Thread: MSDN const_cast sample

So, conclusion is,

1. in const member function, this pointer is a const pointer;
2. in non-const member function, this pointer is a non-const pointer.

More accurately:
1. in const member function, this pointer is a pointer to const (i.e., it points to a const T);
2. in non-const member function, this pointer is a pointer (i.e., it points to a T).

Of course, in the MSDN example perhaps the number member variable should be declared mutable instead of resorting to a const_cast.

EDIT:
The this pointer is not itself const, according to the MSDN doc quoted. From the C++ Standard:

In the body of a nonstatic (9.3) member function, the keyword this is a non-lvalue expression whose
value is the address of the object for which the function is called. The type of this in a member function
of a class X is X*. If the member function is declared const, the type of this is const X*, if the member
function is declared volatile, the type of this is volatile X*, and if the member function is
declared const volatile, the type of this is const volatile X*.

Why this is a non-lvalue in a non-static member function?

I am curious about that too since the C++ standard makes it clear that "every expression is either an lvalue or an rvalue", so I do not understand why it does not simply say "the keyword this is an rvalue expression". The non-static member function part is obvious since static member functions do not have the this pointer.

I think this is a pointer variable and it should be addressable, it should be a lvalue?

A simple definition of lvalue is "an expression that may appear on the left-hand side of an assignment". So by saying that this is not an lvalue, the standard says that the this pointer cannot be on the left hand side of an assignment.

In early versions of C++, it was actually possible to assign to the this pointer. The standard probably uses the wording it does to make it clear that this is not possible anymore.

This is const pointer

It is not a const pointer. It is a pointer to const.

and addressable, and it should be a un-modifiable lvalue.

What exactly do you mean by "addressable"? The standard says that it is a non-lvalue, so it is not an lvalue that cannot be modified, but an rvalue. Consequently, I do not think you can take the address of this.

You can't. Being able to take the address of something (using the native & operator, not an overloaded version) is the main mark of an lvalue - after all, there are const lvalues, which can't appear on the left side of an assignment.