Transfer a boost::ptr_list from a library to a client

Question

I dynamically load a library in C++ like described here.

My abstract base class looks like this:

#include <boost/ptr_container/ptr_list.hpp>
class Base {
public:
    virtual void get_list(boost::ptr_list<AnotherObject>& list) const = 0;
};

And my library now provides a derived class Derived

class Derived : public Base { ... };

void Derived::get_list(boost::ptr_list<AnotherObject& list) const {
    list.push_back(new AnotherObject(1));
    list.push_back(new AnotherObject(2));
}

and create and destroy functions

extern "C" {
    Base* create() { new Derived; }
    destroy(Base* p) { delete p; }
}

My client program loads the library and the two create and destroy functions. Then it creates an instance of Derived and uses it:

Base* obj = create();
boost::ptr_list<AnotherObject> list;
obj->get_list(list);

Now my problem: When the list is filled by the library the library's new is called to create the AnotherObjects. On the other hand when the list is destroyed the client's delete is called for destroying the AnotherObjects. What can I do to avoid this problem?

Answer 1

The easy answer is to insist that both application and library are compiled with the same version of the compiler, in which case they will both get the same new/delete versions.

Answer 2

The best way is to have one operator new and one operator delete for the whole program. There are linking options which can help (I remember -Wl,--export-dynamic but it could be for a different but related problem).

If that isn't possible, ensure that all delete operation are made by the same entity which does the new, so don't define them in inline functions.

Answer 3

1. Use a std::list<shared_ptr<AnotherObject> >.
2. Pass a custom deleter to the shared_ptr that calls the proper delete.