如何在for_each中使用dynamic_cast

Question

I have the following code:

vector<C1*>::iterator itr = vec.begin();
for (; itr != vec.end(); ++itr) {
  C2 *c = dynamic_cast<C2*>(*itr);
  c->f();
}

I am wondering if I could use one-line for_each to replace it. I tried the following:

for_each(vec.begin(), vec.end(), bind2nd(mem_fun(&C2::f), dynamic_cast<C2*>));

But I get a compile error,

expected unqualified-id before 'dynamic_cast'

What should be the right then?

[EDIT] I cannot use c++11. Looks like I have to define an extra functor, sigh.

For some questionings about the code itself: C1 and C2 are 2 pure interfaces; f() is only available as C2's API. The vector "vec" has a list of objects which have both C1 and C2 interfaces, but they are passed to this piece of code as vector of C1*.

Answer 1

Under C++11, instead of doing all this bind stuff, I would use a lambda :

for_each (vec.begin(), vec.end(), [] (C1* c1) 
{
  C2* c2 = dynamic_cast <C2*> (c1);
  if (c2)
  { 
    c2->f();
  }
});

If using C++11 isn't possible, or if for some other reason you shy away from this, then I would construct a functor to wrap this in:

struct call_f
:
  public std::unary_function <C1*, void>
{
  void operator () (C1* c1) const
  {
    C2* c2 = dynamic_cast <C2*> (c1);
    if (c2)
    {
      c2->f();
    }
  }
};

// ...

for_each (vec.begin(), vec.end(), call_f());

Answer 2

dynamic_cast<...>() may look like a function but it isn't one. You could use something like this:

template <typename T>
struct dynamic_cast_fun {
    template <typename F>
    T* operator()(F* from) const {
        return dynamic_cast<T*>(F* from);
    }
};

(possibly with some extra overloads to deal with the constness of the argument).