[C++-sig] std::vector

[David Abrahams]

Hi Scott,

I think Ralf Grosse-Kunstleve is probably the one to answer your questions.
He's the one who implemented the import/export stuff for Boost.Python v1,
and has the most expertise in translating containers. He also has
implemented a much better mechanism for Boost.Python v2. He's been
travelling, but IIUC he might be able to get back to you by the end of the
week.

-Dave

-----------------------------------------------------------
           David Abrahams * Boost Consulting
dave at boost-consulting.com * http://www.boost-consulting.com


----- Original Message -----
From: "Scott A. Smith" <ssmith at magnet.fsu.edu>
To: <c++-sig at python.org>
Sent: Wednesday, October 02, 2002 10:02 AM
Subject: [C++-sig] std::vector


> Hello,
>
> I have been reading the documentation on dealing with std::vector<> in
> Boost.Python, http://www.boost.org/libs/python/doc/cross_module.html, and
> this is exactly what I need for both vectors of built-in types and those
> using my own classes. I have used the class builder to expose such a
vector
> as a Python object and now need to be able to go back and export some C++
> functions that use them as arguments or as a return type.
>
> Is there a module already in Boost.Python that has "std_vector"? I cannot
> find anything on it and the html page above only supposes that one had
such
> a module. I think it would help me out quite a bit if I could play with
some
> vector<int> functions to try out what is suggested. Even more, if some of
> this is already in Boost.Python I would surely like to use it rather than
> begin doing so for all the class types I am using with std::vector.
>
> For example, I have this to expose my std::vector<std::string>:
>
>     boost::python::class_builder<std::vector<std::string> >
> Vstring(PyModule, "Vstring");
>     Vstring.def(boost::python::constructor<>());
>     Vstring.def(Vstring_push_back, "push_back");
>
> and this allows me to make objects of Vstring in Python just fine. The
> push_back stuff is done as shown in the comprehensive test. Now, how do I
> get
>
> VS = Vstring()
> VS = MyFunctionReturningStdVectorOfStrings()
> MyFunctionUsingStdVectorOfStrings(VS)
>
> by exporting C++ functions that are something like
>
> std::vector<std::string> MyFunctionReturningStdVectorOfStrings();
> void MyFunctionUsingStdVectorOfStrings(std::vector<std::string>);
>
> to work in Python. Do I need import_converters/export_converters? Do I
need
> them even when everything is in the same module? Neither the
"vector_double"
> nor "string_map" in the comprehensive test show this and AFAIK the test
does
> have any code where C++ functions using and returning std::vector<double>
> are exported and making use of vector_double.
>
> Is there other documentation on this, or perhaps a place where I can
easily
> search for such info?
>
> Thanks,
> Scott
>
>
>  =======================================
>  Dr. Scott A. Smith
>  Associate in Research
>  National High Magnetic Field Laboratory
>  1800 East Paul Dirac Drive
>  Tallahassee, FL 32310
>
>  phone: (850) 644-6348
>  FAX:   (850) 644-1366
>  email: ssmith at magnet.fsu.edu
>  http://www.magnet.fsu.edu
>  http://gamma.magnet.fsu.edu
>
>
>
> > -----Original Message-----
> > From: c++-sig-admin at python.org [mailto:c++-sig-admin at python.org]On
> > Behalf Of David Abrahams
> > Sent: Wednesday, October 02, 2002 8:05 AM
> > To: c++-sig at python.org
> > Subject: Re: [C++-sig] Pointer manipulation Boost.Python - C++
> >
> >
> > I'm going to answer this in terms of Boost.Python v2, since v1 is now
> > retired and won't be in the upcoming release.
> >
> > From: "Mathieu Tremblay" <mtremblay at golemlabs.com>
> >
> >
> > > Hello,
> > > I am taking a look at Boost.Python and I wonder if it is possible
> > > to convert pointers to existing classes to PyObjects* and then be
> > > able to pass an existing instance of an object directly to and from
> > > python:
> >
> > It is.
> >
> > >  Example:
> > >   In C++ I create a CWheel and I set its member m_diameter to 1233.
In
> > >  python I have a function that receives a CWheel and displays the
> > >  diameter (Lets suppose that Python knows the CWheel from
Boost.Python
> > > :-) )
> > >              Ex : def printCWheelDiam(awheel):
> > >                          print awheel.m_diameter
> > >
> > >              What I would like to do Is to create the CWheel in C++,
> > >  pass its pointer to python so it can manipulate
> > >  it (and see that its diameter is 1233)  and then return a
> > >  CWheel that I could map from a PyObject to a CWheel in C++.
> >
> > The safest thing to do is to create the CWheel by invoking its class
> > wrapper:
> >
> >     // Declare the CWheel extension class
> >     object wheel_class =
> >         class_<CWheel>("CWheel")
> >             .def_readonly("m_diameter", &CWheel::m_diameter)
> >             .def("some_member_function", &CWheel::some_member_function)
> >             ...
> >             ;
> >
> >     object wheel_obj = wheel_class(); // construct one
> >
> > Now you can pass wheel_obj back to python, and all reference counts are
> > nicely managed. You don't need to "map" anything between C++ and
Python;
> > the library takes care of that for you.
> >
> > If you really want to pass pointers around, it's certainly
> > possible to tell
> > the library to build a Python object around the pointer, but then you
need
> > to make sure the lifetime of the C++ object being referenced by
> > the pointer
> > extends past the lifetime of all Python references to the object or
your
> > program will crash.
> >
> >
> > -----------------------------------------------------------
> >            David Abrahams * Boost Consulting
> > dave at boost-consulting.com * http://www.boost-consulting.com
> >
> >
> >
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>
>
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