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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>
41 <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
42 <li><a href="#cxx_access_control_sfinae">C++0x SFINAE includes access control</a></li>
43 <li><a href="#cxx_alias_templates">C++0x alias templates</a></li>
44 <li><a href="#cxx_attributes">C++0x attributes</a></li>
45 <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]46 <li><a href="#cxx_delegating_constructor">C++0x delegating constructors</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]47 <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame^]48 <li><a href="#cxx_generalized_initializers">C++0x generalized initializers</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]49 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
50 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
51 <li><a href="#cxx_override_control">C++0x override control</a></li>
52 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
53 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
54 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
55 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
56 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
57 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
58 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
59 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
60 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
61 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]62 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]63 <li><a href="#c1x">C1X</a>
64 <ul>
65 <li><a href="#c_generic_selections">C1X generic selections</a></li>
66 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]67 </ul></li>
68 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]69<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]70<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]71<li><a href="#objc_features">Objective-C Features</a>
72 <ul>
73 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]74 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]75 </ul>
76</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]77<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]78<li><a href="#builtins">Builtin Functions</a>
79 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]80 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]81 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]82 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]83 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]84</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]85<li><a href="#targetspecific">Target-Specific Extensions</a>
86 <ul>
87 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
88 </ul>
89</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]90<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]91<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
92 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]93 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
94 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
95 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]96 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
97 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]98 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
99 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
100 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
101 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
102 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
103 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
104 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
105 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
106 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
107 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
108 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
109 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
110 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]111 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]112</ul>
113
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]114<!-- ======================================================================= -->
115<h2 id="intro">Introduction</h2>
116<!-- ======================================================================= -->
117
118<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]119addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]120range of GCC extensions. Please see the <a
121href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
122more information on these extensions.</p>
123
124<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]125<h2 id="feature_check">Feature Checking Macros</h2>
126<!-- ======================================================================= -->
127
128<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]129on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]130function-like macros. This allows you to directly test for a feature in your
131code without having to resort to something like autoconf or fragile "compiler
132version checks".</p>
133
134<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]135<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]136<!-- ======================================================================= -->
137
138<p>This function-like macro takes a single identifier argument that is the name
139of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
140not. It can be used like this:</p>
141
142<blockquote>
143<pre>
144#ifndef __has_builtin // Optional of course.
145 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
146#endif
147
148...
149#if __has_builtin(__builtin_trap)
150 __builtin_trap();
151#else
152 abort();
153#endif
154...
155</pre>
156</blockquote>
157
158
159<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]160<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]161<!-- ======================================================================= -->
162
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]163<p>These function-like macros take a single identifier argument that is the
164name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
165is both supported by Clang and standardized in the current language standard
166or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
167<code>__has_extension</code> evaluates to 1 if the feature is supported by
168Clang in the current language (either as a language extension or a standard
169language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]170
171<blockquote>
172<pre>
173#ifndef __has_feature // Optional of course.
174 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
175#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]176#ifndef __has_extension
177 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
178#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]179
180...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]181#if __has_feature(cxx_rvalue_references)
182// This code will only be compiled with the -std=c++0x and -std=gnu++0x
183// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]184#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]185
186#if __has_extension(cxx_rvalue_references)
187// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
188// and -std=gnu++98 options, because rvalue references are supported as a
189// language extension in C++98.
190#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]191</pre>
192</blockquote>
193
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]194<p id="has_feature_back_compat">For backwards compatibility reasons,
195<code>__has_feature</code> can also be used to test for support for
196non-standardized features, i.e. features not prefixed <code>c_</code>,
197<code>cxx_</code> or <code>objc_</code>.</p>
198
199<p>If the <code>-pedantic-errors</code> option is given,
200<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
201
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]202<p>The feature tag is described along with the language feature below.</p>
203
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]204<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]205<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]206<!-- ======================================================================= -->
207
208<p>This function-like macro takes a single identifier argument that is the name
209of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
210can be used like this:</p>
211
212<blockquote>
213<pre>
214#ifndef __has_attribute // Optional of course.
215 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
216#endif
217
218...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]219#if __has_attribute(always_inline)
220#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]221#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]222#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]223#endif
224...
225</pre>
226</blockquote>
227
228<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]229<h2 id="has_include">Include File Checking Macros</h2>
230<!-- ======================================================================= -->
231
232<p>Not all developments systems have the same include files.
233The <a href="#__has_include">__has_include</a> and
234<a href="#__has_include_next">__has_include_next</a> macros allow you to
235check for the existence of an include file before doing
236a possibly failing #include directive.</p>
237
238<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]239<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]240<!-- ======================================================================= -->
241
242<p>This function-like macro takes a single file name string argument that
243is the name of an include file. It evaluates to 1 if the file can
244be found using the include paths, or 0 otherwise:</p>
245
246<blockquote>
247<pre>
248// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]249#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]250# include "myinclude.h"
251#endif
252
253// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]254#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]255# include "myinclude.h"
256#endif
257</pre>
258</blockquote>
259
260<p>To test for this feature, use #if defined(__has_include).</p>
261
262<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]263<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]264<!-- ======================================================================= -->
265
266<p>This function-like macro takes a single file name string argument that
267is the name of an include file. It is like __has_include except that it
268looks for the second instance of the given file found in the include
269paths. It evaluates to 1 if the second instance of the file can
270be found using the include paths, or 0 otherwise:</p>
271
272<blockquote>
273<pre>
274// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]275#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]276# include_next "myinclude.h"
277#endif
278
279// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]280#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]281# include_next "myinclude.h"
282#endif
283</pre>
284</blockquote>
285
286<p>Note that __has_include_next, like the GNU extension
287#include_next directive, is intended for use in headers only,
288and will issue a warning if used in the top-level compilation
289file. A warning will also be issued if an absolute path
290is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]291
292<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]293<h2 id="builtinmacros">Builtin Macros</h2>
294<!-- ======================================================================= -->
295
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]296<dl>
297 <dt><code>__BASE_FILE__</code></dt>
298 <dd>Defined to a string that contains the name of the main input
299 file passed to Clang.</dd>
300
301 <dt><code>__COUNTER__</code></dt>
302 <dd>Defined to an integer value that starts at zero and is
303 incremented each time the <code>__COUNTER__</code> macro is
304 expanded.</dd>
305
306 <dt><code>__INCLUDE_LEVEL__</code></dt>
307 <dd>Defined to an integral value that is the include depth of the
308 file currently being translated. For the main file, this value is
309 zero.</dd>
310
311 <dt><code>__TIMESTAMP__</code></dt>
312 <dd>Defined to the date and time of the last modification of the
313 current source file.</dd>
314
315 <dt><code>__clang__</code></dt>
316 <dd>Defined when compiling with Clang</dd>
317
318 <dt><code>__clang_major__</code></dt>
319 <dd>Defined to the major version number of Clang (e.g., the 2 in
320 2.0.1).</dd>
321
322 <dt><code>__clang_minor__</code></dt>
323 <dd>Defined to the minor version number of Clang (e.g., the 0 in
324 2.0.1).</dd>
325
326 <dt><code>__clang_patchlevel__</code></dt>
327 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
328
329 <dt><code>__clang_version__</code></dt>
330 <dd>Defined to a string that captures the Clang version, including
331 the Subversion tag or revision number, e.g., "1.5 (trunk
332 102332)".</dd>
333</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]334
335<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]336<h2 id="vectors">Vectors and Extended Vectors</h2>
337<!-- ======================================================================= -->
338
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]339<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
340
341<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
342syntax and other tidbits as seen in OpenCL. An example is:</p>
343
344<blockquote>
345<pre>
346typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
347typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
348
349float4 foo(float2 a, float2 b) {
350 float4 c;
351 c.xz = a;
352 c.yw = b;
353 return c;
354}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]355</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]356</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]357
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]358<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]359
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]360<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
361
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]362<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]363<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]364<!-- ======================================================================= -->
365
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]366<p>An optional string message can be added to the <tt>deprecated</tt>
367and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]368
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]369<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]370<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]371</blockquote>
372
373<p>If the deprecated or unavailable declaration is used, the message
374will be incorporated into the appropriate diagnostic:</p>
375
376<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]377<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]378 explode();
379 ^</pre>
380</blockquote>
381
382<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]383with <tt>__has_extension(attribute_deprecated_with_message)</tt>
384and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]385
386<!-- ======================================================================= -->
387<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
388<!-- ======================================================================= -->
389
390<p>Clang allows attributes to be written on individual enumerators.
391This allows enumerators to be deprecated, made unavailable, etc. The
392attribute must appear after the enumerator name and before any
393initializer, like so:</p>
394
395<blockquote>
396<pre>enum OperationMode {
397 OM_Invalid,
398 OM_Normal,
399 OM_Terrified __attribute__((deprecated)),
400 OM_AbortOnError __attribute__((deprecated)) = 4
401};</pre>
402</blockquote>
403
404<p>Attributes on the <tt>enum</tt> declaration do not apply to
405individual enumerators.</p>
406
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]407<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]408
409<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]410<h2 id="checking_language_features">Checks for Standard Language Features</h2>
411<!-- ======================================================================= -->
412
413<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
414enabled. Those features are listed here.</p>
415
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]416<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]417
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]418<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]419example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]420
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]421<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]422
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]423<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]424compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]425
426<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]427<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
428<!-- ======================================================================= -->
429
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]430<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
431to query if certain upcoming standard language features are enabled. Those
432features are listed here. Features that are not yet implemented will be
433noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]434
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]435<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]436
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]437<p>The features listed below are slated for inclusion in the upcoming
438C++0x standard. As a result, all these features are enabled
439with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]440
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]441<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]442
443<p>Use <tt>__has_feature(cxx_decltype)</tt> or
444<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]445<tt>decltype()</tt> specifier is enabled.</p>
446
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]447<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]448
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]449<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]450
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]451<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]452
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]453<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
454<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]455C++0x's alias declarations and alias templates is enabled.</p>
456
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]457<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]458
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]459<p>Use <tt>__has_feature(cxx_attributes)</tt> or
460<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
461parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]462
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]463<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]464
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]465<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
466<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
467if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]468
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]469<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
470
471<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
472support for delegating constructors is enabled.</p>
473
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]474<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]475
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]476<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
477<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]478deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]479
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame^]480<h4 id="cxx_generalized_initializers">C++0x generalized initializers</h4>
481
482<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
483support for generalized initializers (using braced lists and
484<tt>std::initializer_list</tt>) is enabled. clang does not currently implement
485this feature.
486
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]487<h4 id="cxx_lambdas">C++0x lambdas</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_lambdas)</tt> or
490<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
491is enabled. clang does not currently implement this feature.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]492
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]493<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]494
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]495<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
496<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]497<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]498
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]499<h4 id="cxx_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]500
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]501<p>Use <tt>__has_feature(cxx_override_control)</tt> or
502<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]503the override control keywords is enabled.</p>
504
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]505<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]506<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
507<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
508if support for reference-qualified functions (e.g., member functions with
509<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
510is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]511
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]512<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]513
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]514<p>Use <tt>__has_feature(cxx_range_for)</tt> or
515<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
516range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]517
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]518<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]519
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]520<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
521<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]522rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]523
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]524<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]525
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]526<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
527<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]528compile-time assertions using <tt>static_assert</tt> is enabled.</p>
529
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]530<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]531
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]532<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
533<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
534supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
535will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]536
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]537<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]538
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]539<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
540<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
Douglas Gregor83d77812011-01-19 23:15:20 +0000[diff] [blame]541for variadic templates is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]542
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]543<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]544
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]545<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
546<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]547inline namespaces is enabled.</p>
548
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]549<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]550
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]551<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
552<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
553alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]554
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]555<h4 id="cxx_noexcept">C++0x noexcept</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]556
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]557<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
558<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
559exception specifications is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]560
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]561<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]562
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]563<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
564<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]565strongly typed, scoped enumerations is enabled.</p>
566
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]567<h3 id="c1x">C1X</h3>
568
569<p>The features listed below are slated for inclusion in the upcoming
570C1X standard. As a result, all these features are enabled
571with the <tt>-std=c1x</tt> option when compiling C code.</p>
572
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]573<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]574
575<p>Use <tt>__has_feature(c_generic_selections)</tt> or
576<tt>__has_extension(c_generic_selections)</tt> to determine if support for
577generic selections is enabled.</p>
578
579<p>As an extension, the C1X generic selection expression is available in all
580languages supported by Clang. The syntax is the same as that given in the
581C1X draft standard.</p>
582
583<p>In C, type compatibility is decided according to the rules given in the
584appropriate standard, but in C++, which lacks the type compatibility rules
585used in C, types are considered compatible only if they are equivalent.</p>
586
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]587<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]588
589<p>Use <tt>__has_feature(c_static_assert)</tt> or
590<tt>__has_extension(c_static_assert)</tt> to determine if support for
591compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
592
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]593<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]594<h2 id="checking_type_traits">Checks for Type Traits</h2>
595<!-- ======================================================================= -->
596
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]597<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]598<blockquote>
599<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]600#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]601template&lt;typename From, typename To&gt;
602struct is_convertible_to {
603 static const bool value = __is_convertible_to(From, To);
604};
605#else
606// Emulate type trait
607#endif
608</pre>
609</blockquote>
610
611<p>The following type traits are supported by Clang:</p>
612<ul>
613 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
614 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
615 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
616 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
617 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
618 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
619 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
620 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
621 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
622 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
623 <li><code>__is_class</code> (GNU, Microsoft)</li>
624 <li><code>__is_convertible_to</code> (Microsoft)</li>
625 <li><code>__is_empty</code> (GNU, Microsoft)</li>
626 <li><code>__is_enum</code> (GNU, Microsoft)</li>
627 <li><code>__is_pod</code> (GNU, Microsoft)</li>
628 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
629 <li><code>__is_union</code> (GNU, Microsoft)</li>
630 <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]631 <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]632</ul>
633
634<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]635<h2 id="blocks">Blocks</h2>
636<!-- ======================================================================= -->
637
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]638<p>The syntax and high level language feature description is in <a
639href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
640details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]641href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]642
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]643
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]644<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]645
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]646<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]647<h2 id="objc_features">Objective-C Features</h2>
648<!-- ======================================================================= -->
649
650<h3 id="objc_instancetype">Related result types</h3>
651
652<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>
653
654<blockquote>
655<pre>
656@interface NSObject
657+ (id)alloc;
658- (id)init;
659@end
660
661@interface NSArray : NSObject
662@end
663</pre>
664</blockquote>
665
666<p>and this common initialization pattern</p>
667
668<blockquote>
669<pre>
670NSArray *array = [[NSArray alloc] init];
671</pre>
672</blockquote>
673
674<p>the type of the expression <code>[NSArray alloc]</code> is
675<code>NSArray*</code> because <code>alloc</code> implicitly has a
676related result type. Similarly, the type of the expression
677<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
678<code>init</code> has a related result type and its receiver is known
679to 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>
680
681<p>To determine whether a method has a related result type, the first
682word in the camel-case selector (e.g., "init" in "initWithObjects") is
683considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]684type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]685
686<ul>
687
688 <li>the first word is "alloc" or "new", and the method is a class
689 method, or</li>
690
691 <li>the first word is "autorelease", "init", "retain", or "self",
692 and the method is an instance method.</li>
693
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]694</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]695
696<p>If a method with a related result type is overridden by a subclass
697method, the subclass method must also return a type that is compatible
698with the subclass type. For example:</p>
699
700<blockquote>
701<pre>
702@interface NSString : NSObject
703- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
704@end
705</pre>
706</blockquote>
707
708<p>Related result types only affect the type of a message send or
709property access via the given method. In all other respects, a method
710with a related result type is treated the same way as method without a
711related result type.</p>
712
713<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]714<h2 id="objc_arc">Automatic reference counting </h2>
715<!-- ======================================================================= -->
716
717<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>
718
719<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]720<h2 id="overloading-in-c">Function Overloading in C</h2>
721<!-- ======================================================================= -->
722
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]723<p>Clang provides support for C++ function overloading in C. Function
724overloading in C is introduced using the <tt>overloadable</tt> attribute. For
725example, one might provide several overloaded versions of a <tt>tgsin</tt>
726function that invokes the appropriate standard function computing the sine of a
727value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
728precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]729
730<blockquote>
731<pre>
732#include &lt;math.h&gt;
733float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
734double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
735long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
736</pre>
737</blockquote>
738
739<p>Given these declarations, one can call <tt>tgsin</tt> with a
740<tt>float</tt> value to receive a <tt>float</tt> result, with a
741<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
742overloading in C follows the rules of C++ function overloading to pick
743the best overload given the call arguments, with a few C-specific
744semantics:</p>
745<ul>
746 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
747 double</tt> is ranked as a floating-point promotion (per C99) rather
748 than as a floating-point conversion (as in C++).</li>
749
750 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
751 <tt>U*</tt> is considered a pointer conversion (with conversion
752 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
753
754 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
755 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
756 conversion is given "conversion" rank.</li>
757</ul>
758
759<p>The declaration of <tt>overloadable</tt> functions is restricted to
760function declarations and definitions. Most importantly, if any
761function with a given name is given the <tt>overloadable</tt>
762attribute, then all function declarations and definitions with that
763name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]764attribute. This rule even applies to redeclarations of functions whose original
765declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]766
767<blockquote>
768<pre>
769int f(int) __attribute__((overloadable));
770float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
771
772int g(int) __attribute__((overloadable));
773int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
774</pre>
775</blockquote>
776
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]777<p>Functions marked <tt>overloadable</tt> must have
778prototypes. Therefore, the following code is ill-formed:</p>
779
780<blockquote>
781<pre>
782int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
783</pre>
784</blockquote>
785
786<p>However, <tt>overloadable</tt> functions are allowed to use a
787ellipsis 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>
788
789<blockquote>
790<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]791void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]792</pre>
793</blockquote>
794
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]795<p>Functions declared with the <tt>overloadable</tt> attribute have
796their names mangled according to the same rules as C++ function
797names. For example, the three <tt>tgsin</tt> functions in our
798motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]799<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]800caveats to this use of name mangling:</p>
801
802<ul>
803
804 <li>Future versions of Clang may change the name mangling of
805 functions overloaded in C, so you should not depend on an specific
806 mangling. To be completely safe, we strongly urge the use of
807 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
808
809 <li>The <tt>overloadable</tt> attribute has almost no meaning when
810 used in C++, because names will already be mangled and functions are
811 already overloadable. However, when an <tt>overloadable</tt>
812 function occurs within an <tt>extern "C"</tt> linkage specification,
813 it's name <i>will</i> be mangled in the same way as it would in
814 C.</li>
815</ul>
816
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]817<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]818
819
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]820<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]821<h2 id="builtins">Builtin Functions</h2>
822<!-- ======================================================================= -->
823
824<p>Clang supports a number of builtin library functions with the same syntax as
825GCC, including things like <tt>__builtin_nan</tt>,
826<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
827<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
828addition to the GCC builtins, Clang supports a number of builtins that GCC does
829not, which are listed here.</p>
830
831<p>Please note that Clang does not and will not support all of the GCC builtins
832for vector operations. Instead of using builtins, you should use the functions
833defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
834define portable wrappers for these. Many of the Clang versions of these
835functions are implemented directly in terms of <a href="#vectors">extended
836vector support</a> instead of builtins, in order to reduce the number of
837builtins that we need to implement.</p>
838
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]839<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]840<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]841<!-- ======================================================================= -->
842
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]843<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]844permutation/shuffle/swizzle operations. This builtin is also very important for
845the implementation of various target-specific header files like
846<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]847</p>
848
849<p><b>Syntax:</b></p>
850
851<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]852__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]853</pre>
854
855<p><b>Examples:</b></p>
856
857<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]858 // Identity operation - return 4-element vector V1.
859 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
860
861 // "Splat" element 0 of V1 into a 4-element result.
862 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
863
864 // Reverse 4-element vector V1.
865 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
866
867 // Concatenate every other element of 4-element vectors V1 and V2.
868 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
869
870 // Concatenate every other element of 8-element vectors V1 and V2.
871 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]872</pre>
873
874<p><b>Description:</b></p>
875
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]876<p>The first two arguments to __builtin_shufflevector are vectors that have the
877same element type. The remaining arguments are a list of integers that specify
878the elements indices of the first two vectors that should be extracted and
879returned in a new vector. These element indices are numbered sequentially
880starting with the first vector, continuing into the second vector. Thus, if
881vec1 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]882</p>
883
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]884<p>The result of __builtin_shufflevector is a vector
885with the same element type as vec1/vec2 but that has an element count equal to
886the number of indices specified.
887</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]888
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]889<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
890
891<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]892<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]893<!-- ======================================================================= -->
894
895<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
896the program cannot be reached, even if the compiler might otherwise think it
897can. This is useful to improve optimization and eliminates certain warnings.
898For example, without the <tt>__builtin_unreachable</tt> in the example below,
899the compiler assumes that the inline asm can fall through and prints a "function
900declared 'noreturn' should not return" warning.
901</p>
902
903<p><b>Syntax:</b></p>
904
905<pre>
906__builtin_unreachable()
907</pre>
908
909<p><b>Example of Use:</b></p>
910
911<pre>
912void myabort(void) __attribute__((noreturn));
913void myabort(void) {
914 asm("int3");
915 __builtin_unreachable();
916}
917</pre>
918
919<p><b>Description:</b></p>
920
921<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
922it has undefined behavior, it is a statement that it is never reached and the
923optimizer can take advantage of this to produce better code. This builtin takes
924no arguments and produces a void result.
925</p>
926
927<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
928
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]929<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]930<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]931<!-- ======================================================================= -->
932
933<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
934memory.
935</p>
936
937<p><b>Syntax:</b></p>
938
939<pre>
940<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
941</pre>
942
943<p><b>Example of Use:</b></p>
944
945<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]946int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]947</pre>
948
949<p><b>Description:</b></p>
950
951<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
952intrinsics to allow code to atomically swap the current value with the new
953value. More importantly, it helps developers write more efficient and correct
954code by avoiding expensive loops around __sync_bool_compare_and_swap() or
955relying on the platform specific implementation details of
956__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
957</p>
958
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]959
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]960<!-- ======================================================================= -->
961<h2 id="targetspecific">Target-Specific Extensions</h2>
962<!-- ======================================================================= -->
963
964<p>Clang supports some language features conditionally on some targets.</p>
965
966<!-- ======================================================================= -->
967<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
968<!-- ======================================================================= -->
969
970<p>The X86 backend has these language extensions:</p>
971
972<!-- ======================================================================= -->
973<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
974<!-- ======================================================================= -->
975
976<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]977relative to the X86 GS segment register, and address space #257 causes it to be
978relative to the X86 FS segment. Note that this is a very very low-level
979feature that should only be used if you know what you're doing (for example in
980an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]981
982<p>Here is an example:</p>
983
984<pre>
985#define GS_RELATIVE __attribute__((address_space(256)))
986int foo(int GS_RELATIVE *P) {
987 return *P;
988}
989</pre>
990
991<p>Which compiles to (on X86-32):</p>
992
993<pre>
994_foo:
995 movl 4(%esp), %eax
996 movl %gs:(%eax), %eax
997 ret
998</pre>
999
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1000<!-- ======================================================================= -->
1001<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1002<!-- ======================================================================= -->
1003
1004<p>Clang supports additional attributes that are useful for documenting program
1005invariants and rules for static analysis tools. The extensions documented here
1006are used by the <a
1007href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1008engine</a> that is part of Clang's Analysis library.</p>
1009
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1010<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1011
1012<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1013attribute. This attribute, which is typically affixed to a function prototype,
1014indicates that a call to a given function never returns. Function prototypes for
1015common functions like <tt>exit</tt> are typically annotated with this attribute,
1016as well as a variety of common assertion handlers. Users can educate the static
1017analyzer about their own custom assertion handles (thus cutting down on false
1018positives due to false paths) by marking their own &quot;panic&quot; functions
1019with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1020
1021<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1022there are special functions that for all intents and purposes should be
1023considered panic functions (i.e., they are only called when an internal program
1024error occurs) but may actually return so that the program can fail gracefully.
1025The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1026as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1027pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1028<tt>noreturn</tt>).</p>
1029
1030<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]1031same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1032placed at the end of function prototypes:</p>
1033
1034<pre>
1035 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1036</pre>
1037
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1038<p>Query for this feature with
1039<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1040
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1041<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1042
1043<p>Many methods in Objective-C have conventional meanings determined
1044by their selectors. For the purposes of static analysis, it is
1045sometimes useful to be able to mark a method as having a particular
1046conventional meaning despite not having the right selector, or as not
1047having the conventional meaning that its selector would suggest.
1048For these use cases, we provide an attribute to specifically describe
1049the <q>method family</q> that a method belongs to.</p>
1050
1051<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1052where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1053<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1054can only be placed at the end of a method declaration:</p>
1055
1056<pre>
1057 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1058</pre>
1059
1060<p>Users who do not wish to change the conventional meaning of a
1061method, and who merely want to document its non-standard retain and
1062release semantics, should use the
1063<a href="#attr_retain_release">retaining behavior attributes</a>
1064described below.</p>
1065
1066<p>Query for this feature with
1067<tt>__has_attribute(objc_method_family)</tt>.</p>
1068
1069<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1070
1071<p>In Objective-C, functions and methods are generally assumed to take
1072and return objects with +0 retain counts, with some exceptions for
1073special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1074there are exceptions, and so Clang provides attributes to allow these
1075exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1076ignore non-leaks). Some exceptions may be better described using
1077the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1078attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1079
1080<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1081<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1082and <tt>cf_returns_not_retained</tt> attributes can be placed on
1083methods and functions that return Objective-C or CoreFoundation
1084objects. They are commonly placed at the end of a function prototype
1085or method declaration:</p>
1086
1087<pre>
1088 id foo() <b>__attribute__((ns_returns_retained))</b>;
1089
1090 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1091</pre>
1092
1093<p>The <tt>*_returns_retained</tt> attributes specify that the
1094returned object has a +1 retain count.
1095The <tt>*_returns_not_retained</tt> attributes specify that the return
1096object has a +0 retain count, even if the normal convention for its
1097selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1098returned object is +0, but is guaranteed to live at least as long as the
1099next flush of an autorelease pool.</p>
1100
1101<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1102attributes can be placed on an parameter declaration; they specify
1103that the argument is expected to have a +1 retain count, which will be
1104balanced in some way by the function or method.
1105The <tt>ns_consumes_self</tt> attribute can only be placed on an
1106Objective-C method; it specifies that the method expects
1107its <tt>self</tt> parameter to have a +1 retain count, which it will
1108balance in some way.</p>
1109
1110<pre>
1111 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1112
1113 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1114 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1115</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1116
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1117<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1118<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1119
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1120
1121<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1122<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1123<!-- ======================================================================= -->
1124
1125<p>Clang supports additional attributes for checking basic locking policies in
1126multithreaded programs.
1127Clang currently parses the following list of attributes, although
1128<b>the implementation for these annotations is currently in development.</b>
1129For more details, see the
1130<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1131</p>
1132
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1133<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1134
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1135<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1136declaration to specify that the thread safety analysis should not be run on that
1137function. This attribute provides an escape hatch (e.g. for situations when it
1138is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1139
1140<h4 id="ts_lockable">lockable</h4>
1141
1142<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1143that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1144used to check consistency.</p>
1145
1146<h4 id="ts_scopedlockable">scoped_lockable</h4>
1147
1148<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1149specify that it has a "scoped" lockable type. Objects of this type will acquire
1150the lock upon construction and release it upon going out of scope.
1151 This annotation is primarily used to check
1152consistency.</p>
1153
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1154<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1155
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1156<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1157specify that the variable must be accessed while holding some lock.</p>
1158
1159<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1160
1161<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1162specify that the pointer must be dereferenced while holding some lock.</p>
1163
1164<h4 id="ts_guardedby">guarded_by(l)</h4>
1165
1166<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
1167specify that the variable must be accessed while holding lock l.</p>
1168
1169<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1170
1171<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
1172specify that the pointer must be dereferenced while holding lock l.</p>
1173
1174<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1175
1176<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1177of a lockable variable to specify that the lock must be acquired before all
1178attribute arguments. Arguments must be lockable type, and there must be at
1179least one argument.</p>
1180
1181<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1182
1183<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1184of a lockable variable to specify that the lock must be acquired after all
1185attribute arguments. Arguments must be lockable type, and there must be at
1186least one argument.</p>
1187
1188<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1189
1190<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1191declaration to specify that the function acquires all listed locks
1192exclusively. This attribute takes zero or more
1193arguments: either of lockable type or integers indexing into
1194function parameters of lockable type. If no arguments are given, the acquired
1195lock is implicitly <tt>this</tt> of the enclosing object.</p>
1196
1197<h4 id="ts_slf">shared_lock_function(...)</h4>
1198
1199<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1200declaration to specify that the function acquires all listed locks, although
1201 the locks may be shared (e.g. read locks).
1202This attribute takes zero or more
1203arguments: either of lockable type or integers indexing into
1204function parameters of lockable type. If no arguments are given, the acquired
1205lock is implicitly <tt>this</tt> of the enclosing object.</p>
1206
1207<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1208
1209<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1210declaration to specify that the function will try (without blocking) to acquire
1211all listed locks exclusively. This attribute takes one or more
1212arguments. The first argument is an integer or boolean value specifying the
1213return value of a successful lock acquisition. The remaining arugments are
1214either of lockable type or integers indexing into
1215function parameters of lockable type. If only one argument is given, the
1216acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1217
1218<h4 id="ts_stf">shared_trylock_function(...)</h4>
1219
1220<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1221declaration to specify that the function will try (without blocking) to acquire
1222all listed locks, although
1223 the locks may be shared (e.g. read locks).
1224This attribute takes one or more
1225arguments. The first argument is an integer or boolean value specifying the
1226return value of a successful lock acquisition. The remaining arugments are
1227either of lockable type or integers indexing into
1228function parameters of lockable type. If only one argument is given, the
1229acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1230
1231<h4 id="ts_uf">unlock_function(...)</h4>
1232
1233<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
1234declaration to specify that the function release all listed locks.
1235 This attribute takes zero or more
1236arguments: either of lockable type or integers indexing into
1237function parameters of lockable type. If no arguments are given, the acquired
1238lock is implicitly <tt>this</tt> of the enclosing object.</p>
1239
1240<h4 id="ts_lr">lock_returned(l)</h4>
1241
1242<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
1243declaration to specify that the function returns lock l (l must be of lockable
1244type). This annotation is used
1245to aid in resolving lock expressions.</p>
1246
1247<h4 id="ts_le">locks_excluded(...)</h4>
1248
1249<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
1250to specify that the function must not be called with the listed locks.
1251Arguments must be lockable type, and there must be at
1252least one argument.</p>
1253
1254<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1255
1256<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1257declaration to specify that the function must be called while holding the listed
1258exclusive locks. Arguments must be lockable type, and there must be at
1259least one argument.</p>
1260
1261<h4 id="ts_slr">shared_locks_required(...)</h4>
1262
1263<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1264declaration to specify that the function must be called while holding the listed
1265shared locks. Arguments must be lockable type, and there must be at
1266least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1267
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1268</div>
1269</body>
1270</html>