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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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	</div>

	<div class="submenu">
	<label>libc++ Info</label>
	<a href="/index.html">About</a>
	</div>

	<div class="submenu">
	<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>