Question

Im currently learning multiple inheritance and ran into a problem creating a function that inherits its previous ancestors variables and functions. The problem occurs in the showRoomServiceMeal() functions where i do the multiple inheriting. When i compile i get errors stating that the corresponding inherited variables cannot be inherited because they are protected and that the inherited functions are used without objects.

I thought that the protected assessors allows the variables to be used by its children and to access the corresponding functions and protected variables the scope resolution operator (::) is to be used? Can anyone help explain why im getting these errors?

#include<iostream>
#include<string>
using namespace std;

class RestaurantMeal
{
protected:
    string entree;
    int price;
public:
    RestaurantMeal(string , int );
    void showRestaurantMeal();
};

RestaurantMeal::RestaurantMeal(string meal, int pr)
{
    entree = meal;
    price = pr;
}

void RestaurantMeal::showRestaurantMeal()
{
    cout<<entree<<" $"<<price<<endl;
}

class HotelService
{
protected:
    string service;
    double serviceFee;
    int roomNumber;
public:
    HotelService(string, double, int);
    void showHotelService();
};

HotelService::HotelService(string serv, double fee, int rm) 
{
    service = serv;
    serviceFee = fee;
    roomNumber = rm;
}

void HotelService::showHotelService()
{
    cout<<service<<" service fee $"<<serviceFee<<
    " to room #"<<roomNumber<<endl;
}

class RoomServiceMeal : public RestaurantMeal, public HotelService
{
public:
    RoomServiceMeal(string , double , int );
    void showRoomServiceMeal();
};

RoomServiceMeal::RoomServiceMeal(string entree, double price, int roomNum) : 
RestaurantMeal(entree, price), HotelService("room service", 4.00, roomNum)
{
}

void showRoomServiceMeal()
{
    double total = RestaurantMeal::price + HotelService::serviceFee;
    RestaurantMeal::showRestaurantMeal();
    HotelService::showHotelService();
    cout<<"Total is $"<<total<<endl;
}


int main()
{
    RoomServiceMeal rs("steak dinner",199.99, 1202);
    cout<<"Room service ordering now:"<<endl;
    rs.showRoomServiceMeal();
    return 0;
}

using g++ i get this error:

RoomService.cpp: In function ‘void showRoomServiceMeal()’:
RoomService.cpp:18: error: ‘int RestaurantMeal::price’ is protected
RoomService.cpp:73: error: within this context
RoomService.cpp:18: error: invalid use of non-static data member ‘RestaurantMeal::price’
RoomService.cpp:73: error: from this location
RoomService.cpp:39: error: ‘double HotelService::serviceFee’ is protected
RoomService.cpp:73: error: within this context
RoomService.cpp:39: error: invalid use of non-static data member ‘HotelService::serviceFee’
RoomService.cpp:73: error: from this location
RoomService.cpp:74: error: cannot call member function ‘void RestaurantMeal::showRestaurantMeal()’ without object
RoomService.cpp:75: error: cannot call member function ‘void HotelService::showHotelService()’ without object

Answer 1

You don’t define the function showRoomServiceMeal as a part of the RoomServiceMeal class:

void showRoomServiceMeal()
{
    ...
}

Change to

void RoomServiceMeal::showRoomServiceMeal()
{
    ...
}

Also, in the showRoomServiceMeal method you don’t have to use the class prefix when accessing the parent classes members. Instead of using e.g. RestaurantMeal::price you can just use price. This is because the variables and functions are unique in each class.