What is this error LNK2019 and 1120

Question

#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

//In this section I create the class HotelRoom

class HotelRoom
{
protected:
    HotelRoom(){}
    char room_Number[4];
    char* guestName;
    double rate;

public:

    HotelRoom(char Num[], double daily, char* name);
    HotelRoom(const HotelRoom &);
    ~HotelRoom();
    int Get_Capacity();
    int Get_Status();
    double Get_Rate();
    const char* Get_Number();
    const char* Get_Guest();
    int Change_Status(int Stat);
};

HotelRoom::HotelRoom(char Num[], double daily, char* name)
{
    strcpy_s(room_Number, 4, Num);
    guestName = new char[strlen(name) + 1];
    strcpy_s(guestName, 20, name);
    rate = daily;
}
HotelRoom::HotelRoom(const HotelRoom& room_r)
{
    strcpy_s(room_Number, room_r.room_Number);
    guestName = new char[strlen(room_r.guestName) + 1];
    strcpy_s(guestName, 20, room_r.guestName);
    rate = room_r.rate; 
}
HotelRoom::~HotelRoom()
{
    cout << endl << endl;
    cout << "Decunstructor Activated." << endl;
    delete[] guestName;
}

double HotelRoom::Get_Rate()
{
    return rate;
}
const char* HotelRoom::Get_Number()
{
    return room_Number;
}
const char* HotelRoom::Get_Guest()
{
    return guestName;
}
class DerivedGuestRoom : public HotelRoom
{
public:
    DerivedGuestRoom(int max, int stat, int nights);
    DerivedGuestRoom(const DerivedGuestRoom&);
    ~DerivedGuestRoom();

protected:
    int capacity;
    int status = 0; //0 if unoccupied
    int days;

};

DerivedGuestRoom::DerivedGuestRoom(int max, int stat, int nights) :  capacity(max), status(stat), days(nights)
{
    cout << "data members set";
}

DerivedGuestRoom::~DerivedGuestRoom()
{
    cout << "\ndecunstrucor";
}
class DerivedMeetingRoom : public HotelRoom
{
public:
    DerivedMeetingRoom(int seat, int stat);
    DerivedMeetingRoom(const DerivedMeetingRoom&);
    ~DerivedMeetingRoom();

protected:
    int seats;
    int status; //1 if booked for meeting 0 otherwise
};
DerivedMeetingRoom::DerivedMeetingRoom(int seat, int stat) : seats(seat), status(stat)
{
    cout << "data members set";
}

DerivedMeetingRoom::~DerivedMeetingRoom()
{
    cout << "\ndecunstrucor";
}
void Display_info(HotelRoom&);
HotelRoom* Create_Hotel();
int main()
{
    cout << setprecision(2)
        << setiosflags(ios::fixed)
        << setiosflags(ios::showpoint);

    HotelRoom* Hotel_Rooms[200];

    int count = 0;
    char response;

    cout << endl;
    cout << "Do you want to enter information about a hotel room?(Y/N): ";
    response = cin.get();
    cin.get();

    while (toupper(response) == 'Y' && count < 10)
    {
        Hotel_Rooms[count] = Create_Hotel();
        ++count;
        cout << endl;
        cout << "Do you want to enter information about a hotel room?(Y/N): ";
        response = cin.get();
        cin.get();
    }
    //Display the accounts created
    for (int i = 0; i < count; ++i)
        Display_info(*Hotel_Rooms[i]);

    for (int i = 0; i < count; ++i)
        delete Hotel_Rooms[i];

    cout << endl;
    system("PAUSE");
    return 0;
}
void Display_info(HotelRoom& room)
{
    cout << "\n\nGuest's Name: " << room.Get_Guest() << endl << endl;

    cout << "\nYour room number is " << room.Get_Number() << endl << endl;

    cout << "\nDaily rate is: " << room.Get_Rate() << endl << endl;
    cout << endl;
    cout << endl;
}
HotelRoom* Create_Hotel()
{
    //These are the variables that will be holding data then passed through objects

    char roomNumber[4];
    char guestName[20];

    double dailyRate = 89.00;

    HotelRoom* room_ptr;

    //This portion asks for user input

    cout << "\nEnter Guest information\n\n";

    cout << "Enter the room number: ";
    cin.getline(roomNumber, 4);

    cout << "Enter the guest's name: ";
    cin.getline(guestName, 20);
    cout << endl;

    cin.get(); //Clears input buffer

    room_ptr = new HotelRoom(roomNumber, dailyRate, guestName);

    return room_ptr;
}

I took out HotelRoom(); from parent class constructor and I removed from the child class constructors. I Now only have this error:

LearningOOP.exe has triggered a breakpoint.

Which I have never encountered this so not sure what it means.

Answer 1

You haven't defined your default constructor for the HotelRoom class.

class HotelRoom
{
protected:
    char room_Number[4];
    char* guestName;
    double rate;

public:
    HotelRoom(); //< Not defined!
    HotelRoom(char Num[], double daily, char* name);
    HotelRoom(const HotelRoom &);
    ~HotelRoom();
    int Get_Capacity();
    int Get_Status();
    double Get_Rate();
    const char* Get_Number();
    const char* Get_Guest();
    int Change_Status(int Stat);
};

An "Unresolved external symbol" linker error means that you've declared and used a piece of code in your application, but you haven't defined it before using it.

EDIT (Based on your follow up comment below):

You can't take the constructor out because it's needed in other parts of your code. See this line in your code:

DerivedGuestRoom::DerivedGuestRoom(int max, int stat, int nights) : HotelRoom(), capacity(max), status(stat), days(nights)
//                                                                  ^---------^
//                                                                       |
//                                                            Using the default constructor.

DerivedMeetingRoom::DerivedMeetingRoom(int seat, int stat) : HotelRoom(), seats(seat), status(stat)
//                                                           ^---------^
//                                                                |
//                                                         And again here!

You either need to remove implement the default constructor for the HotelRoom class, or add parameters to your DerivedMeetingRoom and DerivedGuestRoom class constructors so that you can use the HotelRoom(char Num[], double daily, char* name) constructor.

Answer 2

You declared a default constructor:

class HotelRoom
{
public:
  HotelRoom();
}

and there is no implementation for that default constructor method. You can change to:

class HotelRoom
{
public:
  HotelRoom() {}
}

or implement HotelRoom:HotelRoom { } in your cpp file.