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Chris Lattnera535ffd2010-05-11 20:53:16 +000025 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
26 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
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34 <!--*********************************************************************-->
35 <h1>"libc++" C++ Standard Library</h1>
36 <!--*********************************************************************-->
Howard Hinnantd2bb0322010-08-22 01:04:38 +000037
Howard Hinnantbc8d3f92010-05-11 19:42:16 +000038 <p>libc++ is a new implementation of the C++ standard library, targeting
Howard Hinnantaf347342012-07-19 15:57:51 +000039 C++11.</p>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +000040
Chris Lattnerf38bc6e2010-11-16 21:40:19 +000041 <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>
Howard Hinnantd2bb0322010-08-22 01:04:38 +000044
Howard Hinnantbc8d3f92010-05-11 19:42:16 +000045 <!--=====================================================================-->
46 <h2 id="goals">Features and Goals</h2>
47 <!--=====================================================================-->
Howard Hinnantd2bb0322010-08-22 01:04:38 +000048
Howard Hinnantbc8d3f92010-05-11 19:42:16 +000049 <ul>
Howard Hinnantaf347342012-07-19 15:57:51 +000050 <li>Correctness as defined by the C++11 standard.</li>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +000051 <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>
57 </ul>
58
59 <!--=====================================================================-->
Marshall Clowfaa17162012-11-14 16:31:15 +000060 <h2 id="why">Why a new C++ Standard Library for C++11?</h2>
Chris Lattner24173b82010-05-12 22:21:15 +000061 <!--=====================================================================-->
Howard Hinnantd2bb0322010-08-22 01:04:38 +000062
Chris Lattner24173b82010-05-12 22:21:15 +000063 <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>
Howard Hinnantd2bb0322010-08-22 01:04:38 +000067
Chris Lattner24173b82010-05-12 22:21:15 +000068 <ul>
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
Marshall Clowfaa17162012-11-14 16:31:15 +000075 machines (particularly in C++11, which has rvalue references). Breaking
Chris Lattnera5058d92010-05-12 22:30:22 +000076 ABI compatibility with old versions of the library was
Chris Lattner24173b82010-05-12 22:21:15 +000077 determined to be critical to achieving the performance goals of
78 libc++.</p></li>
Howard Hinnantd2bb0322010-08-22 01:04:38 +000079
Chris Lattner24173b82010-05-12 22:21:15 +000080 <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
Marshall Clowfaa17162012-11-14 16:31:15 +000082 independently extended to support C++11, but this would be a fork of the
Chris Lattnerf3382492010-05-12 22:33:00 +000083 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>
Chris Lattner24173b82010-05-12 22:21:15 +000087 </li>
88
89 <li><p>STLport and the Apache libstdcxx library are two other popular
Marshall Clowfaa17162012-11-14 16:31:15 +000090 candidates, but both lack C++11 support. Our experience (and the
Howard Hinnantaf347342012-07-19 15:57:51 +000091 experience of libstdc++ developers) is that adding support for C++11 (in
Chris Lattner24173b82010-05-12 22:21:15 +000092 particular rvalue references and move-only types) requires changes to
93 almost every class and function, essentially amounting to a rewrite.
Chris Lattnerbfa808e2010-05-12 22:34:21 +000094 Faced with a rewrite, we decided to start from scratch and evaluate every
95 design decision from first principles based on experience.</p>
Howard Hinnantd2bb0322010-08-22 01:04:38 +000096
Chris Lattner24173b82010-05-12 22:21:15 +000097 <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>
99
100 </ul>
101
102 <!--=====================================================================-->
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000103 <h2 id="requirements">Platform Support</h2>
104 <!--=====================================================================-->
105
106 <p>libc++ is known to work on the following platforms, using g++-4.2 and
Howard Hinnantaf347342012-07-19 15:57:51 +0000107 clang (lack of C++11 language support disables some functionality).</p>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000108
109 <ul>
110 <li>Mac OS X i386</li>
111 <li>Mac OS X x86_64</li>
112 </ul>
113
114 <!--=====================================================================-->
115 <h2 id="dir-structure">Current Status</h2>
116 <!--=====================================================================-->
117
Howard Hinnantb0895ff2012-11-27 18:52:32 +0000118 <p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p>
Michael J. Spencerdb8a0302012-12-31 19:34:21 +0000119 <p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p>
Marshall Clow874ec672014-04-03 02:38:12 +0000120 <p>libc++ is also a 100% complete C++14 implementation. A list of new features and changes for
Marshall Clowe4915d92014-04-03 02:35:29 +0000121 C++14 can be found <a href="cxx1y_status.html">here</a>.</p>
Marshall Clowd2f0b5c2014-06-02 23:37:13 +0000122 <p>Implementation of the post-c++14 Technical Specifications is in progress. A list of features and
123 the current status of these features can be found <a href="ts1z_status.html">here</a>.</p>
Howard Hinnant0cbb3a12011-09-28 15:44:39 +0000124 <p>
Howard Hinnantee7a0bf2012-07-31 21:30:28 +0000125 Ports to other platforms are underway. Here are recent test
126 results for <a href="results.Windows.html">Windows</a>
127 and <a href="results.Linux.html">Linux</a>.
Howard Hinnant0cbb3a12011-09-28 15:44:39 +0000128 </p>
129
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000130 <!--=====================================================================-->
131 <h2>Get it and get involved!</h2>
132 <!--=====================================================================-->
Howard Hinnantd2bb0322010-08-22 01:04:38 +0000133
Howard Hinnant2481cba2011-09-30 16:58:02 +0000134 <p>First please review our
135 <a href="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
136
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000137 <p>To check out the code, use:</p>
Howard Hinnantd2bb0322010-08-22 01:04:38 +0000138
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000139 <ul>
Chris Lattner4b748952010-05-11 20:37:52 +0000140 <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
Howard Hinnant65451f12011-01-27 23:18:19 +0000141 </ul>
142
Howard Hinnant704f09b2011-11-17 17:14:16 +0000143 <p>
Howard Hinnant22b781b2012-11-06 21:31:37 +0000144 On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
Howard Hinnant704f09b2011-11-17 17:14:16 +0000145 Xcode 4.2 or later. However if you want to install tip-of-trunk from here
Howard Hinnant271a1c02012-04-03 15:08:42 +0000146 (getting the bleeding edge), read on. However, be warned that Mac OS
147 10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
148 <code>/usr/lib</code>.
Howard Hinnant704f09b2011-11-17 17:14:16 +0000149 </p>
150
Howard Hinnant65451f12011-01-27 23:18:19 +0000151 <p>
152 Next:
153 </p>
154
155 <ul>
156 <li><code>cd libcxx/lib</code></li>
157 <li><code>export TRIPLE=-apple-</code></li>
158 <li><code>./buildit</code></li>
Howard Hinnant22b781b2012-11-06 21:31:37 +0000159 <li><code>ln -sf libc++.1.dylib libc++.dylib</code></li>
Howard Hinnant65451f12011-01-27 23:18:19 +0000160 </ul>
161
162 <p>
Howard Hinnant22b781b2012-11-06 21:31:37 +0000163 That should result in a libc++.1.dylib and libc++.dylib. The safest thing
164 to do is to use it from where your libcxx is installed instead of replacing
165 these in your Mac OS.
Howard Hinnant65451f12011-01-27 23:18:19 +0000166 </p>
167
Howard Hinnant65451f12011-01-27 23:18:19 +0000168 <p>
Howard Hinnant22b781b2012-11-06 21:31:37 +0000169 To use your system-installed libc++ with clang you can:
Howard Hinnant65451f12011-01-27 23:18:19 +0000170 </p>
171
172 <ul>
173 <li><code>clang++ -stdlib=libc++ test.cpp</code></li>
Howard Hinnantaf347342012-07-19 15:57:51 +0000174 <li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000175 </ul>
176
Howard Hinnant22b781b2012-11-06 21:31:37 +0000177 <p>
178 To use your tip-of-trunk libc++ on Mac OS with clang you can:
179 </p>
180
181 <ul>
182 <li><code>export DYLD_LIBRARY_PATH=&lt;path-to-libcxx&gt;/lib</code>
183 <li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++
184 -I&lt;path-to-libcxx&gt;/include -L&lt;path-to-libcxx&gt;/lib
185 test.cpp</code></li>
186 </ul>
187
Marshall Clow08a0b482012-08-22 00:57:11 +0000188 <p>To run the libc++ test suite (recommended):</p>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000189
190 <ul>
Chris Lattner4b748952010-05-11 20:37:52 +0000191 <li><code>cd libcxx/test</code></li>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000192 <li><code>./testit</code></li>
Howard Hinnantf5d76a72011-06-22 12:13:55 +0000193 <ul>
Howard Hinnant22b781b2012-11-06 21:31:37 +0000194 <li>You can alter the command line options <code>testit</code> uses
195 with <code>export OPTIONS="whatever you need"</code></li>
Howard Hinnantf5d76a72011-06-22 12:13:55 +0000196 </ul>
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000197 </ul>
198
Howard Hinnant51065652012-05-20 13:03:53 +0000199 <!--=====================================================================-->
200 <h3>Notes</h3>
201 <!--=====================================================================-->
202
203<p>
204Building libc++ with <code>-fno-rtti</code> is not supported. However linking
205against it with <code>-fno-rtti</code> is supported.
206</p>
207
Howard Hinnantd2bb0322010-08-22 01:04:38 +0000208 <p>Send discussions to the
Howard Hinnant8c217372010-05-11 19:53:34 +0000209 (<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p>
210
Howard Hinnant56f0d5b2010-10-05 16:44:40 +0000211 <!--=====================================================================-->
Marshall Clow992f9d52014-04-03 03:13:12 +0000212 <h2>Bug reports and patches</h2>
213 <!--=====================================================================-->
214
215<p>
216If you think you've found a bug in libc++, please report it using
217the <a href="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you
Marshall Clow3f357192014-04-07 07:28:33 +0000218can post a message to the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
Marshall Clow992f9d52014-04-03 03:13:12 +0000219mailing list or on IRC. Please include "libc++" in your subject.
220</p>
221
222<p>
223If you want to contribute a patch to libc++, the best place for that is the
224<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
225mailing list. Please include "libc++" and "PATCH" in your subject.
226</p>
227
228 <!--=====================================================================-->
Michael J. Spencerdb8a0302012-12-31 19:34:21 +0000229 <h2>Build on Linux using CMake and libsupc++.</h2>
230 <!--=====================================================================-->
231
232 <p>
233 You will need libstdc++ in order to provide libsupc++.
234 </p>
235
236 <p>
237 Figure out where the libsupc++ headers are on your system. On Ubuntu this
238 is <code>/usr/include/c++/&lt;version&gt;</code> and
239 <code>/usr/include/c++/&lt;version&gt;/&lt;target-triple&gt;</code>
240 </p>
241
242 <p>
243 You can also figure this out by running
244 <pre>
245$ echo | g++ -Wp,-v -x c++ - -fsyntax-only
246ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
247ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
248#include "..." search starts here:
249#include &lt;...&gt; search starts here:
250 /usr/include/c++/4.7
251 /usr/include/c++/4.7/x86_64-linux-gnu
252 /usr/include/c++/4.7/backward
253 /usr/lib/gcc/x86_64-linux-gnu/4.7/include
254 /usr/local/include
255 /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
256 /usr/include/x86_64-linux-gnu
257 /usr/include
258End of search list.
259 </pre>
260
261 Note the first two entries happen to be what we are looking for. This
262 may not be correct on other platforms.
263 </p>
264
265 <p>
266 We can now run CMake:
267 <ul>
268 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
Peter Collingbourned0d308f2013-10-06 22:13:19 +0000269 -DLIBCXX_CXX_ABI=libstdc++
Michael J. Spencerdb8a0302012-12-31 19:34:21 +0000270 -DLIBCXX_LIBSUPCXX_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
271 -DCMAKE_BUILD_TYPE=Release
272 -DCMAKE_INSTALL_PREFIX=/usr
273 &lt;libc++-source-dir&gt;</code></li>
Peter Collingbourned0d308f2013-10-06 22:13:19 +0000274 <li>You can also substitute <code>-DLIBCXX_CXX_ABI=libsupc++</code>
275 above, which will cause the library to be linked to libsupc++ instead
276 of libstdc++, but this is only recommended if you know that you will
277 never need to link against libstdc++ in the same executable as libc++.
278 GCC ships libsupc++ separately but only as a static library. If a
279 program also needs to link against libstdc++, it will provide its
280 own copy of libsupc++ and this can lead to subtle problems.
Michael J. Spencerdb8a0302012-12-31 19:34:21 +0000281 <li><code>make</code></li>
282 <li><code>sudo make install</code></li>
283 </ul>
284 <p>
285 You can now run clang with -stdlib=libc++.
286 </p>
287 </p>
288
289 <!--=====================================================================-->
Howard Hinnantaf4d1612013-02-08 19:10:36 +0000290 <h2>Build on Linux using CMake and libc++abi.</h2>
291 <!--=====================================================================-->
292
293 <p>
294 You will need to keep the source tree of <a href="http://libcxxabi.llvm.org">libc++abi</a>
295 available on your build machine and your copy of the libc++abi shared library must
296 be placed where your linker will find it.
297 </p>
298
299 <p>
300 We can now run CMake:
301 <ul>
302 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
303 -DLIBCXX_CXX_ABI=libcxxabi
304 -DLIBCXX_LIBCXXABI_INCLUDE_PATHS="&lt;libc++abi-source-dir&gt;/include"
305 -DCMAKE_BUILD_TYPE=Release
306 -DCMAKE_INSTALL_PREFIX=/usr
307 &lt;libc++-source-dir&gt;</code></li>
308 <li><code>make</code></li>
309 <li><code>sudo make install</code></li>
310 </ul>
311 <p>
312 Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
313 clang is set up to link for libc++ linked to libsupc++. To get around this
314 you'll have to set up your linker yourself (or patch clang). For example,
315 <ul>
316 <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc</code></li>
317 </ul>
318 Alternately, you could just add libc++abi to your libraries list, which in most
319 situations will give the same result:
320 <ul>
321 <li><code>clang++ -stdlib=libc++ helloworld.cpp -lc++abi</code></li>
322 </ul>
323 </p>
324 </p>
325
326 <!--=====================================================================-->
327 <h2>Build on Linux using CMake and libcxxrt.</h2>
328 <!--=====================================================================-->
329
330 <p>
331 You will need to keep the source tree of
332 <a href="https://github.com/pathscale/libcxxrt/">libcxxrt</a> available
333 on your build machine and your copy of the libcxxrt shared library must
334 be placed where your linker will find it.
335 </p>
336
337 <p>
338 We can now run CMake:
339 <ul>
340 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
341 -DLIBCXX_CXX_ABI=libcxxrt
Howard Hinnantfae54b92013-02-26 16:27:55 +0000342 -DLIBCXX_LIBCXXRT_INCLUDE_PATHS="&lt;libcxxrt-source-dir&gt;/src"
Howard Hinnantaf4d1612013-02-08 19:10:36 +0000343 -DCMAKE_BUILD_TYPE=Release
344 -DCMAKE_INSTALL_PREFIX=/usr
345 &lt;libc++-source-dir&gt;</code></li>
346 <li><code>make</code></li>
347 <li><code>sudo make install</code></li>
348 </ul>
349 <p>
350 Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
351 clang is set up to link for libc++ linked to libsupc++. To get around this
352 you'll have to set up your linker yourself (or patch clang). For example,
353 <ul>
354 <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc</code></li>
355 </ul>
356 Alternately, you could just add libcxxrt to your libraries list, which in most
357 situations will give the same result:
358 <ul>
359 <li><code>clang++ -stdlib=libc++ helloworld.cpp -lcxxrt</code></li>
360 </ul>
361 </p>
362 </p>
363
364 <!--=====================================================================-->
Howard Hinnant56f0d5b2010-10-05 16:44:40 +0000365 <h2>Design Documents</h2>
366 <!--=====================================================================-->
367
368<ul>
369<li><a href="atomic_design.html"><tt>&lt;atomic&gt;</tt></a></li>
Howard Hinnant9835d762010-11-19 01:38:58 +0000370<li><a href="type_traits_design.html"><tt>&lt;type_traits&gt;</tt></a></li>
Marshall Clowe47bc9b2013-03-14 19:00:34 +0000371<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>
Howard Hinnantc7cbe502013-03-14 18:37:48 +0000372<li><a href="debug_mode.html">Status of debug mode</a></li>
Howard Hinnant56f0d5b2010-10-05 16:44:40 +0000373</ul>
374
Howard Hinnantbc8d3f92010-05-11 19:42:16 +0000375</div>
376</body>
Chris Lattner4b748952010-05-11 20:37:52 +0000377</html>