C++ Observer Pattern Example (Easy and simple to understand)

main.cpp

#include <iostream>
#include <string>
#include "Subject.h"
#include "Observer.h"

void onChange(string name);

void main() 
{
    Observer ob(onChange);
    Subject sub(ob);
    sub.setName("Gray");
    sub.setName("Kevin");
}

void onChange(string name)
{
    cout << "My name is changed to " << name << "." << endl;
}

Observer.cpp

#include "Observer.h"

Observer::Observer() : function(nullptr)
{
}

Observer::~Observer()
{
    function = nullptr;
}

Observer::Observer(void(*function)(string))
{
    this->function = function;
}

void Observer::invoke(string str)
{
    function(str);
}

Observer.h

#pragma once
#include <string>

using namespace std;

class Observer
{
public:
    Observer();
    ~Observer();
public:
    Observer(void(*function)(string));
    void invoke(string str);
private:
    void(*function)(string);
};

Subject.cpp

#include "Subject.h"

Subject::Subject(Observer observer)
{
    this->observer = observer;
}


void Subject::setName(string name)
{
    this->name = name;
    observer.invoke(this->name);
}

Subject.h

#pragma once
#include "Observer.h"

class Subject
{
public:
    Subject(Observer observer);
    void setName(string name);
private:
    Observer observer;
    string name;
};