用异或操作实现的交换函数用以实现数组逆置中须要注意的问题

用元素交换函数实现数组逆置非常easy，如以下代码：（数组左右元素交换）

#include<iostream>
#include<stdlib.h>
using namespace std;

void swap(int &a, int &b)
{
	int tmp = a;
	a = b;
	b = tmp;
}

int main()
{
	int a[5] = { 1, 2, 3, 4, 5 };
	int lenth = sizeof(a) / sizeof(a[0]);
	int head = 0;
	int tail = lenth - 1;

	while (head <= tail)
	{
		swap(a[head], a[tail]);
		head++;
		tail--;
	}
	for (int i = 0; i < lenth; ++i)
	{
		cout << a[i] << endl;
	}
	system("pause");
}

<span style="font-family:KaiTi_GB2312;">#include<iostream>
#include<stdlib.h>
using namespace std;

void swap(int &a, int &b)
{
	a = a ^ b;
	b = a ^ b;
	a = a ^ b;
}

int main()
{
	int a[5] = { 1, 2, 3, 4, 5 };
	int lenth = sizeof(a) / sizeof(a[0]);
	int head = 0;
	int tail = lenth - 1;

	while (head <= tail)
	{
		swap(a[head], a[tail]);
		head++;
		tail--;
	}
	for (int i = 0; i < lenth; ++i)
	{
		cout << a[i] << endl;
	}
	system("pause");
}</span>

一执行。结果大跌眼镜：0哪来的？？？？

异或操作实现交换的机制: a ^ a = 0即同一个元素相异或之后为0

a =  a ^ b;

b =  a ^ b = a ^ b ^ b = a;

a =  a ^ b = a ^ b ^ a = b;

经分析：原来如此，当head = tail = （lenth-1）/ 2时，二者指向同一个元素，即

a = b = 3(同一块内存)

a = a ^ b = 3 ^ 3 = 0(内存内容改变为0)---->>> a = b = 0;

b = a ^ b = 0 ^ 0 = 0

a = a ^ b = 0 ^ 0 = 0

所以运行之后变为了0

那么该如何改动呢？？？

while (head < tail)//改变此处
	{
		swap(a[head], a[tail]);
		head++;
		tail--;
	}

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