Form Alter: How to check if a node has a Field Type My module provides a field. In hook_form_alter() I need to change only those nodes that have this field set up. (I can't operate use hook_field_form_alter() because it does operates changes for other things than my own field.)

How can check if my field belongs to the node?
Is there an easy function to check if the field type exists in $form?

Otherwise, if I need to look at $form the problem is that I can't know the machine name used for the field by the admin/drupal as it looks like something like $form['my_field_namedbyuser'].
If you are searching for specific field then see the code below 

 function hook_form_alter(&amp;$form, &amp;$form_state, $form_id) {
if ($form_id == 'form_id_name') { 
        $abc = array();
        foreach ( $form_state['field'] as $key =&gt; $value ) {
            $abc[$key] = $key;
        };
}
    }


From this $abc variable you will get all the field name and then you can check from this array to see if the field you want exists or not using any of the php functions.
For e.g.
you can use array_key_exists('field_name', $abc);