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1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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3 <!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
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4 <html>
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5 <head>
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6 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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7 <title>"libc++abi" C++ Standard Library Support</title>
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8 <link type="text/css" rel="stylesheet" href="menu.css">
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9 <link type="text/css" rel="stylesheet" href="content.css">
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10 </head>
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11
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12 <body>
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13 <div id="menu">
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14 <div>
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15 <a href="https://llvm.org/">LLVM Home</a>
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16 </div>
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17
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18 <div class="submenu">
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19 <label>libc++abi Info</label>
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20 <a href="/index.html">About</a>
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21 </div>
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22
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23 <div class="submenu">
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24 <label>Quick Links</label>
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25 <a href="https://libcxx.llvm.org/">libc++</a>
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26 <a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a>
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27 <a href="https://lists.llvm.org/mailman/listinfo/libcxx-commits">libcxx-commits</a>
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28 <a href="https://bugs.llvm.org/">Bug Reports</a>
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29 <a href="https://github.com/llvm/llvm-project/tree/master/libcxxabi/">Browse Sources</a>
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30 </div>
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31 </div>
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32
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33 <div id="content">
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34 <!--*********************************************************************-->
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35 <h1>"libc++abi" C++ Standard Library Support</h1>
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36 <!--*********************************************************************-->
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37
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38 <p>libc++abi is a new implementation of low level support for a standard
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39 C++ library.</p>
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40
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41 <p>All of the code in libc++abi is <a
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42 href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a>
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43 under the MIT license and the UIUC License (a BSD-like license).</p>
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44
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45 <!--=====================================================================-->
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46 <h2 id="goals">Features and Goals</h2>
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47 <!--=====================================================================-->
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48
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49 <ul>
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50 <li>Correctness as defined by the C++11 standard.</li>
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51 <li>Provide a portable sublayer to ease the porting of <a href="https://libcxx.llvm.org/">libc++</a></li>
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52 <li>On Mac OS X, be ABI compatible with the existing low-level support.</li>
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53 </ul>
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54
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55 <!--=====================================================================-->
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56 <h2 id="requirements">Platform Support</h2>
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57 <!--=====================================================================-->
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58
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59 <p>libc++abi is known to work on the following platforms, using clang.</p>
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60
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61 <ul>
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62 <li>Darwin</li>
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63 </ul>
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64
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65 <!--=====================================================================-->
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66 <h2 id="dir-structure">Current Status</h2>
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67 <!--=====================================================================-->
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68
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69 <p>libc++abi is complete. <a href="spec.html">Here</a> is a
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70 list of functionality.</p>
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71
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72 <!--=====================================================================-->
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73 <h2>Get it and get involved!</h2>
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74 <!--=====================================================================-->
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75
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76 <p>To check out the code (including llvm and others), use:</p>
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77
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78 <ul>
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79 <li><code>git clone https://github.com/llvm/llvm-project.git</code></li>
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80 </ul>
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81
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82 <p>To build:</p>
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83 <ul>
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84 <li><code>cd llvm-project</code></li>
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85 <li><code>mkdir build && cd build</code></li>
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86 <li><code>cmake -DLLVM_ENABLE_PROJECTS=libcxxabi ../llvm # on linux you may need to specify -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
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87 <li><code>make</code></li>
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88 </ul>
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89
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90 <p>To do a standalone build:</p>
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91 <ul>
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92 <li>
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93 Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
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94 </li>
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95 <li><code>cd llvm-project</code></li>
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96 <li><code>mkdir build-libcxxabi && cd build-libcxxabi</code></li>
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97 <li><code>cmake -DLIBCXXABI_LIBCXX_PATH=path/to/libcxx ../libcxxabi # on
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98 linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
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99 <li><code>make</code></li>
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100 </ul>
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101 <p> By default CMake uses <code>llvm-config</code> to locate the required
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102 LLVM sources. If CMake cannot find <code>llvm-config</code> then you must
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103 configure CMake using either of the following options.
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104 </p>
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105 <ul>
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106 <li><code>-DLLVM_CONFIG_PATH=path/to/llvm-config</code></li>
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107 <li><code>-DLLVM_PATH=path/to/llvm-source-root</code></li>
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108 </ul>
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109
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110 </p>
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111
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112 <p>To run the tests:</p>
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113 <ul>
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114 <li><code>make check-cxxabi</code></li>
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115 </ul>
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116 <p>Note: in a standalone build, the system's libc++ will be used for tests. If
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117 the system's libc++ was statically linked against libc++abi (or linked against
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118 a different ABI library), this may interfere with test results.</p>
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119
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120 <p>Send discussions to the
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121 (<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev mailing list</a>).</p>
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122
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123 <!--=====================================================================-->
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124 <h2>Frequently asked questions</h2>
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125 <!--=====================================================================-->
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126
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127 <p>Q: Why are the destructors for the standard exception classes defined in libc++abi?
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128 They're just empty, can't they be defined inline?</p>
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129 <p>A: The destructors for them live in libc++abi because they are "key" functions.
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130 The Itanium ABI describes a "key" function as the first virtual declared.
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131 And wherever the key function is defined, that is where the <code>type_info</code> gets defined.
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132 And in libc++ types are the same type if and only if they have the same <code>type_info</code>
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133 (as in there must be only one type info per type in the entire application).
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134 And on OS X, libstdc++ and libc++ share these exception types.
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135 So to be able to throw in one dylib and catch in another (a <code>std::exception</code> for example),
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136 there must be only one <code>std::exception type_info</code> in the entire app.
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137 That typeinfo gets laid down beside <code>~exception()</code> in libc++abi (for both libstdc++ and libc++).</p>
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138 <p>--Howard Hinnant</p>
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139
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140 </div>
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141 </body>
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142 </html>
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