resolving reference in FLTK (Fl_Widget)

Question

hello, thanks for looking I've completed the FLTK chapter in Bjarne's new book but I'm trying to run a simple FLTK code and I'm getting this reference error

error LNK2019: unresolved external symbol "public: __thiscall Fl_Widget::Fl_Widget(int,int,int,int,char const *)" (??0Fl_Widget@@QAE@HHHHPBD@Z) referenced in function "public: __thiscall Fl_Box::Fl_Box(int,int,int,int,char const *)" (??0Fl_Box@@QAE@HHHHPBD@Z) main.obj

I can compile all bjarne's FLTK exmaples but i have a problem with this one, I looked at the Fl_Widget.cpp and doesn't contain a Constructor body.

the code I'm trying to run is (59 lines): http://pastebin.com/m4b43cd63

thank you very much