Understanding a C++ function for reversing a string using ^=

Question

The code below returns a reversed string. For example, it take input " codebyte " and returns " etybedoc ".

string FirstReverse(string str) {
    for(int i = 0, j = str.length() - 1; i < str.length() / 2; i++, j--)
    {
        str[i]^=str[j]^=str[i]^=str[j];
    }
    return str;
}

I am lost as to how this function works:

1. Why is the ^= -operator being used? It is a bitwise operator but why is it being used here?
2. Why is str.length() divided by 2 in the for loop?
3. What is with the alteration of str[i] and str[j] ?

I want to work though it with values but I don't know where to begin. The introductory textbook I used did not cover this.

Answer 1

As an answer:

• It's a swapping functionality similar to the famous bit-twiddling hacks.
  • A detailed explanation of this swapping mechanism can be found here .
• The length is divided by two because otherwise you would undo every swap and end up with the original string again.
• The indices i and j run against each other (from the beginning or end, respectively).