Do something after submit the form at hook_form_alter I want to do something after I submit the node. How can I do that?

I use hook_form_form_id_alter(),but I dont know how to use callback function called after the user submit the form

function mymodule_form_node_form_alter(&amp;$form,&amp;$form_state,$form_id)
{
     if($form['#node']-&gt;type=="my_content_type")
     {
          $form['actions']['submit']['#submit'][]=my_callback_function;
     }
}

function my_callback_function($form,$form_state)
{
     //my code here!!
     //execute after the user submit the node form
     //and then redirect user to another place,after executing the code above

}


it doesn't work! and I don't know why?
Please tell me how can I do that?
Sorry about that! My problem is fixed.

the code belowed is the anwser

function mymodule_form_node_form_alter(&amp;$form,&amp;$form_state,$form_id)
{
     if($form['#node']-&gt;type=="my_content_type")
     {
          $form['actions']['submit']['#submit'][]='my_callback_function';
     }
}

function my_callback_function($form, &amp;$form_state)
{
     //my code here!!
     //execute after the user submit the node form
     //and then redirect user to another place,after executing the code above

}


[Edit] For me, the callback would not fire unless form_state was declared as &amp;$form_state (pass by reference)