复杂的抽象结构举例，求各高手解答 - 编程论坛

#include<iostream>
using namespace std;
class Animal
{
public:
    Animal(int age);
    virtual ~Animal(){cout<<"析构动物..."<<endl;}
    virtual int GetAge(){return itsage;}
    virtual void Propagate()=0;
    virtual void Sleep()=0;
    virtual void Eat()=0;
    virtual void Show()=0;
private:
    int itsage;
};
Animal::Animal(int age):itsage(age)
{
    cout<<"创建动物..."<<endl;
}
class Mammalia:public Animal
{
public:
    Mammalia(int age):Animal(age){cout<<"创建哺乳动物..."<<endl;}
    virtual ~Mammalia(){cout<<"析构哺乳动物..."<<endl;}
    virtual void Propagate(){cout<<"哺乳动物是通过胚胎繁殖的"<<endl;}
};
class Bird:public Animal
{
public:
    Bird(int age):Animal(age){cout<<"创建鸟类..."<<endl;}
    virtual ~Bird(){cout<<"析构鸟类..."<<endl;}
    virtual void Sleep(){cout<<"鸟类是站着睡觉"<<endl;}
    virtual void Eat(){cout<<"鸟类很少是吃肉的"<<endl;}
    virtual void Show(){cout<<"鸟类一般寿命为："<<GetAge()<<"年"<<endl;}
};
class Human:public Mammalia
{
public:
    Human(int age):Mammalia(age){cout<<"创建人类..."<<endl;}
    virtual ~Human(){cout<<"析构人类..."<<endl;}
    virtual void Sleep(){cout<<"人类是在床上睡觉的"<<endl;}
    virtual void Eat(){cout<<"人类不吃生食物"<<endl;}
    virtual void Show(){cout<<"人类一般寿命为："<<GetAge()<<"年"<<endl;}
};
class Big:public Mammalia
{
public:
    Big(int age):Mammalia(age){cout<<"创建猪类..."<<endl;}
    virtual ~Big(){cout<<"析构猪类..."<<endl;}
    virtual void Sleep(){cout<<"猪类喜欢在烂泥中睡觉"<<endl;}
    virtual void Eat(){cout<<"猪类是杂食动物"<<endl;}
    virtual void Show(){cout<<"由于猪会被人类宰了吃，所以猪类一般寿命为："<<GetAge()<<"年"<<endl;}
};
int main(void)
{
    Animal *p=0;
    int choice=0;
    bool quit=false;
    while (choice<4)
    {
        choice=0;
        cout<<"(0)退出，(1)鸟类，(2)人类，(3)猪类：";
        cin>>choice;
        switch (choice)
        {
        case 1: p=new Bird(50);                                //错误全部指向这里
            break;
        case 2: p=new Human(80);
            break;
        case 3: p=new Big(1);
            break;
        default: quit=true;
            break;
        }
        if (quit)
        {
            break;
        }
        p->Propagate();
        p->Sleep();
        p->Eat();
        p->Show();
        delete p;
    }
    return 0;
}
/*
编译时的错误：
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E:\c++\101复杂的抽象结构1\01.cpp(66) : error C2259: 'Bird' : cannot instantiate abstract class due to following members:
        E:\c++\101复杂的抽象结构1\01.cpp(27) : see declaration of 'Bird'
E:\c++\101复杂的抽象结构1\01.cpp(66) : warning C4259: 'void __thiscall Animal::Propagate(void)' : pure virtual function was not defined
        E:\c++\101复杂的抽象结构1\01.cpp(9) : see declaration of 'Propagate'
E:\c++\101复杂的抽象结构1\01.cpp(66) : error C2259: 'Bird' : cannot instantiate abstract class due to following members:
        E:\c++\101复杂的抽象结构1\01.cpp(27) : see declaration of 'Bird'
E:\c++\101复杂的抽象结构1\01.cpp(66) : warning C4259: 'void __thiscall Animal::Propagate(void)' : pure virtual function was not defined
        E:\c++\101复杂的抽象结构1\01.cpp(9) : see declaration of 'Propagate'
Error executing cl.exe.

01.obj - 2 error(s), 2 warning(s)
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*/