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   <!--*********************************************************************-->
   <h1>"libc++" C++ Standard Library</h1>
   <!--*********************************************************************-->

   <p>libc++ is a new implementation of the C++ standard library, targeting
      C++11.</p>

   <p>All of the code in libc++ is <a
      href="http://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="http://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++-4.2 and
     clang (lack of C++11 language support disables some functionality). Note
     that functionality provided by &lt;atomic&gt; 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>
   </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>A list of features and changes for the next C++ standard, known here as
       "C++1z" (probably to be C++17) can be found <a href="cxx1z_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>
    Ports to other platforms are underway. Here are recent test
    results for <a href="results.Windows.html">Windows</a>
    and <a href="results.Linux.html">Linux</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="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.

   <p>
      On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
      Xcode 4.2 or later.  However if you want to install tip-of-trunk from here
      (getting the bleeding edge), read on.  However, be warned that Mac OS
      10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
      <code>/usr/lib</code>.
   </p>

   <p>To check out the code, use:</p>

   <ul>
   <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
   </ul>

   <p>
     Note that for an in-tree build, you should check out libcxx to
     llvm/projects.
   </p>

   <p>
     The following instructions are for building libc++ on FreeBSD, Linux, or Mac
     using <a href="http://libcxxabi.llvm.org/">libc++abi</a> as the C++ ABI
     library. On Linux, it is also possible to use
     <a href="#libsupcxx">libsupc++</a> or <a href="#libcxxrt">libcxxrt</a>.
   </p>

   <p>In-tree build:</p>
   <ul>
     <li><code>cd where-you-want-to-live</code></li>
     <li>Check out libcxx and <a href="http://libcxxabi.llvm.org/">libcxxabi</a>
       into llvm/projects</li>
     <li><code>cd where-you-want-to-build</code></li>
     <li><code>mkdir build &amp;&amp; cd build</code></li>
     <li><code>cmake path/to/llvm # Linux may require -DCMAKE_C_COMPILER=clang
         -DCMAKE_CXX_COMPILER=clang++</code></li>
     <li><code>make cxx</code></li>
   </ul>

   <p>Out-of-tree buildc:</p>
   <ul>
     <li><code>cd where-you-want-to-live</code></li>
     <li>Check out libcxx and llvm</li>
     <li>If not on a Mac, also check out
       <a href="http://libcxxabi.llvm.org/">libcxxabi</a></li>
     <li><code>cd where-you-want-to-build</code></li>
     <li><code>mkdir build &amp;&amp; cd build</code></li>
     <li><code>cmake -DLLVM_PATH=path/to/llvm
         -DLIBCXX_CXX_ABI=libcxxabi
         -DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/libcxxabi/include
         -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
         path/to/libcxx
     </code></li>
     <li><code>make</code></li>
   </ul>

   <p>To run the tests:</p>
   <ul>
   <li><code>make check-libcxx</code></li>
   </ul>

   <p>If you wish to run a subset of the test suite:</p>
   <ul>
     <li><code>cd path/to/libcxx/libcxx</code></li>
     <li><code>alias lit='python path/to/llvm/utils/lit/lit.py'</code></li>
     <li><code>export
         LIBCXX_SITE_CONFIG=path/to/build/dir/projects/libcxx/test/lit.site.cfg
         </code></li>
     <li><code>lit -sv test/re/ # or whichever subset of tests you're interested
         in</code></li>
   </ul>
   <p>The above is currently quite inconvenient. Sorry! We're working on it!</p>

   <p>More information on using LIT can be found
     <a href="http://llvm.org/docs/CommandGuide/lit.html">here</a>. For more
     general information about the LLVM testing infrastructure, see the
     <a href="http://llvm.org/docs/TestingGuide.html">LLVM Testing Infrastructure
       Guide</a>
   </p>

   <p>
     Shared libraries for libc++ should now be present in llvm/build/lib. Note
     that it is safest to use this from its current location rather than
     replacing your system's libc++ (if it has one, if not, go right ahead).
   </p>

   <p>
     Mac users, remember to be careful when replacing the system's libc++.
     <strong>Your system will not be able to boot without a functioning
     libc++.</strong>
   </p>

   <!--=====================================================================-->
   <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>
       <li>
         On OS X v10.8 and older the CMake option
         <code>-DLIBCXX_LIBCPPABI_VERSION=""</code> must be used during
         configuration.
       </li>
     </ul>
   </p>

   <p>Send discussions to the
     <a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">clang mailing list</a>.</p>

   <!--=====================================================================-->
   <h2>Using libc++ in your programs</h2>
   <!--=====================================================================-->

   <!--=====================================================================-->
   <h3>FreeBSD and Mac OS X</h3>
   <!--=====================================================================-->

   <p>
     To use your system-installed libc++ with clang you can:
   </p>

   <ul>
     <li><code>clang++ -stdlib=libc++ test.cpp</code></li>
     <li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li>
   </ul>

   <p>
     To use your tip-of-trunk libc++ on Mac OS with clang you can:
   </p>

   <ul>
     <li><code>export DYLD_LIBRARY_PATH=path/to/build/lib</code>
     <li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++
          -I&lt;path-to-libcxx&gt;/include -L&lt;path-to-libcxx&gt;/lib
          test.cpp</code></li>
   </ul>

   <!--=====================================================================-->
   <h3>Linux</h3>
   <!--=====================================================================-->

   <p>
     You will need to keep the source tree of
     <a href="http://libcxxabi.llvm.org">libc++abi</a> available on your build
     machine and your copy of the libc++abi shared library must be placed where
     your linker will find it.
   </p>

   <p>
     Unfortunately you can't simply run clang with "-stdlib=libc++" at this
     point, as clang is set up to link for libc++ linked to libsupc++.  To get
     around this you'll have to set up your linker yourself (or patch clang).
     For example:
   </p>

   <ul>
     <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc</code></li>
   </ul>

   <p>
     Alternately, you could just add libc++abi to your libraries list, which in
     most situations will give the same result:
   </p>

   <ul>
     <li><code>clang++ -stdlib=libc++ helloworld.cpp -lc++abi</code></li>
   </ul>

   <!--=====================================================================-->
   <h2>Bug reports and patches</h2>
   <!--=====================================================================-->

   <p>
   If you think you've found a bug in libc++, please report it using
   the <a href="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you
   can post a message to the <a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a>
   mailing list or on IRC. Please include "libc++" in your subject.
   </p>

   <p>
   If you want to contribute a patch to libc++, the best place for that is
   <a href="http://llvm.org/docs/Phabricator.html">Phabricator</a>. Please
   include [libc++] in the subject and add cfe-commits as a subscriber.
   </p>

   <!--=====================================================================-->
   <h2 id="libsupcxx">Build on Linux using CMake and libsupc++.</h2>
   <!--=====================================================================-->

   <p>
      You will need libstdc++ in order to provide libsupc++.
   </p>

   <p>
      Figure out where the libsupc++ headers are on your system. On Ubuntu this
      is <code>/usr/include/c++/&lt;version&gt;</code> and
      <code>/usr/include/c++/&lt;version&gt;/&lt;target-triple&gt;</code>
   </p>

   <p>
      You can also figure this out by running
      <pre>
 $ echo | g++ -Wp,-v -x c++ - -fsyntax-only
 ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
 ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
 #include "..." search starts here:
 #include &lt;...&gt; search starts here:
  /usr/include/c++/4.7
  /usr/include/c++/4.7/x86_64-linux-gnu
  /usr/include/c++/4.7/backward
  /usr/lib/gcc/x86_64-linux-gnu/4.7/include
  /usr/local/include
  /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
  /usr/include/x86_64-linux-gnu
  /usr/include
 End of search list.
      </pre>

       Note the first two entries happen to be what we are looking for. This
       may not be correct on other platforms.
   </p>

   <p>
      We can now run CMake:
      <ul>
        <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
                 -DLIBCXX_CXX_ABI=libstdc++
                 -DLIBCXX_CXX_ABI_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
                 -DCMAKE_BUILD_TYPE=Release
                 -DCMAKE_INSTALL_PREFIX=/usr
                 &lt;libc++-source-dir&gt;</code></li>
        <li>You can also substitute <code>-DLIBCXX_CXX_ABI=libsupc++</code>
        above, which will cause the library to be linked to libsupc++ instead
        of libstdc++, but this is only recommended if you know that you will
        never need to link against libstdc++ in the same executable as libc++.
        GCC ships libsupc++ separately but only as a static library.  If a
        program also needs to link against libstdc++, it will provide its
        own copy of libsupc++ and this can lead to subtle problems.
        <li><code>make</code></li>
        <li><code>sudo make install</code></li>
      </ul>
      <p>
         You can now run clang with -stdlib=libc++.
      </p>
   </p>

   <!--=====================================================================-->
   <h2 id="libcxxrt">Build on Linux using CMake and libcxxrt.</h2>
   <!--=====================================================================-->

   <p>
      You will need to keep the source tree of
      <a href="https://github.com/pathscale/libcxxrt/">libcxxrt</a> available
      on your build machine and your copy of the libcxxrt shared library must
      be placed where your linker will find it.
   </p>

   <p>
      We can now run CMake:
      <ul>
        <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
                 -DLIBCXX_CXX_ABI=libcxxrt
                 -DLIBCXX_CXX_ABI_INCLUDE_PATHS="&lt;libcxxrt-source-dir&gt;/src"
                 -DCMAKE_BUILD_TYPE=Release
                 -DCMAKE_INSTALL_PREFIX=/usr
                 &lt;libc++-source-dir&gt;</code></li>
        <li><code>make</code></li>
        <li><code>sudo make install</code></li>
      </ul>
      <p>
         Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
         clang is set up to link for libc++ linked to libsupc++.  To get around this
         you'll have to set up your linker yourself (or patch clang).  For example,
         <ul>
           <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc</code></li>
         </ul>
         Alternately, you could just add libcxxrt to your libraries list, which in most
         situations will give the same result:
         <ul>
           <li><code>clang++ -stdlib=libc++ helloworld.cpp -lcxxrt</code></li>
         </ul>
      </p>
   </p>

   <!--=====================================================================-->
   <h2 id="local-abi">Using a local ABI library</h2>
   <!--=====================================================================-->
   <p>
     <strong>Note: This is not recommended in almost all cases.</strong><br>
     Generally these instructions should only be used when you can't install
     your ABI library.
   </p>
   <p>
     Normally you must link libc++ against a ABI shared library that the
     linker can find.  If you want to build and test libc++ against an ABI
     library not in the linker's path you need to set
     <code>-DLIBCXX_CXX_ABI_LIBRARY_PATH=/path/to/abi/lib</code> when
     configuring CMake.
   </p>
   <p>
     An example build using libc++abi would look like:
     <ul>
     <li><code>CC=clang CXX=clang++ cmake
               -DLIBCXX_CXX_ABI=libc++abi
               -DLIBCXX_CXX_ABI_INCLUDE_PATHS="/path/to/libcxxabi/include"
               -DLIBCXX_CXX_ABI_LIBRARY_PATH="/path/to/libcxxabi-build/lib"
               path/to/libcxx</code></li>
     <li><code>make</code></li>
     </ul>
   </p>
   <p>
     When testing libc++ LIT will automatically link against the proper ABI
     library.
   </p>

   <!--=====================================================================-->
   <h2>Design Documents</h2>
   <!--=====================================================================-->

 <ul>
 <li><a href="atomic_design.html"><tt>&lt;atomic&gt;</tt></a></li>
 <li><a href="type_traits_design.html"><tt>&lt;type_traits&gt;</tt></a></li>
 <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>
 <li><a href="debug_mode.html">Status of debug mode</a></li>
 <li><a href="lit_usage.html">LIT usage guide</a></li>
 </ul>

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	</div>

	<div id="content">
	<!--*********************************************************************-->
	<h1>"libc++" C++ Standard Library</h1>
	<!--*********************************************************************-->

	<p>libc++ is a new implementation of the C++ standard library, targeting
	C++11.</p>

	<p>All of the code in libc++ is <a
	href="http://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="http://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++-4.2 and
	clang (lack of C++11 language support disables some functionality). 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>
	</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>A list of features and changes for the next C++ standard, known here as
	"C++1z" (probably to be C++17) can be found <a href="cxx1z_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>
	Ports to other platforms are underway. Here are recent test
	results for <a href="results.Windows.html">Windows</a>
	and <a href="results.Linux.html">Linux</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="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.

	<p>
	On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
	Xcode 4.2 or later. However if you want to install tip-of-trunk from here
	(getting the bleeding edge), read on. However, be warned that Mac OS
	10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
	<code>/usr/lib</code>.
	</p>

	<p>To check out the code, use:</p>

	<ul>
	<li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
	</ul>

	<p>
	Note that for an in-tree build, you should check out libcxx to
	llvm/projects.
	</p>

	<p>
	The following instructions are for building libc++ on FreeBSD, Linux, or Mac
	using <a href="http://libcxxabi.llvm.org/">libc++abi</a> as the C++ ABI
	library. On Linux, it is also possible to use
	<a href="#libsupcxx">libsupc++</a> or <a href="#libcxxrt">libcxxrt</a>.
	</p>

	<p>In-tree build:</p>
	<ul>
	<li><code>cd where-you-want-to-live</code></li>
	<li>Check out libcxx and <a href="http://libcxxabi.llvm.org/">libcxxabi</a>
	into llvm/projects</li>
	<li><code>cd where-you-want-to-build</code></li>
	<li><code>mkdir build && cd build</code></li>
	<li><code>cmake path/to/llvm # Linux may require -DCMAKE_C_COMPILER=clang
	-DCMAKE_CXX_COMPILER=clang++</code></li>
	<li><code>make cxx</code></li>
	</ul>

	<p>Out-of-tree buildc:</p>
	<ul>
	<li><code>cd where-you-want-to-live</code></li>
	<li>Check out libcxx and llvm</li>
	<li>If not on a Mac, also check out
	<a href="http://libcxxabi.llvm.org/">libcxxabi</a></li>
	<li><code>cd where-you-want-to-build</code></li>
	<li><code>mkdir build && cd build</code></li>
	<li><code>cmake -DLLVM_PATH=path/to/llvm
	-DLIBCXX_CXX_ABI=libcxxabi
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS=path/to/libcxxabi/include
	-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
	path/to/libcxx
	</code></li>
	<li><code>make</code></li>
	</ul>

	<p>To run the tests:</p>
	<ul>
	<li><code>make check-libcxx</code></li>
	</ul>

	<p>If you wish to run a subset of the test suite:</p>
	<ul>
	<li><code>cd path/to/libcxx/libcxx</code></li>
	<li><code>alias lit='python path/to/llvm/utils/lit/lit.py'</code></li>
	<li><code>export
	LIBCXX_SITE_CONFIG=path/to/build/dir/projects/libcxx/test/lit.site.cfg
	</code></li>
	<li><code>lit -sv test/re/ # or whichever subset of tests you're interested
	in</code></li>
	</ul>
	<p>The above is currently quite inconvenient. Sorry! We're working on it!</p>

	<p>More information on using LIT can be found
	<a href="http://llvm.org/docs/CommandGuide/lit.html">here</a>. For more
	general information about the LLVM testing infrastructure, see the
	<a href="http://llvm.org/docs/TestingGuide.html">LLVM Testing Infrastructure
	Guide</a>
	</p>

	<p>
	Shared libraries for libc++ should now be present in llvm/build/lib. Note
	that it is safest to use this from its current location rather than
	replacing your system's libc++ (if it has one, if not, go right ahead).
	</p>

	<p>
	Mac users, remember to be careful when replacing the system's libc++.
	<strong>Your system will not be able to boot without a functioning
	libc++.</strong>
	</p>

	<!--=====================================================================-->
	<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>
	<li>
	On OS X v10.8 and older the CMake option
	<code>-DLIBCXX_LIBCPPABI_VERSION=""</code> must be used during
	configuration.
	</li>
	</ul>
	</p>

	<p>Send discussions to the
	<a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">clang mailing list</a>.</p>

	<!--=====================================================================-->
	<h2>Using libc++ in your programs</h2>
	<!--=====================================================================-->

	<!--=====================================================================-->
	<h3>FreeBSD and Mac OS X</h3>
	<!--=====================================================================-->

	<p>
	To use your system-installed libc++ with clang you can:
	</p>

	<ul>
	<li><code>clang++ -stdlib=libc++ test.cpp</code></li>
	<li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li>
	</ul>

	<p>
	To use your tip-of-trunk libc++ on Mac OS with clang you can:
	</p>

	<ul>
	<li><code>export DYLD_LIBRARY_PATH=path/to/build/lib</code>
	<li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++
	-I<path-to-libcxx>/include -L<path-to-libcxx>/lib
	test.cpp</code></li>
	</ul>

	<!--=====================================================================-->
	<h3>Linux</h3>
	<!--=====================================================================-->

	<p>
	You will need to keep the source tree of
	<a href="http://libcxxabi.llvm.org">libc++abi</a> available on your build
	machine and your copy of the libc++abi shared library must be placed where
	your linker will find it.
	</p>

	<p>
	Unfortunately you can't simply run clang with "-stdlib=libc++" at this
	point, as clang is set up to link for libc++ linked to libsupc++. To get
	around this you'll have to set up your linker yourself (or patch clang).
	For example:
	</p>

	<ul>
	<li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc</code></li>
	</ul>

	<p>
	Alternately, you could just add libc++abi to your libraries list, which in
	most situations will give the same result:
	</p>

	<ul>
	<li><code>clang++ -stdlib=libc++ helloworld.cpp -lc++abi</code></li>
	</ul>

	<!--=====================================================================-->
	<h2>Bug reports and patches</h2>
	<!--=====================================================================-->

	<p>
	If you think you've found a bug in libc++, please report it using
	the <a href="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you
	can post a message to the <a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a>
	mailing list or on IRC. Please include "libc++" in your subject.
	</p>

	<p>
	If you want to contribute a patch to libc++, the best place for that is
	<a href="http://llvm.org/docs/Phabricator.html">Phabricator</a>. Please
	include [libc++] in the subject and add cfe-commits as a subscriber.
	</p>

	<!--=====================================================================-->
	<h2 id="libsupcxx">Build on Linux using CMake and libsupc++.</h2>
	<!--=====================================================================-->

	<p>
	You will need libstdc++ in order to provide libsupc++.
	</p>

	<p>
	Figure out where the libsupc++ headers are on your system. On Ubuntu this
	is <code>/usr/include/c++/<version></code> and
	<code>/usr/include/c++/<version>/<target-triple></code>
	</p>

	<p>
	You can also figure this out by running
	<pre>
	$ echo \| g++ -Wp,-v -x c++ - -fsyntax-only
	ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
	ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
	#include "..." search starts here:
	#include <...> search starts here:
	/usr/include/c++/4.7
	/usr/include/c++/4.7/x86_64-linux-gnu
	/usr/include/c++/4.7/backward
	/usr/lib/gcc/x86_64-linux-gnu/4.7/include
	/usr/local/include
	/usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
	/usr/include/x86_64-linux-gnu
	/usr/include
	End of search list.
	</pre>

	Note the first two entries happen to be what we are looking for. This
	may not be correct on other platforms.
	</p>

	<p>
	We can now run CMake:
	<ul>
	<li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
	-DLIBCXX_CXX_ABI=libstdc++
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
	-DCMAKE_BUILD_TYPE=Release
	-DCMAKE_INSTALL_PREFIX=/usr
	<libc++-source-dir></code></li>
	<li>You can also substitute <code>-DLIBCXX_CXX_ABI=libsupc++</code>
	above, which will cause the library to be linked to libsupc++ instead
	of libstdc++, but this is only recommended if you know that you will
	never need to link against libstdc++ in the same executable as libc++.
	GCC ships libsupc++ separately but only as a static library. If a
	program also needs to link against libstdc++, it will provide its
	own copy of libsupc++ and this can lead to subtle problems.
	<li><code>make</code></li>
	<li><code>sudo make install</code></li>
	</ul>
	<p>
	You can now run clang with -stdlib=libc++.
	</p>
	</p>

	<!--=====================================================================-->
	<h2 id="libcxxrt">Build on Linux using CMake and libcxxrt.</h2>
	<!--=====================================================================-->

	<p>
	You will need to keep the source tree of
	<a href="https://github.com/pathscale/libcxxrt/">libcxxrt</a> available
	on your build machine and your copy of the libcxxrt shared library must
	be placed where your linker will find it.
	</p>

	<p>
	We can now run CMake:
	<ul>
	<li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
	-DLIBCXX_CXX_ABI=libcxxrt
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS="<libcxxrt-source-dir>/src"
	-DCMAKE_BUILD_TYPE=Release
	-DCMAKE_INSTALL_PREFIX=/usr
	<libc++-source-dir></code></li>
	<li><code>make</code></li>
	<li><code>sudo make install</code></li>
	</ul>
	<p>
	Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
	clang is set up to link for libc++ linked to libsupc++. To get around this
	you'll have to set up your linker yourself (or patch clang). For example,
	<ul>
	<li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc</code></li>
	</ul>
	Alternately, you could just add libcxxrt to your libraries list, which in most
	situations will give the same result:
	<ul>
	<li><code>clang++ -stdlib=libc++ helloworld.cpp -lcxxrt</code></li>
	</ul>
	</p>
	</p>

	<!--=====================================================================-->
	<h2 id="local-abi">Using a local ABI library</h2>
	<!--=====================================================================-->
	<p>
	<strong>Note: This is not recommended in almost all cases.</strong><br>
	Generally these instructions should only be used when you can't install
	your ABI library.
	</p>
	<p>
	Normally you must link libc++ against a ABI shared library that the
	linker can find. If you want to build and test libc++ against an ABI
	library not in the linker's path you need to set
	<code>-DLIBCXX_CXX_ABI_LIBRARY_PATH=/path/to/abi/lib</code> when
	configuring CMake.
	</p>
	<p>
	An example build using libc++abi would look like:
	<ul>
	<li><code>CC=clang CXX=clang++ cmake
	-DLIBCXX_CXX_ABI=libc++abi
	-DLIBCXX_CXX_ABI_INCLUDE_PATHS="/path/to/libcxxabi/include"
	-DLIBCXX_CXX_ABI_LIBRARY_PATH="/path/to/libcxxabi-build/lib"
	path/to/libcxx</code></li>
	<li><code>make</code></li>
	</ul>
	</p>
	<p>
	When testing libc++ LIT will automatically link against the proper ABI
	library.
	</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="http://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/">Excellent notes by Marshall Clow</a></li>
	<li><a href="debug_mode.html">Status of debug mode</a></li>
	<li><a href="lit_usage.html">LIT usage guide</a></li>
	</ul>

	</div>
	</body>
	</html>