代码：
#include <iostream>class Pet {public: virtual void speak() = 0; virtual void eat() = 0;};class Dog : public Pet {public: void speak() { std::cout<<"speak"<<std::endl; } void eat() { std::cout<<"eat"<<std::endl; }};class littleDog : public Dog {public: void speak() { std::cout<<"small speak"<<std::endl; } void eat() { std::cout<<"little eat"<<std::endl; }};int main() { Dog dog; littleDog ld; Dog *p = &dog; p->speak(); p->eat(); p = &ld; p->speak(); p->eat(); return 0;}结果： 
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