forked from OSchip/llvm-project
235 lines
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235 lines
10 KiB
HTML
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<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
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<html>
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<head>
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<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>"libc++" C++ Standard Library</title>
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<link type="text/css" rel="stylesheet" href="menu.css">
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<link type="text/css" rel="stylesheet" href="content.css">
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</head>
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<body>
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<div id="menu">
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<div>
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<a href="https://llvm.org/">LLVM Home</a>
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</div>
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<div class="submenu">
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<label>libc++ Info</label>
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<a href="/index.html">About</a>
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</div>
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<div class="submenu">
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<label>Quick Links</label>
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<a href="https://libcxxabi.llvm.org/">libc++abi</a>
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<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a>
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<a href="https://lists.llvm.org/mailman/listinfo/libcxx-commits">libcxx-commits</a>
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<a href="https://bugs.llvm.org/">Bug Reports</a>
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<a href="https://llvm.org/svn/llvm-project/libcxx/trunk/">Browse SVN</a>
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<a href="https://llvm.org/viewvc/llvm-project/libcxx/trunk/">Browse ViewVC</a>
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</div>
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</div>
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<div id="content">
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<!--*********************************************************************-->
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<h1>"libc++" C++ Standard Library</h1>
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<!--*********************************************************************-->
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<p>libc++ is an implementation of the C++ standard library, targeting
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C++11, C++14 and above.</p>
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<p>All of the code in libc++ is <a
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href="https://llvm.org/docs/DeveloperPolicy.html#license">dual licensed</a>
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under the MIT license and the UIUC License (a BSD-like license).</p>
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<!--=====================================================================-->
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<h2>New Documentation Coming Soon!</h2>
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<!--=====================================================================-->
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<p> Looking for documentation on how to use, build and test libc++? If so
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checkout the new libc++ documentation.</p>
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<p><a href="https://libcxx.llvm.org/docs/">
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Click here for the new libc++ documentation.</a></p>
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<!--=====================================================================-->
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<h2 id="goals">Features and Goals</h2>
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<!--=====================================================================-->
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<ul>
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<li>Correctness as defined by the C++11 standard.</li>
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<li>Fast execution.</li>
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<li>Minimal memory use.</li>
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<li>Fast compile times.</li>
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<li>ABI compatibility with gcc's libstdc++ for some low-level features
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such as exception objects, rtti and memory allocation.</li>
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<li>Extensive unit tests.</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="why">Why a new C++ Standard Library for C++11?</h2>
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<!--=====================================================================-->
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<p>After its initial introduction, many people have asked "why start a new
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library instead of contributing to an existing library?" (like Apache's
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libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
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reasons, but some of the major ones are:</p>
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<ul>
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<li><p>From years of experience (including having implemented the standard
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library before), we've learned many things about implementing
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the standard containers which require ABI breakage and fundamental changes
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to how they are implemented. For example, it is generally accepted that
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building std::string using the "short string optimization" instead of
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using Copy On Write (COW) is a superior approach for multicore
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machines (particularly in C++11, which has rvalue references). Breaking
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ABI compatibility with old versions of the library was
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determined to be critical to achieving the performance goals of
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libc++.</p></li>
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<li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
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of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
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independently extended to support C++11, but this would be a fork of the
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codebase (which is often seen as worse for a project than starting a new
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independent one). Another problem with libstdc++ is that it is tightly
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integrated with G++ development, tending to be tied fairly closely to the
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matching version of G++.</p>
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</li>
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<li><p>STLport and the Apache libstdcxx library are two other popular
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candidates, but both lack C++11 support. Our experience (and the
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experience of libstdc++ developers) is that adding support for C++11 (in
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particular rvalue references and move-only types) requires changes to
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almost every class and function, essentially amounting to a rewrite.
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Faced with a rewrite, we decided to start from scratch and evaluate every
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design decision from first principles based on experience.</p>
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<p>Further, both projects are apparently abandoned: STLport 5.2.1 was
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released in Oct'08, and STDCXX 4.2.1 in May'08.</p>
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</ul>
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<!--=====================================================================-->
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<h2 id="requirements">Platform Support</h2>
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<!--=====================================================================-->
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<p>
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libc++ is known to work on the following platforms, using g++ and
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clang. Note that functionality provided by <atomic> is only functional with
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clang.
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</p>
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<ul>
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<li>Mac OS X i386</li>
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<li>Mac OS X x86_64</li>
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<li>FreeBSD 10+ i386</li>
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<li>FreeBSD 10+ x86_64</li>
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<li>FreeBSD 10+ ARM</li>
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<li>Linux i386</li>
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<li>Linux x86_64</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="dir-structure">Current Status</h2>
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<!--=====================================================================-->
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<p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p>
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<p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p>
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<p>libc++ is also a 100% complete C++14 implementation. A list of new features and
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changes for C++14 can be found <a href="cxx1y_status.html">here</a>.</p>
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<p>libc++'s C++17 implementation is not yet complete. A list of features and changes
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for C++17 can be found <a href="cxx1z_status.html">here</a>.</p>
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<p>A list of features and changes for the next C++ standard, known here as
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"C++2a" (probably to be C++20) can be found <a href="cxx2a_status.html">here</a>.</p>
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<p>Implementation of the post-C++14 Technical Specifications is in progress. A list of features
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and the current status of these features can be found <a href="ts1z_status.html">here</a>.</p>
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<p>As features get moved from the Technical Specifications into the main standard, we
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will (after a period for migration) remove them from the TS implementation. This
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process is detailed <a href="TS_deprecation.html">here</a>.</p>
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<!--======================================================================-->
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<h2 id="buildbots">Build Bots</h2>
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<!--======================================================================-->
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<p>The latest libc++ build results can be found at the following locations.</p>
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<ul>
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<li><a href="http://lab.llvm.org:8011/console">
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Buildbot libc++ builders
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</a></li>
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<li><a href="http://lab.llvm.org:8080/green/view/Libcxx/">
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Jenkins libc++ builders
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</a></li>
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</ul>
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<!--=====================================================================-->
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<h2>Get it and get involved!</h2>
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<!--=====================================================================-->
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<p>First please review our
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<a href="https://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
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The documentation for building and using libc++ can be found below.
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<ul>
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<li><a href="https://libcxx.llvm.org/docs/UsingLibcxx.html">
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<b>Using libc++</b></a>
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Documentation on using the library in your programs</li>
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<li><a href="https://libcxx.llvm.org/docs/BuildingLibcxx.html">
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<b>Building libc++</b></a>
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Documentation on building the library using CMake</li>
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<li><a href="https://libcxx.llvm.org/docs/TestingLibcxx.html">
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<b>Testing libc++</b></a>
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Documentation for developers wishing to test the library</li>
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</ul>
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<!--=====================================================================-->
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<h3>Notes and Known Issues</h3>
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<!--=====================================================================-->
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<p>
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<ul>
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<li>
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Building libc++ with <code>-fno-rtti</code> is not supported. However
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linking against it with <code>-fno-rtti</code> is supported.
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</li>
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<li>
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On OS X v10.8 and older the CMake option
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<code>-DLIBCXX_LIBCPPABI_VERSION=""</code> must be used during
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configuration.
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</li>
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</ul>
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</p>
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<p>Send discussions to the
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<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libc++ mailing list</a>.</p>
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<!--=====================================================================-->
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<h2>Bug reports and patches</h2>
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<!--=====================================================================-->
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<p>
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If you think you've found a bug in libc++, please report it using
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the <a href="https://bugs.llvm.org/">LLVM Bugzilla</a>. If you're not sure, you
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can post a message to the <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a>
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mailing list or on IRC.
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</p>
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<p>
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If you want to contribute a patch to libc++, the best place for that is
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<a href="https://llvm.org/docs/Phabricator.html">Phabricator</a>. Please
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add libcxx-commits as a subscriber.
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</p>
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<!--=====================================================================-->
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<h2>Design Documents</h2>
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<!--=====================================================================-->
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<ul>
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<li><a href="atomic_design.html"><tt><atomic></tt></a></li>
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<li><a href="type_traits_design.html"><tt><type_traits></tt></a></li>
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<li><a href="https://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/">Excellent notes by Marshall Clow</a></li>
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</ul>
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</div>
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</body>
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</html>
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