GdkFont::measure
int measure(string text_string);
The return from this method is the equivalent of the right bearing
returned by extents() . It is the
size in pixels of the width of the string, to the point where the final
part of the final character in the string is drawn.
If you need the logical width of the string - that is, to the point
where the next character should be inserted - use
width() instead.