避免内存重叠的memmove（）函数

#include <iostream>
#include <string.h>
using namespace std;
void* memmove(void *dst, const void *src, size_t count){
// 容错处理
if (dst == NULL || src == NULL){
return NULL;
}
unsigned char *pdst = (unsigned char *)dst;
const unsigned char *psrc = (const unsigned char *)src;
//判断内存是否重叠
bool flag1 = (pdst >= psrc && pdst < psrc + count);
bool flag2 = (psrc >= pdst && psrc < pdst + count);
if (flag1 || flag2){
// 倒序拷贝
while (count){
*(pdst + count - 1) = *(psrc + count - 1);
count--;
}//while
}
else{
// 拷贝
while (count--){
*pdst = *psrc;
pdst++;
psrc++;
}//while
}
return dst;
}