How to instance parameters from views_query_alter() in drupal 7?

Hello,

I'm trying to use views_query_alter in drupal 7 to remove a part of the where clause. This is well explained in other topics but here is not the problem.

My problem is that I don't know how to instanciate $view object and $query, the two parameters of the function. For now, a var_dump() over them return null.

My function views_query_alter is located in the template.php. How do you instance those parameters ?

Thanks and merry christmas.