C++ inheritance class virtual functions

Question

I have a base class and a derived class, I am trying to implement a virtual load function to add an extra member engineSize to the SportCar class, it should load the basic car details included in the Car class i.e CarName, Colour etc but also include engineSize which is unique to the SportsCar class. But it does not seem to workout well. Below I have included my code. Currently, it just defaults to the details included in the default constructor i.e. "Unknown".

#include "stdafx.h"

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

using namespace std;

 class Car
{
 public:
   Car();
   virtual void Load(ifstream& carFile);
   int LoadString(string filename);

protected:
  string CarName;
  int Age;
  string Colour;
  double Price;
  int countUsers;
  Car *ptrToCarList;
};

class SportsCar : public Car
{
public: 
  SportsCar();
  virtual void LoadSports(ifstream& carFile);
  int LoadString(string filename);
  void display();
protected:
  int engineSize;
  SportsCar *ptrToSportsCarList;
  int countUsers;

};

Car::Car()
{
  CarName = "Unknown";
  countUsers = 2;
}

void Car::Load(ifstream& carFile)
{
  carFile >> CarName >> Age >> Colour >> Price;
}

int Car::LoadString(string filename)
{
  ifstream inFile(filename);

  if (!inFile)
  {
    cout << "Sorry, file not found" << endl;
    return -1;
  }

ptrToCarList = new Car[countUsers];

for (int i = 0; i < countUsers; i++)
{
    ptrToCarList[i].Load(inFile);
}
inFile.close();
return 0;
}

void SportsCar::display()
{
  cout << CarName << " " << Age << " " << Colour << " " << Price << " " <<engineSize <<endl;

}


void SportsCar::LoadSports(ifstream& carFile)
{
  Car::Load(carFile);
  carFile >> engineSize;
}

SportsCar::SportsCar() :Car()
{


}


int SportsCar::LoadString(string filename)
{
  ifstream inFile(filename);

if (!inFile)
{
    cout << "Sorry, file not found" << endl;
    return -1;
}

ptrToSportsCarList = new SportsCar[countUsers];

for (int i = 0; i < countUsers; i++)
{
    ptrToSportsCarList[i].LoadSports(inFile);
}
inFile.close();
return 0;
}

int main()
{
  SportsCar example2;
  example2.LoadString("sportsCarFile.txt");
  example2.display();
  return 0;
}

do you really need same variable countUsers in SportsCar? SportsCar::LoadString function use countUsers that is not initialized. You are initializing countUsers but from Car class — userbb, Apr 16 '15 at 17:19
Based on what you've done, what do you think `example2.LoadString("sportsCarFile.txt");` does? I mean, what does the code do, not what you want it to do. — ChiefTwoPencils, Apr 16 '15 at 17:21
Why does one car contain both the information for a car *and* a collection of cars? My car is completely unaware of other cars. — molbdnilo, Apr 16 '15 at 17:27
btw this question shows you have not learnt anything from your previous question. http://stackoverflow.com/questions/29593822/c-base-class-load-function — Philip Stuyck, Apr 16 '15 at 17:53
I am still not sure, I am new to programming. You can't be a expert overnight.@Philip Stuyck — BeginnerLK, Apr 17 '15 at 09:49

userbb · Answer 1 · 2015-04-16T17:54:33.770

If you want hold many cars in cars that mean that is somethings wrong with that design.

Consider making class Garage ;)
example2.LoadString("sportsCarFile.txt"); doesn't call LoadSports as you expect because countUsers is 0. Because in derived class you have declaration that is hiding initialization from contructor of Car.
You have ptrToSportsCarList and ptrToCarList. You probably want only ptrToCarList to hold cars because of polymorphism you can use on LoadSports function
Consider moving LoadSports to Base class and rename it to be more generic, and make it virtual so could be called from ptrToCarList, not from ptrToSportsCarList as mentioned in pt. 2.

Thanks for your response, how would I display one car only in the car class if I have a Garage class to deal with the loading and sorting of all the cars. @userbb — BeginnerLK, Apr 19 '15 at 15:07

C++ inheritance class virtual functions

1 Answers1