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450 lines
18 KiB
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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>
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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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<!--=====================================================================-->
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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 changes for
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C++14 can be found <a href="cxx1y_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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<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 id="dir-structure">Build Bots</h2>
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<!--======================================================================-->
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<p>These are the libc++ build bots</p>
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<ul>
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<li><a href="http://lab.llvm.org:8013/builders/libcxx_clang-x86_64-darwin11-RA">
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clang-libcxxabi-x86_64-darwin11
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</a></li>
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<li><a href="http://llvm-amd64.freebsd.your.org/b/builders/libcxx-amd64-freebsd">
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clang-libcxxrt-x86_64-freebsd10
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</a></li>
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<li><a href="http://llvm-amd64.freebsd.your.org/b/builders/libcxx-i386-freebsd">
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clang-libcxxrt-i386-freebsd10
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</a></li>
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<li><a href="http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-debian">
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clang-libcxxabi-x86_64-linux-debian
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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="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
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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>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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Note that for an in-tree build, you should check out libcxx to
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llvm/projects.
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</p>
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<p>
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The following instructions are for building libc++ on FreeBSD, Linux, or Mac
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using <a href="http://libcxxabi.llvm.org/">libc++abi</a> as the C++ ABI
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library. On Linux, it is also possible to use
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<a href="#libsupcxx">libsupc++</a> or <a href="#libcxxrt">libcxxrt</a>.
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</p>
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<p>In-tree build:</p>
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<ul>
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<li>Check out libcxx and <a href="http://libcxxabi.llvm.org/">libcxxabi</a>
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into llvm/projects</li>
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<li><code>cd llvm</code></li>
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<li><code>mkdir build && cd build</code></li>
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<li><code>cmake .. # Linux may require -DCMAKE_C_COMPILER=clang
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-DCMAKE_CXX_COMPILER=clang++</code></li>
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<li><code>make cxx</code></li>
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</ul>
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<p>Out-of-tree build:</p>
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<ul>
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<li>Check out libcxx</li>
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<li>If not on a Mac, also check out
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<a href="http://libcxxabi.llvm.org/">libcxxabi</a></li>
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<li><code>cd libcxx</code></li>
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<li><code>mkdir build && cd build</code></li>
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<li><code>cmake -DLIBCXX_CXX_ABI=libcxxabi
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-DLIBCXX_LIBCXXABI_INCLUDE_PATHS=path/to/libcxxabi/include
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-DLIT_EXECUTABLE=path/to/llvm/utils/lit/lit.py .. # Linux may require
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-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
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<li><code>make</code></li>
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</ul>
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<p>To run the tests:</p>
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<ul>
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<li><code>make check-libcxx</code></li>
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</ul>
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<p>If you wish to run a subset of the test suite:</p>
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<ul>
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<li><code>cd path/to/libcxx/libcxx</code></li>
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<li><code>alias lit='python path/to/llvm/utils/lit/lit.py'</code></li>
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<li><code>ln -s path/to/build/dir/projects/libcxx/test/lit.site.cfg
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test/lit.site.cfg</code></li>
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<li><code>lit -sv test/re/ # or whichever subset of tests you're interested
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in</code></li>
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</ul>
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<p>The above is currently quite inconvenient. Sorry! We're working on it!</p>
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<p>More information on using LIT can be found
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<a href="http://llvm.org/docs/CommandGuide/lit.html">here</a>. For more
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general information about the LLVM testing infrastructure, see the
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<a href="http://llvm.org/docs/TestingGuide.html">LLVM Testing Infrastructure
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Guide</a>
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</p>
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<p>
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Shared libraries for libc++ should now be present in llvm/build/lib. Note
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that it is safest to use this from its current location rather than
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replacing your system's libc++ (if it has one, if not, go right ahead).
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</p>
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<p>
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Mac users, remember to be careful when replacing the system's libc++.
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<strong>Your system will not be able to boot without a funcioning
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libc++.</strong>
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</p>
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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
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linking 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>Using libc++ in your programs</h2>
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<!--=====================================================================-->
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<!--=====================================================================-->
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<h3>FreeBSD and Mac OS X</h3>
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<!--=====================================================================-->
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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/build/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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<!--=====================================================================-->
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<h3>Linux</h3>
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<!--=====================================================================-->
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<p>
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You will need to keep the source tree of
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<a href="http://libcxxabi.llvm.org">libc++abi</a> available on your build
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machine and your copy of the libc++abi shared library must be placed where
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your linker will find it.
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</p>
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<p>
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Unfortunately you can't simply run clang with "-stdlib=libc++" at this
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point, as clang is set up to link for libc++ linked to libsupc++. To get
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around this you'll have to set up your linker yourself (or patch clang).
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For example:
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</p>
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<ul>
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<li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc</code></li>
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</ul>
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<p>
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Alternately, you could just add libc++abi to your libraries list, which in
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most situations will give the same result:
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</p>
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<ul>
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<li><code>clang++ -stdlib=libc++ helloworld.cpp -lc++abi</code></li>
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</ul>
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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.cs.uiuc.edu/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 the
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
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mailing list. Please include "libc++" and "PATCH" in your subject.
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</p>
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<!--=====================================================================-->
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<h2 id="libsupcxx">Build on Linux using CMake and libsupc++.</h2>
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<!--=====================================================================-->
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<p>
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You will need libstdc++ in order to provide libsupc++.
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</p>
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<p>
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Figure out where the libsupc++ headers are on your system. On Ubuntu this
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is <code>/usr/include/c++/<version></code> and
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<code>/usr/include/c++/<version>/<target-triple></code>
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</p>
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<p>
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You can also figure this out by running
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<pre>
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$ echo | g++ -Wp,-v -x c++ - -fsyntax-only
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ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
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ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
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#include "..." search starts here:
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#include <...> search starts here:
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/usr/include/c++/4.7
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/usr/include/c++/4.7/x86_64-linux-gnu
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/usr/include/c++/4.7/backward
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/usr/lib/gcc/x86_64-linux-gnu/4.7/include
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/usr/local/include
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/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
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/usr/include/x86_64-linux-gnu
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/usr/include
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End of search list.
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</pre>
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Note the first two entries happen to be what we are looking for. This
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may not be correct on other platforms.
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</p>
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<p>
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We can now run CMake:
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<ul>
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<li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
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-DLIBCXX_CXX_ABI=libstdc++
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-DLIBCXX_LIBSUPCXX_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
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-DCMAKE_BUILD_TYPE=Release
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-DCMAKE_INSTALL_PREFIX=/usr
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<libc++-source-dir></code></li>
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<li>You can also substitute <code>-DLIBCXX_CXX_ABI=libsupc++</code>
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above, which will cause the library to be linked to libsupc++ instead
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of libstdc++, but this is only recommended if you know that you will
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never need to link against libstdc++ in the same executable as libc++.
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GCC ships libsupc++ separately but only as a static library. If a
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program also needs to link against libstdc++, it will provide its
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own copy of libsupc++ and this can lead to subtle problems.
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<li><code>make</code></li>
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<li><code>sudo make install</code></li>
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</ul>
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<p>
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You can now run clang with -stdlib=libc++.
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</p>
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</p>
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<!--=====================================================================-->
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<h2 id="libcxxrt">Build on Linux using CMake and libcxxrt.</h2>
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<!--=====================================================================-->
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<p>
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You will need to keep the source tree of
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<a href="https://github.com/pathscale/libcxxrt/">libcxxrt</a> available
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on your build machine and your copy of the libcxxrt shared library must
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be placed where your linker will find it.
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</p>
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<p>
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We can now run CMake:
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<ul>
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<li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
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-DLIBCXX_CXX_ABI=libcxxrt
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-DLIBCXX_LIBCXXRT_INCLUDE_PATHS="<libcxxrt-source-dir>/src"
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-DCMAKE_BUILD_TYPE=Release
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-DCMAKE_INSTALL_PREFIX=/usr
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<libc++-source-dir></code></li>
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<li><code>make</code></li>
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<li><code>sudo make install</code></li>
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</ul>
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<p>
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Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
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clang is set up to link for libc++ linked to libsupc++. To get around this
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you'll have to set up your linker yourself (or patch clang). For example,
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<ul>
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<li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc</code></li>
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</ul>
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Alternately, you could just add libcxxrt to your libraries list, which in most
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situations will give the same result:
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<ul>
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<li><code>clang++ -stdlib=libc++ helloworld.cpp -lcxxrt</code></li>
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</ul>
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</p>
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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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<li><a href="debug_mode.html">Status of debug mode</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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