int memcmp(const void *s1,
const void *s2,
size_t n);
memcmp compares the first n characters of the object pointed to by s1 to the first n characters of the object pointed to by s2. memcmp returns an integer greater than, equal to, or less than zero as the object pointed to by s1 is greater than, equal to, or less than the object pointed to by s2.