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Chris Lattner3c9af342010-05-11 20:53:16 +0000[diff] [blame]25 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">cfe-dev</a>
26 <a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits">cfe-commits</a>
Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]27 <a href="http://llvm.org/bugs/">Bug Reports</a>
Howard Hinnant00171852010-05-11 20:51:20 +0000[diff] [blame]28 <a href="http://llvm.org/svn/llvm-project/libcxx/trunk/">Browse SVN</a>
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Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]30 </div>
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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++0X.</p>
40
41 <p>All of the code in libc++ is available under the standard
42 <a href="http://llvm.org/docs/DeveloperPolicy.html#license">LLVM
43 License</a>, a "BSD-style" license.</p>
44
45 <!--=====================================================================-->
46 <h2 id="goals">Features and Goals</h2>
47 <!--=====================================================================-->
48
49 <ul>
50 <li>Correctness as defined by the (currently draft) C++0X standard.</li>
51 <li>Fast execution.</li>
52 <li>Minimal memory use.</li>
53 <li>Fast compile times.</li>
54 <li>ABI compatibility with gcc's libstdc++ for some low-level features
55 such as exception objects, rtti and memory allocation.</li>
56 <li>Extensive unit tests.</li>
57 </ul>
58
59 <!--=====================================================================-->
Chris Lattnere2b07272010-05-12 22:21:15 +0000[diff] [blame]60 <h2 id="why">Why a new C++ Standard Library for C++'0x?</h2>
61 <!--=====================================================================-->
62
63 <p>After its initial introduction, many people have asked "why start a new
64 library instead of contributing to an existing library?" (like Apache's
65 libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
66 reasons, but some of the major ones are:</p>
67
68 <ul>
69 <li><p>From years of experience (including having implemented the standard
70 library before), we've learned many things about implementing
71 the standard containers which require ABI breakage and fundamental changes
72 to how they are implemented. For example, it is generally accepted that
73 building std::string using the "short string optimization" instead of
74 using Copy On Write (COW) is a superior approach for multicore
Chris Lattnerc67061b2010-05-12 22:30:22 +0000[diff] [blame^]75 machines (particularly in C++'0x, which has rvalue references). Breaking
76 ABI compatibility with old versions of the library was
Chris Lattnere2b07272010-05-12 22:21:15 +0000[diff] [blame]77 determined to be critical to achieving the performance goals of
78 libc++.</p></li>
79
80 <li><p>Mainline libstdc++ has switched to GPL3, a license which the developers
81 of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
82 independently extended to support C++'0x, but this would be a fork of the
83 codebase, which is usually seen as worse for a project than starting a new
84 one. Another problem with libstdc++ is that it is tightly integrated with
85 G++ development, tending to be tied fairly closely to the matching
86 version of G++.</p>
87 </li>
88
89 <li><p>STLport and the Apache libstdcxx library are two other popular
90 candidates, but both lack C++'0x support. Our experience (and the
91 experience of libstdc++ developers) is that adding support for C++0x (in
92 particular rvalue references and move-only types) requires changes to
93 almost every class and function, essentially amounting to a rewrite.
94 Faced with a rewrite, we decided to start from scratch and evaluate every
95 decision based from first principles based on experience.</p>
96
97 <p>Further, both projects are apparently abandoned: STLport 5.2.1 was
98 released in Oct'08, and STDCXX 4.2.1 in May'08.</p>
99
100 </ul>
101
102 <!--=====================================================================-->
Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]103 <h2 id="requirements">Platform Support</h2>
104 <!--=====================================================================-->
105
106 <p>libc++ is known to work on the following platforms, using g++-4.2 and
107 clang (lack of C++0X language support disables some functionality).</p>
108
109 <ul>
110 <li>Mac OS X i386</li>
111 <li>Mac OS X x86_64</li>
112 </ul>
113
114 <!--=====================================================================-->
115 <h2 id="dir-structure">Current Status</h2>
116 <!--=====================================================================-->
117
118 <p>libc++ is still under development. It has about 85% of
119 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3092.pdf">N3092</a>
Chris Lattnere2b07272010-05-12 22:21:15 +0000[diff] [blame]120 implemented/tested. C++'98 support is fully featured, and most of C++'0x
121 support is as well. The only major missing pieces of C++'0x support are
122 <code>&lt;future&gt;</code> and <code>&lt;regex&gt;</code>, and parts of
123 <code>&lt;random&gt;</code>.</p>
Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]124
125 <p>libc++ is currently dependent upon a separate library for the low-level
126 ABI compatibility with gcc. As a workaround it can be linked against
127 gcc's libstdc++.</p>
128
129 <!--=====================================================================-->
130 <h2>Get it and get involved!</h2>
131 <!--=====================================================================-->
132
133 <p>To check out the code, use:</p>
134
135 <ul>
Chris Lattnere66f1e32010-05-11 20:37:52 +0000[diff] [blame]136 <li><code>svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx</code></li>
137 <li><code>cd libcxx/lib</code></li>
Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]138 <li><code>./buildit</code></li>
139 </ul>
140
141 <p>To run the libc++ test suit (recommended):</p>
142
143 <ul>
Chris Lattnere66f1e32010-05-11 20:37:52 +0000[diff] [blame]144 <li><code>cd libcxx/test</code></li>
Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]145 <li><code>./testit</code></li>
146 </ul>
147
Howard Hinnantc5b02f22010-05-11 19:53:34 +0000[diff] [blame]148 <p>Send discussions to the
149 (<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">clang mailing list</a>).</p>
150
Howard Hinnantc51e1022010-05-11 19:42:16 +0000[diff] [blame]151</div>
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