#include <iostream>

using namespace std;

class num{

public:

    num(){n=new int;*n=;cout<<"construct:"<<endl;}

    num(int x){n=new int;*n=x;cout<<"construct:"<<endl;}

    ~num(){delete n;n=NULL; cout<<"destruct:"<<endl;}

    //num(num &a){this->x=a.x;cout<<"copy:"<<x<<endl;}

    int getX(){

        return *n;

    }

    void setX(int x)

    {

        *n=x;

    }

    num operator=(num &r){

        cout<<"operator+"<<endl;

        *n=r.getX();

        return *this; //返回two的副本，two的副本返回后进行析构，导致n指向的内存释放

    }

private:

    int *n;

};

int & test(int & x)

{

    cout<<x<<endl;

    return x;

}

int main()

{

    num one,two,three;

    one.setX();

    two=one; //<==> two.operator =(one);

    cout<<two.getX()<<endl;

    return ;

}

#include <iostream>

using namespace std;

class num{

public:

    num(){n=new int;*n=;cout<<"construct:"<<endl;}

    num(int x){n=new int;*n=x;cout<<"construct:"<<endl;}

    ~num(){delete n;n=NULL; cout<<"destruct:"<<endl;}

    num(const num & a){n=new int;*n=a.getX();cout<<"copy:"<<endl;}

    int getX() const {

        return *n;

    }

    void setX(int x)

    {

        *n=x;

    }

     num operator=(num &r){

        cout<<"operator+"<<endl;

        *n=r.getX();

        return *this; //返回two的副本，two的副本返回后进行析构，导致n指向的内存释放

    }

private:

    int *n;

};

int main()

{

    num one,two,three;

    one.setX();

    three=two=one; //<==> two.operator =(one);

    cout<<one.getX()<<endl;

    cout<<two.getX()<<endl;

    cout<<three.getX()<<endl;

    return ;

}

#include <iostream>

using namespace std;

class num{

public:

    num(){n=new int;*n=;cout<<"construct:"<<endl;}

    num(int x){n=new int;*n=x;cout<<"construct:"<<endl;}

    ~num(){delete n;n=NULL; cout<<"destruct:"<<endl;}

    num(const num & a){n=new int;*n=a.getX();cout<<"copy:"<<endl;}

    int getX() const {

        return *n;

    }

    void setX(int x)

    {

        *n=x;

    }

     const num & operator=(const num &r){

        cout<<"operator+"<<endl;

        if(this == &r)

        {

            return *this;

        }

        *n=r.getX();

        return *this; //返回two的副本，two的副本返回后进行析构，导致n指向的内存释放

    }

private:

    int *n;

};

class man{

public :

    man(int x){a=x;}

    man(){}

public :

    int a;

};

int main()

{

    num one(),two,three;

    three=two=one;

    cout<<one.getX()<<endl;

    cout<<two.getX()<<endl;

    cout<<three.getX()<<endl;

    return ;

}

#include <iostream>

using namespace std;

class num{

public:

    num(){n=new int;*n=;cout<<"construct:"<<endl;}

    num(int x){n=new int;*n=x;cout<<"construct:"<<endl;}

    ~num(){delete n;n=NULL; cout<<"destruct:"<<endl;}

    num(const num & a){n=new int;*n=a.getX();cout<<"copy:"<<endl;}

    int getX() const {

        return *n;

    }

    void setX(int x)

    {

        *n=x;

    }

    // const num & operator=(const num &r){

    //    cout<<"operator+"<<endl;

    //    if(this == &r)

    //    {

    //        return *this;

    //    }

    //    *n=r.getX();

    //    return *this; //返回two的副本，two的副本返回后进行析构，导致n指向的内存释放

    //}

private:

    int *n;

};

class man{

public :

    man(int x){a=x;}

    man(){}

public :

    int a;

};

int main()

{

    num one(),two,three;

    two=one;

/**

错误原因:当执行 two=one; 后，两个对象的成员属性，执行了同一内存地址，其中一个先析构了

遍释放了a执行的内存地址，另个对象在析构时便会报错了

*/

    cout<<one.getX()<<endl;

    cout<<two.getX()<<endl;

    return ;

}

#include <iostream>

using namespace std;

class A{

public:

    A(int x, int y=){i=x; cout<<"construct"<<i<<endl;}

    ~A(){cout<<"destruct"<<i<<endl;}

    void geti(){cout<<i<<endl;}

private:

    int i;

};

int main()

{

    A a();

    a=; //相当于 a= A(20); ,先创建一个临时的对象，然后将这个临时对象赋给对象a，完成赋值后调用临时对象的析构函数

    //或 a=A(20);

    return ;

}