Arduino Style Guide for Creating Libraries

This is a style guide to writing library APIs in an Arduino style. Some of these run counter to professional programming practice. We’re aware of that, but it’s what’s made it possible for so many beginners to get started with Arduino easily. So please code with these principles in mind. If you have suggestions on how to make Arduino libraries clearer for that core audience, please jump in the discussion.

Be kind to the end user. Assume you are writing an API for an intelligent person who has not programmed before. Come up with a clear mental model of the concept you’re working with, and the terms and functions you will use.

Match your API to the underlying capabilities. You don’t want to expose implementation details to the user but you also don’t want an API that suggests an inaccurate mental model of the possibilities. For example, if there are only a few possible options for a particular setting, don’t use a function that takes an int, as it implies you can use any value you want.

Organize your public functions around the data and functionality that the user wants. Quite often, the command set for a particular electronic module is overly complicated for the most common uses, or can be re-organized around higher level functionality. Think about what the average person thinks the thing does, and try to organise your API functions around that. Adafruit's BMP085 library is a good example. The

readPressure()

Use full, everyday words. Don’t be terse with your function names or variables. Use everyday terms instead of technical ones. Pick terms that correspond to popular perception of the concept at hand. Don’t assume specialized knowledge. For example, this is why we used

analogWrite()

pwm()

Avoid words that have different meanings to the general public. For example, to programmers, an error is a notification that something happened. To the general public, errors are bad things.

When you have to use a domain-specific term, write a sentence or two describing it to the general public FIRST. You’ll likely come across a better term, and if not, you’ll have started the documentation on your library.

Document and comment as you go. When writing examples and documentation, follow the Writing Style Guide

Use the established core libraries and styles.

• Use

  read()

  to read inputs, and

  write()

  to write to outputs, e.g.

  digitalRead()

  ,

  analogWrite()

  , etc.
• Use the

  Stream

  and

  Print

  classes when dealing with byte streams. If it’s not appropriate, at least try to use its API as a model. For more on this, see below
• For network applications, use the

  Client

  and

  Server

  classes as the basis.
• Use

  begin()

  to initialize a library instance, usually with some settings. Use

  end()

  to stop it.
• Use camel case function names, not underscore. For example, analogRead, not analog_read. Or myNewFunction, not my_new_function. We've adopted this from Processing.org for readability's sake.

LONG_CONSTANT_NAMES_FULL_OF_CAPS are hard to read. Try to simplify when possible, without being terse.

Try to avoid boolean arguments. Instead, consider providing two different functions with names the describe the differences between them.

Don’t assume knowledge of pointers. Beginning users of C find this the biggest roadblock, and get very confused by

&

*

*

Copy
1void printArray(char* array);

can be replaced by

Copy
1void printArray(char[] array);

Though there are some libraries where we pass pointers by using structures like const chars, avoid anything that requires the user to pass them. For example,rather than:

Copy
1foo.readAccel(&x, &y, &z);

use something like this:

Copy
1xAxis = adxl.readX();
2  yAxis = adxl.readY();
3  zAxis = adxl.readZ();

When using serial communication, allow the user to specify any

Stream

Serial

begin()

When writing a library that provides byte-stream communication, inherit Arduino's

Stream

Stream

read()

write()

write()

yield()

Here are a few libraries that are exemplary from Adafruit. She breaks the functions of the devices down into their high-level activities really well.

• https://github.com/adafruit/Adafruit-BMP085-Library
• https://github.com/adafruit/DHT-sensor-library

This does a nice job of abstracting from the Wire (I2C) library: https://github.com/adafruit/RTClib

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.