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://libcxxabi.llvm.org/">libc++abi</a> 26 <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a> 27 <a href="https://lists.llvm.org/mailman/listinfo/libcxx-commits">libcxx-commits</a> 28 <a href="https://bugs.llvm.org/">Bug Reports</a> 29 <a href="https://github.com/llvm/llvm-project/tree/master/libcxx/">Browse Sources</a> 30 </div> 31</div> 32 33<div id="content"> 34 <!--*********************************************************************--> 35 <h1>"libc++" C++ Standard Library</h1> 36 <!--*********************************************************************--> 37 38 <p>libc++ is an implementation of the C++ standard library, targeting 39 C++11, C++14 and above.</p> 40 41 <p>All of the code in libc++ is <a 42 href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">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++ and 118 clang. Note that functionality provided by <atomic> is only functional with 119 clang. 120 </p> 121 122 <ul> 123 <li>Mac OS X i386</li> 124 <li>Mac OS X x86_64</li> 125 <li>FreeBSD 10+ i386</li> 126 <li>FreeBSD 10+ x86_64</li> 127 <li>FreeBSD 10+ ARM</li> 128 <li>Linux i386</li> 129 <li>Linux x86_64</li> 130 </ul> 131 132 <!--=====================================================================--> 133 <h2 id="dir-structure">Current Status</h2> 134 <!--=====================================================================--> 135 136 <p>libc++ is a 100% complete C++11 implementation on Apple's OS X. </p> 137 <p>LLVM and Clang can self host in C++ and C++11 mode with libc++ on Linux.</p> 138 <p>libc++ is also a 100% complete C++14 implementation. A list of new features and 139 changes for C++14 can be found <a href="cxx1y_status.html">here</a>.</p> 140 <p>libc++'s C++17 implementation is not yet complete. A list of features and changes 141 for C++17 can be found <a href="cxx1z_status.html">here</a>.</p> 142 <p>A list of features and changes for the next C++ standard, known here as 143 "C++2a" (probably to be C++20) can be found <a href="cxx2a_status.html">here</a>.</p> 144 <p>Implementation of the post-C++14 Technical Specifications is in progress. A list of features 145 and the current status of these features can be found <a href="ts1z_status.html">here</a>.</p> 146 <p>As features get moved from the Technical Specifications into the main standard, we 147 will (after a period for migration) remove them from the TS implementation. This 148 process is detailed <a href="DesignDocs/ExperimentalFeatures.html">here</a>.</p> 149 150 <!--======================================================================--> 151 <h2 id="buildbots">Build Bots</h2> 152 <!--======================================================================--> 153 <p>The latest libc++ build results can be found at the following locations.</p> 154 <ul> 155 <li><a href="http://lab.llvm.org:8011/console"> 156 Buildbot libc++ builders 157 </a></li> 158 <li><a href="http://lab.llvm.org:8080/green/view/Libcxx/"> 159 Jenkins libc++ builders 160 </a></li> 161 </ul> 162 163 <!--=====================================================================--> 164 <h2>Get it and get involved!</h2> 165 <!--=====================================================================--> 166 167 <p>First please review our 168 <a href="https://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>. 169 170 The documentation for building and using libc++ can be found below. 171 <ul> 172 <li><a href="https://libcxx.llvm.org/docs/UsingLibcxx.html"> 173 <b>Using libc++</b></a> 174 Documentation on using the library in your programs</li> 175 <li><a href="https://libcxx.llvm.org/docs/BuildingLibcxx.html"> 176 <b>Building libc++</b></a> 177 Documentation on building the library using CMake</li> 178 <li><a href="https://libcxx.llvm.org/docs/TestingLibcxx.html"> 179 <b>Testing libc++</b></a> 180 Documentation for developers wishing to test the library</li> 181 </ul> 182 183 <!--=====================================================================--> 184 <h3>Notes and Known Issues</h3> 185 <!--=====================================================================--> 186 187 <p> 188 <ul> 189 <li> 190 Building libc++ with <code>-fno-rtti</code> is not supported. However 191 linking against it with <code>-fno-rtti</code> is supported. 192 </li> 193 </ul> 194 </p> 195 196 <p>Send discussions to the 197 <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libc++ mailing list</a>.</p> 198 199 <!--=====================================================================--> 200 <h2>Bug reports and patches</h2> 201 <!--=====================================================================--> 202 203 <p> 204 If you think you've found a bug in libc++, please report it using 205 the <a href="https://bugs.llvm.org/">LLVM Bugzilla</a>. If you're not sure, you 206 can post a message to the <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a> 207 mailing list or on IRC. 208 </p> 209 210 <p> 211 If you want to contribute a patch to libc++, the best place for that is 212 <a href="https://llvm.org/docs/Phabricator.html">Phabricator</a>. Please 213 add libcxx-commits as a subscriber. 214 </p> 215 216 <!--=====================================================================--> 217 <h2>Design Documents</h2> 218 <!--=====================================================================--> 219 220<ul> 221<li><a href="atomic_design.html"><tt><atomic></tt></a></li> 222<li><a href="type_traits_design.html"><tt><type_traits></tt></a></li> 223<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> 224</ul> 225 226</div> 227</body> 228</html> 229