函数返回值 编译器的优化Release版

 

汇总链接

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;

class Base
{
public:
	Base() :selfid(++n)	{cout << "Base() " << selfid << endl;}
	Base(const Base& other) :selfid(++n){cout << "Base(" << selfid << ") copy from " << other.selfid << endl;}
	Base& operator=(const Base& other){	cout << "Base(" << selfid << ") = " << other.selfid << endl; return *this;}
	virtual ~Base(){cout << "~Base(" << selfid << ") destroyed" << endl;}
public:
	int selfid;
	static int n;
};

int Base::n = 0;

Base Test()
{
	Base b;//b Base() 2 e Base() 3
	return b;
}

int main()
{
	Base b1;//a Base() 1
	b1 = Test();//c Base(1) = 2，d ~Base(2) destroyed
	Base c(Test());//3
	std::cout << c.selfid << endl;
	//f ~Base(3) destroyed ，~Base(1) destroyed
	return 0;
}

可以看出在函数第二次调用图Test()来构造c的时候，整个过程只构造了一个对象。优化的还是很厉害的。