How to get scroll bar infromation in C?

[frank zhang <fz2018 gmail com>]

Hello,

     I am writing a program in C to get the scroll bar information for an
existing application such as a text file or a webpage opened in GNOME
desktop. If the existing application window is the currently active window
and it has scroll bars, my program needs to be able to move the mouse
pointer onto the scroll bar and scroll the content of the window
up/down/left/right depending on the user choice. For example, when the user
holds the 'CTRL' key and 'Right Arrow' key from the keyboard, the mouse
pointer will jump from the current position to the middle of horizontal
scroll bar and the window content scrolls to the right. I understand it is
not a problem if the application window is developed with GTK+. The question
is my program needs to be able to scroll any type of window opened in GNOME
desktop and that window may not be a GTKWindow or GDKWindow.

      Could anyone shed some light on how to use GTK+ or GNOME API to do
this?

Thanks,

Frank