Mixing C++ and Rust for Fun and Profit: Part 3 How to not reinvent the wheel

25.04.2024 Loren Burkholder No comments

In the two previous posts (Part 1 and Part 2), we looked at how to build bindings between C++ and Rust from scratch. However, while building a binding generator from scratch is fun, it’s not necessarily an efficient way to integrate Rust into your C++ project. Let’s look at some existing technologies for mixing C++ and Rust that you can easily deploy today.

bindgen

bindgen is an official tool of the Rust project that can create bindings around C headers. It can also wrap C++ headers, but there are limitations to its C++ support. For example, while you can wrap classes, they won’t have their constructors or destructors automatically called. You can read more about these limitations on the bindgen C++ support page. Another quirk of bindgen is that it only allows you to call C++ from Rust. If you want to go the other way around, you have to add cbindgen to generate C headers for your Rust code.

CXX

CXX is a more powerful framework for integrating C++ and Rust. It’s used in some well-known projects, such as Chromium. It does an excellent job at integrating C++ and Rust, but it is not an actual binding generator. Instead, all of your bindings have to be manually created. You can read the tutorial to learn more about how CXX works.

autocxx

Since CXX doesn’t generate bindings itself, if you want to use it in your project, you’ll need to find a generator that wraps C++ headers with CXX bindings. autocxx is a Google project that does just that, using bindgen to generate Rust bindings around C++ headers. However, it gets better—autocxx can also create C++ bindings for Rust functions.

CXX-Qt

While CXX is one of the best C++/Rust binding generators available, it fails to address Qt users. Since Qt depends so heavily on the moc to enable features like signals and slots, it’s almost impossible to use it with a general-purpose binding generator. That’s where CXX-Qt comes in. KDAB has created the CXX-Qt crate to allow you to integrate Rust into your C++/Qt application. It works by leveraging CXX to generate most of the bindings but then adds a Qt support layer. This allows you to easily use Rust on the backend of your Qt app, whether you’re using Qt Widgets or QML. CXX-Qt is available on Github and crates.io.

If you’re interested in integrating CXX-Qt into your C++ application, let us know. To learn more about CXX-Qt, you can check out this blog.

Other options

There are some other binding generators out there that aren’t necessarily going to work well for migrating your codebase, but you may want to read about them and keep an eye on them:

• Diplomat
• Crubit
• rust-cpp

In addition, there are continuing efforts to improve C++/Rust interoperability. For example, Google recently announced that they are giving $1 million dollars to the Rust foundation to improve interoperability.

Conclusion

In the world of programming tools and frameworks, there is never a single solution that will work for everybody. However, CXX, CXX-Qt, and autocxx seem to be the best options for anyone who wants to port their C++ codebase to Rust. Even if you aren’t looking to completely remove C++ from your codebase, these binding generators may be a good option for you to promote memory safety in critical areas of your application.

Have you successfully integrated Rust in your C++ codebase with one of these tools? Have you used a different tool or perhaps a different programming language entirely? Leave a comment and let us know. Memory-safe programming languages like Rust are here to stay, and it’s always good to see programmers change with the times.