[C++-sig] Continuing Pointer Issue

[CLARKE,RON (HP-Vancouver,ex1)]

David - thanks for the response on the previous message regarding wrapping a
pointer member variable. (see below)
class car
> {
> public:
>     car(void);
>     virtual ~car(void);
> private:
> ... 
> };
>  
> class garage{
> public:
>     garage(void);
>     ~garage(void);
>     car* pCar;
> };
>  
> Class garage contains a public pointer to a car object (I don't have the
> option of changing the C++ code; it would negatively affect too many
users).
> I can create garage and car objects OK and Python understands each one:
> c=car()
> g=garage()
>  
> However, if I try something like this:
>          g.pCar = car()
> the resulting object is null and trying to simply print the object yields
a
> "TypeError: bad argument for built-in operation".
>  
> What have I missed? Can someone please provide an example (other than what
> is in the documentation)?

I think this might work for you:

     class_<garage>("garage")
        .add_property(
            make_getter(&garage::pCar, with_custodian_and_ward<1,2>())
            , make_setter(&garage::pCar, return_internal_reference<>()))

However, if garage::~garage() does "delete pCar" you're going to have
big problems.  Let me know if that's the case and we can try something
else.


------(end of response) ----------

I tried the code as specified, but it did not compile. So based on the
example, I did some more reading of the documentation and source code, and
tried to figure something out, but I'm getting nowhere. I cannot get the
code (or several variations on the them) to compile, much less test
successfully in Python. Here is the code that fails to compile:
BOOST_PYTHON_MODULE(house)
{
    class_<garage>("garage")
        .add_property("pCar"
            , make_getter(&garage::pCar, with_custodian_and_ward<1,2>())
            , make_setter(&garage::pCar, return_internal_reference<>() )
            )
        ;
}

The Visual Studio .NET compiler emits these messages:

f:\Downloads\Python
etc\Boost2\boost_1_29_0\boost\python\data_members.hpp(34) : error C2079:
'cr' uses undefined struct
'boost::python::detail::specify_a_result_policy_to_wrap_functions_returning<
T>'
        with
        [
            T=source 
        ]
        f:\Downloads\Python
etc\Boost2\boost_1_29_0\boost\python\data_members.hpp(27) : while compiling
class-template member function 'PyObject
*boost::python::detail::member<Data,Class,Policies>::get(Data garage::*
,PyObject *,PyObject *,const
boost::python::with_custodian_and_ward<custodian,ward,BasePolicy_> &)'
        with
        [
            Data=car *,
            Class=garage,
 
Policies=boost::python::with_custodian_and_ward<1,2,boost::python::default_c
all_policies>,
            custodian=1,
            ward=2,
            BasePolicy_=boost::python::default_call_policies
        ]
        f:\Downloads\Python
etc\Boost2\boost_1_29_0\boost\python\data_members.hpp(83) : see reference to
class template instantiation
'boost::python::detail::member<Data,Class,Policies>' being compiled
        with
        [
            Data=car *,
            Class=garage,
 
Policies=boost::python::with_custodian_and_ward<1,2,boost::python::default_c
all_policies>
        ]
        f:\boost_tests\simple1\house_boostwrapper\house_boostwrapper.cpp(48)
: see reference to function template instantiation
'boost::python::api::object boost::python::make_getter(D garage::*  ,const
boost::python::with_custodian_and_ward<custodian,ward,BasePolicy_> &)' being
compiled
        with
        [
            D=car *,
            custodian=1,
            ward=2,
            BasePolicy_=boost::python::default_call_policies
        ]
f:\Downloads\Python
etc\Boost2\boost_1_29_0\boost\python\data_members.hpp(35) : error C2228:
left of '.convertible' must have class/struct/union type
f:\Downloads\Python
etc\Boost2\boost_1_29_0\boost\python\data_members.hpp(39) : error C2064:
term does not evaluate to a function

---- (end compiler output) ----

The error message implies I need a result policy, but I cannot find anything
in the documentation that says what a result policy is. Is it the same as a
Call Policy? If so, isn't that what I have in the code being compiled (re:
with_custodian_and_ward and return_internal_reference)?

I would like to be able to do this in Python:
from vehicles import car
from house import *
from parkinglot import *

g = garage() #in house module; garage contains car pointer allocated in
garage constructor
Print "the color of the car is %s", g.pCar.getColor()

pl = parkingLot()
pl.parkTheCar(g.pCar)



Is there a way to make this work in Boost.Python?

Thanks in advance for the assistance.

-Ron


_________________________________________ 
Ron Clarke 
Digital Printing Technologies 
Hewlett-Packard Company 
ron_clarke at hp.com 
360-212-0193