05-使用派生类

13.1.3　使用派生类

要使用派生类，程序必须要能够访问基类声明。程序清单13.4将这两种类的声明置于同一个头文件中。也可以将每个类放在独立的头文件中，但由于这两个类是相关的，所以把其类声明放在一起更合适。

程序清单13.4　tabtenn1.h

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

程序清单13.5是这两个类的方法定义。同样，也可以使用不同的文件，但将定义放在一起更简单。

程序清单13.5　tabtenn1.cpp

//tabtenn1.cpp -- simple base-class methods
#include "tabtenn1.h"
#include <iostream>
TableTennisPlayer::TableTennisPlayer (const string & fn,
    const string & ln, bool ht) : firstname(fn),
        lastname(ln), hasTable(ht) {}
void TableTennisPlayer::Name() const
{
    std::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)
{
}

程序清单13.6创建了TableTennisPlayer类和RatedPlayer类的对象。请注意这两个类对象是如何使用TableTennisPlayer类的Name()和HasTable()方法的。

程序清单13.6　usett1.cpp

// usett1.cpp -- using base class and derived class
#include <iostream>
#include "tabtenn1.h"
int main ( void )
{
    using std::cout;
    using std::endl;
    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;
}

下面是程序清单13.4～程序清单13.6组成的程序的输出：

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