Shared pointers and const correctness

Question

Which is the correct way to extend the const correctness of a class to its pointed members? In the example code, is the constant version of the get method going to create an std::shared_ptr whose reference counter is the same as the internal member m_b, or is it starting again counting from 0?

class A
{
    std::shared_ptr< B > m_b;

public:

    std::shared_ptr< const B > get_b( ) const
    {
        return m_b;
    }

    std::shared_ptr< B > get_b( )
    {
        return m_b;
    }
}

Answer 1

shared_ptr will always preserve reference counts when you construct from another shared_ptr; the only way to use it unsafely is to construct from a raw pointer: shared_ptr<...>(my_ptr.get()) // don't do this .

You may also be interested in the propagate_const wrapper, which is in the Library Fundamentals TS v2 so will probably be available in your implementation quite soon.