Trying new callback directly in command

Wininformations is created provisionally to show a msg, and then I want to remove it completely from memory.

I can not make callback recognize WinInformations. So I can close it.

And I also can not keep the window open for a few seconds because using the sleep command the window is not shown before, as it should!

Is it possible to do that?
Thanks!

{ Fl_Window *WinInformations = new Fl_Window(230, 100);
   WinInformations->border(0);
   WinInformations->position((WinGrid->w() - WinInformations->w())/2 + WinGrid->x(), (WinGrid->h() - WinInformations->h())/2 + WinGrid->y());
   WinInformations->set_modal();

   { Fl_Button *BtExit = new Fl_Button(90, 60, 60, 25);
      BtExit->label("Exit");
      //BtExit->callback([](Fl_Widget*, void*) {WinInformations->hide();}); // NO WORK

      //BtExit->callback([WinInformations](Fl_Widget*, void*) {WinInformations->hide();}); // NO WORK

      BtExit->callback([](Fl_Widget*, void *WinInformations) {
         Fl_Window *Win = (Fl_Window*)WinInformations;
         //Win->hide(); // Segmentation fault
         //delete Win; // NO WORK
      });

   }
   WinInformations->show();
   //sleep(10); // Does not display the above window with this sleep
   //WinInformations->hide();
}