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gerrit-public.fairphone.software / fp2-dev / platform / external / clang / 440ec2ebbe2e7aa2a5f733a41cf845d354d16e23 / . / 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>
43 <li><a href="#cxx_attributes">C++0x attributes</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]44 <li><a href="#cxx_constexpr">C++0x generalized constant expressions</a></li>
45 <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]46 <li><a href="#cxx_default_function_template_args">C++0x default template arguments in function templates</a></li>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]47 <li><a href="#cxx_delegating_constructor">C++0x delegating constructors</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]48 <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]49 <li><a href="#cxx_explicit_conversions">C++0x explicit conversion functions</a></li>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]50 <li><a href="#cxx_generalized_initializers">C++0x generalized initializers</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]51 <li><a href="#cxx_implicit_moves">C++0x implicit move constructors/assignment operators</a></li>
52 <li><a href="#cxx_inheriting_constructors">C++0x inheriting constructors</a></li>
53 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]54 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]55 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
56 <li><a href="#cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]57 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
58 <li><a href="#cxx_override_control">C++0x override control</a></li>
59 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]60 <li><a href="#cxx_raw_string_literals">C++0x raw string literals</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]61 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
62 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
63 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
64 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]65 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]66 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]67 <li><a href="#cxx_unicode_literals">C++0x Unicode string literals</a></li>
68 <li><a href="#cxx_unrestricted_unions">C++0x unrestricted unions</a></li>
69 <li><a href="#cxx_user_literals">C++0x user-defined literals</a></li>
70 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
71 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]72 <li><a href="#c1x">C1X</a>
73 <ul>
74 <li><a href="#c_generic_selections">C1X generic selections</a></li>
75 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]76 </ul></li>
77 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]78<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]79<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]80<li><a href="#objc_features">Objective-C Features</a>
81 <ul>
82 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]83 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]84 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]85 </ul>
86</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]87<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]88<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]89<li><a href="#builtins">Builtin Functions</a>
90 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]91 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]92 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]93 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]94 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]95</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]96<li><a href="#targetspecific">Target-Specific Extensions</a>
97 <ul>
98 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
99 </ul>
100</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]101<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]102<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
103 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]104 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
105 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
106 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]107 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
108 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]109 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
110 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
111 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
112 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
113 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
114 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
115 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
116 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
117 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
118 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
119 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
120 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
121 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]122 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]123</ul>
124
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]125<!-- ======================================================================= -->
126<h2 id="intro">Introduction</h2>
127<!-- ======================================================================= -->
128
129<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]130addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]131range of GCC extensions. Please see the <a
132href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
133more information on these extensions.</p>
134
135<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]136<h2 id="feature_check">Feature Checking Macros</h2>
137<!-- ======================================================================= -->
138
139<p>Language extensions can be very useful, but only if you know you can depend
Chris Lattnerc70e1932011-03-21 16:25:11 +0000[diff] [blame]140on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]141function-like macros. This allows you to directly test for a feature in your
142code without having to resort to something like autoconf or fragile "compiler
143version checks".</p>
144
145<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]146<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]147<!-- ======================================================================= -->
148
149<p>This function-like macro takes a single identifier argument that is the name
150of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
151not. It can be used like this:</p>
152
153<blockquote>
154<pre>
155#ifndef __has_builtin // Optional of course.
156 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
157#endif
158
159...
160#if __has_builtin(__builtin_trap)
161 __builtin_trap();
162#else
163 abort();
164#endif
165...
166</pre>
167</blockquote>
168
169
170<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]171<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]172<!-- ======================================================================= -->
173
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]174<p>These function-like macros take a single identifier argument that is the
175name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
176is both supported by Clang and standardized in the current language standard
177or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
178<code>__has_extension</code> evaluates to 1 if the feature is supported by
179Clang in the current language (either as a language extension or a standard
180language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]181
182<blockquote>
183<pre>
184#ifndef __has_feature // Optional of course.
185 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
186#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]187#ifndef __has_extension
188 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
189#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]190
191...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]192#if __has_feature(cxx_rvalue_references)
193// This code will only be compiled with the -std=c++0x and -std=gnu++0x
194// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]195#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]196
197#if __has_extension(cxx_rvalue_references)
198// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
199// and -std=gnu++98 options, because rvalue references are supported as a
200// language extension in C++98.
201#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]202</pre>
203</blockquote>
204
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]205<p id="has_feature_back_compat">For backwards compatibility reasons,
206<code>__has_feature</code> can also be used to test for support for
207non-standardized features, i.e. features not prefixed <code>c_</code>,
208<code>cxx_</code> or <code>objc_</code>.</p>
209
210<p>If the <code>-pedantic-errors</code> option is given,
211<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
212
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]213<p>The feature tag is described along with the language feature below.</p>
214
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]215<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]216<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]217<!-- ======================================================================= -->
218
219<p>This function-like macro takes a single identifier argument that is the name
220of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
221can be used like this:</p>
222
223<blockquote>
224<pre>
225#ifndef __has_attribute // Optional of course.
226 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
227#endif
228
229...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]230#if __has_attribute(always_inline)
231#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]232#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]233#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]234#endif
235...
236</pre>
237</blockquote>
238
239<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]240<h2 id="has_include">Include File Checking Macros</h2>
241<!-- ======================================================================= -->
242
243<p>Not all developments systems have the same include files.
244The <a href="#__has_include">__has_include</a> and
245<a href="#__has_include_next">__has_include_next</a> macros allow you to
246check for the existence of an include file before doing
247a possibly failing #include directive.</p>
248
249<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]250<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]251<!-- ======================================================================= -->
252
253<p>This function-like macro takes a single file name string argument that
254is the name of an include file. It evaluates to 1 if the file can
255be found using the include paths, or 0 otherwise:</p>
256
257<blockquote>
258<pre>
259// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]260#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]261# include "myinclude.h"
262#endif
263
264// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]265#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]266# include "myinclude.h"
267#endif
268</pre>
269</blockquote>
270
271<p>To test for this feature, use #if defined(__has_include).</p>
272
273<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]274<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]275<!-- ======================================================================= -->
276
277<p>This function-like macro takes a single file name string argument that
278is the name of an include file. It is like __has_include except that it
279looks for the second instance of the given file found in the include
280paths. It evaluates to 1 if the second instance of the file can
281be found using the include paths, or 0 otherwise:</p>
282
283<blockquote>
284<pre>
285// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]286#if __has_include_next("myinclude.h") &amp;&amp; __has_include_next(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]287# include_next "myinclude.h"
288#endif
289
290// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]291#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]292# include_next "myinclude.h"
293#endif
294</pre>
295</blockquote>
296
297<p>Note that __has_include_next, like the GNU extension
298#include_next directive, is intended for use in headers only,
299and will issue a warning if used in the top-level compilation
300file. A warning will also be issued if an absolute path
301is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]302
303<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]304<h2 id="builtinmacros">Builtin Macros</h2>
305<!-- ======================================================================= -->
306
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]307<dl>
308 <dt><code>__BASE_FILE__</code></dt>
309 <dd>Defined to a string that contains the name of the main input
310 file passed to Clang.</dd>
311
312 <dt><code>__COUNTER__</code></dt>
313 <dd>Defined to an integer value that starts at zero and is
314 incremented each time the <code>__COUNTER__</code> macro is
315 expanded.</dd>
316
317 <dt><code>__INCLUDE_LEVEL__</code></dt>
318 <dd>Defined to an integral value that is the include depth of the
319 file currently being translated. For the main file, this value is
320 zero.</dd>
321
322 <dt><code>__TIMESTAMP__</code></dt>
323 <dd>Defined to the date and time of the last modification of the
324 current source file.</dd>
325
326 <dt><code>__clang__</code></dt>
327 <dd>Defined when compiling with Clang</dd>
328
329 <dt><code>__clang_major__</code></dt>
330 <dd>Defined to the major version number of Clang (e.g., the 2 in
331 2.0.1).</dd>
332
333 <dt><code>__clang_minor__</code></dt>
334 <dd>Defined to the minor version number of Clang (e.g., the 0 in
335 2.0.1).</dd>
336
337 <dt><code>__clang_patchlevel__</code></dt>
338 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
339
340 <dt><code>__clang_version__</code></dt>
341 <dd>Defined to a string that captures the Clang version, including
342 the Subversion tag or revision number, e.g., "1.5 (trunk
343 102332)".</dd>
344</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]345
346<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]347<h2 id="vectors">Vectors and Extended Vectors</h2>
348<!-- ======================================================================= -->
349
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]350<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
351
352<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
353syntax and other tidbits as seen in OpenCL. An example is:</p>
354
355<blockquote>
356<pre>
357typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
358typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
359
360float4 foo(float2 a, float2 b) {
361 float4 c;
362 c.xz = a;
363 c.yw = b;
364 return c;
365}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]366</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]367</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]368
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]369<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]370
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]371<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
372
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]373<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]374<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]375<!-- ======================================================================= -->
376
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]377<p>An optional string message can be added to the <tt>deprecated</tt>
378and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]379
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]380<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]381<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]382</blockquote>
383
384<p>If the deprecated or unavailable declaration is used, the message
385will be incorporated into the appropriate diagnostic:</p>
386
387<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]388<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]389 explode();
390 ^</pre>
391</blockquote>
392
393<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]394with <tt>__has_extension(attribute_deprecated_with_message)</tt>
395and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]396
397<!-- ======================================================================= -->
398<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
399<!-- ======================================================================= -->
400
401<p>Clang allows attributes to be written on individual enumerators.
402This allows enumerators to be deprecated, made unavailable, etc. The
403attribute must appear after the enumerator name and before any
404initializer, like so:</p>
405
406<blockquote>
407<pre>enum OperationMode {
408 OM_Invalid,
409 OM_Normal,
410 OM_Terrified __attribute__((deprecated)),
411 OM_AbortOnError __attribute__((deprecated)) = 4
412};</pre>
413</blockquote>
414
415<p>Attributes on the <tt>enum</tt> declaration do not apply to
416individual enumerators.</p>
417
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]418<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]419
420<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]421<h2 id="checking_language_features">Checks for Standard Language Features</h2>
422<!-- ======================================================================= -->
423
424<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
425enabled. Those features are listed here.</p>
426
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]427<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]428
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]429<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]430example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]431
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]432<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]433
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]434<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]435compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]436
437<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]438<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
439<!-- ======================================================================= -->
440
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]441<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
442to query if certain upcoming standard language features are enabled. Those
443features are listed here. Features that are not yet implemented will be
444noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]445
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]446<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]447
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]448<p>The features listed below are slated for inclusion in the upcoming
449C++0x standard. As a result, all these features are enabled
450with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]451
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]452<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]453
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]454<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]455
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]456<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]457
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]458<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
459<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]460C++0x's alias declarations and alias templates is enabled.</p>
461
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]462<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]463
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]464<p>Use <tt>__has_feature(cxx_attributes)</tt> or
465<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
466parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]467
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]468<h4 id="cxx_constexpr">C++0x generalized constant expressions</h4>
469
470<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
471for generalized constant expressions (e.g., <tt>constexpr</tt>) is
472enabled. Clang does not currently implement this feature.</p>
473
474<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
475
476<p>Use <tt>__has_feature(cxx_decltype)</tt> or
477<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
478<tt>decltype()</tt> specifier is enabled.</p>
479
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]480<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]481
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]482<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
483<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
484if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]485
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]486<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
487
488<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
489support for delegating constructors is enabled.</p>
490
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]491<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]492
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]493<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
494<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]495deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]496
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]497<h4 id="cxx_explicit_conversions">C++0x explicit conversion functions</h3>
498<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
499
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]500<h4 id="cxx_generalized_initializers">C++0x generalized initializers</h4>
501
502<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
503support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]504<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
505this feature.</p>
506
507<h4 id="cxx_implicit_moves">C++0x implicit move constructors/assignment operators</h4>
508
509<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will implicitly generate move constructors and move assignment operators where needed. Clang does not currently implement this feature.</p>
510
511<h4 id="cxx_inheriting_constructors">C++0x inheriting constructors</h4>
512
513<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>
514
515<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
516
517<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
518<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
519inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]520
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]521<h4 id="cxx_lambdas">C++0x lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]522
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]523<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
524<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]525is enabled. Clang does not currently implement this feature.</p>
526
527<h4 id="cxx_noexcept">C++0x noexcept</h4>
528
529<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
530<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
531exception specifications is enabled.</p>
532
533<h4 id="cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</h4>
534
535<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]536
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]537<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></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_nullptr)</tt> or
540<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]541<tt>nullptr</tt> 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_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]544
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]545<p>Use <tt>__has_feature(cxx_override_control)</tt> or
546<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]547the override control keywords is enabled.</p>
548
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]549<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]550<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
551<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
552if support for reference-qualified functions (e.g., member functions with
553<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
554is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]555
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]556<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]557
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]558<p>Use <tt>__has_feature(cxx_range_for)</tt> or
559<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
560range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]561
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]562<h4 id="cxx_raw_string_literals">C++0x raw string literals</h4>
563<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>
564
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]565<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]566
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]567<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
568<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]569rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]570
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]571<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]572
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]573<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
574<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]575compile-time assertions using <tt>static_assert</tt> is enabled.</p>
576
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]577<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]578
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]579<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
580<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
581supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
582will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]583
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]584<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]585
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]586<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
587<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
588strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]589
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]590<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]591
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]592<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
593<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
594alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]595
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]596<h4 id="cxx_unicode_literals">C++0x Unicode string literals</h4>
597<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
598support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]599
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]600<h4 id="cxx_unrestricted_unions">C++0x unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]601
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]602<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]603
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]604<h4 id="cxx_user_literals">C++0x user-defined literals</h4>
605
606<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>
607
608<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
609
610<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
611<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
612for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]613
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]614<h3 id="c1x">C1X</h3>
615
616<p>The features listed below are slated for inclusion in the upcoming
617C1X standard. As a result, all these features are enabled
618with the <tt>-std=c1x</tt> option when compiling C code.</p>
619
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]620<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]621
622<p>Use <tt>__has_feature(c_generic_selections)</tt> or
623<tt>__has_extension(c_generic_selections)</tt> to determine if support for
624generic selections is enabled.</p>
625
626<p>As an extension, the C1X generic selection expression is available in all
627languages supported by Clang. The syntax is the same as that given in the
628C1X draft standard.</p>
629
630<p>In C, type compatibility is decided according to the rules given in the
631appropriate standard, but in C++, which lacks the type compatibility rules
632used in C, types are considered compatible only if they are equivalent.</p>
633
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]634<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]635
636<p>Use <tt>__has_feature(c_static_assert)</tt> or
637<tt>__has_extension(c_static_assert)</tt> to determine if support for
638compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
639
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]640<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]641<h2 id="checking_type_traits">Checks for Type Traits</h2>
642<!-- ======================================================================= -->
643
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]644<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]645<blockquote>
646<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]647#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]648template&lt;typename From, typename To&gt;
649struct is_convertible_to {
650 static const bool value = __is_convertible_to(From, To);
651};
652#else
653// Emulate type trait
654#endif
655</pre>
656</blockquote>
657
658<p>The following type traits are supported by Clang:</p>
659<ul>
660 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
661 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
662 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
663 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
664 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
665 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
666 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
667 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
668 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
669 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
670 <li><code>__is_class</code> (GNU, Microsoft)</li>
671 <li><code>__is_convertible_to</code> (Microsoft)</li>
672 <li><code>__is_empty</code> (GNU, Microsoft)</li>
673 <li><code>__is_enum</code> (GNU, Microsoft)</li>
674 <li><code>__is_pod</code> (GNU, Microsoft)</li>
675 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
676 <li><code>__is_union</code> (GNU, Microsoft)</li>
677 <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]678 <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]679</ul>
680
681<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]682<h2 id="blocks">Blocks</h2>
683<!-- ======================================================================= -->
684
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]685<p>The syntax and high level language feature description is in <a
686href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
687details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]688href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]689
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]690
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]691<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]692
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]693<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]694<h2 id="objc_features">Objective-C Features</h2>
695<!-- ======================================================================= -->
696
697<h3 id="objc_instancetype">Related result types</h3>
698
699<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>
700
701<blockquote>
702<pre>
703@interface NSObject
704+ (id)alloc;
705- (id)init;
706@end
707
708@interface NSArray : NSObject
709@end
710</pre>
711</blockquote>
712
713<p>and this common initialization pattern</p>
714
715<blockquote>
716<pre>
717NSArray *array = [[NSArray alloc] init];
718</pre>
719</blockquote>
720
721<p>the type of the expression <code>[NSArray alloc]</code> is
722<code>NSArray*</code> because <code>alloc</code> implicitly has a
723related result type. Similarly, the type of the expression
724<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
725<code>init</code> has a related result type and its receiver is known
726to 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>
727
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]728<p>A method with a related result type can be declared by using the
729type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
730is a contextual keyword that is only permitted in the result type of
731an Objective-C method, e.g.</p>
732
733<pre>
734@interface A
735+ (<b>instancetype</b>)constructAnA;
736@end
737</pre>
738
739<p>The related result type can also be inferred for some methods.
740To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]741word in the camel-case selector (e.g., "init" in "initWithObjects") is
742considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]743type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]744
745<ul>
746
747 <li>the first word is "alloc" or "new", and the method is a class
748 method, or</li>
749
750 <li>the first word is "autorelease", "init", "retain", or "self",
751 and the method is an instance method.</li>
752
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]753</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]754
755<p>If a method with a related result type is overridden by a subclass
756method, the subclass method must also return a type that is compatible
757with the subclass type. For example:</p>
758
759<blockquote>
760<pre>
761@interface NSString : NSObject
762- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
763@end
764</pre>
765</blockquote>
766
767<p>Related result types only affect the type of a message send or
768property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]769with a related result type is treated the same way as method that
770returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]771
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]772<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
773the <tt>instancetype</tt> contextual keyword is available.</p>
774
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]775<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]776<h2 id="objc_arc">Automatic reference counting </h2>
777<!-- ======================================================================= -->
778
779<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>
780
781<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]782<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
783<!-- ======================================================================= -->
784
785<p>Clang provides support for C++0x enumerations with a fixed
786underlying type within Objective-C. For example, one can write an
787enumeration type as:</p>
788
789<pre>
790typedef enum : unsigned char { Red, Green, Blue } Color;
791</pre>
792
793<p>This specifies that the underlying type, which is used to store the
794enumeration value, is <tt>unsigned char</tt>.</p>
795
796<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
797support for fixed underlying types is available in Objective-C.</p>
798
799<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]800<h2 id="overloading-in-c">Function Overloading in C</h2>
801<!-- ======================================================================= -->
802
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]803<p>Clang provides support for C++ function overloading in C. Function
804overloading in C is introduced using the <tt>overloadable</tt> attribute. For
805example, one might provide several overloaded versions of a <tt>tgsin</tt>
806function that invokes the appropriate standard function computing the sine of a
807value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
808precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]809
810<blockquote>
811<pre>
812#include &lt;math.h&gt;
813float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
814double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
815long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
816</pre>
817</blockquote>
818
819<p>Given these declarations, one can call <tt>tgsin</tt> with a
820<tt>float</tt> value to receive a <tt>float</tt> result, with a
821<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
822overloading in C follows the rules of C++ function overloading to pick
823the best overload given the call arguments, with a few C-specific
824semantics:</p>
825<ul>
826 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
827 double</tt> is ranked as a floating-point promotion (per C99) rather
828 than as a floating-point conversion (as in C++).</li>
829
830 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
831 <tt>U*</tt> is considered a pointer conversion (with conversion
832 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
833
834 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
835 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
836 conversion is given "conversion" rank.</li>
837</ul>
838
839<p>The declaration of <tt>overloadable</tt> functions is restricted to
840function declarations and definitions. Most importantly, if any
841function with a given name is given the <tt>overloadable</tt>
842attribute, then all function declarations and definitions with that
843name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]844attribute. This rule even applies to redeclarations of functions whose original
845declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]846
847<blockquote>
848<pre>
849int f(int) __attribute__((overloadable));
850float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
851
852int g(int) __attribute__((overloadable));
853int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
854</pre>
855</blockquote>
856
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]857<p>Functions marked <tt>overloadable</tt> must have
858prototypes. Therefore, the following code is ill-formed:</p>
859
860<blockquote>
861<pre>
862int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
863</pre>
864</blockquote>
865
866<p>However, <tt>overloadable</tt> functions are allowed to use a
867ellipsis 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>
868
869<blockquote>
870<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]871void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]872</pre>
873</blockquote>
874
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]875<p>Functions declared with the <tt>overloadable</tt> attribute have
876their names mangled according to the same rules as C++ function
877names. For example, the three <tt>tgsin</tt> functions in our
878motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]879<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]880caveats to this use of name mangling:</p>
881
882<ul>
883
884 <li>Future versions of Clang may change the name mangling of
885 functions overloaded in C, so you should not depend on an specific
886 mangling. To be completely safe, we strongly urge the use of
887 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
888
889 <li>The <tt>overloadable</tt> attribute has almost no meaning when
890 used in C++, because names will already be mangled and functions are
891 already overloadable. However, when an <tt>overloadable</tt>
892 function occurs within an <tt>extern "C"</tt> linkage specification,
893 it's name <i>will</i> be mangled in the same way as it would in
894 C.</li>
895</ul>
896
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]897<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]898
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]899<!-- ======================================================================= -->
900<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
901<!-- ======================================================================= -->
902
903<p>clang supports an extension which allows the following in C:</p>
904
905<blockquote>
906<pre>
907#include &lt;math.h&gt;
908#include &lt;complex.h&gt;
909complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
910</pre>
911</blockquote>
912
913<p>This construct is useful because there is no way to separately
914initialize the real and imaginary parts of a complex variable in
915standard C, given that clang does not support <code>_Imaginary</code>.
916(clang also supports the <code>__real__</code> and <code>__imag__</code>
917extensions from gcc, which help in some cases, but are not usable in
918static initializers.)
919
920<p>Note that this extension does not allow eliding the braces; the
921meaning of the following two lines is different:</p>
922
923<blockquote>
924<pre>
925complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
926complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
927</pre>
928</blockquote>
929
930<p>This extension also works in C++ mode, as far as that goes, but does not
931 apply to the C++ <code>std::complex</code>. (In C++11, list
932 initialization allows the same syntax to be used with
933 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]934
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]935<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]936<h2 id="builtins">Builtin Functions</h2>
937<!-- ======================================================================= -->
938
939<p>Clang supports a number of builtin library functions with the same syntax as
940GCC, including things like <tt>__builtin_nan</tt>,
941<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
942<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
943addition to the GCC builtins, Clang supports a number of builtins that GCC does
944not, which are listed here.</p>
945
946<p>Please note that Clang does not and will not support all of the GCC builtins
947for vector operations. Instead of using builtins, you should use the functions
948defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
949define portable wrappers for these. Many of the Clang versions of these
950functions are implemented directly in terms of <a href="#vectors">extended
951vector support</a> instead of builtins, in order to reduce the number of
952builtins that we need to implement.</p>
953
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]954<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]955<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]956<!-- ======================================================================= -->
957
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]958<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]959permutation/shuffle/swizzle operations. This builtin is also very important for
960the implementation of various target-specific header files like
961<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]962</p>
963
964<p><b>Syntax:</b></p>
965
966<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]967__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]968</pre>
969
970<p><b>Examples:</b></p>
971
972<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]973 // Identity operation - return 4-element vector V1.
974 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
975
976 // "Splat" element 0 of V1 into a 4-element result.
977 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
978
979 // Reverse 4-element vector V1.
980 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
981
982 // Concatenate every other element of 4-element vectors V1 and V2.
983 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
984
985 // Concatenate every other element of 8-element vectors V1 and V2.
986 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]987</pre>
988
989<p><b>Description:</b></p>
990
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]991<p>The first two arguments to __builtin_shufflevector are vectors that have the
992same element type. The remaining arguments are a list of integers that specify
993the elements indices of the first two vectors that should be extracted and
994returned in a new vector. These element indices are numbered sequentially
995starting with the first vector, continuing into the second vector. Thus, if
996vec1 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]997</p>
998
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]999<p>The result of __builtin_shufflevector is a vector
1000with the same element type as vec1/vec2 but that has an element count equal to
1001the number of indices specified.
1002</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1003
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1004<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1005
1006<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1007<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1008<!-- ======================================================================= -->
1009
1010<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1011the program cannot be reached, even if the compiler might otherwise think it
1012can. This is useful to improve optimization and eliminates certain warnings.
1013For example, without the <tt>__builtin_unreachable</tt> in the example below,
1014the compiler assumes that the inline asm can fall through and prints a "function
1015declared 'noreturn' should not return" warning.
1016</p>
1017
1018<p><b>Syntax:</b></p>
1019
1020<pre>
1021__builtin_unreachable()
1022</pre>
1023
1024<p><b>Example of Use:</b></p>
1025
1026<pre>
1027void myabort(void) __attribute__((noreturn));
1028void myabort(void) {
1029 asm("int3");
1030 __builtin_unreachable();
1031}
1032</pre>
1033
1034<p><b>Description:</b></p>
1035
1036<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1037it has undefined behavior, it is a statement that it is never reached and the
1038optimizer can take advantage of this to produce better code. This builtin takes
1039no arguments and produces a void result.
1040</p>
1041
1042<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1043
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1044<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1045<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1046<!-- ======================================================================= -->
1047
1048<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1049memory.
1050</p>
1051
1052<p><b>Syntax:</b></p>
1053
1054<pre>
1055<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1056</pre>
1057
1058<p><b>Example of Use:</b></p>
1059
1060<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1061int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1062</pre>
1063
1064<p><b>Description:</b></p>
1065
1066<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1067intrinsics to allow code to atomically swap the current value with the new
1068value. More importantly, it helps developers write more efficient and correct
1069code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1070relying on the platform specific implementation details of
1071__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1072</p>
1073
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1074
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1075<!-- ======================================================================= -->
1076<h2 id="targetspecific">Target-Specific Extensions</h2>
1077<!-- ======================================================================= -->
1078
1079<p>Clang supports some language features conditionally on some targets.</p>
1080
1081<!-- ======================================================================= -->
1082<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1083<!-- ======================================================================= -->
1084
1085<p>The X86 backend has these language extensions:</p>
1086
1087<!-- ======================================================================= -->
1088<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1089<!-- ======================================================================= -->
1090
1091<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1092relative to the X86 GS segment register, and address space #257 causes it to be
1093relative to the X86 FS segment. Note that this is a very very low-level
1094feature that should only be used if you know what you're doing (for example in
1095an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1096
1097<p>Here is an example:</p>
1098
1099<pre>
1100#define GS_RELATIVE __attribute__((address_space(256)))
1101int foo(int GS_RELATIVE *P) {
1102 return *P;
1103}
1104</pre>
1105
1106<p>Which compiles to (on X86-32):</p>
1107
1108<pre>
1109_foo:
1110 movl 4(%esp), %eax
1111 movl %gs:(%eax), %eax
1112 ret
1113</pre>
1114
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1115<!-- ======================================================================= -->
1116<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1117<!-- ======================================================================= -->
1118
1119<p>Clang supports additional attributes that are useful for documenting program
1120invariants and rules for static analysis tools. The extensions documented here
1121are used by the <a
1122href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1123engine</a> that is part of Clang's Analysis library.</p>
1124
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1125<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1126
1127<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1128attribute. This attribute, which is typically affixed to a function prototype,
1129indicates that a call to a given function never returns. Function prototypes for
1130common functions like <tt>exit</tt> are typically annotated with this attribute,
1131as well as a variety of common assertion handlers. Users can educate the static
1132analyzer about their own custom assertion handles (thus cutting down on false
1133positives due to false paths) by marking their own &quot;panic&quot; functions
1134with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1135
1136<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1137there are special functions that for all intents and purposes should be
1138considered panic functions (i.e., they are only called when an internal program
1139error occurs) but may actually return so that the program can fail gracefully.
1140The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1141as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1142pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1143<tt>noreturn</tt>).</p>
1144
1145<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]1146same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1147placed at the end of function prototypes:</p>
1148
1149<pre>
1150 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1151</pre>
1152
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1153<p>Query for this feature with
1154<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1155
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1156<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1157
1158<p>Many methods in Objective-C have conventional meanings determined
1159by their selectors. For the purposes of static analysis, it is
1160sometimes useful to be able to mark a method as having a particular
1161conventional meaning despite not having the right selector, or as not
1162having the conventional meaning that its selector would suggest.
1163For these use cases, we provide an attribute to specifically describe
1164the <q>method family</q> that a method belongs to.</p>
1165
1166<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1167where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1168<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1169can only be placed at the end of a method declaration:</p>
1170
1171<pre>
1172 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1173</pre>
1174
1175<p>Users who do not wish to change the conventional meaning of a
1176method, and who merely want to document its non-standard retain and
1177release semantics, should use the
1178<a href="#attr_retain_release">retaining behavior attributes</a>
1179described below.</p>
1180
1181<p>Query for this feature with
1182<tt>__has_attribute(objc_method_family)</tt>.</p>
1183
1184<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1185
1186<p>In Objective-C, functions and methods are generally assumed to take
1187and return objects with +0 retain counts, with some exceptions for
1188special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1189there are exceptions, and so Clang provides attributes to allow these
1190exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1191ignore non-leaks). Some exceptions may be better described using
1192the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1193attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1194
1195<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1196<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1197and <tt>cf_returns_not_retained</tt> attributes can be placed on
1198methods and functions that return Objective-C or CoreFoundation
1199objects. They are commonly placed at the end of a function prototype
1200or method declaration:</p>
1201
1202<pre>
1203 id foo() <b>__attribute__((ns_returns_retained))</b>;
1204
1205 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1206</pre>
1207
1208<p>The <tt>*_returns_retained</tt> attributes specify that the
1209returned object has a +1 retain count.
1210The <tt>*_returns_not_retained</tt> attributes specify that the return
1211object has a +0 retain count, even if the normal convention for its
1212selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1213returned object is +0, but is guaranteed to live at least as long as the
1214next flush of an autorelease pool.</p>
1215
1216<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1217attributes can be placed on an parameter declaration; they specify
1218that the argument is expected to have a +1 retain count, which will be
1219balanced in some way by the function or method.
1220The <tt>ns_consumes_self</tt> attribute can only be placed on an
1221Objective-C method; it specifies that the method expects
1222its <tt>self</tt> parameter to have a +1 retain count, which it will
1223balance in some way.</p>
1224
1225<pre>
1226 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1227
1228 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1229 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1230</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1231
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1232<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1233<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1234
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1235
1236<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1237<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1238<!-- ======================================================================= -->
1239
1240<p>Clang supports additional attributes for checking basic locking policies in
1241multithreaded programs.
1242Clang currently parses the following list of attributes, although
1243<b>the implementation for these annotations is currently in development.</b>
1244For more details, see the
1245<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1246</p>
1247
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1248<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1249
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1250<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1251declaration to specify that the thread safety analysis should not be run on that
1252function. This attribute provides an escape hatch (e.g. for situations when it
1253is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1254
1255<h4 id="ts_lockable">lockable</h4>
1256
1257<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1258that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1259used to check consistency.</p>
1260
1261<h4 id="ts_scopedlockable">scoped_lockable</h4>
1262
1263<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1264specify that it has a "scoped" lockable type. Objects of this type will acquire
1265the lock upon construction and release it upon going out of scope.
1266 This annotation is primarily used to check
1267consistency.</p>
1268
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1269<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1270
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1271<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1272specify that the variable must be accessed while holding some lock.</p>
1273
1274<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1275
1276<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1277specify that the pointer must be dereferenced while holding some lock.</p>
1278
1279<h4 id="ts_guardedby">guarded_by(l)</h4>
1280
1281<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1282specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1283
1284<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1285
1286<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1287specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1288
1289<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1290
1291<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1292of a lockable variable to specify that the lock must be acquired before all
1293attribute arguments. Arguments must be lockable type, and there must be at
1294least one argument.</p>
1295
1296<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1297
1298<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1299of a lockable variable to specify that the lock must be acquired after all
1300attribute arguments. Arguments must be lockable type, and there must be at
1301least one argument.</p>
1302
1303<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1304
1305<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1306declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1307exclusively. This attribute takes zero or more arguments: either of lockable
1308type or integers indexing into function parameters of lockable type. If no
1309arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1310enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1311
1312<h4 id="ts_slf">shared_lock_function(...)</h4>
1313
1314<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1315declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1316 the locks may be shared (e.g. read locks). This attribute takes zero or more
1317arguments: either of lockable type or integers indexing into function
1318parameters of lockable type. If no arguments are given, the acquired lock is
1319implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1320
1321<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1322
1323<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1324declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1325all listed locks exclusively. This attribute takes one or more arguments. The
1326first argument is an integer or boolean value specifying the return value of a
1327successful lock acquisition. The remaining arugments are either of lockable type
1328or integers indexing into function parameters of lockable type. If only one
1329argument is given, the acquired lock is implicitly <tt>this</tt> of the
1330enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1331
1332<h4 id="ts_stf">shared_trylock_function(...)</h4>
1333
1334<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1335declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1336all listed locks, although the locks may be shared (e.g. read locks). This
1337attribute takes one or more arguments. The first argument is an integer or
1338boolean value specifying the return value of a successful lock acquisition. The
1339remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1340function parameters of lockable type. If only one argument is given, the
1341acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1342
1343<h4 id="ts_uf">unlock_function(...)</h4>
1344
1345<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1346declaration to specify that the function release all listed locks. This
1347attribute takes zero or more arguments: either of lockable type or integers
1348indexing into function parameters of lockable type. If no arguments are given,
1349the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1350
1351<h4 id="ts_lr">lock_returned(l)</h4>
1352
1353<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1354declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1355must be of lockable type). This annotation is used to aid in resolving lock
1356expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1357
1358<h4 id="ts_le">locks_excluded(...)</h4>
1359
1360<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1361to specify that the function must not be called with the listed locks. Arguments
1362must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1363
1364<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1365
1366<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1367declaration to specify that the function must be called while holding the listed
1368exclusive locks. Arguments must be lockable type, and there must be at
1369least one argument.</p>
1370
1371<h4 id="ts_slr">shared_locks_required(...)</h4>
1372
1373<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1374declaration to specify that the function must be called while holding the listed
1375shared locks. Arguments must be lockable type, and there must be at
1376least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1377
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1378</div>
1379</body>
1380</html>