2010-08-22 09:04:38 +08:00
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2010-05-12 03:42:16 +08:00
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<title>"libc++" C++ Standard Library</title>
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<a href="http://llvm.org/">LLVM Home</a>
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2010-08-22 09:04:38 +08:00
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2010-05-12 03:42:16 +08:00
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<label>libc++ Info</label>
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<label>Quick Links</label>
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2010-05-12 04:53:16 +08:00
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
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2010-05-12 03:42:16 +08:00
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2010-05-12 04:51:20 +08:00
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2010-05-12 03:42:16 +08:00
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<!--*********************************************************************-->
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<h1>"libc++" C++ Standard Library</h1>
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<!--*********************************************************************-->
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2010-08-22 09:04:38 +08:00
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2010-05-12 03:42:16 +08:00
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<p>libc++ is a new implementation of the C++ standard library, targeting
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C++0X.</p>
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2010-11-17 05:40:19 +08:00
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<p>All of the code in libc++ is <a
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href="http://llvm.org/docs/DeveloperPolicy.html#license">dual licensed</a>
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under the MIT license and the UIUC License (a BSD-like license).</p>
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2010-08-22 09:04:38 +08:00
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2010-05-12 03:42:16 +08:00
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<!--=====================================================================-->
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<h2 id="goals">Features and Goals</h2>
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<!--=====================================================================-->
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2010-08-22 09:04:38 +08:00
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2010-05-12 03:42:16 +08:00
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<ul>
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<li>Correctness as defined by the (currently draft) C++0X standard.</li>
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<li>Fast execution.</li>
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<li>Minimal memory use.</li>
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<li>Fast compile times.</li>
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<li>ABI compatibility with gcc's libstdc++ for some low-level features
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such as exception objects, rtti and memory allocation.</li>
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<li>Extensive unit tests.</li>
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</ul>
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2010-05-13 06:21:15 +08:00
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<!--=====================================================================-->
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<h2 id="why">Why a new C++ Standard Library for C++'0x?</h2>
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<!--=====================================================================-->
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2010-08-22 09:04:38 +08:00
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2010-05-13 06:21:15 +08:00
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<p>After its initial introduction, many people have asked "why start a new
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library instead of contributing to an existing library?" (like Apache's
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libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
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reasons, but some of the major ones are:</p>
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2010-08-22 09:04:38 +08:00
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2010-05-13 06:21:15 +08:00
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<ul>
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<li><p>From years of experience (including having implemented the standard
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library before), we've learned many things about implementing
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the standard containers which require ABI breakage and fundamental changes
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to how they are implemented. For example, it is generally accepted that
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building std::string using the "short string optimization" instead of
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using Copy On Write (COW) is a superior approach for multicore
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2010-05-13 06:30:22 +08:00
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machines (particularly in C++'0x, which has rvalue references). Breaking
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ABI compatibility with old versions of the library was
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2010-05-13 06:21:15 +08:00
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determined to be critical to achieving the performance goals of
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libc++.</p></li>
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2010-08-22 09:04:38 +08:00
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2010-05-13 06:21:15 +08:00
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<li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
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of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
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independently extended to support C++'0x, but this would be a fork of the
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2010-05-13 06:33:00 +08:00
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codebase (which is often seen as worse for a project than starting a new
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independent one). Another problem with libstdc++ is that it is tightly
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integrated with G++ development, tending to be tied fairly closely to the
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matching version of G++.</p>
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2010-05-13 06:21:15 +08:00
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</li>
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<li><p>STLport and the Apache libstdcxx library are two other popular
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candidates, but both lack C++'0x support. Our experience (and the
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experience of libstdc++ developers) is that adding support for C++0x (in
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particular rvalue references and move-only types) requires changes to
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almost every class and function, essentially amounting to a rewrite.
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2010-05-13 06:34:21 +08:00
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Faced with a rewrite, we decided to start from scratch and evaluate every
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design decision from first principles based on experience.</p>
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2010-08-22 09:04:38 +08:00
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2010-05-13 06:21:15 +08:00
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<p>Further, both projects are apparently abandoned: STLport 5.2.1 was
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released in Oct'08, and STDCXX 4.2.1 in May'08.</p>
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</ul>
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2010-05-12 03:42:16 +08:00
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<!--=====================================================================-->
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<h2 id="requirements">Platform Support</h2>
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<!--=====================================================================-->
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<p>libc++ is known to work on the following platforms, using g++-4.2 and
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clang (lack of C++0X language support disables some functionality).</p>
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<ul>
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<li>Mac OS X i386</li>
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<li>Mac OS X x86_64</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="dir-structure">Current Status</h2>
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<!--=====================================================================-->
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2010-09-06 01:31:48 +08:00
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<p>libc++ is still under development. It has about 98% of
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3126.pdf">N3126</a>
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implemented/tested. C++'98 support is fully featured, and most of C++'0x
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2010-09-06 01:31:48 +08:00
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support is as well. The only major missing piece of C++'0x support is
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<code><atomic></code>.</p>
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2010-05-12 03:42:16 +08:00
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2010-05-14 04:10:39 +08:00
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<p><a href="libcxx_by_chapter.pdf">Here</a> is a by-chapter breakdown of what
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is passing tests and what isn't. This chart is currently based on testing
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2010-06-04 22:16:02 +08:00
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against g++-4.4.0 with -std=c++0x. </p>
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2010-05-14 04:10:39 +08:00
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2011-09-28 23:44:39 +08:00
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<p>
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A Windows port is underway. <a href="results.Windows.html">Here</a> are
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recent test results.
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</p>
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2010-05-12 03:42:16 +08:00
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<!--=====================================================================-->
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<h2>Get it and get involved!</h2>
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<!--=====================================================================-->
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2010-08-22 09:04:38 +08:00
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2011-10-01 00:58:02 +08:00
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<p>First please review our
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<a href="http://llvm.org/docs/DeveloperPolicy.html">Developer's Policy</a>.
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2010-05-12 03:42:16 +08:00
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<p>To check out the code, use:</p>
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2010-05-12 03:42:16 +08:00
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<ul>
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2010-05-12 04:37:52 +08:00
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<li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
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2011-01-28 07:18:19 +08:00
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</ul>
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<p>To build on Mac OS X 10.6, you need a helper library and header
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<a href="http://home.roadrunner.com/~hinnant/libcppabi.zip">found here</a>.
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cp cxxabi.h to /usr/include, and cp libc++abi.dylib to /usr/lib.
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<p>
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<p>
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Next:
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</p>
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<ul>
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<li><code>cd libcxx/lib</code></li>
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<li><code>export TRIPLE=-apple-</code></li>
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2011-10-09 23:25:34 +08:00
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<li><code>export MACOSX_DEPLOYMENT_TARGET=10.6</code></li>
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2011-01-28 07:18:19 +08:00
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<li><code>./buildit</code></li>
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</ul>
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<p>
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That should result in a libc++.1.dylib. To install it I like to use links
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instead of copying, but either should work:
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</p>
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<ul>
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<li><code>cd /usr/lib</code></li>
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2011-02-22 22:18:34 +08:00
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<li><code>sudo ln -sf path-to-libcxx/lib/libc++.1.dylib libc++.1.dylib</code></li>
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<li><code>sudo ln -sf libc++.1.dylib libc++.dylib</code></li>
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2011-01-28 07:18:19 +08:00
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<li><code>cd /usr/include/c++</code></li>
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<li><code>sudo ln -sf path-to-libcxx/include v1</code></li>
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</ul>
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<p>
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To use with clang you can:
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</p>
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<ul>
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<li><code>clang++ -stdlib=libc++ test.cpp</code></li>
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<li><code>clang++ -std=c++0x -stdlib=libc++ test.cpp</code></li>
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2010-05-12 03:42:16 +08:00
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</ul>
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<p>To run the libc++ test suit (recommended):</p>
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<ul>
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2010-05-12 04:37:52 +08:00
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<li><code>cd libcxx/test</code></li>
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<li><code>./testit</code></li>
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2011-06-22 20:13:55 +08:00
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<ul>
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2011-09-12 22:15:45 +08:00
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<li>On Mac OS 10.6, to work around bugs in libc headers like
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math.h and inttypes.h, add "-U__STRICT_ANSI__" and
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"-D__STDC_FORMAT_MACROS" to the command line with:
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<blockquote>
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<pre>export OPTIONS="-std=c++0x -stdlib=libc++ -U__STRICT_ANSI__ -D__STDC_FORMAT_MACROS"</pre>
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</blockquote></li>
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<li>People porting libc++ to other OSes will likely have to
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define similar macros.</li>
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2011-06-22 20:13:55 +08:00
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</ul>
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2010-05-12 03:42:16 +08:00
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</ul>
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2010-08-22 09:04:38 +08:00
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<p>Send discussions to the
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2010-05-12 03:53:34 +08:00
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(<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p>
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2010-10-06 00:44:40 +08:00
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<!--=====================================================================-->
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<h2>Design Documents</h2>
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<!--=====================================================================-->
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<ul>
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<li><a href="atomic_design.html"><tt><atomic></tt></a></li>
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2010-11-19 09:38:58 +08:00
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<li><a href="type_traits_design.html"><tt><type_traits></tt></a></li>
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2010-10-06 00:44:40 +08:00
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</ul>
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2010-05-12 03:42:16 +08:00
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</div>
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</body>
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2010-05-12 04:37:52 +08:00
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</html>
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