派生类对象可以对基类对象赋值，赋值时属于派生类独有的部分就舍弃不用。
#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 ;}
