Re: Clone an object with an abstract base class

I want to clone an object through a pointer to its abstract base
class. Say I have the following classes

     class B {
             virtual void foo() = 0; // abstract base class
     };
     class D1 : public B {
             virtual void foo();
     };
     class D2 : public B {
             virtual void foo();
     };

Then I can clone objects when I know the subclass of B

     void f1(D1 *d1, D2 *d2) {
             B *b1 = new D1(*d1);
             B *b2 = new D2(*d2);
     }

but not if I only have a pointer to the abstract base class

     void f2(B *b) {
             B *b1 = new B(*b); // error: cannot create a B
     }

With GCC and -std=c++11 I can write

     void f2(B *b) {
             B *b1 = new auto(*b);
     }

Is this the correct and preferred way in C++11?

In C++98 the only way I found is to add a pure virtual function

     B *B::clone() const

and

     B *D1::close() const { return new D1(*this); }
     B *D2::close() const { return new D2(*this); }

and then call b->clone() instead of the new operator.

Is there a way to do this in C++98 without the need to add a new
function like clone() in each derived class?

urs