Diff Between Call By Reference And Call By Pointer [duplicate]

Question

Can any one tell me the exact diff between call by pointer and call by reference. Actually what is happening on both case?

Eg:

Call By Reference:

void swap(int &x, int &y)
{
   int temp;
   temp = x; /* save the value at address x */
   x = y;    /* put y into x */
   y = temp; /* put x into y */

   return;
}

swap(a, b);

Call By Pointer:

void swap(int *x, int *y)
{
   int temp;
   temp = *x; /* save the value at address x */
   *x = *y; /* put y into x */
   *y = temp; /* put x into y */

   return;
}

  swap(&a, &b);

Answer 1

The both cases do exactly the same.

However, the small difference is, that references are never null (and inside function you are sure, that they are referencing valid variable). On the other hand, pointers may be empty or may point to invalid place in memory, causing an AV.

Answer 2

Semantically these calls have identical results; under the hood references are implemented with pointers.

The important difference between using references and pointers is with references you have a lot less rope to hang yourself with. References are always pointing to "something", where as pointers can point to anything. For example, it is perfectly possible to do something like this

 void swap(int *x, int *y)
 {
    int temp;
    temp = *x; /* save the value at address x */
    ++x;
    *x = *y; /* put y into x */
    *y = temp; /* put x into y */

    return;
 }

And now this code could do anything, crash, run, have monkeys fly out of your noes, anything.

When in doubt, prefer references. They are a higher, safer level of abstraction on pointers.