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From: Jason Shankel <no_spam.shankel@crl.com>
Subject: Re: C++ Class
Date: 1997/02/12
Message-ID: <33023238.7F28@crl.com>#1/1
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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

In C++, you're talking about an abstract base class.
An abstract class in C++ is a class which has at least one
pure virtual function, which must be overridden by a child class.
Pure virtual functions are designated by the "=0" idiom.
Abstract base classes cannot be instantiated:


class IFoo
{
	public:
		virtual void Method() = 0; //Pure virtual function
};

class CFoo : public IFoo
{
	public:
		virtual void Method(){}; //Overridden
};

void main()
{
	IFoo *object;

	object = new IFoo(); //ERROR, cannot instantiate abstract class
	object = new CFoo(); //Legal
};