Libc++ 9.0.0 Release Notes

Written by the Libc++ Team


This document contains the release notes for the libc++ C++ Standard Library, part of the LLVM Compiler Infrastructure, release 9.0.0. 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.

What’s New in Libc++ 9.0.0?


  • Minor fixes to std::chrono operators.
  • libc++ now correctly handles Objective-C++ ARC qualifiers in std::is_pointer.
  • std::span general updates and fixes.
  • Updates to the std::abs implementation.
  • std::to_chars now adds leading zeros.
  • Ensure std::tuple is trivially constructible.
  • std::aligned_union now works in C++03.
  • Output of nullptr to std::basic_ostream is formatted properly.


  • Implemented P0608: sane variant converting constructor.
  • Added ssize function.
  • Added front and back methods in std::span.
  • std::is_unbounded_array and std::is_bounded_array added to type traits.
  • std::atomic now includes many new features and specialization including improved Freestanding support.
  • Added std::midpoint and std::lerp math functions.
  • Added the function std::is_constant_evaluated.
  • Erase-like algorithms now return size type.
  • Added contains method to container types.
  • std::swap is now a constant expression.


  • libc++ dropped support for GCC 4.9; we now support GCC 5.1 and above.
  • libc++ added explicit support for WebAssembly System Interface (WASI).
  • Progress towards full support of rvalues and variadics in C++03 mode. std::move and std::forward now both work in C++03 mode.