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

   <p>libc++abi is a new implementation of low level support for a standard
      C++ library.</p>

   <p>All of the code in libc++abi is <a
      href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a>
      under the MIT license and the UIUC License (a BSD-like license).</p>

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

     <ul>
         <li>Correctness as defined by the C++11 standard.</li>
         <li>Provide a portable sublayer to ease the porting of <a href="https://libcxx.llvm.org/">libc++</a></li>
         <li>On Mac OS X, be ABI compatible with the existing low-level support.</li>
     </ul>

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

    <p>libc++abi is known to work on the following platforms, using clang.</p>

     <ul>
     <li>Darwin</li>
     </ul>

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

    <p>libc++abi is complete.  <a href="spec.html">Here</a> is a
    list of functionality.</p>

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

   <p>For building libc++abi, please see the libc++ documentation on
      <a href="https://libcxx.llvm.org/BuildingLibcxx.html">building the runtimes</a>.
   </p>

   <p>For getting involved with libc++abi, please see the libc++ documentation on
       <a href="https://libcxx.llvm.org/Contributing.html">getting involved</a>.
   </p>

   <!--=====================================================================-->
   <h2>Frequently asked questions</h2>
   <!--=====================================================================-->

   <p>Q: Why are the destructors for the standard exception classes defined in libc++abi?
      They're just empty, can't they be defined inline?</p>
   <p>A: The destructors for them live in libc++abi because they are "key" functions.
      The Itanium ABI describes a "key" function as the first virtual declared.
      And wherever the key function is defined, that is where the <code>type_info</code> gets defined.
      And in libc++ types are the same type if and only if they have the same <code>type_info</code>
      (as in there must be only one type info per type in the entire application).
      And on OS X, libstdc++ and libc++ share these exception types.
      So to be able to throw in one dylib and catch in another (a <code>std::exception</code> for example),
      there must be only one <code>std::exception type_info</code> in the entire app.
      That typeinfo gets laid down beside <code>~exception()</code> in libc++abi (for both libstdc++ and libc++).</p>
      <p>--Howard Hinnant</p>

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	<div id="menu">
	<div>
	<a href="https://llvm.org/">LLVM Home</a>
	</div>

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

	<div class="submenu">
	<label>Quick Links</label>
	<a href="https://libcxx.llvm.org/">libc++</a>
	<a href="https://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a>
	<a href="https://lists.llvm.org/mailman/listinfo/libcxx-commits">libcxx-commits</a>
	<a href="https://bugs.llvm.org/">Bug Reports</a>
	<a href="https://github.com/llvm/llvm-project/tree/main/libcxxabi/">Browse Sources</a>
	</div>
	</div>

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

	<p>libc++abi is a new implementation of low level support for a standard
	C++ library.</p>

	<p>All of the code in libc++abi is <a
	href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a>
	under the MIT license and the UIUC License (a BSD-like license).</p>

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

	<ul>
	<li>Correctness as defined by the C++11 standard.</li>
	<li>Provide a portable sublayer to ease the porting of <a href="https://libcxx.llvm.org/">libc++</a></li>
	<li>On Mac OS X, be ABI compatible with the existing low-level support.</li>
	</ul>

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

	<p>libc++abi is known to work on the following platforms, using clang.</p>

	<ul>
	<li>Darwin</li>
	</ul>

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

	<p>libc++abi is complete. <a href="spec.html">Here</a> is a
	list of functionality.</p>

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

	<p>For building libc++abi, please see the libc++ documentation on
	<a href="https://libcxx.llvm.org/BuildingLibcxx.html">building the runtimes</a>.
	</p>

	<p>For getting involved with libc++abi, please see the libc++ documentation on
	<a href="https://libcxx.llvm.org/Contributing.html">getting involved</a>.
	</p>

	<!--=====================================================================-->
	<h2>Frequently asked questions</h2>
	<!--=====================================================================-->

	<p>Q: Why are the destructors for the standard exception classes defined in libc++abi?
	They're just empty, can't they be defined inline?</p>
	<p>A: The destructors for them live in libc++abi because they are "key" functions.
	The Itanium ABI describes a "key" function as the first virtual declared.
	And wherever the key function is defined, that is where the <code>type_info</code> gets defined.
	And in libc++ types are the same type if and only if they have the same <code>type_info</code>
	(as in there must be only one type info per type in the entire application).
	And on OS X, libstdc++ and libc++ share these exception types.
	So to be able to throw in one dylib and catch in another (a <code>std::exception</code> for example),
	there must be only one <code>std::exception type_info</code> in the entire app.
	That typeinfo gets laid down beside <code>~exception()</code> in libc++abi (for both libstdc++ and libc++).</p>
	<p>--Howard Hinnant</p>

	</div>
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