Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / clang / 60d222f6f5bbf6613ff0ba5564c466ce15036998 / . / docs / LanguageExtensions.html
blob: ef57a659c4de4be8ae8b352d80837a769b01e378 [file] [log] [blame]
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]4<html>
5<head>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]6 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]7 <title>Clang Language Extensions</title>
Sean Hunt64f857b2011-06-23 01:22:53 +0000[diff] [blame]8 <link type="text/css" rel="stylesheet" href="../menu.css">
9 <link type="text/css" rel="stylesheet" href="../content.css">
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]10 <style type="text/css">
11 td {
12 vertical-align: top;
13 }
14 </style>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]15</head>
16<body>
17
18<!--#include virtual="../menu.html.incl"-->
19
20<div id="content">
21
22<h1>Clang Language Extensions</h1>
23
24<ul>
25<li><a href="#intro">Introduction</a></li>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]26<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]27<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]28<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]29<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]30<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
31<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]32<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]33 <ul>
34 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
35 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]36 </ul></li>
37<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]38 <ul>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]39 <li><a href="#cxx0x">C++0x</a>
40 <ul>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]41 <li><a href="#cxx_access_control_sfinae">C++0x SFINAE includes access control</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]42 <li><a href="#cxx_alias_templates">C++0x alias templates</a></li>
43 <li><a href="#cxx_attributes">C++0x attributes</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]44 <li><a href="#cxx_constexpr">C++0x generalized constant expressions</a></li>
45 <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]46 <li><a href="#cxx_default_function_template_args">C++0x default template arguments in function templates</a></li>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]47 <li><a href="#cxx_delegating_constructor">C++0x delegating constructors</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]48 <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]49 <li><a href="#cxx_explicit_conversions">C++0x explicit conversion functions</a></li>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]50 <li><a href="#cxx_generalized_initializers">C++0x generalized initializers</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]51 <li><a href="#cxx_implicit_moves">C++0x implicit move constructors/assignment operators</a></li>
52 <li><a href="#cxx_inheriting_constructors">C++0x inheriting constructors</a></li>
53 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]54 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]55 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
56 <li><a href="#cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]57 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
58 <li><a href="#cxx_override_control">C++0x override control</a></li>
59 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]60 <li><a href="#cxx_raw_string_literals">C++0x raw string literals</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]61 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
62 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
63 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
64 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]65 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]66 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]67 <li><a href="#cxx_unicode_literals">C++0x Unicode string literals</a></li>
68 <li><a href="#cxx_unrestricted_unions">C++0x unrestricted unions</a></li>
69 <li><a href="#cxx_user_literals">C++0x user-defined literals</a></li>
70 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
71 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]72 <li><a href="#c1x">C1X</a>
73 <ul>
74 <li><a href="#c_generic_selections">C1X generic selections</a></li>
75 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]76 </ul></li>
77 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]78<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]79<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]80<li><a href="#objc_features">Objective-C Features</a>
81 <ul>
82 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]83 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]84 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]85 </ul>
86</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]87<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]88<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]89<li><a href="#builtins">Builtin Functions</a>
90 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]91 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]92 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]93 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]94 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]95</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]96<li><a href="#targetspecific">Target-Specific Extensions</a>
97 <ul>
98 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
99 </ul>
100</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]101<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]102<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
103 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]104 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
105 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
106 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]107 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
108 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]109 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
110 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
111 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
112 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
113 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
114 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
115 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
116 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
117 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
118 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
119 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
120 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
121 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]122 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]123</ul>
124
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]125<!-- ======================================================================= -->
126<h2 id="intro">Introduction</h2>
127<!-- ======================================================================= -->
128
129<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]130addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]131range of GCC extensions. Please see the <a
132href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
133more information on these extensions.</p>
134
135<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]136<h2 id="feature_check">Feature Checking Macros</h2>
137<!-- ======================================================================= -->
138
139<p>Language extensions can be very useful, but only if you know you can depend
Chris Lattnerc70e1932011-03-21 16:25:11 +0000[diff] [blame]140on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]141function-like macros. This allows you to directly test for a feature in your
142code without having to resort to something like autoconf or fragile "compiler
143version checks".</p>
144
145<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]146<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]147<!-- ======================================================================= -->
148
149<p>This function-like macro takes a single identifier argument that is the name
150of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
151not. It can be used like this:</p>
152
153<blockquote>
154<pre>
155#ifndef __has_builtin // Optional of course.
156 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
157#endif
158
159...
160#if __has_builtin(__builtin_trap)
161 __builtin_trap();
162#else
163 abort();
164#endif
165...
166</pre>
167</blockquote>
168
169
170<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]171<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]172<!-- ======================================================================= -->
173
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]174<p>These function-like macros take a single identifier argument that is the
175name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
176is both supported by Clang and standardized in the current language standard
177or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
178<code>__has_extension</code> evaluates to 1 if the feature is supported by
179Clang in the current language (either as a language extension or a standard
180language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]181
182<blockquote>
183<pre>
184#ifndef __has_feature // Optional of course.
185 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
186#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]187#ifndef __has_extension
188 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
189#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]190
191...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]192#if __has_feature(cxx_rvalue_references)
193// This code will only be compiled with the -std=c++0x and -std=gnu++0x
194// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]195#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]196
197#if __has_extension(cxx_rvalue_references)
198// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
199// and -std=gnu++98 options, because rvalue references are supported as a
200// language extension in C++98.
201#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]202</pre>
203</blockquote>
204
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]205<p id="has_feature_back_compat">For backwards compatibility reasons,
206<code>__has_feature</code> can also be used to test for support for
207non-standardized features, i.e. features not prefixed <code>c_</code>,
208<code>cxx_</code> or <code>objc_</code>.</p>
209
210<p>If the <code>-pedantic-errors</code> option is given,
211<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
212
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]213<p>The feature tag is described along with the language feature below.</p>
214
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]215<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]216<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]217<!-- ======================================================================= -->
218
219<p>This function-like macro takes a single identifier argument that is the name
220of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
221can be used like this:</p>
222
223<blockquote>
224<pre>
225#ifndef __has_attribute // Optional of course.
226 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
227#endif
228
229...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]230#if __has_attribute(always_inline)
231#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]232#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]233#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]234#endif
235...
236</pre>
237</blockquote>
238
239<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]240<h2 id="has_include">Include File Checking Macros</h2>
241<!-- ======================================================================= -->
242
243<p>Not all developments systems have the same include files.
244The <a href="#__has_include">__has_include</a> and
245<a href="#__has_include_next">__has_include_next</a> macros allow you to
246check for the existence of an include file before doing
247a possibly failing #include directive.</p>
248
249<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]250<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]251<!-- ======================================================================= -->
252
253<p>This function-like macro takes a single file name string argument that
254is the name of an include file. It evaluates to 1 if the file can
255be found using the include paths, or 0 otherwise:</p>
256
257<blockquote>
258<pre>
259// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]260#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]261# include "myinclude.h"
262#endif
263
264// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]265#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]266# include "myinclude.h"
267#endif
268</pre>
269</blockquote>
270
271<p>To test for this feature, use #if defined(__has_include).</p>
272
273<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]274<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]275<!-- ======================================================================= -->
276
277<p>This function-like macro takes a single file name string argument that
278is the name of an include file. It is like __has_include except that it
279looks for the second instance of the given file found in the include
280paths. It evaluates to 1 if the second instance of the file can
281be found using the include paths, or 0 otherwise:</p>
282
283<blockquote>
284<pre>
285// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]286#if __has_include_next("myinclude.h") &amp;&amp; __has_include_next(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]287# include_next "myinclude.h"
288#endif
289
290// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]291#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]292# include_next "myinclude.h"
293#endif
294</pre>
295</blockquote>
296
297<p>Note that __has_include_next, like the GNU extension
298#include_next directive, is intended for use in headers only,
299and will issue a warning if used in the top-level compilation
300file. A warning will also be issued if an absolute path
301is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]302
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]303
304<!-- ======================================================================= -->
305<h3><a name="__has_warning">__has_warning</a></h3>
306<!-- ======================================================================= -->
307
308<p>This function-like macro takes a string literal that represents a command
309 line option for a warning and returns true if that is a valid warning
310 option.</p>
311
312<blockquote>
313<pre>
314#if __has_warning("-Wformat")
315...
316#endif
317</pre>
318</blockquote>
319
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]320<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]321<h2 id="builtinmacros">Builtin Macros</h2>
322<!-- ======================================================================= -->
323
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]324<dl>
325 <dt><code>__BASE_FILE__</code></dt>
326 <dd>Defined to a string that contains the name of the main input
327 file passed to Clang.</dd>
328
329 <dt><code>__COUNTER__</code></dt>
330 <dd>Defined to an integer value that starts at zero and is
331 incremented each time the <code>__COUNTER__</code> macro is
332 expanded.</dd>
333
334 <dt><code>__INCLUDE_LEVEL__</code></dt>
335 <dd>Defined to an integral value that is the include depth of the
336 file currently being translated. For the main file, this value is
337 zero.</dd>
338
339 <dt><code>__TIMESTAMP__</code></dt>
340 <dd>Defined to the date and time of the last modification of the
341 current source file.</dd>
342
343 <dt><code>__clang__</code></dt>
344 <dd>Defined when compiling with Clang</dd>
345
346 <dt><code>__clang_major__</code></dt>
347 <dd>Defined to the major version number of Clang (e.g., the 2 in
348 2.0.1).</dd>
349
350 <dt><code>__clang_minor__</code></dt>
351 <dd>Defined to the minor version number of Clang (e.g., the 0 in
352 2.0.1).</dd>
353
354 <dt><code>__clang_patchlevel__</code></dt>
355 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
356
357 <dt><code>__clang_version__</code></dt>
358 <dd>Defined to a string that captures the Clang version, including
359 the Subversion tag or revision number, e.g., "1.5 (trunk
360 102332)".</dd>
361</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]362
363<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]364<h2 id="vectors">Vectors and Extended Vectors</h2>
365<!-- ======================================================================= -->
366
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]367<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
368
369<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
370syntax and other tidbits as seen in OpenCL. An example is:</p>
371
372<blockquote>
373<pre>
374typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
375typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
376
377float4 foo(float2 a, float2 b) {
378 float4 c;
379 c.xz = a;
380 c.yw = b;
381 return c;
382}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]383</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]384</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]385
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]386<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]387
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]388<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
389
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]390<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]391<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]392<!-- ======================================================================= -->
393
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]394<p>An optional string message can be added to the <tt>deprecated</tt>
395and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]396
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]397<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]398<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]399</blockquote>
400
401<p>If the deprecated or unavailable declaration is used, the message
402will be incorporated into the appropriate diagnostic:</p>
403
404<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]405<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! [-Wdeprecated-declarations]
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]406 explode();
407 ^</pre>
408</blockquote>
409
410<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]411with <tt>__has_extension(attribute_deprecated_with_message)</tt>
412and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]413
414<!-- ======================================================================= -->
415<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
416<!-- ======================================================================= -->
417
418<p>Clang allows attributes to be written on individual enumerators.
419This allows enumerators to be deprecated, made unavailable, etc. The
420attribute must appear after the enumerator name and before any
421initializer, like so:</p>
422
423<blockquote>
424<pre>enum OperationMode {
425 OM_Invalid,
426 OM_Normal,
427 OM_Terrified __attribute__((deprecated)),
428 OM_AbortOnError __attribute__((deprecated)) = 4
429};</pre>
430</blockquote>
431
432<p>Attributes on the <tt>enum</tt> declaration do not apply to
433individual enumerators.</p>
434
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]435<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]436
437<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]438<h2 id="checking_language_features">Checks for Standard Language Features</h2>
439<!-- ======================================================================= -->
440
441<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
442enabled. Those features are listed here.</p>
443
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]444<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]445
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]446<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For
Sean Hunt647ba1b2011-06-23 00:42:53 +0000[diff] [blame]447example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]448
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]449<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]450
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]451<p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example,
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]452compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]453
454<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]455<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
456<!-- ======================================================================= -->
457
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]458<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
459to query if certain upcoming standard language features are enabled. Those
460features are listed here. Features that are not yet implemented will be
461noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]462
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]463<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]464
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]465<p>The features listed below are slated for inclusion in the upcoming
466C++0x standard. As a result, all these features are enabled
467with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]468
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]469<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]470
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]471<p>Use <tt>__has_feature(cxx_access_control_sfinae)</tt> or <tt>__has_extension(cxx_access_control_sfinae)</tt> to determine whether access-control errors (e.g., calling a private constructor) are considered to be template argument deduction errors (aka SFINAE errors), per <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170">C++ DR1170</a>.</p>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]472
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]473<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]474
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]475<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
476<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]477C++0x's alias declarations and alias templates is enabled.</p>
478
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]479<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]480
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]481<p>Use <tt>__has_feature(cxx_attributes)</tt> or
482<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
483parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]484
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]485<h4 id="cxx_constexpr">C++0x generalized constant expressions</h4>
486
487<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
488for generalized constant expressions (e.g., <tt>constexpr</tt>) is
489enabled. Clang does not currently implement this feature.</p>
490
491<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
492
493<p>Use <tt>__has_feature(cxx_decltype)</tt> or
494<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
495<tt>decltype()</tt> specifier is enabled.</p>
496
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]497<h4 id="cxx_default_function_template_args">C++0x default template arguments in function templates</h4>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]498
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]499<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
500<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
501if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]502
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]503<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
504
505<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
506support for delegating constructors is enabled.</p>
507
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]508<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]509
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]510<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
511<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]512deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]513
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]514<h4 id="cxx_explicit_conversions">C++0x explicit conversion functions</h3>
515<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
516
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]517<h4 id="cxx_generalized_initializers">C++0x generalized initializers</h4>
518
519<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
520support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]521<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
522this feature.</p>
523
524<h4 id="cxx_implicit_moves">C++0x implicit move constructors/assignment operators</h4>
525
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]526<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
527implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]528
529<h4 id="cxx_inheriting_constructors">C++0x inheriting constructors</h4>
530
531<p>Use <tt>__has_feature(cxx_inheriting_constructors)</tt> to determine if support for inheriting constructors is enabled. Clang does not currently implement this feature.</p>
532
533<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
534
535<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
536<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
537inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]538
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]539<h4 id="cxx_lambdas">C++0x lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]540
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]541<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
542<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]543is enabled. Clang does not currently implement this feature.</p>
544
545<h4 id="cxx_noexcept">C++0x noexcept</h4>
546
547<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
548<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
549exception specifications is enabled.</p>
550
551<h4 id="cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</h4>
552
553<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]554
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]555<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]556
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]557<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
558<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]559<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]560
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]561<h4 id="cxx_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]562
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]563<p>Use <tt>__has_feature(cxx_override_control)</tt> or
564<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]565the override control keywords is enabled.</p>
566
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]567<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]568<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
569<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
570if support for reference-qualified functions (e.g., member functions with
571<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
572is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]573
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]574<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]575
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]576<p>Use <tt>__has_feature(cxx_range_for)</tt> or
577<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
578range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]579
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]580<h4 id="cxx_raw_string_literals">C++0x raw string literals</h4>
581<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support for raw string literals (e.g., <tt>R"foo\bar"</tt>) is enabled.</p>
582
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]583<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]584
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]585<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
586<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]587rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]588
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]589<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]590
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]591<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
592<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]593compile-time assertions using <tt>static_assert</tt> is enabled.</p>
594
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]595<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]596
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]597<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
598<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
599supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
600will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]601
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]602<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]603
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]604<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
605<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
606strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]607
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]608<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]609
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]610<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
611<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
612alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]613
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]614<h4 id="cxx_unicode_literals">C++0x Unicode string literals</h4>
615<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
616support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]617
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]618<h4 id="cxx_unrestricted_unions">C++0x unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]619
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]620<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled. Clang does not currently support this feature.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]621
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]622<h4 id="cxx_user_literals">C++0x user-defined literals</h4>
623
624<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled. Clang does not currently support this feature.</p>
625
626<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
627
628<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
629<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
630for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]631
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]632<h3 id="c1x">C1X</h3>
633
634<p>The features listed below are slated for inclusion in the upcoming
635C1X standard. As a result, all these features are enabled
636with the <tt>-std=c1x</tt> option when compiling C code.</p>
637
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]638<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]639
640<p>Use <tt>__has_feature(c_generic_selections)</tt> or
641<tt>__has_extension(c_generic_selections)</tt> to determine if support for
642generic selections is enabled.</p>
643
644<p>As an extension, the C1X generic selection expression is available in all
645languages supported by Clang. The syntax is the same as that given in the
646C1X draft standard.</p>
647
648<p>In C, type compatibility is decided according to the rules given in the
649appropriate standard, but in C++, which lacks the type compatibility rules
650used in C, types are considered compatible only if they are equivalent.</p>
651
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]652<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]653
654<p>Use <tt>__has_feature(c_static_assert)</tt> or
655<tt>__has_extension(c_static_assert)</tt> to determine if support for
656compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
657
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]658<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]659<h2 id="checking_type_traits">Checks for Type Traits</h2>
660<!-- ======================================================================= -->
661
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]662<p>Clang supports the <a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html">GNU C++ type traits</a> and a subset of the <a href="http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx">Microsoft Visual C++ Type traits</a>. For each supported type trait <code>__X</code>, <code>__has_extension(X)</code> indicates the presence of the type trait. For example:
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]663<blockquote>
664<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]665#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]666template&lt;typename From, typename To&gt;
667struct is_convertible_to {
668 static const bool value = __is_convertible_to(From, To);
669};
670#else
671// Emulate type trait
672#endif
673</pre>
674</blockquote>
675
676<p>The following type traits are supported by Clang:</p>
677<ul>
678 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
679 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
680 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
681 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
682 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
683 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
684 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
685 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
686 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
687 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
688 <li><code>__is_class</code> (GNU, Microsoft)</li>
689 <li><code>__is_convertible_to</code> (Microsoft)</li>
690 <li><code>__is_empty</code> (GNU, Microsoft)</li>
691 <li><code>__is_enum</code> (GNU, Microsoft)</li>
692 <li><code>__is_pod</code> (GNU, Microsoft)</li>
693 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
694 <li><code>__is_union</code> (GNU, Microsoft)</li>
695 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
Sean Hunt1fba8282011-07-18 17:22:33 +0000[diff] [blame]696 <li><code>__underlying_type(type)</code>: Retrieves the underlying type for a given <code>enum</code> type. This trait is required to implement the C++0x standard library.</li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]697</ul>
698
699<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]700<h2 id="blocks">Blocks</h2>
701<!-- ======================================================================= -->
702
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]703<p>The syntax and high level language feature description is in <a
704href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
705details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]706href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]707
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]708
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]709<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]710
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]711<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]712<h2 id="objc_features">Objective-C Features</h2>
713<!-- ======================================================================= -->
714
715<h3 id="objc_instancetype">Related result types</h3>
716
717<p>According to Cocoa conventions, Objective-C methods with certain names ("init", "alloc", etc.) always return objects that are an instance of the receiving class's type. Such methods are said to have a "related result type", meaning that a message send to one of these methods will have the same static type as an instance of the receiver class. For example, given the following classes:</p>
718
719<blockquote>
720<pre>
721@interface NSObject
722+ (id)alloc;
723- (id)init;
724@end
725
726@interface NSArray : NSObject
727@end
728</pre>
729</blockquote>
730
731<p>and this common initialization pattern</p>
732
733<blockquote>
734<pre>
735NSArray *array = [[NSArray alloc] init];
736</pre>
737</blockquote>
738
739<p>the type of the expression <code>[NSArray alloc]</code> is
740<code>NSArray*</code> because <code>alloc</code> implicitly has a
741related result type. Similarly, the type of the expression
742<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
743<code>init</code> has a related result type and its receiver is known
744to have the type <code>NSArray *</code>. If neither <code>alloc</code> nor <code>init</code> had a related result type, the expressions would have had type <code>id</code>, as declared in the method signature.</p>
745
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]746<p>A method with a related result type can be declared by using the
747type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
748is a contextual keyword that is only permitted in the result type of
749an Objective-C method, e.g.</p>
750
751<pre>
752@interface A
753+ (<b>instancetype</b>)constructAnA;
754@end
755</pre>
756
757<p>The related result type can also be inferred for some methods.
758To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]759word in the camel-case selector (e.g., "init" in "initWithObjects") is
760considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]761type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]762
763<ul>
764
765 <li>the first word is "alloc" or "new", and the method is a class
766 method, or</li>
767
768 <li>the first word is "autorelease", "init", "retain", or "self",
769 and the method is an instance method.</li>
770
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]771</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]772
773<p>If a method with a related result type is overridden by a subclass
774method, the subclass method must also return a type that is compatible
775with the subclass type. For example:</p>
776
777<blockquote>
778<pre>
779@interface NSString : NSObject
780- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
781@end
782</pre>
783</blockquote>
784
785<p>Related result types only affect the type of a message send or
786property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]787with a related result type is treated the same way as method that
788returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]789
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]790<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
791the <tt>instancetype</tt> contextual keyword is available.</p>
792
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]793<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]794<h2 id="objc_arc">Automatic reference counting </h2>
795<!-- ======================================================================= -->
796
797<p>Clang provides support for <a href="AutomaticReferenceCounting.html">automated reference counting</a> in Objective-C, which eliminates the need for manual retain/release/autorelease message sends. There are two feature macros associated with automatic reference counting: <code>__has_feature(objc_arc)</code> indicates the availability of automated reference counting in general, while <code>__has_feature(objc_arc_weak)</code> indicates that automated reference counting also includes support for <code>__weak</code> pointers to Objective-C objects.</p>
798
799<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]800<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
801<!-- ======================================================================= -->
802
803<p>Clang provides support for C++0x enumerations with a fixed
804underlying type within Objective-C. For example, one can write an
805enumeration type as:</p>
806
807<pre>
808typedef enum : unsigned char { Red, Green, Blue } Color;
809</pre>
810
811<p>This specifies that the underlying type, which is used to store the
812enumeration value, is <tt>unsigned char</tt>.</p>
813
814<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
815support for fixed underlying types is available in Objective-C.</p>
816
817<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]818<h2 id="overloading-in-c">Function Overloading in C</h2>
819<!-- ======================================================================= -->
820
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]821<p>Clang provides support for C++ function overloading in C. Function
822overloading in C is introduced using the <tt>overloadable</tt> attribute. For
823example, one might provide several overloaded versions of a <tt>tgsin</tt>
824function that invokes the appropriate standard function computing the sine of a
825value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
826precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]827
828<blockquote>
829<pre>
830#include &lt;math.h&gt;
831float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
832double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
833long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
834</pre>
835</blockquote>
836
837<p>Given these declarations, one can call <tt>tgsin</tt> with a
838<tt>float</tt> value to receive a <tt>float</tt> result, with a
839<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
840overloading in C follows the rules of C++ function overloading to pick
841the best overload given the call arguments, with a few C-specific
842semantics:</p>
843<ul>
844 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
845 double</tt> is ranked as a floating-point promotion (per C99) rather
846 than as a floating-point conversion (as in C++).</li>
847
848 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
849 <tt>U*</tt> is considered a pointer conversion (with conversion
850 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
851
852 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
853 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
854 conversion is given "conversion" rank.</li>
855</ul>
856
857<p>The declaration of <tt>overloadable</tt> functions is restricted to
858function declarations and definitions. Most importantly, if any
859function with a given name is given the <tt>overloadable</tt>
860attribute, then all function declarations and definitions with that
861name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]862attribute. This rule even applies to redeclarations of functions whose original
863declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]864
865<blockquote>
866<pre>
867int f(int) __attribute__((overloadable));
868float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
869
870int g(int) __attribute__((overloadable));
871int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
872</pre>
873</blockquote>
874
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]875<p>Functions marked <tt>overloadable</tt> must have
876prototypes. Therefore, the following code is ill-formed:</p>
877
878<blockquote>
879<pre>
880int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
881</pre>
882</blockquote>
883
884<p>However, <tt>overloadable</tt> functions are allowed to use a
885ellipsis even if there are no named parameters (as is permitted in C++). This feature is particularly useful when combined with the <tt>unavailable</tt> attribute:</p>
886
887<blockquote>
888<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]889void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]890</pre>
891</blockquote>
892
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]893<p>Functions declared with the <tt>overloadable</tt> attribute have
894their names mangled according to the same rules as C++ function
895names. For example, the three <tt>tgsin</tt> functions in our
896motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]897<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]898caveats to this use of name mangling:</p>
899
900<ul>
901
902 <li>Future versions of Clang may change the name mangling of
903 functions overloaded in C, so you should not depend on an specific
904 mangling. To be completely safe, we strongly urge the use of
905 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
906
907 <li>The <tt>overloadable</tt> attribute has almost no meaning when
908 used in C++, because names will already be mangled and functions are
909 already overloadable. However, when an <tt>overloadable</tt>
910 function occurs within an <tt>extern "C"</tt> linkage specification,
911 it's name <i>will</i> be mangled in the same way as it would in
912 C.</li>
913</ul>
914
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]915<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]916
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]917<!-- ======================================================================= -->
918<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
919<!-- ======================================================================= -->
920
921<p>clang supports an extension which allows the following in C:</p>
922
923<blockquote>
924<pre>
925#include &lt;math.h&gt;
926#include &lt;complex.h&gt;
927complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
928</pre>
929</blockquote>
930
931<p>This construct is useful because there is no way to separately
932initialize the real and imaginary parts of a complex variable in
933standard C, given that clang does not support <code>_Imaginary</code>.
934(clang also supports the <code>__real__</code> and <code>__imag__</code>
935extensions from gcc, which help in some cases, but are not usable in
936static initializers.)
937
938<p>Note that this extension does not allow eliding the braces; the
939meaning of the following two lines is different:</p>
940
941<blockquote>
942<pre>
943complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
944complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
945</pre>
946</blockquote>
947
948<p>This extension also works in C++ mode, as far as that goes, but does not
949 apply to the C++ <code>std::complex</code>. (In C++11, list
950 initialization allows the same syntax to be used with
951 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]952
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]953<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]954<h2 id="builtins">Builtin Functions</h2>
955<!-- ======================================================================= -->
956
957<p>Clang supports a number of builtin library functions with the same syntax as
958GCC, including things like <tt>__builtin_nan</tt>,
959<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
960<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
961addition to the GCC builtins, Clang supports a number of builtins that GCC does
962not, which are listed here.</p>
963
964<p>Please note that Clang does not and will not support all of the GCC builtins
965for vector operations. Instead of using builtins, you should use the functions
966defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
967define portable wrappers for these. Many of the Clang versions of these
968functions are implemented directly in terms of <a href="#vectors">extended
969vector support</a> instead of builtins, in order to reduce the number of
970builtins that we need to implement.</p>
971
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]972<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]973<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]974<!-- ======================================================================= -->
975
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]976<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]977permutation/shuffle/swizzle operations. This builtin is also very important for
978the implementation of various target-specific header files like
979<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]980</p>
981
982<p><b>Syntax:</b></p>
983
984<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]985__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]986</pre>
987
988<p><b>Examples:</b></p>
989
990<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]991 // Identity operation - return 4-element vector V1.
992 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
993
994 // "Splat" element 0 of V1 into a 4-element result.
995 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
996
997 // Reverse 4-element vector V1.
998 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
999
1000 // Concatenate every other element of 4-element vectors V1 and V2.
1001 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1002
1003 // Concatenate every other element of 8-element vectors V1 and V2.
1004 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1005</pre>
1006
1007<p><b>Description:</b></p>
1008
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1009<p>The first two arguments to __builtin_shufflevector are vectors that have the
1010same element type. The remaining arguments are a list of integers that specify
1011the elements indices of the first two vectors that should be extracted and
1012returned in a new vector. These element indices are numbered sequentially
1013starting with the first vector, continuing into the second vector. Thus, if
1014vec1 is a 4-element vector, index 5 would refer to the second element of vec2.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1015</p>
1016
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1017<p>The result of __builtin_shufflevector is a vector
1018with the same element type as vec1/vec2 but that has an element count equal to
1019the number of indices specified.
1020</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1021
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1022<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1023
1024<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1025<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1026<!-- ======================================================================= -->
1027
1028<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1029the program cannot be reached, even if the compiler might otherwise think it
1030can. This is useful to improve optimization and eliminates certain warnings.
1031For example, without the <tt>__builtin_unreachable</tt> in the example below,
1032the compiler assumes that the inline asm can fall through and prints a "function
1033declared 'noreturn' should not return" warning.
1034</p>
1035
1036<p><b>Syntax:</b></p>
1037
1038<pre>
1039__builtin_unreachable()
1040</pre>
1041
1042<p><b>Example of Use:</b></p>
1043
1044<pre>
1045void myabort(void) __attribute__((noreturn));
1046void myabort(void) {
1047 asm("int3");
1048 __builtin_unreachable();
1049}
1050</pre>
1051
1052<p><b>Description:</b></p>
1053
1054<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1055it has undefined behavior, it is a statement that it is never reached and the
1056optimizer can take advantage of this to produce better code. This builtin takes
1057no arguments and produces a void result.
1058</p>
1059
1060<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1061
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1062<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1063<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1064<!-- ======================================================================= -->
1065
1066<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1067memory.
1068</p>
1069
1070<p><b>Syntax:</b></p>
1071
1072<pre>
1073<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1074</pre>
1075
1076<p><b>Example of Use:</b></p>
1077
1078<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1079int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1080</pre>
1081
1082<p><b>Description:</b></p>
1083
1084<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1085intrinsics to allow code to atomically swap the current value with the new
1086value. More importantly, it helps developers write more efficient and correct
1087code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1088relying on the platform specific implementation details of
1089__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1090</p>
1091
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1092
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1093<!-- ======================================================================= -->
1094<h2 id="targetspecific">Target-Specific Extensions</h2>
1095<!-- ======================================================================= -->
1096
1097<p>Clang supports some language features conditionally on some targets.</p>
1098
1099<!-- ======================================================================= -->
1100<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1101<!-- ======================================================================= -->
1102
1103<p>The X86 backend has these language extensions:</p>
1104
1105<!-- ======================================================================= -->
1106<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1107<!-- ======================================================================= -->
1108
1109<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1110relative to the X86 GS segment register, and address space #257 causes it to be
1111relative to the X86 FS segment. Note that this is a very very low-level
1112feature that should only be used if you know what you're doing (for example in
1113an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1114
1115<p>Here is an example:</p>
1116
1117<pre>
1118#define GS_RELATIVE __attribute__((address_space(256)))
1119int foo(int GS_RELATIVE *P) {
1120 return *P;
1121}
1122</pre>
1123
1124<p>Which compiles to (on X86-32):</p>
1125
1126<pre>
1127_foo:
1128 movl 4(%esp), %eax
1129 movl %gs:(%eax), %eax
1130 ret
1131</pre>
1132
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1133<!-- ======================================================================= -->
1134<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1135<!-- ======================================================================= -->
1136
1137<p>Clang supports additional attributes that are useful for documenting program
1138invariants and rules for static analysis tools. The extensions documented here
1139are used by the <a
1140href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1141engine</a> that is part of Clang's Analysis library.</p>
1142
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1143<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1144
1145<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1146attribute. This attribute, which is typically affixed to a function prototype,
1147indicates that a call to a given function never returns. Function prototypes for
1148common functions like <tt>exit</tt> are typically annotated with this attribute,
1149as well as a variety of common assertion handlers. Users can educate the static
1150analyzer about their own custom assertion handles (thus cutting down on false
1151positives due to false paths) by marking their own &quot;panic&quot; functions
1152with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1153
1154<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1155there are special functions that for all intents and purposes should be
1156considered panic functions (i.e., they are only called when an internal program
1157error occurs) but may actually return so that the program can fail gracefully.
1158The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1159as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1160pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1161<tt>noreturn</tt>).</p>
1162
1163<p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1164same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1165placed at the end of function prototypes:</p>
1166
1167<pre>
1168 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1169</pre>
1170
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1171<p>Query for this feature with
1172<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1173
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1174<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1175
1176<p>Many methods in Objective-C have conventional meanings determined
1177by their selectors. For the purposes of static analysis, it is
1178sometimes useful to be able to mark a method as having a particular
1179conventional meaning despite not having the right selector, or as not
1180having the conventional meaning that its selector would suggest.
1181For these use cases, we provide an attribute to specifically describe
1182the <q>method family</q> that a method belongs to.</p>
1183
1184<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1185where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1186<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1187can only be placed at the end of a method declaration:</p>
1188
1189<pre>
1190 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1191</pre>
1192
1193<p>Users who do not wish to change the conventional meaning of a
1194method, and who merely want to document its non-standard retain and
1195release semantics, should use the
1196<a href="#attr_retain_release">retaining behavior attributes</a>
1197described below.</p>
1198
1199<p>Query for this feature with
1200<tt>__has_attribute(objc_method_family)</tt>.</p>
1201
1202<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1203
1204<p>In Objective-C, functions and methods are generally assumed to take
1205and return objects with +0 retain counts, with some exceptions for
1206special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1207there are exceptions, and so Clang provides attributes to allow these
1208exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1209ignore non-leaks). Some exceptions may be better described using
1210the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1211attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1212
1213<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1214<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1215and <tt>cf_returns_not_retained</tt> attributes can be placed on
1216methods and functions that return Objective-C or CoreFoundation
1217objects. They are commonly placed at the end of a function prototype
1218or method declaration:</p>
1219
1220<pre>
1221 id foo() <b>__attribute__((ns_returns_retained))</b>;
1222
1223 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1224</pre>
1225
1226<p>The <tt>*_returns_retained</tt> attributes specify that the
1227returned object has a +1 retain count.
1228The <tt>*_returns_not_retained</tt> attributes specify that the return
1229object has a +0 retain count, even if the normal convention for its
1230selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1231returned object is +0, but is guaranteed to live at least as long as the
1232next flush of an autorelease pool.</p>
1233
1234<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1235attributes can be placed on an parameter declaration; they specify
1236that the argument is expected to have a +1 retain count, which will be
1237balanced in some way by the function or method.
1238The <tt>ns_consumes_self</tt> attribute can only be placed on an
1239Objective-C method; it specifies that the method expects
1240its <tt>self</tt> parameter to have a +1 retain count, which it will
1241balance in some way.</p>
1242
1243<pre>
1244 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1245
1246 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1247 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1248</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1249
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1250<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1251<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1252
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1253
1254<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1255<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1256<!-- ======================================================================= -->
1257
1258<p>Clang supports additional attributes for checking basic locking policies in
1259multithreaded programs.
1260Clang currently parses the following list of attributes, although
1261<b>the implementation for these annotations is currently in development.</b>
1262For more details, see the
1263<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1264</p>
1265
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1266<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1267
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1268<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1269declaration to specify that the thread safety analysis should not be run on that
1270function. This attribute provides an escape hatch (e.g. for situations when it
1271is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1272
1273<h4 id="ts_lockable">lockable</h4>
1274
1275<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1276that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1277used to check consistency.</p>
1278
1279<h4 id="ts_scopedlockable">scoped_lockable</h4>
1280
1281<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1282specify that it has a "scoped" lockable type. Objects of this type will acquire
1283the lock upon construction and release it upon going out of scope.
1284 This annotation is primarily used to check
1285consistency.</p>
1286
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1287<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1288
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1289<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1290specify that the variable must be accessed while holding some lock.</p>
1291
1292<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1293
1294<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1295specify that the pointer must be dereferenced while holding some lock.</p>
1296
1297<h4 id="ts_guardedby">guarded_by(l)</h4>
1298
1299<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1300specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1301
1302<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1303
1304<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1305specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1306
1307<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1308
1309<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1310of a lockable variable to specify that the lock must be acquired before all
1311attribute arguments. Arguments must be lockable type, and there must be at
1312least one argument.</p>
1313
1314<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1315
1316<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1317of a lockable variable to specify that the lock must be acquired after all
1318attribute arguments. Arguments must be lockable type, and there must be at
1319least one argument.</p>
1320
1321<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1322
1323<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1324declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1325exclusively. This attribute takes zero or more arguments: either of lockable
1326type or integers indexing into function parameters of lockable type. If no
1327arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1328enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1329
1330<h4 id="ts_slf">shared_lock_function(...)</h4>
1331
1332<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1333declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1334 the locks may be shared (e.g. read locks). This attribute takes zero or more
1335arguments: either of lockable type or integers indexing into function
1336parameters of lockable type. If no arguments are given, the acquired lock is
1337implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1338
1339<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1340
1341<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1342declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1343all listed locks exclusively. This attribute takes one or more arguments. The
1344first argument is an integer or boolean value specifying the return value of a
1345successful lock acquisition. The remaining arugments are either of lockable type
1346or integers indexing into function parameters of lockable type. If only one
1347argument is given, the acquired lock is implicitly <tt>this</tt> of the
1348enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1349
1350<h4 id="ts_stf">shared_trylock_function(...)</h4>
1351
1352<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1353declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1354all listed locks, although the locks may be shared (e.g. read locks). This
1355attribute takes one or more arguments. The first argument is an integer or
1356boolean value specifying the return value of a successful lock acquisition. The
1357remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1358function parameters of lockable type. If only one argument is given, the
1359acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1360
1361<h4 id="ts_uf">unlock_function(...)</h4>
1362
1363<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1364declaration to specify that the function release all listed locks. This
1365attribute takes zero or more arguments: either of lockable type or integers
1366indexing into function parameters of lockable type. If no arguments are given,
1367the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1368
1369<h4 id="ts_lr">lock_returned(l)</h4>
1370
1371<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1372declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1373must be of lockable type). This annotation is used to aid in resolving lock
1374expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1375
1376<h4 id="ts_le">locks_excluded(...)</h4>
1377
1378<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1379to specify that the function must not be called with the listed locks. Arguments
1380must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1381
1382<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1383
1384<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1385declaration to specify that the function must be called while holding the listed
1386exclusive locks. Arguments must be lockable type, and there must be at
1387least one argument.</p>
1388
1389<h4 id="ts_slr">shared_locks_required(...)</h4>
1390
1391<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1392declaration to specify that the function must be called while holding the listed
1393shared locks. Arguments must be lockable type, and there must be at
1394least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1395
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1396</div>
1397</body>
1398</html>