[Boost-users] enable_shared_from_this and inheritance

22 Oct 2003

      I'm trying to use enable_shared_from_this with my classes that have an 
inheritance structure and a virtual function.
I'd like to get a shared pointer to the descendant class B.  I've 
attached 2 files. One compiles but errors at runtime, the other doesn;t 
compile.

The first method uses makes both class A and B inherit from 
enable_shared_from_this. The 2nd method makes only the base class A 
inherit from enable_shared_from_this and tries to dynamic cast to 
shared_ptr<B>.

-- 
sashan
http://www.cs.auckland.ac.nz/~sgov008/

#include <iostream>
#include <boost/enable_shared_from_this.hpp>

using namespace std;
using namespace boost;

class A :
	public enable_shared_from_this<A>
{
public:
	A(){ cout << "A" << endl; }
	virtual void f() { shared_ptr<A> pA(shared_from_this());}
};

class B : 
	public A,
	public enable_shared_from_this<B>

{
public:
	B() { cout << "B" << endl;}
	virtual void f() 
	{		
		shared_ptr<B> pB(enable_shared_from_this<B>::shared_from_this());		
	}
};
void main()
{
	shared_ptr<A> a(new A);
	a->f();
	shared_ptr<B> b(new B);
	b->f();
}

#include <iostream>
#include <boost/enable_shared_from_this.hpp>

using namespace std;
using namespace boost;

class A :
	public enable_shared_from_this<A>
{
public:
	A(){ cout << "A" << endl; }
	virtual void f() { shared_ptr<A> pA(shared_from_this());}
};

class B : 
	public A

{
public:
	B() { cout << "B" << endl;}
	virtual void f() 
	{		
		shared_ptr<A> pA(shared_from_this());
		shared_ptr<B> pB(dynamic_pointer_cast< shared_ptr<B> >(pA));		
	}
};
void main()
{
	shared_ptr<A> a(new A);
	a->f();
	shared_ptr<B> b(new B);
	b->f();
}