[Boost-users] [shared pointer] - question about different types pointing to the same object

6 Jun 2009

      I've looked through the shared_ptr documentation and am still puzzled about 
something.

suppose I have

class base1 {
    virtual ~base1;
    ...
};
class derived1 : public base1
{
....
};

shared_ptr<derived1> pd1(new derived1)
shared_ptr<base1> pb1(pd);

? do pd1 and pb1 refer to the same object?

class base2 {
    virtual ~base2;
    ...
};
class derived3 : public base1, public base2 {
    ...
};

shared_ptr<base2> pb2(pd1);

? do pb1 and pb2 refer to the same object?

I'm presuming they do, but it's not really clear to me that
this would work.  To check this I could downcast everything to derived3.
BUT when I have pb1 and pb2, I don't know what to downcast to. since
there could be

class derived4 : public base1, public base2 {
    ...
};

So how could I verify whether an arbitrary pb1 and pb2 point to the
same object or not?

Robert Ramey