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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>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]90</ul>
91
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]92<!-- ======================================================================= -->
93<h2 id="intro">Introduction</h2>
94<!-- ======================================================================= -->
95
96<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]97addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]98range of GCC extensions. Please see the <a
99href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
100more information on these extensions.</p>
101
102<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]103<h2 id="feature_check">Feature Checking Macros</h2>
104<!-- ======================================================================= -->
105
106<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]107on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]108function-like macros. This allows you to directly test for a feature in your
109code without having to resort to something like autoconf or fragile "compiler
110version checks".</p>
111
112<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]113<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]114<!-- ======================================================================= -->
115
116<p>This function-like macro takes a single identifier argument that is the name
117of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
118not. It can be used like this:</p>
119
120<blockquote>
121<pre>
122#ifndef __has_builtin // Optional of course.
123 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
124#endif
125
126...
127#if __has_builtin(__builtin_trap)
128 __builtin_trap();
129#else
130 abort();
131#endif
132...
133</pre>
134</blockquote>
135
136
137<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]138<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]139<!-- ======================================================================= -->
140
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]141<p>These function-like macros take a single identifier argument that is the
142name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
143is both supported by Clang and standardized in the current language standard
144or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
145<code>__has_extension</code> evaluates to 1 if the feature is supported by
146Clang in the current language (either as a language extension or a standard
147language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]148
149<blockquote>
150<pre>
151#ifndef __has_feature // Optional of course.
152 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
153#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]154#ifndef __has_extension
155 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
156#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]157
158...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]159#if __has_feature(cxx_rvalue_references)
160// This code will only be compiled with the -std=c++0x and -std=gnu++0x
161// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]162#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]163
164#if __has_extension(cxx_rvalue_references)
165// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
166// and -std=gnu++98 options, because rvalue references are supported as a
167// language extension in C++98.
168#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]169</pre>
170</blockquote>
171
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]172<p id="has_feature_back_compat">For backwards compatibility reasons,
173<code>__has_feature</code> can also be used to test for support for
174non-standardized features, i.e. features not prefixed <code>c_</code>,
175<code>cxx_</code> or <code>objc_</code>.</p>
176
177<p>If the <code>-pedantic-errors</code> option is given,
178<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
179
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]180<p>The feature tag is described along with the language feature below.</p>
181
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]182<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]183<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]184<!-- ======================================================================= -->
185
186<p>This function-like macro takes a single identifier argument that is the name
187of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
188can be used like this:</p>
189
190<blockquote>
191<pre>
192#ifndef __has_attribute // Optional of course.
193 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
194#endif
195
196...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]197#if __has_attribute(always_inline)
198#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]199#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]200#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]201#endif
202...
203</pre>
204</blockquote>
205
206<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]207<h2 id="has_include">Include File Checking Macros</h2>
208<!-- ======================================================================= -->
209
210<p>Not all developments systems have the same include files.
211The <a href="#__has_include">__has_include</a> and
212<a href="#__has_include_next">__has_include_next</a> macros allow you to
213check for the existence of an include file before doing
214a possibly failing #include directive.</p>
215
216<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]217<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]218<!-- ======================================================================= -->
219
220<p>This function-like macro takes a single file name string argument that
221is the name of an include file. It evaluates to 1 if the file can
222be found using the include paths, or 0 otherwise:</p>
223
224<blockquote>
225<pre>
226// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]227#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]228# include "myinclude.h"
229#endif
230
231// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]232#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]233# include "myinclude.h"
234#endif
235</pre>
236</blockquote>
237
238<p>To test for this feature, use #if defined(__has_include).</p>
239
240<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]241<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]242<!-- ======================================================================= -->
243
244<p>This function-like macro takes a single file name string argument that
245is the name of an include file. It is like __has_include except that it
246looks for the second instance of the given file found in the include
247paths. It evaluates to 1 if the second instance of the file can
248be found using the include paths, or 0 otherwise:</p>
249
250<blockquote>
251<pre>
252// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]253#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]254# include_next "myinclude.h"
255#endif
256
257// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]258#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]259# include_next "myinclude.h"
260#endif
261</pre>
262</blockquote>
263
264<p>Note that __has_include_next, like the GNU extension
265#include_next directive, is intended for use in headers only,
266and will issue a warning if used in the top-level compilation
267file. A warning will also be issued if an absolute path
268is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]269
270<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]271<h2 id="builtinmacros">Builtin Macros</h2>
272<!-- ======================================================================= -->
273
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]274<dl>
275 <dt><code>__BASE_FILE__</code></dt>
276 <dd>Defined to a string that contains the name of the main input
277 file passed to Clang.</dd>
278
279 <dt><code>__COUNTER__</code></dt>
280 <dd>Defined to an integer value that starts at zero and is
281 incremented each time the <code>__COUNTER__</code> macro is
282 expanded.</dd>
283
284 <dt><code>__INCLUDE_LEVEL__</code></dt>
285 <dd>Defined to an integral value that is the include depth of the
286 file currently being translated. For the main file, this value is
287 zero.</dd>
288
289 <dt><code>__TIMESTAMP__</code></dt>
290 <dd>Defined to the date and time of the last modification of the
291 current source file.</dd>
292
293 <dt><code>__clang__</code></dt>
294 <dd>Defined when compiling with Clang</dd>
295
296 <dt><code>__clang_major__</code></dt>
297 <dd>Defined to the major version number of Clang (e.g., the 2 in
298 2.0.1).</dd>
299
300 <dt><code>__clang_minor__</code></dt>
301 <dd>Defined to the minor version number of Clang (e.g., the 0 in
302 2.0.1).</dd>
303
304 <dt><code>__clang_patchlevel__</code></dt>
305 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
306
307 <dt><code>__clang_version__</code></dt>
308 <dd>Defined to a string that captures the Clang version, including
309 the Subversion tag or revision number, e.g., "1.5 (trunk
310 102332)".</dd>
311</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]312
313<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]314<h2 id="vectors">Vectors and Extended Vectors</h2>
315<!-- ======================================================================= -->
316
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]317<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
318
319<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
320syntax and other tidbits as seen in OpenCL. An example is:</p>
321
322<blockquote>
323<pre>
324typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
325typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
326
327float4 foo(float2 a, float2 b) {
328 float4 c;
329 c.xz = a;
330 c.yw = b;
331 return c;
332}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]333</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]334</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]335
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]336<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]337
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]338<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
339
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]340<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]341<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]342<!-- ======================================================================= -->
343
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]344<p>An optional string message can be added to the <tt>deprecated</tt>
345and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]346
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]347<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]348<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]349</blockquote>
350
351<p>If the deprecated or unavailable declaration is used, the message
352will be incorporated into the appropriate diagnostic:</p>
353
354<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]355<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]356 explode();
357 ^</pre>
358</blockquote>
359
360<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]361with <tt>__has_extension(attribute_deprecated_with_message)</tt>
362and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]363
364<!-- ======================================================================= -->
365<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
366<!-- ======================================================================= -->
367
368<p>Clang allows attributes to be written on individual enumerators.
369This allows enumerators to be deprecated, made unavailable, etc. The
370attribute must appear after the enumerator name and before any
371initializer, like so:</p>
372
373<blockquote>
374<pre>enum OperationMode {
375 OM_Invalid,
376 OM_Normal,
377 OM_Terrified __attribute__((deprecated)),
378 OM_AbortOnError __attribute__((deprecated)) = 4
379};</pre>
380</blockquote>
381
382<p>Attributes on the <tt>enum</tt> declaration do not apply to
383individual enumerators.</p>
384
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]385<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]386
387<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]388<h2 id="checking_language_features">Checks for Standard Language Features</h2>
389<!-- ======================================================================= -->
390
391<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
392enabled. Those features are listed here.</p>
393
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]394<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]395
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]396<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]397example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]398
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]399<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]400
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]401<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]402compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]403
404<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]405<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
406<!-- ======================================================================= -->
407
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]408<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
409to query if certain upcoming standard language features are enabled. Those
410features are listed here. Features that are not yet implemented will be
411noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]412
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]413<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]414
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]415<p>The features listed below are slated for inclusion in the upcoming
416C++0x standard. As a result, all these features are enabled
417with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]418
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]419<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]420
421<p>Use <tt>__has_feature(cxx_decltype)</tt> or
422<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]423<tt>decltype()</tt> specifier is enabled.</p>
424
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]425<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]426
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]427<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]428
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]429<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]430
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]431<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
432<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]433C++0x's alias declarations and alias templates is enabled.</p>
434
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]435<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]436
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]437<p>Use <tt>__has_feature(cxx_attributes)</tt> or
438<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
439parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]440
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]441<h4 id="cxx_default_function_template_args">C++0x default template arguments in function templates</h4>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]442
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]443<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
444<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
445if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]446
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]447<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
448
449<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
450support for delegating constructors is enabled.</p>
451
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]452<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]453
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]454<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
455<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]456deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]457
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]458<h4 id="cxx_lambdas">C++0x lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]459
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]460<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
461<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
462is enabled. clang does not currently implement this feature.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]463
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]464<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]465
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]466<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
467<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]468<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]469
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]470<h4 id="cxx_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]471
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]472<p>Use <tt>__has_feature(cxx_override_control)</tt> or
473<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]474the override control keywords is enabled.</p>
475
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]476<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]477<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
478<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
479if support for reference-qualified functions (e.g., member functions with
480<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
481is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]482
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]483<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]484
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]485<p>Use <tt>__has_feature(cxx_range_for)</tt> or
486<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
487range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]488
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]489<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]490
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]491<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
492<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]493rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]494
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]495<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]496
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]497<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
498<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]499compile-time assertions using <tt>static_assert</tt> is enabled.</p>
500
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]501<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]502
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]503<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
504<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
505supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
506will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]507
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]508<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]509
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]510<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
511<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
Douglas Gregor83d77812011-01-19 23:15:20 +0000[diff] [blame]512for variadic templates is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]513
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]514<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]515
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]516<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
517<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]518inline namespaces is enabled.</p>
519
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]520<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]521
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]522<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
523<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
524alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]525
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]526<h4 id="cxx_noexcept">C++0x noexcept</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]527
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]528<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
529<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
530exception specifications is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]531
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]532<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]533
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]534<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
535<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]536strongly typed, scoped enumerations is enabled.</p>
537
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]538<h3 id="c1x">C1X</h3>
539
540<p>The features listed below are slated for inclusion in the upcoming
541C1X standard. As a result, all these features are enabled
542with the <tt>-std=c1x</tt> option when compiling C code.</p>
543
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]544<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]545
546<p>Use <tt>__has_feature(c_generic_selections)</tt> or
547<tt>__has_extension(c_generic_selections)</tt> to determine if support for
548generic selections is enabled.</p>
549
550<p>As an extension, the C1X generic selection expression is available in all
551languages supported by Clang. The syntax is the same as that given in the
552C1X draft standard.</p>
553
554<p>In C, type compatibility is decided according to the rules given in the
555appropriate standard, but in C++, which lacks the type compatibility rules
556used in C, types are considered compatible only if they are equivalent.</p>
557
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]558<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]559
560<p>Use <tt>__has_feature(c_static_assert)</tt> or
561<tt>__has_extension(c_static_assert)</tt> to determine if support for
562compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
563
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]564<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]565<h2 id="checking_type_traits">Checks for Type Traits</h2>
566<!-- ======================================================================= -->
567
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]568<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]569<blockquote>
570<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]571#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]572template&lt;typename From, typename To&gt;
573struct is_convertible_to {
574 static const bool value = __is_convertible_to(From, To);
575};
576#else
577// Emulate type trait
578#endif
579</pre>
580</blockquote>
581
582<p>The following type traits are supported by Clang:</p>
583<ul>
584 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
585 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
586 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
587 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
588 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
589 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
590 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
591 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
592 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
593 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
594 <li><code>__is_class</code> (GNU, Microsoft)</li>
595 <li><code>__is_convertible_to</code> (Microsoft)</li>
596 <li><code>__is_empty</code> (GNU, Microsoft)</li>
597 <li><code>__is_enum</code> (GNU, Microsoft)</li>
598 <li><code>__is_pod</code> (GNU, Microsoft)</li>
599 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
600 <li><code>__is_union</code> (GNU, Microsoft)</li>
601 <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]602 <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]603</ul>
604
605<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]606<h2 id="blocks">Blocks</h2>
607<!-- ======================================================================= -->
608
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]609<p>The syntax and high level language feature description is in <a
610href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
611details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]612href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]613
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]614
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]615<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]616
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]617<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]618<h2 id="objc_features">Objective-C Features</h2>
619<!-- ======================================================================= -->
620
621<h3 id="objc_instancetype">Related result types</h3>
622
623<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>
624
625<blockquote>
626<pre>
627@interface NSObject
628+ (id)alloc;
629- (id)init;
630@end
631
632@interface NSArray : NSObject
633@end
634</pre>
635</blockquote>
636
637<p>and this common initialization pattern</p>
638
639<blockquote>
640<pre>
641NSArray *array = [[NSArray alloc] init];
642</pre>
643</blockquote>
644
645<p>the type of the expression <code>[NSArray alloc]</code> is
646<code>NSArray*</code> because <code>alloc</code> implicitly has a
647related result type. Similarly, the type of the expression
648<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
649<code>init</code> has a related result type and its receiver is known
650to 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>
651
652<p>To determine whether a method has a related result type, the first
653word in the camel-case selector (e.g., "init" in "initWithObjects") is
654considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]655type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]656
657<ul>
658
659 <li>the first word is "alloc" or "new", and the method is a class
660 method, or</li>
661
662 <li>the first word is "autorelease", "init", "retain", or "self",
663 and the method is an instance method.</li>
664
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]665</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]666
667<p>If a method with a related result type is overridden by a subclass
668method, the subclass method must also return a type that is compatible
669with the subclass type. For example:</p>
670
671<blockquote>
672<pre>
673@interface NSString : NSObject
674- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
675@end
676</pre>
677</blockquote>
678
679<p>Related result types only affect the type of a message send or
680property access via the given method. In all other respects, a method
681with a related result type is treated the same way as method without a
682related result type.</p>
683
684<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]685<h2 id="objc_arc">Automatic reference counting </h2>
686<!-- ======================================================================= -->
687
688<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>
689
690<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]691<h2 id="overloading-in-c">Function Overloading in C</h2>
692<!-- ======================================================================= -->
693
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]694<p>Clang provides support for C++ function overloading in C. Function
695overloading in C is introduced using the <tt>overloadable</tt> attribute. For
696example, one might provide several overloaded versions of a <tt>tgsin</tt>
697function that invokes the appropriate standard function computing the sine of a
698value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
699precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]700
701<blockquote>
702<pre>
703#include &lt;math.h&gt;
704float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
705double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
706long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
707</pre>
708</blockquote>
709
710<p>Given these declarations, one can call <tt>tgsin</tt> with a
711<tt>float</tt> value to receive a <tt>float</tt> result, with a
712<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
713overloading in C follows the rules of C++ function overloading to pick
714the best overload given the call arguments, with a few C-specific
715semantics:</p>
716<ul>
717 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
718 double</tt> is ranked as a floating-point promotion (per C99) rather
719 than as a floating-point conversion (as in C++).</li>
720
721 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
722 <tt>U*</tt> is considered a pointer conversion (with conversion
723 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
724
725 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
726 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
727 conversion is given "conversion" rank.</li>
728</ul>
729
730<p>The declaration of <tt>overloadable</tt> functions is restricted to
731function declarations and definitions. Most importantly, if any
732function with a given name is given the <tt>overloadable</tt>
733attribute, then all function declarations and definitions with that
734name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]735attribute. This rule even applies to redeclarations of functions whose original
736declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]737
738<blockquote>
739<pre>
740int f(int) __attribute__((overloadable));
741float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
742
743int g(int) __attribute__((overloadable));
744int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
745</pre>
746</blockquote>
747
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]748<p>Functions marked <tt>overloadable</tt> must have
749prototypes. Therefore, the following code is ill-formed:</p>
750
751<blockquote>
752<pre>
753int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
754</pre>
755</blockquote>
756
757<p>However, <tt>overloadable</tt> functions are allowed to use a
758ellipsis 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>
759
760<blockquote>
761<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]762void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]763</pre>
764</blockquote>
765
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]766<p>Functions declared with the <tt>overloadable</tt> attribute have
767their names mangled according to the same rules as C++ function
768names. For example, the three <tt>tgsin</tt> functions in our
769motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]770<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]771caveats to this use of name mangling:</p>
772
773<ul>
774
775 <li>Future versions of Clang may change the name mangling of
776 functions overloaded in C, so you should not depend on an specific
777 mangling. To be completely safe, we strongly urge the use of
778 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
779
780 <li>The <tt>overloadable</tt> attribute has almost no meaning when
781 used in C++, because names will already be mangled and functions are
782 already overloadable. However, when an <tt>overloadable</tt>
783 function occurs within an <tt>extern "C"</tt> linkage specification,
784 it's name <i>will</i> be mangled in the same way as it would in
785 C.</li>
786</ul>
787
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]788<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]789
790
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]791<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]792<h2 id="builtins">Builtin Functions</h2>
793<!-- ======================================================================= -->
794
795<p>Clang supports a number of builtin library functions with the same syntax as
796GCC, including things like <tt>__builtin_nan</tt>,
797<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
798<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
799addition to the GCC builtins, Clang supports a number of builtins that GCC does
800not, which are listed here.</p>
801
802<p>Please note that Clang does not and will not support all of the GCC builtins
803for vector operations. Instead of using builtins, you should use the functions
804defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
805define portable wrappers for these. Many of the Clang versions of these
806functions are implemented directly in terms of <a href="#vectors">extended
807vector support</a> instead of builtins, in order to reduce the number of
808builtins that we need to implement.</p>
809
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]810<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]811<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]812<!-- ======================================================================= -->
813
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]814<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]815permutation/shuffle/swizzle operations. This builtin is also very important for
816the implementation of various target-specific header files like
817<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]818</p>
819
820<p><b>Syntax:</b></p>
821
822<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]823__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]824</pre>
825
826<p><b>Examples:</b></p>
827
828<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]829 // Identity operation - return 4-element vector V1.
830 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
831
832 // "Splat" element 0 of V1 into a 4-element result.
833 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
834
835 // Reverse 4-element vector V1.
836 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
837
838 // Concatenate every other element of 4-element vectors V1 and V2.
839 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
840
841 // Concatenate every other element of 8-element vectors V1 and V2.
842 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]843</pre>
844
845<p><b>Description:</b></p>
846
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]847<p>The first two arguments to __builtin_shufflevector are vectors that have the
848same element type. The remaining arguments are a list of integers that specify
849the elements indices of the first two vectors that should be extracted and
850returned in a new vector. These element indices are numbered sequentially
851starting with the first vector, continuing into the second vector. Thus, if
852vec1 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]853</p>
854
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]855<p>The result of __builtin_shufflevector is a vector
856with the same element type as vec1/vec2 but that has an element count equal to
857the number of indices specified.
858</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]859
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]860<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
861
862<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]863<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]864<!-- ======================================================================= -->
865
866<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
867the program cannot be reached, even if the compiler might otherwise think it
868can. This is useful to improve optimization and eliminates certain warnings.
869For example, without the <tt>__builtin_unreachable</tt> in the example below,
870the compiler assumes that the inline asm can fall through and prints a "function
871declared 'noreturn' should not return" warning.
872</p>
873
874<p><b>Syntax:</b></p>
875
876<pre>
877__builtin_unreachable()
878</pre>
879
880<p><b>Example of Use:</b></p>
881
882<pre>
883void myabort(void) __attribute__((noreturn));
884void myabort(void) {
885 asm("int3");
886 __builtin_unreachable();
887}
888</pre>
889
890<p><b>Description:</b></p>
891
892<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
893it has undefined behavior, it is a statement that it is never reached and the
894optimizer can take advantage of this to produce better code. This builtin takes
895no arguments and produces a void result.
896</p>
897
898<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
899
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]900<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]901<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]902<!-- ======================================================================= -->
903
904<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
905memory.
906</p>
907
908<p><b>Syntax:</b></p>
909
910<pre>
911<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
912</pre>
913
914<p><b>Example of Use:</b></p>
915
916<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]917int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]918</pre>
919
920<p><b>Description:</b></p>
921
922<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
923intrinsics to allow code to atomically swap the current value with the new
924value. More importantly, it helps developers write more efficient and correct
925code by avoiding expensive loops around __sync_bool_compare_and_swap() or
926relying on the platform specific implementation details of
927__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
928</p>
929
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]930
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]931<!-- ======================================================================= -->
932<h2 id="targetspecific">Target-Specific Extensions</h2>
933<!-- ======================================================================= -->
934
935<p>Clang supports some language features conditionally on some targets.</p>
936
937<!-- ======================================================================= -->
938<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
939<!-- ======================================================================= -->
940
941<p>The X86 backend has these language extensions:</p>
942
943<!-- ======================================================================= -->
944<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
945<!-- ======================================================================= -->
946
947<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]948relative to the X86 GS segment register, and address space #257 causes it to be
949relative to the X86 FS segment. Note that this is a very very low-level
950feature that should only be used if you know what you're doing (for example in
951an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]952
953<p>Here is an example:</p>
954
955<pre>
956#define GS_RELATIVE __attribute__((address_space(256)))
957int foo(int GS_RELATIVE *P) {
958 return *P;
959}
960</pre>
961
962<p>Which compiles to (on X86-32):</p>
963
964<pre>
965_foo:
966 movl 4(%esp), %eax
967 movl %gs:(%eax), %eax
968 ret
969</pre>
970
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]971<!-- ======================================================================= -->
972<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
973<!-- ======================================================================= -->
974
975<p>Clang supports additional attributes that are useful for documenting program
976invariants and rules for static analysis tools. The extensions documented here
977are used by the <a
978href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
979engine</a> that is part of Clang's Analysis library.</p>
980
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]981<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]982
983<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]984attribute. This attribute, which is typically affixed to a function prototype,
985indicates that a call to a given function never returns. Function prototypes for
986common functions like <tt>exit</tt> are typically annotated with this attribute,
987as well as a variety of common assertion handlers. Users can educate the static
988analyzer about their own custom assertion handles (thus cutting down on false
989positives due to false paths) by marking their own &quot;panic&quot; functions
990with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]991
992<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]993there are special functions that for all intents and purposes should be
994considered panic functions (i.e., they are only called when an internal program
995error occurs) but may actually return so that the program can fail gracefully.
996The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
997as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]998pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]999<tt>noreturn</tt>).</p>
1000
1001<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]1002same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1003placed at the end of function prototypes:</p>
1004
1005<pre>
1006 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1007</pre>
1008
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1009<p>Query for this feature with
1010<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1011
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1012<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1013
1014<p>Many methods in Objective-C have conventional meanings determined
1015by their selectors. For the purposes of static analysis, it is
1016sometimes useful to be able to mark a method as having a particular
1017conventional meaning despite not having the right selector, or as not
1018having the conventional meaning that its selector would suggest.
1019For these use cases, we provide an attribute to specifically describe
1020the <q>method family</q> that a method belongs to.</p>
1021
1022<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1023where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1024<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1025can only be placed at the end of a method declaration:</p>
1026
1027<pre>
1028 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1029</pre>
1030
1031<p>Users who do not wish to change the conventional meaning of a
1032method, and who merely want to document its non-standard retain and
1033release semantics, should use the
1034<a href="#attr_retain_release">retaining behavior attributes</a>
1035described below.</p>
1036
1037<p>Query for this feature with
1038<tt>__has_attribute(objc_method_family)</tt>.</p>
1039
1040<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1041
1042<p>In Objective-C, functions and methods are generally assumed to take
1043and return objects with +0 retain counts, with some exceptions for
1044special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1045there are exceptions, and so Clang provides attributes to allow these
1046exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1047ignore non-leaks). Some exceptions may be better described using
1048the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1049attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1050
1051<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1052<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1053and <tt>cf_returns_not_retained</tt> attributes can be placed on
1054methods and functions that return Objective-C or CoreFoundation
1055objects. They are commonly placed at the end of a function prototype
1056or method declaration:</p>
1057
1058<pre>
1059 id foo() <b>__attribute__((ns_returns_retained))</b>;
1060
1061 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1062</pre>
1063
1064<p>The <tt>*_returns_retained</tt> attributes specify that the
1065returned object has a +1 retain count.
1066The <tt>*_returns_not_retained</tt> attributes specify that the return
1067object has a +0 retain count, even if the normal convention for its
1068selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1069returned object is +0, but is guaranteed to live at least as long as the
1070next flush of an autorelease pool.</p>
1071
1072<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1073attributes can be placed on an parameter declaration; they specify
1074that the argument is expected to have a +1 retain count, which will be
1075balanced in some way by the function or method.
1076The <tt>ns_consumes_self</tt> attribute can only be placed on an
1077Objective-C method; it specifies that the method expects
1078its <tt>self</tt> parameter to have a +1 retain count, which it will
1079balance in some way.</p>
1080
1081<pre>
1082 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1083
1084 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1085 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1086</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1087
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1088<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1089<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1090
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1091</div>
1092</body>
1093</html>