Observer Design Pattern Example code in C++

Here is the Observer Design Pattern Example code in C++.

#include <vector>
#include <iostream>

class Observer
{
  public:
    virtual void update(int value) = 0;
};

class Subject
{
    int m_value;
    vector m_views;
  public:
    void attach(Observer *obs)
    {
        m_views.push_back(obs);
    }
    void set_val(int value)
    {
        m_value = value;
        notify();
    }
    void notify()
    {
        for (int i = 0; i < m_views.size(); ++i)
          m_views[i]->update(m_value);
    }
};

class DivObserver: public Observer
{
    int m_div;
  public:
    DivObserver(Subject *model, int div)
    {
        model->attach(this);
        m_div = div;
    }
     /* virtual */void update(int v)
    {
        cout << v << " div " << m_div << " is " << v / m_div << '\n';
    }
};

class ModObserver: public Observer
{
    int m_mod;
  public:
    ModObserver(Subject *model, int mod)
    {
        model->attach(this);
        m_mod = mod;
    }
     /* virtual */void update(int v)
    {
        cout << v << " mod " << m_mod << " is " << v % m_mod << '\n';
    }
};

int main()
{
  Subject subj;
  DivObserver divObs1(&subj, 4);
  DivObserver divObs2(&subj, 3);
  ModObserver modObs3(&subj, 3);
  subj.set_val(14);
}