Why we cannot create a object inside class?

Question

class Sololearn
{
Sololearn *obj;// It is accepted
Sololearn ob;//It is not accepted
};

why?

Answer 1

Thank you
Great Explanation

Answer 2

The pointer works since it is not pointing at anything yet. You have to instantiate a 'real' object at runtime, something like this:

class S {
S *obj;
};

S c1;
S c2;
c1.obj = &c2;

But note that c2's obj pointer is still uninitialized - it is not pointing at anything (yet). So now you can do:
S c3;
c2.obj = &c3; //Which is the same as c1.obj->obj

And you can keep going like this as 'deep' as you want. But the main thing to grasp is that the 'deepest' S* obj is always uninitialized at first (not pointing at anything).

But now compare it to this case:
class S{
S ob;
};

Even as part of the definition of the class it contains an instance of S (S::obj) which, in turn, contains an instance of s (S::obj::obj) which, in turn, contains an instance of S.... and so on - and we have infinite regress!