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gerrit-public.fairphone.software / platform / external / clang / fd5f6866a7574f12ecac5cceb7359ff253f83145 / . / docs / LanguageExtensions.html
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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>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame^]43 <li><a href="#cxx_alignas">C++0x alignment specifiers</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]44 <li><a href="#cxx_attributes">C++0x attributes</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]45 <li><a href="#cxx_constexpr">C++0x generalized constant expressions</a></li>
46 <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]47 <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]48 <li><a href="#cxx_delegating_constructor">C++0x delegating constructors</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]49 <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]50 <li><a href="#cxx_explicit_conversions">C++0x explicit conversion functions</a></li>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]51 <li><a href="#cxx_generalized_initializers">C++0x generalized initializers</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]52 <li><a href="#cxx_implicit_moves">C++0x implicit move constructors/assignment operators</a></li>
53 <li><a href="#cxx_inheriting_constructors">C++0x inheriting constructors</a></li>
54 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]55 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]56 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
57 <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]58 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
59 <li><a href="#cxx_override_control">C++0x override control</a></li>
60 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]61 <li><a href="#cxx_raw_string_literals">C++0x raw string literals</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]62 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
63 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
64 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
65 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]66 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]67 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]68 <li><a href="#cxx_unicode_literals">C++0x Unicode string literals</a></li>
69 <li><a href="#cxx_unrestricted_unions">C++0x unrestricted unions</a></li>
70 <li><a href="#cxx_user_literals">C++0x user-defined literals</a></li>
71 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
72 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]73 <li><a href="#c1x">C1X</a>
74 <ul>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame^]75 <li><a href="#c_alignas">C1X alignment specifiers</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]76 <li><a href="#c_generic_selections">C1X generic selections</a></li>
77 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]78 </ul></li>
79 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]80<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]81<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]82<li><a href="#objc_features">Objective-C Features</a>
83 <ul>
84 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]85 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]86 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]87 </ul>
88</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]89<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]90<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]91<li><a href="#builtins">Builtin Functions</a>
92 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]93 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]94 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]95 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]96 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]97</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]98<li><a href="#targetspecific">Target-Specific Extensions</a>
99 <ul>
100 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
101 </ul>
102</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]103<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]104<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
105 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]106 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
107 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
108 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]109 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
110 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]111 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
112 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
113 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
114 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
115 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
116 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
117 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
118 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
119 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
120 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
121 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
122 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
123 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]124 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]125</ul>
126
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]127<!-- ======================================================================= -->
128<h2 id="intro">Introduction</h2>
129<!-- ======================================================================= -->
130
131<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]132addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]133range of GCC extensions. Please see the <a
134href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
135more information on these extensions.</p>
136
137<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]138<h2 id="feature_check">Feature Checking Macros</h2>
139<!-- ======================================================================= -->
140
141<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]142on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]143function-like macros. This allows you to directly test for a feature in your
144code without having to resort to something like autoconf or fragile "compiler
145version checks".</p>
146
147<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]148<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]149<!-- ======================================================================= -->
150
151<p>This function-like macro takes a single identifier argument that is the name
152of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
153not. It can be used like this:</p>
154
155<blockquote>
156<pre>
157#ifndef __has_builtin // Optional of course.
158 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
159#endif
160
161...
162#if __has_builtin(__builtin_trap)
163 __builtin_trap();
164#else
165 abort();
166#endif
167...
168</pre>
169</blockquote>
170
171
172<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]173<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]174<!-- ======================================================================= -->
175
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]176<p>These function-like macros take a single identifier argument that is the
177name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
178is both supported by Clang and standardized in the current language standard
179or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
180<code>__has_extension</code> evaluates to 1 if the feature is supported by
181Clang in the current language (either as a language extension or a standard
182language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]183
184<blockquote>
185<pre>
186#ifndef __has_feature // Optional of course.
187 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
188#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]189#ifndef __has_extension
190 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
191#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]192
193...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]194#if __has_feature(cxx_rvalue_references)
195// This code will only be compiled with the -std=c++0x and -std=gnu++0x
196// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]197#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]198
199#if __has_extension(cxx_rvalue_references)
200// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
201// and -std=gnu++98 options, because rvalue references are supported as a
202// language extension in C++98.
203#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]204</pre>
205</blockquote>
206
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]207<p id="has_feature_back_compat">For backwards compatibility reasons,
208<code>__has_feature</code> can also be used to test for support for
209non-standardized features, i.e. features not prefixed <code>c_</code>,
210<code>cxx_</code> or <code>objc_</code>.</p>
211
212<p>If the <code>-pedantic-errors</code> option is given,
213<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
214
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]215<p>The feature tag is described along with the language feature below.</p>
216
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]217<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]218<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]219<!-- ======================================================================= -->
220
221<p>This function-like macro takes a single identifier argument that is the name
222of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
223can be used like this:</p>
224
225<blockquote>
226<pre>
227#ifndef __has_attribute // Optional of course.
228 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
229#endif
230
231...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]232#if __has_attribute(always_inline)
233#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]234#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]235#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]236#endif
237...
238</pre>
239</blockquote>
240
241<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]242<h2 id="has_include">Include File Checking Macros</h2>
243<!-- ======================================================================= -->
244
245<p>Not all developments systems have the same include files.
246The <a href="#__has_include">__has_include</a> and
247<a href="#__has_include_next">__has_include_next</a> macros allow you to
248check for the existence of an include file before doing
249a possibly failing #include directive.</p>
250
251<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]252<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]253<!-- ======================================================================= -->
254
255<p>This function-like macro takes a single file name string argument that
256is the name of an include file. It evaluates to 1 if the file can
257be found using the include paths, or 0 otherwise:</p>
258
259<blockquote>
260<pre>
261// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]262#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]263# include "myinclude.h"
264#endif
265
266// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]267#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]268# include "myinclude.h"
269#endif
270</pre>
271</blockquote>
272
273<p>To test for this feature, use #if defined(__has_include).</p>
274
275<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]276<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]277<!-- ======================================================================= -->
278
279<p>This function-like macro takes a single file name string argument that
280is the name of an include file. It is like __has_include except that it
281looks for the second instance of the given file found in the include
282paths. It evaluates to 1 if the second instance of the file can
283be found using the include paths, or 0 otherwise:</p>
284
285<blockquote>
286<pre>
287// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]288#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]289# include_next "myinclude.h"
290#endif
291
292// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]293#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]294# include_next "myinclude.h"
295#endif
296</pre>
297</blockquote>
298
299<p>Note that __has_include_next, like the GNU extension
300#include_next directive, is intended for use in headers only,
301and will issue a warning if used in the top-level compilation
302file. A warning will also be issued if an absolute path
303is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]304
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]305
306<!-- ======================================================================= -->
307<h3><a name="__has_warning">__has_warning</a></h3>
308<!-- ======================================================================= -->
309
310<p>This function-like macro takes a string literal that represents a command
311 line option for a warning and returns true if that is a valid warning
312 option.</p>
313
314<blockquote>
315<pre>
316#if __has_warning("-Wformat")
317...
318#endif
319</pre>
320</blockquote>
321
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]322<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]323<h2 id="builtinmacros">Builtin Macros</h2>
324<!-- ======================================================================= -->
325
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]326<dl>
327 <dt><code>__BASE_FILE__</code></dt>
328 <dd>Defined to a string that contains the name of the main input
329 file passed to Clang.</dd>
330
331 <dt><code>__COUNTER__</code></dt>
332 <dd>Defined to an integer value that starts at zero and is
333 incremented each time the <code>__COUNTER__</code> macro is
334 expanded.</dd>
335
336 <dt><code>__INCLUDE_LEVEL__</code></dt>
337 <dd>Defined to an integral value that is the include depth of the
338 file currently being translated. For the main file, this value is
339 zero.</dd>
340
341 <dt><code>__TIMESTAMP__</code></dt>
342 <dd>Defined to the date and time of the last modification of the
343 current source file.</dd>
344
345 <dt><code>__clang__</code></dt>
346 <dd>Defined when compiling with Clang</dd>
347
348 <dt><code>__clang_major__</code></dt>
349 <dd>Defined to the major version number of Clang (e.g., the 2 in
350 2.0.1).</dd>
351
352 <dt><code>__clang_minor__</code></dt>
353 <dd>Defined to the minor version number of Clang (e.g., the 0 in
354 2.0.1).</dd>
355
356 <dt><code>__clang_patchlevel__</code></dt>
357 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
358
359 <dt><code>__clang_version__</code></dt>
360 <dd>Defined to a string that captures the Clang version, including
361 the Subversion tag or revision number, e.g., "1.5 (trunk
362 102332)".</dd>
363</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]364
365<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]366<h2 id="vectors">Vectors and Extended Vectors</h2>
367<!-- ======================================================================= -->
368
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]369<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
370
371<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
372syntax and other tidbits as seen in OpenCL. An example is:</p>
373
374<blockquote>
375<pre>
376typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
377typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
378
379float4 foo(float2 a, float2 b) {
380 float4 c;
381 c.xz = a;
382 c.yw = b;
383 return c;
384}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]385</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]386</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]387
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]388<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]389
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]390<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
391
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]392<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]393<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]394<!-- ======================================================================= -->
395
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]396<p>An optional string message can be added to the <tt>deprecated</tt>
397and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]398
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]399<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]400<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]401</blockquote>
402
403<p>If the deprecated or unavailable declaration is used, the message
404will be incorporated into the appropriate diagnostic:</p>
405
406<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]407<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]408 explode();
409 ^</pre>
410</blockquote>
411
412<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]413with <tt>__has_extension(attribute_deprecated_with_message)</tt>
414and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]415
416<!-- ======================================================================= -->
417<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
418<!-- ======================================================================= -->
419
420<p>Clang allows attributes to be written on individual enumerators.
421This allows enumerators to be deprecated, made unavailable, etc. The
422attribute must appear after the enumerator name and before any
423initializer, like so:</p>
424
425<blockquote>
426<pre>enum OperationMode {
427 OM_Invalid,
428 OM_Normal,
429 OM_Terrified __attribute__((deprecated)),
430 OM_AbortOnError __attribute__((deprecated)) = 4
431};</pre>
432</blockquote>
433
434<p>Attributes on the <tt>enum</tt> declaration do not apply to
435individual enumerators.</p>
436
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]437<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]438
439<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]440<h2 id="checking_language_features">Checks for Standard Language Features</h2>
441<!-- ======================================================================= -->
442
443<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
444enabled. Those features are listed here.</p>
445
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]446<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]447
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]448<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]449example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]450
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]451<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]452
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]453<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]454compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]455
456<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]457<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
458<!-- ======================================================================= -->
459
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]460<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
461to query if certain upcoming standard language features are enabled. Those
462features are listed here. Features that are not yet implemented will be
463noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]464
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]465<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]466
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]467<p>The features listed below are slated for inclusion in the upcoming
468C++0x standard. As a result, all these features are enabled
469with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]470
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]471<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]472
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]473<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]474
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]475<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]476
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]477<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
478<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]479C++0x's alias declarations and alias templates is enabled.</p>
480
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame^]481<h4 id="cxx_alignas">C++0x alignment specifiers</h4>
482
483<p>Use <tt>__has_feature(cxx_alignas)</tt> or
484<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
485specifiers using <tt>alignas</tt> is enabled.</p>
486
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]487<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]488
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]489<p>Use <tt>__has_feature(cxx_attributes)</tt> or
490<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
491parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]492
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]493<h4 id="cxx_constexpr">C++0x generalized constant expressions</h4>
494
495<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
496for generalized constant expressions (e.g., <tt>constexpr</tt>) is
497enabled. Clang does not currently implement this feature.</p>
498
499<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
500
501<p>Use <tt>__has_feature(cxx_decltype)</tt> or
502<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
503<tt>decltype()</tt> specifier is enabled.</p>
504
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]505<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]506
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]507<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
508<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
509if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]510
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]511<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
512
513<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
514support for delegating constructors is enabled.</p>
515
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]516<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]517
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]518<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
519<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]520deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]521
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]522<h4 id="cxx_explicit_conversions">C++0x explicit conversion functions</h3>
523<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
524
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]525<h4 id="cxx_generalized_initializers">C++0x generalized initializers</h4>
526
527<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
528support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]529<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
530this feature.</p>
531
532<h4 id="cxx_implicit_moves">C++0x implicit move constructors/assignment operators</h4>
533
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]534<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
535implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]536
537<h4 id="cxx_inheriting_constructors">C++0x inheriting constructors</h4>
538
539<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>
540
541<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
542
543<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
544<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
545inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]546
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]547<h4 id="cxx_lambdas">C++0x lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]548
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]549<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
550<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]551is enabled. Clang does not currently implement this feature.</p>
552
553<h4 id="cxx_noexcept">C++0x noexcept</h4>
554
555<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
556<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
557exception specifications is enabled.</p>
558
559<h4 id="cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</h4>
560
561<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]562
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]563<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]564
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]565<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
566<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]567<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]568
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]569<h4 id="cxx_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]570
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]571<p>Use <tt>__has_feature(cxx_override_control)</tt> or
572<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]573the override control keywords is enabled.</p>
574
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]575<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]576<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
577<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
578if support for reference-qualified functions (e.g., member functions with
579<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
580is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]581
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]582<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]583
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]584<p>Use <tt>__has_feature(cxx_range_for)</tt> or
585<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
586range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]587
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]588<h4 id="cxx_raw_string_literals">C++0x raw string literals</h4>
589<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>
590
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]591<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]592
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]593<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
594<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]595rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]596
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]597<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]598
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]599<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
600<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]601compile-time assertions using <tt>static_assert</tt> is enabled.</p>
602
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]603<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]604
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]605<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
606<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
607supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
608will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]609
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]610<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]611
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]612<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
613<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
614strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]615
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]616<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]617
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]618<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
619<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
620alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]621
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]622<h4 id="cxx_unicode_literals">C++0x Unicode string literals</h4>
623<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
624support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]625
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]626<h4 id="cxx_unrestricted_unions">C++0x unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]627
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]628<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]629
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]630<h4 id="cxx_user_literals">C++0x user-defined literals</h4>
631
632<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>
633
634<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
635
636<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
637<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
638for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]639
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]640<h3 id="c1x">C1X</h3>
641
642<p>The features listed below are slated for inclusion in the upcoming
643C1X standard. As a result, all these features are enabled
644with the <tt>-std=c1x</tt> option when compiling C code.</p>
645
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame^]646<h4 id="c_alignas">C1X alignment specifiers</h4>
647
648<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
649to determine if support for alignment specifiers using <tt>_Alignas</tt>
650is enabled.</p>
651
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]652<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]653
654<p>Use <tt>__has_feature(c_generic_selections)</tt> or
655<tt>__has_extension(c_generic_selections)</tt> to determine if support for
656generic selections is enabled.</p>
657
658<p>As an extension, the C1X generic selection expression is available in all
659languages supported by Clang. The syntax is the same as that given in the
660C1X draft standard.</p>
661
662<p>In C, type compatibility is decided according to the rules given in the
663appropriate standard, but in C++, which lacks the type compatibility rules
664used in C, types are considered compatible only if they are equivalent.</p>
665
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]666<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]667
668<p>Use <tt>__has_feature(c_static_assert)</tt> or
669<tt>__has_extension(c_static_assert)</tt> to determine if support for
670compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
671
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]672<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]673<h2 id="checking_type_traits">Checks for Type Traits</h2>
674<!-- ======================================================================= -->
675
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]676<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]677<blockquote>
678<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]679#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]680template&lt;typename From, typename To&gt;
681struct is_convertible_to {
682 static const bool value = __is_convertible_to(From, To);
683};
684#else
685// Emulate type trait
686#endif
687</pre>
688</blockquote>
689
690<p>The following type traits are supported by Clang:</p>
691<ul>
692 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
693 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
694 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
695 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
696 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
697 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
698 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
699 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
700 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
701 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
702 <li><code>__is_class</code> (GNU, Microsoft)</li>
703 <li><code>__is_convertible_to</code> (Microsoft)</li>
704 <li><code>__is_empty</code> (GNU, Microsoft)</li>
705 <li><code>__is_enum</code> (GNU, Microsoft)</li>
706 <li><code>__is_pod</code> (GNU, Microsoft)</li>
707 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
708 <li><code>__is_union</code> (GNU, Microsoft)</li>
709 <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]710 <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]711</ul>
712
713<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]714<h2 id="blocks">Blocks</h2>
715<!-- ======================================================================= -->
716
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]717<p>The syntax and high level language feature description is in <a
718href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
719details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]720href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]721
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]722
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]723<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]724
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]725<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]726<h2 id="objc_features">Objective-C Features</h2>
727<!-- ======================================================================= -->
728
729<h3 id="objc_instancetype">Related result types</h3>
730
731<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>
732
733<blockquote>
734<pre>
735@interface NSObject
736+ (id)alloc;
737- (id)init;
738@end
739
740@interface NSArray : NSObject
741@end
742</pre>
743</blockquote>
744
745<p>and this common initialization pattern</p>
746
747<blockquote>
748<pre>
749NSArray *array = [[NSArray alloc] init];
750</pre>
751</blockquote>
752
753<p>the type of the expression <code>[NSArray alloc]</code> is
754<code>NSArray*</code> because <code>alloc</code> implicitly has a
755related result type. Similarly, the type of the expression
756<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
757<code>init</code> has a related result type and its receiver is known
758to 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>
759
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]760<p>A method with a related result type can be declared by using the
761type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
762is a contextual keyword that is only permitted in the result type of
763an Objective-C method, e.g.</p>
764
765<pre>
766@interface A
767+ (<b>instancetype</b>)constructAnA;
768@end
769</pre>
770
771<p>The related result type can also be inferred for some methods.
772To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]773word in the camel-case selector (e.g., "init" in "initWithObjects") is
774considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]775type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]776
777<ul>
778
779 <li>the first word is "alloc" or "new", and the method is a class
780 method, or</li>
781
782 <li>the first word is "autorelease", "init", "retain", or "self",
783 and the method is an instance method.</li>
784
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]785</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]786
787<p>If a method with a related result type is overridden by a subclass
788method, the subclass method must also return a type that is compatible
789with the subclass type. For example:</p>
790
791<blockquote>
792<pre>
793@interface NSString : NSObject
794- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
795@end
796</pre>
797</blockquote>
798
799<p>Related result types only affect the type of a message send or
800property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]801with a related result type is treated the same way as method that
802returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]803
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]804<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
805the <tt>instancetype</tt> contextual keyword is available.</p>
806
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]807<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]808<h2 id="objc_arc">Automatic reference counting </h2>
809<!-- ======================================================================= -->
810
811<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>
812
813<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]814<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
815<!-- ======================================================================= -->
816
817<p>Clang provides support for C++0x enumerations with a fixed
818underlying type within Objective-C. For example, one can write an
819enumeration type as:</p>
820
821<pre>
822typedef enum : unsigned char { Red, Green, Blue } Color;
823</pre>
824
825<p>This specifies that the underlying type, which is used to store the
826enumeration value, is <tt>unsigned char</tt>.</p>
827
828<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
829support for fixed underlying types is available in Objective-C.</p>
830
831<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]832<h2 id="overloading-in-c">Function Overloading in C</h2>
833<!-- ======================================================================= -->
834
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]835<p>Clang provides support for C++ function overloading in C. Function
836overloading in C is introduced using the <tt>overloadable</tt> attribute. For
837example, one might provide several overloaded versions of a <tt>tgsin</tt>
838function that invokes the appropriate standard function computing the sine of a
839value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
840precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]841
842<blockquote>
843<pre>
844#include &lt;math.h&gt;
845float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
846double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
847long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
848</pre>
849</blockquote>
850
851<p>Given these declarations, one can call <tt>tgsin</tt> with a
852<tt>float</tt> value to receive a <tt>float</tt> result, with a
853<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
854overloading in C follows the rules of C++ function overloading to pick
855the best overload given the call arguments, with a few C-specific
856semantics:</p>
857<ul>
858 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
859 double</tt> is ranked as a floating-point promotion (per C99) rather
860 than as a floating-point conversion (as in C++).</li>
861
862 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
863 <tt>U*</tt> is considered a pointer conversion (with conversion
864 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
865
866 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
867 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
868 conversion is given "conversion" rank.</li>
869</ul>
870
871<p>The declaration of <tt>overloadable</tt> functions is restricted to
872function declarations and definitions. Most importantly, if any
873function with a given name is given the <tt>overloadable</tt>
874attribute, then all function declarations and definitions with that
875name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]876attribute. This rule even applies to redeclarations of functions whose original
877declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]878
879<blockquote>
880<pre>
881int f(int) __attribute__((overloadable));
882float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
883
884int g(int) __attribute__((overloadable));
885int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
886</pre>
887</blockquote>
888
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]889<p>Functions marked <tt>overloadable</tt> must have
890prototypes. Therefore, the following code is ill-formed:</p>
891
892<blockquote>
893<pre>
894int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
895</pre>
896</blockquote>
897
898<p>However, <tt>overloadable</tt> functions are allowed to use a
899ellipsis 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>
900
901<blockquote>
902<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]903void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]904</pre>
905</blockquote>
906
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]907<p>Functions declared with the <tt>overloadable</tt> attribute have
908their names mangled according to the same rules as C++ function
909names. For example, the three <tt>tgsin</tt> functions in our
910motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]911<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]912caveats to this use of name mangling:</p>
913
914<ul>
915
916 <li>Future versions of Clang may change the name mangling of
917 functions overloaded in C, so you should not depend on an specific
918 mangling. To be completely safe, we strongly urge the use of
919 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
920
921 <li>The <tt>overloadable</tt> attribute has almost no meaning when
922 used in C++, because names will already be mangled and functions are
923 already overloadable. However, when an <tt>overloadable</tt>
924 function occurs within an <tt>extern "C"</tt> linkage specification,
925 it's name <i>will</i> be mangled in the same way as it would in
926 C.</li>
927</ul>
928
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]929<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]930
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]931<!-- ======================================================================= -->
932<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
933<!-- ======================================================================= -->
934
935<p>clang supports an extension which allows the following in C:</p>
936
937<blockquote>
938<pre>
939#include &lt;math.h&gt;
940#include &lt;complex.h&gt;
941complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
942</pre>
943</blockquote>
944
945<p>This construct is useful because there is no way to separately
946initialize the real and imaginary parts of a complex variable in
947standard C, given that clang does not support <code>_Imaginary</code>.
948(clang also supports the <code>__real__</code> and <code>__imag__</code>
949extensions from gcc, which help in some cases, but are not usable in
950static initializers.)
951
952<p>Note that this extension does not allow eliding the braces; the
953meaning of the following two lines is different:</p>
954
955<blockquote>
956<pre>
957complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
958complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
959</pre>
960</blockquote>
961
962<p>This extension also works in C++ mode, as far as that goes, but does not
963 apply to the C++ <code>std::complex</code>. (In C++11, list
964 initialization allows the same syntax to be used with
965 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]966
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]967<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]968<h2 id="builtins">Builtin Functions</h2>
969<!-- ======================================================================= -->
970
971<p>Clang supports a number of builtin library functions with the same syntax as
972GCC, including things like <tt>__builtin_nan</tt>,
973<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
974<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
975addition to the GCC builtins, Clang supports a number of builtins that GCC does
976not, which are listed here.</p>
977
978<p>Please note that Clang does not and will not support all of the GCC builtins
979for vector operations. Instead of using builtins, you should use the functions
980defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
981define portable wrappers for these. Many of the Clang versions of these
982functions are implemented directly in terms of <a href="#vectors">extended
983vector support</a> instead of builtins, in order to reduce the number of
984builtins that we need to implement.</p>
985
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]986<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]987<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]988<!-- ======================================================================= -->
989
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]990<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]991permutation/shuffle/swizzle operations. This builtin is also very important for
992the implementation of various target-specific header files like
993<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]994</p>
995
996<p><b>Syntax:</b></p>
997
998<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]999__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1000</pre>
1001
1002<p><b>Examples:</b></p>
1003
1004<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1005 // Identity operation - return 4-element vector V1.
1006 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1007
1008 // "Splat" element 0 of V1 into a 4-element result.
1009 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1010
1011 // Reverse 4-element vector V1.
1012 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1013
1014 // Concatenate every other element of 4-element vectors V1 and V2.
1015 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1016
1017 // Concatenate every other element of 8-element vectors V1 and V2.
1018 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1019</pre>
1020
1021<p><b>Description:</b></p>
1022
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1023<p>The first two arguments to __builtin_shufflevector are vectors that have the
1024same element type. The remaining arguments are a list of integers that specify
1025the elements indices of the first two vectors that should be extracted and
1026returned in a new vector. These element indices are numbered sequentially
1027starting with the first vector, continuing into the second vector. Thus, if
1028vec1 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]1029</p>
1030
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1031<p>The result of __builtin_shufflevector is a vector
1032with the same element type as vec1/vec2 but that has an element count equal to
1033the number of indices specified.
1034</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1035
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1036<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1037
1038<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1039<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1040<!-- ======================================================================= -->
1041
1042<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1043the program cannot be reached, even if the compiler might otherwise think it
1044can. This is useful to improve optimization and eliminates certain warnings.
1045For example, without the <tt>__builtin_unreachable</tt> in the example below,
1046the compiler assumes that the inline asm can fall through and prints a "function
1047declared 'noreturn' should not return" warning.
1048</p>
1049
1050<p><b>Syntax:</b></p>
1051
1052<pre>
1053__builtin_unreachable()
1054</pre>
1055
1056<p><b>Example of Use:</b></p>
1057
1058<pre>
1059void myabort(void) __attribute__((noreturn));
1060void myabort(void) {
1061 asm("int3");
1062 __builtin_unreachable();
1063}
1064</pre>
1065
1066<p><b>Description:</b></p>
1067
1068<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1069it has undefined behavior, it is a statement that it is never reached and the
1070optimizer can take advantage of this to produce better code. This builtin takes
1071no arguments and produces a void result.
1072</p>
1073
1074<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1075
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1076<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1077<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1078<!-- ======================================================================= -->
1079
1080<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1081memory.
1082</p>
1083
1084<p><b>Syntax:</b></p>
1085
1086<pre>
1087<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1088</pre>
1089
1090<p><b>Example of Use:</b></p>
1091
1092<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1093int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1094</pre>
1095
1096<p><b>Description:</b></p>
1097
1098<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1099intrinsics to allow code to atomically swap the current value with the new
1100value. More importantly, it helps developers write more efficient and correct
1101code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1102relying on the platform specific implementation details of
1103__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1104</p>
1105
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1106
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1107<!-- ======================================================================= -->
1108<h2 id="targetspecific">Target-Specific Extensions</h2>
1109<!-- ======================================================================= -->
1110
1111<p>Clang supports some language features conditionally on some targets.</p>
1112
1113<!-- ======================================================================= -->
1114<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1115<!-- ======================================================================= -->
1116
1117<p>The X86 backend has these language extensions:</p>
1118
1119<!-- ======================================================================= -->
1120<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1121<!-- ======================================================================= -->
1122
1123<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1124relative to the X86 GS segment register, and address space #257 causes it to be
1125relative to the X86 FS segment. Note that this is a very very low-level
1126feature that should only be used if you know what you're doing (for example in
1127an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1128
1129<p>Here is an example:</p>
1130
1131<pre>
1132#define GS_RELATIVE __attribute__((address_space(256)))
1133int foo(int GS_RELATIVE *P) {
1134 return *P;
1135}
1136</pre>
1137
1138<p>Which compiles to (on X86-32):</p>
1139
1140<pre>
1141_foo:
1142 movl 4(%esp), %eax
1143 movl %gs:(%eax), %eax
1144 ret
1145</pre>
1146
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1147<!-- ======================================================================= -->
1148<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1149<!-- ======================================================================= -->
1150
1151<p>Clang supports additional attributes that are useful for documenting program
1152invariants and rules for static analysis tools. The extensions documented here
1153are used by the <a
1154href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1155engine</a> that is part of Clang's Analysis library.</p>
1156
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1157<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1158
1159<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1160attribute. This attribute, which is typically affixed to a function prototype,
1161indicates that a call to a given function never returns. Function prototypes for
1162common functions like <tt>exit</tt> are typically annotated with this attribute,
1163as well as a variety of common assertion handlers. Users can educate the static
1164analyzer about their own custom assertion handles (thus cutting down on false
1165positives due to false paths) by marking their own &quot;panic&quot; functions
1166with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1167
1168<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1169there are special functions that for all intents and purposes should be
1170considered panic functions (i.e., they are only called when an internal program
1171error occurs) but may actually return so that the program can fail gracefully.
1172The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1173as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1174pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1175<tt>noreturn</tt>).</p>
1176
1177<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]1178same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1179placed at the end of function prototypes:</p>
1180
1181<pre>
1182 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1183</pre>
1184
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1185<p>Query for this feature with
1186<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1187
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1188<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1189
1190<p>Many methods in Objective-C have conventional meanings determined
1191by their selectors. For the purposes of static analysis, it is
1192sometimes useful to be able to mark a method as having a particular
1193conventional meaning despite not having the right selector, or as not
1194having the conventional meaning that its selector would suggest.
1195For these use cases, we provide an attribute to specifically describe
1196the <q>method family</q> that a method belongs to.</p>
1197
1198<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1199where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1200<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1201can only be placed at the end of a method declaration:</p>
1202
1203<pre>
1204 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1205</pre>
1206
1207<p>Users who do not wish to change the conventional meaning of a
1208method, and who merely want to document its non-standard retain and
1209release semantics, should use the
1210<a href="#attr_retain_release">retaining behavior attributes</a>
1211described below.</p>
1212
1213<p>Query for this feature with
1214<tt>__has_attribute(objc_method_family)</tt>.</p>
1215
1216<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1217
1218<p>In Objective-C, functions and methods are generally assumed to take
1219and return objects with +0 retain counts, with some exceptions for
1220special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1221there are exceptions, and so Clang provides attributes to allow these
1222exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1223ignore non-leaks). Some exceptions may be better described using
1224the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1225attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1226
1227<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1228<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1229and <tt>cf_returns_not_retained</tt> attributes can be placed on
1230methods and functions that return Objective-C or CoreFoundation
1231objects. They are commonly placed at the end of a function prototype
1232or method declaration:</p>
1233
1234<pre>
1235 id foo() <b>__attribute__((ns_returns_retained))</b>;
1236
1237 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1238</pre>
1239
1240<p>The <tt>*_returns_retained</tt> attributes specify that the
1241returned object has a +1 retain count.
1242The <tt>*_returns_not_retained</tt> attributes specify that the return
1243object has a +0 retain count, even if the normal convention for its
1244selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1245returned object is +0, but is guaranteed to live at least as long as the
1246next flush of an autorelease pool.</p>
1247
1248<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1249attributes can be placed on an parameter declaration; they specify
1250that the argument is expected to have a +1 retain count, which will be
1251balanced in some way by the function or method.
1252The <tt>ns_consumes_self</tt> attribute can only be placed on an
1253Objective-C method; it specifies that the method expects
1254its <tt>self</tt> parameter to have a +1 retain count, which it will
1255balance in some way.</p>
1256
1257<pre>
1258 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1259
1260 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1261 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1262</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1263
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1264<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1265<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1266
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1267
1268<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1269<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1270<!-- ======================================================================= -->
1271
1272<p>Clang supports additional attributes for checking basic locking policies in
1273multithreaded programs.
1274Clang currently parses the following list of attributes, although
1275<b>the implementation for these annotations is currently in development.</b>
1276For more details, see the
1277<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1278</p>
1279
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1280<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1281
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1282<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1283declaration to specify that the thread safety analysis should not be run on that
1284function. This attribute provides an escape hatch (e.g. for situations when it
1285is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1286
1287<h4 id="ts_lockable">lockable</h4>
1288
1289<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1290that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1291used to check consistency.</p>
1292
1293<h4 id="ts_scopedlockable">scoped_lockable</h4>
1294
1295<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1296specify that it has a "scoped" lockable type. Objects of this type will acquire
1297the lock upon construction and release it upon going out of scope.
1298 This annotation is primarily used to check
1299consistency.</p>
1300
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1301<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1302
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1303<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1304specify that the variable must be accessed while holding some lock.</p>
1305
1306<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1307
1308<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1309specify that the pointer must be dereferenced while holding some lock.</p>
1310
1311<h4 id="ts_guardedby">guarded_by(l)</h4>
1312
1313<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1314specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1315
1316<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1317
1318<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1319specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1320
1321<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1322
1323<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1324of a lockable variable to specify that the lock must be acquired before all
1325attribute arguments. Arguments must be lockable type, and there must be at
1326least one argument.</p>
1327
1328<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1329
1330<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1331of a lockable variable to specify that the lock must be acquired after all
1332attribute arguments. Arguments must be lockable type, and there must be at
1333least one argument.</p>
1334
1335<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1336
1337<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1338declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1339exclusively. This attribute takes zero or more arguments: either of lockable
1340type or integers indexing into function parameters of lockable type. If no
1341arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1342enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1343
1344<h4 id="ts_slf">shared_lock_function(...)</h4>
1345
1346<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1347declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1348 the locks may be shared (e.g. read locks). This attribute takes zero or more
1349arguments: either of lockable type or integers indexing into function
1350parameters of lockable type. If no arguments are given, the acquired lock is
1351implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1352
1353<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1354
1355<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1356declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1357all listed locks exclusively. This attribute takes one or more arguments. The
1358first argument is an integer or boolean value specifying the return value of a
1359successful lock acquisition. The remaining arugments are either of lockable type
1360or integers indexing into function parameters of lockable type. If only one
1361argument is given, the acquired lock is implicitly <tt>this</tt> of the
1362enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1363
1364<h4 id="ts_stf">shared_trylock_function(...)</h4>
1365
1366<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1367declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1368all listed locks, although the locks may be shared (e.g. read locks). This
1369attribute takes one or more arguments. The first argument is an integer or
1370boolean value specifying the return value of a successful lock acquisition. The
1371remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1372function parameters of lockable type. If only one argument is given, the
1373acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1374
1375<h4 id="ts_uf">unlock_function(...)</h4>
1376
1377<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1378declaration to specify that the function release all listed locks. This
1379attribute takes zero or more arguments: either of lockable type or integers
1380indexing into function parameters of lockable type. If no arguments are given,
1381the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1382
1383<h4 id="ts_lr">lock_returned(l)</h4>
1384
1385<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1386declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1387must be of lockable type). This annotation is used to aid in resolving lock
1388expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1389
1390<h4 id="ts_le">locks_excluded(...)</h4>
1391
1392<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1393to specify that the function must not be called with the listed locks. Arguments
1394must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1395
1396<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1397
1398<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1399declaration to specify that the function must be called while holding the listed
1400exclusive locks. Arguments must be lockable type, and there must be at
1401least one argument.</p>
1402
1403<h4 id="ts_slr">shared_locks_required(...)</h4>
1404
1405<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1406declaration to specify that the function must be called while holding the listed
1407shared locks. Arguments must be lockable type, and there must be at
1408least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1409
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1410</div>
1411</body>
1412</html>