Re: [Boost-users] Accessing members from a shared pointer passed as argument to a function gives incorrect results without typecast

Subject: Re: [Boost-users] Accessing members from a shared pointer passed as argument to a function gives incorrect results without typecast
From: Jeff Flinn (Jeffrey.Flinn_at_[hidden])
Date: 2013-04-15 07:32:02

On 4/15/2013 6:02 AM, Deepak Gunjal wrote:
> Hi,
>
> class A;
> class B;
> typedef boost::shared_ptr<A> pSharedPtrA;
> typedef boost::shared_ptr<B> pSharedPtrB;
>
> class B   {
> public:
> int memberB;
> };
>
> Class A   {
>
> public:
>
>   pSharedPtrB pMember;
>
> };
>
> Suppose i have one shared pointer of type pSharedPtrA pointing to an
> object of class A and the member variable pMember pinging to a valid
> object of class B.
>
> Now if i pass the shared pointer of type pSharedPtrA to a function
> suppose Test_Func(pSharedPtrA):
> void Test_Func(pSharedPtrA  pLocalA)
> {
>   pSharedPtrA ptrA =  boost::static_pointer_cast<A> (pLocalA)
>
>
>   pSharedPtrB tmpB = boost::static_pointer_cast<B>(ptrA->pMember)
>
>    Another_Func(tmpB)
> }
>
> Another_Func(pSharedPtrB pLocalB)
> {
>     int x = pLocalB->memberB; //Gives WRONG value
>    pSharedPtrB   ptmp = boost::static_pointer_cast<B> (pLocalB)
>    x = ptmp ->memberB; //Gives CORRECT Value
>
> }
>
> The problem is when typecast is not used then in function
> Another_Func(pSharedPtrB pLocalB), pLocalB->memberB is not giving the
> correct result but after typecast it is giving the correct results.

In the code above memberB is never initialized, so how do you know what 
is the correct value?

Provide a minimal fully compiling, runnable example. Doing so will 
probably uncover your problem, and at least will allow others to run 
your example.

Jeff