Re: polymorphism

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Fri, 12 Jun 2009 13:35:36 +0200

Message-ID:

<h0teig$9bn$1@news.eternal-september.org>

* Vicky:

On Jun 12, 3:15 pm, Anees <anees.hai...@gmail.com> wrote:

Dear Fellows:

I am using visual studio 2008. Can anyone help, why does the following
polymorphism not working? It is keep giving "base" as output :(

#include <iostream>

using namespace std;

class base {
public:
        base() {
                print();
        }

protected:
        virtual void print() {
                cout << "base" << endl;
        }

};

class derived:public base {
protected:
        virtual void print() {
                cout << "derived" << endl;
        }

};

int _tmain(int argc, _TCHAR* argv[]){
        derived d;

}

Never call virtual function inside ctor and dctor.

Well, that's one opinion.

For C++ some people find it practical to do so.

For e.g. Java, which is not as safe as C++ is in this regard, it's IMHO good
advice to stay away from virtual calls (on the same class) in a constructor.
It's one of the most common bug causes in Java. However, in C++ it's safe.

It's behaviour doesn't meet standard C++.

I'm happy that that's incorrect. :-)

Consult with Effective C++ by Scott Meyer.

That's generally good advice.

Cheers & hth.,

- Alf

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