Expanding Entry size when container box is horizontal

[a <vis 314 15 gmail com>]

Hi,

I have a Gtk::Entry text box inside of a Gtk::Box and the box's 
orientation is set to horizontal, so when I change the window size the 
Entry text box width size does not increase. When I set it to vertical 
the width will increase with the window size. How can I have the box's 
orientation set to horizontal and have the entry text box increase?

Thank you.

Tim O.