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From: Luis Espinal <lespin03@solix.fiu.edu>
Subject: Re: C++ Class [ not a good answer ]
Date: 1997/03/03
Message-ID: <331B1B88.612E@solix.fiu.edu>#1/1
X-Deja-AN: 222805154
References: <JSA.97Jan3143208@alexandria> <fxtu3oysbzp.fsf@isolde.mti.sgi.com>
 <JSA.97Jan6190704@alexandria> <E3uK9F.CzG@research.att.com>
 <E5Dx8v.6y3@tip.nl> <cjolley-1002971634080001@news.zippo.com>
 <dewar.855671030@merv> <33018394.1718@scf.usc.edu>
 <5dsgh1$hlt@nnrp1.farm.idt.net>
Organization: ARMS - Systems
Newsgroups: 
 comp.lang.c++,comp.lang.smalltalk,comp.lang.eiffel,comp.lang.ada,comp.object,comp.software-eng
Date: 1997-03-03T00:00:00+00:00
List-Id: <comp.lang.ada>


> Read about polymorphism and virtual functions.
> 

This is a better answer to the original question.

Lock Minh, what you need is a class that has at least one pure virtual 
function in it. That way, nobody can instantiate an object from it and
still use it as a base class.
.ie.

class MyBase
{
	MyBase(){...}
	virtual ~MyBase(){ ... }
	virtual void SomeFunction() = 0; // a pure virtual function.
};

// you still need to implement the pure virtual func.
void MyBase::SomeFunction(){}

class AChild : public MyBase
{
	... here goes the constructors, destructors, etc.
	// you need to implement the pure virtual function
	// defined in MyBase; otherwise, you won't be 
	// able to instantiate a AChild object either.
	virtual void SomeFunction();
};

void AChild::SomeFunction()
{
// some code in here.
}

AChild someChild; // ok...

MyBase someBase; // eeek! can't compile.
		 // can't instantiate a class with 
		 // a pure virtual function in it.

Hope it helps.

Luis Espinal

p.s. cryptic answers don't help.
-- 
Luis++ lespin03@solix.fiu.edu
What does not kill us, makes us stronger...
What does not break us, makes us...
That which does not break, must bend...