实现memcpy函数
#include <bits/stdc++.h>
using namespace std;
void *Memcpy(void *dst, const void *src, size_t size)
{
char *psrc;
char *pdst;
if(NULL == dst || NULL == src)
{
return NULL;
}
if((src < dst) && (char *)src + size > (char *)dst) // 自后向前拷贝
{
psrc = (char *)src + size - 1;
pdst = (char *)dst + size