[C++-sig] Boost Python: Howto wrap "out" arguments of a methode

[David Abrahams]

on Mon Jun 04 2007, Alexander Eisenhuth <newsuser-AT-stacom-software.de> wrote:

> How to wrap methode Get with Boost.Python?

First, I suggest you take your question to the C++-sig
(http://www.boost.org/more/mailing_lists.htm#cplussig).


>
>       class MyClass {
>       public:
>           MyClass();
>
>           void GetX(double &pos_x);
> [...]
>
>
> I'v tried it with:
>
>           .def(
>               "GetX"
>               , &::MyClass::GetX
>               , bp::arg("")
>               , bp::return_value_policy<bp::return_arg<1>() >()
>
> But when I try it in python:
>
> Boost.Python.ArgumentError: Python argument types in
>       MyClass.GetX(MyClass, int)
> did not match C++ signature:
>       GetX(class MyClass::LedPosition_C {lvalue}, int {lvalue} )
>
> Any ideas?

return_value_policy is only good for telling Boost.Python how to
handle the actual (non-void) return value of your C++ function.  In
your case, create a thin wrapper function:

     double GetX2(MyClass& self, double pos_x) 
     { self.GetX(pos_x); return pos_x; }

and wrap that instead of GetX:

           .def("GetX", GetX2)




-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com