#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <array>
#include <iomanip>
#include <set>
#include <tuple>
#include <algorithm>
#include <vector>
#include <bitset>
#include <list>
#include <fstream>
#include <memory>
#include <sstream>
#include <chrono>
#include <ctime>
#include <iomanip>
#include <locale>
#include <cstring>
#include <cmath>
#include <complex>
#include <queue>
#include <cstdint>
#include <random>
#include <array>
#include <typeinfo>
#include <thread>
#include <mutex>
#include <cassert>
#include <functional>
#include <atomic>
#include <future>
#include <tuple>
#include <iterator>
#include <unordered_map>
#include <deque>

using namespace std;



class A
{
protected:
    int m_X;
public:
    A() { 
        std::cout << "in A ctor" << std::endl; 
        m_X = 0;
    }
    virtual void printX(){ std::cout << "in A " << m_X << std::endl; }
};

class B : public A
{
public:
    B() {
        std::cout << "in B ctor" << std::endl; 
        m_X = 1;
    }
    virtual void printX(){ std::cout << "in B " << m_X << std::endl; }
};

class As
{
public:
    void AddA(  A &a ){ m_As.push_back( std::ref(a) ); }
    void PrintXs() const
    {
        for ( auto a : m_As )
        {
            a.get().printX();
        }
    }
private:
    std::vector<std::reference_wrapper<A>> m_As;
};

int main()
{
    As as;
    B b;
    as.AddA( b );
    as.PrintXs();
    system("pause");
    return 0;
}