Why does const_cast remove constness for a pointer but not for a pointer to a const?

Question

I understand that const_cast works with pointers and references.

I\'m assuming that the input to const_cast should be a pointe

Answer 1

(2) and (3) has the same principle, so I'll talk about (2) only.

The line

const_cast(ri) = 321;

has undefined behavior.

You cannot modify a const object according to the standard, not even with const_cast. If you remove const from a pointer/reference, and modify the pointed/referenced object, the pointed/referenced object must not been declared as const in the first place.

const_cast should be used only, when you have a const pointer to something for some reason, and you know that something is not declared as const.