按值传递：不改变外部对象
按引用传递&&按地址传递：允许改变外部对象
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
//passing by refedrence
void f(int &r)
{
cout << "r = " << r << endl;
cout << "&r = " << &r << endl;
r = 5 ;
cout << "r = " << r << endl;
}
//passing by value
void f(int a)
{
cout<<"a= "<<a<<endl;
a = 5;
cout << "a= " << a <<endl;
}
//passing by address
void f(int *p)
{
cout << "p = " << p << endl;
cout << "*p = " << *p << endl;
*p = 5;
cout << "p = " << p << endl;
}
int main()
{
//passing by reference
int x = 47 ;
cout << "x = " << x <<endl;
cout << "&x = " << &x << endl;
f(x);//Looks like pass-by-value
//is actually pass by reference
cout << "x = " << x << endl;
//output
x = 47
&x = 0x7FFF1D5C9B4C
r = 47
&r = 0x7FFF1D5C9B4C
r = 5
x = 5
//passing by address
int x = 47;
cout << "x = " << x << endl;
cout << "&x = " << &x << endl;
f(&x);
cout << "x = " << x << endl;
//output
////////////////////////////////
x = 47
&x = 0x7FFF9746423c
p = 0x7FFF9746423c
*p = 47
p = 0x7FFF9746423c
x = 5
//passing by value
int x = 97 ;
cout << "x=" << x <<endl;
f(x);
cout << "x=" << x <<endl;
//output
///////////////////////////////
x = 47
a = 47
a = 5
x = 47
}