How do realloc and memcpy work?

Question

I have two questions.

1. Do realloc() and memcpy() copy the entries in an array to another in a way faster than just iterating on eac

Answer 1

1. There is absolutely no way to copy N items faster than O(N). However, it might be able to copy multiple items at once, or use special processor instructions - so it still might be faster than you could do it yourself.
2. I don't know for sure, but I'd assume that the memory is completely reallocated. That's the safest assumption, and it's probably implementation dependent anyway.