98.重载的三种方式以及重载符号的交换律

#include "mainwindow.h"
#include <QApplication>
#include <QPushButton>>

//重载的三种形式,成员函数重载
//友元函数重载,可以使用私有变量以及保护变量
//一般函数重载都是公有变量

class button
{
    QPushButton *p;
    int x,y;

    friend void operator *(button &buttonx,int n);
    friend void operator *(int n,button &buttonx);
public:
    button():x(500),y(400)
    {
        p = new QPushButton;
        p->resize(x,y);
        p->show();
    }
    ~button()
    {
        delete p;
    }
    
    bool operator < (button &buttonx)
    {
        return this->x*this->y < buttonx.x*buttonx.y;
    }
};

void operator *(button &buttonx,int n)
{
    buttonx.x*=n;
    buttonx.y*=n;
    buttonx.p->resize(buttonx.x,buttonx.y);
}

void operator *(int n,button &buttonx)
{
    buttonx.x*=n;
    buttonx.y*=n;
    buttonx.p->resize(buttonx.x,buttonx.y);
}

//涉及this指针则不可以在友元函数或外部函数中重载
//void operator [](button &buttonx)
// = [] () ->等这些运算符涉及到this指针,必须不能用友元函数以及外部函数

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    button b;
    2*b;

    qDebug() << "hello" << endl;
    return a.exec();
}