What is being declared in Dog copy constructor [:Mammal(rhs)]?

Question

While reading "Sams teach yourself c++ in 21 days" I cannot understand how does virtual copy constructor work. Full code from book is here: [http://cboard.cprogramming.com/cplusplus-programming/9392-virtual-copy-constructor-help.html][1]

Especially virtual method Clone() calls Mammal copy constructor and Dog copy constructor because it returns "Mammal*" and returns "new dog (*this)"

  Mammal::Mammal(const Mammal &rhs):itsAge(rhs.GetAge())
    {
    cout <<  "Mammal copy constructor\n";
    };

Dog::Dog (const Dog &rhs):Mammal(rhs) //what is ":Mammal(rhs)" here -     
                                      // call of Mammal copy constructor?  
                                      //if not why is it required?
                                      //or what is it here?
{
    cout << "Dog copy constructor\n";
};

And what does return "return new Dog(*this)"? new object or pointer at new object?

Thank you for your answers. P.S. Sorry for my previous answer with wrong tags. It is my first experience of using 'stackoverflow"

Please consider studying [a good textbook on C++](http://stackoverflow.com/q/388242/596781). — Kerrek SB, Jul 05 '13 at 13:06
`new Dog(*this)` will create a copy of `*this` that is dynamically allocated and return the pointer to that copy. — Matthieu M., Jul 05 '13 at 13:06
If you really want to learn C++, stop reading and throw that book away right now and get a decent one: http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list — Sceptical Jule, Jul 05 '13 at 13:08

score 0 · Answer 1 · answered Jul 05 '13 at 13:17

Dog(*this);

creates an object of type Dog by calling the copy constructor. Since Dog derives from Mammal, the Mammal constructor is called. In particular, you can see from this code

Dog::Dog(const Dog & rhs):
Mammal(rhs)

that the copy constructor of Mammal gets called, which is passed rhs as a parameter.

new Dog(*this);

returns the pointer to a heap-allocated object of type Dog, which is initialized using the copy constructor (see above). When

virtual Mammal* Clone() { return new Dog(*this); }

gets called, the Dog* returned by the new operator gets converted to a Mammal* and returned.

What is being declared in Dog copy constructor [:Mammal(rhs)]?

1 Answers1