Weird XOR swap behavior while zeroing out data

Question

Thanks Doug. Here\'s the fix:

void swap(int& a, int& b) {
    if (&a == &b) // added this check to ensure the same address is not passed in
              


        

Answer 1

Anything xor'd with itself is zero.

Answer 2

Your swap a and b are the same location. The XOR hack only works when they are different locations.

I think in C; here's a table:

           &a != &b  &a == &b
           *a   *b   *a   *b
           -5   -5   -5   -5
*a ^= *b;   0   -5    0    0
*b ^= *a;   0   -5    0    0
*a ^= *b;  -5   -5    0    0

Answer 3

In addition to the existing answers, I'll just add that if you're going to do a test before swapping then you might as well change:

if (&a == &b) // added this check to ensure the same address is not passed in
    return;

to:

if (a == b) // check that values are different
    return;

This will handle the case where &a == &b and also the case where a == b, which may save some unnecessary swapping.