How to stop a class from being inheritance?

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As per information from internet there are two ways create a Final class:-
1. by using "final" keyword after class name(c++11)

C++

class end final
{ };

2. by creating a prefinal class with private constructor, making final class as friend of prefinal class and virtually inherit the prefinal class in final class.

C++

class preFinal
{
  preFinal(){}
  friend class FINAL;
};
class FINAL:virtual public preFinal  //No class can derive this class.
{
};
class Derived:public FINAL //Compilation error,private constructor of preFinal class
{};

But third option I can think of is, if we define constructor in private itself then also we can't inherit a class, as below:-

C++

class Final
{
   Final(){}
};
class Derived:public Final{  //This will give error as Final constructor is in private.
};
int main()
{
   Final fo;
}

What I have tried:

Then why we need final keyword or to create prefinal class(option-2)?

Can anyone please let me know any case in which we can inherit a class with private constructor?

Posted 11-Nov-18 3:49am

GeekyMukesh

Updated 11-Nov-18 17:30pm

v3

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3 solutions

Solution 1

See final Specifier | Microsoft Docs[^]

Posted 11-Nov-18 4:55am

Richard MacCutchan

Solution 2

Thanks Richard,
You send me link for final keyword description. I wanted to know if I define the constructor in private to make a class as final is there any thing wrong in it.

BTW through your link I also came to know that we can use "final" keyword for preventing virtual function over-riding in derived class. So I am clear about final keyword usage now. But do we need to follow option 2 I mentioned above when we can achieve the same by just keeping constructor in private?

Posted 11-Nov-18 5:22am

GeekyMukesh

Comments

Richard MacCutchan 12-Nov-18 5:48am

Do it the right way with the correct language specification. If you try to invent your own work around there is a chance that it will cause problems in the future.

Also, please do not post replies as solutions (which they are not), use the Reply button below the message you are referring to.

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Manish K. Agarwal · Accepted Answer · 2018-11-11T17:30:00

Solution 3

If you are making constructor as private to make it final, how you will make the object of that class?

class Final
{
private:
  Final(){}
public:
  // other members
};

void someFunc() {
   Final myFinal; // compilation error
}

Posted 11-Nov-18 17:30pm

Manish K. Agarwal

Updated 11-Nov-18 17:33pm

v2