On Wednesday 21 May 2008, Jordi Gutiérrez Hermoso wrote:
> The following code will not compile:
>
> class foo{};
>
> class A{
> public:
> void f(int a ){a++;};
> private:
> virtual void f(foo a) = 0;
> };
>
> class B : public A{
> private:
> virtual void f(foo a){};
> };
>
> int main(){
> B b;
> int a=0;
> b.f(a);
> }
>
> The problem seems to be that all of my functions being named
> f are somehow colliding with each other. It seems to me that
> the call b.f(a) is unambiguosly pointing to A::f(int), but
> gcc disagrees.
You might as well have written:
class A{
public:
void f(int a ){a++;};
};
class B : public A{
private:
virtual void f(foo a){};
};
f in B has the same name as f in A but different args.
This is usually a mistake, so they made it illegal.
If you override one f, you need to override them all.
(or change the name)
To fix:
class B : public A{
public:
void f(int a){A::f(a);}
private:
virtual void f(foo a){};
};
Now, try this:
class A{
private:
virtual void f(foo a)=0;
};
class B : public A {
private:
virtual void f(foo a){}
};
This doesn't work either, because f in A is private, so B
doesn't know it exists. I don't know what it will do. I think
you get 2 f's, and still can't make an instance of B because f
is pure virtual. Change the private in A to protected, so B
will see it.
It really is off topic....
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