Re: Undefined reference to...

From:

Andrea Crotti <andrea.crotti.0@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 11 Nov 2010 10:22:06 +0100

Message-ID:

<m1sjz8cj0h.fsf@ip1-201.halifax.rwth-aachen.de>

"Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> writes:

Problems with the above include

* 'getLower' attempts to return an object of abstract class.

* A local variable is declared with incomplete type 'Extended'.

What do you incomplete type?
Because I had the forward declaration maybe?

  * If those obstacles weren't in the way, 'getLower' would perform
    a *slicing*, returning only the Base part of 'e', and then of type
    'Base'.

It's not clear what you're attempting, but it may be that you want a
Meyers' singleton:

  class Base
  {
  public:
      virtual void printOut() = 0;
      static Base& getLower();
  };

  class Extended: public Base
  {
  public:
      void printOut() { cout << "hello"; }
  };

  Base& Base::getLower()
  {
      static Extended e;
      // Whatever code you were intending to have here, then:
      return e;
  }

Note that with this scheme you always get the same object -- a singleton --
from 'getLower'.

Cheers & hth.,

- Alf

Anyway thanks but no, I don't think that's what I need, the simplest
solution is just to avoid the pure function so I don't have an abstract
class anymore and I can actually return something of that type.

The other solution I guess is to use a pointer as Paul suggested.
Thanks