Using a Derived Class

To use a derived class, a program needs access to the base-class declarations. Listing 13.4 places both class declarations in the same header file. You could give each class its own header file, but because the two classes are related, it makes more organizational sense to keep the class declarations together.

Listing 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

Listing 13.5 provides the method definitions for both classes. Again, you could use separate files, but it’s simpler to keep the definitions together.

Listing 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)
{
}

Listing 13.6 creates objects of both the TableTennisPlayer class and the RatedPlayer class. Notice that objects of both classes can use the TableTennisPlayer class Name() and HasTable() methods.

Listing 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. ";
    else
        cout << ": hasn't a table. ";
    player1.Name();           // base object uses base method
    if (player1.HasTable())
        cout << ": has a table";
    else
        cout << ": hasn't a table. ";
    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;
}

Here is the output of the program in Listings 13.4, 13.5, and 13.6:

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