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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>
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]49 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]50 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
51 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
52 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
53 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
54 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
55 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
56 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
57 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
58 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
59 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
60 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
61 <li><a href="#cxx_override_control">C++11 override control</a></li>
62 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
63 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
64 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
65 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
66 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
67 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
68 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
69 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
70 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
71 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
72 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
73 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]74 </ul></li>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]75 <li><a href="#c11">C11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]76 <ul>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]77 <li><a href="#c_alignas">C11 alignment specifiers</a></li>
78 <li><a href="#c_generic_selections">C11 generic selections</a></li>
79 <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]80 </ul></li>
81 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]82<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]83<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]84<li><a href="#objc_features">Objective-C Features</a>
85 <ul>
86 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]87 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]88 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]89 </ul>
90</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]91<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]92<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]93<li><a href="#builtins">Builtin Functions</a>
94 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]95 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]96 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]97 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]98 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]99</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]100<li><a href="#targetspecific">Target-Specific Extensions</a>
101 <ul>
102 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
103 </ul>
104</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]105<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]106<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a></li>
107 <ul>
108 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
109 </ul>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]110<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
111 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]112 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
113 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
114 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]115 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
116 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]117 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
118 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
119 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
120 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
121 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
122 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
123 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
124 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
125 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
126 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
127 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
128 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
129 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]130 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]131</ul>
132
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]133<!-- ======================================================================= -->
134<h2 id="intro">Introduction</h2>
135<!-- ======================================================================= -->
136
137<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]138addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]139range of GCC extensions. Please see the <a
140href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
141more information on these extensions.</p>
142
143<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]144<h2 id="feature_check">Feature Checking Macros</h2>
145<!-- ======================================================================= -->
146
147<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]148on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]149function-like macros. This allows you to directly test for a feature in your
150code without having to resort to something like autoconf or fragile "compiler
151version checks".</p>
152
153<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]154<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]155<!-- ======================================================================= -->
156
157<p>This function-like macro takes a single identifier argument that is the name
158of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
159not. It can be used like this:</p>
160
161<blockquote>
162<pre>
163#ifndef __has_builtin // Optional of course.
164 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
165#endif
166
167...
168#if __has_builtin(__builtin_trap)
169 __builtin_trap();
170#else
171 abort();
172#endif
173...
174</pre>
175</blockquote>
176
177
178<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]179<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]180<!-- ======================================================================= -->
181
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]182<p>These function-like macros take a single identifier argument that is the
183name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
184is both supported by Clang and standardized in the current language standard
185or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
186<code>__has_extension</code> evaluates to 1 if the feature is supported by
187Clang in the current language (either as a language extension or a standard
188language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]189
190<blockquote>
191<pre>
192#ifndef __has_feature // Optional of course.
193 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
194#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]195#ifndef __has_extension
196 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
197#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]198
199...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]200#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]201// This code will only be compiled with the -std=c++11 and -std=gnu++11
202// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]203#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]204
205#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]206// 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]207// and -std=gnu++98 options, because rvalue references are supported as a
208// language extension in C++98.
209#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]210</pre>
211</blockquote>
212
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]213<p id="has_feature_back_compat">For backwards compatibility reasons,
214<code>__has_feature</code> can also be used to test for support for
215non-standardized features, i.e. features not prefixed <code>c_</code>,
216<code>cxx_</code> or <code>objc_</code>.</p>
217
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]218<p id="has_feature_for_non_language_features">
219Another use of <code>__has_feature</code> is to check for compiler features
220not related to the language standard, such as e.g.
221<a href="AddressSanitizer.html">AddressSanitizer</a>.
222
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]223<p>If the <code>-pedantic-errors</code> option is given,
224<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
225
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]226<p>The feature tag is described along with the language feature below.</p>
227
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]228<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]229<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]230<!-- ======================================================================= -->
231
232<p>This function-like macro takes a single identifier argument that is the name
233of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
234can be used like this:</p>
235
236<blockquote>
237<pre>
238#ifndef __has_attribute // Optional of course.
239 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
240#endif
241
242...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]243#if __has_attribute(always_inline)
244#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]245#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]246#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]247#endif
248...
249</pre>
250</blockquote>
251
252<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]253<h2 id="has_include">Include File Checking Macros</h2>
254<!-- ======================================================================= -->
255
256<p>Not all developments systems have the same include files.
257The <a href="#__has_include">__has_include</a> and
258<a href="#__has_include_next">__has_include_next</a> macros allow you to
259check for the existence of an include file before doing
260a possibly failing #include directive.</p>
261
262<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]263<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]264<!-- ======================================================================= -->
265
266<p>This function-like macro takes a single file name string argument that
267is the name of an include file. It evaluates to 1 if the file can
268be found using the include paths, or 0 otherwise:</p>
269
270<blockquote>
271<pre>
272// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]273#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]274# include "myinclude.h"
275#endif
276
277// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]278#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]279# include "myinclude.h"
280#endif
281</pre>
282</blockquote>
283
284<p>To test for this feature, use #if defined(__has_include).</p>
285
286<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]287<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]288<!-- ======================================================================= -->
289
290<p>This function-like macro takes a single file name string argument that
291is the name of an include file. It is like __has_include except that it
292looks for the second instance of the given file found in the include
293paths. It evaluates to 1 if the second instance of the file can
294be found using the include paths, or 0 otherwise:</p>
295
296<blockquote>
297<pre>
298// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]299#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]300# include_next "myinclude.h"
301#endif
302
303// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]304#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]305# include_next "myinclude.h"
306#endif
307</pre>
308</blockquote>
309
310<p>Note that __has_include_next, like the GNU extension
311#include_next directive, is intended for use in headers only,
312and will issue a warning if used in the top-level compilation
313file. A warning will also be issued if an absolute path
314is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]315
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]316
317<!-- ======================================================================= -->
318<h3><a name="__has_warning">__has_warning</a></h3>
319<!-- ======================================================================= -->
320
321<p>This function-like macro takes a string literal that represents a command
322 line option for a warning and returns true if that is a valid warning
323 option.</p>
324
325<blockquote>
326<pre>
327#if __has_warning("-Wformat")
328...
329#endif
330</pre>
331</blockquote>
332
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]333<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]334<h2 id="builtinmacros">Builtin Macros</h2>
335<!-- ======================================================================= -->
336
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]337<dl>
338 <dt><code>__BASE_FILE__</code></dt>
339 <dd>Defined to a string that contains the name of the main input
340 file passed to Clang.</dd>
341
342 <dt><code>__COUNTER__</code></dt>
343 <dd>Defined to an integer value that starts at zero and is
344 incremented each time the <code>__COUNTER__</code> macro is
345 expanded.</dd>
346
347 <dt><code>__INCLUDE_LEVEL__</code></dt>
348 <dd>Defined to an integral value that is the include depth of the
349 file currently being translated. For the main file, this value is
350 zero.</dd>
351
352 <dt><code>__TIMESTAMP__</code></dt>
353 <dd>Defined to the date and time of the last modification of the
354 current source file.</dd>
355
356 <dt><code>__clang__</code></dt>
357 <dd>Defined when compiling with Clang</dd>
358
359 <dt><code>__clang_major__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]360 <dd>Defined to the major marketing version number of Clang (e.g., the
361 2 in 2.0.1). Note that marketing version numbers should not be used to
362 check for language features, as different vendors use different numbering
363 schemes. Instead, use the <a href="#feature_check">feature checking
364 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]365
366 <dt><code>__clang_minor__</code></dt>
367 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]368 2.0.1). Note that marketing version numbers should not be used to
369 check for language features, as different vendors use different numbering
370 schemes. Instead, use the <a href="#feature_check">feature checking
371 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]372
373 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]374 <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]375
376 <dt><code>__clang_version__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]377 <dd>Defined to a string that captures the Clang marketing version, including
378 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]379</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]380
381<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]382<h2 id="vectors">Vectors and Extended Vectors</h2>
383<!-- ======================================================================= -->
384
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]385<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
386
387<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
388syntax and other tidbits as seen in OpenCL. An example is:</p>
389
390<blockquote>
391<pre>
392typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
393typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
394
395float4 foo(float2 a, float2 b) {
396 float4 c;
397 c.xz = a;
398 c.yw = b;
399 return c;
400}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]401</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]402</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]403
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]404<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]405
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]406<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
407
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]408<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]409<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]410<!-- ======================================================================= -->
411
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]412<p>An optional string message can be added to the <tt>deprecated</tt>
413and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]414
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]415<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]416<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]417</blockquote>
418
419<p>If the deprecated or unavailable declaration is used, the message
420will be incorporated into the appropriate diagnostic:</p>
421
422<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]423<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]424 explode();
425 ^</pre>
426</blockquote>
427
428<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]429with <tt>__has_extension(attribute_deprecated_with_message)</tt>
430and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]431
432<!-- ======================================================================= -->
433<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
434<!-- ======================================================================= -->
435
436<p>Clang allows attributes to be written on individual enumerators.
437This allows enumerators to be deprecated, made unavailable, etc. The
438attribute must appear after the enumerator name and before any
439initializer, like so:</p>
440
441<blockquote>
442<pre>enum OperationMode {
443 OM_Invalid,
444 OM_Normal,
445 OM_Terrified __attribute__((deprecated)),
446 OM_AbortOnError __attribute__((deprecated)) = 4
447};</pre>
448</blockquote>
449
450<p>Attributes on the <tt>enum</tt> declaration do not apply to
451individual enumerators.</p>
452
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]453<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]454
455<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]456<h2 id="checking_language_features">Checks for Standard Language Features</h2>
457<!-- ======================================================================= -->
458
459<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
460enabled. Those features are listed here.</p>
461
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]462<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]463
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]464<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]465example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]466
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]467<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]468
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]469<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]470compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]471
472<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]473<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
474<!-- ======================================================================= -->
475
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]476<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
477to query if certain upcoming standard language features are enabled. Those
478features are listed here. Features that are not yet implemented will be
479noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]480
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]481<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]482
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]483<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]484C++11 standard. As a result, all these features are enabled
485with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]486
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]487<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]488
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]489<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]490
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]491<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]492
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]493<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
494<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]495C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]496
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]497<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]498
499<p>Use <tt>__has_feature(cxx_alignas)</tt> or
500<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
501specifiers using <tt>alignas</tt> is enabled.</p>
502
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]503<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]504
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]505<p>Use <tt>__has_feature(cxx_attributes)</tt> or
506<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]507parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]508
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]509<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]510
511<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
512for generalized constant expressions (e.g., <tt>constexpr</tt>) is
513enabled. Clang does not currently implement this feature.</p>
514
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]515<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]516
517<p>Use <tt>__has_feature(cxx_decltype)</tt> or
518<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
519<tt>decltype()</tt> specifier is enabled.</p>
520
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]521<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]522
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]523<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
524<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
525if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]526
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]527<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
528
529<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
530<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
531defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
532
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]533<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]534
535<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
536support for delegating constructors is enabled.</p>
537
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]538<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]539
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]540<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
541<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]542deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]543
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]544<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h3>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]545<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
546
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]547<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]548
549<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
550support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]551<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
552this feature.</p>
553
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]554<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]555
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]556<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
557implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]558
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]559<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]560
561<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>
562
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]563<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]564
565<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
566<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
567inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]568
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]569<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]570
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]571<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
572<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]573is enabled. Clang does not currently implement this feature.</p>
574
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]575<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]576
577<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
578<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
579exception specifications is enabled.</p>
580
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]581<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]582
583<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]584
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]585<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]586
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]587<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
588<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]589<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]590
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]591<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]592
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]593<p>Use <tt>__has_feature(cxx_override_control)</tt> or
594<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]595the override control keywords is enabled.</p>
596
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]597<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]598<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
599<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
600if support for reference-qualified functions (e.g., member functions with
601<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
602is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]603
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]604<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]605
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]606<p>Use <tt>__has_feature(cxx_range_for)</tt> or
607<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
608range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]609
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]610<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]611<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>
612
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]613<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]614
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]615<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
616<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]617rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]618
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]619<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]620
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]621<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
622<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]623compile-time assertions using <tt>static_assert</tt> is enabled.</p>
624
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]625<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]626
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]627<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]628<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]629supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
630will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]631
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]632<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]633
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]634<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
635<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
636strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]637
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]638<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]639
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]640<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
641<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
642alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]643
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]644<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]645<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
646support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]647
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]648<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]649
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]650<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]651
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]652<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]653
654<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>
655
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]656<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]657
658<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
659<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
660for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]661
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]662<h3 id="c11">C11</h3>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]663
664<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]665C11 standard. As a result, all these features are enabled
666with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]667
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]668<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]669
670<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
671to determine if support for alignment specifiers using <tt>_Alignas</tt>
672is enabled.</p>
673
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]674<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]675
676<p>Use <tt>__has_feature(c_generic_selections)</tt> or
677<tt>__has_extension(c_generic_selections)</tt> to determine if support for
678generic selections is enabled.</p>
679
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]680<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]681languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]682C11 standard.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]683
684<p>In C, type compatibility is decided according to the rules given in the
685appropriate standard, but in C++, which lacks the type compatibility rules
686used in C, types are considered compatible only if they are equivalent.</p>
687
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame^]688<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]689
690<p>Use <tt>__has_feature(c_static_assert)</tt> or
691<tt>__has_extension(c_static_assert)</tt> to determine if support for
692compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
693
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]694<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]695<h2 id="checking_type_traits">Checks for Type Traits</h2>
696<!-- ======================================================================= -->
697
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]698<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]699<blockquote>
700<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]701#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]702template&lt;typename From, typename To&gt;
703struct is_convertible_to {
704 static const bool value = __is_convertible_to(From, To);
705};
706#else
707// Emulate type trait
708#endif
709</pre>
710</blockquote>
711
712<p>The following type traits are supported by Clang:</p>
713<ul>
714 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
715 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
716 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
717 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
718 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
719 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
720 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
721 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
722 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
723 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
724 <li><code>__is_class</code> (GNU, Microsoft)</li>
725 <li><code>__is_convertible_to</code> (Microsoft)</li>
726 <li><code>__is_empty</code> (GNU, Microsoft)</li>
727 <li><code>__is_enum</code> (GNU, Microsoft)</li>
728 <li><code>__is_pod</code> (GNU, Microsoft)</li>
729 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
730 <li><code>__is_union</code> (GNU, Microsoft)</li>
731 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
Douglas Gregor5e9392b2011-12-03 18:14:24 +0000[diff] [blame]732 <li><code>__is_final</code>: Determines whether the given type is declared with a <code>final</code> class-virt-specifier.</li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]733 <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]734</ul>
735
736<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]737<h2 id="blocks">Blocks</h2>
738<!-- ======================================================================= -->
739
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]740<p>The syntax and high level language feature description is in <a
741href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
742details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]743href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]744
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]745
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]746<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]747
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]748<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]749<h2 id="objc_features">Objective-C Features</h2>
750<!-- ======================================================================= -->
751
752<h3 id="objc_instancetype">Related result types</h3>
753
754<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>
755
756<blockquote>
757<pre>
758@interface NSObject
759+ (id)alloc;
760- (id)init;
761@end
762
763@interface NSArray : NSObject
764@end
765</pre>
766</blockquote>
767
768<p>and this common initialization pattern</p>
769
770<blockquote>
771<pre>
772NSArray *array = [[NSArray alloc] init];
773</pre>
774</blockquote>
775
776<p>the type of the expression <code>[NSArray alloc]</code> is
777<code>NSArray*</code> because <code>alloc</code> implicitly has a
778related result type. Similarly, the type of the expression
779<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
780<code>init</code> has a related result type and its receiver is known
781to 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>
782
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]783<p>A method with a related result type can be declared by using the
784type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
785is a contextual keyword that is only permitted in the result type of
786an Objective-C method, e.g.</p>
787
788<pre>
789@interface A
790+ (<b>instancetype</b>)constructAnA;
791@end
792</pre>
793
794<p>The related result type can also be inferred for some methods.
795To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]796word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]797considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]798type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]799
800<ul>
801
802 <li>the first word is "alloc" or "new", and the method is a class
803 method, or</li>
804
805 <li>the first word is "autorelease", "init", "retain", or "self",
806 and the method is an instance method.</li>
807
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]808</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]809
810<p>If a method with a related result type is overridden by a subclass
811method, the subclass method must also return a type that is compatible
812with the subclass type. For example:</p>
813
814<blockquote>
815<pre>
816@interface NSString : NSObject
817- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
818@end
819</pre>
820</blockquote>
821
822<p>Related result types only affect the type of a message send or
823property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]824with a related result type is treated the same way as method that
825returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]826
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]827<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
828the <tt>instancetype</tt> contextual keyword is available.</p>
829
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]830<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]831<h2 id="objc_arc">Automatic reference counting </h2>
832<!-- ======================================================================= -->
833
834<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>
835
836<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]837<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
838<!-- ======================================================================= -->
839
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]840<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]841underlying type within Objective-C. For example, one can write an
842enumeration type as:</p>
843
844<pre>
845typedef enum : unsigned char { Red, Green, Blue } Color;
846</pre>
847
848<p>This specifies that the underlying type, which is used to store the
849enumeration value, is <tt>unsigned char</tt>.</p>
850
851<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
852support for fixed underlying types is available in Objective-C.</p>
853
854<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]855<h2 id="overloading-in-c">Function Overloading in C</h2>
856<!-- ======================================================================= -->
857
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]858<p>Clang provides support for C++ function overloading in C. Function
859overloading in C is introduced using the <tt>overloadable</tt> attribute. For
860example, one might provide several overloaded versions of a <tt>tgsin</tt>
861function that invokes the appropriate standard function computing the sine of a
862value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
863precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]864
865<blockquote>
866<pre>
867#include &lt;math.h&gt;
868float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
869double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
870long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
871</pre>
872</blockquote>
873
874<p>Given these declarations, one can call <tt>tgsin</tt> with a
875<tt>float</tt> value to receive a <tt>float</tt> result, with a
876<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
877overloading in C follows the rules of C++ function overloading to pick
878the best overload given the call arguments, with a few C-specific
879semantics:</p>
880<ul>
881 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
882 double</tt> is ranked as a floating-point promotion (per C99) rather
883 than as a floating-point conversion (as in C++).</li>
884
885 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
886 <tt>U*</tt> is considered a pointer conversion (with conversion
887 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
888
889 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
890 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
891 conversion is given "conversion" rank.</li>
892</ul>
893
894<p>The declaration of <tt>overloadable</tt> functions is restricted to
895function declarations and definitions. Most importantly, if any
896function with a given name is given the <tt>overloadable</tt>
897attribute, then all function declarations and definitions with that
898name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]899attribute. This rule even applies to redeclarations of functions whose original
900declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]901
902<blockquote>
903<pre>
904int f(int) __attribute__((overloadable));
905float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
906
907int g(int) __attribute__((overloadable));
908int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
909</pre>
910</blockquote>
911
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]912<p>Functions marked <tt>overloadable</tt> must have
913prototypes. Therefore, the following code is ill-formed:</p>
914
915<blockquote>
916<pre>
917int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
918</pre>
919</blockquote>
920
921<p>However, <tt>overloadable</tt> functions are allowed to use a
922ellipsis 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>
923
924<blockquote>
925<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]926void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]927</pre>
928</blockquote>
929
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]930<p>Functions declared with the <tt>overloadable</tt> attribute have
931their names mangled according to the same rules as C++ function
932names. For example, the three <tt>tgsin</tt> functions in our
933motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]934<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]935caveats to this use of name mangling:</p>
936
937<ul>
938
939 <li>Future versions of Clang may change the name mangling of
940 functions overloaded in C, so you should not depend on an specific
941 mangling. To be completely safe, we strongly urge the use of
942 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
943
944 <li>The <tt>overloadable</tt> attribute has almost no meaning when
945 used in C++, because names will already be mangled and functions are
946 already overloadable. However, when an <tt>overloadable</tt>
947 function occurs within an <tt>extern "C"</tt> linkage specification,
948 it's name <i>will</i> be mangled in the same way as it would in
949 C.</li>
950</ul>
951
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]952<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]953
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]954<!-- ======================================================================= -->
955<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
956<!-- ======================================================================= -->
957
958<p>clang supports an extension which allows the following in C:</p>
959
960<blockquote>
961<pre>
962#include &lt;math.h&gt;
963#include &lt;complex.h&gt;
964complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
965</pre>
966</blockquote>
967
968<p>This construct is useful because there is no way to separately
969initialize the real and imaginary parts of a complex variable in
970standard C, given that clang does not support <code>_Imaginary</code>.
971(clang also supports the <code>__real__</code> and <code>__imag__</code>
972extensions from gcc, which help in some cases, but are not usable in
973static initializers.)
974
975<p>Note that this extension does not allow eliding the braces; the
976meaning of the following two lines is different:</p>
977
978<blockquote>
979<pre>
980complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
981complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
982</pre>
983</blockquote>
984
985<p>This extension also works in C++ mode, as far as that goes, but does not
986 apply to the C++ <code>std::complex</code>. (In C++11, list
987 initialization allows the same syntax to be used with
988 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]989
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]990<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]991<h2 id="builtins">Builtin Functions</h2>
992<!-- ======================================================================= -->
993
994<p>Clang supports a number of builtin library functions with the same syntax as
995GCC, including things like <tt>__builtin_nan</tt>,
996<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
997<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
998addition to the GCC builtins, Clang supports a number of builtins that GCC does
999not, which are listed here.</p>
1000
1001<p>Please note that Clang does not and will not support all of the GCC builtins
1002for vector operations. Instead of using builtins, you should use the functions
1003defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1004define portable wrappers for these. Many of the Clang versions of these
1005functions are implemented directly in terms of <a href="#vectors">extended
1006vector support</a> instead of builtins, in order to reduce the number of
1007builtins that we need to implement.</p>
1008
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1009<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1010<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1011<!-- ======================================================================= -->
1012
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1013<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1014permutation/shuffle/swizzle operations. This builtin is also very important for
1015the implementation of various target-specific header files like
1016<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1017</p>
1018
1019<p><b>Syntax:</b></p>
1020
1021<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1022__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1023</pre>
1024
1025<p><b>Examples:</b></p>
1026
1027<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1028 // Identity operation - return 4-element vector V1.
1029 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1030
1031 // "Splat" element 0 of V1 into a 4-element result.
1032 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1033
1034 // Reverse 4-element vector V1.
1035 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1036
1037 // Concatenate every other element of 4-element vectors V1 and V2.
1038 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1039
1040 // Concatenate every other element of 8-element vectors V1 and V2.
1041 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1042</pre>
1043
1044<p><b>Description:</b></p>
1045
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1046<p>The first two arguments to __builtin_shufflevector are vectors that have the
1047same element type. The remaining arguments are a list of integers that specify
1048the elements indices of the first two vectors that should be extracted and
1049returned in a new vector. These element indices are numbered sequentially
1050starting with the first vector, continuing into the second vector. Thus, if
1051vec1 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]1052</p>
1053
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1054<p>The result of __builtin_shufflevector is a vector
1055with the same element type as vec1/vec2 but that has an element count equal to
1056the number of indices specified.
1057</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1058
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1059<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1060
1061<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1062<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1063<!-- ======================================================================= -->
1064
1065<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1066the program cannot be reached, even if the compiler might otherwise think it
1067can. This is useful to improve optimization and eliminates certain warnings.
1068For example, without the <tt>__builtin_unreachable</tt> in the example below,
1069the compiler assumes that the inline asm can fall through and prints a "function
1070declared 'noreturn' should not return" warning.
1071</p>
1072
1073<p><b>Syntax:</b></p>
1074
1075<pre>
1076__builtin_unreachable()
1077</pre>
1078
1079<p><b>Example of Use:</b></p>
1080
1081<pre>
1082void myabort(void) __attribute__((noreturn));
1083void myabort(void) {
1084 asm("int3");
1085 __builtin_unreachable();
1086}
1087</pre>
1088
1089<p><b>Description:</b></p>
1090
1091<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1092it has undefined behavior, it is a statement that it is never reached and the
1093optimizer can take advantage of this to produce better code. This builtin takes
1094no arguments and produces a void result.
1095</p>
1096
1097<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1098
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1099<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1100<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1101<!-- ======================================================================= -->
1102
1103<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1104memory.
1105</p>
1106
1107<p><b>Syntax:</b></p>
1108
1109<pre>
1110<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1111</pre>
1112
1113<p><b>Example of Use:</b></p>
1114
1115<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1116int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1117</pre>
1118
1119<p><b>Description:</b></p>
1120
1121<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1122intrinsics to allow code to atomically swap the current value with the new
1123value. More importantly, it helps developers write more efficient and correct
1124code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1125relying on the platform specific implementation details of
1126__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1127</p>
1128
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1129
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1130<!-- ======================================================================= -->
1131<h2 id="targetspecific">Target-Specific Extensions</h2>
1132<!-- ======================================================================= -->
1133
1134<p>Clang supports some language features conditionally on some targets.</p>
1135
1136<!-- ======================================================================= -->
1137<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1138<!-- ======================================================================= -->
1139
1140<p>The X86 backend has these language extensions:</p>
1141
1142<!-- ======================================================================= -->
1143<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1144<!-- ======================================================================= -->
1145
1146<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1147relative to the X86 GS segment register, and address space #257 causes it to be
1148relative to the X86 FS segment. Note that this is a very very low-level
1149feature that should only be used if you know what you're doing (for example in
1150an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1151
1152<p>Here is an example:</p>
1153
1154<pre>
1155#define GS_RELATIVE __attribute__((address_space(256)))
1156int foo(int GS_RELATIVE *P) {
1157 return *P;
1158}
1159</pre>
1160
1161<p>Which compiles to (on X86-32):</p>
1162
1163<pre>
1164_foo:
1165 movl 4(%esp), %eax
1166 movl %gs:(%eax), %eax
1167 ret
1168</pre>
1169
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1170<!-- ======================================================================= -->
1171<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1172<!-- ======================================================================= -->
1173
1174<p>Clang supports additional attributes that are useful for documenting program
1175invariants and rules for static analysis tools. The extensions documented here
1176are used by the <a
1177href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1178engine</a> that is part of Clang's Analysis library.</p>
1179
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1180<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1181
1182<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1183attribute. This attribute, which is typically affixed to a function prototype,
1184indicates that a call to a given function never returns. Function prototypes for
1185common functions like <tt>exit</tt> are typically annotated with this attribute,
1186as well as a variety of common assertion handlers. Users can educate the static
1187analyzer about their own custom assertion handles (thus cutting down on false
1188positives due to false paths) by marking their own &quot;panic&quot; functions
1189with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1190
1191<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1192there are special functions that for all intents and purposes should be
1193considered panic functions (i.e., they are only called when an internal program
1194error occurs) but may actually return so that the program can fail gracefully.
1195The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1196as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1197pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1198<tt>noreturn</tt>).</p>
1199
1200<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]1201same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1202placed at the end of function prototypes:</p>
1203
1204<pre>
1205 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1206</pre>
1207
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1208<p>Query for this feature with
1209<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1210
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1211<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1212
1213<p>Many methods in Objective-C have conventional meanings determined
1214by their selectors. For the purposes of static analysis, it is
1215sometimes useful to be able to mark a method as having a particular
1216conventional meaning despite not having the right selector, or as not
1217having the conventional meaning that its selector would suggest.
1218For these use cases, we provide an attribute to specifically describe
1219the <q>method family</q> that a method belongs to.</p>
1220
1221<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1222where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1223<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1224can only be placed at the end of a method declaration:</p>
1225
1226<pre>
1227 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1228</pre>
1229
1230<p>Users who do not wish to change the conventional meaning of a
1231method, and who merely want to document its non-standard retain and
1232release semantics, should use the
1233<a href="#attr_retain_release">retaining behavior attributes</a>
1234described below.</p>
1235
1236<p>Query for this feature with
1237<tt>__has_attribute(objc_method_family)</tt>.</p>
1238
1239<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1240
1241<p>In Objective-C, functions and methods are generally assumed to take
1242and return objects with +0 retain counts, with some exceptions for
1243special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1244there are exceptions, and so Clang provides attributes to allow these
1245exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1246ignore non-leaks). Some exceptions may be better described using
1247the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1248attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1249
1250<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1251<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1252and <tt>cf_returns_not_retained</tt> attributes can be placed on
1253methods and functions that return Objective-C or CoreFoundation
1254objects. They are commonly placed at the end of a function prototype
1255or method declaration:</p>
1256
1257<pre>
1258 id foo() <b>__attribute__((ns_returns_retained))</b>;
1259
1260 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1261</pre>
1262
1263<p>The <tt>*_returns_retained</tt> attributes specify that the
1264returned object has a +1 retain count.
1265The <tt>*_returns_not_retained</tt> attributes specify that the return
1266object has a +0 retain count, even if the normal convention for its
1267selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1268returned object is +0, but is guaranteed to live at least as long as the
1269next flush of an autorelease pool.</p>
1270
1271<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1272attributes can be placed on an parameter declaration; they specify
1273that the argument is expected to have a +1 retain count, which will be
1274balanced in some way by the function or method.
1275The <tt>ns_consumes_self</tt> attribute can only be placed on an
1276Objective-C method; it specifies that the method expects
1277its <tt>self</tt> parameter to have a +1 retain count, which it will
1278balance in some way.</p>
1279
1280<pre>
1281 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1282
1283 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1284 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1285</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1286
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1287<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1288<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1289
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1290<!-- ======================================================================= -->
1291<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1292<!-- ======================================================================= -->
1293<h3 id="address_sanitizer">AddressSanitizer</h3>
1294<p> Use <code>__has_feature(address_sanitizer)</code>
1295to check if the code is being built with <a
1296 href="AddressSanitizer.html">AddressSanitizer</a>.
1297</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1298
1299<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1300<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1301<!-- ======================================================================= -->
1302
1303<p>Clang supports additional attributes for checking basic locking policies in
1304multithreaded programs.
1305Clang currently parses the following list of attributes, although
1306<b>the implementation for these annotations is currently in development.</b>
1307For more details, see the
1308<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1309</p>
1310
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1311<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1312
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1313<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1314declaration to specify that the thread safety analysis should not be run on that
1315function. This attribute provides an escape hatch (e.g. for situations when it
1316is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1317
1318<h4 id="ts_lockable">lockable</h4>
1319
1320<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1321that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1322used to check consistency.</p>
1323
1324<h4 id="ts_scopedlockable">scoped_lockable</h4>
1325
1326<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1327specify that it has a "scoped" lockable type. Objects of this type will acquire
1328the lock upon construction and release it upon going out of scope.
1329 This annotation is primarily used to check
1330consistency.</p>
1331
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1332<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1333
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1334<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1335specify that the variable must be accessed while holding some lock.</p>
1336
1337<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1338
1339<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1340specify that the pointer must be dereferenced while holding some lock.</p>
1341
1342<h4 id="ts_guardedby">guarded_by(l)</h4>
1343
1344<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1345specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1346
1347<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1348
1349<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1350specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1351
1352<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1353
1354<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1355of a lockable variable to specify that the lock must be acquired before all
1356attribute arguments. Arguments must be lockable type, and there must be at
1357least one argument.</p>
1358
1359<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1360
1361<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1362of a lockable variable to specify that the lock must be acquired after all
1363attribute arguments. Arguments must be lockable type, and there must be at
1364least one argument.</p>
1365
1366<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1367
1368<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1369declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1370exclusively. This attribute takes zero or more arguments: either of lockable
1371type or integers indexing into function parameters of lockable type. If no
1372arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1373enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1374
1375<h4 id="ts_slf">shared_lock_function(...)</h4>
1376
1377<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1378declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1379 the locks may be shared (e.g. read locks). This attribute takes zero or more
1380arguments: either of lockable type or integers indexing into function
1381parameters of lockable type. If no arguments are given, the acquired lock is
1382implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1383
1384<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1385
1386<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1387declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1388all listed locks exclusively. This attribute takes one or more arguments. The
1389first argument is an integer or boolean value specifying the return value of a
1390successful lock acquisition. The remaining arugments are either of lockable type
1391or integers indexing into function parameters of lockable type. If only one
1392argument is given, the acquired lock is implicitly <tt>this</tt> of the
1393enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1394
1395<h4 id="ts_stf">shared_trylock_function(...)</h4>
1396
1397<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1398declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1399all listed locks, although the locks may be shared (e.g. read locks). This
1400attribute takes one or more arguments. The first argument is an integer or
1401boolean value specifying the return value of a successful lock acquisition. The
1402remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1403function parameters of lockable type. If only one argument is given, the
1404acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1405
1406<h4 id="ts_uf">unlock_function(...)</h4>
1407
1408<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1409declaration to specify that the function release all listed locks. This
1410attribute takes zero or more arguments: either of lockable type or integers
1411indexing into function parameters of lockable type. If no arguments are given,
1412the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1413
1414<h4 id="ts_lr">lock_returned(l)</h4>
1415
1416<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1417declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1418must be of lockable type). This annotation is used to aid in resolving lock
1419expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1420
1421<h4 id="ts_le">locks_excluded(...)</h4>
1422
1423<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1424to specify that the function must not be called with the listed locks. Arguments
1425must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1426
1427<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1428
1429<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1430declaration to specify that the function must be called while holding the listed
1431exclusive locks. Arguments must be lockable type, and there must be at
1432least one argument.</p>
1433
1434<h4 id="ts_slr">shared_locks_required(...)</h4>
1435
1436<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1437declaration to specify that the function must be called while holding the listed
1438shared locks. Arguments must be lockable type, and there must be at
1439least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1440
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1441</div>
1442</body>
1443</html>