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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 <!--=====================================================================-->
106 <p>libc++ is known to work on the following platforms, using g++-4.2 and
107 clang (lack of C++11 language support disables some functionality).</p>
110 <li>Mac OS X i386</li>
111 <li>Mac OS X x86_64</li>
114 <!--=====================================================================-->
115 <h2 id="dir-structure">Current Status</h2>
116 <!--=====================================================================-->
118 <p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p>
119 <p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p>
120 <p>libc++ is also a 100% complete C++14 implementation. A list of new features and changes for
121 C++14 can be found <a href="cxx1y_status.html">here</a>.</p>
123 Ports to other platforms are underway. Here are recent test
124 results for <a href="results.Windows.html">Windows</a>
125 and <a href="results.Linux.html">Linux</a>.
128 <!--=====================================================================-->
129 <h2>Get it and get involved!</h2>
130 <!--=====================================================================-->
132 <p>First please review our
133 <a href="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
135 <p>To check out the code, use:</p>
138 <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
142 On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install
143 Xcode 4.2 or later. However if you want to install tip-of-trunk from here
144 (getting the bleeding edge), read on. However, be warned that Mac OS
145 10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
146 <code>/usr/lib</code>.
154 <li><code>cd libcxx/lib</code></li>
155 <li><code>export TRIPLE=-apple-</code></li>
156 <li><code>./buildit</code></li>
157 <li><code>ln -sf libc++.1.dylib libc++.dylib</code></li>
161 That should result in a libc++.1.dylib and libc++.dylib. The safest thing
162 to do is to use it from where your libcxx is installed instead of replacing
163 these in your Mac OS.
167 To use your system-installed libc++ with clang you can:
171 <li><code>clang++ -stdlib=libc++ test.cpp</code></li>
172 <li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li>
176 To use your tip-of-trunk libc++ on Mac OS with clang you can:
180 <li><code>export DYLD_LIBRARY_PATH=<path-to-libcxx>/lib</code>
181 <li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++
182 -I<path-to-libcxx>/include -L<path-to-libcxx>/lib
186 <p>To run the libc++ test suite (recommended):</p>
189 <li><code>cd libcxx/test</code></li>
190 <li><code>./testit</code></li>
192 <li>You can alter the command line options <code>testit</code> uses
193 with <code>export OPTIONS="whatever you need"</code></li>
197 <!--=====================================================================-->
199 <!--=====================================================================-->
202 Building libc++ with <code>-fno-rtti</code> is not supported. However linking
203 against it with <code>-fno-rtti</code> is supported.
206 <p>Send discussions to the
207 (<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p>
209 <!--=====================================================================-->
210 <h2>Bug reports and patches</h2>
211 <!--=====================================================================-->
214 If you think you've found a bug in libc++, please report it using
215 the <a href="http://llvm.org/bugs">LLVM Bugzilla</a>. If you're not sure, you
216 can post a message to the <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
217 mailing list or on IRC. Please include "libc++" in your subject.
221 If you want to contribute a patch to libc++, the best place for that is the
222 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
223 mailing list. Please include "libc++" and "PATCH" in your subject.
226 <!--=====================================================================-->
227 <h2>Build on Linux using CMake and libsupc++.</h2>
228 <!--=====================================================================-->
231 You will need libstdc++ in order to provide libsupc++.
235 Figure out where the libsupc++ headers are on your system. On Ubuntu this
236 is <code>/usr/include/c++/<version></code> and
237 <code>/usr/include/c++/<version>/<target-triple></code>
241 You can also figure this out by running
243 $ echo | g++ -Wp,-v -x c++ - -fsyntax-only
244 ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
245 ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
246 #include "..." search starts here:
247 #include <...> search starts here:
249 /usr/include/c++/4.7/x86_64-linux-gnu
250 /usr/include/c++/4.7/backward
251 /usr/lib/gcc/x86_64-linux-gnu/4.7/include
253 /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
254 /usr/include/x86_64-linux-gnu
259 Note the first two entries happen to be what we are looking for. This
260 may not be correct on other platforms.
264 We can now run CMake:
266 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
267 -DLIBCXX_CXX_ABI=libstdc++
268 -DLIBCXX_LIBSUPCXX_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/"
269 -DCMAKE_BUILD_TYPE=Release
270 -DCMAKE_INSTALL_PREFIX=/usr
271 <libc++-source-dir></code></li>
272 <li>You can also substitute <code>-DLIBCXX_CXX_ABI=libsupc++</code>
273 above, which will cause the library to be linked to libsupc++ instead
274 of libstdc++, but this is only recommended if you know that you will
275 never need to link against libstdc++ in the same executable as libc++.
276 GCC ships libsupc++ separately but only as a static library. If a
277 program also needs to link against libstdc++, it will provide its
278 own copy of libsupc++ and this can lead to subtle problems.
279 <li><code>make</code></li>
280 <li><code>sudo make install</code></li>
283 You can now run clang with -stdlib=libc++.
287 <!--=====================================================================-->
288 <h2>Build on Linux using CMake and libc++abi.</h2>
289 <!--=====================================================================-->
292 You will need to keep the source tree of <a href="http://libcxxabi.llvm.org">libc++abi</a>
293 available on your build machine and your copy of the libc++abi shared library must
294 be placed where your linker will find it.
298 We can now run CMake:
300 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
301 -DLIBCXX_CXX_ABI=libcxxabi
302 -DLIBCXX_LIBCXXABI_INCLUDE_PATHS="<libc++abi-source-dir>/include"
303 -DCMAKE_BUILD_TYPE=Release
304 -DCMAKE_INSTALL_PREFIX=/usr
305 <libc++-source-dir></code></li>
306 <li><code>make</code></li>
307 <li><code>sudo make install</code></li>
310 Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
311 clang is set up to link for libc++ linked to libsupc++. To get around this
312 you'll have to set up your linker yourself (or patch clang). For example,
314 <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lc++abi -lm -lc -lgcc_s -lgcc</code></li>
316 Alternately, you could just add libc++abi to your libraries list, which in most
317 situations will give the same result:
319 <li><code>clang++ -stdlib=libc++ helloworld.cpp -lc++abi</code></li>
324 <!--=====================================================================-->
325 <h2>Build on Linux using CMake and libcxxrt.</h2>
326 <!--=====================================================================-->
329 You will need to keep the source tree of
330 <a href="https://github.com/pathscale/libcxxrt/">libcxxrt</a> available
331 on your build machine and your copy of the libcxxrt shared library must
332 be placed where your linker will find it.
336 We can now run CMake:
338 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles"
339 -DLIBCXX_CXX_ABI=libcxxrt
340 -DLIBCXX_LIBCXXRT_INCLUDE_PATHS="<libcxxrt-source-dir>/src"
341 -DCMAKE_BUILD_TYPE=Release
342 -DCMAKE_INSTALL_PREFIX=/usr
343 <libc++-source-dir></code></li>
344 <li><code>make</code></li>
345 <li><code>sudo make install</code></li>
348 Unfortunately you can't simply run clang with "-stdlib=libc++" at this point, as
349 clang is set up to link for libc++ linked to libsupc++. To get around this
350 you'll have to set up your linker yourself (or patch clang). For example,
352 <li><code>clang++ -stdlib=libc++ helloworld.cpp -nodefaultlibs -lc++ -lcxxrt -lm -lc -lgcc_s -lgcc</code></li>
354 Alternately, you could just add libcxxrt to your libraries list, which in most
355 situations will give the same result:
357 <li><code>clang++ -stdlib=libc++ helloworld.cpp -lcxxrt</code></li>
362 <!--=====================================================================-->
363 <h2>Design Documents</h2>
364 <!--=====================================================================-->
367 <li><a href="atomic_design.html"><tt><atomic></tt></a></li>
368 <li><a href="type_traits_design.html"><tt><type_traits></tt></a></li>
369 <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>
370 <li><a href="debug_mode.html">Status of debug mode</a></li>