[C++-sig] exposing pointers using boost

[Roman Yakovenko]

On 9/4/07, Furkan Kuru <furkankuru at gmail.com> wrote:
>
> Hello,
>
> Is there a way to expose structs containing pointers of their types?


There is another problem here

Let's say, I have a very simple doubly-linked list.
>
> struct Node {
>         Node* next;
>         Node* prev;
>         int value;
> };
>
> I expose it like this:
>
> class_<Node>("Node")
>         .def_readwrite("value", &Node::value)
>         .def_readwrite("next", &Node::next)
>         .def_readwrite("prev", &Node::prev);
>
> When I try to access the next and prev attributes of a Node instance in
> python,
> I get this error:
>
> TypeError: No to_python (by-value) converter found for C++ type: struct
> Node *



If you would have access to Py++, it would generate the right code for you.


Here is cut and paste of the relevant code from the unittests:


struct tree_node_t{
    ...
    tree_node_t *left;
    ...
};

struct tree_node_t_wrapper : tree_node_t, bp::wrapper< tree_node_t > {
   ...

    static tree_node_t * get_right(tree_node_t const & inst ){
        return inst.right;
    }

    static void set_right( tree_node_t & inst, tree_node_t * new_value ){
        inst.right = new_value;
    }

};


   { //::tree_node_t
        typedef bp::class_< tree_node_t_wrapper > tree_node_t_exposer_t;
        tree_node_t_exposer_t tree_node_t_exposer = tree_node_t_exposer_t(
"tree_node_t", "documentation", bp::init< bp::optional<
member_variables::pointers::tree_node_t const * > >((
bp::arg("parent")=bp::object() ), "documentation") );
        bp::scope tree_node_t_scope( tree_node_t_exposer );
        tree_node_t_exposer.add_property( "right"
                    , bp::make_function( (::tree_node_t * (*)( ::tree_node_t
const & ))(&tree_node_t_wrapper::get_right), bp::return_internal_reference<
>() )
                    , bp::make_function( (void (*)( ::tree_node_t
&,::tree_node_t * ))(&tree_node_t_wrapper::set_right),
bp::with_custodian_and_ward_postcall< 1, 2 >() ));
    }

Pay attention to used call policies. They are very important.

HTH

-- 
Roman Yakovenko
C++ Python language binding
http://www.language-binding.net/
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