1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ --> 4<html> 5<head> 6 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 7 <title>"libc++" C++ Standard Library</title> 8 <link type="text/css" rel="stylesheet" href="menu.css"> 9 <link type="text/css" rel="stylesheet" href="content.css"> 10</head> 11 12<body> 13<div id="menu"> 14 <div> 15 <a href="http://llvm.org/">LLVM Home</a> 16 </div> 17 18 <div class="submenu"> 19 <label>libc++ Info</label> 20 <a href="/index.html">About</a> 21 </div> 22 23 <div class="submenu"> 24 <label>Quick Links</label> 25 <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> 27 <a href="http://llvm.org/bugs/">Bug Reports</a> 28 <a href="http://llvm.org/svn/llvm-project/libcxx/trunk/">Browse SVN</a> 29 <a href="http://llvm.org/viewvc/llvm-project/libcxx/trunk/">Browse ViewVC</a> 30 </div> 31</div> 32 33<div id="content"> 34 <!--*********************************************************************--> 35 <h1>"libc++" C++ Standard Library</h1> 36 <!--*********************************************************************--> 37 38 <p>libc++ is a new implementation of the C++ standard library, targeting 39 C++11.</p> 40 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> 44 45 <!--=====================================================================--> 46 <h2 id="goals">Features and Goals</h2> 47 <!--=====================================================================--> 48 49 <ul> 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> 57 </ul> 58 59 <!--=====================================================================--> 60 <h2 id="why">Why a new C++ Standard Library for C++11?</h2> 61 <!--=====================================================================--> 62 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> 67 68 <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 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 78 libc++.</p></li> 79 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> 87 </li> 88 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> 96 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> 99 100 </ul> 101 102 <!--=====================================================================--> 103 <h2 id="requirements">Platform Support</h2> 104 <!--=====================================================================--> 105 106 <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> 108 109 <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 <!--=====================================================================--> 117 118 <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> 120 121 <p> 122 Ports to other platforms are underway. Here are recent test 123 results for <a href="results.Windows.html">Windows</a> 124 and <a href="results.Linux.html">Linux</a>. 125 </p> 126 127 <!--=====================================================================--> 128 <h2>Get it and get involved!</h2> 129 <!--=====================================================================--> 130 131 <p>First please review our 132 <a href="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>. 133 134 <p>To check out the code, use:</p> 135 136 <ul> 137 <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li> 138 </ul> 139 140 <p> 141 On Mac OS 10.7 (Lion) and later, the easiest way to get this library is to install 142 Xcode 4.2 or later. However if you want to install tip-of-trunk from here 143 (getting the bleeding edge), read on. However, be warned that Mac OS 144 10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in 145 <code>/usr/lib</code>. 146 </p> 147 148 <p> 149 Next: 150 </p> 151 152 <ul> 153 <li><code>cd libcxx/lib</code></li> 154 <li><code>export TRIPLE=-apple-</code></li> 155 <li><code>./buildit</code></li> 156 <li><code>ln -sf libc++.1.dylib libc++.dylib</code></li> 157 </ul> 158 159 <p> 160 That should result in a libc++.1.dylib and libc++.dylib. The safest thing 161 to do is to use it from where your libcxx is installed instead of replacing 162 these in your Mac OS. 163 </p> 164 165 <p> 166 To use your system-installed libc++ with clang you can: 167 </p> 168 169 <ul> 170 <li><code>clang++ -stdlib=libc++ test.cpp</code></li> 171 <li><code>clang++ -std=c++11 -stdlib=libc++ test.cpp</code></li> 172 </ul> 173 174 <p> 175 To use your tip-of-trunk libc++ on Mac OS with clang you can: 176 </p> 177 178 <ul> 179 <li><code>export DYLD_LIBRARY_PATH=<path-to-libcxx>/lib</code> 180 <li><code>clang++ -std=c++11 -stdlib=libc++ -nostdinc++ 181 -I<path-to-libcxx>/include -L<path-to-libcxx>/lib 182 test.cpp</code></li> 183 </ul> 184 185 <p>To run the libc++ test suite (recommended):</p> 186 187 <ul> 188 <li><code>cd libcxx/test</code></li> 189 <li><code>./testit</code></li> 190 <ul> 191 <li>You can alter the command line options <code>testit</code> uses 192 with <code>export OPTIONS="whatever you need"</code></li> 193 </ul> 194 </ul> 195 196 <!--=====================================================================--> 197 <h3>Notes</h3> 198 <!--=====================================================================--> 199 200<p> 201Building libc++ with <code>-fno-rtti</code> is not supported. However linking 202against it with <code>-fno-rtti</code> is supported. 203</p> 204 205 <p>Send discussions to the 206 (<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p> 207 208 <!--=====================================================================--> 209 <h2>Build on Linux using CMake and libsupc++.</h2> 210 <!--=====================================================================--> 211 212 <p> 213 You will need libstdc++ in order to provide libsupc++. 214 </p> 215 216 <p> 217 Figure out where the libsupc++ headers are on your system. On Ubuntu this 218 is <code>/usr/include/c++/<version></code> and 219 <code>/usr/include/c++/<version>/<target-triple></code> 220 </p> 221 222 <p> 223 You can also figure this out by running 224 <pre> 225$ echo | g++ -Wp,-v -x c++ - -fsyntax-only 226ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" 227ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include" 228#include "..." search starts here: 229#include <...> search starts here: 230 /usr/include/c++/4.7 231 /usr/include/c++/4.7/x86_64-linux-gnu 232 /usr/include/c++/4.7/backward 233 /usr/lib/gcc/x86_64-linux-gnu/4.7/include 234 /usr/local/include 235 /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed 236 /usr/include/x86_64-linux-gnu 237 /usr/include 238End of search list. 239 </pre> 240 241 Note the first two entries happen to be what we are looking for. This 242 may not be correct on other platforms. 243 </p> 244 245 <p> 246 We can now run CMake: 247 <ul> 248 <li><code>CC=clang CXX=clang++ cmake -G "Unix Makefiles" 249 -DLIBCXX_CXX_ABI=libsupc++ 250 -DLIBCXX_LIBSUPCXX_INCLUDE_PATHS="/usr/include/c++/4.7/;/usr/include/c++/4.7/x86_64-linux-gnu/" 251 -DCMAKE_BUILD_TYPE=Release 252 -DCMAKE_INSTALL_PREFIX=/usr 253 <libc++-source-dir></code></li> 254 <li><code>make</code></li> 255 <li><code>sudo make install</code></li> 256 </ul> 257 <p> 258 You can now run clang with -stdlib=libc++. 259 </p> 260 </p> 261 262 <!--=====================================================================--> 263 <h2>Design Documents</h2> 264 <!--=====================================================================--> 265 266<ul> 267<li><a href="atomic_design.html"><tt><atomic></tt></a></li> 268<li><a href="type_traits_design.html"><tt><type_traits></tt></a></li> 269<li><a href="http://marshall.calepin.co/llvmclang-and-standard-libraries-on-mac-os-x.html">Excellent notes by Marshall Clow</a></li> 270</ul> 271 272</div> 273</body> 274</html> 275