This issue collects all possible candidates and their pros and cons regarding their usability in ReactOS.

Everything is WIP!

Clang's libc++

• https://libcxx.llvm.org/
• https://github.com/llvm/llvm-project/tree/master/libcxx

License:

• According to the website: All of the code in libc++ is dual licensed under the MIT license and the UIUC License (a BSD-like license).
• According to the source files: Apache-2.0 WITH LLVM-exception (https://llvm.org/LICENSE.txt)

 Pros

• Compiles with GCC and Clang (on the supported platforms).
• Chromium for Windows switched to libc++ (Issue 801780: Switch to libc++ on Windows)

Cons

• No official commitment to Windows (only for Mac OS X, FreeBSD and Linux). But (some?) Windows support is implemented.
• According to the Website C++17 implementation is not yet complete.
• Uses #include_next, which MSVC not supports.
  • Workaround: Replace #include_next<stdio.h> with something like #include <../crt/stdio.h>

MSVC's C++ Standard Library

• https://devblogs.microsoft.com/cppblog/open-sourcing-msvcs-stl/
• https://github.com/microsoft/STL

License: Apache-2.0 WITH LLVM-exception

Pros

• Full Windows and MSVC support
• Clang 10+ support
• Supported standards 11, 14, 17 and 20 is WIP

Cons

• Depends on VCRuntime and Universal CRT (see Block Diagram), which ReactOS is currently lacking
• Requires MSVC 19.26 (Visual Studio 2019 16.6 Preview 2) or newer (Require MSVC 19.26 and Clang 10 in the STL)