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19
20<div id="content">
21
22<h1>Clang Language Extensions</h1>
23
24<ul>
25<li><a href="#intro">Introduction</a></li>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]26<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]27<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]28<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]29<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]30<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
31<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]32<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]33 <ul>
34 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
35 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]36 </ul></li>
37<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]38 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]39 <li><a href="#cxx0x">C++11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]40 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]41 <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes
42 access control</a></li>
43 <li><a href="#cxx_alias_templates">C++11 alias templates</a></li>
44 <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li>
45 <li><a href="#cxx_attributes">C++11 attributes</a></li>
46 <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li>
47 <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li>
48 <li><a href="#cxx_default_function_template_args">C++11 default template arguments in function templates</a></li>
49 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
50 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
51 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
52 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
53 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
54 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
55 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
56 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
57 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
58 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
59 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
60 <li><a href="#cxx_override_control">C++11 override control</a></li>
61 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
62 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
63 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
64 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
65 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
66 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
67 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
68 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
69 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
70 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
71 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
72 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]73 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]74 <li><a href="#c1x">C1X</a>
75 <ul>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]76 <li><a href="#c_alignas">C1X alignment specifiers</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]77 <li><a href="#c_generic_selections">C1X generic selections</a></li>
78 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]79 </ul></li>
80 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]81<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]82<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]83<li><a href="#objc_features">Objective-C Features</a>
84 <ul>
85 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]86 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]87 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]88 </ul>
89</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]90<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]91<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]92<li><a href="#builtins">Builtin Functions</a>
93 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]94 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]95 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]96 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]97 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]98</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]99<li><a href="#targetspecific">Target-Specific Extensions</a>
100 <ul>
101 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
102 </ul>
103</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]104<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]105<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
106 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]107 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
108 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
109 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]110 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
111 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]112 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
113 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
114 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
115 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
116 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
117 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
118 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
119 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
120 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
121 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
122 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
123 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
124 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]125 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]126</ul>
127
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]128<!-- ======================================================================= -->
129<h2 id="intro">Introduction</h2>
130<!-- ======================================================================= -->
131
132<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]133addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]134range of GCC extensions. Please see the <a
135href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
136more information on these extensions.</p>
137
138<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]139<h2 id="feature_check">Feature Checking Macros</h2>
140<!-- ======================================================================= -->
141
142<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]143on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]144function-like macros. This allows you to directly test for a feature in your
145code without having to resort to something like autoconf or fragile "compiler
146version checks".</p>
147
148<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]149<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]150<!-- ======================================================================= -->
151
152<p>This function-like macro takes a single identifier argument that is the name
153of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
154not. It can be used like this:</p>
155
156<blockquote>
157<pre>
158#ifndef __has_builtin // Optional of course.
159 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
160#endif
161
162...
163#if __has_builtin(__builtin_trap)
164 __builtin_trap();
165#else
166 abort();
167#endif
168...
169</pre>
170</blockquote>
171
172
173<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]174<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]175<!-- ======================================================================= -->
176
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]177<p>These function-like macros take a single identifier argument that is the
178name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
179is both supported by Clang and standardized in the current language standard
180or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
181<code>__has_extension</code> evaluates to 1 if the feature is supported by
182Clang in the current language (either as a language extension or a standard
183language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]184
185<blockquote>
186<pre>
187#ifndef __has_feature // Optional of course.
188 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
189#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]190#ifndef __has_extension
191 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
192#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]193
194...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]195#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]196// This code will only be compiled with the -std=c++11 and -std=gnu++11
197// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]198#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]199
200#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]201// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]202// and -std=gnu++98 options, because rvalue references are supported as a
203// language extension in C++98.
204#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]205</pre>
206</blockquote>
207
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]208<p id="has_feature_back_compat">For backwards compatibility reasons,
209<code>__has_feature</code> can also be used to test for support for
210non-standardized features, i.e. features not prefixed <code>c_</code>,
211<code>cxx_</code> or <code>objc_</code>.</p>
212
213<p>If the <code>-pedantic-errors</code> option is given,
214<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
215
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]216<p>The feature tag is described along with the language feature below.</p>
217
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]218<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]219<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]220<!-- ======================================================================= -->
221
222<p>This function-like macro takes a single identifier argument that is the name
223of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
224can be used like this:</p>
225
226<blockquote>
227<pre>
228#ifndef __has_attribute // Optional of course.
229 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
230#endif
231
232...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]233#if __has_attribute(always_inline)
234#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]235#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]236#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]237#endif
238...
239</pre>
240</blockquote>
241
242<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]243<h2 id="has_include">Include File Checking Macros</h2>
244<!-- ======================================================================= -->
245
246<p>Not all developments systems have the same include files.
247The <a href="#__has_include">__has_include</a> and
248<a href="#__has_include_next">__has_include_next</a> macros allow you to
249check for the existence of an include file before doing
250a possibly failing #include directive.</p>
251
252<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]253<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]254<!-- ======================================================================= -->
255
256<p>This function-like macro takes a single file name string argument that
257is the name of an include file. It evaluates to 1 if the file can
258be found using the include paths, or 0 otherwise:</p>
259
260<blockquote>
261<pre>
262// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]263#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]264# include "myinclude.h"
265#endif
266
267// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]268#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]269# include "myinclude.h"
270#endif
271</pre>
272</blockquote>
273
274<p>To test for this feature, use #if defined(__has_include).</p>
275
276<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]277<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]278<!-- ======================================================================= -->
279
280<p>This function-like macro takes a single file name string argument that
281is the name of an include file. It is like __has_include except that it
282looks for the second instance of the given file found in the include
283paths. It evaluates to 1 if the second instance of the file can
284be found using the include paths, or 0 otherwise:</p>
285
286<blockquote>
287<pre>
288// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]289#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]290# include_next "myinclude.h"
291#endif
292
293// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]294#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]295# include_next "myinclude.h"
296#endif
297</pre>
298</blockquote>
299
300<p>Note that __has_include_next, like the GNU extension
301#include_next directive, is intended for use in headers only,
302and will issue a warning if used in the top-level compilation
303file. A warning will also be issued if an absolute path
304is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]305
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]306
307<!-- ======================================================================= -->
308<h3><a name="__has_warning">__has_warning</a></h3>
309<!-- ======================================================================= -->
310
311<p>This function-like macro takes a string literal that represents a command
312 line option for a warning and returns true if that is a valid warning
313 option.</p>
314
315<blockquote>
316<pre>
317#if __has_warning("-Wformat")
318...
319#endif
320</pre>
321</blockquote>
322
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]323<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]324<h2 id="builtinmacros">Builtin Macros</h2>
325<!-- ======================================================================= -->
326
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]327<dl>
328 <dt><code>__BASE_FILE__</code></dt>
329 <dd>Defined to a string that contains the name of the main input
330 file passed to Clang.</dd>
331
332 <dt><code>__COUNTER__</code></dt>
333 <dd>Defined to an integer value that starts at zero and is
334 incremented each time the <code>__COUNTER__</code> macro is
335 expanded.</dd>
336
337 <dt><code>__INCLUDE_LEVEL__</code></dt>
338 <dd>Defined to an integral value that is the include depth of the
339 file currently being translated. For the main file, this value is
340 zero.</dd>
341
342 <dt><code>__TIMESTAMP__</code></dt>
343 <dd>Defined to the date and time of the last modification of the
344 current source file.</dd>
345
346 <dt><code>__clang__</code></dt>
347 <dd>Defined when compiling with Clang</dd>
348
349 <dt><code>__clang_major__</code></dt>
350 <dd>Defined to the major version number of Clang (e.g., the 2 in
351 2.0.1).</dd>
352
353 <dt><code>__clang_minor__</code></dt>
354 <dd>Defined to the minor version number of Clang (e.g., the 0 in
355 2.0.1).</dd>
356
357 <dt><code>__clang_patchlevel__</code></dt>
358 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
359
360 <dt><code>__clang_version__</code></dt>
361 <dd>Defined to a string that captures the Clang version, including
362 the Subversion tag or revision number, e.g., "1.5 (trunk
363 102332)".</dd>
364</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]365
366<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]367<h2 id="vectors">Vectors and Extended Vectors</h2>
368<!-- ======================================================================= -->
369
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]370<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
371
372<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
373syntax and other tidbits as seen in OpenCL. An example is:</p>
374
375<blockquote>
376<pre>
377typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
378typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
379
380float4 foo(float2 a, float2 b) {
381 float4 c;
382 c.xz = a;
383 c.yw = b;
384 return c;
385}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]386</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]387</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]388
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]389<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]390
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]391<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
392
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]393<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]394<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]395<!-- ======================================================================= -->
396
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]397<p>An optional string message can be added to the <tt>deprecated</tt>
398and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]399
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]400<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]401<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]402</blockquote>
403
404<p>If the deprecated or unavailable declaration is used, the message
405will be incorporated into the appropriate diagnostic:</p>
406
407<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]408<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]409 explode();
410 ^</pre>
411</blockquote>
412
413<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]414with <tt>__has_extension(attribute_deprecated_with_message)</tt>
415and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]416
417<!-- ======================================================================= -->
418<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
419<!-- ======================================================================= -->
420
421<p>Clang allows attributes to be written on individual enumerators.
422This allows enumerators to be deprecated, made unavailable, etc. The
423attribute must appear after the enumerator name and before any
424initializer, like so:</p>
425
426<blockquote>
427<pre>enum OperationMode {
428 OM_Invalid,
429 OM_Normal,
430 OM_Terrified __attribute__((deprecated)),
431 OM_AbortOnError __attribute__((deprecated)) = 4
432};</pre>
433</blockquote>
434
435<p>Attributes on the <tt>enum</tt> declaration do not apply to
436individual enumerators.</p>
437
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]438<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]439
440<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]441<h2 id="checking_language_features">Checks for Standard Language Features</h2>
442<!-- ======================================================================= -->
443
444<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
445enabled. Those features are listed here.</p>
446
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]447<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]448
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]449<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]450example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]451
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]452<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]453
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]454<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]455compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]456
457<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]458<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
459<!-- ======================================================================= -->
460
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]461<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
462to query if certain upcoming standard language features are enabled. Those
463features are listed here. Features that are not yet implemented will be
464noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]465
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]466<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]467
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]468<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]469C++11 standard. As a result, all these features are enabled
470with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]471
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]472<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]473
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]474<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]475
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]476<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]477
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]478<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
479<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]480C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]481
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]482<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]483
484<p>Use <tt>__has_feature(cxx_alignas)</tt> or
485<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
486specifiers using <tt>alignas</tt> is enabled.</p>
487
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]488<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]489
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]490<p>Use <tt>__has_feature(cxx_attributes)</tt> or
491<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]492parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]493
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]494<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]495
496<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
497for generalized constant expressions (e.g., <tt>constexpr</tt>) is
498enabled. Clang does not currently implement this feature.</p>
499
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]500<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]501
502<p>Use <tt>__has_feature(cxx_decltype)</tt> or
503<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
504<tt>decltype()</tt> specifier is enabled.</p>
505
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]506<h4 id="cxx_default_function_template_args">C++11 default template arguments in function templates</h4>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]507
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]508<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
509<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
510if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]511
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]512<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]513
514<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
515support for delegating constructors is enabled.</p>
516
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]517<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]518
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]519<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
520<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]521deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]522
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]523<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h3>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]524<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
525
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]526<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]527
528<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
529support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]530<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
531this feature.</p>
532
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]533<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]534
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]535<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
536implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]537
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]538<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]539
540<p>Use <tt>__has_feature(cxx_inheriting_constructors)</tt> to determine if support for inheriting constructors is enabled. Clang does not currently implement this feature.</p>
541
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]542<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]543
544<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
545<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
546inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]547
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]548<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]549
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]550<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
551<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]552is enabled. Clang does not currently implement this feature.</p>
553
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]554<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]555
556<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
557<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
558exception specifications is enabled.</p>
559
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]560<h4 id="cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]561
562<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]563
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]564<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]565
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]566<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
567<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]568<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]569
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]570<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]571
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]572<p>Use <tt>__has_feature(cxx_override_control)</tt> or
573<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]574the override control keywords is enabled.</p>
575
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]576<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]577<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
578<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
579if support for reference-qualified functions (e.g., member functions with
580<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
581is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]582
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]583<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]584
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]585<p>Use <tt>__has_feature(cxx_range_for)</tt> or
586<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
587range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]588
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]589<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]590<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support for raw string literals (e.g., <tt>R"foo\bar"</tt>) is enabled.</p>
591
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]592<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]593
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]594<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
595<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]596rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]597
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]598<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]599
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]600<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
601<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]602compile-time assertions using <tt>static_assert</tt> is enabled.</p>
603
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]604<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]605
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]606<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]607<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]608supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
609will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]610
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]611<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]612
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]613<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
614<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
615strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]616
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]617<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]618
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]619<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
620<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
621alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]622
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]623<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]624<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
625support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]626
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]627<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]628
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]629<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled. Clang does not currently support this feature.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]630
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]631<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]632
633<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled. Clang does not currently support this feature.</p>
634
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]635<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]636
637<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
638<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
639for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]640
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]641<h3 id="c1x">C1X</h3>
642
643<p>The features listed below are slated for inclusion in the upcoming
644C1X standard. As a result, all these features are enabled
645with the <tt>-std=c1x</tt> option when compiling C code.</p>
646
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]647<h4 id="c_alignas">C1X alignment specifiers</h4>
648
649<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
650to determine if support for alignment specifiers using <tt>_Alignas</tt>
651is enabled.</p>
652
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]653<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]654
655<p>Use <tt>__has_feature(c_generic_selections)</tt> or
656<tt>__has_extension(c_generic_selections)</tt> to determine if support for
657generic selections is enabled.</p>
658
659<p>As an extension, the C1X generic selection expression is available in all
660languages supported by Clang. The syntax is the same as that given in the
661C1X draft standard.</p>
662
663<p>In C, type compatibility is decided according to the rules given in the
664appropriate standard, but in C++, which lacks the type compatibility rules
665used in C, types are considered compatible only if they are equivalent.</p>
666
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]667<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]668
669<p>Use <tt>__has_feature(c_static_assert)</tt> or
670<tt>__has_extension(c_static_assert)</tt> to determine if support for
671compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
672
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]673<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]674<h2 id="checking_type_traits">Checks for Type Traits</h2>
675<!-- ======================================================================= -->
676
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]677<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]678<blockquote>
679<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]680#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]681template&lt;typename From, typename To&gt;
682struct is_convertible_to {
683 static const bool value = __is_convertible_to(From, To);
684};
685#else
686// Emulate type trait
687#endif
688</pre>
689</blockquote>
690
691<p>The following type traits are supported by Clang:</p>
692<ul>
693 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
694 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
695 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
696 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
697 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
698 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
699 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
700 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
701 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
702 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
703 <li><code>__is_class</code> (GNU, Microsoft)</li>
704 <li><code>__is_convertible_to</code> (Microsoft)</li>
705 <li><code>__is_empty</code> (GNU, Microsoft)</li>
706 <li><code>__is_enum</code> (GNU, Microsoft)</li>
707 <li><code>__is_pod</code> (GNU, Microsoft)</li>
708 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
709 <li><code>__is_union</code> (GNU, Microsoft)</li>
710 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]711 <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++11 standard library.</li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]712</ul>
713
714<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]715<h2 id="blocks">Blocks</h2>
716<!-- ======================================================================= -->
717
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]718<p>The syntax and high level language feature description is in <a
719href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
720details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]721href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]722
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]723
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]724<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]725
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]726<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]727<h2 id="objc_features">Objective-C Features</h2>
728<!-- ======================================================================= -->
729
730<h3 id="objc_instancetype">Related result types</h3>
731
732<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>
733
734<blockquote>
735<pre>
736@interface NSObject
737+ (id)alloc;
738- (id)init;
739@end
740
741@interface NSArray : NSObject
742@end
743</pre>
744</blockquote>
745
746<p>and this common initialization pattern</p>
747
748<blockquote>
749<pre>
750NSArray *array = [[NSArray alloc] init];
751</pre>
752</blockquote>
753
754<p>the type of the expression <code>[NSArray alloc]</code> is
755<code>NSArray*</code> because <code>alloc</code> implicitly has a
756related result type. Similarly, the type of the expression
757<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
758<code>init</code> has a related result type and its receiver is known
759to 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>
760
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]761<p>A method with a related result type can be declared by using the
762type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
763is a contextual keyword that is only permitted in the result type of
764an Objective-C method, e.g.</p>
765
766<pre>
767@interface A
768+ (<b>instancetype</b>)constructAnA;
769@end
770</pre>
771
772<p>The related result type can also be inferred for some methods.
773To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]774word in the camel-case selector (e.g., "init" in "initWithObjects") is
775considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]776type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]777
778<ul>
779
780 <li>the first word is "alloc" or "new", and the method is a class
781 method, or</li>
782
783 <li>the first word is "autorelease", "init", "retain", or "self",
784 and the method is an instance method.</li>
785
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]786</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]787
788<p>If a method with a related result type is overridden by a subclass
789method, the subclass method must also return a type that is compatible
790with the subclass type. For example:</p>
791
792<blockquote>
793<pre>
794@interface NSString : NSObject
795- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
796@end
797</pre>
798</blockquote>
799
800<p>Related result types only affect the type of a message send or
801property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]802with a related result type is treated the same way as method that
803returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]804
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]805<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
806the <tt>instancetype</tt> contextual keyword is available.</p>
807
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]808<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]809<h2 id="objc_arc">Automatic reference counting </h2>
810<!-- ======================================================================= -->
811
812<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>
813
814<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]815<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
816<!-- ======================================================================= -->
817
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame^]818<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]819underlying type within Objective-C. For example, one can write an
820enumeration type as:</p>
821
822<pre>
823typedef enum : unsigned char { Red, Green, Blue } Color;
824</pre>
825
826<p>This specifies that the underlying type, which is used to store the
827enumeration value, is <tt>unsigned char</tt>.</p>
828
829<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
830support for fixed underlying types is available in Objective-C.</p>
831
832<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]833<h2 id="overloading-in-c">Function Overloading in C</h2>
834<!-- ======================================================================= -->
835
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]836<p>Clang provides support for C++ function overloading in C. Function
837overloading in C is introduced using the <tt>overloadable</tt> attribute. For
838example, one might provide several overloaded versions of a <tt>tgsin</tt>
839function that invokes the appropriate standard function computing the sine of a
840value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
841precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]842
843<blockquote>
844<pre>
845#include &lt;math.h&gt;
846float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
847double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
848long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
849</pre>
850</blockquote>
851
852<p>Given these declarations, one can call <tt>tgsin</tt> with a
853<tt>float</tt> value to receive a <tt>float</tt> result, with a
854<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
855overloading in C follows the rules of C++ function overloading to pick
856the best overload given the call arguments, with a few C-specific
857semantics:</p>
858<ul>
859 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
860 double</tt> is ranked as a floating-point promotion (per C99) rather
861 than as a floating-point conversion (as in C++).</li>
862
863 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
864 <tt>U*</tt> is considered a pointer conversion (with conversion
865 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
866
867 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
868 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
869 conversion is given "conversion" rank.</li>
870</ul>
871
872<p>The declaration of <tt>overloadable</tt> functions is restricted to
873function declarations and definitions. Most importantly, if any
874function with a given name is given the <tt>overloadable</tt>
875attribute, then all function declarations and definitions with that
876name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]877attribute. This rule even applies to redeclarations of functions whose original
878declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]879
880<blockquote>
881<pre>
882int f(int) __attribute__((overloadable));
883float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
884
885int g(int) __attribute__((overloadable));
886int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
887</pre>
888</blockquote>
889
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]890<p>Functions marked <tt>overloadable</tt> must have
891prototypes. Therefore, the following code is ill-formed:</p>
892
893<blockquote>
894<pre>
895int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
896</pre>
897</blockquote>
898
899<p>However, <tt>overloadable</tt> functions are allowed to use a
900ellipsis 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>
901
902<blockquote>
903<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]904void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]905</pre>
906</blockquote>
907
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]908<p>Functions declared with the <tt>overloadable</tt> attribute have
909their names mangled according to the same rules as C++ function
910names. For example, the three <tt>tgsin</tt> functions in our
911motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]912<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]913caveats to this use of name mangling:</p>
914
915<ul>
916
917 <li>Future versions of Clang may change the name mangling of
918 functions overloaded in C, so you should not depend on an specific
919 mangling. To be completely safe, we strongly urge the use of
920 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
921
922 <li>The <tt>overloadable</tt> attribute has almost no meaning when
923 used in C++, because names will already be mangled and functions are
924 already overloadable. However, when an <tt>overloadable</tt>
925 function occurs within an <tt>extern "C"</tt> linkage specification,
926 it's name <i>will</i> be mangled in the same way as it would in
927 C.</li>
928</ul>
929
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]930<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]931
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]932<!-- ======================================================================= -->
933<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
934<!-- ======================================================================= -->
935
936<p>clang supports an extension which allows the following in C:</p>
937
938<blockquote>
939<pre>
940#include &lt;math.h&gt;
941#include &lt;complex.h&gt;
942complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
943</pre>
944</blockquote>
945
946<p>This construct is useful because there is no way to separately
947initialize the real and imaginary parts of a complex variable in
948standard C, given that clang does not support <code>_Imaginary</code>.
949(clang also supports the <code>__real__</code> and <code>__imag__</code>
950extensions from gcc, which help in some cases, but are not usable in
951static initializers.)
952
953<p>Note that this extension does not allow eliding the braces; the
954meaning of the following two lines is different:</p>
955
956<blockquote>
957<pre>
958complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
959complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
960</pre>
961</blockquote>
962
963<p>This extension also works in C++ mode, as far as that goes, but does not
964 apply to the C++ <code>std::complex</code>. (In C++11, list
965 initialization allows the same syntax to be used with
966 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]967
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]968<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]969<h2 id="builtins">Builtin Functions</h2>
970<!-- ======================================================================= -->
971
972<p>Clang supports a number of builtin library functions with the same syntax as
973GCC, including things like <tt>__builtin_nan</tt>,
974<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
975<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
976addition to the GCC builtins, Clang supports a number of builtins that GCC does
977not, which are listed here.</p>
978
979<p>Please note that Clang does not and will not support all of the GCC builtins
980for vector operations. Instead of using builtins, you should use the functions
981defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
982define portable wrappers for these. Many of the Clang versions of these
983functions are implemented directly in terms of <a href="#vectors">extended
984vector support</a> instead of builtins, in order to reduce the number of
985builtins that we need to implement.</p>
986
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]987<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]988<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]989<!-- ======================================================================= -->
990
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]991<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]992permutation/shuffle/swizzle operations. This builtin is also very important for
993the implementation of various target-specific header files like
994<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]995</p>
996
997<p><b>Syntax:</b></p>
998
999<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1000__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1001</pre>
1002
1003<p><b>Examples:</b></p>
1004
1005<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1006 // Identity operation - return 4-element vector V1.
1007 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1008
1009 // "Splat" element 0 of V1 into a 4-element result.
1010 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1011
1012 // Reverse 4-element vector V1.
1013 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1014
1015 // Concatenate every other element of 4-element vectors V1 and V2.
1016 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1017
1018 // Concatenate every other element of 8-element vectors V1 and V2.
1019 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1020</pre>
1021
1022<p><b>Description:</b></p>
1023
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1024<p>The first two arguments to __builtin_shufflevector are vectors that have the
1025same element type. The remaining arguments are a list of integers that specify
1026the elements indices of the first two vectors that should be extracted and
1027returned in a new vector. These element indices are numbered sequentially
1028starting with the first vector, continuing into the second vector. Thus, if
1029vec1 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]1030</p>
1031
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1032<p>The result of __builtin_shufflevector is a vector
1033with the same element type as vec1/vec2 but that has an element count equal to
1034the number of indices specified.
1035</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1036
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1037<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1038
1039<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1040<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1041<!-- ======================================================================= -->
1042
1043<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1044the program cannot be reached, even if the compiler might otherwise think it
1045can. This is useful to improve optimization and eliminates certain warnings.
1046For example, without the <tt>__builtin_unreachable</tt> in the example below,
1047the compiler assumes that the inline asm can fall through and prints a "function
1048declared 'noreturn' should not return" warning.
1049</p>
1050
1051<p><b>Syntax:</b></p>
1052
1053<pre>
1054__builtin_unreachable()
1055</pre>
1056
1057<p><b>Example of Use:</b></p>
1058
1059<pre>
1060void myabort(void) __attribute__((noreturn));
1061void myabort(void) {
1062 asm("int3");
1063 __builtin_unreachable();
1064}
1065</pre>
1066
1067<p><b>Description:</b></p>
1068
1069<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1070it has undefined behavior, it is a statement that it is never reached and the
1071optimizer can take advantage of this to produce better code. This builtin takes
1072no arguments and produces a void result.
1073</p>
1074
1075<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1076
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1077<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1078<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1079<!-- ======================================================================= -->
1080
1081<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1082memory.
1083</p>
1084
1085<p><b>Syntax:</b></p>
1086
1087<pre>
1088<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1089</pre>
1090
1091<p><b>Example of Use:</b></p>
1092
1093<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1094int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1095</pre>
1096
1097<p><b>Description:</b></p>
1098
1099<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1100intrinsics to allow code to atomically swap the current value with the new
1101value. More importantly, it helps developers write more efficient and correct
1102code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1103relying on the platform specific implementation details of
1104__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1105</p>
1106
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1107
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1108<!-- ======================================================================= -->
1109<h2 id="targetspecific">Target-Specific Extensions</h2>
1110<!-- ======================================================================= -->
1111
1112<p>Clang supports some language features conditionally on some targets.</p>
1113
1114<!-- ======================================================================= -->
1115<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1116<!-- ======================================================================= -->
1117
1118<p>The X86 backend has these language extensions:</p>
1119
1120<!-- ======================================================================= -->
1121<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1122<!-- ======================================================================= -->
1123
1124<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1125relative to the X86 GS segment register, and address space #257 causes it to be
1126relative to the X86 FS segment. Note that this is a very very low-level
1127feature that should only be used if you know what you're doing (for example in
1128an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1129
1130<p>Here is an example:</p>
1131
1132<pre>
1133#define GS_RELATIVE __attribute__((address_space(256)))
1134int foo(int GS_RELATIVE *P) {
1135 return *P;
1136}
1137</pre>
1138
1139<p>Which compiles to (on X86-32):</p>
1140
1141<pre>
1142_foo:
1143 movl 4(%esp), %eax
1144 movl %gs:(%eax), %eax
1145 ret
1146</pre>
1147
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1148<!-- ======================================================================= -->
1149<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1150<!-- ======================================================================= -->
1151
1152<p>Clang supports additional attributes that are useful for documenting program
1153invariants and rules for static analysis tools. The extensions documented here
1154are used by the <a
1155href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1156engine</a> that is part of Clang's Analysis library.</p>
1157
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1158<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1159
1160<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1161attribute. This attribute, which is typically affixed to a function prototype,
1162indicates that a call to a given function never returns. Function prototypes for
1163common functions like <tt>exit</tt> are typically annotated with this attribute,
1164as well as a variety of common assertion handlers. Users can educate the static
1165analyzer about their own custom assertion handles (thus cutting down on false
1166positives due to false paths) by marking their own &quot;panic&quot; functions
1167with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1168
1169<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1170there are special functions that for all intents and purposes should be
1171considered panic functions (i.e., they are only called when an internal program
1172error occurs) but may actually return so that the program can fail gracefully.
1173The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1174as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1175pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1176<tt>noreturn</tt>).</p>
1177
1178<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]1179same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1180placed at the end of function prototypes:</p>
1181
1182<pre>
1183 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1184</pre>
1185
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1186<p>Query for this feature with
1187<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1188
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1189<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1190
1191<p>Many methods in Objective-C have conventional meanings determined
1192by their selectors. For the purposes of static analysis, it is
1193sometimes useful to be able to mark a method as having a particular
1194conventional meaning despite not having the right selector, or as not
1195having the conventional meaning that its selector would suggest.
1196For these use cases, we provide an attribute to specifically describe
1197the <q>method family</q> that a method belongs to.</p>
1198
1199<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1200where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1201<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1202can only be placed at the end of a method declaration:</p>
1203
1204<pre>
1205 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1206</pre>
1207
1208<p>Users who do not wish to change the conventional meaning of a
1209method, and who merely want to document its non-standard retain and
1210release semantics, should use the
1211<a href="#attr_retain_release">retaining behavior attributes</a>
1212described below.</p>
1213
1214<p>Query for this feature with
1215<tt>__has_attribute(objc_method_family)</tt>.</p>
1216
1217<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1218
1219<p>In Objective-C, functions and methods are generally assumed to take
1220and return objects with +0 retain counts, with some exceptions for
1221special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1222there are exceptions, and so Clang provides attributes to allow these
1223exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1224ignore non-leaks). Some exceptions may be better described using
1225the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1226attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1227
1228<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1229<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1230and <tt>cf_returns_not_retained</tt> attributes can be placed on
1231methods and functions that return Objective-C or CoreFoundation
1232objects. They are commonly placed at the end of a function prototype
1233or method declaration:</p>
1234
1235<pre>
1236 id foo() <b>__attribute__((ns_returns_retained))</b>;
1237
1238 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1239</pre>
1240
1241<p>The <tt>*_returns_retained</tt> attributes specify that the
1242returned object has a +1 retain count.
1243The <tt>*_returns_not_retained</tt> attributes specify that the return
1244object has a +0 retain count, even if the normal convention for its
1245selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1246returned object is +0, but is guaranteed to live at least as long as the
1247next flush of an autorelease pool.</p>
1248
1249<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1250attributes can be placed on an parameter declaration; they specify
1251that the argument is expected to have a +1 retain count, which will be
1252balanced in some way by the function or method.
1253The <tt>ns_consumes_self</tt> attribute can only be placed on an
1254Objective-C method; it specifies that the method expects
1255its <tt>self</tt> parameter to have a +1 retain count, which it will
1256balance in some way.</p>
1257
1258<pre>
1259 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1260
1261 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1262 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1263</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1264
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1265<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1266<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1267
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1268
1269<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1270<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1271<!-- ======================================================================= -->
1272
1273<p>Clang supports additional attributes for checking basic locking policies in
1274multithreaded programs.
1275Clang currently parses the following list of attributes, although
1276<b>the implementation for these annotations is currently in development.</b>
1277For more details, see the
1278<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1279</p>
1280
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1281<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1282
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1283<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1284declaration to specify that the thread safety analysis should not be run on that
1285function. This attribute provides an escape hatch (e.g. for situations when it
1286is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1287
1288<h4 id="ts_lockable">lockable</h4>
1289
1290<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1291that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1292used to check consistency.</p>
1293
1294<h4 id="ts_scopedlockable">scoped_lockable</h4>
1295
1296<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1297specify that it has a "scoped" lockable type. Objects of this type will acquire
1298the lock upon construction and release it upon going out of scope.
1299 This annotation is primarily used to check
1300consistency.</p>
1301
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1302<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1303
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1304<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1305specify that the variable must be accessed while holding some lock.</p>
1306
1307<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1308
1309<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1310specify that the pointer must be dereferenced while holding some lock.</p>
1311
1312<h4 id="ts_guardedby">guarded_by(l)</h4>
1313
1314<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1315specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1316
1317<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1318
1319<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1320specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1321
1322<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1323
1324<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1325of a lockable variable to specify that the lock must be acquired before all
1326attribute arguments. Arguments must be lockable type, and there must be at
1327least one argument.</p>
1328
1329<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1330
1331<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1332of a lockable variable to specify that the lock must be acquired after all
1333attribute arguments. Arguments must be lockable type, and there must be at
1334least one argument.</p>
1335
1336<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1337
1338<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1339declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1340exclusively. This attribute takes zero or more arguments: either of lockable
1341type or integers indexing into function parameters of lockable type. If no
1342arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1343enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1344
1345<h4 id="ts_slf">shared_lock_function(...)</h4>
1346
1347<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1348declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1349 the locks may be shared (e.g. read locks). This attribute takes zero or more
1350arguments: either of lockable type or integers indexing into function
1351parameters of lockable type. If no arguments are given, the acquired lock is
1352implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1353
1354<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1355
1356<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1357declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1358all listed locks exclusively. This attribute takes one or more arguments. The
1359first argument is an integer or boolean value specifying the return value of a
1360successful lock acquisition. The remaining arugments are either of lockable type
1361or integers indexing into function parameters of lockable type. If only one
1362argument is given, the acquired lock is implicitly <tt>this</tt> of the
1363enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1364
1365<h4 id="ts_stf">shared_trylock_function(...)</h4>
1366
1367<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1368declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1369all listed locks, although the locks may be shared (e.g. read locks). This
1370attribute takes one or more arguments. The first argument is an integer or
1371boolean value specifying the return value of a successful lock acquisition. The
1372remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1373function parameters of lockable type. If only one argument is given, the
1374acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1375
1376<h4 id="ts_uf">unlock_function(...)</h4>
1377
1378<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1379declaration to specify that the function release all listed locks. This
1380attribute takes zero or more arguments: either of lockable type or integers
1381indexing into function parameters of lockable type. If no arguments are given,
1382the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1383
1384<h4 id="ts_lr">lock_returned(l)</h4>
1385
1386<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1387declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1388must be of lockable type). This annotation is used to aid in resolving lock
1389expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1390
1391<h4 id="ts_le">locks_excluded(...)</h4>
1392
1393<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1394to specify that the function must not be called with the listed locks. Arguments
1395must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1396
1397<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1398
1399<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1400declaration to specify that the function must be called while holding the listed
1401exclusive locks. Arguments must be lockable type, and there must be at
1402least one argument.</p>
1403
1404<h4 id="ts_slr">shared_locks_required(...)</h4>
1405
1406<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1407declaration to specify that the function must be called while holding the listed
1408shared locks. Arguments must be lockable type, and there must be at
1409least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1410
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1411</div>
1412</body>
1413</html>