this one function) where it refuses to reference the global variables that I define in the plugin.

Take the below as an example (proper code attached at the bottom):

require 'mcn_constants.php';

$mcn_test_blabla    =   "Well ??????";

register_deactivation_hook(__FILE__, 'mcn_test_uninstall' ) ;

add_action('parse_query', 'mcn_test_check');

function mcn_test_install() {
    global $this_is_broke, $mcn_test_blabla;

    add_option("mcn_test_value", "The value is: $this_is_broke And :: $mcn_test_blabla ");

function mcn_test_uninstall() {

function mcn_test_check() {
    global $this_is_broke;

    echo get_option("mcn_test_value");
    echo "Proper value : $this_is_broke";

When you load the front page of your blog with the above plugin code activated you should see :

The value is: YES I AM BROKE!!!!!
And ::Well ??????

Proper value : YES I AM BROKE!!!!!

… but instead you see:

The value is:
And ::

Proper value : YES I AM BROKE!!!!!

As you can see – the $this_is_broke and $mcn_test_blabla variables are not being set in the Option “mcn_test_value”.

Yet calling the global variable in the function “mcn_test_check”, which is called as part of the “parse query” action, will show the global variable – as it should.

So – is this a bug or am I missing something fundamentally different in WordPress 2.6? Using global variables in WordPress 2.3.2 worked just fine.

I have attached a sample plugin that will replicate this issue.

Any ideas?


Tags: , , , ,

Categories: ALM, Programming, Wordpress

4 Responses to “WordPress 2.6: register_activation_hook Cannot See Global Variables”

  1. ishek says:

    Global scope issue

  2. You should add

    global $mcn_test_blabla;

    at the beginning.
    Good luck!

  3. Tonelli says:

    were you able to solve this problem???

    I can`t even make the app call register_activation_hook;

    does not work, can you help me???

    • mcnicholl says:

      Hi Tonelli,

      This issue was resolved by making all variables defined outside of a function as global.


      global $variable_name;

      instead of:


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