const Pointers

The keyword const for pointers can appear before the type, after the type, or in both places. The following are legal declarations:

const int * ptr1;       /* A pointer to a constant integer:
                             the value pointed to cannot be changed  */
int * const ptr2;       /* A constant pointer to integer:
                             the integer can be changed, but ptr2
                             cannot point to anything else           */
const int * const ptr3; /* A constant pointer to a constant integer:
                             neither the value pointed to
                             nor the pointer itself can be changed   */

Declaring an object to be const means that the this pointer is a pointer to a const object. A const this pointer can by used only with const member functions.