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220 lines
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220 lines
8.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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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="http://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="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
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<a href="http://llvm.org/bugs/">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>
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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 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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<!--=====================================================================-->
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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>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).</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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</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>
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Ports to other platforms are underway. Here are recent test
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results for <a href="results.Windows.html">Windows</a>
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and <a href="results.Linux.html">Linux</a>.
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</p>
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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="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
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<p>To check out the code, use:</p>
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<ul>
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<li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
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</ul>
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<p>
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On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
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Xcode 4.2 or later. However if you want to install tip-of-trunk from here
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(getting the bleeding edge), read on. However, be warned that Mac OS
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10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
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<code>/usr/lib</code>.
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</p>
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<p>
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Next:
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</p>
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<ul>
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<li><code>cd libcxx/lib</code></li>
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<li><code>export TRIPLE=-apple-</code></li>
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<li><code>./buildit</code></li>
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<li><code>ln -sf libc++.1.dylib libc++.dylib</code></li>
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</ul>
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<p>
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That should result in a libc++.1.dylib and libc++.dylib. The safest thing
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to do is to use it from where your libcxx is installed instead of replacing
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these in your Mac OS.
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</p>
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<p>
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To use your system-installed libc++ with clang you can:
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</p>
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<ul>
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<li><code>clang++ -stdlib=libc++ test.cpp</code></li>
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<li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li>
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</ul>
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<p>
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To use your tip-of-trunk libc++ on Mac OS with clang you can:
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</p>
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<ul>
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<li><code>export DYLD_LIBRARY_PATH=<path-to-libcxx>/lib</code>
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<li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++
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-I<path-to-libcxx>/include -L<path-to-libcxx>/lib
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test.cpp</code></li>
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</ul>
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<p>To run the libc++ test suite (recommended):</p>
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<ul>
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<li><code>cd libcxx/test</code></li>
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<li><code>./testit</code></li>
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<ul>
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<li>You can alter the command line options <code>testit</code> uses
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with <code>export OPTIONS="whatever you need"</code></li>
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</ul>
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</ul>
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<!--=====================================================================-->
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<h3>Notes</h3>
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<!--=====================================================================-->
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<p>
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Building libc++ with <code>-fno-rtti</code> is not supported. However linking
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against it with <code>-fno-rtti</code> is supported.
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</p>
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<p>Send discussions to the
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(<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</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://marshall.calepin.co/llvmclang-and-standard-libraries-on-mac-os-x.html">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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