Re: Undefined References

[Ted Byers <r dot ted dot byers at rogers dot com>]

--- Tom Browder <tom.browder@gmail.com> wrote:

> On Dec 1, 2007 9:34 AM, Michael Sullivan
> <michael@espersunited.com> wrote:
> ...
> > The virtual destructor is there because g++ was
> giving me a warning
> > about setCurrentSprite(int), which will be
> implemented in classes Ally
> > and Enemy - both descended from Character.  I've
> commented out the
> > virtual destructor in character.h and used your
> Makefile with the
> > following output:
> 
> Then problem is Character needs to have the virtual
> function defined,
> even if it does nothing.  So:
> 

This is true only if the class is not abstract, but
then there is something wrong with the design if there
is to be a noop function.  If it can properly be used
as an abstract base class, then declare the virtual
function in question to be a pure virtual function, as
in:

  virtual void foo(int) = 0;

But this will introduce compile time errors if there
is an attempt to instantiate it, in which case a
choice is to be made as to whether or not the class
can function as an abstract base class.  If it should
not be abstract, then something is wrong with the
design if there is a function that is merely a no-op
stub.  If it should be abstract, then the calling code
that tries to intantiate it is broken.

The practice of making the destructor virtual is a
good one, especially since the OP expressed the intent
of deriving a number of classes from the class in
question.

Ted