c++中map的insert函数，请问是拷贝，还是引用？

// map_Test.cpp : 定义控制台应用程序的入口点。

#include "stdafx.h"

#include

#include

using namespace std;

int main()

{

class a

{

public:

int z = 8;

};

map my_map;

a a1;

cout << "显示初始化a类的值" << std::endl;

cout << a1.z << std::endl;

cout << "加入map中..." << std::endl;

my_map.insert(::pair(1, a1));

a1.z = 6;

cout << "++显示map外修改a类值" << std::endl;

cout << a1.z << std::endl;

map::iterator iter = my_map.begin();

while (iter != my_map.end())

{

cout << "__打印map中a值" << std::endl;

cout <second.z<< std::endl;

cout << "获取map中a并修改" << std::endl;

a a2 = iter->second;

a2.z = 3;

cout << a2.z << std::endl;

cout << "__map中a值再打印打印" << std::endl;

cout << iter->second.z << std::endl;

iter->second.z = 9;

cout << "__map中指针直接修改a值再打印打印" << std::endl;

cout << iter->second.z << std::endl;

iter++;

}

cout << "++显示外部的a值" << std::endl;

cout << a1.z << std::endl;

system("pause");

 return 0;

}