随记，虚函数与引用

#include <QCoreApplication>#include<stdio.h>class A{protected:    int x;public:    A(int xx):x(xx) {}    virtual void say(){printf("a say %d\n",x);}};class B:public A{protected:    int y;public:    B(int xx,int yy):y(yy),A(xx) {}    void say(){printf("b say %d %d\n",x,y);}    void haha(){printf("b hahahaah\n");}};int main(int argc, char *argv[]){    QCoreApplication a(argc, argv);    A aa(8);    aa.say();    B b(1,2);    b.say();    A &aaa=b;//把b代表的空间取小名aaa，并当做A类型对象来看，    aaa.say();    b.haha();    A zda=b;//    zda.say();    return a.exec();}上面A zda=b调用复制构造函数