几种交换两个数函数（swap函数）的写法和解析

#include <iostream>
using namespace std;
 
/*值传递，局部变量a和b的值确实在调用swap0时变化了，当结束时，他们绳命周期结束*/
void swap0(int a, int b)
{
	int tem = a;
	a = b;
	b = a;
}
 
/*没有初始化指针就开始用，该函数是有问题的*/
void swap1(int *a, int *b)
{
	int *tem;					/*注意tem没有分配内存*/
 
	*tem = *a;
	*a = *b;
	*b = *tem;
}
 
/*函数内只是指针的变化，指针的值没有变化*/
void swap2(int *a, int *b)
{
	int *tem;
 
	tem = a;
	a = b;
	b = tem;
 
}
 
/*指针传递实现两个数的交换*/
void swap3(int *a, int *b)
{
	int tem;
 
	tem = *a;
	*a = *b;
	*b = tem;
}
 
/*指针传递实现两个数的交换*/
void swap4(int &a, int &b)
{
	int tem;
 
	tem = a;
	a = b;
	b = tem;
}
 
int main()
{
	int num1 = 1;
	int num2 = 2;
 
	//swap0(num1, num2);
 
	//swap1(&num1, &num2);
 
	//swap2(&num1, &num2);
 
	//swap3(&num1, &num2);
 
    swap4(num1, num2);
 
	cout << num1 << endl << num2 << endl;
	return 0;
}