C++(11)：智能指针shared_ptr

shared_ptr是通过引用计数维护内存的所有权，因此可以多个智能指针共享同一块内存：

#include <memory>
using namespace std;

class A{
public:
	A(int d):m_data(d)
	{
		cout<<"Construct A to:"<<m_data<<" this addr:"<<this<<endl;
	}
	~A()
	{
		cout<<"Destruct A, this addr:"<<this<<endl;
	}
	int m_data;
};

ostream& operator<<(ostream& os, const A &a)
{
	os<<a.m_data<<" addr:"<<&a;
	return os;
}

int main(){

	shared_ptr<A> up1(new A(1));        //调用构造函数，构造匿名对象，记作a，输出：Construct A to:1 this addr:0x6d6f90
	cout<<"pos1 m_data:"<<*up1<<endl;   //访问up1指向的对象a，输出：pos1 m_data:1 addr:0x6d6f90
	shared_ptr<A> up2 = up1;            //up2与up1共享同对内存对象a的访问
	cout<<"pos2 m_data:"<<*up2<<endl;   //输出：pos2 m_data:1 addr:0x6d6f90
	up1.reset();                        //up1释放对a的访问权，降低引用计数，由于此时up2还拥有对内存对象a的访问权，因此不会释放对象a
	cout<<"pos3 m_data:"<<*up2<<endl;   //输出：pos3 m_data:1 addr:0x6d6f90
	up2.reset();                        //up2释放对a的访问权，降低引用计数，由于此时引用计数为0，释放内存，调用析构函数，输出：Destruct A, this addr:0x6d6f90
	return 0;
}