Change value of Object Variable through a vector - c++

Question

I'm developing a simulation game in cpp using Visual Studio 2017 for School and in the development phase I got stuck in this situation.
So, what I did was create a new project to try and recreate that issue in the simplest form, so that it would be easier to debug.
Below is the main file and all the associated source codes:
main.cpp
#include "header.h"
#include "Vehicle.h"
#include "Car.h"
int main() {
Vehicle v;
v.addCar(1);
v.addCar(2);
v.addCar(3);
cout << v.getCars()[1].id << endl;
v.getCars()[1].id = 99;
cout << v.getCars()[1].id << endl;
system("pause");
return 0;
}
header.h
#ifndef CLUSTE2R_H
#define CLUSTE2R_H
#pragma once
#include <iostream>
#include <vector>
using namespace std;
#endif
Car.h
#ifndef CLUSTE1R_H
#define CLUSTE1R_H
#pragma once
#include "Vehicle.h"
using namespace std;
class Car : public Vehicle
{
public:
int id;
Car(int id);
~Car();
};
#endif
Car.cpp
#include "Car.h"
Car::Car(int id)
{
this->id = id;
}
Car::~Car()
{
}
Vehicle.h
#ifndef CLUSTER_H
#define CLUSTER_H
#pragma once
#include <vector>
//#include "Car.h"
class Car;
using namespace std;
class Vehicle
{
private:
vector<Car> cars;
public:
Vehicle();
~Vehicle();
vector<Car> getCars();
void addCar(int id);
};
#endif
Vehicle.cpp
#include "Vehicle.h"
#include "Car.h"
#include <vector>
using namespace std;
//class Car;
Vehicle::Vehicle()
{
}
Vehicle::~Vehicle()
{
}
vector<Car> Vehicle::getCars()
{
return this->cars;
}
void Vehicle::addCar(int id)
{
Car c(id);
cars.reserve(cars.size() + 1);
cars.push_back(c);
}
So, what I'm trying to do is to get the following output:
2 \n 99
This is what I'm getting:
2 \n 2
What am I doing wrong? I believe the issue is associated with the main.cpp file. But I'm not quite sure how to achieve what I want in any other way...

Answer 1

Currently, you are returning a new instance of a vector when you call getCars() function from your Vehicle, this means that all changes to the vector will not be applied to the original vector in the class.
To fix this you could just return a reference of the vector(changing the vector<Car> getCars(); to std::vector<Car>& getCars()).
You could also make a local copy of the vector and then setting the vector to the class.