Re: [Boost-Users] Passing shared_ptr to function that creates obj that shared_ptr points to

From: Dean Brettle (dean_at_[hidden])
Date: 2003-06-20 16:14:15

Hi Drew,

You should probably add:

void Fn(DerivedPtr& pObj)
{
  pObj = DerivedPtr(new Derived());
  pObj->m_value = 10;
}

since having a DerivedPtr (or a Derived* for that matter) point to an instance of Base is generally a bad idea.  Consider what would happen if you called pDerived->method_only_in_derived().

--Dean
  ----- Original Message ----- 
  From: Drew 
  To: Boost-Users_at_[hidden] 
  Sent: Thursday, June 19, 2003 8:38 AM
  Subject: [Boost-Users] Passing shared_ptr to function that creates obj that shared_ptr points to

  [Moderator's note: The only apparent connection this message has to Boost is in the subject line. I am approving it on the assumption that the missing declarations for ParentPtr and DerivedPtr are typedefs using boost::shared_ptr.]

  Hello everyone...

  I am attempting to do the following:

  class Parent
  {
  public:
    int m_value;
  };

  class Derived : public Parent
  {
  };

  void Fn(ParentPtr& pObj)
  {
    pObj = ParentPtr(new Parent());
    pObj->m_value = 10;
  }

  int main()
  {
    ParentPtr pParent;
    DerivedPtr pDerived;

    Fn(pDerived);

    return 0;
  }

  If I pass the parent pointer, it compiles and works fine. If I pass 
  the derived pointer I get:

  error C2664: 'Fn' : cannot convert parameter 1 from 'DerivedPtr' 
  to 'ParentPtr &'

  Does anyone know how to solve my problem?

  TIA,
  Drew

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