Re: [Boost-users] Problem with weak_ptr exception

28 Oct 2009


      On 10/28/09 15:56, Stefan Strasser wrote:
...
I can't make sense of your code ("weakThis" in both A and B, even though B is
derived from A?), but have a look at boost::shared_from_this
If I don't have a weak_ptr in B I get this error when trying to create a 
shared_ptr<B> from a weak_ptr<A>:
/shared_ptr.hpp:207: error: invalid conversion from 'A* const' to 'B*'

I've already tried boost::shared_from_this and it gives me the same result.
...
Am Wednesday 28 October 2009 12:43:08 schrieb Jacob Carlborg:
...
I'm having some problems with bad_weak_ptr exceptions. I have reduced my
code into this test case:
#include
#include
using boost::shared_ptr;
using boost::weak_ptr;
class A
{
      weak_ptr<A>  weakThis;
public:
      virtual ~A(){}
shared_ptr<A>  a;
shared_ptr<A>  getThis ()
  {
      shared_ptr<A>  x(weakThis);
      return x;
  }
void init ()
  {
      a = getThis();
  }
static shared_ptr<A>  create ()
  {
      shared_ptr<A>  x(new A);
x->weakThis = x;
      x->init();
return x;
  }
};
class B : public A
{
      weak_ptr<B>  weakThis;
  public:
      virtual ~B(){}
shared_ptr<B>  getThis ()
  {
      shared_ptr<B>  b(weakThis);
      return b;
  }
static shared_ptr<B>  create ()
  {
      shared_ptr<B>  x(new B);
      x->weakThis = x;
      x->init();
return x;
  }
};
int main (char** argv, int argc)
{
  shared_ptr<B>  b = B::create();
return 0;
}
If I create an instance of A instead of B or doesn't call x->init() in
the B's create function I don't get an exception. The problem is
creating a shared_ptr from the weak_ptr in getThis.
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