Re: Abstract classes, multiple inheritance, and implemention question

From:

"Alex Blekhman" <tkfx.REMOVE@yahoo.com>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 21 Jun 2008 19:15:00 +0300

Message-ID:

<elUOnl70IHA.4364@TK2MSFTNGP02.phx.gbl>

"Bogdan" wrote:

Hi,

I have 2 abstract structs as follows:

struct s1 {
   virtual void f1() = 0;
   virtual void f2() = 0;
};

struct s2 : public s1{
   virtual void f3() = 0;
};

I also have 2 implementation classes:

class s1imp : pubic s1 {
   virtual void f1() {}
   virtual void f2() {}
};

class s2imp : public s2 {
  virtual void f1() {}
  virtual void f2() {}
  virtual void f3() {}
};

Is there a way for class s2imp to derive from s1imp to take
advantage of its implementation of s1 (i.e. f1() and f2()) and
provide the implementation of f3() only?

You can do this, however you will required to surpress one nasty
warning.

First, make inheritance virtual:

struct s2 : virtual public s1{
    virtual void f3() = 0;
};

I also have 2 implementation classes:

struct s1imp : virtual pubic s1 {
    virtual void f1() {}
    virtual void f2() {}
};

Second, handle the C4250 warning:

#pragma warning(push)
#pragma warning(disable: 4250)

struct s2imp : public s1imp, public s2 {
    virtual void f3() { PRINTME(); }
};

#pragma warning(pop)
#pragma

Third, use the code:

s2imp s2i;

s2i.f1(); // calls s1imp::f1
s2i.f2(); // calls s1imp::f2
s2i.f3(); // calls s2imp::f3

HTH
Alex