Sharing vectors between two class instances

Question

I am getting the values of the vector size as 1 and 0 I know there are 2 different instances but I want it to be common between both the instances

I am not sure what would be the right approach need some insights on what will suffice in my case.

#include <iostream>
#include <memory>
#include <vector>

class Fruit
{
  public:
   Fruit(std::vector<int>& number);
   Fruit();
  int numOfApple();
  private:
  std::vector<int> number;
};

Fruit::Fruit() {}

class Apple
{
  public:
  Apple();
  Apple(Fruit &fruit);
  int appleCount();

  private:
  Fruit fruit;

};

Apple::Apple() {}

Apple::Apple(Fruit &fruit):fruit(fruit) {}

int Fruit::numOfApple()
{
  std::cout<<"vector size is"<<number.size()<<std::endl;
  for (auto& fruz : number) {
   std::cout<<"do nothing"<<std::endl;
  }

  return 0;
}


int Apple::appleCount()
{
  fruit.numOfApple();
  return 0;
}

Fruit::Fruit(std::vector<int>& number):number(number) {}

int main()
{
  std::vector<int> fru;
  fru.push_back(1);

  Fruit fruit1(fru);

  Apple apple(fruit1);
  fruit1.numOfApple(); // the size of the vector here is 1

  // Now try to simulate server code

  Fruit fruit2;
  fruit2.numOfApple(); // the size of vector in this is 0

  return 0;
}

Output

./a.out
vector size is1
do nothing
vector size is0

Answer 1

You can use a std::shared_ptr for this purpose. It lives as long as any of the objects referencing it are alive and allows multiple objects to share ownership of its contents.

class Fruit
{
  Fruit::Fruit()
    : number(std::make_shared<std::vector<int>>())
  {}

  Fruit(std::vector<int>& numberNew)
    : number(std::make_shared<std::vector<int>>(numberNew))
  {}

  std::shared_ptr<std::vector<int>> number;
}

Now when your class is copied, the copy of the shared_ptr will not copy the vector but just refer to the same one and deal with all lifetime management for you.

int Fruit::numOfApple()
{
  std::cout << "vector size is" << number->size() << std::endl;
  for (auto& fruz : *number) {
   std::cout << "do nothing" << std::endl;
  }

  return 0;
}

I strongly advise against making anything static unless that is absolutely necessary. It is not necessary here, and you can prevent future growth pains by going for a proper solution right now.