In the body of a non-static member function, the keyword this is a prvalue 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*. [ Note: Thus in a const member function, the object for which the function is called is accessed through a const access path. — end note ] [ Example:
struct s {
int a;
int f() const;
int g() { return a++; }
int h() const { return a++; } // error
};
int s::f() const { return a; }The a++ in the body of s::h is ill-formed because it tries to modify (a part of) the object for which s::h() is called. This is not allowed in a const member function because this is a pointer to const; that is, *this has const type. — end example ]
Similarly, volatile semantics apply in volatile member functions when accessing the object and its non-static data members.
A cv-qualified member function can be called on an object-expression only if the object-expression is as cv-qualified or less-cv-qualified than the member function. [ Example:
void k(s& x, const s& y) {
x.f();
x.g();
y.f();
y.g(); // error
}The call y.g() is ill-formed because y is const and s::g() is a non-const member function, that is, s::g() is less-qualified than the object-expression y. — end example ]
Constructors and destructors shall not be declared const, volatile or const volatile. [ Note: However, these functions can be invoked to create and destroy objects with cv-qualified types, see [class.ctor] and [class.dtor]. — end note ]