Libc++ 12.0.0 (In-Progress) Release Notes

Written by the Libc++ Team


These are in-progress notes for the upcoming libc++ 12 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 12.0.0. 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++ 12.0.0?

API Changes

  • By default, libc++ will _not_ include the definition for new and delete, since those are provided in libc++abi. Vendors wishing to provide new and delete in libc++ can build the library with -DLIBCXX_ENABLE_NEW_DELETE_DEFINITIONS=ON to get back the old behavior. This was done to avoid providing new and delete in both libc++ and libc++abi, which is technically an ODR violation. Also note that we couldn’t decide to put the operators in libc++ only, because they are needed from libc++abi (which would create a circular dependency).
  • During the C++20 standardization process some new low-level bit functions have been renamed. Libc++ has renamed these functions to match the C++20 Standard. - ispow2 has been renamed to has_single_bit - ceil2 has been renamed to bit_ceil - floor2 has been renamed to bit_floor - log2p1 has been renamed to bit_width