64bit shift problem

Question

Why this code does not write 0 as a last element but 18446744073709551615? (compiled with g++)

#include <iostream>

using namespace std;
int main(){
    unsigned long long x = (unsigned long long) (-1);
    for(int i=0; i <= 64; i++)
        cout << i << " " << (x >> i) << endl;
    cout << (x >> 64) << endl;
    return 0;
}

Answer 1

When you shift a value by more bits than word size, it usually gets shifted by mod word-size. Basically, shifting it by 64 means shifting by 0 bits which is equal to no shifting at all. You shouldn't rely on this though as it's not defined by the standard and it can be different on different architectures.