The adjustable widgets can be roughly divided into those which use and require specific units for these values, and those which treat them as arbitrary numbers.

The group which treats the values as arbitrary numbers includes the Range widgets (Scrollbars and Scales, the Progressbar widget, and the SpinButton widget). These widgets are typically "adjusted" directly by the user with the mouse or keyboard. They will treat the lower and upper values of an adjustment as a range within which the user can manipulate the adjustment's value. By default, they will only modify the value of an adjustment.

The other group includes the Viewport widget and the ScrolledWindow widget. All of these widgets use pixel values for their adjustments. These are also typically adjusted indirectly using scrollbars. While all widgets which use adjustments can either create their own adjustments or use ones you supply, you'll generally want to let this particular category of widgets create its own adjustments.

TODO: Text widget is deprecated: Look at GTK+ tutorial for up-to-date example. If you share an adjustment object between a Scrollbar and a Text widget, manipulating the scrollbar will automagically adjust the Text widget. You can set it up like this:

// creates its own adjustments
Gtk::Text text(0, 0);
// uses the newly-created adjustment for the scrollbar as well
Gtk::VScrollbar vscrollbar (*(text.get_vadjustment()));