1========================================= 2Libc++ 12.0.0 (In-Progress) Release Notes 3========================================= 4 5.. contents:: 6 :local: 7 :depth: 2 8 9Written by the `Libc++ Team <https://libcxx.llvm.org>`_ 10 11.. warning:: 12 13 These are in-progress notes for the upcoming libc++ 12 release. 14 Release notes for previous releases can be found on 15 `the Download Page <https://releases.llvm.org/download.html>`_. 16 17Introduction 18============ 19 20This document contains the release notes for the libc++ C++ Standard Library, 21part of the LLVM Compiler Infrastructure, release 12.0.0. Here we describe the 22status of libc++ in some detail, including major improvements from the previous 23release and new feature work. For the general LLVM release notes, see `the LLVM 24documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may 25be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_. 26 27For more information about libc++, please see the `Libc++ Web Site 28<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_. 29 30Note that if you are reading this file from a Git checkout or the 31main Libc++ web page, this document applies to the *next* release, not 32the current one. To see the release notes for a specific release, please 33see the `releases page <https://llvm.org/releases/>`_. 34 35What's New in Libc++ 12.0.0? 36============================ 37 38New Features 39------------ 40 41- ... 42 43API Changes 44----------- 45- By default, libc++ will _not_ include the definition for new and delete, 46 since those are provided in libc++abi. Vendors wishing to provide new and 47 delete in libc++ can build the library with ``-DLIBCXX_ENABLE_NEW_DELETE_DEFINITIONS=ON`` 48 to get back the old behavior. This was done to avoid providing new and delete 49 in both libc++ and libc++abi, which is technically an ODR violation. Also 50 note that we couldn't decide to put the operators in libc++ only, because 51 they are needed from libc++abi (which would create a circular dependency). 52- During the C++20 standardization process some new low-level bit functions 53 have been renamed. Libc++ has renamed these functions to match the C++20 54 Standard. 55 - ``ispow2`` has been renamed to ``has_single_bit`` 56 - ``ceil2`` has been renamed to ``bit_ceil`` 57 - ``floor2`` has been renamed to ``bit_floor`` 58 - ``log2p1`` has been renamed to ``bit_width`` 59 60- In C++20 mode, ``std::filesystem::path::u8string()`` and 61 ``generic_u8string()`` now return ``std::u8string`` according to P0428, 62 while they return ``std::string`` in C++17. This can cause source 63 incompatibility, which is discussed and acknowledged in P1423, but that 64 paper doesn't suggest any remediation for this incompatibility. 65