35d775d0e4
Okay, so this actually does more than just that. I've rearranged most of the information on the page to try to make it more helpful and flow better. Essentially, the differences between Mac and Linux, the various ABI libraries, and in-tree versus out-of-tree builds were cluttering things. To clean up, I've done the following: * Only describe the cmake process. buildit doesn't work out of the box on Linux, and we need to stop having duplicates for every process. * Use libc++abi for the default instructions. This works on the major platforms. * Describe both in-tree and out-of-tree builds. Previously it wasn't clear that in-tree builds were even possible for libc++. * Separate the documentation about using libc++ from that about building and testing libc++. git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@215358 91177308-0d34-0410-b5e6-96231b3b80d8
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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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>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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|
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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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