Gtk-- Entry Size

[Kevin Handy <kth srv net>]

I want to create an entry widget that has been sized to
approximately the number of characters that it can contain.
(This gives a visual cue for the data entry people)
The only size function I can find is the set_usize function
which wants the size in pixels.

I've tried to use gdk_string_width, but it needs the font to use,
and I cannot find a function to tell me what font the the entry
field will use. I did come up with

	GdkFont* font = efield.get_style()->gtkstyle->font;
	width = gtk_string_width(font, "X") * fieldsize;

but that will no longer compile with Gtk--0.11.1 (the error is
'gtkstyle is a protected member of class Gtk_Style').

So, what is the official way to set the size of an entry/label/...
widget using Gtk--? Also how much space do you need to add for
the border inside the widget? I don't want to hardcode the size of
a character, because I end up with problems due to differences in
X-Terminals/fonts, but it's beginning to look like that is going
to be the only way to do it.