[C++-sig] Lifetime of Python object for a pointer argument

[Min Xu]

Hi, 

I am a newbie of boost python. In the process of converting a SWIG
wrapping of a C++ library to boost python, I encounter the following
problem:

// C++ part
class grid
{
public:
   grid() { ... }
   ...
};

class geometry 
{ 
public:
    geometry(const grid * gd) : gd(gd) {}
    const grid* getGrid() const { return gd; }
private:
    const grid* gd;
};

// Wrapper
#include <boost/python/class_builder.hpp>
namespace python = boost::python;

PyObject* to_python(const grid* g) {
     return to_python(*g); // convert const grid* in terms of const 
grid&
}

BOOST_PYTHON_MODULE_INIT(ngf2)
{
  try
  {
    python::module_builder this_module("ngf2");
    python::class_builder<grid> grid_class(this_module, "grid");
    grid_class.def(python::constructor<>());
    python::class_builder<geometry> geometry_class(this_module,
"geometry");
    geometry_class.def(python::constructor<const grid*>());
  }
  ...
}

The compilation works well (the newest CVS version of boost python).
In python:
>>> from ngf2 import *
>>> a=geometry (grid())
>>> a.getGrid ().a()
8.6723632812500586   # corrupted as grid() is deleted automatically? 
>>> g=grid()
>>> b=geometry (g)
>>> b.getGrid ().a() 
1.0                  # expected.
>>> del g
>>> b.getGrid ().a()
1.3285421879284814e-269 # corrupted 

I understand it may be a ref counting problem. Is there any way to make
the first idiom work? 

Thanks!


Min Xu