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Au: A C++14-compatible units library, by Aurora

Au (pronounced "ay yoo") is a C++ units library, by Aurora. What the <chrono> library did for time variables, Au does for all physical quantities (lengths, speeds, voltages, and so on). Namely:

• Catch unit errors at compile time, with no runtime penalty.
• Make unit conversions effortless to get right.
• Accelerate and improve your general developer experience.

In short: if your C++ programs handle physical quantities, Au will make you faster and more effective at your job. You'll find everything you need in our full documentation website.

Try it out on Compiler Explorer ("godbolt")!

Why Au?

There are many other C++ units libraries, several quite well established. Each of them offers some of the following properties, but only Au offers all of them:

• Wide compatibility with C++ versions (anything C++14 or newer).
• Easy installation in any project (including a customizable single-header option).
• Small compile time burden.
• Concise, readable typenames in compiler errors.

We also provide several totally new features, including fully unit-safe APIs, an adaptive "safety surface" that protects conversions against overflow, unit-aware rounding and inverse functions, and many more.

Forged in the crucible of Aurora's diverse, demanding use cases, Au has a proven track record of usability and reliability. This includes embedded support: Aurora's embedded teams have been first class customers since the library's inception.

To learn more about our place in the C++ units library ecosystem, see our detailed library comparison.

Getting started

Our installation instructions can have you up and running in minutes, in any project that supports C++14 or newer.

To use the library effectively, we recommend working through the tutorials, starting with Au 101: Quantity Makers. To get set up with the tutorials — or, to contribute to the library — check out our development guide.

As seen at CppCon 2021

At CppCon 2021, we presented the properties we found to be most important in units libraries, and advice on using them effectively. Because Au was designed from the ground up with these best practices in mind, it thoroughly exemplifies them. Check out the video below, and follow along with the slide deck if you like.

NOTE: This open-source version has been significantly improved from what was presented in the talk: both in its user interfaces, and under the hood! The one downside is that matrix and vector support hasn't yet been implemented. See #70 for more details, and subscribe to that issue to watch for progress.

...and, at CppCon 2023

After CppCon 2021, we found that telling people what to look for in a units library wasn't good enough, if they couldn't find one that met those criteria. We saw so many people struggling with problems that we had already solved robustly! So, we set about sharing our work. With a clean slate, we made a new library that was a drop-in replacement for Aurora's internal library, but with zero Aurora-internal dependencies, so that we could easily open source it. The result was Au, and we shared it at CppCon 2023. Check out the video below, and follow along with the slide deck if you like.