Re: simple inheritance(?) question

From:

"Michael" <michael5139@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 10 Mar 2007 08:51:40 +0800

Message-ID:

<45f2010c$0$8402$5a62ac22@per-qv1-newsreader-01.iinet.net.au>

<dasteph@gmail.com> wrote in message
news:1173442768.831478.7740@v33g2000cwv.googlegroups.com...

On 9 Mrz., 11:22, "Michael" <michael5...@yahoo.com> wrote:

Hi All,

if I have a class BaseClass and two derived classes Class1 and Class2 and
I
don't know which derived class I will need, is it ok for me to do the
following:

BaseClass* base;

if(some_test){
base = new Class1;} else {

base = new Class2;

}

I know it works, but is it somehow dodgy? I have a feeling there is a
better
way but I'm not sure what to search for.

Thanks for your help.

Regards

Michael

What you have discovered is the base class pointer. What you are doing
is a common practiced method for polymorphism. Just have a look at
http://www.cplusplus.com/doc/tutorial/polymorphism.html for instance.
Keep in Mind that with a base class pointer you can only access
members that are defined in the base class.

Regards

Stephan

Thanks for your help.

I am a bit confused by my ability to use a member attribute that is only
present in Class1, not in BaseClass, after I do the base = new Class1.

I would have expected that I could only access functions and variables
defined in the BaseClass, and that any additional functionality (including
additional attributes) added by Class1 or Class2 would be lost, but this
appears to not be the case. It seems that since I am using the redefined
function from Class1 it also has access to the member attributes from
Class1. Would this be correct?

Can anyone explain why for me?

Thanks

Michael