Is there any way to write a class such that no class can be inherited from it ?

Question

Hi, From link http://www.coolinterview.com/interview/10842/

Is there any way to write a class such that no class can be inherited from it ?

From suggestions in the above link, i tried below code

class A
{
    A(){}
    ~A(){}
    A(const A&);
    A& operator=(const A&);
};

class B: public A
{
};

The above code doesn't produce any error. If i try to instantiate B like below

int main()
{
    B ob;
}

then it gives error

error C2248: 'A::A' : cannot access private member declared in class 'A'

So inheritance its allowing but instantiation its not allowing.

Is there any other way of blocking inheritance itself ?

Answer 1

Not via an explicit keyword. Some languages have a "sealed" keyword, or similar, that does exactly that, but not C++.

It can be done, (see that useful comment from liaK) but it's really awkward, you would have to have a really good reason to want to do it.

Answer 2

There is no equivalent to the final keyword in Java or C♯'s sealed in C++. You can certainly prevent inheritance by making the class constructors private, or by following liaK's link and having a class subclass a class that has private constructors and is its friend.

In general though:

You can just make your destructor non-virtual to signal that you do not intend for the class to be polymorphic, and document that this is your intention. Of course, if users of your class decide to ignore this, they could run into problems of their own for their hubris. ;)

Additionally: http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.11