类的复制构造函数调用

复制构造函数调用条件：

(1)一个对象以值传递的方式传入函数体

(2)一个对象以值传递的方式从函数体返回

(3)一个对象需要通过另外一个对象进行初始化

#include<stdio.h>
#include<iostream>
#include<stack>
#include<math.h>
#include<string.h>
using namespace std;




class A{
public:
    A(){}
    A(const A&a){
    cout << "copy"<<endl;}
private:
};




A f(A a){
    A v(a);
    cout<<"1"<<endl;
    A b= v;
    cout<<"2"<<endl;
    return b;
}


class Test
{
public:
    int a;
    Test(int x)
    {
        a = x;
    }
    Test(Test &test)//复制构造函数
    {
        cout<<"copy constructor"<<endl;
    }
};


void fun1(Test test)    //(1)值传递传入函数体
{
    cout << "fun1()...." <<endl;
}


void fun2()             //(2)值传递从函数体返回
{
    Test t(2);
    cout << "fun2()...." <<endl;
    return t;
}


int main(){
    A x;
    A y;
    cout<<"==========="<<endl;
    A d=f(y);
    cout<<"==========="<<endl;
    f(y);
    cout<<"==========="<<endl;
    A c=f(f(x));
    cout<<"==========="<<endl;
    Test t1(1);
    Test t2 = t1;       //(3)用t1对t2做初始化
    cout << "before fun1()...." <<endl;
    fun1(t1);


    Test t3 = fun2();
    cout << "before fun2()...." <<endl;


    return 0;
}

输出：