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<title>Clang - C++1z, C++14, C++11 and C++98 Status</title>
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<h1>C++ Support in Clang</h1>
<!--*************************************************************************-->
<p>Last updated: $Date$</p>
<p>Clang fully implements all published ISO C++ standards (<a
href="#cxx98">C++98 / C++03</a>, <a
href="#cxx11">C++11</a>, and <a
href="#cxx14">C++14</a>), and most of the upcoming <a
href="#cxx17">C++1z</a> standard.
<p>The Clang community is continually striving to improve C++ standards
compliance between releases by submitting and tracking <a
href="cxx_dr_status.html">C++ Defect Reports</a> and implementing resolutions
as they become available.</p>
<p>Experimental work is also under way to implement <a href="#ts">C++ Technical
Specifications</a> that will help drive the future of the C++ programming
language.</p>
<p>The <a href="http://llvm.org/bugs/">LLVM bug tracker</a> contains Clang
C++ components that track known bugs with Clang's language conformance in
each language mode.</p>
<h2 id="cxx98">C++98 implementation status</h2>
<p>Clang implements all of the ISO C++ 1998 standard
(including the defects addressed in the ISO C++ 2003 standard)
except for <tt>export</tt> (which was removed in C++11).
<h2 id="cxx11">C++11 implementation status</h2>
<p>Clang 3.3 and later implement all of the <a
href="http://www.iso.org/iso/catalogue_detail.htm?csnumber=50372">ISO
C++ 2011 standard</a>. The following table describes the Clang version
in which each feature became available.</p>
<p>By default, Clang builds C++ code according to the C++98 standard, with many
C++11 features accepted as extensions. You can use Clang in C++11 mode with the
<code>-std=c++11</code> option. Clang's C++11 mode can be used
with <a href="http://libcxx.llvm.org/">libc++</a> or with gcc's libstdc++.
<table width="689" border="1" cellspacing="0">
<tr>
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<th>Language Feature</th>
<th>C++11 Proposal</th>
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<th>Available in Clang?</th>
</tr>
<tr>
<td>Rvalue references</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2118.html">N2118</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>&nbsp;&nbsp;&nbsp;&nbsp;Rvalue references for <code>*this</code></td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2439.htm">N2439</a></td>
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<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Initialization of class objects by rvalues</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1610.html">N1610</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Non-static data member initializers</td>
<td><a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2008/n2756.htm">N2756</a></td>
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<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Variadic templates</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2242.pdf">N2242</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>&nbsp;&nbsp;&nbsp;&nbsp;Extending variadic template template parameters</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2555.pdf">N2555</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Initializer lists</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2672.htm">N2672</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Static assertions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1720.html">N1720</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td><code>auto</code>-typed variables</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1984.pdf">N1984</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>&nbsp;&nbsp;&nbsp;&nbsp;Multi-declarator <code>auto</code></td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1737.pdf">N1737</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>&nbsp;&nbsp;&nbsp;&nbsp;Removal of auto as a storage-class specifier</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2546.htm">N2546</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>&nbsp;&nbsp;&nbsp;&nbsp;New function declarator syntax</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2541.htm">N2541</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Lambda expressions</td>
<td><a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2009/n2927.pdf">N2927</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Declared type of an expression</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2343.pdf">N2343</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>&nbsp;&nbsp;&nbsp;&nbsp;Incomplete return types</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3276.pdf">N3276</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Right angle brackets</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1757.html">N1757</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Default template arguments for function templates</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#226">DR226</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Solving the SFINAE problem for expressions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2634.html">DR339</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Alias templates</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2258.pdf">N2258</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Extern templates</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1987.htm">N1987</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Null pointer constant</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2431.pdf">N2431</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Strongly-typed enums</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf">N2347</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Forward declarations for enums</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2764.pdf">N2764</a>
<br><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1206">DR1206</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Standardized attribute syntax</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2761.pdf">N2761</a></td>
<td class="full" align="center">Clang 3.3 <a href="#n2761">(1)</a></td>
</tr>
<tr>
<td>Generalized constant expressions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2235.pdf">N2235</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Alignment support</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2341.pdf">N2341</a></td>
<td class="full" align="center">Clang 3.3</td>
</tr>
<tr>
<td>Conditionally-support behavior</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1627.pdf">N1627</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Changing undefined behavior into diagnosable errors</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1727.pdf">N1727</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Delegating constructors</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1986.pdf">N1986</a></td>
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<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Inheriting constructors</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2540.htm">N2540</a></td>
<td class="full" align="center">Clang 3.3</td>
</tr>
<tr>
<td>Explicit conversion operators</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2437.pdf">N2437</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>New character types</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2249.html">N2249</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Unicode string literals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2442.htm">N2442</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Raw string literals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2442.htm">N2442</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Universal character names in literals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2170.html">N2170</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>User-defined literals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2765.pdf">N2765</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Standard Layout Types</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2342.htm">N2342</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Defaulted functions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2346.htm">N2346</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Deleted functions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2346.htm">N2346</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Extended friend declarations</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1791.pdf">N1791</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Extending <code>sizeof</code></td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2253.html">N2253</a>
<br><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#850">DR850</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Inline namespaces</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2535.htm">N2535</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Unrestricted unions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2544.pdf">N2544</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Local and unnamed types as template arguments</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm">N2657</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Range-based for</td>
<td><a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2009/n2930.html">N2930</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Explicit virtual overrides</td>
<td><a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2009/n2928.htm">N2928</a>
<br><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3206.htm">N3206</a>
<br><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3272.htm">N3272</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Minimal support for garbage collection and reachability-based leak detection</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2670.htm">N2670</a></td>
<td class="na" align="center">N/A <a href="#n2670">(2)</a></td>
</tr>
<tr>
<td>Allowing move constructors to throw [noexcept]</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3050.html">N3050</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr>
<td>Defining move special member functions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3053.html">N3053</a></td>
<td class="full" align="center">Clang 3.0</td>
</tr>
<tr class="separator">
2011-11-05 18:11:36 +08:00
<th align="center" colspan="3">Concurrency</th>
</tr>
<tr>
<td>Sequence points</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2239.html">N2239</a></td>
<td class="full" align="center">Clang 3.3</td>
</tr>
<tr>
<td>Atomic operations</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2427.html">N2427</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Strong Compare and Exchange</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2748.html">N2748</a></td>
<td class="full" align="center">Clang 3.1 <a href="#n2748">(3)</a></td>
</tr>
<tr>
<td>Bidirectional Fences</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2752.htm">N2752</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Memory model</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2429.htm">N2429</a></td>
<td class="full" align="center">Clang 3.2</td>
</tr>
<tr>
<td>Data-dependency ordering: atomics and memory model</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2664.htm">N2664</a></td>
<td class="full" align="center">Clang 3.2 <a href="#n2664">(4)</a></td>
</tr>
<tr>
<td>Propagating exceptions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2179.html">N2179</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Allow atomics use in signal handlers</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2547.htm">N2547</a></td>
<td class="full" align="center">Clang 3.1</td>
</tr>
<tr>
<td>Thread-local storage</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2659.htm">N2659</a></td>
<td class="full" align="center">Clang 3.3 <a href="#n2659">(5)</a></td>
</tr>
<tr>
<td>Dynamic initialization and destruction with concurrency</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2660.htm">N2660</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr class="separator">
<th align="center" colspan="3">C99 Features in C++11</th>
</tr>
<tr>
<td><code>__func__</code> predefined identifier</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2340.htm">N2340</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>C99 preprocessor</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1653.htm">N1653</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td><code>long long</code></td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1811.pdf">N1811</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>Extended integral types</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1988.pdf">N1988</a></td>
<td class="na" align="center">N/A <a href="#n1988">(6)</a></td>
</tr>
</table>
<p>
<span id="n2761">(1): The <code>[[carries_dependency]]</code> attribute
has no effect.</span><br>
<span id="n2670">(2): No compiler changes are required for an implementation
such as Clang that does not provide garbage collection.</span><br>
<span id="n2748">(3): All compare-exchange operations are emitted as
strong compare-exchanges.</span><br>
<span id="n2664">(4): <code>memory_order_consume</code> is lowered to
<code>memory_order_acquire</code>.</span><br>
<span id="n2659">(5): <code>thread_local</code> support
requires a C++ runtime library providing <code>__cxa_thread_atexit</code>, such
as <a href="http://libcxxabi.llvm.org">libc++abi</a> 3.6 or later,
or libsupc++ 4.8 or later.</span><br>
<span id="n1988">(6): No compiler changes are required for an implementation
such as Clang that does not provide any extended integer types.
<code>__int128</code> is not treated as an extended integer type,
because changing <code>intmax_t</code> would be an ABI-incompatible
change.</span>
</p>
<h2 id="cxx14">C++14 implementation status</h2>
<p>Clang 3.4 and later implement all of the <a
href="http://www.iso.org/iso/catalogue_detail.htm?csnumber=64029">ISO
C++ 2014 standard</a>. The following table describes the
Clang version in which each feature became available.</p>
<p>You can use Clang in C++14 mode with the <code>-std=c++14</code> option
(use <code>-std=c++1y</code> in Clang 3.4 and earlier).</p>
<table width="689" border="1" cellspacing="0">
<tr>
<th>Language Feature</th>
<th>C++14 Proposal</th>
<th>Available in Clang?</th>
</tr>
<tr>
<td>Tweak to certain C++ contextual conversions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3323.pdf">N3323</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Binary literals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3472.pdf">N3472</a></td>
<td class="full" align="center">Clang 2.9</td>
</tr>
<tr>
<td>decltype(auto)</td>
<td rowspan=2 style="vertical-align:middle"><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3638.html">N3638</a></td>
<td class="full" align="center">Clang 3.3</td>
</tr>
<tr>
<td>Return type deduction for normal functions</td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Initialized lambda captures</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3648.html">N3648</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Generic lambdas</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3649.html">N3649</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Variable templates</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3651.pdf">N3651</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Relaxing requirements on constexpr functions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3652.html">N3652</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Member initializers and aggregates</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3653.html">N3653</a></td>
<td class="full" align="center">Clang 3.3</td>
</tr>
<tr>
<td>Clarifying memory allocation</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3664.html">N3664</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td><tt>[[deprecated]]</tt> attribute</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3760.html">N3760</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>Single quotation mark as digit separator</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3781.pdf">N3781</a></td>
<td class="full" align="center">Clang 3.4</td>
</tr>
<tr>
<td>C++ Sized Deallocation</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3778.html">N3778</a></td>
<td class="full" align="center">Clang 3.4 <a href="#n3778">(7)</a></td>
</tr>
</table>
C++14: Disable sized deallocation by default due to ABI breakage There are no widely deployed standard libraries providing sized deallocation functions, so we have to punt and ask the user if they want us to use sized deallocation. In the future, when such libraries are deployed, we can teach the driver to detect them and enable this feature. N3536 claimed that a weak thunk from sized to unsized deallocation could be emitted to avoid breaking backwards compatibility with standard libraries not providing sized deallocation. However, this approach and other variations don't work in practice. With the weak function approach, the thunk has to have default visibility in order to ensure that it is overridden by other DSOs providing sized deallocation. Weak, default visibility symbols are particularly expensive on MachO, so John McCall was considering disabling this feature by default on Darwin. It also changes behavior ELF linking behavior, causing certain otherwise unreferenced object files from an archive to be pulled into the link. Our second approach was to use an extern_weak function declaration and do an inline conditional branch at the deletion call site. This doesn't work because extern_weak only works on MachO if you have some archive providing the default value of the extern_weak symbol. Arranging to provide such an archive has the same challenges as providing the symbol in the standard library. Not to mention that extern_weak doesn't really work on COFF. Reviewers: rsmith, rjmccall Differential Revision: http://reviews.llvm.org/D8467 llvm-svn: 232788
2015-03-20 08:31:07 +08:00
<p>
<span id="n3778">(7): In Clang 3.7 and later, sized deallocation is only enabled
C++14: Disable sized deallocation by default due to ABI breakage There are no widely deployed standard libraries providing sized deallocation functions, so we have to punt and ask the user if they want us to use sized deallocation. In the future, when such libraries are deployed, we can teach the driver to detect them and enable this feature. N3536 claimed that a weak thunk from sized to unsized deallocation could be emitted to avoid breaking backwards compatibility with standard libraries not providing sized deallocation. However, this approach and other variations don't work in practice. With the weak function approach, the thunk has to have default visibility in order to ensure that it is overridden by other DSOs providing sized deallocation. Weak, default visibility symbols are particularly expensive on MachO, so John McCall was considering disabling this feature by default on Darwin. It also changes behavior ELF linking behavior, causing certain otherwise unreferenced object files from an archive to be pulled into the link. Our second approach was to use an extern_weak function declaration and do an inline conditional branch at the deletion call site. This doesn't work because extern_weak only works on MachO if you have some archive providing the default value of the extern_weak symbol. Arranging to provide such an archive has the same challenges as providing the symbol in the standard library. Not to mention that extern_weak doesn't really work on COFF. Reviewers: rsmith, rjmccall Differential Revision: http://reviews.llvm.org/D8467 llvm-svn: 232788
2015-03-20 08:31:07 +08:00
if the user passes the <code>-fsized-deallocation</code> flag. The user must
supply definitions of the sized deallocation functions, either by providing them
explicitly or by using a C++ standard library that does. <code>libstdc++</code>
added these functions in version 5.0, and <code>libc++</code> added them in
version 3.7.
</span>
</p>
<h2 id="cxx17">C++1z implementation status</h2>
<p>Clang has <b>experimental</b> support for some proposed features of
the C++ standard following C++14, provisionally named C++1z.
The following table describes which C++1z features
have been implemented in Clang and in which Clang version they became
available.</p>
<p>Note that support for these features may change or be removed without notice,
as the draft C++1z standard evolves.</p>
<p>You can use Clang in C++1z mode with the <code>-std=c++1z</code> option.</p>
<table width="689" border="1" cellspacing="0">
<tr>
<th>Language Feature</th>
<th>C++1z Proposal</th>
<th>Available in Clang?</th>
</tr>
<!-- Issaquah papers -->
<tr>
<td><tt>static_assert</tt> with no message</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3928.pdf">N3928</a></td>
<td class="full" align="center">Clang 3.5</td>
</tr>
<!-- Rapperswil papers -->
<tr>
<td>Disabling trigraph expansion by default</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4086.html">N4086</a></td>
<td class="full" align="center">Clang 3.5</td>
</tr>
<!--
<tr>
<td rowspan="2">Terse range-based for loops (removed from C++1z)</td>
<td rowspan="2"><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3994.htm">N3994</a></td>
<td class="none" align="center">Clang 3.5: Yes</td>
</tr>
<tr>
<td class="svn" align="center">SVN: No</td>
</tr>
-->
<tr>
<td><tt>typename</tt> in a template template parameter</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4051.html">N4051</a></td>
<td class="full" align="center">Clang 3.5</td>
</tr>
<tr>
<td>New <tt>auto</tt> rules for direct-list-initialization
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3922.html">N3922</a></td>
<td class="full" align="center">Clang 3.8 <a href="#n3922">(8)</a></td>
</tr>
<!-- Urbana papers -->
<tr>
<td rowspan="2">Fold expressions</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4295.html">N4295</a></td>
<td class="full" align="center">Clang 3.6</td>
</tr>
<tr> <!-- from Jacksonville -->
<td><a href="http://wg21.link/p0036r0">P0036R0</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td><tt>u8</tt> character literals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4267.html">N4267</a></td>
<td class="full" align="center">Clang 3.6</td>
</tr>
<tr>
<td>Nested namespace definition</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4230.html">N4230</a></td>
<td class="full" align="center">Clang 3.6</td>
</tr>
<tr>
<td>Attributes for namespaces and enumerators</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4266.html">N4266</a></td>
<td class="full" align="center">Clang 3.6</td>
</tr>
<tr>
<td>Allow constant evaluation for all non-type template arguments</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4268.html">N4268</a></td>
<td class="full" align="center">Clang 3.6</td>
</tr>
<!-- Kona papers -->
<tr>
<td>Remove deprecated <tt>register</tt> storage class</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0001r1.html">P0001R1</a></td>
<td class="full" align="center">Clang 3.8</td>
</tr>
<tr>
<td>Remove deprecated <tt>bool</tt> increment</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0002r1.html">P0002R1</a></td>
<td class="full" align="center">Clang 3.8</td>
</tr>
<tr>
<td>Make exception specifications part of the type system</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0012r1.html">P0012R1</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td><tt>__has_include</tt> in preprocessor conditionals</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0061.html">P0061R1</a></td>
<td class="full" align="center">Yes</td>
</tr>
<tr>
<td>New specification for inheriting constructors (<a href="cxx_dr_status.html#1941">DR1941</a> et al)</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0136r1.html">P0136R1</a></td>
<td class="full" align="center">Clang 3.9 <a href="#p0136">(9)</a></td>
</tr>
<!-- Jacksonville papers -->
<tr>
<td><tt>[[fallthrough]]</tt> attribute</td>
<td><a href="http://wg21.link/p0188r1">P0188R1</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td><tt>[[nodiscard]]</tt> attribute</td>
<td><a href="http://wg21.link/p0189r1">P0189R1</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td><tt>[[maybe_unused]]</tt> attribute</td>
<td><a href="http://wg21.link/p0212r1">P0212R1</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Aggregate initialization of classes with base classes</td>
<td><a href="http://wg21.link/p0017r1">P0017R1</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td><tt>constexpr</tt> lambda expressions</td>
<td><a href="http://wg21.link/p0170r1">P0170R1</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>Differing <tt>begin</tt> and <tt>end</tt> types in range-based <tt>for</tt></td>
<td><a href="http://wg21.link/p0184r0">P0184R0</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Lambda capture of <tt>*this</tt></td>
<td><a href="http://wg21.link/p0018r3">P0018R3</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Direct-list-initialization of <tt>enum</tt>s</td>
<td><a href="http://wg21.link/p0138r2">P0138R2</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Hexadecimal floating-point literals</td>
<td><a href="http://wg21.link/p0245r1">P0245R1</a></td>
<td class="full" align="center">Yes</td>
</tr>
<!-- Oulu papers -->
<tr>
<td>Using attribute namespaces without repetition</td>
<td><a href="http://wg21.link/p0028r4">P0028R4</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Dynamic memory allocation for over-aligned data</td>
<td><a href="http://wg21.link/p0035r4">P0035R4</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>Template argument deduction for class templates</td>
<td><a href="http://wg21.link/p0091r3">P0091R3</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>Non-type template parameters with <tt>auto</tt> type</td>
<td><a href="http://wg21.link/p0127r2">P0127R2</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>Guaranteed copy elision</td>
<td><a href="http://wg21.link/p0135r1">P0135R1</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td rowspan=2>Stricter expression evaluation order</td>
<td><a href="http://wg21.link/p0145r3">P0145R3</a></td>
<td class="svn" align="center" rowspan=2>SVN <a href="#p0145">(10)</a></td>
</tr>
<tr>
<td><a href="http://wg21.link/p0400r0">P0400R0</a></td>
</tr>
<tr>
<td>Requirement to ignore unknown attributes</td>
<td><a href="http://wg21.link/p0283r2">P0283R2</a></td>
<td class="full" align="center">Yes</td>
</tr>
<tr>
<td><tt>constexpr</tt> <em>if-statement</em>s</td>
<td><a href="http://wg21.link/p0292r2">P0292R2</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Inline variables</td>
<td><a href="http://wg21.link/p0386r2">P0386R2</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
<tr>
<td>Structured bindings</td>
<td><a href="http://wg21.link/p0217r3">P0217R3</a></td>
<td class="partial" align="center">Partial</td>
</tr>
<tr>
<td>Separate variable and condition for <tt>if</tt> and <tt>switch</tt></td>
<td><a href="http://wg21.link/p0305r1">P0305R1</a></td>
<td class="full" align="center">Clang 3.9</td>
</tr>
</table>
<p>
<span id="n3922">(8): This is a backwards-incompatible change that is applied to
all language versions that allow type deduction from <tt>auto</tt>
(per the request of the C++ committee).
In Clang 3.7, a warning is emitted for all cases that would change meaning.
</span><br>
P0136R1, DR1573, DR1645, DR1715, DR1736, DR1903, DR1941, DR1959, DR1991: Replace inheriting constructors implementation with new approach, voted into C++ last year as a DR against C++11. Instead of synthesizing a set of derived class constructors for each inherited base class constructor, we make the constructors of the base class visible to constructor lookup in the derived class, using the normal rules for using-declarations. For constructors, UsingShadowDecl now has a ConstructorUsingShadowDecl derived class that tracks the requisite additional information. We create shadow constructors (not found by name lookup) in the derived class to model the actual initialization, and have a new expression node, CXXInheritedCtorInitExpr, to model the initialization of a base class from such a constructor. (This initialization is special because it performs real perfect forwarding of arguments.) In cases where argument forwarding is not possible (for inalloca calls, variadic calls, and calls with callee parameter cleanup), the shadow inheriting constructor is not emitted and instead we directly emit the initialization code into the caller of the inherited constructor. Note that this new model is not perfectly compatible with the old model in some corner cases. In particular: * if B inherits a private constructor from A, and C uses that constructor to construct a B, then we previously required that A befriends B and B befriends C, but the new rules require A to befriend C directly, and * if a derived class has its own constructors (and so its implicit default constructor is suppressed), it may still inherit a default constructor from a base class llvm-svn: 274049
2016-06-29 03:03:57 +08:00
<span id="p0136">(9): This is the resolution to a Defect Report, so is applied
to all language versions supporting inheriting constructors.
</span><br>
<span id="p0145">(10): Under the MS ABI, this feature is not fully implementable,
because the calling convention requires that function parameters are destroyed
from left to right in the callee. In order to guarantee that destruction order
is reverse construction order, the operands of overloaded
<tt>operator&lt;&lt;</tt>, <tt>operator&gt;&gt;</tt>, <tt>operator-&gt;*</tt>,
<tt>operator&amp;&amp;</tt>, <tt>operator||</tt>, and <tt>operator,</tt>
functions are evaluated right-to-left under the MS ABI when called using operator
syntax, not left-to-right as P0145R3 requires.
P0136R1, DR1573, DR1645, DR1715, DR1736, DR1903, DR1941, DR1959, DR1991: Replace inheriting constructors implementation with new approach, voted into C++ last year as a DR against C++11. Instead of synthesizing a set of derived class constructors for each inherited base class constructor, we make the constructors of the base class visible to constructor lookup in the derived class, using the normal rules for using-declarations. For constructors, UsingShadowDecl now has a ConstructorUsingShadowDecl derived class that tracks the requisite additional information. We create shadow constructors (not found by name lookup) in the derived class to model the actual initialization, and have a new expression node, CXXInheritedCtorInitExpr, to model the initialization of a base class from such a constructor. (This initialization is special because it performs real perfect forwarding of arguments.) In cases where argument forwarding is not possible (for inalloca calls, variadic calls, and calls with callee parameter cleanup), the shadow inheriting constructor is not emitted and instead we directly emit the initialization code into the caller of the inherited constructor. Note that this new model is not perfectly compatible with the old model in some corner cases. In particular: * if B inherits a private constructor from A, and C uses that constructor to construct a B, then we previously required that A befriends B and B befriends C, but the new rules require A to befriend C directly, and * if a derived class has its own constructors (and so its implicit default constructor is suppressed), it may still inherit a default constructor from a base class llvm-svn: 274049
2016-06-29 03:03:57 +08:00
</span>
</p>
<h2 id="ts">Technical specifications and standing documents</h2>
<p>ISO C++ also publishes a number of documents describing additional language
and library features that are not part of standard C++. The following table
describes which language features have been implemented in Clang and in which
Clang version they became available:</p>
<table width="689" border="1" cellspacing="0">
<tr>
<th>Document</th>
<th>Latest draft</th>
<th>Available in Clang?</th>
</tr>
<tr>
<td rowspan="2">SD-6: SG10 feature test recommendations</td>
<td rowspan="2"><a href="http://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations">SD-6</a></td>
<td class="full" align="center">
Clang 3.4 (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3745">N3745</a>)</br>
</td>
</tr>
<tr>
<td class="full" align="center">
Clang 3.6 (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4200">N4200</a>)</a>
</td>
</tr>
<tr>
<td class="svn" align="center">
SVN (<a href="http://wg21.link/p0096r2">P0096R2</a>)</a>
</td>
</tr>
<!-- FIXME: Implement latest recommendations.
<tr>
<td class="svn" align="center">
SVN (<a href="http://wg21.link/p0096r3">P0096R3</a>)</a>
</td>
</tr>
-->
<!-- No compiler support is known to be needed for:
* Concurrency TS
* Parallelism TS
* Ranges TS
* Networking TS
* File System TS
-->
<tr>
<td>[TS] Concepts</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0121r0.pdf">P0121R0</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>[TS] Library Fundamentals, Version 1 (invocation type traits)</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4480.html">N4480</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>[DRAFT TS] Library Fundamentals, Version 2 (<tt>source_location</tt>)</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4529.html">N4529</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>[TS] Modules</td>
<td><a href="http://wg21.link/p0143r2">P0143R2</a></td>
<td class="none" align="center">No</td>
</tr>
<tr>
<td>[TS] Transactional Memory</td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4514.pdf">N4514</a></td>
<td class="none" align="center">No</td>
</tr>
</table>
</div>
</body>
</html>