How to define the access resolution to call a function pointer - class data member

I was trying to play around the messages posted; while doing so, i
came across something weird (atleast for me) to call a class level
function pointer like this
((*obj).*(((*obj).f)))()

If i do not specify the instance name 2nd time, MSVC8.0 complains that
'f' is undeclared identifier. Any idea about this weird access
resolution is required:
#include <algorithm>
#include <vector>
#include <functional>

class A{
public:
    typedef void (A::*FN)();
    FN f;
    A(): f(&A::show){}
    virtual void show()
    {
        std::cout<<"TEST A"<<std::endl;
    }
    virtual ~A(){}
};

class B : public A
{
public:
    typedef void (B::*FN)();

    FN f;
    B(): f(&B::show){}
    void show()
    {
        std::cout<<"TEST B"<<std::endl;
    }
    virtual ~B(){}
};

template<class T1, class T2>
struct IsOfT2Type : public std::unary_function<T1*, bool>
{
    IsOfT2Type() : result(){}
    std::vector<T1*> result;
    bool operator()(T1* obj)
    {
        if(dynamic_cast<T2*>(obj) != 0)
        {
            result.push_back(obj);
            return true;
        }
        return false;
    }
};

struct CallShow : public std::unary_function<A*, void>
{
    void operator()(A* obj)
    {
        (obj->*f)();
        ((*obj).*((f)))();
    }
};

int main ()
{
    std::vector<A*> col;

    col.push_back (new A());
    col.push_back (new B());
    col.push_back (new A());
    col.push_back (new A());
    col.push_back (new B());

    IsOfT2Type<A, B> objB = std::for_each(col.begin(), col.end(),
IsOfT2Type<A, B>());
    for_each(objB.result.begin(), objB.result.end(), CallShow());
    return 0;
}

leave the memory leaks for now!

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