[C++-sig] Re: Virtual member functions cause exception in get_derived_class_object

[David Rostowsky]

Attached are the files in question. Thanks for the direction. Im a newbie to
these lists. In my original post I was trying to post the minimal that
failed, so hence I wanted to give everything in the follow-up. Ill try to
find a happier middle ground for future posts.




"David Abrahams" <dave at boost-consulting.com> wrote in message
news:uwu4zvpit.fsf at boost-consulting.com...
>
> Hi David,
>
> First of all, please bring Boost.Python questions to the C++-sig:
> http://www.boost.org/more/mailing_lists.htm#cplussig
>
> "David Rostowsky" <davros1 at covad.net> writes:
>
> > I have a couple of really simple classes:
> >
> > class MyBase
> > {
> > public:
> >   int x;
> >   virtual int foo(int new_x) { }; // our derived classes may or may
> > not override this function. Coders choice.
> > };
> >
> > class MyDerived: public MyBase
> > {
> > public:
> >   int y;
> >   MyDerived() { y = 0; };
> >   int Get(void) { return y; };
> >   void Set(int val) { y = val; };
> > };
> >
> > My main goal in life is to create an instance of MyDerived class in
> > C++:
> > MyDerived my_derived = new MyDerived();
> >
> > and then pass the pointer to a Python script where the Python script
> > can call any of the public member functions. Yes, I am careful to keep
> > the pointer around in the C++ code while the Python script uses it.
> > So I expose the class (this may or may not be the source of my
> > problems, need help):
> >
> > BOOST_PYTHON_MODULE(test)
> > {
> >     using namespace boost::python;
> >
> >     class_<MyDerived>("MyDerived")
> >         .def("Get", &MyDerived::Get)
> >         .def("Set", &MyDerived::Set)
> >         ;
> > } /* test*/
> >
> > My impasse is that the virtual function seems to really give Boost
> > hell when Im trying to pass the pointer to the class over to the
> > python script. Heres the code snippet for that.
>
> Please post a complete, minimal, reproducible example.
>
> > Its the conversion thats just KILLING me.
>
> Chill, dude.  You're still alive.  At least someone's sending email
> on your behalf ;-)
>
> > If I comment out the virtual function, everything works perfectly! I
> > can pass the pointer over to my script, it calls the public member
> > functions, and Im happy. HOWEVER, if I put the virtual function back
> > in, the following line of code
>
> Well you've posted several lines there; can you be specific about
> which one you're having problems with?
>
> > just EXPLODES!
>
> What does "EXPLODES" mean?  Do you get a compilation error, a runtime
> error, or something else?
>
> > // It crashes and burns in make_ptr_instance.cpp, function
> > get_derived_class_object()
> > boost::python::object my_arg(boost::ref(my_derived));
> >
> > // pass the pointer over to the script now.
> > int rval = callPython("myTestFunc", "Test String argument from c++",
> > my_arg);
>
> -- 
> Dave Abrahams
> Boost Consulting
> www.boost-consulting.com
>
> _______________________________________________
> Unsubscribe & other changes:
http://lists.boost.org/mailman/listinfo.cgi/boost
>


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