A scrollbar needs a GtkAdjustment in order to operate. The values that you give to the adjustment object will depend on the situation where the scrollbar is intended to be used.

All scrollable widgets have their own adjustment object(s), and in all instances where you are most likely to need a vertical scrollbar it is possible to create a handle for the widget's vertical GtkAdjustment and assign that as the new scrollbar's adjustment object.

For example:

<?php

$text = &new GtkText();
$adjustment = $text->vadj;
$scrollbar = &new GtkVScrollbar($adjustment);

?>