Question

I fail to understand is why does the code print ‘3’ in VS2010 (release build), whether I leave the declaration of ‘r’ or comment it out.

int main(){
    int arr1[2];
    int &r = arr1[0];
    int arr2[2];

    cout << (&arr1[1] - &arr2[0]);
}

So, three questions:

a. why does the code print 3?

b. why does it print 3 even if the declaration of ‘r’ is present? (Is it because that in C++ whether a reference occupies storage or not is implementation defined?)

c. Does this code have undefined behavior or implementation defined behavior?

Answer 1

&arr1[1] - &arr2[0]

Pointer arithmetic is only well-defined within the same array. It does not matter what you think this code snippet does or should do, you are invoking undefined behavior. Your program could do anything.