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19 <label>libc++ Info</label>
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34 <!--*********************************************************************-->
35 <h1>"libc++" C++ Standard Library</h1>
36 <!--*********************************************************************-->
38 <p>libc++ is a new implementation of the C++ standard library, targeting
41 <p>All of the code in libc++ is <a
42 href="http://llvm.org/docs/DeveloperPolicy.html#license">dual licensed</a>
43 under the MIT license and the UIUC License (a BSD-like license).</p>
45 <!--=====================================================================-->
46 <h2>New Documentation Coming Soon!</h2>
47 <!--=====================================================================-->
49 <p> Looking for documentation on how to use, build and test libc++? If so
50 checkout the new libc++ documentation.</p>
52 <p><a href="http://libcxx.llvm.org/docs/">
53 Click here for the new libc++ documentation.</a></p>
55 <!--=====================================================================-->
56 <h2 id="goals">Features and Goals</h2>
57 <!--=====================================================================-->
60 <li>Correctness as defined by the C++11 standard.</li>
61 <li>Fast execution.</li>
62 <li>Minimal memory use.</li>
63 <li>Fast compile times.</li>
64 <li>ABI compatibility with gcc's libstdc++ for some low-level features
65 such as exception objects, rtti and memory allocation.</li>
66 <li>Extensive unit tests.</li>
69 <!--=====================================================================-->
70 <h2 id="why">Why a new C++ Standard Library for C++11?</h2>
71 <!--=====================================================================-->
73 <p>After its initial introduction, many people have asked "why start a new
74 library instead of contributing to an existing library?" (like Apache's
75 libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
76 reasons, but some of the major ones are:</p>
79 <li><p>From years of experience (including having implemented the standard
80 library before), we've learned many things about implementing
81 the standard containers which require ABI breakage and fundamental changes
82 to how they are implemented. For example, it is generally accepted that
83 building std::string using the "short string optimization" instead of
84 using Copy On Write (COW) is a superior approach for multicore
85 machines (particularly in C++11, which has rvalue references). Breaking
86 ABI compatibility with old versions of the library was
87 determined to be critical to achieving the performance goals of
90 <li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
91 of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
92 independently extended to support C++11, but this would be a fork of the
93 codebase (which is often seen as worse for a project than starting a new
94 independent one). Another problem with libstdc++ is that it is tightly
95 integrated with G++ development, tending to be tied fairly closely to the
96 matching version of G++.</p>
99 <li><p>STLport and the Apache libstdcxx library are two other popular
100 candidates, but both lack C++11 support. Our experience (and the
101 experience of libstdc++ developers) is that adding support for C++11 (in
102 particular rvalue references and move-only types) requires changes to
103 almost every class and function, essentially amounting to a rewrite.
104 Faced with a rewrite, we decided to start from scratch and evaluate every
105 design decision from first principles based on experience.</p>
107 <p>Further, both projects are apparently abandoned: STLport 5.2.1 was
108 released in Oct'08, and STDCXX 4.2.1 in May'08.</p>
112 <!--=====================================================================-->
113 <h2 id="requirements">Platform Support</h2>
114 <!--=====================================================================-->
117 libc++ is known to work on the following platforms, using g++-4.2 and
118 clang (lack of C++11 language support disables some functionality). Note
119 that functionality provided by <atomic> is only functional with
124 <li>Mac OS X i386</li>
125 <li>Mac OS X x86_64</li>
126 <li>FreeBSD 10+ i386</li>
127 <li>FreeBSD 10+ x86_64</li>
128 <li>FreeBSD 10+ ARM</li>
131 <!--=====================================================================-->
132 <h2 id="dir-structure">Current Status</h2>
133 <!--=====================================================================-->
135 <p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p>
136 <p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p>
137 <p>libc++ is also a 100% complete C++14 implementation. A list of new features and changes for
138 C++14 can be found <a href="cxx1y_status.html">here</a>.</p>
139 <p>A list of features and changes for the next C++ standard, known here as
140 "C++1z" (probably to be C++17) can be found <a href="cxx1z_status.html">here</a>.</p>
141 <p>Implementation of the post-c++14 Technical Specifications is in progress. A list of features and
142 the current status of these features can be found <a href="ts1z_status.html">here</a>.</p>
144 <!--======================================================================-->
145 <h2 id="buildbots">Build Bots</h2>
146 <!--======================================================================-->
147 <p>The latest libc++ build results can be found at the following locations.</p>
149 <li><a href="http://lab.llvm.org:8011/console">
150 Buildbot libc++ builders
152 <li><a href="http://lab.llvm.org:8080/green/view/Libcxx/">
153 Jenkins libc++ builders
157 <!--=====================================================================-->
158 <h2>Get it and get involved!</h2>
159 <!--=====================================================================-->
161 <p>First please review our
162 <a href="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
164 The documentation for building and using libc++ can be found below.
166 <li><a href="http://libcxx.llvm.org/docs/UsingLibcxx.html">
167 <b>Using libc++</b></a>
168 Documentation on using the library in your programs</li>
169 <li><a href="http://libcxx.llvm.org/docs/BuildingLibcxx.html">
170 <b>Building libc++</b></a>
171 Documentation on building the library using CMake</li>
172 <li><a href="http://libcxx.llvm.org/docs/TestingLibcxx.html">
173 <b>Testing libc++</b></a>
174 Documentation for developers wishing to test the library</li>
177 <!--=====================================================================-->
178 <h3>Notes and Known Issues</h3>
179 <!--=====================================================================-->
184 Building libc++ with <code>-fno-rtti</code> is not supported. However
185 linking against it with <code>-fno-rtti</code> is supported.
188 On OS X v10.8 and older the CMake option
189 <code>-DLIBCXX_LIBCPPABI_VERSION=""</code> must be used during
195 <p>Send discussions to the
196 <a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">clang mailing list</a>.</p>
198 <!--=====================================================================-->
199 <h2>Bug reports and patches</h2>
200 <!--=====================================================================-->
203 If you think you've found a bug in libc++, please report it using
204 the <a href="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you
205 can post a message to the <a href="http://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a>
206 mailing list or on IRC. Please include "libc++" in your subject.
210 If you want to contribute a patch to libc++, the best place for that is
211 <a href="http://llvm.org/docs/Phabricator.html">Phabricator</a>. Please
212 include [libc++] in the subject and add cfe-commits as a subscriber.
215 <!--=====================================================================-->
216 <h2>Design Documents</h2>
217 <!--=====================================================================-->
220 <li><a href="atomic_design.html"><tt><atomic></tt></a></li>
221 <li><a href="type_traits_design.html"><tt><type_traits></tt></a></li>
222 <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>