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<html>
<head>
<title>Clang Language Extensions</title>
<link type="text/css" rel="stylesheet" href="../menu.css" />
<link type="text/css" rel="stylesheet" href="../content.css" />
<style type="text/css">
td {
vertical-align: top;
}
</style>
</head>
<body>
<!--#include virtual="../menu.html.incl"-->
<div id="content">
<h1>Clang Language Extensions</h1>
<ul>
<li><a href="#intro">Introduction</a></li>
<li><a href="#feature_check">Feature Checking Macros</a></li>
<li><a href="#has_include">Include File Checking Macros</a></li>
<li><a href="#builtinmacros">Builtin Macros</a></li>
<li><a href="#vectors">Vectors and Extended Vectors</a></li>
<li><a href="#checking_language_features">Checks for Standard Language Features</a></li>
<ul>
<li><a href="#cxx_exceptions">C++ exceptions</a></li>
<li><a href="#cxx_rtti">C++ RTTI</a></li>
</ul>
<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a></li>
<ul>
<li><a href="#cxx_attributes">C++0x attributes</a></li>
<li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
<li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
<li><a href="#cxx_concepts">C++ TR concepts</a></li>
<li><a href="#cxx_lambdas">C++0x lambdas</a></li>
<li><a href="#cxx_nullptr">C++0x nullptr</a></li>
<li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
<li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
<li><a href="#cxx_auto_type">C++0x type inference</a></li>
<li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
</ul>
<li><a href="#blocks">Blocks</a></li>
<li><a href="#overloading-in-c">Function Overloading in C</a></li>
<li><a href="#builtins">Builtin Functions</a>
<ul>
<li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
<li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
</ul>
</li>
<li><a href="#targetspecific">Target-Specific Extensions</a>
<ul>
<li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
</ul>
</li>
<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a>
<ul>
<li><a href="#analyzerattributes">Analyzer Attributes</a></li>
</ul>
</li>
</ul>
<!-- ======================================================================= -->
<h2 id="intro">Introduction</h2>
<!-- ======================================================================= -->
<p>This document describes the language extensions provided by Clang. In
addition to the language extensions listed here, Clang aims to support a broad
range of GCC extensions. Please see the <a
href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
more information on these extensions.</p>
<!-- ======================================================================= -->
<h2 id="feature_check">Feature Checking Macros</h2>
<!-- ======================================================================= -->
<p>Language extensions can be very useful, but only if you know you can depend
on them. In order to allow fine-grain features checks, we support two builtin
function-like macros. This allows you to directly test for a feature in your
code without having to resort to something like autoconf or fragile "compiler
version checks".</p>
<!-- ======================================================================= -->
<h3 id="__has_builtin">__has_builtin</h3>
<!-- ======================================================================= -->
<p>This function-like macro takes a single identifier argument that is the name
of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
not. It can be used like this:</p>
<blockquote>
<pre>
#ifndef __has_builtin // Optional of course.
#define __has_builtin(x) 0 // Compatibility with non-clang compilers.
#endif
...
#if __has_builtin(__builtin_trap)
__builtin_trap();
#else
abort();
#endif
...
</pre>
</blockquote>
<!-- ======================================================================= -->
<h3 id="__has_feature">__has_feature</h3>
<!-- ======================================================================= -->
<p>This function-like macro takes a single identifier argument that is the name
of a feature. It evaluates to 1 if the feature is supported or 0 if not. It
can be used like this:</p>
<blockquote>
<pre>
#ifndef __has_feature // Optional of course.
#define __has_feature(x) 0 // Compatibility with non-clang compilers.
#endif
...
#if __has_feature(attribute_overloadable) || \
__has_feature(blocks)
...
#endif
...
</pre>
</blockquote>
<p>The feature tag is described along with the language feature below.</p>
<!-- ======================================================================= -->
<h2 id="has_include">Include File Checking Macros</h2>
<!-- ======================================================================= -->
<p>Not all developments systems have the same include files.
The <a href="#__has_include">__has_include</a> and
<a href="#__has_include_next">__has_include_next</a> macros allow you to
check for the existence of an include file before doing
a possibly failing #include directive.</p>
<!-- ======================================================================= -->
<h3 id="__has_include">__has_include</h3>
<!-- ======================================================================= -->
<p>This function-like macro takes a single file name string argument that
is the name of an include file. It evaluates to 1 if the file can
be found using the include paths, or 0 otherwise:</p>
<blockquote>
<pre>
// Note the two possible file name string formats.
#if __has_include("myinclude.h") && __has_include(<stdint.h>)
# include "myinclude.h"
#endif
// To avoid problem with non-clang compilers not having this macro.
#if defined(__has_include) && __has_include("myinclude.h")
# include "myinclude.h"
#endif
</pre>
</blockquote>
<p>To test for this feature, use #if defined(__has_include).</p>
<!-- ======================================================================= -->
<h3 id="__has_include_next">__has_include_next</h3>
<!-- ======================================================================= -->
<p>This function-like macro takes a single file name string argument that
is the name of an include file. It is like __has_include except that it
looks for the second instance of the given file found in the include
paths. It evaluates to 1 if the second instance of the file can
be found using the include paths, or 0 otherwise:</p>
<blockquote>
<pre>
// Note the two possible file name string formats.
#if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>)
# include_next "myinclude.h"
#endif
// To avoid problem with non-clang compilers not having this macro.
#if defined(__has_include_next) && __has_include_next("myinclude.h")
# include_next "myinclude.h"
#endif
</pre>
</blockquote>
<p>Note that __has_include_next, like the GNU extension
#include_next directive, is intended for use in headers only,
and will issue a warning if used in the top-level compilation
file. A warning will also be issued if an absolute path
is used in the file argument.</p>
<!-- ======================================================================= -->
<h2 id="builtinmacros">Builtin Macros</h2>
<!-- ======================================================================= -->
<dl>
<dt><code>__BASE_FILE__</code></dt>
<dd>Defined to a string that contains the name of the main input
file passed to Clang.</dd>
<dt><code>__COUNTER__</code></dt>
<dd>Defined to an integer value that starts at zero and is
incremented each time the <code>__COUNTER__</code> macro is
expanded.</dd>
<dt><code>__INCLUDE_LEVEL__</code></dt>
<dd>Defined to an integral value that is the include depth of the
file currently being translated. For the main file, this value is
zero.</dd>
<dt><code>__TIMESTAMP__</code></dt>
<dd>Defined to the date and time of the last modification of the
current source file.</dd>
<dt><code>__clang__</code></dt>
<dd>Defined when compiling with Clang</dd>
<dt><code>__clang_major__</code></dt>
<dd>Defined to the major version number of Clang (e.g., the 2 in
2.0.1).</dd>
<dt><code>__clang_minor__</code></dt>
<dd>Defined to the minor version number of Clang (e.g., the 0 in
2.0.1).</dd>
<dt><code>__clang_patchlevel__</code></dt>
<dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
<dt><code>__clang_version__</code></dt>
<dd>Defined to a string that captures the Clang version, including
the Subversion tag or revision number, e.g., "1.5 (trunk
102332)".</dd>
</dl>
<!-- ======================================================================= -->
<h2 id="vectors">Vectors and Extended Vectors</h2>
<!-- ======================================================================= -->
<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
syntax and other tidbits as seen in OpenCL. An example is:</p>
<blockquote>
<pre>
typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
float4 foo(float2 a, float2 b) {
float4 c;
c.xz = a;
c.yw = b;
return c;
}
</blockquote>
<p>Query for this feature with __has_feature(attribute_ext_vector_type).</p>
<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
<!-- ======================================================================= -->
<h2 id="checking_language_features">Checks for Standard Language Features</h2>
<!-- ======================================================================= -->
<p>The <tt>__has_feature</tt> macro can be
|
