《C++游戏编程入门》第10章 继承与多态：Blackjack

10.1 继承简介

从已有类派生新类，自动继承已有类的数据成员与成员函数。
可重用性的好处：

• 减少工作量。功能函数不必再次编写。
• 减少错误。
• 代码更加清晰。

10.simple_boss.cpp

#include <iostream>
using namespace std;

class Enemy
{
   
public:
    int m_Damage;

    Enemy();
    void Attack() const;
};

Enemy::Enemy()
    : m_Damage(10)
{
   
}

void Enemy::Attack() const
{
   
    cout << "Attack inflicts " << m_Damage << " damage points!\n";
}

class Boss : public Enemy//基类派生，构造、析构、拷贝构造、拷贝赋值运算符未被继承
{
   
public:
    int m_DamageMultiplier;

    Boss();
    void SpecialAttack() const;
};

Boss::Boss()
    : m_DamageMultiplier(3)
{
   
}

void Boss::SpecialAttack() const
{
   
    cout << "Special Attack inflicts " << (m_DamageMultiplier * m_Damage);
    cout << " damage points!\n";
}

int main()
{
   
    cout << "Creating an enemy.\n";
    Enemy enemy1;
    enemy1.Attack();

    cout << "\nCreating a boss.\n";
    Boss boss1;
    boss1.Attack();
    boss1.SpecialAttack();

    return 0;
}

10.2 继承访问权的控制

public、protected、private只为派生类提供基类成员的必要的访问权。

• public：可被程序中所有代码访问。
• protected：本类和派生类访问。
• private：只能本类访问。

10.simple_boss2.cpp

#include <iostream>
using namespace std;

class Enemy
{
   
public:
    Enemy();
    void Attack() const;

protected:
    int m_Damage;
};

Enemy::Enemy()
    : m_Damage(10)
{
   
}

void Enemy::Attack() const
{
   
    cout << "Attack inflicts " << m_Damage << " damage points!\n";
}

class Boss : public Enemy
{
   
public:
    Boss();
    void SpecialAttack() const;

private:
    int m_DamageMultiplier;
};

Boss::Boss()
    : m_DamageMultiplier(3)
{
   
}

void Boss::SpecialAttack() const
{
   
    cout << "Special Attack inflicts " << (m_DamageMultiplier * m_Damage);
    cout << " damage points!\n";
}

int main()
{
   
    cout << "Creating an enemy.\n";
    Enemy enemy1;
    enemy1.Attack();

    cout << "\nCreating a boss.\n";
    Boss boss1;
    boss1.Attack();
    boss1.SpecialAttack();

    return 0;
}

10.3 调用与重写基类成员函数

派生类中可重写基类的成员函数或者调用。

10.overriding_boss.cpp

#include <iostream>
using namespace std;

class Enemy
{
   
public:
    Enemy(int damage = 10);
    virtual void Taunt() const;  // 声明虚基类成员函数
    virtual void Attack() const; // 重写函数声明成虚函数

private:
    int m_Damage;
};

Enemy::Enemy(int damage)
    : m_Damage(damage)
{
   
}

void Enemy::Taunt() const
{
   
    cout << "The enemy says he will fight you.\n";
}

void Enemy::Attack() const
{
   
    cout << "Attack! Inflicts " << m_Damage << " damage points.";
}

class Boss : public Enemy
{
   
public:
    Boss(int damage = 30);
    virtual void Taunt() const;           // virtual可省略
    virtual void Attack() const override; // override建议增加
};

Boss::Boss(int damage)
    : Enemy(damage) // 调用基类构造函数
{
   
    cout << "damage in Boss(int damage): " << damage << endl;
}

void Boss::Taunt() const // override base class member function
{
   
    cout << "The boss says he will end your pitiful existence.\n";
}

void Boss::Attack() const // override base class member function
{
   
    Enemy::Attack(); // 调用基类成员函数
    cout << " And laughs heartily at you.\n";
}

int main()