bad weak pointer when base and derived class both inherit from boost::enable_shared_from_this

Question

I have a base class which derives from boost::enable_shared_from_this, and then another class which derives from both the base class and boost::enable_shared_from_this:

Answer 1

You shouldn't inherit from enable_shared_from_this more than once in a given inheritance chain.

In this case, you can leave the base class A inheriting from enable_shared_from_this, and have the derived class B return a shared_ptr and then static_pointer_cast it to shared_ptr.

Or as Omnifarious pointed out, you could have a function in B which does this for you. Although, rather than overloading shared_from_this() I would favour explicitly-named functions to minimise surprises for clients of the class:

#include 
#include 

using boost::shared_ptr;

class A : public boost::enable_shared_from_this { };

class B : public A {
public:
    using enable_shared_from_this::shared_from_this;
    shared_ptr shared_B_from_this() {
        return boost::static_pointer_cast(shared_from_this());
    }
    shared_ptr shared_B_from_this() const {
        return boost::static_pointer_cast(shared_from_this());
    }
};

int main() {
    shared_ptr b = shared_ptr(new B);
    shared_ptr b1 = boost::static_pointer_cast(b->shared_from_this());
    shared_ptr b2 = b->shared_B_from_this();
    return 0;
}