What’s New in Libc++ 12.0.0?
New Features
Random device support has been made optional. It’s enabled by default and can be disabled by building libc++ with -DLIBCXX_ENABLE_RANDOM_DEVICE=OFF. Disabling random device support can be useful when building the library for platforms that don’t have a source of randomness, such as some embedded platforms. When this is not supported, most of <random> will still be available, but std::random_device will not.
Localization support has been made optional. It’s enabled by default and can be disabled by building libc++ with -DLIBCXX_ENABLE_LOCALIZATION=OFF. Disabling localization can be useful when porting to platforms that don’t support the C locale API (e.g. embedded). When localization is not supported, several parts of the library will be disabled: <iostream>, <regex>, <locale> will be completely unusable, and other parts may be only partly available.
If libc++ is compiled with a C++20 capable compiler it will be compiled in C++20 mode. Else libc++ will be compiled in C++17 mode.
Several unqualified lookups in libc++ have been changed to qualified lookups. This makes libc++ more ADL-proof.
The libc++ implementation status pages have been overhauled. Like other parts documentation they now use restructured text instead of html. Starting with libc++12 the status pages are part of libc++’s documentation.
More C++20 features have been implemented. libc++ C++20 Status has the full overview of libc++’s C++20 implementation status.
Work has started to implement new C++2b features. libc++ C++2b Status has the full overview of libc++’s C++2b implementation status.
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
In C++20 mode, std::filesystem::path::u8string() and generic_u8string() now return std::u8string according to P0428, while they return std::string in C++17. This can cause source incompatibility, which is discussed and acknowledged in P1423, but that paper doesn’t suggest any remediation for this incompatibility.
Libc++ 9.0.0
Fixes
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.
Features
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.
Updates
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.
LLVM 8.0.1 is now available! Download it now, or read the release notes.
This release contains bug-fixes for the LLVM 8.0.0 release. This
release is API and ABI compatible with 8.0.0.
What’s New in Libc++ 8.0.0?
API Changes
Building libc++ for Mac OSX 10.6 is not supported anymore.
Starting with LLVM 8.0.0, users that wish to link together translation units built with different versions of libc++’s headers into the same final linked image MUST define the _LIBCPP_HIDE_FROM_ABI_PER_TU macro to 1 when building those translation units. Not defining _LIBCPP_HIDE_FROM_ABI_PER_TU to 1 and linking translation units built with different versions of libc++’s headers together may lead to ODR violations and ABI issues. On the flipside, code size improvements should be expected for everyone not defining the macro.
Starting with LLVM 8.0.0, std::dynarray has been removed from the library. std::dynarray was a feature proposed for C++14 that was pulled from the Standard at the last minute and was never standardized. Since there are no plans to standardize this facility it is being removed.
Starting with LLVM 8.0.0, std::bad_array_length has been removed from the library. std::bad_array_length was a feature proposed for C++14 alongside std::dynarray, but it never actually made it into the C++ Standard. There are no plans to standardize this feature at this time. Formally speaking, this removal constitutes an ABI break because the symbols were shipped in the shared library. However, on macOS systems, the feature was not usable because it was hidden behind availability annotations. We do not expect any actual breakage to happen from this change.
LLVM 7.0.0 Release
The release contains the work on trunk up to SVN revision 338536 plus
work on the release branch. It is the result of the community's work
over the past six months, including: function multiversioning in Clang
with the 'target' attribute for ELF-based x86/x86_64 targets, improved
PCH support in clang-cl, preliminary DWARF v5 support, basic support
for OpenMP 4.5 offloading to NVPTX, OpenCL C++ support, MSan, X-Ray
and libFuzzer support for FreeBSD, early UBSan, X-Ray and libFuzzer
support for OpenBSD, UBSan checks for implicit conversions, many
long-tail compatibility issues fixed in lld which is now production
ready for ELF, COFF and MinGW, new tools llvm-exegesis, llvm-mca and
diagtool. And as usual, many optimizations, improved diagnostics, and
bug fixes.
For more details, see the release notes:
https://llvm.org/releases/7.0.0/docs/ReleaseNotes.htmlhttps://llvm.org/releases/7.0.0/tools/clang/docs/ReleaseNotes.htmlhttps://llvm.org/releases/7.0.0/tools/clang/tools/extra/docs/ReleaseNotes.htmlhttps://llvm.org/releases/7.0.0/tools/lld/docs/ReleaseNotes.html
libc++ is a new implementation of the C++ standard library, targeting
C++11.
Features and Goals
* Correctness as defined by the C++11 standard.
* Fast execution.
* Minimal memory use.
* Fast compile times.
* ABI compatibility with gcc's libstdc++ for some low-level features
such as exception objects, rtti and memory allocation.
* Extensive unit tests.
