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19<!--#include virtual="../menu.html.incl"-->
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21<div id="content">
22
23<h1>Clang Language Extensions</h1>
24
25<ul>
26<li><a href="#intro">Introduction</a></li>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]27<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]28<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner7de64562009-04-13 02:45:46 +0000[diff] [blame]29<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]30<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]31<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
32<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]33<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]34 <ul>
35 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
36 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]37 </ul></li>
38<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]39 <ul>
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]40 <li><a href="#cxx0x">C++11</a>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]41 <ul>
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]42 <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes
43 access control</a></li>
44 <li><a href="#cxx_alias_templates">C++11 alias templates</a></li>
45 <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li>
46 <li><a href="#cxx_attributes">C++11 attributes</a></li>
47 <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li>
48 <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li>
49 <li><a href="#cxx_default_function_template_args">C++11 default template arguments in function templates</a></li>
Douglas Gregor3c469762011-11-01 01:19:34 +0000[diff] [blame]50 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]51 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
52 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
53 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
54 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
55 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
56 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
57 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
58 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
59 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
60 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
61 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
62 <li><a href="#cxx_override_control">C++11 override control</a></li>
63 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
64 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
65 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
66 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
67 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
68 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
69 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
70 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
71 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
72 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
73 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
74 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]75 </ul></li>
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]76 <li><a href="#c11">C11</a>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]77 <ul>
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]78 <li><a href="#c_alignas">C11 alignment specifiers</a></li>
79 <li><a href="#c_generic_selections">C11 generic selections</a></li>
80 <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li>
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]81 </ul></li>
82 </ul> </li>
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]83<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]84<li><a href="#blocks">Blocks</a></li>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]85<li><a href="#objc_features">Objective-C Features</a>
86 <ul>
87 <li><a href="#objc_instancetype">Related result types</a></li>
John McCall31168b02011-06-15 23:02:42 +0000[diff] [blame]88 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor8b7d4032011-09-08 17:18:35 +0000[diff] [blame]89 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]90 </ul>
91</li>
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]92<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman6b9c41e2011-09-19 23:17:44 +0000[diff] [blame]93<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]94<li><a href="#builtins">Builtin Functions</a>
95 <ul>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]96 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]97 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]98 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]99 </ul>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]100</li>
Chris Lattnerc86ffc32009-04-09 19:58:15 +0000[diff] [blame]101<li><a href="#targetspecific">Target-Specific Extensions</a>
102 <ul>
103 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
104 </ul>
105</li>
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]106<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Benjamin Kramereaa262b2012-01-15 15:26:07 +0000[diff] [blame]107<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a>
Kostya Serebryany9751d342011-11-28 20:51:02 +0000[diff] [blame]108 <ul>
109 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
110 </ul>
Benjamin Kramereaa262b2012-01-15 15:26:07 +0000[diff] [blame]111</li>
112<li><a href="#threadsafety">Thread Safety Annotation Checking</a>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]113 <ul>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]114 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
115 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
116 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]117 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
118 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]119 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
120 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
121 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
122 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
123 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
124 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
125 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
126 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
127 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
128 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
129 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
130 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
131 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]132 </ul>
Benjamin Kramereaa262b2012-01-15 15:26:07 +0000[diff] [blame]133</li>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]134</ul>
135
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]136<!-- ======================================================================= -->
137<h2 id="intro">Introduction</h2>
138<!-- ======================================================================= -->
139
140<p>This document describes the language extensions provided by Clang. In
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]141addition to the language extensions listed here, Clang aims to support a broad
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]142range of GCC extensions. Please see the <a
143href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
144more information on these extensions.</p>
145
146<!-- ======================================================================= -->
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]147<h2 id="feature_check">Feature Checking Macros</h2>
148<!-- ======================================================================= -->
149
150<p>Language extensions can be very useful, but only if you know you can depend
Chris Lattner04fe64f2011-03-21 16:25:11 +0000[diff] [blame]151on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]152function-like macros. This allows you to directly test for a feature in your
153code without having to resort to something like autoconf or fragile "compiler
154version checks".</p>
155
156<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]157<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]158<!-- ======================================================================= -->
159
160<p>This function-like macro takes a single identifier argument that is the name
161of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
162not. It can be used like this:</p>
163
164<blockquote>
165<pre>
166#ifndef __has_builtin // Optional of course.
167 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
168#endif
169
170...
171#if __has_builtin(__builtin_trap)
172 __builtin_trap();
173#else
174 abort();
175#endif
176...
177</pre>
178</blockquote>
179
180
181<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]182<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]183<!-- ======================================================================= -->
184
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]185<p>These function-like macros take a single identifier argument that is the
186name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
187is both supported by Clang and standardized in the current language standard
188or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
189<code>__has_extension</code> evaluates to 1 if the feature is supported by
190Clang in the current language (either as a language extension or a standard
191language feature) or 0 if not. They can be used like this:</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]192
193<blockquote>
194<pre>
195#ifndef __has_feature // Optional of course.
196 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
197#endif
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]198#ifndef __has_extension
199 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
200#endif
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]201
202...
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]203#if __has_feature(cxx_rvalue_references)
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]204// This code will only be compiled with the -std=c++11 and -std=gnu++11
205// options, because rvalue references are only standardized in C++11.
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]206#endif
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]207
208#if __has_extension(cxx_rvalue_references)
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]209// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]210// and -std=gnu++98 options, because rvalue references are supported as a
211// language extension in C++98.
212#endif
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]213</pre>
214</blockquote>
215
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]216<p id="has_feature_back_compat">For backwards compatibility reasons,
217<code>__has_feature</code> can also be used to test for support for
218non-standardized features, i.e. features not prefixed <code>c_</code>,
219<code>cxx_</code> or <code>objc_</code>.</p>
220
Kostya Serebryany9751d342011-11-28 20:51:02 +0000[diff] [blame]221<p id="has_feature_for_non_language_features">
222Another use of <code>__has_feature</code> is to check for compiler features
223not related to the language standard, such as e.g.
224<a href="AddressSanitizer.html">AddressSanitizer</a>.
225
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]226<p>If the <code>-pedantic-errors</code> option is given,
227<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
228
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]229<p>The feature tag is described along with the language feature below.</p>
230
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]231<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]232<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlsson274a70e2010-10-20 02:31:43 +0000[diff] [blame]233<!-- ======================================================================= -->
234
235<p>This function-like macro takes a single identifier argument that is the name
236of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
237can be used like this:</p>
238
239<blockquote>
240<pre>
241#ifndef __has_attribute // Optional of course.
242 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
243#endif
244
245...
Anders Carlsson3bbfb7f2011-01-24 03:54:51 +0000[diff] [blame]246#if __has_attribute(always_inline)
247#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlsson274a70e2010-10-20 02:31:43 +0000[diff] [blame]248#else
Anders Carlsson3bbfb7f2011-01-24 03:54:51 +0000[diff] [blame]249#define ALWAYS_INLINE
Anders Carlsson274a70e2010-10-20 02:31:43 +0000[diff] [blame]250#endif
251...
252</pre>
253</blockquote>
254
255<!-- ======================================================================= -->
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]256<h2 id="has_include">Include File Checking Macros</h2>
257<!-- ======================================================================= -->
258
259<p>Not all developments systems have the same include files.
260The <a href="#__has_include">__has_include</a> and
261<a href="#__has_include_next">__has_include_next</a> macros allow you to
262check for the existence of an include file before doing
263a possibly failing #include directive.</p>
264
265<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]266<h3><a name="__has_include">__has_include</a></h3>
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]267<!-- ======================================================================= -->
268
269<p>This function-like macro takes a single file name string argument that
270is the name of an include file. It evaluates to 1 if the file can
271be found using the include paths, or 0 otherwise:</p>
272
273<blockquote>
274<pre>
275// Note the two possible file name string formats.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]276#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]277# include "myinclude.h"
278#endif
279
280// To avoid problem with non-clang compilers not having this macro.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]281#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]282# include "myinclude.h"
283#endif
284</pre>
285</blockquote>
286
287<p>To test for this feature, use #if defined(__has_include).</p>
288
289<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]290<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]291<!-- ======================================================================= -->
292
293<p>This function-like macro takes a single file name string argument that
294is the name of an include file. It is like __has_include except that it
295looks for the second instance of the given file found in the include
296paths. It evaluates to 1 if the second instance of the file can
297be found using the include paths, or 0 otherwise:</p>
298
299<blockquote>
300<pre>
301// Note the two possible file name string formats.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]302#if __has_include_next("myinclude.h") &amp;&amp; __has_include_next(&lt;stdint.h&gt;)
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]303# include_next "myinclude.h"
304#endif
305
306// To avoid problem with non-clang compilers not having this macro.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]307#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]308# include_next "myinclude.h"
309#endif
310</pre>
311</blockquote>
312
313<p>Note that __has_include_next, like the GNU extension
314#include_next directive, is intended for use in headers only,
315and will issue a warning if used in the top-level compilation
316file. A warning will also be issued if an absolute path
317is used in the file argument.</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]318
Ted Kremeneka35d67d2011-10-12 19:46:30 +0000[diff] [blame]319
320<!-- ======================================================================= -->
321<h3><a name="__has_warning">__has_warning</a></h3>
322<!-- ======================================================================= -->
323
324<p>This function-like macro takes a string literal that represents a command
325 line option for a warning and returns true if that is a valid warning
326 option.</p>
327
328<blockquote>
329<pre>
330#if __has_warning("-Wformat")
331...
332#endif
333</pre>
334</blockquote>
335
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]336<!-- ======================================================================= -->
Chris Lattner7de64562009-04-13 02:45:46 +0000[diff] [blame]337<h2 id="builtinmacros">Builtin Macros</h2>
338<!-- ======================================================================= -->
339
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]340<dl>
341 <dt><code>__BASE_FILE__</code></dt>
342 <dd>Defined to a string that contains the name of the main input
343 file passed to Clang.</dd>
344
345 <dt><code>__COUNTER__</code></dt>
346 <dd>Defined to an integer value that starts at zero and is
347 incremented each time the <code>__COUNTER__</code> macro is
348 expanded.</dd>
349
350 <dt><code>__INCLUDE_LEVEL__</code></dt>
351 <dd>Defined to an integral value that is the include depth of the
352 file currently being translated. For the main file, this value is
353 zero.</dd>
354
355 <dt><code>__TIMESTAMP__</code></dt>
356 <dd>Defined to the date and time of the last modification of the
357 current source file.</dd>
358
359 <dt><code>__clang__</code></dt>
360 <dd>Defined when compiling with Clang</dd>
361
362 <dt><code>__clang_major__</code></dt>
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]363 <dd>Defined to the major marketing version number of Clang (e.g., the
364 2 in 2.0.1). Note that marketing version numbers should not be used to
365 check for language features, as different vendors use different numbering
366 schemes. Instead, use the <a href="#feature_check">feature checking
367 macros</a>.</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]368
369 <dt><code>__clang_minor__</code></dt>
370 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]371 2.0.1). Note that marketing version numbers should not be used to
372 check for language features, as different vendors use different numbering
373 schemes. Instead, use the <a href="#feature_check">feature checking
374 macros</a>.</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]375
376 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]377 <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]378
379 <dt><code>__clang_version__</code></dt>
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]380 <dd>Defined to a string that captures the Clang marketing version, including
381 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]382</dl>
Chris Lattner7de64562009-04-13 02:45:46 +0000[diff] [blame]383
384<!-- ======================================================================= -->
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]385<h2 id="vectors">Vectors and Extended Vectors</h2>
386<!-- ======================================================================= -->
387
Anton Yartseve8985672012-01-15 16:22:24 +0000[diff] [blame]388<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]389
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]390<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
391support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An
392example is:</p>
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]393
394<blockquote>
395<pre>
396typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
397typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
398
399float4 foo(float2 a, float2 b) {
400 float4 c;
401 c.xz = a;
402 c.yw = b;
403 return c;
404}
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]405</pre>
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]406</blockquote>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]407
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]408<p>Query for this feature with
409<tt>__has_extension(attribute_ext_vector_type)</tt>.</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]410
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]411<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector
412syntax and functions. For example:</p>
Anton Yartseve8985672012-01-15 16:22:24 +0000[diff] [blame]413
414<blockquote>
415<pre>
416vector float foo(vector int a) {
417 vector int b;
418 b = vec_add(a, a) + a;
419 return (vector float)b;
420}
421</pre>
422</blockquote>
423
424<p>NEON vector types are created using <tt>neon_vector_type</tt> and
425<tt>neon_polyvector_type</tt> attributes. For example:</p>
426
427<blockquote>
428<pre>
429typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
430typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
431
432int8x8_t foo(int8x8_t a) {
433 int8x8_t v;
434 v = a;
435 return v;
436}
437</pre>
438</blockquote>
439
440<!-- ======================================================================= -->
441<h3><a name="vector_literals">Vector Literals</a></h3>
442<!-- ======================================================================= -->
443
444<p>Vector literals can be used to create vectors from a set of scalars, or
445vectors. Either parentheses or braces form can be used. In the parentheses form
446the number of literal values specified must be one, i.e. referring to a scalar
447value, or must match the size of the vector type being created. If a single
448scalar literal value is specified, the scalar literal value will be replicated
449to all the components of the vector type. In the brackets form any number of
450literals can be specified. For example:</p>
451
452<blockquote>
453<pre>
454typedef int v4si __attribute__((__vector_size__(16)));
455typedef float float4 __attribute__((ext_vector_type(4)));
456typedef float float2 __attribute__((ext_vector_type(2)));
457
458v4si vsi = (v4si){1, 2, 3, 4};
459float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
460vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
461vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
462vector int vi3 = (vector int)(1, 2); // error
463vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
464vector int vi5 = (vector int)(1, 2, 3, 4);
465float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
466</pre>
467</blockquote>
468
469<!-- ======================================================================= -->
470<h3><a name="vector_operations">Vector Operations</a></h3>
471<!-- ======================================================================= -->
472
473<p>The table below shows the support for each operation by vector extension.
474A dash indicates that an operation is not accepted according to a corresponding
475specification.</p>
476
477<table width="500" border="1" cellspacing="0">
478 <tr>
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]479 <th>Operator</th>
480 <th>OpenCL</th>
481 <th>AltiVec</th>
482 <th>GCC</th>
483 <th>NEON</th>
Anton Yartseve8985672012-01-15 16:22:24 +0000[diff] [blame]484 </tr>
485 <tr>
486 <td>[]</td>
487 <td align="center">yes</td>
488 <td align="center">yes</td>
489 <td align="center">yes</td>
490 <td align="center">-</td>
491 </tr>
492 <tr>
493 <td>unary operators +, -</td>
494 <td align="center">yes</td>
495 <td align="center">yes</td>
496 <td align="center">yes</td>
497 <td align="center">-</td>
498 </tr>
499 <tr>
500 <td>++, --</td>
501 <td align="center">yes</td>
502 <td align="center">yes</td>
503 <td align="center">-</td>
504 <td align="center">-</td>
505 </tr>
506 <tr>
507 <td>+, -, *, /, %</td>
508 <td align="center">yes</td>
509 <td align="center">yes</td>
510 <td align="center">yes</td>
511 <td align="center">-</td>
512 </tr>
513 <tr>
514 <td>bitwise operators &, |, ^, ~</td>
515 <td align="center">yes</td>
516 <td align="center">yes</td>
517 <td align="center">yes</td>
518 <td align="center">-</td>
519 </tr>
520 <tr>
521 <td>&gt&gt, &lt&lt</td>
522 <td align="center">yes</td>
523 <td align="center">yes</td>
524 <td align="center">yes</td>
525 <td align="center">-</td>
526 </tr>
527 <tr>
528 <td>!, &&,||</td>
529 <td align="center">no</td>
530 <td align="center">-</td>
531 <td align="center">-</td>
532 <td align="center">-</td>
533 </tr>
534 <tr>
535 <td>==,!=, >, <, >=, <=</td>
536 <td align="center">yes</td>
537 <td align="center">yes</td>
538 <td align="center">-</td>
539 <td align="center">-</td>
540 </tr>
541 <tr>
542 <td>=</td>
543 <td align="center">yes</td>
544 <td align="center">yes</td>
545 <td align="center">yes</td>
546 <td align="center">yes</td>
547 </tr>
548 <tr>
549 <td>:?</td>
550 <td align="center">yes</td>
551 <td align="center">-</td>
552 <td align="center">-</td>
553 <td align="center">-</td>
554 </tr>
555 <tr>
556 <td>sizeof</td>
557 <td align="center">yes</td>
558 <td align="center">yes</td>
559 <td align="center">yes</td>
560 <td align="center">yes</td>
561 </tr>
562</table>
563
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]564<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
565
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]566<!-- ======================================================================= -->
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]567<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc74073c2010-10-06 23:12:32 +0000[diff] [blame]568<!-- ======================================================================= -->
569
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]570<p>An optional string message can be added to the <tt>deprecated</tt>
571and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc74073c2010-10-06 23:12:32 +0000[diff] [blame]572
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]573<blockquote>
Chris Lattnere56c7862010-11-09 19:43:35 +0000[diff] [blame]574<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]575</blockquote>
576
577<p>If the deprecated or unavailable declaration is used, the message
578will be incorporated into the appropriate diagnostic:</p>
579
580<blockquote>
Chris Lattnere56c7862010-11-09 19:43:35 +0000[diff] [blame]581<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! [-Wdeprecated-declarations]
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]582 explode();
583 ^</pre>
584</blockquote>
585
586<p>Query for this feature
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]587with <tt>__has_extension(attribute_deprecated_with_message)</tt>
588and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]589
590<!-- ======================================================================= -->
591<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
592<!-- ======================================================================= -->
593
594<p>Clang allows attributes to be written on individual enumerators.
595This allows enumerators to be deprecated, made unavailable, etc. The
596attribute must appear after the enumerator name and before any
597initializer, like so:</p>
598
599<blockquote>
600<pre>enum OperationMode {
601 OM_Invalid,
602 OM_Normal,
603 OM_Terrified __attribute__((deprecated)),
604 OM_AbortOnError __attribute__((deprecated)) = 4
605};</pre>
606</blockquote>
607
608<p>Attributes on the <tt>enum</tt> declaration do not apply to
609individual enumerators.</p>
610
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]611<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc74073c2010-10-06 23:12:32 +0000[diff] [blame]612
613<!-- ======================================================================= -->
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]614<h2 id="checking_language_features">Checks for Standard Language Features</h2>
615<!-- ======================================================================= -->
616
617<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
618enabled. Those features are listed here.</p>
619
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]620<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]621
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]622<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For
Alexis Huntc0a2ab62011-06-23 00:42:53 +0000[diff] [blame]623example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]624
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]625<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]626
Ted Kremenek72de23e2009-12-03 02:06:43 +0000[diff] [blame]627<p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example,
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]628compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]629
630<!-- ======================================================================= -->
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]631<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
632<!-- ======================================================================= -->
633
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]634<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
635to query if certain upcoming standard language features are enabled. Those
636features are listed here. Features that are not yet implemented will be
637noted.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]638
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]639<h3 id="cxx0x">C++11</h3>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]640
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]641<p>The features listed below are slated for inclusion in the upcoming
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]642C++11 standard. As a result, all these features are enabled
643with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]644
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]645<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor347d6262011-05-11 23:45:11 +0000[diff] [blame]646
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]647<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 Gregor347d6262011-05-11 23:45:11 +0000[diff] [blame]648
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]649<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3f1b5d02011-05-05 21:57:07 +0000[diff] [blame]650
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]651<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
652<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]653C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3f1b5d02011-05-05 21:57:07 +0000[diff] [blame]654
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]655<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbourne60188eb2011-10-14 23:44:46 +0000[diff] [blame]656
657<p>Use <tt>__has_feature(cxx_alignas)</tt> or
658<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
659specifiers using <tt>alignas</tt> is enabled.</p>
660
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]661<h4 id="cxx_attributes">C++11 attributes</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]662
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]663<p>Use <tt>__has_feature(cxx_attributes)</tt> or
664<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]665parsing with C++11's square bracket notation is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]666
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]667<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]668
669<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
670for generalized constant expressions (e.g., <tt>constexpr</tt>) is
Richard Smith1cb2af02012-02-14 22:56:17 +0000[diff] [blame]671enabled.</p>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]672
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]673<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]674
675<p>Use <tt>__has_feature(cxx_decltype)</tt> or
676<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
677<tt>decltype()</tt> specifier is enabled.</p>
678
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]679<h4 id="cxx_default_function_template_args">C++11 default template arguments in function templates</h4>
Douglas Gregor7115aee2011-02-05 20:35:30 +0000[diff] [blame]680
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]681<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
682<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
683if support for default template arguments in function templates is enabled.</p>
Douglas Gregor7115aee2011-02-05 20:35:30 +0000[diff] [blame]684
Douglas Gregor3c469762011-11-01 01:19:34 +0000[diff] [blame]685<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
686
687<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
688<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
689defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
690
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]691<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Alexis Huntb0d81992011-06-23 06:11:37 +0000[diff] [blame]692
693<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
694support for delegating constructors is enabled.</p>
695
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]696<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]697
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]698<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
699<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redla93bb5b2010-08-31 23:28:47 +0000[diff] [blame]700deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]701
Benjamin Kramereaa262b2012-01-15 15:26:07 +0000[diff] [blame]702<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]703<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
704
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]705<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Alexis Hunt7d1492a2011-08-07 00:34:32 +0000[diff] [blame]706
707<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
708support for generalized initializers (using braced lists and
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]709<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
710this feature.</p>
711
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]712<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]713
Sebastian Redl6ce53ae2011-10-10 18:10:00 +0000[diff] [blame]714<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
715implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]716
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]717<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]718
719<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>
720
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]721<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]722
723<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
724<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
725inline namespaces is enabled.</p>
Alexis Hunt7d1492a2011-08-07 00:34:32 +0000[diff] [blame]726
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]727<h4 id="cxx_lambdas">C++11 lambdas</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]728
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]729<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
730<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]731is enabled. Clang does not currently implement this feature.</p>
732
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]733<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]734
735<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
736<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
737exception specifications is enabled.</p>
738
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]739<h4 id="cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]740
741<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]742
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]743<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]744
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]745<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
746<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor80af3132011-05-21 23:15:46 +0000[diff] [blame]747<tt>nullptr</tt> is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]748
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]749<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlsson69f1f932011-03-25 15:04:23 +0000[diff] [blame]750
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]751<p>Use <tt>__has_feature(cxx_override_control)</tt> or
752<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlsson69f1f932011-03-25 15:04:23 +0000[diff] [blame]753the override control keywords is enabled.</p>
754
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]755<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]756<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
757<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
758if support for reference-qualified functions (e.g., member functions with
759<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
760is enabled.</p>
Douglas Gregor56d5f0a2011-01-26 21:25:54 +0000[diff] [blame]761
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]762<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smith9bc6eed2011-04-15 15:14:40 +0000[diff] [blame]763
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]764<p>Use <tt>__has_feature(cxx_range_for)</tt> or
765<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
766range-based for loop is enabled. </p>
Richard Smith9bc6eed2011-04-15 15:14:40 +0000[diff] [blame]767
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]768<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]769<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>
770
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]771<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]772
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]773<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
774<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56d5f0a2011-01-26 21:25:54 +0000[diff] [blame]775rvalue references is enabled. </p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]776
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]777<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]778
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]779<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
780<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]781compile-time assertions using <tt>static_assert</tt> is enabled.</p>
782
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]783<h4 id="cxx_auto_type">C++11 type inference</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]784
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]785<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]786<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]787supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
788will instead be a storage class specifier, as in C or C++98.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]789
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]790<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]791
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]792<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
793<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
794strongly typed, scoped enumerations is enabled.</p>
Sebastian Redla93bb5b2010-08-31 23:28:47 +0000[diff] [blame]795
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]796<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregor7fb25412010-10-01 18:44:50 +0000[diff] [blame]797
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]798<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
799<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
800alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregor7fb25412010-10-01 18:44:50 +0000[diff] [blame]801
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]802<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]803<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
804support for Unicode string literals is enabled.</p>
Sebastian Redlc17003c2011-03-15 21:17:12 +0000[diff] [blame]805
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]806<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redlc17003c2011-03-15 21:17:12 +0000[diff] [blame]807
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]808<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 Gregor0bf31402010-10-08 23:50:27 +0000[diff] [blame]809
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]810<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]811
812<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>
813
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]814<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]815
816<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
817<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
818for variadic templates is enabled.</p>
Douglas Gregor0bf31402010-10-08 23:50:27 +0000[diff] [blame]819
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]820<h3 id="c11">C11</h3>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]821
822<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]823C11 standard. As a result, all these features are enabled
824with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]825
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]826<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbourne60188eb2011-10-14 23:44:46 +0000[diff] [blame]827
828<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
829to determine if support for alignment specifiers using <tt>_Alignas</tt>
830is enabled.</p>
831
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]832<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]833
834<p>Use <tt>__has_feature(c_generic_selections)</tt> or
835<tt>__has_extension(c_generic_selections)</tt> to determine if support for
836generic selections is enabled.</p>
837
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]838<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]839languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]840C11 standard.</p>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]841
842<p>In C, type compatibility is decided according to the rules given in the
843appropriate standard, but in C++, which lacks the type compatibility rules
844used in C, types are considered compatible only if they are equivalent.</p>
845
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]846<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]847
848<p>Use <tt>__has_feature(c_static_assert)</tt> or
849<tt>__has_extension(c_static_assert)</tt> to determine if support for
850compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
851
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]852<!-- ======================================================================= -->
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]853<h2 id="checking_type_traits">Checks for Type Traits</h2>
854<!-- ======================================================================= -->
855
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]856<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 Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]857<blockquote>
858<pre>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]859#if __has_extension(is_convertible_to)
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]860template&lt;typename From, typename To&gt;
861struct is_convertible_to {
862 static const bool value = __is_convertible_to(From, To);
863};
864#else
865// Emulate type trait
866#endif
867</pre>
868</blockquote>
869
870<p>The following type traits are supported by Clang:</p>
871<ul>
872 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
873 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
874 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
875 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
876 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
877 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
878 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
879 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
880 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
881 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
882 <li><code>__is_class</code> (GNU, Microsoft)</li>
883 <li><code>__is_convertible_to</code> (Microsoft)</li>
884 <li><code>__is_empty</code> (GNU, Microsoft)</li>
885 <li><code>__is_enum</code> (GNU, Microsoft)</li>
886 <li><code>__is_pod</code> (GNU, Microsoft)</li>
887 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
888 <li><code>__is_union</code> (GNU, Microsoft)</li>
889 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
Douglas Gregordca70af2011-12-03 18:14:24 +0000[diff] [blame]890 <li><code>__is_final</code>: Determines whether the given type is declared with a <code>final</code> class-virt-specifier.</li>
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]891 <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 Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]892</ul>
893
894<!-- ======================================================================= -->
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]895<h2 id="blocks">Blocks</h2>
896<!-- ======================================================================= -->
897
Chris Lattner14aea9a2009-03-09 07:03:22 +0000[diff] [blame]898<p>The syntax and high level language feature description is in <a
899href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
900details for the clang implementation are in <a
Chris Lattner87c5e2f2010-03-16 21:43:03 +0000[diff] [blame]901href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]902
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]903
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]904<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]905
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]906<!-- ======================================================================= -->
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]907<h2 id="objc_features">Objective-C Features</h2>
908<!-- ======================================================================= -->
909
910<h3 id="objc_instancetype">Related result types</h3>
911
912<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>
913
914<blockquote>
915<pre>
916@interface NSObject
917+ (id)alloc;
918- (id)init;
919@end
920
921@interface NSArray : NSObject
922@end
923</pre>
924</blockquote>
925
926<p>and this common initialization pattern</p>
927
928<blockquote>
929<pre>
930NSArray *array = [[NSArray alloc] init];
931</pre>
932</blockquote>
933
934<p>the type of the expression <code>[NSArray alloc]</code> is
935<code>NSArray*</code> because <code>alloc</code> implicitly has a
936related result type. Similarly, the type of the expression
937<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
938<code>init</code> has a related result type and its receiver is known
939to 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>
940
Douglas Gregorbab8a962011-09-08 01:46:34 +0000[diff] [blame]941<p>A method with a related result type can be declared by using the
942type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
943is a contextual keyword that is only permitted in the result type of
944an Objective-C method, e.g.</p>
945
946<pre>
947@interface A
948+ (<b>instancetype</b>)constructAnA;
949@end
950</pre>
951
952<p>The related result type can also be inferred for some methods.
953To determine whether a method has an inferred related result type, the first
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]954word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregorf8b02ca2011-11-03 18:33:01 +0000[diff] [blame]955considered, and the method will have a related result type if its return
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]956type is compatible with the type of its class and if</p>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]957
958<ul>
959
960 <li>the first word is "alloc" or "new", and the method is a class
961 method, or</li>
962
963 <li>the first word is "autorelease", "init", "retain", or "self",
964 and the method is an instance method.</li>
965
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]966</ul>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]967
968<p>If a method with a related result type is overridden by a subclass
969method, the subclass method must also return a type that is compatible
970with the subclass type. For example:</p>
971
972<blockquote>
973<pre>
974@interface NSString : NSObject
975- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
976@end
977</pre>
978</blockquote>
979
980<p>Related result types only affect the type of a message send or
981property access via the given method. In all other respects, a method
Douglas Gregorbab8a962011-09-08 01:46:34 +0000[diff] [blame]982with a related result type is treated the same way as method that
983returns <tt>id</tt>.</p>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]984
Douglas Gregordc28ba12011-09-08 17:19:31 +0000[diff] [blame]985<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
986the <tt>instancetype</tt> contextual keyword is available.</p>
987
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]988<!-- ======================================================================= -->
John McCall31168b02011-06-15 23:02:42 +0000[diff] [blame]989<h2 id="objc_arc">Automatic reference counting </h2>
990<!-- ======================================================================= -->
991
992<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>
993
994<!-- ======================================================================= -->
Douglas Gregor8b7d4032011-09-08 17:18:35 +0000[diff] [blame]995<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
996<!-- ======================================================================= -->
997
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]998<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor8b7d4032011-09-08 17:18:35 +0000[diff] [blame]999underlying type within Objective-C. For example, one can write an
1000enumeration type as:</p>
1001
1002<pre>
1003typedef enum : unsigned char { Red, Green, Blue } Color;
1004</pre>
1005
1006<p>This specifies that the underlying type, which is used to store the
1007enumeration value, is <tt>unsigned char</tt>.</p>
1008
1009<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1010support for fixed underlying types is available in Objective-C.</p>
1011
1012<!-- ======================================================================= -->
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1013<h2 id="overloading-in-c">Function Overloading in C</h2>
1014<!-- ======================================================================= -->
1015
Chris Lattnerb3ef5332009-02-13 21:51:45 +0000[diff] [blame]1016<p>Clang provides support for C++ function overloading in C. Function
1017overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1018example, one might provide several overloaded versions of a <tt>tgsin</tt>
1019function that invokes the appropriate standard function computing the sine of a
1020value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1021precision:</p>
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1022
1023<blockquote>
1024<pre>
1025#include &lt;math.h&gt;
1026float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1027double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1028long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1029</pre>
1030</blockquote>
1031
1032<p>Given these declarations, one can call <tt>tgsin</tt> with a
1033<tt>float</tt> value to receive a <tt>float</tt> result, with a
1034<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1035overloading in C follows the rules of C++ function overloading to pick
1036the best overload given the call arguments, with a few C-specific
1037semantics:</p>
1038<ul>
1039 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1040 double</tt> is ranked as a floating-point promotion (per C99) rather
1041 than as a floating-point conversion (as in C++).</li>
1042
1043 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1044 <tt>U*</tt> is considered a pointer conversion (with conversion
1045 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1046
1047 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1048 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1049 conversion is given "conversion" rank.</li>
1050</ul>
1051
1052<p>The declaration of <tt>overloadable</tt> functions is restricted to
1053function declarations and definitions. Most importantly, if any
1054function with a given name is given the <tt>overloadable</tt>
1055attribute, then all function declarations and definitions with that
1056name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerb3ef5332009-02-13 21:51:45 +0000[diff] [blame]1057attribute. This rule even applies to redeclarations of functions whose original
1058declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1059
1060<blockquote>
1061<pre>
1062int f(int) __attribute__((overloadable));
1063float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1064
1065int g(int) __attribute__((overloadable));
1066int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1067</pre>
1068</blockquote>
1069
Douglas Gregor94349fd2009-02-18 07:07:28 +0000[diff] [blame]1070<p>Functions marked <tt>overloadable</tt> must have
1071prototypes. Therefore, the following code is ill-formed:</p>
1072
1073<blockquote>
1074<pre>
1075int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1076</pre>
1077</blockquote>
1078
1079<p>However, <tt>overloadable</tt> functions are allowed to use a
1080ellipsis 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>
1081
1082<blockquote>
1083<pre>
Chris Lattnerfaca7d92009-02-18 22:27:46 +0000[diff] [blame]1084void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor94349fd2009-02-18 07:07:28 +0000[diff] [blame]1085</pre>
1086</blockquote>
1087
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1088<p>Functions declared with the <tt>overloadable</tt> attribute have
1089their names mangled according to the same rules as C++ function
1090names. For example, the three <tt>tgsin</tt> functions in our
1091motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner19e0fd02010-11-28 18:19:13 +0000[diff] [blame]1092<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1093caveats to this use of name mangling:</p>
1094
1095<ul>
1096
1097 <li>Future versions of Clang may change the name mangling of
1098 functions overloaded in C, so you should not depend on an specific
1099 mangling. To be completely safe, we strongly urge the use of
1100 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1101
1102 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1103 used in C++, because names will already be mangled and functions are
1104 already overloadable. However, when an <tt>overloadable</tt>
1105 function occurs within an <tt>extern "C"</tt> linkage specification,
1106 it's name <i>will</i> be mangled in the same way as it would in
1107 C.</li>
1108</ul>
1109
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]1110<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1111
Eli Friedman6b9c41e2011-09-19 23:17:44 +0000[diff] [blame]1112<!-- ======================================================================= -->
1113<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1114<!-- ======================================================================= -->
1115
1116<p>clang supports an extension which allows the following in C:</p>
1117
1118<blockquote>
1119<pre>
1120#include &lt;math.h&gt;
1121#include &lt;complex.h&gt;
1122complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1123</pre>
1124</blockquote>
1125
1126<p>This construct is useful because there is no way to separately
1127initialize the real and imaginary parts of a complex variable in
1128standard C, given that clang does not support <code>_Imaginary</code>.
1129(clang also supports the <code>__real__</code> and <code>__imag__</code>
1130extensions from gcc, which help in some cases, but are not usable in
1131static initializers.)
1132
1133<p>Note that this extension does not allow eliding the braces; the
1134meaning of the following two lines is different:</p>
1135
1136<blockquote>
1137<pre>
1138complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1139complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1140</pre>
1141</blockquote>
1142
1143<p>This extension also works in C++ mode, as far as that goes, but does not
1144 apply to the C++ <code>std::complex</code>. (In C++11, list
1145 initialization allows the same syntax to be used with
1146 <code>std::complex</code> with the same meaning.)
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1147
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1148<!-- ======================================================================= -->
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1149<h2 id="builtins">Builtin Functions</h2>
1150<!-- ======================================================================= -->
1151
1152<p>Clang supports a number of builtin library functions with the same syntax as
1153GCC, including things like <tt>__builtin_nan</tt>,
1154<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1155<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1156addition to the GCC builtins, Clang supports a number of builtins that GCC does
1157not, which are listed here.</p>
1158
1159<p>Please note that Clang does not and will not support all of the GCC builtins
1160for vector operations. Instead of using builtins, you should use the functions
1161defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1162define portable wrappers for these. Many of the Clang versions of these
1163functions are implemented directly in terms of <a href="#vectors">extended
1164vector support</a> instead of builtins, in order to reduce the number of
1165builtins that we need to implement.</p>
1166
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1167<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1168<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1169<!-- ======================================================================= -->
1170
Chris Lattnerc15c2522009-09-16 18:56:12 +0000[diff] [blame]1171<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1172permutation/shuffle/swizzle operations. This builtin is also very important for
1173the implementation of various target-specific header files like
1174<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1175</p>
1176
1177<p><b>Syntax:</b></p>
1178
1179<pre>
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1180__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1181</pre>
1182
1183<p><b>Examples:</b></p>
1184
1185<pre>
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1186 // Identity operation - return 4-element vector V1.
1187 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1188
1189 // "Splat" element 0 of V1 into a 4-element result.
1190 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1191
1192 // Reverse 4-element vector V1.
1193 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1194
1195 // Concatenate every other element of 4-element vectors V1 and V2.
1196 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1197
1198 // Concatenate every other element of 8-element vectors V1 and V2.
1199 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1200</pre>
1201
1202<p><b>Description:</b></p>
1203
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1204<p>The first two arguments to __builtin_shufflevector are vectors that have the
1205same element type. The remaining arguments are a list of integers that specify
1206the elements indices of the first two vectors that should be extracted and
1207returned in a new vector. These element indices are numbered sequentially
1208starting with the first vector, continuing into the second vector. Thus, if
1209vec1 is a 4-element vector, index 5 would refer to the second element of vec2.
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1210</p>
1211
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1212<p>The result of __builtin_shufflevector is a vector
1213with the same element type as vec1/vec2 but that has an element count equal to
1214the number of indices specified.
1215</p>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1216
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]1217<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1218
1219<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1220<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]1221<!-- ======================================================================= -->
1222
1223<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1224the program cannot be reached, even if the compiler might otherwise think it
1225can. This is useful to improve optimization and eliminates certain warnings.
1226For example, without the <tt>__builtin_unreachable</tt> in the example below,
1227the compiler assumes that the inline asm can fall through and prints a "function
1228declared 'noreturn' should not return" warning.
1229</p>
1230
1231<p><b>Syntax:</b></p>
1232
1233<pre>
1234__builtin_unreachable()
1235</pre>
1236
1237<p><b>Example of Use:</b></p>
1238
1239<pre>
1240void myabort(void) __attribute__((noreturn));
1241void myabort(void) {
1242 asm("int3");
1243 __builtin_unreachable();
1244}
1245</pre>
1246
1247<p><b>Description:</b></p>
1248
1249<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1250it has undefined behavior, it is a statement that it is never reached and the
1251optimizer can take advantage of this to produce better code. This builtin takes
1252no arguments and produces a void result.
1253</p>
1254
1255<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1256
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]1257<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1258<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]1259<!-- ======================================================================= -->
1260
1261<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1262memory.
1263</p>
1264
1265<p><b>Syntax:</b></p>
1266
1267<pre>
1268<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1269</pre>
1270
1271<p><b>Example of Use:</b></p>
1272
1273<pre>
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1274int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]1275</pre>
1276
1277<p><b>Description:</b></p>
1278
1279<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1280intrinsics to allow code to atomically swap the current value with the new
1281value. More importantly, it helps developers write more efficient and correct
1282code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1283relying on the platform specific implementation details of
1284__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1285</p>
1286
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]1287
Chris Lattnerc86ffc32009-04-09 19:58:15 +0000[diff] [blame]1288<!-- ======================================================================= -->
1289<h2 id="targetspecific">Target-Specific Extensions</h2>
1290<!-- ======================================================================= -->
1291
1292<p>Clang supports some language features conditionally on some targets.</p>
1293
1294<!-- ======================================================================= -->
1295<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1296<!-- ======================================================================= -->
1297
1298<p>The X86 backend has these language extensions:</p>
1299
1300<!-- ======================================================================= -->
1301<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1302<!-- ======================================================================= -->
1303
1304<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnerb7323972009-05-05 18:54:47 +0000[diff] [blame]1305relative to the X86 GS segment register, and address space #257 causes it to be
1306relative to the X86 FS segment. Note that this is a very very low-level
1307feature that should only be used if you know what you're doing (for example in
1308an OS kernel).</p>
Chris Lattnerc86ffc32009-04-09 19:58:15 +0000[diff] [blame]1309
1310<p>Here is an example:</p>
1311
1312<pre>
1313#define GS_RELATIVE __attribute__((address_space(256)))
1314int foo(int GS_RELATIVE *P) {
1315 return *P;
1316}
1317</pre>
1318
1319<p>Which compiles to (on X86-32):</p>
1320
1321<pre>
1322_foo:
1323 movl 4(%esp), %eax
1324 movl %gs:(%eax), %eax
1325 ret
1326</pre>
1327
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1328<!-- ======================================================================= -->
1329<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1330<!-- ======================================================================= -->
1331
1332<p>Clang supports additional attributes that are useful for documenting program
1333invariants and rules for static analysis tools. The extensions documented here
1334are used by the <a
1335href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1336engine</a> that is part of Clang's Analysis library.</p>
1337
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1338<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1339
1340<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek86ee0592009-04-10 05:04:22 +0000[diff] [blame]1341attribute. This attribute, which is typically affixed to a function prototype,
1342indicates that a call to a given function never returns. Function prototypes for
1343common functions like <tt>exit</tt> are typically annotated with this attribute,
1344as well as a variety of common assertion handlers. Users can educate the static
1345analyzer about their own custom assertion handles (thus cutting down on false
1346positives due to false paths) by marking their own &quot;panic&quot; functions
1347with this attribute.</p>
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1348
1349<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewyckybe42c112009-06-14 04:08:08 +0000[diff] [blame]1350there are special functions that for all intents and purposes should be
1351considered panic functions (i.e., they are only called when an internal program
1352error occurs) but may actually return so that the program can fail gracefully.
1353The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1354as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattnerbb72f772009-04-10 05:54:56 +0000[diff] [blame]1355pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1356<tt>noreturn</tt>).</p>
1357
1358<p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the
Chris Lattnerbb72f772009-04-10 05:54:56 +0000[diff] [blame]1359same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1360placed at the end of function prototypes:</p>
1361
1362<pre>
1363 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1364</pre>
1365
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1366<p>Query for this feature with
1367<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1368
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1369<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1370
1371<p>Many methods in Objective-C have conventional meanings determined
1372by their selectors. For the purposes of static analysis, it is
1373sometimes useful to be able to mark a method as having a particular
1374conventional meaning despite not having the right selector, or as not
1375having the conventional meaning that its selector would suggest.
1376For these use cases, we provide an attribute to specifically describe
1377the <q>method family</q> that a method belongs to.</p>
1378
1379<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1380where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1381<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1382can only be placed at the end of a method declaration:</p>
1383
1384<pre>
1385 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1386</pre>
1387
1388<p>Users who do not wish to change the conventional meaning of a
1389method, and who merely want to document its non-standard retain and
1390release semantics, should use the
1391<a href="#attr_retain_release">retaining behavior attributes</a>
1392described below.</p>
1393
1394<p>Query for this feature with
1395<tt>__has_attribute(objc_method_family)</tt>.</p>
1396
1397<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall46669c02011-01-25 04:26:21 +0000[diff] [blame]1398
1399<p>In Objective-C, functions and methods are generally assumed to take
1400and return objects with +0 retain counts, with some exceptions for
1401special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1402there are exceptions, and so Clang provides attributes to allow these
1403exceptions to be documented, which helps the analyzer find leaks (and
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1404ignore non-leaks). Some exceptions may be better described using
1405the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1406attribute instead.</p>
John McCall46669c02011-01-25 04:26:21 +0000[diff] [blame]1407
1408<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1409<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1410and <tt>cf_returns_not_retained</tt> attributes can be placed on
1411methods and functions that return Objective-C or CoreFoundation
1412objects. They are commonly placed at the end of a function prototype
1413or method declaration:</p>
1414
1415<pre>
1416 id foo() <b>__attribute__((ns_returns_retained))</b>;
1417
1418 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1419</pre>
1420
1421<p>The <tt>*_returns_retained</tt> attributes specify that the
1422returned object has a +1 retain count.
1423The <tt>*_returns_not_retained</tt> attributes specify that the return
1424object has a +0 retain count, even if the normal convention for its
1425selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1426returned object is +0, but is guaranteed to live at least as long as the
1427next flush of an autorelease pool.</p>
1428
1429<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1430attributes can be placed on an parameter declaration; they specify
1431that the argument is expected to have a +1 retain count, which will be
1432balanced in some way by the function or method.
1433The <tt>ns_consumes_self</tt> attribute can only be placed on an
1434Objective-C method; it specifies that the method expects
1435its <tt>self</tt> parameter to have a +1 retain count, which it will
1436balance in some way.</p>
1437
1438<pre>
1439 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1440
1441 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1442 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1443</pre>
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1444
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1445<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1446<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1447
Kostya Serebryany9751d342011-11-28 20:51:02 +0000[diff] [blame]1448<!-- ======================================================================= -->
1449<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1450<!-- ======================================================================= -->
1451<h3 id="address_sanitizer">AddressSanitizer</h3>
1452<p> Use <code>__has_feature(address_sanitizer)</code>
1453to check if the code is being built with <a
1454 href="AddressSanitizer.html">AddressSanitizer</a>.
1455</p>
Kostya Serebryany588d6ab2012-01-24 19:25:38 +0000[diff] [blame]1456<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function
1457declaration to specify that address safety instrumentation (e.g.
1458AddressSanitizer) should not be applied to that function.
1459</p>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1460
1461<!-- ======================================================================= -->
Caitlin Sadowski13d44442011-07-28 18:38:36 +0000[diff] [blame]1462<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1463<!-- ======================================================================= -->
1464
1465<p>Clang supports additional attributes for checking basic locking policies in
1466multithreaded programs.
1467Clang currently parses the following list of attributes, although
1468<b>the implementation for these annotations is currently in development.</b>
1469For more details, see the
1470<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1471</p>
1472
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1473<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1474
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1475<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1476declaration to specify that the thread safety analysis should not be run on that
1477function. This attribute provides an escape hatch (e.g. for situations when it
1478is difficult to annotate the locking policy). </p>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1479
1480<h4 id="ts_lockable">lockable</h4>
1481
1482<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1483that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1484used to check consistency.</p>
1485
1486<h4 id="ts_scopedlockable">scoped_lockable</h4>
1487
1488<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1489specify that it has a "scoped" lockable type. Objects of this type will acquire
1490the lock upon construction and release it upon going out of scope.
1491 This annotation is primarily used to check
1492consistency.</p>
1493
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1494<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1495
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1496<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1497specify that the variable must be accessed while holding some lock.</p>
1498
1499<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1500
1501<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1502specify that the pointer must be dereferenced while holding some lock.</p>
1503
1504<h4 id="ts_guardedby">guarded_by(l)</h4>
1505
1506<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1507specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1508
1509<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1510
1511<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1512specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1513
1514<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1515
1516<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1517of a lockable variable to specify that the lock must be acquired before all
1518attribute arguments. Arguments must be lockable type, and there must be at
1519least one argument.</p>
1520
1521<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1522
1523<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1524of a lockable variable to specify that the lock must be acquired after all
1525attribute arguments. Arguments must be lockable type, and there must be at
1526least one argument.</p>
1527
1528<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1529
1530<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1531declaration to specify that the function acquires all listed locks
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1532exclusively. This attribute takes zero or more arguments: either of lockable
1533type or integers indexing into function parameters of lockable type. If no
1534arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1535enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1536
1537<h4 id="ts_slf">shared_lock_function(...)</h4>
1538
1539<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1540declaration to specify that the function acquires all listed locks, although
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1541 the locks may be shared (e.g. read locks). This attribute takes zero or more
1542arguments: either of lockable type or integers indexing into function
1543parameters of lockable type. If no arguments are given, the acquired lock is
1544implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1545
1546<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1547
1548<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1549declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1550all listed locks exclusively. This attribute takes one or more arguments. The
1551first argument is an integer or boolean value specifying the return value of a
1552successful lock acquisition. The remaining arugments are either of lockable type
1553or integers indexing into function parameters of lockable type. If only one
1554argument is given, the acquired lock is implicitly <tt>this</tt> of the
1555enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1556
1557<h4 id="ts_stf">shared_trylock_function(...)</h4>
1558
1559<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1560declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1561all listed locks, although the locks may be shared (e.g. read locks). This
1562attribute takes one or more arguments. The first argument is an integer or
1563boolean value specifying the return value of a successful lock acquisition. The
1564remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1565function parameters of lockable type. If only one argument is given, the
1566acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1567
1568<h4 id="ts_uf">unlock_function(...)</h4>
1569
1570<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1571declaration to specify that the function release all listed locks. This
1572attribute takes zero or more arguments: either of lockable type or integers
1573indexing into function parameters of lockable type. If no arguments are given,
1574the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1575
1576<h4 id="ts_lr">lock_returned(l)</h4>
1577
1578<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1579declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1580must be of lockable type). This annotation is used to aid in resolving lock
1581expressions.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1582
1583<h4 id="ts_le">locks_excluded(...)</h4>
1584
1585<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1586to specify that the function must not be called with the listed locks. Arguments
1587must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1588
1589<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1590
1591<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1592declaration to specify that the function must be called while holding the listed
1593exclusive locks. Arguments must be lockable type, and there must be at
1594least one argument.</p>
1595
1596<h4 id="ts_slr">shared_locks_required(...)</h4>
1597
1598<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1599declaration to specify that the function must be called while holding the listed
1600shared locks. Arguments must be lockable type, and there must be at
1601least one argument.</p>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1602
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1603</div>
1604</body>
1605</html>