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Libc++ 14.0.0 (In-Progress) Release Notes
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Written by the `Libc++ Team <>`_
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These are in-progress notes for the upcoming libc++ 14 release.
Release notes for previous releases can be found on
`the Download Page <>`_.
This document contains the release notes for the libc++ C++ Standard Library,
part of the LLVM Compiler Infrastructure, release 14.0.0. Here we describe the
status of libc++ in some detail, including major improvements from the previous
release and new feature work. For the general LLVM release notes, see `the LLVM
documentation <>`_. All LLVM releases may
be downloaded from the `LLVM releases web site <>`_.
For more information about libc++, please see the `Libc++ Web Site
<>`_ or the `LLVM Web Site <>`_.
Note that if you are reading this file from a Git checkout or the
main Libc++ web page, this document applies to the *next* release, not
the current one. To see the release notes for a specific release, please
see the `releases page <>`_.
What's New in Libc++ 14.0.0?
New Features
- There's initial support for the C++20 header ``<format>``. The implementation
is incomplete. Some functions are known to be inefficient; both in memory
usage and performance. The implementation is considered experimental and isn't
considered ABI stable.
- There's a new CMake option ``LIBCXX_ENABLE_UNICODE`` to disable Unicode
support in the ``<format>`` header. This only affects the estimation of the
output width of the format functions.
API Changes
- ...
Build System Changes
- Building the libc++ shared or static library requires a C++ 20 capable compiler.
Use ``-DLLVM_ENABLE_PROJECTS='clang;compiler-rt' -DLLVM_ENABLE_RUNTIMES='libcxx;libcxxabi'``
to build libc++ using a fresh build of Clang.
- The functions ``std::atomic<T*>::fetch_(add|sub)`` and
``std::atomic_fetch_(add|sub)`` no longer accept a function pointer. While
this is technically an API break, the invalid syntax isn't supported by
libstc++ and MSVC STL. See
- The call of the functions ``std::atomic_(add|sub)(std::atomic<T*>*, ...)``
with the explicit template argument ``T`` are now ill-formed. While this is
technically an API break, the invalid syntax isn't supported by libstc++ and
Due to this change it's now possible to call these functions with the
explicit template argument ``T*``. This allows using the same syntax on the
major Standard library implementations.
Calls to these functions where the template argument was deduced by the
compiler are unaffected by this change.