How to execute a function once

Hi,

I want to execute a function only once per session

I tried this :

1- I created a file test.php with a php function and uploaded in root

2- in inc/design.inc.php I added require_once( 'test.php' );

The function works one time (example in search.php),

but after that, when I click to any other pages, all pages are blank...

Is someone know a better way ?

Thanks