C++: inheritance problem

Question

It's quite hard to explain what I'm trying to do, I'll try: Imagine a base class A which contains some variables, and a set of classes deriving from A which all implement some method bool test() that operates on the variables inherited from A.

class A {
   protected:
   int somevar;
   // ...
};

class B : public A {
   public:
   bool test() {
      return (somevar == 42);
   }
};

class C : public A {
   public:
   bool test() {
      return (somevar > 23);
   }
};

// ... more classes deriving from A

Now I have an instance of class A and I have set the value of somevar.

int main(int, char* []) {
    A a;
    a.somevar = 42;

Now, I need some kind of container that allows me to iterate over the elements i of this container, calling i::test() in the context of a... that is:

    std::vector<...> vec;
    // push B and C into vec, this is pseudo-code
    vec.push_back(&B);
    vec.push_back(&C);

    bool ret = true;
    for(i = vec.begin(); i != vec.end(); ++i) {
       // call B::test(), C::test(), setting *this to a
       ret &= ( a .* (&(*i)::test) )();
    }
    return ret;
 }

How can I do this? I've tried two methods:

1. forcing a cast from B::* to A::*, adapting a pointer to call a method of a type on an object of a different type (works, but seems to be bad);
2. using std::bind + the solution above, ugly hack;
3. changing the signature of bool test() so that it takes an argument of type const A& instead of inheriting from A, I don't really like this solution because somevar must be public.

EDIT:

Solution (1) is:

typedef bool (A::*)() mptr;
std::vector<mptr> vec;
vec.push_back(static_cast<mptr>(&T::test));

std::vector<mptr>::iterator i;
for(i = vec.begin(); i != vec.end(); ++i) {
   (a .* (*i))();
}

I'm not sure the static cast is safe.

Answer 1

The cleanest solution is the last one you suggest, make test a (pure) virtual function in A:

virtual bool test(const A& value) = 0;

If you're bothered with making somevar public keep it private and supply only a public get function:

int getvar() const {return somevar;}