参考答案

 void*  memmove(void * dest, const void * src, size_t n)
  { 
       void* temp = dest; 

       if (dest <= src || (char *)dest >= ((char *)src + n)) //无内存地址重叠
       {
           while (n--) 
           {
              *(char *)dest = *(char *)src;
              dest = (char *)dest + 1;
              src = (char *)src + 1;
            }
        }
        else                 //有内存地址重叠
        {                               
           dest = (char *)dest + n - 1;
           src = (char *)src + n - 1;
           while (n--) 
           {
               *(char *)dest = *(char *)src;
               dest = (char *)dest - 1;
               src = (char *)src - 1;
            }
        }

        return (temp);
   }