Microsoft open-sources its C++ Standard Library (STL) used by MSVC tool-chain and Visual Studio

Last week, Microsoft open-sourced its implementation of the C++ Standard Library, also known as STL. The library is shipped along with MSVC (Microsoft Visual C++ compiler) toolset and the Visual Studio IDE. This announcement was made by MSVC team at the CppCon 2019 conference, two days ago. Users can use the C++ library repo for participating in the STL's development by reporting issues and commenting on pull requests.

The MSVC team is still working on migrating the C++ Standard Library to GitHub. Currently, the Github repository contains all of MSVC's product source code including a new CMake build system and a README. The team also plans to use the GitHub issues to track C++20 features, LWG issues, conformance bugs, performance improvements, and other todos. The roadmap and iteration plans of the C++ Standard Library is also under progress.

Why Microsoft open-sourced the C++ Standard Library?

Microsoft has open-sourced STL to allow it’s users easy access to all the latest developments in C++ by trying out latest changes and improving pull requests by reviewing them. The MSVC team hopes that as C++ standardization accelerates, it will be easier for users to accept the major features.

Microsoft chose to open-source STL particularly due to its unique design and fast-evolving nature when compared to other MSVC libraries and compiler. It is also “easy to contribute to, and somewhat loosely coupled, unlike the compiler.”

The official blog post adds, “We also want to contribute back to the C++ community by making it possible to take our implementations of major features.”

What are the primary goals of the C++ Standard Library?

Microsoft is implementing the latest C++ Working Draft, which will eventually become the next C++ International Standard. The goals of the Microsoft C++ Standard Library are to be conformant to spec, extremely fast, usable, and extensive compatibility.

Speed being the core strength of C++, STL needs to be extremely fast at runtime. Thus, the MSVC team spends more time on the optimization of the C++ Standard Library than the most general-purpose libraries. They are also working on parts of the programming experience like compiler throughput, diagnostic messages, and debugging checks. They are also keeping VS 2019 binary-compatible with VS 2017 and VS 2015. They consider source compatibility to be important, but not all-important; breaking source compatibility can be an acceptable cost if done for the right reasons in the right way.

The blog post states that MSVC’s STL is distributed under the Apache License v2.0 with LLVM Exceptions and is distinct from the libc++ library. However, if any libc++’s maintainers are interested in taking feature implementations from MSVC’s STL or in collaborating on the development of new features in both libraries simultaneously, the MSVC team will help irrespective of the licensing.

Users have welcomed Microsoft’s move to open-source it’s C++ Standard Library (STL).

A Redditor says, “Thank you! Absolutely amazing. It's been one of my guilty pleasures ever since I started with C++ to prod about in your internals to see how stuff works so this is like being taken to the magical chocolate factory for me.”

Another user comments, “thank you for giving back to the open source world. ❤🤘”

Interested readers can learn how to build with the Native Tools Command Prompt and a Visual Studio IDE on Github.