On 1/26/22 16:49 Apprentice wrote:

The solution I could find to close the window was like this. Of course if someone has a better solution, thank you too!

BtExit->callback([](Fl_Widget *, void *data) {
   ((Fl_Window*)data)->hide();
}, (void*)WinInformations);

If you add more and more code to your lambda _expression_ it seems to become easier to add a static callback...

That said, if you want to close the window that contains the BtExit button you don't need to "send" the window in the data pointer, you can also use the window() method on the exit button which is always in the Fl_Widget pointer, something like

BtExit->callback([](Fl_Widget *button, void *) {
  button->window()->hide();
};

should work (untested).