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="https://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="https://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a> 26 <a href="https://lists.llvm.org/mailman/listinfo/cfe-commits">cfe-commits</a> 27 <a href="https://bugs.llvm.org/">Bug Reports</a> 28 <a href="https://llvm.org/svn/llvm-project/libcxx/trunk/">Browse SVN</a> 29 <a href="https://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="https://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>New Documentation Coming Soon!</h2> 47 <!--=====================================================================--> 48 49 <p> Looking for documentation on how to use, build and test libc++? If so 50 checkout the new libc++ documentation.</p> 51 52 <p><a href="https://libcxx.llvm.org/docs/"> 53 Click here for the new libc++ documentation.</a></p> 54 55 <!--=====================================================================--> 56 <h2 id="goals">Features and Goals</h2> 57 <!--=====================================================================--> 58 59 <ul> 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> 67 </ul> 68 69 <!--=====================================================================--> 70 <h2 id="why">Why a new C++ Standard Library for C++11?</h2> 71 <!--=====================================================================--> 72 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> 77 78 <ul> 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 88 libc++.</p></li> 89 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> 97 </li> 98 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> 106 107 <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> 109 110 </ul> 111 112 <!--=====================================================================--> 113 <h2 id="requirements">Platform Support</h2> 114 <!--=====================================================================--> 115 116 <p> 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 120 clang. 121 </p> 122 123 <ul> 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> 129 </ul> 130 131 <!--=====================================================================--> 132 <h2 id="dir-structure">Current Status</h2> 133 <!--=====================================================================--> 134 135 <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 138 changes for C++14 can be found <a href="cxx1y_status.html">here</a>.</p> 139 <p>libc++'s C++17 implementation is not yet complete. A list of features and changes 140 for C++17 can be found <a href="cxx1z_status.html">here</a>.</p> 141 <p>A list of features and changes for the next C++ standard, known here as 142 "C++2a" (probably to be C++20) can be found <a href="cxx2a_status.html">here</a>.</p> 143 <p>Implementation of the post-C++14 Technical Specifications is in progress. A list of features 144 and the current status of these features can be found <a href="ts1z_status.html">here</a>.</p> 145 <p>As features get moved from the Technical Specifications into the main standard, we 146 will (after a period for migration) remove them from the TS implementation. This 147 process is detailed <a href="TS_deprecation.html">here</a>.</p> 148 149 <!--======================================================================--> 150 <h2 id="buildbots">Build Bots</h2> 151 <!--======================================================================--> 152 <p>The latest libc++ build results can be found at the following locations.</p> 153 <ul> 154 <li><a href="http://lab.llvm.org:8011/console"> 155 Buildbot libc++ builders 156 </a></li> 157 <li><a href="http://lab.llvm.org:8080/green/view/Libcxx/"> 158 Jenkins libc++ builders 159 </a></li> 160 </ul> 161 162 <!--=====================================================================--> 163 <h2>Get it and get involved!</h2> 164 <!--=====================================================================--> 165 166 <p>First please review our 167 <a href="https://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>. 168 169 The documentation for building and using libc++ can be found below. 170 <ul> 171 <li><a href="https://libcxx.llvm.org/docs/UsingLibcxx.html"> 172 <b>Using libc++</b></a> 173 Documentation on using the library in your programs</li> 174 <li><a href="https://libcxx.llvm.org/docs/BuildingLibcxx.html"> 175 <b>Building libc++</b></a> 176 Documentation on building the library using CMake</li> 177 <li><a href="https://libcxx.llvm.org/docs/TestingLibcxx.html"> 178 <b>Testing libc++</b></a> 179 Documentation for developers wishing to test the library</li> 180 </ul> 181 182 <!--=====================================================================--> 183 <h3>Notes and Known Issues</h3> 184 <!--=====================================================================--> 185 186 <p> 187 <ul> 188 <li> 189 Building libc++ with <code>-fno-rtti</code> is not supported. However 190 linking against it with <code>-fno-rtti</code> is supported. 191 </li> 192 <li> 193 On OS X v10.8 and older the CMake option 194 <code>-DLIBCXX_LIBCPPABI_VERSION=""</code> must be used during 195 configuration. 196 </li> 197 </ul> 198 </p> 199 200 <p>Send discussions to the 201 <a href="https://lists.llvm.org/mailman/listinfo/cfe-dev">clang mailing list</a>.</p> 202 203 <!--=====================================================================--> 204 <h2>Bug reports and patches</h2> 205 <!--=====================================================================--> 206 207 <p> 208 If you think you've found a bug in libc++, please report it using 209 the <a href="https://bugs.llvm.org/">LLVM Bugzilla</a>. If you're not sure, you 210 can post a message to the <a href="https://lists.llvm.org/mailman/listinfo/cfe-dev">cfe-dev</a> 211 mailing list or on IRC. Please include "libc++" in your subject. 212 </p> 213 214 <p> 215 If you want to contribute a patch to libc++, the best place for that is 216 <a href="https://llvm.org/docs/Phabricator.html">Phabricator</a>. Please 217 include [libc++] in the subject and add cfe-commits as a subscriber. 218 </p> 219 220 <!--=====================================================================--> 221 <h2>Design Documents</h2> 222 <!--=====================================================================--> 223 224 <ul> 225 <li><a href="atomic_design.html"><tt><atomic></tt></a></li> 226 <li><a href="type_traits_design.html"><tt><type_traits></tt></a></li> 227 <li><a href="https://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/">Excellent notes by Marshall Clow</a></li> 228 </ul> 229 230 </div> 231 </body> 232 </html> 233
