Class inheritance issues c++

Question

So I'm creating this for an assignment in Uni.

It has to use a class structure with 'Vehicle' as the main class, and two classes which inherit some functions from it; 'Car' and 'Lorry'.

So I've created my class structure successfully (I think) but I need to create a basic UI for this, bearing it mind it is a console application, I am just creating a basic menu using switches.

How ever, in my "getDetails" section, it is only grabbing the 'Vehicle::getDetails' when it should be also getting the 'Car/lorry::getdetails', as well as the vehicle details.

Any ideas what could be causing that?

First post here, so sorry if my post is bad :(.

Thanks!

#include <iostream> 
#include <string>
#include <fstream>

using namespace std;


class vehicle {    

public:     

string manufacturer;
int year;
string regnum;

void getDetails() { 

    cout << "Please enter the details for your vehicle"<< endl;
    cout << "Please enter the manufacturer of your vehicle: "<< endl;
    cin >> manufacturer;
    cout << "Please enter the year of your vehicle's manufacture: "<< endl;
    cin >> year;
    cout << "Please enter your vehicle's registration number:  "<< endl;
    cin >> regnum;

}


void printDetails() {

    cout << "Your vehicle's details are as follows: " << endl;
    cout << "Your Vehicle's manufacturer is " << manufacturer << endl;
    cout << "Your Vehicle's year of manufacture is " << year << endl;
    cout << "Your Vehicle's registration number is " << regnum << endl;
}

void saveDetails() { 

    ofstream vehiclefile;
    vehiclefile.open ("vehicle.txt");
    vehiclefile << "***Your Vehicle's Details***" << endl;
    vehiclefile << "Manufacturer:" << manufacturer << endl;
    vehiclefile << "Year of Manufacture:" << year << endl;
    vehiclefile << "Registration Number: " << regnum << endl;
    vehiclefile.close();
}

void openVehicleDetails() { 

}
};


class car : public vehicle{

public:

int numpassengers;
string cartype;

void getDetails() { 

    vehicle::getDetails();

    cout << "Please enter the number of maximum passengers your car can hold: "<< endl;
    cin >> numpassengers;
    cout << "Please enter the car body type: "<< endl;
    cin >> cartype;
    cout << "Thank your for your details"<< endl;
}

void printDetails() {

    vehicle::printDetails();

    cout << "Your car's maximum passengers is: " << numpassengers << endl;
    cout << "The body type of your car is: " << cartype << endl;
}

void saveDetails() { 

    vehicle::saveDetails();

    ofstream vehiclefile;
    vehiclefile.open ("vehicle.txt");
    vehiclefile << "Car or Lorry: Car" << endl;
    vehiclefile << "Number of passengers: " << numpassengers << endl;
    vehiclefile << "Type of car: " << cartype << endl;
    vehiclefile.close();
}
};


class lorry : public vehicle{

public:

double tonnage;
string bodtype;

void getDetails() {

    vehicle::getDetails();

    cout << "Please enter the gross weight of your Lorry: "<< endl;
    cin >> tonnage;
    cout << "Please enter the body type of your Lorry: "<< endl;
    cin >> bodtype;
    cout << "Thank your for your details"<< endl;
}

void printDetails() {

    vehicle::printDetails();

    cout << "Your lorry's details are as follows: " << endl;
    cout << "Your lorry's maximum weight is: " << tonnage << endl;
    cout << "The body type of your lorry is: " << bodtype << endl;
}

void saveDetails() { 

    vehicle::saveDetails();

    ofstream vehiclefile;
    vehiclefile.open ("vehicle.txt");
    vehiclefile << "Car or Lorry: Lorry" << endl;
    vehiclefile << "Maximum weight: " << tonnage << endl;
    vehiclefile << "Body type: " << bodtype << endl;
    vehiclefile.close();
}

};


int main () {

int flag = 0;
char choice;
int ifchoice;

vehicle*v;


while (flag == 0){

    cout << "***Main Menu***" << endl;      //Menu to allow ease of access within the program.
    cout << "Select by letter:" << endl;     
    cout << "1 - Add new entry" << endl;
    cout << "2 - Show entry" << endl;
    cout << "3 - Save entry" << endl;
    cout << "4 - Open saved document" << endl;
    cout << "5 - Delete entry" << endl;
    cin >> choice;          

    switch(choice) {       

    case '1':

        cout << "Is your vehicle a Car or a Lorry? " << endl;
        cout << "Press '1' for Car " << endl;
        cout << "Press '2' for Lorry " << endl;
        cin >> ifchoice;

            if (ifchoice == 1)
            {
                v = new car();
            }
            if (ifchoice == 2)
            {
                v = new lorry();
            }

            v->getDetails();

        break;

    case '2':

        v -> printDetails();

        break;

    case '3': 

        v -> saveDetails();

        break;




   }    

}
}

You need to declare the `getDetails` function as virtual if you want to use polymorphism. — perencia, Apr 15 '14 at 21:10

score 2 · Accepted Answer · edited May 23 '17 at 12:05

2

The key point of the exercise is to make the void getDetails() method virtual in the base vehicle class.

(I'd also define a virtual destructor in the vehicle class as well, as good coding practice.)

class vehicle {    
public:         
    string manufacturer;
    int year;
    string regnum;

    // Make this virtual
    virtual void getDetails() { 
         ...

In the derived classes you may want to use the new C++11 override specifier as well.

edited May 23 '17 at 12:05

Community

1
1

answered Apr 15 '14 at 21:13

Mr.C64

41,637
14
86
162

The virtual keyword signals to the compiler to create a hidden member pointer to a vtable. This is the foundation for how polymorphism works as the correct function call can be determined at run time. One kind of gotcha with using virtual is it deceptively increases the size of your objects (hidden vtable ptr)! – Paul Renton Apr 15 '14 at 21:29

score 0 · Answer 2 · answered Apr 15 '14 at 21:16

0

In c++, if you want a function to be overridable by a deriving class, you label it virtual, i.e.:

class vehicle {
    ...
    virtual void getDetails()
    {
        ...
    }
    ...
}

answered Apr 15 '14 at 21:16

joc

1,058
7
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Class inheritance issues c++

2 Answers2