C++(11)：std::move

移动构造函数的触发有个前提，就是构造时需要基于一个临时对象。

标准库提供了move函数，可以把一个左值转换为右值，从而可以触发移动构造函数。

#include <iostream>
using namespace std;

class A{
public:
	A()
	{
		m_i = new int(1);
		cout<<"Construct A, this addr:"<<this<<", m_i addr:"<<m_i<<endl;
	}
	A(const A &a):m_i(new int(*a.m_i))
	{
		cout<<"Copy Construct A, ori addr:"<<&a<<" ori m_i addr:"<<a.m_i<<" *m_i="<<*a.m_i<<", this addr:"<<this<<" m_i addr:"<<m_i<<" *a.m_i="<<*a.m_i<<endl;
	}
	A(A&& a):m_i(a.m_i)//移动构造函数接受一个所谓的“右值引用”的参数，完成资源的转移
	{
		cout<<"Move Construct A, ori addr:"<<&a<<" ori m_i addr:"<<a.m_i<<" *m_i="<<*a.m_i<<", this addr:"<<this<<" m_i addr:"<<m_i<<" *a.m_i="<<*a.m_i<<endl;
		a.m_i = 0;
	}
	~A()
    {
		cout<<"Destruct A, this addr:"<<this<<" m_i addr:"<<m_i<<endl;
		if(m_i)
		{
			free(m_i);
			m_i = 0;
		}
    }
	int *m_i;
};

int main(){
	A a1;            //通过默认构造函数构造对象a1
	A a2 = move(a1); //通过move，将a1转换为右值，从而触发移动构造函数，构造对象a2
	cout<<"a2 addr:"<<&a2<<" a2.m_i addr:"<<a2.m_i<<" *a2.m_i="<<*a2.m_i<<endl;
	return 0;
}

运行程序输出：
//构造对象a1
Construct A, this addr:0x63fe08, m_i addr:0x7a6f90

//将a1转换为右值，从而触发移动构造函数，构造对象a2
Move Construct A, ori addr:0x63fe08 ori m_i addr:0x7a6f90 *m_i=1, this addr:0x63fe00 m_i addr:0x7a6f90 *a.m_i=1

//a2的成员m_i指向的地址与a1.m_i相同
a2 addr:0x63fe00 a2.m_i addr:0x7a6f90 *a2.m_i=1

//a2析构
Destruct A, this addr:0x63fe00 m_i addr:0x7a6f90

//a1析构
Destruct A, this addr:0x63fe08 m_i addr:0