Code snippet that help me understand std::rotate

string_rotate_left.cpp

// A reference to the idea is here: http://en.cppreference.com/w/cpp/algorithm/rotate
// Actually its idea is recursion, as shown as follow:
void str_rotate(char* first, char* middle, char* last)
{
    char* next = middle;
    while (first != middle && next != last)
    {
        std::iter_swap(first++, next++);
    }
    if (first == middle && next == last)
    {
        return;
    }
    else if (first == middle)
    {
        str_rotate(first, next, last);
    }
    else // next == last
    {
        str_rotate(first, middle, last);
    }
}