In C++, this pointer is passed as a hidden argument to all non-static member function calls. The type of this depends upon function declaration. If the member function of a class X is declared const, the type of this is const X* (see code 1 below), if the member function is declared volatile, the type of this is volatile X* (see code 2 below), and if the member function is declared const volatile, the type of this is const volatile X* (see code 3 below).

Code 1

#include<iostream>
class X {
void fun() const {

// this is passed as hidden argument to fun().
// Type of this is const X* const
}
};
Code 2

#include<iostream>
class X {
void fun() volatile {

// this is passed as hidden argument to fun().
// Type of this is volatile X* const
}
};
Code 3

#include<iostream>
class X {
void fun() const volatile {

// this is passed as hidden argument to fun().
// Type of this is const volatile X* const
}
};