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  <!--*********************************************************************-->
  <h1>"libc++" C++ Standard Library</h1>
  <!--*********************************************************************-->

  <p>libc++ is a new implementation of the C++ standard library, targeting
  C++0X.</p>

  <p>All of the code in libc++ is available under the standard
  <a href="http://llvm.org/docs/DeveloperPolicy.html#license">LLVM
  License</a>, a "BSD-style" license.</p>

  <!--=====================================================================-->
  <h2 id="goals">Features and Goals</h2>
  <!--=====================================================================-->

  <ul>
  <li>Correctness as defined by the (currently draft) C++0X standard.</li>
  <li>Fast execution.</li>
  <li>Minimal memory use.</li>
  <li>Fast compile times.</li>
  <li>ABI compatibility with gcc's libstdc++ for some low-level features
  such as exception objects, rtti and memory allocation.</li>
  <li>Extensive unit tests.</li>
  </ul>

  <!--=====================================================================-->
  <h2 id="why">Why a new C++ Standard Library for C++'0x?</h2>
  <!--=====================================================================-->

  <p>After its initial introduction, many people have asked "why start a new
  library instead of contributing to an existing library?" (like Apache's
  libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
  reasons, but some of the major ones are:</p>

  <ul>
  <li><p>From years of experience (including having implemented the standard
  library before), we've learned many things about implementing
  the standard containers which require ABI breakage and fundamental changes
  to how they are implemented. For example, it is generally accepted that
  building std::string using the "short string optimization" instead of
  using Copy On Write (COW) is a superior approach for multicore
  machines (particularly in C++'0x, which has rvalue references). Breaking
  ABI compatibility with old versions of the library was
  determined to be critical to achieving the performance goals of
  libc++.</p></li>

  <li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
  of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
  independently extended to support C++'0x, but this would be a fork of the
  codebase (which is often seen as worse for a project than starting a new
  independent one). Another problem with libstdc++ is that it is tightly
  integrated with G++ development, tending to be tied fairly closely to the
  matching version of G++.</p>
  </li>

  <li><p>STLport and the Apache libstdcxx library are two other popular
  candidates, but both lack C++'0x support. Our experience (and the
  experience of libstdc++ developers) is that adding support for C++0x (in
  particular rvalue references and move-only types) requires changes to
  almost every class and function, essentially amounting to a rewrite.
  Faced with a rewrite, we decided to start from scratch and evaluate every
  design decision from first principles based on experience.</p>

  <p>Further, both projects are apparently abandoned: STLport 5.2.1 was
  released in Oct'08, and STDCXX 4.2.1 in May'08.</p>

  </ul>

  <!--=====================================================================-->
  <h2 id="requirements">Platform Support</h2>
  <!--=====================================================================-->

  <p>libc++ is known to work on the following platforms, using g++-4.2 and
  clang (lack of C++0X language support disables some functionality).</p>

  <ul>
  <li>Mac OS X i386</li>
  <li>Mac OS X x86_64</li>
  </ul>

  <!--=====================================================================-->
  <h2 id="dir-structure">Current Status</h2>
  <!--=====================================================================-->

  <p>libc++ is still under development. It has about 98% of
  <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3126.pdf">N3126</a>
  implemented/tested. C++'98 support is fully featured, and most of C++'0x
  support is as well. The only major missing piece of C++'0x support is
  <code>&lt;atomic&gt;</code>.</p>

  <p>libc++ is currently dependent upon a separate library for the low-level
  ABI compatibility with gcc. As a workaround it can be linked against
  gcc's libstdc++, or on Mac OS X
  <a href="http://home.roadrunner.com/~hinnant/libcppabi.zip">this library</a>.</p>

  <p><a href="libcxx_by_chapter.pdf">Here</a> is a by-chapter breakdown of what
  is passing tests and what isn't. This chart is currently based on testing
  against g++-4.4.0 with -std=c++0x. </p>

  <!--=====================================================================-->
  <h2>Get it and get involved!</h2>
  <!--=====================================================================-->

  <p>To check out the code, use:</p>

  <ul>
  <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
  <li><code>cd libcxx/lib</code></li>
  <li><code>./buildit</code></li>
  </ul>

  <p>To run the libc++ test suit (recommended):</p>

  <ul>
  <li><code>cd libcxx/test</code></li>
  <li><code>./testit</code></li>
  </ul>

  <p>Send discussions to the
  (<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p>

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	<a href="/index.html">About</a>
	</div>

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	<label>Quick Links</label>
	<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
	<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
	<a href="http://llvm.org/bugs/">Bug Reports</a>
	<a href="http://llvm.org/svn/llvm-project/libcxx/trunk/">Browse SVN</a>
	<a href="http://llvm.org/viewvc/llvm-project/libcxx/trunk/">Browse ViewVC</a>
	</div>
	</div>

	<div id="content">
	<!--*********************************************************************-->
	<h1>"libc++" C++ Standard Library</h1>
	<!--*********************************************************************-->

	<p>libc++ is a new implementation of the C++ standard library, targeting
	C++0X.</p>

	<p>All of the code in libc++ is available under the standard
	<a href="http://llvm.org/docs/DeveloperPolicy.html#license">LLVM
	License</a>, a "BSD-style" license.</p>

	<!--=====================================================================-->
	<h2 id="goals">Features and Goals</h2>
	<!--=====================================================================-->

	<ul>
	<li>Correctness as defined by the (currently draft) C++0X standard.</li>
	<li>Fast execution.</li>
	<li>Minimal memory use.</li>
	<li>Fast compile times.</li>
	<li>ABI compatibility with gcc's libstdc++ for some low-level features
	such as exception objects, rtti and memory allocation.</li>
	<li>Extensive unit tests.</li>
	</ul>

	<!--=====================================================================-->
	<h2 id="why">Why a new C++ Standard Library for C++'0x?</h2>
	<!--=====================================================================-->

	<p>After its initial introduction, many people have asked "why start a new
	library instead of contributing to an existing library?" (like Apache's
	libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
	reasons, but some of the major ones are:</p>

	<ul>
	<li><p>From years of experience (including having implemented the standard
	library before), we've learned many things about implementing
	the standard containers which require ABI breakage and fundamental changes
	to how they are implemented. For example, it is generally accepted that
	building std::string using the "short string optimization" instead of
	using Copy On Write (COW) is a superior approach for multicore
	machines (particularly in C++'0x, which has rvalue references). Breaking
	ABI compatibility with old versions of the library was
	determined to be critical to achieving the performance goals of
	libc++.</p></li>

	<li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
	of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
	independently extended to support C++'0x, but this would be a fork of the
	codebase (which is often seen as worse for a project than starting a new
	independent one). Another problem with libstdc++ is that it is tightly
	integrated with G++ development, tending to be tied fairly closely to the
	matching version of G++.</p>
	</li>

	<li><p>STLport and the Apache libstdcxx library are two other popular
	candidates, but both lack C++'0x support. Our experience (and the
	experience of libstdc++ developers) is that adding support for C++0x (in
	particular rvalue references and move-only types) requires changes to
	almost every class and function, essentially amounting to a rewrite.
	Faced with a rewrite, we decided to start from scratch and evaluate every
	design decision from first principles based on experience.</p>

	<p>Further, both projects are apparently abandoned: STLport 5.2.1 was
	released in Oct'08, and STDCXX 4.2.1 in May'08.</p>

	</ul>

	<!--=====================================================================-->
	<h2 id="requirements">Platform Support</h2>
	<!--=====================================================================-->

	<p>libc++ is known to work on the following platforms, using g++-4.2 and
	clang (lack of C++0X language support disables some functionality).</p>

	<ul>
	<li>Mac OS X i386</li>
	<li>Mac OS X x86_64</li>
	</ul>

	<!--=====================================================================-->
	<h2 id="dir-structure">Current Status</h2>
	<!--=====================================================================-->

	<p>libc++ is still under development. It has about 98% of
	<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3126.pdf">N3126</a>
	implemented/tested. C++'98 support is fully featured, and most of C++'0x
	support is as well. The only major missing piece of C++'0x support is
	<code><atomic></code>.</p>

	<p>libc++ is currently dependent upon a separate library for the low-level
	ABI compatibility with gcc. As a workaround it can be linked against
	gcc's libstdc++, or on Mac OS X
	<a href="http://home.roadrunner.com/~hinnant/libcppabi.zip">this library</a>.</p>

	<p><a href="libcxx_by_chapter.pdf">Here</a> is a by-chapter breakdown of what
	is passing tests and what isn't. This chart is currently based on testing
	against g++-4.4.0 with -std=c++0x. </p>

	<!--=====================================================================-->
	<h2>Get it and get involved!</h2>
	<!--=====================================================================-->

	<p>To check out the code, use:</p>

	<ul>
	<li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
	<li><code>cd libcxx/lib</code></li>
	<li><code>./buildit</code></li>
	</ul>

	<p>To run the libc++ test suit (recommended):</p>

	<ul>
	<li><code>cd libcxx/test</code></li>
	<li><code>./testit</code></li>
	</ul>

	<p>Send discussions to the
	(<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p>

	</div>
	</body>
	</html>