#include <iostream>using namespace std;class DemoA{public:    int m_a;    void show();    DemoA(int val);};DemoA::DemoA(int val){    m_a = val ;}void DemoA::show(){    cout<<"ashow: DemoA.m_a="<<this->m_a<<endl;}//-------------------class DemoB :public DemoA{public:    int m_b;    void show();    DemoB(int aval , int bval);};DemoB::DemoB(int aval,int bval):DemoA(aval){    m_b = bval ;}void DemoB::show(){    cout<<"bshow: DemoB.m_a="<<this->m_a<<endl;    cout<<"bshow: DemoB.m_b="<<this->m_b<<endl;}//---------------int main(){    DemoA ca(11);    DemoB cb(111,222);    ca.show();    cb.show();    ca = cb;//派生类对象可以对基类赋值    ca.show();//     cb=ca;//基类对派生类不可以赋值 error C2679: 二进制“=”: 没有找到接受“DemoA”类型的右操作数的运算符(或没有可接受的转换)//     cb.show();//         while(1);    return 0 ;}