Re: [gtk-list] gtk--: segfault in destructor of spinbutton!
- From: Guillaume Laurent <glaurent worldnet fr>
- To: gtk-list redhat com
- cc: Gtk-- mailing-list <gtkmm modeemi cs tut fi>
- Subject: Re: [gtk-list] gtk--: segfault in destructor of spinbutton!
- Date: 05 Aug 1998 19:28:26 +0200
(cc-ing to the Gtk-- mailing list)
Oliver Freyd <firstname.lastname@example.org> writes:
> I've found out now why my app crashes on exit, when the windows are destroyed.
> A stack strace with gdb show that the Gtk_Spinbutton wants to delete its
> Gtk_Adjustment. Now I've declared both elements on the stack, so they get
> deleted automatically when the MainWindow gets destroyed. So in effect
> Gtk_Adjustment gets killed twice!
It's a bug all right. We're deleting something we have no idea if we
actually can. Also, the get_adjustment() method will crash too.
> So this is an ownership problem. In my opinion gtk-- should only delete
> a contained object if it was created on the heap, but not if it lives on the
> stack, as in that case it will "die" by itself, when the object it
> lives in gets out of scope. Only I have no idea how to find out if an object
> was created by "new" or just on the stack.
You can't, AFAIK. (writing our own operator new perhaps ?)
> Maybe someone else knows more, or should I better create everything
> with new and delete it in the destructor. But then how do I know if
> a container will delete what it contains or if I should do it
This is precisely the problem Tero and I have been trying to tackle
(see the Gtk_SpinButton::get_adjustment() method for a scheme of the
solution): How to handle methods which return pointers to newly
created objects... You've just proved we've been a bit overzealous.
- We could be leaving it to the user to delete whatever needs to be
deleted. Since the Gtk_Adjustment can be passed as an argument to the
constructor, or set later on, there's no way we can know for sure if
the adjustment member (adjustment_widget) points to something we can
(or should) delete.
OTOH, this means that calling get_adjustment() means you have to
delete the result. Not very consistent with the gtk API, this is
supposed to be a simple accessor.
- Or, we could overload both set_adjustment() and the constructor to
take Gtk_Adjustment&, and those would set some internal flag which
would tell the destructor and get_adjustment() to leave the adjustment
member alone ?
Like this :
gfloat climb_rate, gint digits) :
m_delete_adjustment = false;
if(adjustment_widget && m_delete_adjustment) delete adjustment_widget;
This means the only thing the user has to take care of is not to pass
the address of a stack object to the constructor or set_adjustment(),
but that's a much lighter burden than deleting the result of a trivial
- Finally, may be the simplest solution would be not to delete anything,
but have get_adjustment() be a simple accessor indeed, and simply
return adjustment_widget, instead of calling
gtk_spin_button_get_adjustment() and wrapping a new Gtk_Adjustment
around the result. adjustment_widget would of course be maintained by
the constructor and set_adjustment().
I prefer the third and last solution, unless some of you have better
] [Thread Prev