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C++之智能指针

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#include <stdio.h>
#include <iostream>

using namespace std;

class Test
{
private:
    int i;

public:
   Test(int obj)
    {
        i=obj;
        cout <<"Test(int obj)"<<endl;
    }

    int value()
    {
        return i;
    }
    ~Test()
    {
        cout <<"~Test()"<<endl;
    }

};

class Pointer
{
private:
    Test *m_pointer;
public:
    Pointer(Test* pointer = NULL)    //构造函数将空指针赋值给新创建的对象
    {
        m_pointer=pointer;
        cout << "Pointer(Test* pointer=NULL)" <<endl;
    }
    Pointer(const Pointer& obj)     //拷贝构造，要将后者的值置为空，要不delete 后者，相当于delete两次一个空间就会造成段错误
    {
        m_pointer=obj.m_pointer;
        const_cast<Pointer&>(obj).m_pointer=NULL;
    }
    Pointer& operator=(const Pointer& obj)  //和拷贝构造的区别是，赋值是已经申请的内存空间，而拷贝构造后者没有内存空间，故赋值要将前者的内存释放掉
    {
        cout <<"operator="<<endl;
        if(this != &obj)
        {
            delete m_pointer;      //释放前者内存空间
            m_pointer=obj.m_pointer;   //将后者内存指针赋值给一个空的指针，
            const_cast<Pointer&>(obj).m_pointer=NULL;  //将后者释放掉，不然也会造成构造的那种段错误
            cout <<"if(this != &obj)"<<endl;
        }

        return *this;
    }
    bool isNULL()
    {
        return (m_pointer==NULL);
    }

    Test* operator ->()
    {
        return m_pointer;
    }

    Test& operator *()
    {
        return *m_pointer;
    }
    ~Pointer()
    {
        delete m_pointer;
        cout <<"~Pointer()" <<endl;
    }
};

int main(void)
{
    Pointer p1=new Test(1);
    Pointer p3=new Test(3);

    cout << "p1value=" <<p1->value()<<endl;

    Pointer p2=p1;          //此处p1已经为空，
    cout << "p1isNUll=" <<p1.isNULL()<<endl;

    p3=p1;                  //此处p1已经为空，p1赋值给p3只能是一个空指针

    cout << "p3value=" <<p3->value()<<endl;   //空指针肯定打印不出来
    
    cout << "p3isNUll=" <<p3.isNULL()<<endl;  //error
    cout << "p1isNUll=" <<p1.isNULL()<<endl;   //error
    

    return 0;
}
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