This is a simple sketch of a Observer design pattern with smart pointer. The idea is to have a simple implementation handy to apply in any application.
As reference, the following resource was used.
https://refactoring.guru/design-patterns/observer/cpp/example#lang-features
Feel free to use it in your project.
To build the project in a Linux distribution, follow the bellow steps.
$ mkdir build && cd build
$ cmake ..
$ make