C++学习笔记－－继承

When one class inherits from another, the original class is called a base class, and the inheriting class is called a derived class. So to illustrate inheritance, let’s begin with a base class.

当一个类继承另外一个类时，被继承的类称为父类，继承类称为子类，先从定义父类开始：

// tabtenn0.h -- a table-tennis base class
#ifndef TABTENN0_H_
#define TABTENN0_H_
#include <string>
using namespace std;
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

//tabtenn0.cpp -- simple base-class methods
#include "tabtenn0.h"
#include <iostream>
TableTennisPlayer::TableTennisPlayer(const string & fn,
    const string & ln, bool ht):firstname(fn),lastname(ln),hasTable(ht) {}
void TableTennisPlayer::Name() const
{
    cout << lastname << ", " << firstname;
}

// usett0.cpp -- using a base class
#include <iostream>
#include "tabtenn0.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;
}

输出：

wang@wang:~/c++$ ./a.out
Blizzard, Chuck: has a table.
Boomdea, Tara: hasn't a table.

When a program constructs a derived-class object, it first constructs the base-class object.

在初始化子类的对象时，应该先初始化父类的对象，实现如下：

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

// tabtenn1.h -- a table-tennis base class
#ifndef TABTENN1_H_
#define TABtENN1_H_
#include <string>
using namespace std;
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

// tabtenn1.cpp -- simple base-class methods
#include "tabtenn1.h"
#include <iostream>
using namespace std;
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) {}

// usett1.cpp -- using base class and derived class
#include <iostream>
#include "tabtenn1.h"
using namespace std;
int main(void)
{
    TableTennisPlayer player1("Tara", "Boomdea", false);
    RatedPlayer rplayer1(1140, "Mallory", "Duck", true);
    rplayer1.Name();
    if (rplayer1.HasTable())
        cout << ": has a table.\n";
    else
        cout << ": hasn't a table.\n";
    player1.Name();
    if (player1.HasTable())
        cout << ": has a table";
    else
        cout << ": hasn't a table.\n";
    cout << "Name: ";
    rplayer1.Name();
    cout << "; Rating: " << rplayer1.Rating() << endl;
    // initalize RatedPlayer using TableTennisPlayer object
    RatedPlayer rplayer2(1212, player1);
    cout << "Name: ";
    rplayer2.Name();
    cout << "; Rating: " << rplayer2.Rating() << endl;
    return 0;
}

输出：

wang@wang:~/c++$ ./a.out
Duck, Mallory: has a table.
Boomdea, Tara: hasn't a table.
Name: Duck, Mallory; Rating: 1140
Name: Boomdea, Tara; Rating: 1212

A base-class pointer can point to a derived-class object without an explicit type cast and that a base-class reference can refer to a
derived-class object without an explicit type cast:
RatedPlayer rplayer1(1140, "Mallory", "Duck", true);
TableTennisPlayer & rt = rplayer;
TableTennisPlayer * pt = &rplayer;
rt.Name(); // invoke Name() with reference
pt->Name(); // invoke Name() with pointer

父类的指针可以指向子类的对象，而没有进行类型转换；父类的引用也可以引用子类的对象，而没有类型转换，但是只限于调用父类的方法。