Observer Pattern Example in C++
Problem statement: Suppose you are developing a weather monitoring application, in which multiple weather stations are responsible for collecting weather data, and you want to create a system where multiple displays can show real-time weather updates. When a weather station collects new data, all registered displays should be updated automatically with the latest information.
Below is the implementation of the above example problem in C++:
#include <iostream>
#include <vector>
// Observer interface
class Observer {
public:
virtual void update(float temperature, float humidity, float pressure) = 0;
};
// Subject (WeatherStation) class
class WeatherStation {
private:
float temperature;
float humidity;
float pressure;
std::vector<Observer*> observers;
public:
void registerObserver(Observer* observer) {
observers.push_back(observer);
}
void removeObserver(Observer* observer) {
// You can implement the removal logic if needed.
}
void notifyObservers() {
for (Observer* observer : observers) {
observer->update(temperature, humidity, pressure);
}
}
void setMeasurements(float temp, float hum, float press) {
temperature = temp;
humidity = hum;
pressure = press;
notifyObservers();
}
};
// Concrete Observer
class Display : public Observer {
public:
void update(float temperature, float humidity, float pressure) {
std::cout << "Display: Temperature = " << temperature
<< "°C, Humidity = " << humidity
<< "%, Pressure = " << pressure << " hPa"
<< std::endl;
}
};
int main() {
WeatherStation weatherStation;
// Create displays
Display display1;
Display display2;
// Register displays as observers
weatherStation.registerObserver(&display1);
weatherStation.registerObserver(&display2);
// Simulate weather data updates
weatherStation.setMeasurements(25.5, 60, 1013.2);
weatherStation.setMeasurements(24.8, 58, 1014.5);
return 0;
}
Output:
Display: Temperature = 25.5°C, Humidity = 60%, Pressure = 1013.2 hPa
Display: Temperature = 25.5°C, Humidity = 60%, Pressure = 1013.2 hPa
Display: Temperature = 24.8°C, Humidity = 58%, Pressure = 1014.5 hPa
Display: Temperature = 24.8°C, Humidity = 58%, Pressure = 1014.5 hPa
Code Explaination:
- We defined an Observer interface with an update method that concrete observers must implement to display weather data.
- The WeatherStation class serves as the subject. It maintains the weather data (temperature, humidity, and pressure) and a list of registered observers.
- It provides methods to register, remove, and notify observers, as well as setting measurements and triggering updates.
- The Display class is a concrete observer that implements the update method to display weather data.
- In the main function:
- we create a WeatherStation instance and two Display instances, which act as observers.
- We register the displays with the weather station, and then simulate weather data updates.
Observer Pattern | C++ Design Patterns
The Observer Pattern is a behavioral design pattern that defines a one-to-many dependency between objects, meaning that when one object (the subject) changes its state, all its dependents (observers) are notified and updated automatically. This pattern is used to build distributed event-handling systems and is a crucial part of many software architectures, including Model-View-Controller (MVC).
Important Topics for the Observer Pattern in C++ Design Patterns
- Key Concepts of the Observer Pattern
- Observer Pattern Example in C++:
- Advantages of the Observer Pattern in C++ Design Patterns
- Disadvantages of the Observer Pattern in C++ Design Patterns