SYNOPSIS       #include <string.h>       void *memcpy(void *dest, const void *src, size_t n);DESCRIPTION       The memcpy() function copies n bytes from memory area src to memory area dest.  The memory areas must not overlap.  Use memmove(3) if       the memory areas do overlap.RETURN VALUE       The memcpy() function returns a pointer to dest.

 1 void* memcpy2(void* dest, void* src, size_t n) { 2     if (dest == NULL || src =http://www.mamicode.com/= NULL) return NULL; 3     char* pa = (char*)dest, *pb = (char*)src; 4     if (pa <= pb) { 5         while (n--) { 6             *pa++ = *pb++; 7         } 8     } else { 9         pa += n - 1; 10         pb += n - 1;11         while (n--) {12             *pa-- = *pb--;13         }14     }15     return dest;16 }