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227 lines
9.6 KiB
227 lines
9.6 KiB
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<title>"libc++" C++ Standard Library</title> |
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<a href="http://llvm.org/">LLVM Home</a> |
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<label>libc++ Info</label> |
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<a href="/index.html">About</a> |
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<div class="submenu"> |
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<label>Quick Links</label> |
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<a href="https://bugs.llvm.org/">Bug Reports</a> |
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<a href="http://llvm.org/svn/llvm-project/libcxx/trunk/">Browse SVN</a> |
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<a href="http://llvm.org/viewvc/llvm-project/libcxx/trunk/">Browse ViewVC</a> |
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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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<p>libc++ is a new implementation of the C++ standard library, targeting |
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C++11.</p> |
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<p>All of the code in libc++ is <a |
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href="http://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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<h2>New Documentation Coming Soon!</h2> |
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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="http://libcxx.llvm.org/docs/"> |
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Click here for the new libc++ documentation.</a></p> |
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<h2 id="goals">Features and Goals</h2> |
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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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<h2 id="why">Why a new C++ Standard Library for C++11?</h2> |
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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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<h2 id="requirements">Platform Support</h2> |
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<p> |
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libc++ is known to work on the following platforms, using g++-4.2 and |
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clang (lack of C++11 language support disables some functionality). Note |
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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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</ul> |
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<h2 id="dir-structure">Current Status</h2> |
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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 changes for |
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C++14 can be found <a href="cxx1y_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++1z" (probably to be C++17) can be found <a href="cxx1z_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 and |
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the current status of these features can be found <a href="ts1z_status.html">here</a>.</p> |
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<h2 id="buildbots">Build Bots</h2> |
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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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<h2>Get it and get involved!</h2> |
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<p>First please review our |
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<a href="http://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="http://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="http://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="http://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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<h3>Notes and Known Issues</h3> |
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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="http://lists.llvm.org/mailman/listinfo/cfe-dev">clang 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="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you |
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can post a message to the <a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a> |
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mailing list or on IRC. Please include "libc++" in your subject. |
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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="http://llvm.org/docs/Phabricator.html">Phabricator</a>. Please |
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include [libc++] in the subject and add cfe-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="http://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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