.. _index: ============================= "libc++" C++ Standard Library ============================= Overview ======== libc++ is a new implementation of the C++ standard library, targeting C++11 and above. * 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. * Design and Implementation: * Extensive unit tests * Internal linker model can be dumped/read to textual format * Additional linking features can be plugged in as "passes" * OS specific and CPU specific code factored out Getting Started with libc++ --------------------------- .. toctree:: :maxdepth: 2 ReleaseNotes UsingLibcxx BuildingLibcxx TestingLibcxx Contributing Cxx1yStatus Cxx1zStatus Cxx2aStatus Cxx2bStatus .. toctree:: :hidden: AddingNewCIJobs FeatureTestMacroTable Current Status -------------- After its initial introduction, many people have asked "why start a new library instead of contributing to an existing library?" (like Apache's libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing reasons, but some of the major ones are: * From years of experience (including having implemented the standard library before), we've learned many things about implementing the standard containers which require ABI breakage and fundamental changes to how they are implemented. For example, it is generally accepted that building std::string using the "short string optimization" instead of using Copy On Write (COW) is a superior approach for multicore machines (particularly in C++11, which has rvalue references). Breaking ABI compatibility with old versions of the library was determined to be critical to achieving the performance goals of libc++. * Mainline libstdc++ has switched to GPL3, a license which the developers of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be independently extended to support C++11, but this would be a fork of the codebase (which is often seen as worse for a project than starting a new independent one). Another problem with libstdc++ is that it is tightly integrated with G++ development, tending to be tied fairly closely to the matching version of G++. * STLport and the Apache libstdcxx library are two other popular candidates, but both lack C++11 support. Our experience (and the experience of libstdc++ developers) is that adding support for C++11 (in particular rvalue references and move-only types) requires changes to almost every class and function, essentially amounting to a rewrite. Faced with a rewrite, we decided to start from scratch and evaluate every design decision from first principles based on experience. Further, both projects are apparently abandoned: STLport 5.2.1 was released in Oct'08, and STDCXX 4.2.1 in May'08. Platform and Compiler Support ----------------------------- For using the libc++ headers ############################ The libc++ headers are known to work on the following platforms, using GCC and Clang. Note that functionality provided by ```` is only functional with Clang and GCC. ============ ==================== ============ OS Arch Compilers ============ ==================== ============ macOS 10.9+ i386, x86_64 Clang, GCC FreeBSD 10+ i386, x86_64, ARM Clang, GCC Linux i386, x86_64 Clang, GCC ============ ==================== ============ The following minimum compiler versions are required: * Clang 4.0 and above * GCC 5.0 and above. The C++03 dialect is only supported with Clang. For building the libc++ library ############################### Building the libc++ library (static or shared) requires some features from the operating system. As such, it has its own set of (slightly different) system requirements. ============ ==================== ============ ======================== OS Arch Compilers ABI Library ============ ==================== ============ ======================== macOS 10.12+ i386, x86_64 Clang, GCC libc++abi FreeBSD 10+ i386, x86_64, ARM Clang, GCC libcxxrt, libc++abi Linux i386, x86_64 Clang, GCC libc++abi ============ ==================== ============ ======================== The following minimum compiler versions are required: * Clang 4.0 and above * GCC 5.0 and above. C++ Dialect Support --------------------- * C++11 - Complete * :ref:`C++14 - Complete ` * :ref:`C++17 - In Progress ` * :ref:`C++20 - In Progress ` * :ref:`C++2b - Not Started ` * `Post C++14 Technical Specifications - In Progress `__ * :ref:`C++ Feature Test Macro Status ` Notes and Known Issues ---------------------- This list contains known issues with libc++ * Building libc++ with ``-fno-rtti`` is not supported. However linking against it with ``-fno-rtti`` is supported. A full list of currently open libc++ bugs can be `found here`__. .. __: https://bugs.llvm.org/buglist.cgi?component=All%20Bugs&product=libc%2B%2B&query_format=advanced&resolution=---&order=changeddate%20DESC%2Cassigned_to%20DESC%2Cbug_status%2Cpriority%2Cbug_id&list_id=74184 Design Documents ---------------- .. toctree:: :maxdepth: 1 DesignDocs/DebugMode DesignDocs/CapturingConfigInfo DesignDocs/ABIVersioning DesignDocs/ExperimentalFeatures DesignDocs/VisibilityMacros DesignDocs/ThreadingSupportAPI DesignDocs/FileTimeType DesignDocs/FeatureTestMacros DesignDocs/ExtendedCXX03Support DesignDocs/UniquePtrTrivialAbi * ` design `_ * ` design `_ * `Notes by Marshall Clow`__ .. __: https://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/ Build Bots and Test Coverage ---------------------------- * `Buildkite CI pipeline `_ * `LLVM Buildbot Builders `_ * :ref:`Adding New CI Jobs ` Getting Involved ================ First please review our `Developer's Policy `__ and `Getting started with LLVM `__. **Bug Reports** If you think you've found a bug in libc++, please report it using the `LLVM Bugzilla`_. If you're not sure, you can post a message to the `libcxx-dev mailing list`_ or on IRC. **Patches** If you want to contribute a patch to libc++, the best place for that is `Phabricator `_. Please add `libcxx-commits` as a subscriber. Also make sure you are subscribed to the `libcxx-commits mailing list `_. **Discussion and Questions** Send discussions and questions to the `libcxx-dev mailing list `_. Quick Links =========== * `LLVM Homepage `_ * `libc++abi Homepage `_ * `LLVM Bugzilla `_ * `libcxx-commits Mailing List`_ * `libcxx-dev Mailing List`_ * `Browse libc++ Sources `_