What is the difference between memmove and memcpy?

Question

What is the difference between memmove and memcpy? Which one do you usually use and how?

Answer 1

memmove can handle overlapping memory, memcpy can't.

Consider

char[] str = "foo-bar";
memcpy(&str[3],&str[4],4); //might blow up

Obviously the source and destination now overlap, we're overwriting "-bar" with "bar". It's undefined behavior using memcpy if the source and destination overlap so in this case cases we need memmove.

memmove(&str[3],&str[4],4); //fine