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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 id="goals">Features and Goals</h2>
47 <!--=====================================================================-->
50 <li>Correctness as defined by the C++11 standard.</li>
51 <li>Fast execution.</li>
52 <li>Minimal memory use.</li>
53 <li>Fast compile times.</li>
54 <li>ABI compatibility with gcc's libstdc++ for some low-level features
55 such as exception objects, rtti and memory allocation.</li>
56 <li>Extensive unit tests.</li>
59 <!--=====================================================================-->
60 <h2 id="why">Why a new C++ Standard Library for C++11?</h2>
61 <!--=====================================================================-->
63 <p>After its initial introduction, many people have asked "why start a new
64 library instead of contributing to an existing library?" (like Apache's
65 libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
66 reasons, but some of the major ones are:</p>
69 <li><p>From years of experience (including having implemented the standard
70 library before), we've learned many things about implementing
71 the standard containers which require ABI breakage and fundamental changes
72 to how they are implemented. For example, it is generally accepted that
73 building std::string using the "short string optimization" instead of
74 using Copy On Write (COW) is a superior approach for multicore
75 machines (particularly in C++11, which has rvalue references). Breaking
76 ABI compatibility with old versions of the library was
77 determined to be critical to achieving the performance goals of
80 <li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
81 of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
82 independently extended to support C++11, but this would be a fork of the
83 codebase (which is often seen as worse for a project than starting a new
84 independent one). Another problem with libstdc++ is that it is tightly
85 integrated with G++ development, tending to be tied fairly closely to the
86 matching version of G++.</p>
89 <li><p>STLport and the Apache libstdcxx library are two other popular
90 candidates, but both lack C++11 support. Our experience (and the
91 experience of libstdc++ developers) is that adding support for C++11 (in
92 particular rvalue references and move-only types) requires changes to
93 almost every class and function, essentially amounting to a rewrite.
94 Faced with a rewrite, we decided to start from scratch and evaluate every
95 design decision from first principles based on experience.</p>
97 <p>Further, both projects are apparently abandoned: STLport 5.2.1 was
98 released in Oct'08, and STDCXX 4.2.1 in May'08.</p>
102 <!--=====================================================================-->
103 <h2 id="requirements">Platform Support</h2>
104 <!--=====================================================================-->
107 libc++ is known to work on the following platforms, using g++-4.2 and
108 clang (lack of C++11 language support disables some functionality). Note
109 that functionality provided by <atomic> is only functional with
114 <li>Mac OS X i386</li>
115 <li>Mac OS X x86_64</li>
116 <li>FreeBSD 10+ i386</li>
117 <li>FreeBSD 10+ x86_64</li>
118 <li>FreeBSD 10+ ARM</li>
121 <!--=====================================================================-->
122 <h2 id="dir-structure">Current Status</h2>
123 <!--=====================================================================-->
125 <p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p>
126 <p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p>
127 <p>libc++ is also a 100% complete C++14 implementation. A list of new features and changes for
128 C++14 can be found <a href="cxx1y_status.html">here</a>.</p>
129 <p>Implementation of the post-c++14 Technical Specifications is in progress. A list of features and
130 the current status of these features can be found <a href="ts1z_status.html">here</a>.</p>
132 Ports to other platforms are underway. Here are recent test
133 results for <a href="results.Windows.html">Windows</a>
134 and <a href="results.Linux.html">Linux</a>.
137 <!--======================================================================-->
138 <h2 id="dir-structure">Build Bots</h2>
139 <!--======================================================================-->
140 <p>These are the libc++ build bots</p>
142 <li><a href="http://lab.llvm.org:8013/builders/libcxx_clang-x86_64-darwin11-RA">
143 clang-libcxxabi-x86_64-darwin11
145 <li><a href="http://llvm-amd64.freebsd.your.org/b/builders/libcxx-amd64-freebsd">
146 clang-libcxxrt-x86_64-freebsd10
148 <li><a href="http://llvm-amd64.freebsd.your.org/b/builders/libcxx-i386-freebsd">
149 clang-libcxxrt-i386-freebsd10
151 <li><a href="http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-debian">
152 clang-libcxxabi-x86_64-linux-debian
156 <!--=====================================================================-->
157 <h2>Get it and get involved!</h2>
158 <!--=====================================================================-->
160 <p>First please review our
161 <a href="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
164 On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
165 Xcode 4.2 or later. However if you want to install tip-of-trunk from here
166 (getting the bleeding edge), read on. However, be warned that Mac OS
167 10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
168 <code>/usr/lib</code>.
171 <p>To check out the code, use:</p>
174 <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
178 Note that for an in-tree build, you should check out libcxx to
183 The following instructions are for building libc++ on FreeBSD, Linux, or Mac
184 using <a href="http://libcxxabi.llvm.org/">libc++abi</a> as the C++ ABI
185 library. On Linux, it is also possible to use
186 <a href="#libsupcxx">libsupc++</a> or <a href="#libcxxrt">libcxxrt</a>.
189 <p>In-tree build:</p>
191 <li>Check out libcxx and <a href="http://libcxxabi.llvm.org/">libcxxabi</a>
192 into llvm/projects</li>
193 <li><code>cd llvm</code></li>
194 <li><code>mkdir build && cd build</code></li>
195 <li><code>cmake .. # Linux may require -DCMAKE_C_COMPILER=clang
196 -DCMAKE_CXX_COMPILER=clang++</code></li>
197 <li><code>make cxx</code></li>
200 <p>Out-of-tree build:</p>
202 <li>Check out libcxx</li>
203 <li>If not on a Mac, also check out
204 <a href="http://libcxxabi.llvm.org/">libcxxabi</a></li>
205 <li><code>cd libcxx</code></li>
206 <li><code>mkdir build && cd build</code></li>
207 <li><code>cmake -DLIBCXX_CXX_ABI=libcxxabi
208 -DLIBCXX_LIBCXXABI_INCLUDE_PATHS=path/to/libcxxabi/include
209 -DLIT_EXECUTABLE=path/to/llvm/utils/lit/lit.py .. # Linux may require
210 -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
211 <li><code>make</code></li>
214 <p>To run the tests:</p>
216 <li><code>make check-libcxx</code></li>
219 <p>If you wish to run a subset of the test suite:</p>
221 <li><code>cd path/to/libcxx/libcxx</code></li>
222 <li><code>alias lit='python path/to/llvm/utils/lit/lit.py'</code></li>
223 <li><code>ln -s path/to/build/dir/projects/libcxx/test/lit.site.cfg
224 test/lit.site.cfg</code></li>
225 <li><code>lit -sv test/re/ # or whichever subset of tests you're interested
228 <p>The above is currently quite inconvenient. Sorry! We're working on it!</p>
230 <p>More information on using LIT can be found
231 <a href="http://llvm.org/docs/CommandGuide/lit.html">here</a>. For more
232 general information about the LLVM testing infrastructure, see the
233 <a href="http://llvm.org/docs/TestingGuide.html">LLVM Testing Infrastructure
238 Shared libraries for libc++ should now be present in llvm/build/lib. Note
239 that it is safest to use this from its current location rather than
240 replacing your system's libc++ (if it has one, if not, go right ahead).
244 Mac users, remember to be careful when replacing the system's libc++.
245 <strong>Your system will not be able to boot without a funcioning
249 <!--=====================================================================-->
251 <!--=====================================================================-->
254 Building libc++ with <code>-fno-rtti</code> is not supported. However
255 linking against it with <code>-fno-rtti</code> is supported.
258 <p>Send discussions to the
259 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>.</p>
261 <!--=====================================================================-->
262 <h2>Using libc++ in your programs</h2>
263 <!--=====================================================================-->
265 <!--=====================================================================-->
266 <h3>FreeBSD and Mac OS X</h3>
267 <!--=====================================================================-->
270 To use your system-installed libc++ with clang you can:
274 <li><code>clang++ -stdlib=libc++ test.cpp</code></li>
275 <li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li>
279 To use your tip-of-trunk libc++ on Mac OS with clang you can:
283 <li><code>export DYLD_LIBRARY_PATH=path/to/build/lib</code>
284 <li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++
285 -I<path-to-libcxx>/include -L<path-to-libcxx>/lib
289 <!--=====================================================================-->
291 <!--=====================================================================-->
294 You will need to keep the source tree of
295 <a href="http://libcxxabi.llvm.org">libc++abi</a> available on your build
296 machine and your copy of the libc++abi shared library must be placed where
297 your linker will find it.
301 Unfortunately you can't simply run clang with "-stdlib=libc++" at this
302 point, as clang is set up to link for libc++ linked to libsupc++. To get
303 around this you'll have to set up your linker yourself (or patch clang).
308 <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc</code></li>
312 Alternately, you could just add libc++abi to your libraries list, which in
313 most situations will give the same result:
317 <li><code>clang++ -stdlib=libc++ helloworld.cpp -lc++abi</code></li>
320 <!--=====================================================================-->
321 <h2>Bug reports and patches</h2>
322 <!--=====================================================================-->
325 If you think you've found a bug in libc++, please report it using
326 the <a href="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you
327 can post a message to the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
328 mailing list or on IRC. Please include "libc++" in your subject.
332 If you want to contribute a patch to libc++, the best place for that is the
333 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
334 mailing list. Please include "libc++" and "PATCH" in your subject.
337 <!--=====================================================================-->
338 <h2 id="libsupcxx">Build on Linux using CMake and libsupc++.</h2>
339 <!--=====================================================================-->
342 You will need libstdc++ in order to provide libsupc++.
346 Figure out where the libsupc++ headers are on your system. On Ubuntu this
347 is <code>/usr/include/c++/<version></code> and
348 <code>/usr/include/c++/<version>/<target-triple></code>
352 You can also figure this out by running
354 $ echo | g++ -Wp,-v -x c++ - -fsyntax-only
355 ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
356 ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
357 #include "..." search starts here:
358 #include <...> search starts here:
360 /usr/include/c++/4.7/x86_64-linux-gnu
361 /usr/include/c++/4.7/backward
362 /usr/lib/gcc/x86_64-linux-gnu/4.7/include
364 /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
365 /usr/include/x86_64-linux-gnu
370 Note the first two entries happen to be what we are looking for. This
371 may not be correct on other platforms.
375 We can now run CMake:
377 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
378 -DLIBCXX_CXX_ABI=libstdc++
379 -DLIBCXX_LIBSUPCXX_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
380 -DCMAKE_BUILD_TYPE=Release
381 -DCMAKE_INSTALL_PREFIX=/usr
382 <libc++-source-dir></code></li>
383 <li>You can also substitute <code>-DLIBCXX_CXX_ABI=libsupc++</code>
384 above, which will cause the library to be linked to libsupc++ instead
385 of libstdc++, but this is only recommended if you know that you will
386 never need to link against libstdc++ in the same executable as libc++.
387 GCC ships libsupc++ separately but only as a static library. If a
388 program also needs to link against libstdc++, it will provide its
389 own copy of libsupc++ and this can lead to subtle problems.
390 <li><code>make</code></li>
391 <li><code>sudo make install</code></li>
394 You can now run clang with -stdlib=libc++.
398 <!--=====================================================================-->
399 <h2 id="libcxxrt">Build on Linux using CMake and libcxxrt.</h2>
400 <!--=====================================================================-->
403 You will need to keep the source tree of
404 <a href="https://github.com/pathscale/libcxxrt/">libcxxrt</a> available
405 on your build machine and your copy of the libcxxrt shared library must
406 be placed where your linker will find it.
410 We can now run CMake:
412 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
413 -DLIBCXX_CXX_ABI=libcxxrt
414 -DLIBCXX_LIBCXXRT_INCLUDE_PATHS="<libcxxrt-source-dir>/src"
415 -DCMAKE_BUILD_TYPE=Release
416 -DCMAKE_INSTALL_PREFIX=/usr
417 <libc++-source-dir></code></li>
418 <li><code>make</code></li>
419 <li><code>sudo make install</code></li>
422 Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
423 clang is set up to link for libc++ linked to libsupc++. To get around this
424 you'll have to set up your linker yourself (or patch clang). For example,
426 <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc</code></li>
428 Alternately, you could just add libcxxrt to your libraries list, which in most
429 situations will give the same result:
431 <li><code>clang++ -stdlib=libc++ helloworld.cpp -lcxxrt</code></li>
436 <!--=====================================================================-->
437 <h2>Design Documents</h2>
438 <!--=====================================================================-->
441 <li><a href="atomic_design.html"><tt><atomic></tt></a></li>
442 <li><a href="type_traits_design.html"><tt><type_traits></tt></a></li>
443 <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>
444 <li><a href="debug_mode.html">Status of debug mode</a></li>