C++ 类的继承与派生 第七章

派生类

定义：

派生类成员是指除了从基类继承的所有成员之外，新增加的数据和函数成员

派生类生成过程：

访问控制：

类型兼容规则（必须有继承关系）

• 实现基类的复制构造函数
  
• 实现派生类的复制构造
  
  
• 实现派生类调用基类
  
  首先会调用基类的构造函数其次在实现派生类的构造函数，而析构函数函数的调用顺序刚好与构造函数相反，先执行派生类的析构函数最后实现基类的析构函数。

  #include <iostream>
  #include <cstring>
  using namespace std;
  class Base
  {
  public:Base(int n):m_i(n){cout<<"Base::Base()"<<endl;}~Base(){cout<<"Base::~Base()"<<endl;}
  private:int m_i;
  };class Derived : public Base
  {
  public:Derived(int a,int b ):Base(b),m_k(a){cout<<"Derived()"<<endl;}~Derived(){cout<<"~Derived()"<<endl;}
  private:int m_k;
  };
  int main()
  {Derived d(10,20);return 0;
  }

• 基类指针指向派生类
  派生类可以调取到基类函数的相关数据（体现了就近原则会先调用基类自己的相关函数数据），但是基类不一定能调取到派生类的数据，如时钟习题，但是也存在调取可能如下列代码运用到了隐函数

  #include <iostream>
  using namespace std;// 基类
  class Base {
  public:virtual void show() {cout << "Base show()" << endl;}virtual ~Base() {} //
  };// 派生类
  class Derived : public Base {
  public:void show() override 
  { 
  // 使用override关键字明确表明这是一个重函数cout << "Derived show()" << endl;}
  };
  int main() {// 派生类对象Derived d;// 基类指针指向派生类对象Base* basePtr = &d;// 通过基类指针调用虚函数，执行的是派生类中的版本basePtr->show(); // 输出: Derived show()return 0;
  }

🙋‍♂️练习：从时分秒的到年月日时分秒的实现

其中运用到了 基类指针指向派生类，体现就近原则所以只打印了基类函数中存在的时分秒

#include <iostream>using namespace std;class Clock
{
public:Clock(int h, int m, int s) : hour(h), minute(m), second(s){cout << "Clock(int, int, int)" << endl;}Clock(const Clock &other) : hour(other.hour), minute(other.minute), second(other.second){cout << "Clock(Clock &)" << endl;}~Clock(){cout << "~Clock()" << endl;}void setTime(int h, int m, int s) //this{this->hour = h;minute = m;second = s;}void showTime() const// const Clock *this{cout << this->hour << ":" << this->minute << ":" << this->second << endl;}protected:int hour;int minute;int second;
};
class CalendarClock : public Clock
{public:CalendarClock(int y,int M,int d,int h,int m,int s):Clock(h,m,s),year(y),month(M),day(d){cout <<"CalendarClock::()"<<endl;}CalendarClock(const CalendarClock &other):Clock(other),year(other.year),month(other.month),day(other.month){cout<<"CalendarClock (CalenderClock &)"<<endl;}~CalendarClock(){cout<<"CalenderClock~"<<endl;}void setTime(int y,int M,int d,int h,int m,int s){year = y;month = M;day = d;Clock::setTime(h,m,s);
//            hour = h;
//            minute = m;
//            second = s;}void showTime() const{cout<<year<<"-"<<month<<"-"<<day<<"-"<<hour<<":"<<minute<<":"<<second<<":"<<endl;//Clock::setTime();}
private:int year;int month;int day;
};int main()
{CalendarClock c(2024,8,9,10,38,21);c.showTime();
//基类指针指向派生类指针Clock *p = &c;p->showTime();//c.show();
}