1.. _index: 2 3============================= 4"libc++" C++ Standard Library 5============================= 6 7Overview 8======== 9 10libc++ is a new implementation of the C++ standard library, targeting C++11 and 11above. 12 13* Features and Goals 14 15 * Correctness as defined by the C++11 standard. 16 * Fast execution. 17 * Minimal memory use. 18 * Fast compile times. 19 * ABI compatibility with gcc's libstdc++ for some low-level features 20 such as exception objects, rtti and memory allocation. 21 * Extensive unit tests. 22 23* Design and Implementation: 24 25 * Extensive unit tests 26 * Internal linker model can be dumped/read to textual format 27 * Additional linking features can be plugged in as "passes" 28 * OS specific and CPU specific code factored out 29 30 31Getting Started with libc++ 32=========================== 33 34.. toctree:: 35 :maxdepth: 1 36 37 ReleaseNotes 38 UserDocumentation 39 VendorDocumentation 40 Contributing 41 CodingGuidelines 42 TestingLibcxx 43 ImplementationDefinedBehavior 44 Modules 45 Hardening 46 ReleaseProcedure 47 Status/Cxx17 48 Status/Cxx20 49 Status/Cxx23 50 Status/Cxx2c 51 Status/Format 52 Status/Parallelism 53 Status/PSTL 54 55 56.. toctree:: 57 :hidden: 58 59 AddingNewCIJobs 60 FeatureTestMacroTable 61 62 63Current Status 64============== 65 66libc++ has become the default C++ Standard Library implementation for many major platforms, including Apple's macOS, 67iOS, watchOS, and tvOS, Google Search, the Android operating system, and FreeBSD. As a result, libc++ has an estimated 68user base of over 1 billion daily active users. 69 70Since its inception, libc++ has focused on delivering high performance, standards-conformance, and portability. It has 71been extensively tested and optimized, making it robust and production ready. libc++ fully implements C++11 and C++14, 72with C++17, C++20, C++23, and C++26 features being actively developed and making steady progress. 73 74libc++ is continuously integrated and tested on a wide range of platforms and configurations, ensuring its reliability 75and compatibility across various systems. The library's extensive test suite and rigorous quality assurance process have 76made it a top choice for platform providers looking to offer their users a robust and efficient C++ Standard Library. 77 78As an open-source project, libc++ benefits from a vibrant community of contributors who work together to improve the 79library and add new features. This ongoing development and support ensure that libc++ remains at the forefront of 80C++ standardization efforts and continues to meet the evolving needs of C++ developers worldwide. 81 82 83History 84------- 85After its initial introduction, many people have asked "why start a new 86library instead of contributing to an existing library?" (like Apache's 87libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing 88reasons, but some of the major ones are: 89 90* From years of experience (including having implemented the standard 91 library before), we've learned many things about implementing 92 the standard containers which require ABI breakage and fundamental changes 93 to how they are implemented. For example, it is generally accepted that 94 building std::string using the "short string optimization" instead of 95 using Copy On Write (COW) is a superior approach for multicore 96 machines (particularly in C++11, which has rvalue references). Breaking 97 ABI compatibility with old versions of the library was 98 determined to be critical to achieving the performance goals of 99 libc++. 100 101* Mainline libstdc++ has switched to GPL3, a license which the developers 102 of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be 103 independently extended to support C++11, but this would be a fork of the 104 codebase (which is often seen as worse for a project than starting a new 105 independent one). Another problem with libstdc++ is that it is tightly 106 integrated with G++ development, tending to be tied fairly closely to the 107 matching version of G++. 108 109* STLport and the Apache libstdcxx library are two other popular 110 candidates, but both lack C++11 support. Our experience (and the 111 experience of libstdc++ developers) is that adding support for C++11 (in 112 particular rvalue references and move-only types) requires changes to 113 almost every class and function, essentially amounting to a rewrite. 114 Faced with a rewrite, we decided to start from scratch and evaluate every 115 design decision from first principles based on experience. 116 Further, both projects are apparently abandoned: STLport 5.2.1 was 117 released in Oct'08, and STDCXX 4.2.1 in May'08. 118 119.. 120 LLVM RELEASE bump version 121 122.. _SupportedPlatforms: 123 124Platform and Compiler Support 125============================= 126 127Libc++ aims to support common compilers that implement the C++11 Standard. In order to strike a 128good balance between stability for users and maintenance cost, testing coverage and development 129velocity, libc++ drops support for older compilers as newer ones are released. 130 131============ =============== ========================== ===================== 132Compiler Versions Restrictions Support policy 133============ =============== ========================== ===================== 134Clang 17, 18, 19-git latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version 135AppleClang 15 latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_ 136Open XL 17.1 (AIX) latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_ 137GCC 14 In C++11 or later only latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_ 138============ =============== ========================== ===================== 139 140Libc++ also supports common platforms and architectures: 141 142===================== ========================= ============================ 143Target platform Target architecture Notes 144===================== ========================= ============================ 145macOS 10.13+ i386, x86_64, arm64 146FreeBSD 12+ i386, x86_64, arm 147Linux i386, x86_64, arm, arm64 Only glibc-2.24 and later and no other libc is officially supported 148Android 5.0+ i386, x86_64, arm, arm64 149Windows i386, x86_64 Both MSVC and MinGW style environments, ABI in MSVC environments is :doc:`unstable <DesignDocs/ABIVersioning>` 150AIX 7.2TL5+ powerpc, powerpc64 151Embedded (picolibc) arm 152===================== ========================= ============================ 153 154Generally speaking, libc++ should work on any platform that provides a fairly complete 155C Standard Library. It is also possible to turn off parts of the library for use on 156systems that provide incomplete support. 157 158However, libc++ aims to provide a high-quality implementation of the C++ Standard 159Library, especially when it comes to correctness. As such, we aim to have test coverage 160for all the platforms and compilers that we claim to support. If a platform or compiler 161is not listed here, it is not officially supported. It may happen to work, and 162in practice the library is known to work on some platforms not listed here, but 163we don't make any guarantees. If you would like your compiler and/or platform 164to be formally supported and listed here, please work with the libc++ team to set 165up testing for your configuration. 166 167 168C++ Standards Conformance 169========================= 170 171Libc++ provides full support for C++11 and C++14, and provides most of newer standards 172with a few omissions. The conformance status of the library's tip is tracked in real-time 173using `this page <https://github.com/orgs/llvm/projects/31>`_. The conformance status of 174this release is described in the pages below: 175 176* C++11 - Complete 177* C++14 - Complete 178* :ref:`C++17 - In Progress <cxx17-status>` 179* :ref:`C++20 - In Progress <cxx20-status>` 180* :ref:`C++23 - In Progress <cxx23-status>` 181* :ref:`C++2c - In Progress <cxx2c-status>` 182* :ref:`C++ Feature Test Macro Status <feature-status>` 183 184 185Getting Involved 186================ 187 188First please review our `Developer's Policy <https://llvm.org/docs/DeveloperPolicy.html>`__ 189and `Getting started with LLVM <https://llvm.org/docs/GettingStarted.html>`__. 190 191**Bug Reports** 192 193If you think you've found a bug in libc++, please report it using the `LLVM bug tracker`_. 194If you're not sure, you can ask for support on the `libc++ forum`_ or in the `libc++ chat`_. 195 196**Patches** 197 198If you want to contribute a patch to libc++, please start by reviewing our 199:ref:`documentation about contributing <ContributingToLibcxx>`. 200 201**Discussion and Questions** 202 203Send discussions and questions to the `libc++ forum`_. 204 205 206Design Documents 207================ 208 209.. toctree:: 210 :maxdepth: 1 211 212 DesignDocs/ABIVersioning 213 DesignDocs/AtomicDesign 214 DesignDocs/CapturingConfigInfo 215 DesignDocs/ExperimentalFeatures 216 DesignDocs/ExtendedCXX03Support 217 DesignDocs/FeatureTestMacros 218 DesignDocs/FileTimeType 219 DesignDocs/HeaderRemovalPolicy 220 DesignDocs/NoexceptPolicy 221 DesignDocs/PSTLIntegration 222 DesignDocs/ThreadingSupportAPI 223 DesignDocs/UniquePtrTrivialAbi 224 DesignDocs/UnspecifiedBehaviorRandomization 225 DesignDocs/VisibilityMacros 226 DesignDocs/TimeZone 227 228 229Build Bots and Test Coverage 230============================ 231 232* `Github Actions CI pipeline <https://github.com/llvm/llvm-project/actions/workflows/libcxx-build-and-test.yaml>`_ 233* `Buildkite CI pipeline <https://buildkite.com/llvm-project/libcxx-ci>`_ 234* `LLVM Buildbot Builders <https://lab.llvm.org/buildbot>`_ 235* :ref:`Adding New CI Jobs <AddingNewCIJobs>` 236 237 238Quick Links 239=========== 240* `LLVM Homepage <https://llvm.org/>`_ 241* `libc++abi Homepage <http://libcxxabi.llvm.org/>`_ 242* `LLVM Bug Tracker <https://github.com/llvm/llvm-project/labels/libc++/>`_ 243* `libcxx-commits Mailing List <http://lists.llvm.org/mailman/listinfo/libcxx-commits>`_ 244* `libc++ forum <https://discourse.llvm.org/c/runtimes/libcxx/>`_ 245* `libc++ chat <https://discord.com/channels/636084430946959380/636732894974312448>`_ 246* `Browse libc++ Sources <https://github.com/llvm/llvm-project/tree/main/libcxx/>`_ 247