¿Pueden las funciones virtuales ser privadas en C++?

C++

// C++ program to demonstrate how a
// virtual function can be private
#include <iostream>
 
class base {
public:
    // default base constructor
    base() { std::cout << "base class constructor\n"; }
 
    // virtual base destructor
    // always use virtual base
    // destructors when you know you
    // will inherit this class
    virtual ~base()
    {
        std::cout << "base class destructor\n";
    }
    // public method in base class
    void show()
    {
        std::cout << "show() called on base class\n";
    }
 
    // public virtual function in base class,
    // contents of this function are printed when called
    // with base class object when called with base class
    // pointer contents of derived class are printed on
    // screen
    virtual void print()
    {
        std::cout << "print() called on base class\n";
    }
};
 
class derived : public base {
public:
    // default derived constructor
    derived()
        : base()
    {
        std::cout << "derived class constructor\n";
    }
    // virtual derived destructor
    // always use virtual destructors
    // when inheriting from a
    // base class
    virtual ~derived()
    {
        std::cout << "derived class destructor\n";
    }
 
private:
    // private virtual function in derived class overwrites
    // base class virtual method contents of this function
    // are printed when called with base class pointer or
    // when called with derived class object
    virtual void print()
    {
        std::cout << "print() called on derived class\n";
    }
};
 
int main()
{
    std::cout << "printing with base class pointer\n";
 
    // construct base class pointer with derived class
    // memory
    base* b_ptr = new derived();
 
    // call base class show()
    b_ptr->show();
 
    // call virtual print in base class but it is overridden
    // in derived class also note that print() is private
    // member in derived class, still the contents of
    // derived class are printed this code works because
    // base class defines a public interface and drived
    // class overrides it in its implementation
    b_ptr->print();
 
    delete b_ptr;
}