[gtkmm] adding icons to buttons in gtkmm

[Tim Flechtner <timf trdlnk com>]

i am having the hardest time figuring out how to add an icon to a button 
in gtkmm.  i know it can be done, because i can set it up that way in 
glade, and instantiate it from libglademm.

what i'd like to do is have a button with the stock up arrow centered, 
and no label.  i see that Gtk::Bin has add_pixmap function

void
add_pixmap (const Glib::RefPtr<Gdk::Pixmap>& pixmap, const 
Glib::RefPtr<Gdk::Bitmap>& mask)

and that Gdk::Pixmap can be created from a .xpm, but i can't find where 
the stock icons are installed, and i suspect they'd be .pngs anyway. 
can anyone point me towards documentation that explains how to add a 
stock icon to a button through gtkmm?

thanks!
-tim