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| <label>libc++ Info</label> |
| <a href="/index.html">About</a> |
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| <a href="https://libcxxabi.llvm.org/">libc++abi</a> |
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| <!--*********************************************************************--> |
| <h1>"libc++" C++ Standard Library</h1> |
| <!--*********************************************************************--> |
| |
| <p>libc++ is an implementation of the C++ standard library, targeting |
| C++11, C++14 and above.</p> |
| |
| <p>All of the code in libc++ is <a |
| href="https://llvm.org/docs/DeveloperPolicy.html#license">dual licensed</a> |
| under the MIT license and the UIUC License (a BSD-like license).</p> |
| |
| <!--=====================================================================--> |
| <h2>New Documentation Coming Soon!</h2> |
| <!--=====================================================================--> |
| |
| <p> Looking for documentation on how to use, build and test libc++? If so |
| checkout the new libc++ documentation.</p> |
| |
| <p><a href="https://libcxx.llvm.org/docs/"> |
| Click here for the new libc++ documentation.</a></p> |
| |
| <!--=====================================================================--> |
| <h2 id="goals">Features and Goals</h2> |
| <!--=====================================================================--> |
| |
| <ul> |
| <li>Correctness as defined by the C++11 standard.</li> |
| <li>Fast execution.</li> |
| <li>Minimal memory use.</li> |
| <li>Fast compile times.</li> |
| <li>ABI compatibility with gcc's libstdc++ for some low-level features |
| such as exception objects, rtti and memory allocation.</li> |
| <li>Extensive unit tests.</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="why">Why a new C++ Standard Library for C++11?</h2> |
| <!--=====================================================================--> |
| |
| <p>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:</p> |
| |
| <ul> |
| <li><p>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++.</p></li> |
| |
| <li><p>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++.</p> |
| </li> |
| |
| <li><p>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.</p> |
| |
| <p>Further, both projects are apparently abandoned: STLport 5.2.1 was |
| released in Oct'08, and STDCXX 4.2.1 in May'08.</p> |
| |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="requirements">Platform Support</h2> |
| <!--=====================================================================--> |
| |
| <p> |
| libc++ is known to work on the following platforms, using g++ and |
| clang. Note that functionality provided by <atomic> is only functional with |
| clang. |
| </p> |
| |
| <ul> |
| <li>Mac OS X i386</li> |
| <li>Mac OS X x86_64</li> |
| <li>FreeBSD 10+ i386</li> |
| <li>FreeBSD 10+ x86_64</li> |
| <li>FreeBSD 10+ ARM</li> |
| <li>Linux i386</li> |
| <li>Linux x86_64</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2 id="dir-structure">Current Status</h2> |
| <!--=====================================================================--> |
| |
| <p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p> |
| <p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p> |
| <p>libc++ is also a 100% complete C++14 implementation. A list of new features and |
| changes for C++14 can be found <a href="cxx1y_status.html">here</a>.</p> |
| <p>libc++'s C++17 implementation is not yet complete. A list of features and changes |
| for C++17 can be found <a href="cxx1z_status.html">here</a>.</p> |
| <p>A list of features and changes for the next C++ standard, known here as |
| "C++2a" (probably to be C++20) can be found <a href="cxx2a_status.html">here</a>.</p> |
| <p>Implementation of the post-C++14 Technical Specifications is in progress. A list of features |
| and the current status of these features can be found <a href="ts1z_status.html">here</a>.</p> |
| <p>As features get moved from the Technical Specifications into the main standard, we |
| will (after a period for migration) remove them from the TS implementation. This |
| process is detailed <a href="TS_deprecation.html">here</a>.</p> |
| |
| <!--======================================================================--> |
| <h2 id="buildbots">Build Bots</h2> |
| <!--======================================================================--> |
| <p>The latest libc++ build results can be found at the following locations.</p> |
| <ul> |
| <li><a href="http://lab.llvm.org:8011/console"> |
| Buildbot libc++ builders |
| </a></li> |
| <li><a href="http://lab.llvm.org:8080/green/view/Libcxx/"> |
| Jenkins libc++ builders |
| </a></li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h2>Get it and get involved!</h2> |
| <!--=====================================================================--> |
| |
| <p>First please review our |
| <a href="https://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>. |
| |
| The documentation for building and using libc++ can be found below. |
| <ul> |
| <li><a href="https://libcxx.llvm.org/docs/UsingLibcxx.html"> |
| <b>Using libc++</b></a> |
| Documentation on using the library in your programs</li> |
| <li><a href="https://libcxx.llvm.org/docs/BuildingLibcxx.html"> |
| <b>Building libc++</b></a> |
| Documentation on building the library using CMake</li> |
| <li><a href="https://libcxx.llvm.org/docs/TestingLibcxx.html"> |
| <b>Testing libc++</b></a> |
| Documentation for developers wishing to test the library</li> |
| </ul> |
| |
| <!--=====================================================================--> |
| <h3>Notes and Known Issues</h3> |
| <!--=====================================================================--> |
| |
| <p> |
| <ul> |
| <li> |
| Building libc++ with <code>-fno-rtti</code> is not supported. However |
| linking against it with <code>-fno-rtti</code> is supported. |
| </li> |
| </ul> |
| </p> |
| |
| <p>Send discussions to the |
| <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libc++ mailing list</a>.</p> |
| |
| <!--=====================================================================--> |
| <h2>Bug reports and patches</h2> |
| <!--=====================================================================--> |
| |
| <p> |
| If you think you've found a bug in libc++, please report it using |
| the <a href="https://bugs.llvm.org/">LLVM Bugzilla</a>. If you're not sure, you |
| can post a message to the <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a> |
| mailing list or on IRC. |
| </p> |
| |
| <p> |
| If you want to contribute a patch to libc++, the best place for that is |
| <a href="https://llvm.org/docs/Phabricator.html">Phabricator</a>. Please |
| add libcxx-commits as a subscriber. |
| </p> |
| |
| <!--=====================================================================--> |
| <h2>Design Documents</h2> |
| <!--=====================================================================--> |
| |
| <ul> |
| <li><a href="atomic_design.html"><tt><atomic></tt></a></li> |
| <li><a href="type_traits_design.html"><tt><type_traits></tt></a></li> |
| <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> |
| </ul> |
| |
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