copy and swap

#ifndef WIDGET_H

#define WIDGET_H

#include <iostream>

using namespace std;

class Widget

{

public:

Widget(int* elem);

~Widget(){delete _elem;cout<<"~~~"<<endl;}

Widget(const Widget& co);

Widget& operator=(const Widget& co);

void swap(Widget& co);

void show() const{cout<<*_elem<<endl;}

private:

int* _elem;

};

#endif // WIDGET_H

#include "widget.h"

Widget::Widget(int *elem):_elem(elem)

{

}

Widget::Widget(const Widget &co)

{

_elem = new int(*co._elem);

}

Widget& Widget::operator=(const Widget&co)

{

Widget temp(co);

swap(temp);

return *this;

}

void Widget::swap(Widget &co)

{

int *temp = _elem;

_elem = co._elem;

co._elem = temp;

}

#include <iostream>

#include "decoratorclass.h"

#include "subclass_1.h"

using namespace std;

#include "test.h"

#include "widget.h"

int main()

{

Widget w1(new int(2));

cout<<"show w1_elem:";

w1.show();

Widget w2(new int(4));

cout<<"show w2_elem:";

w2.show();

cout<<"w1 = w2";

w1 = w2;//这里有一次析构，因为使用了局部变量，所以运行时，有三次“~~”不要奇怪

cout<<"show w1_elem:";

w1.show();
return 0;
}