Classes and access to outside variables

Hi there,

I am new to PHP classes and I do want to access a variable outside the class, but somehow that does not work. global also does not have any effect.

In the following example I would like to be able to access $dbh from inside the class like I did in that example. This does not work. Can somebody please give me a hint on the right syntax?

$dbh = 'test';

class search_helper extends AjaxACApplication
{
/**
* Database connection details
*/

var $db_hostname = $dbh;

Thank you for any help,

Merlin
.