Calling inherited functions and overriding behavior in c++ - c++

Question

Why does this give this error -
'void D::func(const D &)': cannot convert argument 1 from 'const C' to 'const D &'
How to correct this, I want to call Base's func from Derived's func but note func is a friend function?
class C
{
public:
C()
{
cout << "in C ctor" << endl;
}
friend void func(const C& abc1)
{
cout << "in C's func" << endl;
}
};
class D : public C
{
public:
D()
{
cout << "in D ctor" << endl;
}
void func(const D& abc)
{
func(static_cast<const C&>(abc));
cout << "in D's func" << endl;
}
};
int main()
{
D d;
d.func(d);
}
why does this similar e.g. work though -
https://ideone.com/eNmvng

Answer 1

I'm not sure what that syntaxis does with function visibility, but this works:
class C
{
public:
C()
{
cout << "in C ctor" << endl;
}
friend void func(const C& abc1);
};
void func(const C& abc1)
{
cout << "in C's func" << endl;
}
class D : public C
{
public:
D()
{
cout << "in D ctor" << endl;
}
void func(const D& abc)
{
::func(abc);
cout << "in D's func" << endl;
}
};
int main()
{
D d;
d.func(d);
}
Just for completeness sake, this works too:
class C
{
public:
C()
{
cout << "in C ctor" << endl;
}
friend void func(const C& abc1)
{
cout << "in C's func" << endl;
}
};
// Make function visible in global scope
void func(const C& abc1);
class D : public C
{
public:
D()
{
cout << "in D ctor" << endl;
}
void func(const D& abc)
{
::func(abc);
cout << "in D's func" << endl;
}
};
int main()
{
D d;
d.func(d);
}