Appendix C. Libraries
In chapter 4 we covered software libraries and how they’re used to extend the basic functionality of the Arduino. Other chapters have provided examples of how using libraries in your own projects can easily extend their functionality.
When you’ve gained some experience in writing your own sketches there will come a time when you develop a sketch that you could reuse in future projects or that may be useful to the Arduino community. You can either keep the developed code in a sketch or split it out into a library. Splitting the sketch out into a library will probably make it more useful to other users.
This appendix will guide you through the anatomy of a library so that you can see what’s involved in writing your own. ...