C++ Primer Plus 第十三章知识点简化

• 1. 简单的基类
• 2. 派生一个类
• 3. 派生类和基类的特殊关系
• Reference：

1. 简单的基类

       由于面向对象编程主要目的之一就是提供可重写的代码，对于扩展和修改类，除了去源码中修改之外，还有就是类继承；从一个类派生出另一个类时，原始类称为 基类，继承类称为 派生类。简单看下下面的程序：

#ifndef HEAD_H_
#define HEAD_H_
#include<iostream>
#include<string>
using namespace std;

// ============ simple base class ==================
class TableTennisPlayer{
private:
	string firstname;
	string lastname;
	bool hasTable;
public:
	TableTennisPlayer(const string& fn = "none", const string& ln = "none", bool ht = false);
	void Name() const;
	bool HasTable() const { return hasTable; };
	void ResetTable(bool v) { hasTable = v; };
};
#endif

#include "head.h"

TableTennisPlayer::TableTennisPlayer(const string& fn, const string& ln, 
	bool ht) : firstname(fn), lastname(ln), hasTable(ht) {}
//TableTennisPlayer::TableTennisPlayer(const string& fn, const string& ln, bool ht) {
//	firstname = fn;
//	lastname = ln;
//	hasTable = ht;
//}

void TableTennisPlayer::Name() const{
	cout << lastname << ", " << firstname;
}

#include <iostream>
#include "head.h"
using namespace std;

int main(void){
	TableTennisPlayer player1("Chuck", "Blizzard", true);
	TableTennisPlayer player2("Tara", "Boomdea", false);
	
	player1.Name();
	if (player1.HasTable())
		cout << ": has a table.\n";
	else
		cout << ": hasn't a table.\n";
	
	player2.Name();
	if (player2.HasTable())
		cout << ": has a table";
	else
		cout << ": hasn't a table.\n";

	return 0;
}

 

---

2. 派生一个类

       在基类继承的时候，若是class B : public A，那么A是基类且B是公有派生。此时基类成员和共有派生类成员之间的关系是怎样？尤其是私有成员有哪些需要注意？

公有派生的知识点：

• 基类的公有成员成为派生类的公有成员；
• 基类的私有部分只能通过基类的公有和保护方法访问；
• 基类指针可以不进行显示类型转换的情况下指向派生类对象，基类引用也可以不进行~来引用派生类对象。

#ifndef HEAD_H_
#define HEAD_H_
#include<iostream>
#include<string>
using namespace std;

// ================= simple base class =======================
class TableTennisPlayer{
private:
	string firstname;
	string lastname;
	bool hasTable;
public:
	TableTennisPlayer(const string& fn = "none",
		const string& ln = "none", bool ht = false);
	void Name() const;
	bool HasTable() const { return hasTable; };
	void ResetTable(bool v) { hasTable = v; };
};

// ================ simple derived class =====================
class RatedPlayer : public TableTennisPlayer{
private:
	unsigned int rating;
public:
	RatedPlayer(unsigned int r = 0, const string& fn = "none",
		const string& ln = "none", bool ht = false);
	RatedPlayer(unsigned int r, const TableTennisPlayer& tp);
	unsigned int Rating() const { return rating; }
	void ResetRating(unsigned int r) { rating = r; }
};

#endif

#include "head.h"

TableTennisPlayer::TableTennisPlayer(const string& fn,
	const string& ln, bool ht) : firstname(fn),
	lastname(ln), hasTable(ht) {}

void TableTennisPlayer::Name() const{
	cout << lastname << ", " << firstname;
}

// RatedPlayer methods
RatedPlayer::RatedPlayer(unsigned int r, const string& fn,
	const string& ln, bool ht) : TableTennisPlayer(fn, ln, ht){
	rating = r;
}

RatedPlayer::RatedPlayer(unsigned int r, const TableTennisPlayer & tp)
	: TableTennisPlayer(tp), rating(r)
{}

#include <iostream>
#include "head.h"
using namespace std;

int main(void){

	TableTennisPlayer player1("Tara", "Boomdea", false);
	RatedPlayer rplayer1(1140, "Mallory", "Duck", true);

	rplayer1.Name();          // derived object uses base method
	if (rplayer1.HasTable())
		cout << ": has a table.\n";
	else
		cout << ": hasn't a table.\n";

	player1.Name();           // base object uses base method
	if (player1.HasTable())
		cout << ": has a table";
	else
		cout << ": hasn't a table.\n";
	cout << "Name: ";
	rplayer1.Name();
	cout << "; Rating: " << rplayer1.Rating() << endl;
	// initialize RatedPlayer using TableTennisPlayer object
	RatedPlayer rplayer2(1212, player1);
	cout << "Name: ";
	rplayer2.Name();
	cout << "; Rating: " << rplayer2.Rating() << endl;

	return 0;
}

输出：
Duck, Mallory: has a table.
Boomdea, Tara: hasn't a table.
Name: Duck, Mallory; Rating: 1140
Name: Boomdea, Tara; Rating: 1212

 

---

3. 派生类和基类的特殊关系

• 基类指针可以指向派生类对象，基类引用可以引用派生类对象；
  即： 定义个基类指针或者引用，都可以用派生类对象赋给他们，好比作double->int，但这样做会使得只能调用基类的方法。只要形参是基类，实参既可以是基类也可以是派生类。

  int main(){
  	RatedPlayer rplayer(1140, "Mallory", "Duck", true);
  	TableTennisPlayer& rt = rplayer;
  	TableTennisPlayer* pt = &rplayer;
  	rt.Name();
  	pt->Name();
  }
  

  int main(){
  	TableTennisPlayer player("Mallory", "Duck", true);
  	RatedPlayer& rt = player;
  	RatedPlayer* pt = &player;
  }
  
  ERROR：E0144	"TableTennisPlayer *" 类型的值不能用于初始化 "RatedPlayer *" 类型的实体
  

• 对于非类方法的使用（引用）

  void Show(const TableTennisPlayer& rt) {
  	cout << "Name: ";
  	rt.Name();
  }
  

  int main(){
  	TableTennisPlayer tplayer("Mallory", "Duck", true);
  	RatedPlayer rplayer(1140, "Mallory", "Duck", true);
  	Show(tplayer);
  	Show(rplayer);
  }
  

• 对于非类方法的使用（指针==>和引用写法差不多）
   

---

Reference：

• 《C++ Primer Plus》第六版 Stephen Prata 著