docs/index.rst - llvm-project/libcxx - Git at Google

 .. _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 ``<atomic>`` 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 <cxx1y-status>`
 * :ref:`C++17 - In Progress <cxx1z-status>`
 * :ref:`C++20 - In Progress <cxx2a-status>`
 * :ref:`C++2b - In Progress <cxx2b-status>`
 * `Post C++14 Technical Specifications - In Progress <http://libcxx.llvm.org/ts1z_status.html>`__
 * :ref:`C++ Feature Test Macro Status <feature-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
    DesignDocs/NoexceptPolicy

 * `<atomic> design <http://libcxx.llvm.org/atomic_design.html>`_
 * `<type_traits> design <http://libcxx.llvm.org/type_traits_design.html>`_
 * `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 <https://buildkite.com/llvm-project/libcxx-ci>`_
 * `LLVM Buildbot Builders <http://lab.llvm.org:8011>`_
 * :ref:`Adding New CI Jobs <AddingNewCIJobs>`

 Getting Involved
 ================

 First please review our `Developer's Policy <https://llvm.org/docs/DeveloperPolicy.html>`__
 and `Getting started with LLVM <https://llvm.org/docs/GettingStarted.html>`__.

 **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 <https://llvm.org/docs/Phabricator.html>`_. Please add `libcxx-commits` as a subscriber.
 Also make sure you are subscribed to the `libcxx-commits mailing list <http://lists.llvm.org/mailman/listinfo/libcxx-commits>`_.

 **Discussion and Questions**

 Send discussions and questions to the
 `libcxx-dev mailing list <http://lists.llvm.org/mailman/listinfo/libcxx-dev>`_.


 Quick Links
 ===========
 * `LLVM Homepage <https://llvm.org/>`_
 * `libc++abi Homepage <http://libcxxabi.llvm.org/>`_
 * `LLVM Bugzilla <https://bugs.llvm.org/>`_
 * `libcxx-commits Mailing List`_
 * `libcxx-dev Mailing List`_
 * `Browse libc++ Sources <https://github.com/llvm/llvm-project/tree/main/libcxx/>`_
	.. _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 ``<atomic>`` 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 <cxx1y-status>`
	* :ref:`C++17 - In Progress <cxx1z-status>`
	* :ref:`C++20 - In Progress <cxx2a-status>`
	* :ref:`C++2b - In Progress <cxx2b-status>`
	* `Post C++14 Technical Specifications - In Progress <http://libcxx.llvm.org/ts1z_status.html>`__
	* :ref:`C++ Feature Test Macro Status <feature-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
	DesignDocs/NoexceptPolicy

	* `<atomic> design <http://libcxx.llvm.org/atomic_design.html>`_
	* `<type_traits> design <http://libcxx.llvm.org/type_traits_design.html>`_
	* `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 <https://buildkite.com/llvm-project/libcxx-ci>`_
	* `LLVM Buildbot Builders <http://lab.llvm.org:8011>`_
	* :ref:`Adding New CI Jobs <AddingNewCIJobs>`

	Getting Involved
	================

	First please review our `Developer's Policy <https://llvm.org/docs/DeveloperPolicy.html>`__
	and `Getting started with LLVM <https://llvm.org/docs/GettingStarted.html>`__.

	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 <https://llvm.org/docs/Phabricator.html>`_. Please add `libcxx-commits` as a subscriber.
	Also make sure you are subscribed to the `libcxx-commits mailing list <http://lists.llvm.org/mailman/listinfo/libcxx-commits>`_.

	Discussion and Questions

	Send discussions and questions to the
	`libcxx-dev mailing list <http://lists.llvm.org/mailman/listinfo/libcxx-dev>`_.



	Quick Links
	===========
	* `LLVM Homepage <https://llvm.org/>`_
	* `libc++abi Homepage <http://libcxxabi.llvm.org/>`_
	* `LLVM Bugzilla <https://bugs.llvm.org/>`_
	* `libcxx-commits Mailing List`_
	* `libcxx-dev Mailing List`_
	* `Browse libc++ Sources <https://github.com/llvm/llvm-project/tree/main/libcxx/>`_