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From: kjhopps@mmm.com (Kevin J. Hopps)
Subject: Re: C++ Class
Date: 1997/02/12
Message-ID: <3301D986.1733@mmm.com>#1/1
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References: <JSA.97Jan3143208@alexandria> <fxtu3oysbzp.fsf@isolde.mti.sgi.com>
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Date: 1997-02-12T00:00:00+00:00
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Loc Minh Phan Van wrote:
> 
> Hi,
>         Is there anyway that we can Define a class that can not be instantiated
> in any way by the user (that is, you can not have objects of that type),
> but it can be used as a base class.
> 
>         If so please give me a little example.
> 
> Thanks
> 
> Fr, Loc Phan

If a class has a "pure virtual function" it cannot be instantiated
directly, but only as a base class of a derivative that implements the
function.  For example:

class Cloneable
{
public:
	virtual Cloneable* clone() = 0;
};

class Thing : public Cloneable
{
public:
	virtual Thing* clone();
};

int main()
{
	Cloneable c;	// error
	Thing t;	// ok
	return 0;
}
-- 
Kevin J. Hopps, Imation          kjhopps@imation.com

My opinions are my own.  I speak neither for Imation nor 3M.



Opinions expressed herein are my own and may not represent those of my employer.