The #c++channel on irc.gnome.org seemed not very verboose, but I was in need for help. And danielk, one of the authors of regexxer, took the time to look from very close to my problem(s). Together, we ported the inkscape code to gtkmm2.4 and libsigc++2, and he found that the bug in my code was to try to access the Pixbuf before the Gtk::Main instanciation. Of course he was right, because there were no Gtk::Main instanciation, but a simple gtk_init. Now it works and I have a proof !

Looks like I will be able to continue the work I intended after all ...

By the way, regexxer is a nice tool for programmers and anyone doing recursive greps ...