VMS Help CC, Run-time functions, memmove  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Copies a specified number of bytes from one object to another.

  Use memmove rather than memcpy if the area pointed to by the
  destination string could overlap the area pointed to by the source
  string; memmove safely handle copies between overlapping objects;
  memcpy gives undefined behavior.

  Syntax:

       #include <string.h>

       void *memmove(void *destination_str, const void *source_str,
                     size_t size);