纯虚函数

class Base
{
public:
    Base(){};
    virtual ~Base(){};
};

//类A是一个抽象类
class A : public Base
{
public:
    A(){}
    virtual ~A(){}
    virtual void fun() = 0; //纯虚函数
};

class B : public A
{
public:
    B(){}
    virtual ~B(){}
    virtual void fun()
    {
        std::cout<<"B"<<std::endl;
    }
};

int main()
{
    //A a; //抽象类A不能实例化对象，编译器会报错
    A *a = new B;
    a->fun();
    B b;
    b.fun();    

    return 0;
}