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.