如何在派生class中实现虚函数？

Question

考虑以下 UML：

当我尝试在Single.cpp中实现虚函数rate()时，出现错误：无法分配抽象类型的对象'Single'
预定* b = new Single();

addBooking() 函数应该创建一个 Single 类型的指针 Booking，添加指向 QList 的指针（BookingList 派生自 QList<Booking*>) 和 return Booking 指针。

当我注释掉虚函数时，一切正常。为什么会发生这种情况，我该如何解决？

下面是我的程序的最小版本：

#ifndef BOOKING_H
#define BOOKING_H

class Booking
{
public:
    Booking();
    double SINGLE_PPPN = 200.00;
    virtual double rate() = 0;
};

#endif // BOOKING_H

#include "booking.h"

Booking::Booking()
{
}

#ifndef BOOKINGLIST_H
#define BOOKINGLIST_H
#include <QList>
#include <iostream>
#include "booking.h"
#include "single.h"

using namespace std;

class BookingList : public QList<Booking*>
{
public:
    BookingList();
    Booking* addBooking();
    void deleteAll();
};

#endif // BOOKINGLIST_H

#include "bookinglist.h"

BookingList::BookingList()
{
}

Booking* BookingList::addBooking()
{
    Booking* b = new Single();

    this->append(b);

    cout << "Total bookings: " << this->size() << "\n\n" <<endl;

    return b;
}

void BookingList::deleteAll()
{
    for (int i = 0; i < this->count(); i++)
    {
        cout << "Deleting Item At: " << i << endl;
        delete this->at(i);
    }
}

#ifndef SINGLE_H
#define SINGLE_H
#include "booking.h"

class Single : public Booking
{
public:
    Single();
};

#endif // SINGLE_H

#include "single.h"

Single::Single()
{
}

double Single::rate()
{
    return Booking::SINGLE_PPPN;
}

#include <QCoreApplication>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    return a.exec();
}

Answer 1

您需要在 class 定义中声明您的方法 override

class Single : public Booking
{
public:
    Single();
    double rate() override;  // this line
};

然后你就可以在你的cpp文件中实际实现这个方法了

double Single::rate()
{
    return Booking::SINGLE_PPPN;
}

如何在派生class中实现虚函数？

How to implement a virtual function in derived class?

c++

virtual