# Question about pure virtual functions

Discussion in 'C++' started by Sergey, Oct 31, 2005.

1. ### SergeyGuest

Is it possible to realize such an algorithm (this one is not working):

class a1 {

public:

void af () { bf(); }
virtual void bf () = 0;

};

class b1 {

public:

virtual void bf () { }

};

class c1 : public a1, public b1 { };

main () {

c1 x;

}

The general idea is in that if you have one group of classes for one
option and another group of classes for another option you can combine
the general class by any class from the first group and by any class
from the second group. Question is how can functions of one group refer
to functions of another?
Thank you for answers.
Sergey

Sergey, Oct 31, 2005

2. ### David HilseeGuest

"Sergey" <> wrote in message
news:dk3npq\$6ek\$...
> Is it possible to realize such an algorithm (this one is not working):
>
> class a1 {
>
> public:
>
> void af () { bf(); }
> virtual void bf () = 0;
>
> };
>
> class b1 {
>
> public:
>
> virtual void bf () { }
>
> };
>
> class c1 : public a1, public b1 { };
>
> main () {
>
> c1 x;
>
> }
>
> The general idea is in that if you have one group of classes for one
> option and another group of classes for another option you can combine
> the general class by any class from the first group and by any class
> from the second group. Question is how can functions of one group refer
> to functions of another?
> Thank you for answers.
> Sergey

I'm not 100% sure of what you're trying to do, but it looks like some sort
of "mixin" where the b1 class contains the implementation for a1::bf(), but
it does not inherit from a1, and c1 must somehow "combine" the relationship
between the two classes. You can do this with a simple, straightforward
"override and delegate" function:

class c1 : public a1, public b1 {
virtual void bf() {
b1::bf();
}
};

Here, c1::bf() is invoked, and it calls b1::bf().

--
David Hilsee

David Hilsee, Oct 31, 2005

3. ### John CarsonGuest

"Sergey" <> wrote in message
news:dk3npq\$6ek\$
> Is it possible to realize such an algorithm (this one is not working):
>
> class a1 {
>
> public:
>
> void af () { bf(); }
> virtual void bf () = 0;
>
> };
>
> class b1 {
>
> public:
>
> virtual void bf () { }
>
> };
>
> class c1 : public a1, public b1 { };
>
> main () {
>
> c1 x;
>
> }
>
> The general idea is in that if you have one group of classes for one
> option and another group of classes for another option you can combine
> the general class by any class from the first group and by any class
> from the second group. Question is how can functions of one group
> refer to functions of another?
> Thank you for answers.
> Sergey

You can give them a common base class and move the virtual function to it:

#include <iostream>
using namespace std;

class Base
{
public:
virtual void bf () = 0;
};

class a1 : virtual public Base
{
public:
void af () { bf(); }
};

class b1 : virtual public Base
{
public:
virtual void bf ()
{
cout << "This is the b1 override of bf\n";
}
};

class c1 : public a1, public b1 { };

int main ()
{
c1 x;
x.af();
}

--
John Carson

John Carson, Oct 31, 2005