Re: Why doesn't this multiple virtual inheritance code compile?

From:

Chris Stankevitz <chrisstankevitz@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 3 Jan 2012 13:35:10 -0800 (PST)

Message-ID:

<0309c5f0-974c-4f2b-96e5-b951d83bedb8@h12g2000yqg.googlegroups.com>

On Jan 2, 11:20 pm, Paavo Helde <myfirstn...@osa.pri.ee> wrote:

Strange, compiles fine with my MSVC2010 and gcc (though MSVC issues a
strange warning):

Paavo,

Thank you for your help and for posting the valid source in its
entirety. I have it compiling now. The mistake I made was: missing
"virtual" in the declaration for class Shape. "Virtual" must appear
in the class declarations for "Shape" and "ObserverImp". Apparently I
had trouble parsing people's "english" description of my mistake but I
had no trouble parsing the c++ code in its entirety.

The code that compiles and the g++ invocation appear below.

Thank you again,

Chris

===

struct Observer
{
  virtual void Notify() = 0;
};

struct ObserverImp : public virtual Observer
{
  void Notify() {}
};

struct Shape : public virtual Observer
{
};

struct Square : public Shape, public ObserverImp
{
};

Shape* ShapeFactory()
{
  return new Square;
}

====

$ g++ -Wall -c test.cpp