Auto-resize scrolled window

[Subsentient <thinkingrodent gmail com>]

When I resize the window, I'm having difficulty finding a way to make a 
scrolled window automatically resize with it. I can't use 
gtk_widget_set_size_request(), because then I won't be able to shrink it 
down again.
Working in C. How can I have a widget automatically resize to fill all 
available space given by a window, and then be willing to shrink again 
if the user tries to resize the window?

Thanks.