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gerrit-public.fairphone.software / platform / external / clang / 73cbbc8d786e54a7a61c2880ad1b9a596d235286 / . / docs / LanguageExtensions.html
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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>
48 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
49 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
50 <li><a href="#cxx_override_control">C++0x override control</a></li>
51 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
52 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
53 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
54 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
55 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
56 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
57 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
58 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
59 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
60 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]61 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]62 <li><a href="#c1x">C1X</a>
63 <ul>
64 <li><a href="#c_generic_selections">C1X generic selections</a></li>
65 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]66 </ul></li>
67 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]68<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]69<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]70<li><a href="#objc_features">Objective-C Features</a>
71 <ul>
72 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]73 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]74 </ul>
75</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]76<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]77<li><a href="#builtins">Builtin Functions</a>
78 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]79 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]80 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]81 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]82 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]83</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]84<li><a href="#targetspecific">Target-Specific Extensions</a>
85 <ul>
86 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
87 </ul>
88</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]89<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]90<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
91 <ul>
92 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
93 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</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>
96 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
97 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]98</ul>
99
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]100<!-- ======================================================================= -->
101<h2 id="intro">Introduction</h2>
102<!-- ======================================================================= -->
103
104<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]105addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]106range of GCC extensions. Please see the <a
107href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
108more information on these extensions.</p>
109
110<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]111<h2 id="feature_check">Feature Checking Macros</h2>
112<!-- ======================================================================= -->
113
114<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]115on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]116function-like macros. This allows you to directly test for a feature in your
117code without having to resort to something like autoconf or fragile "compiler
118version checks".</p>
119
120<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]121<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]122<!-- ======================================================================= -->
123
124<p>This function-like macro takes a single identifier argument that is the name
125of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
126not. It can be used like this:</p>
127
128<blockquote>
129<pre>
130#ifndef __has_builtin // Optional of course.
131 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
132#endif
133
134...
135#if __has_builtin(__builtin_trap)
136 __builtin_trap();
137#else
138 abort();
139#endif
140...
141</pre>
142</blockquote>
143
144
145<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]146<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]147<!-- ======================================================================= -->
148
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]149<p>These function-like macros take a single identifier argument that is the
150name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
151is both supported by Clang and standardized in the current language standard
152or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
153<code>__has_extension</code> evaluates to 1 if the feature is supported by
154Clang in the current language (either as a language extension or a standard
155language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]156
157<blockquote>
158<pre>
159#ifndef __has_feature // Optional of course.
160 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
161#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]162#ifndef __has_extension
163 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
164#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]165
166...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]167#if __has_feature(cxx_rvalue_references)
168// This code will only be compiled with the -std=c++0x and -std=gnu++0x
169// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]170#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]171
172#if __has_extension(cxx_rvalue_references)
173// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
174// and -std=gnu++98 options, because rvalue references are supported as a
175// language extension in C++98.
176#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]177</pre>
178</blockquote>
179
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]180<p id="has_feature_back_compat">For backwards compatibility reasons,
181<code>__has_feature</code> can also be used to test for support for
182non-standardized features, i.e. features not prefixed <code>c_</code>,
183<code>cxx_</code> or <code>objc_</code>.</p>
184
185<p>If the <code>-pedantic-errors</code> option is given,
186<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
187
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]188<p>The feature tag is described along with the language feature below.</p>
189
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]190<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]191<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]192<!-- ======================================================================= -->
193
194<p>This function-like macro takes a single identifier argument that is the name
195of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
196can be used like this:</p>
197
198<blockquote>
199<pre>
200#ifndef __has_attribute // Optional of course.
201 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
202#endif
203
204...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]205#if __has_attribute(always_inline)
206#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]207#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]208#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]209#endif
210...
211</pre>
212</blockquote>
213
214<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]215<h2 id="has_include">Include File Checking Macros</h2>
216<!-- ======================================================================= -->
217
218<p>Not all developments systems have the same include files.
219The <a href="#__has_include">__has_include</a> and
220<a href="#__has_include_next">__has_include_next</a> macros allow you to
221check for the existence of an include file before doing
222a possibly failing #include directive.</p>
223
224<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]225<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]226<!-- ======================================================================= -->
227
228<p>This function-like macro takes a single file name string argument that
229is the name of an include file. It evaluates to 1 if the file can
230be found using the include paths, or 0 otherwise:</p>
231
232<blockquote>
233<pre>
234// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]235#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]236# include "myinclude.h"
237#endif
238
239// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]240#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]241# include "myinclude.h"
242#endif
243</pre>
244</blockquote>
245
246<p>To test for this feature, use #if defined(__has_include).</p>
247
248<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]249<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]250<!-- ======================================================================= -->
251
252<p>This function-like macro takes a single file name string argument that
253is the name of an include file. It is like __has_include except that it
254looks for the second instance of the given file found in the include
255paths. It evaluates to 1 if the second instance of the file can
256be found using the include paths, or 0 otherwise:</p>
257
258<blockquote>
259<pre>
260// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]261#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]262# include_next "myinclude.h"
263#endif
264
265// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]266#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]267# include_next "myinclude.h"
268#endif
269</pre>
270</blockquote>
271
272<p>Note that __has_include_next, like the GNU extension
273#include_next directive, is intended for use in headers only,
274and will issue a warning if used in the top-level compilation
275file. A warning will also be issued if an absolute path
276is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]277
278<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]279<h2 id="builtinmacros">Builtin Macros</h2>
280<!-- ======================================================================= -->
281
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]282<dl>
283 <dt><code>__BASE_FILE__</code></dt>
284 <dd>Defined to a string that contains the name of the main input
285 file passed to Clang.</dd>
286
287 <dt><code>__COUNTER__</code></dt>
288 <dd>Defined to an integer value that starts at zero and is
289 incremented each time the <code>__COUNTER__</code> macro is
290 expanded.</dd>
291
292 <dt><code>__INCLUDE_LEVEL__</code></dt>
293 <dd>Defined to an integral value that is the include depth of the
294 file currently being translated. For the main file, this value is
295 zero.</dd>
296
297 <dt><code>__TIMESTAMP__</code></dt>
298 <dd>Defined to the date and time of the last modification of the
299 current source file.</dd>
300
301 <dt><code>__clang__</code></dt>
302 <dd>Defined when compiling with Clang</dd>
303
304 <dt><code>__clang_major__</code></dt>
305 <dd>Defined to the major version number of Clang (e.g., the 2 in
306 2.0.1).</dd>
307
308 <dt><code>__clang_minor__</code></dt>
309 <dd>Defined to the minor version number of Clang (e.g., the 0 in
310 2.0.1).</dd>
311
312 <dt><code>__clang_patchlevel__</code></dt>
313 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
314
315 <dt><code>__clang_version__</code></dt>
316 <dd>Defined to a string that captures the Clang version, including
317 the Subversion tag or revision number, e.g., "1.5 (trunk
318 102332)".</dd>
319</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]320
321<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]322<h2 id="vectors">Vectors and Extended Vectors</h2>
323<!-- ======================================================================= -->
324
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]325<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
326
327<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
328syntax and other tidbits as seen in OpenCL. An example is:</p>
329
330<blockquote>
331<pre>
332typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
333typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
334
335float4 foo(float2 a, float2 b) {
336 float4 c;
337 c.xz = a;
338 c.yw = b;
339 return c;
340}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]341</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]342</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]343
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]344<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]345
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]346<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
347
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]348<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]349<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]350<!-- ======================================================================= -->
351
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]352<p>An optional string message can be added to the <tt>deprecated</tt>
353and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]354
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]355<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]356<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]357</blockquote>
358
359<p>If the deprecated or unavailable declaration is used, the message
360will be incorporated into the appropriate diagnostic:</p>
361
362<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]363<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]364 explode();
365 ^</pre>
366</blockquote>
367
368<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]369with <tt>__has_extension(attribute_deprecated_with_message)</tt>
370and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]371
372<!-- ======================================================================= -->
373<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
374<!-- ======================================================================= -->
375
376<p>Clang allows attributes to be written on individual enumerators.
377This allows enumerators to be deprecated, made unavailable, etc. The
378attribute must appear after the enumerator name and before any
379initializer, like so:</p>
380
381<blockquote>
382<pre>enum OperationMode {
383 OM_Invalid,
384 OM_Normal,
385 OM_Terrified __attribute__((deprecated)),
386 OM_AbortOnError __attribute__((deprecated)) = 4
387};</pre>
388</blockquote>
389
390<p>Attributes on the <tt>enum</tt> declaration do not apply to
391individual enumerators.</p>
392
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]393<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]394
395<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]396<h2 id="checking_language_features">Checks for Standard Language Features</h2>
397<!-- ======================================================================= -->
398
399<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
400enabled. Those features are listed here.</p>
401
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]402<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]403
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]404<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]405example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]406
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]407<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]408
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]409<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]410compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]411
412<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]413<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
414<!-- ======================================================================= -->
415
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]416<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
417to query if certain upcoming standard language features are enabled. Those
418features are listed here. Features that are not yet implemented will be
419noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]420
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]421<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]422
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]423<p>The features listed below are slated for inclusion in the upcoming
424C++0x standard. As a result, all these features are enabled
425with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]426
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]427<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]428
429<p>Use <tt>__has_feature(cxx_decltype)</tt> or
430<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]431<tt>decltype()</tt> specifier is enabled.</p>
432
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]433<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]434
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]435<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]436
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]437<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]438
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]439<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
440<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]441C++0x's alias declarations and alias templates is enabled.</p>
442
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]443<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]444
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]445<p>Use <tt>__has_feature(cxx_attributes)</tt> or
446<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
447parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]448
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]449<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]450
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]451<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
452<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
453if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]454
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]455<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
456
457<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
458support for delegating constructors is enabled.</p>
459
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]460<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]461
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]462<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
463<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]464deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]465
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]466<h4 id="cxx_lambdas">C++0x lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]467
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]468<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
469<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
470is enabled. clang does not currently implement this feature.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]471
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]472<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]473
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]474<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
475<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]476<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]477
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]478<h4 id="cxx_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]479
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]480<p>Use <tt>__has_feature(cxx_override_control)</tt> or
481<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]482the override control keywords is enabled.</p>
483
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]484<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]485<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
486<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
487if support for reference-qualified functions (e.g., member functions with
488<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
489is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]490
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]491<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]492
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]493<p>Use <tt>__has_feature(cxx_range_for)</tt> or
494<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
495range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]496
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]497<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]498
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]499<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
500<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]501rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]502
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]503<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]504
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]505<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
506<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]507compile-time assertions using <tt>static_assert</tt> is enabled.</p>
508
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]509<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]510
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]511<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
512<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
513supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
514will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]515
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]516<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]517
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]518<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
519<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
Douglas Gregor83d77812011-01-19 23:15:20 +0000[diff] [blame]520for variadic templates is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]521
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]522<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]523
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]524<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
525<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]526inline namespaces is enabled.</p>
527
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]528<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]529
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]530<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
531<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
532alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]533
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]534<h4 id="cxx_noexcept">C++0x noexcept</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]535
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]536<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
537<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
538exception specifications is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]539
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]540<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]541
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]542<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
543<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]544strongly typed, scoped enumerations is enabled.</p>
545
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]546<h3 id="c1x">C1X</h3>
547
548<p>The features listed below are slated for inclusion in the upcoming
549C1X standard. As a result, all these features are enabled
550with the <tt>-std=c1x</tt> option when compiling C code.</p>
551
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]552<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]553
554<p>Use <tt>__has_feature(c_generic_selections)</tt> or
555<tt>__has_extension(c_generic_selections)</tt> to determine if support for
556generic selections is enabled.</p>
557
558<p>As an extension, the C1X generic selection expression is available in all
559languages supported by Clang. The syntax is the same as that given in the
560C1X draft standard.</p>
561
562<p>In C, type compatibility is decided according to the rules given in the
563appropriate standard, but in C++, which lacks the type compatibility rules
564used in C, types are considered compatible only if they are equivalent.</p>
565
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]566<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]567
568<p>Use <tt>__has_feature(c_static_assert)</tt> or
569<tt>__has_extension(c_static_assert)</tt> to determine if support for
570compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
571
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]572<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]573<h2 id="checking_type_traits">Checks for Type Traits</h2>
574<!-- ======================================================================= -->
575
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]576<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]577<blockquote>
578<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]579#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]580template&lt;typename From, typename To&gt;
581struct is_convertible_to {
582 static const bool value = __is_convertible_to(From, To);
583};
584#else
585// Emulate type trait
586#endif
587</pre>
588</blockquote>
589
590<p>The following type traits are supported by Clang:</p>
591<ul>
592 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
593 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
594 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
595 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
596 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
597 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
598 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
599 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
600 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
601 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
602 <li><code>__is_class</code> (GNU, Microsoft)</li>
603 <li><code>__is_convertible_to</code> (Microsoft)</li>
604 <li><code>__is_empty</code> (GNU, Microsoft)</li>
605 <li><code>__is_enum</code> (GNU, Microsoft)</li>
606 <li><code>__is_pod</code> (GNU, Microsoft)</li>
607 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
608 <li><code>__is_union</code> (GNU, Microsoft)</li>
609 <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]610 <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]611</ul>
612
613<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]614<h2 id="blocks">Blocks</h2>
615<!-- ======================================================================= -->
616
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]617<p>The syntax and high level language feature description is in <a
618href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
619details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]620href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]621
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]622
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]623<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]624
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]625<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]626<h2 id="objc_features">Objective-C Features</h2>
627<!-- ======================================================================= -->
628
629<h3 id="objc_instancetype">Related result types</h3>
630
631<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>
632
633<blockquote>
634<pre>
635@interface NSObject
636+ (id)alloc;
637- (id)init;
638@end
639
640@interface NSArray : NSObject
641@end
642</pre>
643</blockquote>
644
645<p>and this common initialization pattern</p>
646
647<blockquote>
648<pre>
649NSArray *array = [[NSArray alloc] init];
650</pre>
651</blockquote>
652
653<p>the type of the expression <code>[NSArray alloc]</code> is
654<code>NSArray*</code> because <code>alloc</code> implicitly has a
655related result type. Similarly, the type of the expression
656<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
657<code>init</code> has a related result type and its receiver is known
658to 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>
659
660<p>To determine whether a method has a related result type, the first
661word in the camel-case selector (e.g., "init" in "initWithObjects") is
662considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]663type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]664
665<ul>
666
667 <li>the first word is "alloc" or "new", and the method is a class
668 method, or</li>
669
670 <li>the first word is "autorelease", "init", "retain", or "self",
671 and the method is an instance method.</li>
672
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]673</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]674
675<p>If a method with a related result type is overridden by a subclass
676method, the subclass method must also return a type that is compatible
677with the subclass type. For example:</p>
678
679<blockquote>
680<pre>
681@interface NSString : NSObject
682- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
683@end
684</pre>
685</blockquote>
686
687<p>Related result types only affect the type of a message send or
688property access via the given method. In all other respects, a method
689with a related result type is treated the same way as method without a
690related result type.</p>
691
692<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]693<h2 id="objc_arc">Automatic reference counting </h2>
694<!-- ======================================================================= -->
695
696<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>
697
698<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]699<h2 id="overloading-in-c">Function Overloading in C</h2>
700<!-- ======================================================================= -->
701
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]702<p>Clang provides support for C++ function overloading in C. Function
703overloading in C is introduced using the <tt>overloadable</tt> attribute. For
704example, one might provide several overloaded versions of a <tt>tgsin</tt>
705function that invokes the appropriate standard function computing the sine of a
706value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
707precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]708
709<blockquote>
710<pre>
711#include &lt;math.h&gt;
712float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
713double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
714long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
715</pre>
716</blockquote>
717
718<p>Given these declarations, one can call <tt>tgsin</tt> with a
719<tt>float</tt> value to receive a <tt>float</tt> result, with a
720<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
721overloading in C follows the rules of C++ function overloading to pick
722the best overload given the call arguments, with a few C-specific
723semantics:</p>
724<ul>
725 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
726 double</tt> is ranked as a floating-point promotion (per C99) rather
727 than as a floating-point conversion (as in C++).</li>
728
729 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
730 <tt>U*</tt> is considered a pointer conversion (with conversion
731 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
732
733 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
734 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
735 conversion is given "conversion" rank.</li>
736</ul>
737
738<p>The declaration of <tt>overloadable</tt> functions is restricted to
739function declarations and definitions. Most importantly, if any
740function with a given name is given the <tt>overloadable</tt>
741attribute, then all function declarations and definitions with that
742name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]743attribute. This rule even applies to redeclarations of functions whose original
744declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]745
746<blockquote>
747<pre>
748int f(int) __attribute__((overloadable));
749float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
750
751int g(int) __attribute__((overloadable));
752int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
753</pre>
754</blockquote>
755
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]756<p>Functions marked <tt>overloadable</tt> must have
757prototypes. Therefore, the following code is ill-formed:</p>
758
759<blockquote>
760<pre>
761int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
762</pre>
763</blockquote>
764
765<p>However, <tt>overloadable</tt> functions are allowed to use a
766ellipsis 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>
767
768<blockquote>
769<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]770void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]771</pre>
772</blockquote>
773
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]774<p>Functions declared with the <tt>overloadable</tt> attribute have
775their names mangled according to the same rules as C++ function
776names. For example, the three <tt>tgsin</tt> functions in our
777motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]778<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]779caveats to this use of name mangling:</p>
780
781<ul>
782
783 <li>Future versions of Clang may change the name mangling of
784 functions overloaded in C, so you should not depend on an specific
785 mangling. To be completely safe, we strongly urge the use of
786 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
787
788 <li>The <tt>overloadable</tt> attribute has almost no meaning when
789 used in C++, because names will already be mangled and functions are
790 already overloadable. However, when an <tt>overloadable</tt>
791 function occurs within an <tt>extern "C"</tt> linkage specification,
792 it's name <i>will</i> be mangled in the same way as it would in
793 C.</li>
794</ul>
795
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]796<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]797
798
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]799<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]800<h2 id="builtins">Builtin Functions</h2>
801<!-- ======================================================================= -->
802
803<p>Clang supports a number of builtin library functions with the same syntax as
804GCC, including things like <tt>__builtin_nan</tt>,
805<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
806<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
807addition to the GCC builtins, Clang supports a number of builtins that GCC does
808not, which are listed here.</p>
809
810<p>Please note that Clang does not and will not support all of the GCC builtins
811for vector operations. Instead of using builtins, you should use the functions
812defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
813define portable wrappers for these. Many of the Clang versions of these
814functions are implemented directly in terms of <a href="#vectors">extended
815vector support</a> instead of builtins, in order to reduce the number of
816builtins that we need to implement.</p>
817
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]818<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]819<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]820<!-- ======================================================================= -->
821
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]822<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]823permutation/shuffle/swizzle operations. This builtin is also very important for
824the implementation of various target-specific header files like
825<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]826</p>
827
828<p><b>Syntax:</b></p>
829
830<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]831__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]832</pre>
833
834<p><b>Examples:</b></p>
835
836<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]837 // Identity operation - return 4-element vector V1.
838 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
839
840 // "Splat" element 0 of V1 into a 4-element result.
841 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
842
843 // Reverse 4-element vector V1.
844 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
845
846 // Concatenate every other element of 4-element vectors V1 and V2.
847 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
848
849 // Concatenate every other element of 8-element vectors V1 and V2.
850 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]851</pre>
852
853<p><b>Description:</b></p>
854
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]855<p>The first two arguments to __builtin_shufflevector are vectors that have the
856same element type. The remaining arguments are a list of integers that specify
857the elements indices of the first two vectors that should be extracted and
858returned in a new vector. These element indices are numbered sequentially
859starting with the first vector, continuing into the second vector. Thus, if
860vec1 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]861</p>
862
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]863<p>The result of __builtin_shufflevector is a vector
864with the same element type as vec1/vec2 but that has an element count equal to
865the number of indices specified.
866</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]867
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]868<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
869
870<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]871<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]872<!-- ======================================================================= -->
873
874<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
875the program cannot be reached, even if the compiler might otherwise think it
876can. This is useful to improve optimization and eliminates certain warnings.
877For example, without the <tt>__builtin_unreachable</tt> in the example below,
878the compiler assumes that the inline asm can fall through and prints a "function
879declared 'noreturn' should not return" warning.
880</p>
881
882<p><b>Syntax:</b></p>
883
884<pre>
885__builtin_unreachable()
886</pre>
887
888<p><b>Example of Use:</b></p>
889
890<pre>
891void myabort(void) __attribute__((noreturn));
892void myabort(void) {
893 asm("int3");
894 __builtin_unreachable();
895}
896</pre>
897
898<p><b>Description:</b></p>
899
900<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
901it has undefined behavior, it is a statement that it is never reached and the
902optimizer can take advantage of this to produce better code. This builtin takes
903no arguments and produces a void result.
904</p>
905
906<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
907
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]908<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]909<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]910<!-- ======================================================================= -->
911
912<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
913memory.
914</p>
915
916<p><b>Syntax:</b></p>
917
918<pre>
919<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
920</pre>
921
922<p><b>Example of Use:</b></p>
923
924<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]925int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]926</pre>
927
928<p><b>Description:</b></p>
929
930<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
931intrinsics to allow code to atomically swap the current value with the new
932value. More importantly, it helps developers write more efficient and correct
933code by avoiding expensive loops around __sync_bool_compare_and_swap() or
934relying on the platform specific implementation details of
935__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
936</p>
937
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]938
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]939<!-- ======================================================================= -->
940<h2 id="targetspecific">Target-Specific Extensions</h2>
941<!-- ======================================================================= -->
942
943<p>Clang supports some language features conditionally on some targets.</p>
944
945<!-- ======================================================================= -->
946<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
947<!-- ======================================================================= -->
948
949<p>The X86 backend has these language extensions:</p>
950
951<!-- ======================================================================= -->
952<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
953<!-- ======================================================================= -->
954
955<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]956relative to the X86 GS segment register, and address space #257 causes it to be
957relative to the X86 FS segment. Note that this is a very very low-level
958feature that should only be used if you know what you're doing (for example in
959an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]960
961<p>Here is an example:</p>
962
963<pre>
964#define GS_RELATIVE __attribute__((address_space(256)))
965int foo(int GS_RELATIVE *P) {
966 return *P;
967}
968</pre>
969
970<p>Which compiles to (on X86-32):</p>
971
972<pre>
973_foo:
974 movl 4(%esp), %eax
975 movl %gs:(%eax), %eax
976 ret
977</pre>
978
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]979<!-- ======================================================================= -->
980<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
981<!-- ======================================================================= -->
982
983<p>Clang supports additional attributes that are useful for documenting program
984invariants and rules for static analysis tools. The extensions documented here
985are used by the <a
986href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
987engine</a> that is part of Clang's Analysis library.</p>
988
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]989<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]990
991<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]992attribute. This attribute, which is typically affixed to a function prototype,
993indicates that a call to a given function never returns. Function prototypes for
994common functions like <tt>exit</tt> are typically annotated with this attribute,
995as well as a variety of common assertion handlers. Users can educate the static
996analyzer about their own custom assertion handles (thus cutting down on false
997positives due to false paths) by marking their own &quot;panic&quot; functions
998with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]999
1000<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1001there are special functions that for all intents and purposes should be
1002considered panic functions (i.e., they are only called when an internal program
1003error occurs) but may actually return so that the program can fail gracefully.
1004The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1005as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1006pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1007<tt>noreturn</tt>).</p>
1008
1009<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]1010same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1011placed at the end of function prototypes:</p>
1012
1013<pre>
1014 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1015</pre>
1016
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1017<p>Query for this feature with
1018<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1019
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1020<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1021
1022<p>Many methods in Objective-C have conventional meanings determined
1023by their selectors. For the purposes of static analysis, it is
1024sometimes useful to be able to mark a method as having a particular
1025conventional meaning despite not having the right selector, or as not
1026having the conventional meaning that its selector would suggest.
1027For these use cases, we provide an attribute to specifically describe
1028the <q>method family</q> that a method belongs to.</p>
1029
1030<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1031where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1032<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1033can only be placed at the end of a method declaration:</p>
1034
1035<pre>
1036 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1037</pre>
1038
1039<p>Users who do not wish to change the conventional meaning of a
1040method, and who merely want to document its non-standard retain and
1041release semantics, should use the
1042<a href="#attr_retain_release">retaining behavior attributes</a>
1043described below.</p>
1044
1045<p>Query for this feature with
1046<tt>__has_attribute(objc_method_family)</tt>.</p>
1047
1048<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1049
1050<p>In Objective-C, functions and methods are generally assumed to take
1051and return objects with +0 retain counts, with some exceptions for
1052special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1053there are exceptions, and so Clang provides attributes to allow these
1054exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1055ignore non-leaks). Some exceptions may be better described using
1056the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1057attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1058
1059<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1060<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1061and <tt>cf_returns_not_retained</tt> attributes can be placed on
1062methods and functions that return Objective-C or CoreFoundation
1063objects. They are commonly placed at the end of a function prototype
1064or method declaration:</p>
1065
1066<pre>
1067 id foo() <b>__attribute__((ns_returns_retained))</b>;
1068
1069 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1070</pre>
1071
1072<p>The <tt>*_returns_retained</tt> attributes specify that the
1073returned object has a +1 retain count.
1074The <tt>*_returns_not_retained</tt> attributes specify that the return
1075object has a +0 retain count, even if the normal convention for its
1076selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1077returned object is +0, but is guaranteed to live at least as long as the
1078next flush of an autorelease pool.</p>
1079
1080<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1081attributes can be placed on an parameter declaration; they specify
1082that the argument is expected to have a +1 retain count, which will be
1083balanced in some way by the function or method.
1084The <tt>ns_consumes_self</tt> attribute can only be placed on an
1085Objective-C method; it specifies that the method expects
1086its <tt>self</tt> parameter to have a +1 retain count, which it will
1087balance in some way.</p>
1088
1089<pre>
1090 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1091
1092 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1093 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1094</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1095
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1096<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1097<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1098
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1099
1100<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame^]1101<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1102<!-- ======================================================================= -->
1103
1104<p>Clang supports additional attributes for checking basic locking policies in
1105multithreaded programs.
1106Clang currently parses the following list of attributes, although
1107<b>the implementation for these annotations is currently in development.</b>
1108For more details, see the
1109<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1110</p>
1111
1112<h4 id="ts_guardedvar">guarded_var</h4>
1113
1114<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1115specify that the variable must be accessed while holding some lock.</p>
1116
1117<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1118
1119<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1120specify that the pointer must be dereferenced while holding some lock.</p>
1121
1122<h4 id="ts_lockable">lockable</h4>
1123
1124<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1125that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1126used to check consistency.</p>
1127
1128<h4 id="ts_scopedlockable">scoped_lockable</h4>
1129
1130<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1131specify that it has a "scoped" lockable type. Objects of this type will acquire
1132the lock upon construction and release it upon going out of scope.
1133 This annotation is primarily used to check
1134consistency.</p>
1135
1136<h4 id="ts_noanal">no_thread_safety_analysis</h4>
1137
1138<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1139declaration to specify that the thread safety analysis should not be run on that
1140function. This attribute provides an escape hatch (e.g. for situations when it
1141is difficult to annotate the locking policy). </p>
1142
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1143</div>
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