Re: derived class and virtual function

* On Aug 17, 1:48 pm, James Kanze <james.ka...@gmail.com> wrote:


                                                      ^^^^^^^^^^^


  ^^^^^^^
   [...]


Here I write down the complete paragraph; perhaps that will be useful
in explaining the last sentence.

In Stanley Lippman's 'C++ Primer Fourth Edition', in page 564, the
following is mentioned:

"With one exception, the declaration of a virtual function in the
derived class must exactly match the way the function is defined in
the base. That exception applies to virtuals that return a
reference(or pointer) to a type that is itself a base class. A virtual
function in the derived class can return a reference or pointer to a
class that is PUBLICLY derived from the type returned by the base
class function."

I have written the follwing program a.cpp after going through one of
Stuart Redmann's replies in this thread:

#include <cstdlib>
#include <iostream>

using namespace std;

class X
{
public:
        void print(void) const;
};

inline void X::print(void) const
{
        cout << "from X::print() function" << endl;

        return;
}

class Y : public X
{
public:
        void print(void) const;
};

inline void Y::print(void) const
{
        cout << "from Y::print() function" << endl;

        return;
}

class Base
{
public:
        virtual X* get(X& x) const;
        virtual ~Base();
};

inline X* Base::get(X& x) const
{
        cout << "Base::get() called" << endl;

        return &x;
}

inline Base::~Base()
{
}

class Derived : public Base
{
public:
        virtual Y* get(Y& y) const;
        virtual ~Derived();
};

inline Y* Derived::get(Y& y) const
{
        cout << "Derived::get() called" << endl;

        return &y;
}

inline Derived::~Derived()
{
}

int main()
{
        X x;
        Y y;
        Derived* pd = new Derived();
        Y* py = pd->get(y);
        py->print();
        delete pd;
        pd = 0;
        Base* pb = new Base();
        X* px = pb->get(x);
        px->print();
        delete pb;
        pb = 0;

        return EXIT_SUCCESS;
}

This program compiles fine with g++ and produces the output:

Derived::get() called
from Y::print() function
Base::get() called
from X::print() function

Does the above program correctly demonstrate what is mentioned in the
paragraph(in Stanley Lippman's book - page 564) that I had mentioned
completely above? Kindly reply. If I am wrong in understanding that
paragraph, please explain it.

Thanks
V.Subramanian