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19<!--#include virtual="../menu.html.incl"-->
20
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
Richard Smith2cca7b52012-02-25 10:41:10 +0000[diff] [blame]231<p>The feature name or extension name can also be specified with a preceding and
232following <code>__</code> (double underscore) to avoid interference from a macro
233with the same name. For instance, <code>__always_inline__</code> can be used
234instead of <code>always_inline</code>.</p>
235
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]236<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]237<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlsson274a70e2010-10-20 02:31:43 +0000[diff] [blame]238<!-- ======================================================================= -->
239
240<p>This function-like macro takes a single identifier argument that is the name
241of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
242can be used like this:</p>
243
244<blockquote>
245<pre>
246#ifndef __has_attribute // Optional of course.
247 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
248#endif
249
250...
Anders Carlsson3bbfb7f2011-01-24 03:54:51 +0000[diff] [blame]251#if __has_attribute(always_inline)
252#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlsson274a70e2010-10-20 02:31:43 +0000[diff] [blame]253#else
Anders Carlsson3bbfb7f2011-01-24 03:54:51 +0000[diff] [blame]254#define ALWAYS_INLINE
Anders Carlsson274a70e2010-10-20 02:31:43 +0000[diff] [blame]255#endif
256...
257</pre>
258</blockquote>
259
260<!-- ======================================================================= -->
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]261<h2 id="has_include">Include File Checking Macros</h2>
262<!-- ======================================================================= -->
263
264<p>Not all developments systems have the same include files.
265The <a href="#__has_include">__has_include</a> and
266<a href="#__has_include_next">__has_include_next</a> macros allow you to
267check for the existence of an include file before doing
268a possibly failing #include directive.</p>
269
270<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]271<h3><a name="__has_include">__has_include</a></h3>
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]272<!-- ======================================================================= -->
273
274<p>This function-like macro takes a single file name string argument that
275is the name of an include file. It evaluates to 1 if the file can
276be found using the include paths, or 0 otherwise:</p>
277
278<blockquote>
279<pre>
280// Note the two possible file name string formats.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]281#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]282# include "myinclude.h"
283#endif
284
285// To avoid problem with non-clang compilers not having this macro.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]286#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]287# include "myinclude.h"
288#endif
289</pre>
290</blockquote>
291
292<p>To test for this feature, use #if defined(__has_include).</p>
293
294<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]295<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]296<!-- ======================================================================= -->
297
298<p>This function-like macro takes a single file name string argument that
299is the name of an include file. It is like __has_include except that it
300looks for the second instance of the given file found in the include
301paths. It evaluates to 1 if the second instance of the file can
302be found using the include paths, or 0 otherwise:</p>
303
304<blockquote>
305<pre>
306// Note the two possible file name string formats.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]307#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]308# include_next "myinclude.h"
309#endif
310
311// To avoid problem with non-clang compilers not having this macro.
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]312#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompsonac0b0982009-11-02 22:28:12 +0000[diff] [blame]313# include_next "myinclude.h"
314#endif
315</pre>
316</blockquote>
317
318<p>Note that __has_include_next, like the GNU extension
319#include_next directive, is intended for use in headers only,
320and will issue a warning if used in the top-level compilation
321file. A warning will also be issued if an absolute path
322is used in the file argument.</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]323
Ted Kremeneka35d67d2011-10-12 19:46:30 +0000[diff] [blame]324
325<!-- ======================================================================= -->
326<h3><a name="__has_warning">__has_warning</a></h3>
327<!-- ======================================================================= -->
328
329<p>This function-like macro takes a string literal that represents a command
330 line option for a warning and returns true if that is a valid warning
331 option.</p>
332
333<blockquote>
334<pre>
335#if __has_warning("-Wformat")
336...
337#endif
338</pre>
339</blockquote>
340
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]341<!-- ======================================================================= -->
Chris Lattner7de64562009-04-13 02:45:46 +0000[diff] [blame]342<h2 id="builtinmacros">Builtin Macros</h2>
343<!-- ======================================================================= -->
344
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]345<dl>
346 <dt><code>__BASE_FILE__</code></dt>
347 <dd>Defined to a string that contains the name of the main input
348 file passed to Clang.</dd>
349
350 <dt><code>__COUNTER__</code></dt>
351 <dd>Defined to an integer value that starts at zero and is
352 incremented each time the <code>__COUNTER__</code> macro is
353 expanded.</dd>
354
355 <dt><code>__INCLUDE_LEVEL__</code></dt>
356 <dd>Defined to an integral value that is the include depth of the
357 file currently being translated. For the main file, this value is
358 zero.</dd>
359
360 <dt><code>__TIMESTAMP__</code></dt>
361 <dd>Defined to the date and time of the last modification of the
362 current source file.</dd>
363
364 <dt><code>__clang__</code></dt>
365 <dd>Defined when compiling with Clang</dd>
366
367 <dt><code>__clang_major__</code></dt>
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]368 <dd>Defined to the major marketing version number of Clang (e.g., the
369 2 in 2.0.1). Note that marketing version numbers should not be used to
370 check for language features, as different vendors use different numbering
371 schemes. Instead, use the <a href="#feature_check">feature checking
372 macros</a>.</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]373
374 <dt><code>__clang_minor__</code></dt>
375 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]376 2.0.1). Note that marketing version numbers should not be used to
377 check for language features, as different vendors use different numbering
378 schemes. Instead, use the <a href="#feature_check">feature checking
379 macros</a>.</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]380
381 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]382 <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]383
384 <dt><code>__clang_version__</code></dt>
Chris Lattneree9c24a2011-12-15 19:06:36 +0000[diff] [blame]385 <dd>Defined to a string that captures the Clang marketing version, including
386 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor6602c252010-04-30 02:51:06 +0000[diff] [blame]387</dl>
Chris Lattner7de64562009-04-13 02:45:46 +0000[diff] [blame]388
389<!-- ======================================================================= -->
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]390<h2 id="vectors">Vectors and Extended Vectors</h2>
391<!-- ======================================================================= -->
392
Anton Yartseve8985672012-01-15 16:22:24 +0000[diff] [blame]393<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]394
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]395<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
396support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An
397example is:</p>
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]398
399<blockquote>
400<pre>
401typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
402typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
403
404float4 foo(float2 a, float2 b) {
405 float4 c;
406 c.xz = a;
407 c.yw = b;
408 return c;
409}
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]410</pre>
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]411</blockquote>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]412
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]413<p>Query for this feature with
414<tt>__has_extension(attribute_ext_vector_type)</tt>.</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]415
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]416<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector
417syntax and functions. For example:</p>
Anton Yartseve8985672012-01-15 16:22:24 +0000[diff] [blame]418
419<blockquote>
420<pre>
421vector float foo(vector int a) {
422 vector int b;
423 b = vec_add(a, a) + a;
424 return (vector float)b;
425}
426</pre>
427</blockquote>
428
429<p>NEON vector types are created using <tt>neon_vector_type</tt> and
430<tt>neon_polyvector_type</tt> attributes. For example:</p>
431
432<blockquote>
433<pre>
434typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
435typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
436
437int8x8_t foo(int8x8_t a) {
438 int8x8_t v;
439 v = a;
440 return v;
441}
442</pre>
443</blockquote>
444
445<!-- ======================================================================= -->
446<h3><a name="vector_literals">Vector Literals</a></h3>
447<!-- ======================================================================= -->
448
449<p>Vector literals can be used to create vectors from a set of scalars, or
450vectors. Either parentheses or braces form can be used. In the parentheses form
451the number of literal values specified must be one, i.e. referring to a scalar
452value, or must match the size of the vector type being created. If a single
453scalar literal value is specified, the scalar literal value will be replicated
454to all the components of the vector type. In the brackets form any number of
455literals can be specified. For example:</p>
456
457<blockquote>
458<pre>
459typedef int v4si __attribute__((__vector_size__(16)));
460typedef float float4 __attribute__((ext_vector_type(4)));
461typedef float float2 __attribute__((ext_vector_type(2)));
462
463v4si vsi = (v4si){1, 2, 3, 4};
464float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
465vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
466vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
467vector int vi3 = (vector int)(1, 2); // error
468vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
469vector int vi5 = (vector int)(1, 2, 3, 4);
470float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
471</pre>
472</blockquote>
473
474<!-- ======================================================================= -->
475<h3><a name="vector_operations">Vector Operations</a></h3>
476<!-- ======================================================================= -->
477
478<p>The table below shows the support for each operation by vector extension.
479A dash indicates that an operation is not accepted according to a corresponding
480specification.</p>
481
482<table width="500" border="1" cellspacing="0">
483 <tr>
Benjamin Kramer83369b32012-01-15 16:42:14 +0000[diff] [blame]484 <th>Operator</th>
485 <th>OpenCL</th>
486 <th>AltiVec</th>
487 <th>GCC</th>
488 <th>NEON</th>
Anton Yartseve8985672012-01-15 16:22:24 +0000[diff] [blame]489 </tr>
490 <tr>
491 <td>[]</td>
492 <td align="center">yes</td>
493 <td align="center">yes</td>
494 <td align="center">yes</td>
495 <td align="center">-</td>
496 </tr>
497 <tr>
498 <td>unary operators +, -</td>
499 <td align="center">yes</td>
500 <td align="center">yes</td>
501 <td align="center">yes</td>
502 <td align="center">-</td>
503 </tr>
504 <tr>
505 <td>++, --</td>
506 <td align="center">yes</td>
507 <td align="center">yes</td>
508 <td align="center">-</td>
509 <td align="center">-</td>
510 </tr>
511 <tr>
512 <td>+, -, *, /, %</td>
513 <td align="center">yes</td>
514 <td align="center">yes</td>
515 <td align="center">yes</td>
516 <td align="center">-</td>
517 </tr>
518 <tr>
519 <td>bitwise operators &, |, ^, ~</td>
520 <td align="center">yes</td>
521 <td align="center">yes</td>
522 <td align="center">yes</td>
523 <td align="center">-</td>
524 </tr>
525 <tr>
526 <td>&gt&gt, &lt&lt</td>
527 <td align="center">yes</td>
528 <td align="center">yes</td>
529 <td align="center">yes</td>
530 <td align="center">-</td>
531 </tr>
532 <tr>
533 <td>!, &&,||</td>
534 <td align="center">no</td>
535 <td align="center">-</td>
536 <td align="center">-</td>
537 <td align="center">-</td>
538 </tr>
539 <tr>
540 <td>==,!=, >, <, >=, <=</td>
541 <td align="center">yes</td>
542 <td align="center">yes</td>
543 <td align="center">-</td>
544 <td align="center">-</td>
545 </tr>
546 <tr>
547 <td>=</td>
548 <td align="center">yes</td>
549 <td align="center">yes</td>
550 <td align="center">yes</td>
551 <td align="center">yes</td>
552 </tr>
553 <tr>
554 <td>:?</td>
555 <td align="center">yes</td>
556 <td align="center">-</td>
557 <td align="center">-</td>
558 <td align="center">-</td>
559 </tr>
560 <tr>
561 <td>sizeof</td>
562 <td align="center">yes</td>
563 <td align="center">yes</td>
564 <td align="center">yes</td>
565 <td align="center">yes</td>
566 </tr>
567</table>
568
Owen Anderson029eb7d2010-01-27 01:22:36 +0000[diff] [blame]569<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
570
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]571<!-- ======================================================================= -->
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]572<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc74073c2010-10-06 23:12:32 +0000[diff] [blame]573<!-- ======================================================================= -->
574
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]575<p>An optional string message can be added to the <tt>deprecated</tt>
576and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc74073c2010-10-06 23:12:32 +0000[diff] [blame]577
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]578<blockquote>
Chris Lattnere56c7862010-11-09 19:43:35 +0000[diff] [blame]579<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]580</blockquote>
581
582<p>If the deprecated or unavailable declaration is used, the message
583will be incorporated into the appropriate diagnostic:</p>
584
585<blockquote>
Chris Lattnere56c7862010-11-09 19:43:35 +0000[diff] [blame]586<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]587 explode();
588 ^</pre>
589</blockquote>
590
591<p>Query for this feature
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]592with <tt>__has_extension(attribute_deprecated_with_message)</tt>
593and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCallf71b4532010-11-08 19:48:17 +0000[diff] [blame]594
595<!-- ======================================================================= -->
596<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
597<!-- ======================================================================= -->
598
599<p>Clang allows attributes to be written on individual enumerators.
600This allows enumerators to be deprecated, made unavailable, etc. The
601attribute must appear after the enumerator name and before any
602initializer, like so:</p>
603
604<blockquote>
605<pre>enum OperationMode {
606 OM_Invalid,
607 OM_Normal,
608 OM_Terrified __attribute__((deprecated)),
609 OM_AbortOnError __attribute__((deprecated)) = 4
610};</pre>
611</blockquote>
612
613<p>Attributes on the <tt>enum</tt> declaration do not apply to
614individual enumerators.</p>
615
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]616<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc74073c2010-10-06 23:12:32 +0000[diff] [blame]617
618<!-- ======================================================================= -->
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]619<h2 id="checking_language_features">Checks for Standard Language Features</h2>
620<!-- ======================================================================= -->
621
622<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
623enabled. Those features are listed here.</p>
624
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]625<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]626
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]627<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]628example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]629
Ted Kremenek71d74632009-12-03 02:05:57 +0000[diff] [blame]630<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]631
Ted Kremenek72de23e2009-12-03 02:06:43 +0000[diff] [blame]632<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]633compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek51540f92009-12-03 02:04:01 +0000[diff] [blame]634
635<!-- ======================================================================= -->
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]636<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
637<!-- ======================================================================= -->
638
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]639<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
640to query if certain upcoming standard language features are enabled. Those
641features are listed here. Features that are not yet implemented will be
642noted.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]643
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]644<h3 id="cxx0x">C++11</h3>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]645
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]646<p>The features listed below are slated for inclusion in the upcoming
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]647C++11 standard. As a result, all these features are enabled
648with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]649
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]650<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor347d6262011-05-11 23:45:11 +0000[diff] [blame]651
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]652<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]653
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]654<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3f1b5d02011-05-05 21:57:07 +0000[diff] [blame]655
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]656<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
657<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]658C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3f1b5d02011-05-05 21:57:07 +0000[diff] [blame]659
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]660<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbourne60188eb2011-10-14 23:44:46 +0000[diff] [blame]661
662<p>Use <tt>__has_feature(cxx_alignas)</tt> or
663<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
664specifiers using <tt>alignas</tt> is enabled.</p>
665
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]666<h4 id="cxx_attributes">C++11 attributes</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]667
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]668<p>Use <tt>__has_feature(cxx_attributes)</tt> or
669<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]670parsing with C++11's square bracket notation is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]671
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]672<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]673
674<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
675for generalized constant expressions (e.g., <tt>constexpr</tt>) is
Richard Smith1cb2af02012-02-14 22:56:17 +0000[diff] [blame]676enabled.</p>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]677
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]678<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]679
680<p>Use <tt>__has_feature(cxx_decltype)</tt> or
681<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
682<tt>decltype()</tt> specifier is enabled.</p>
683
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]684<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]685
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]686<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
687<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
688if support for default template arguments in function templates is enabled.</p>
Douglas Gregor7115aee2011-02-05 20:35:30 +0000[diff] [blame]689
Douglas Gregor3c469762011-11-01 01:19:34 +0000[diff] [blame]690<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
691
692<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
693<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
694defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
695
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]696<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Alexis Huntb0d81992011-06-23 06:11:37 +0000[diff] [blame]697
698<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
699support for delegating constructors is enabled.</p>
700
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]701<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]702
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]703<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
704<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redla93bb5b2010-08-31 23:28:47 +0000[diff] [blame]705deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]706
Benjamin Kramereaa262b2012-01-15 15:26:07 +0000[diff] [blame]707<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]708<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
709
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]710<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Alexis Hunt7d1492a2011-08-07 00:34:32 +0000[diff] [blame]711
712<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
713support for generalized initializers (using braced lists and
Richard Smith2dc867f2012-02-26 07:09:21 +0000[diff] [blame]714<tt>std::initializer_list</tt>) is enabled.</p>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]715
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]716<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]717
Sebastian Redl6ce53ae2011-10-10 18:10:00 +0000[diff] [blame]718<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
719implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]720
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]721<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]722
723<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>
724
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]725<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]726
727<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
728<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
729inline namespaces is enabled.</p>
Alexis Hunt7d1492a2011-08-07 00:34:32 +0000[diff] [blame]730
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]731<h4 id="cxx_lambdas">C++11 lambdas</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]732
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]733<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
734<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregor64bfb2e2012-02-23 05:44:09 +0000[diff] [blame]735is enabled. </p>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]736
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]737<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]738
739<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
740<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
741exception specifications is enabled.</p>
742
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]743<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]744
745<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]746
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]747<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]748
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]749<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
750<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor80af3132011-05-21 23:15:46 +0000[diff] [blame]751<tt>nullptr</tt> is enabled.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]752
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]753<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlsson69f1f932011-03-25 15:04:23 +0000[diff] [blame]754
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]755<p>Use <tt>__has_feature(cxx_override_control)</tt> or
756<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlsson69f1f932011-03-25 15:04:23 +0000[diff] [blame]757the override control keywords is enabled.</p>
758
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]759<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]760<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
761<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
762if support for reference-qualified functions (e.g., member functions with
763<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
764is enabled.</p>
Douglas Gregor56d5f0a2011-01-26 21:25:54 +0000[diff] [blame]765
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]766<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smith9bc6eed2011-04-15 15:14:40 +0000[diff] [blame]767
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]768<p>Use <tt>__has_feature(cxx_range_for)</tt> or
769<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
770range-based for loop is enabled. </p>
Richard Smith9bc6eed2011-04-15 15:14:40 +0000[diff] [blame]771
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]772<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]773<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>
774
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]775<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]776
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]777<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
778<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56d5f0a2011-01-26 21:25:54 +0000[diff] [blame]779rvalue references is enabled. </p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]780
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]781<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]782
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]783<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
784<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]785compile-time assertions using <tt>static_assert</tt> is enabled.</p>
786
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]787<h4 id="cxx_auto_type">C++11 type inference</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]788
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]789<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]790<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]791supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
792will instead be a storage class specifier, as in C or C++98.</p>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]793
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]794<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]795
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]796<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
797<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
798strongly typed, scoped enumerations is enabled.</p>
Sebastian Redla93bb5b2010-08-31 23:28:47 +0000[diff] [blame]799
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]800<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregor7fb25412010-10-01 18:44:50 +0000[diff] [blame]801
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]802<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
803<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
804alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregor7fb25412010-10-01 18:44:50 +0000[diff] [blame]805
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]806<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]807<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
808support for Unicode string literals is enabled.</p>
Sebastian Redlc17003c2011-03-15 21:17:12 +0000[diff] [blame]809
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]810<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redlc17003c2011-03-15 21:17:12 +0000[diff] [blame]811
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]812<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]813
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]814<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]815
816<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>
817
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]818<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregor26858b72011-08-29 17:28:38 +0000[diff] [blame]819
820<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
821<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
822for variadic templates is enabled.</p>
Douglas Gregor0bf31402010-10-08 23:50:27 +0000[diff] [blame]823
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]824<h3 id="c11">C11</h3>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]825
826<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]827C11 standard. As a result, all these features are enabled
828with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]829
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]830<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbourne60188eb2011-10-14 23:44:46 +0000[diff] [blame]831
832<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
833to determine if support for alignment specifiers using <tt>_Alignas</tt>
834is enabled.</p>
835
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]836<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]837
838<p>Use <tt>__has_feature(c_generic_selections)</tt> or
839<tt>__has_extension(c_generic_selections)</tt> to determine if support for
840generic selections is enabled.</p>
841
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]842<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]843languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]844C11 standard.</p>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]845
846<p>In C, type compatibility is decided according to the rules given in the
847appropriate standard, but in C++, which lacks the type compatibility rules
848used in C, types are considered compatible only if they are equivalent.</p>
849
Benjamin Kramere56f3932011-12-23 17:00:35 +0000[diff] [blame]850<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]851
852<p>Use <tt>__has_feature(c_static_assert)</tt> or
853<tt>__has_extension(c_static_assert)</tt> to determine if support for
854compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
855
Alexis Huntaf4e28d2010-01-13 08:31:49 +0000[diff] [blame]856<!-- ======================================================================= -->
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]857<h2 id="checking_type_traits">Checks for Type Traits</h2>
858<!-- ======================================================================= -->
859
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]860<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]861<blockquote>
862<pre>
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]863#if __has_extension(is_convertible_to)
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]864template&lt;typename From, typename To&gt;
865struct is_convertible_to {
866 static const bool value = __is_convertible_to(From, To);
867};
868#else
869// Emulate type trait
870#endif
871</pre>
872</blockquote>
873
874<p>The following type traits are supported by Clang:</p>
875<ul>
876 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
877 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
878 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
879 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
880 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
881 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
882 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
883 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
884 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
885 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
886 <li><code>__is_class</code> (GNU, Microsoft)</li>
887 <li><code>__is_convertible_to</code> (Microsoft)</li>
888 <li><code>__is_empty</code> (GNU, Microsoft)</li>
889 <li><code>__is_enum</code> (GNU, Microsoft)</li>
890 <li><code>__is_pod</code> (GNU, Microsoft)</li>
891 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
892 <li><code>__is_union</code> (GNU, Microsoft)</li>
893 <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]894 <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]895 <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 Gregor29c42f22012-02-24 07:38:34 +0000[diff] [blame]896 <li><code>__is_trivially_assignable(totype, fromtype)</code>: Determines whether a value of type <tt>totype</tt> can be assigned to from a value of type <tt>fromtype</tt> such that no non-trivial functions are called as part of that assignment. This trait is required to implement the C++11 standard library.</li>
897 <li><code>__is_trivially_constructible(type, argtypes...)</code>: Determines whether a value of type <tt>type</tt> can be direct-initialized with arguments of types <tt>argtypes...</tt> such that no non-trivial functions are called as part of that initialization. This trait is required to implement the C++11 standard library.</li>
Douglas Gregor7c607682011-02-03 21:57:35 +0000[diff] [blame]898</ul>
899
900<!-- ======================================================================= -->
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]901<h2 id="blocks">Blocks</h2>
902<!-- ======================================================================= -->
903
Chris Lattner14aea9a2009-03-09 07:03:22 +0000[diff] [blame]904<p>The syntax and high level language feature description is in <a
905href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
906details for the clang implementation are in <a
Chris Lattner87c5e2f2010-03-16 21:43:03 +0000[diff] [blame]907href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]908
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]909
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]910<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]911
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]912<!-- ======================================================================= -->
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]913<h2 id="objc_features">Objective-C Features</h2>
914<!-- ======================================================================= -->
915
916<h3 id="objc_instancetype">Related result types</h3>
917
918<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>
919
920<blockquote>
921<pre>
922@interface NSObject
923+ (id)alloc;
924- (id)init;
925@end
926
927@interface NSArray : NSObject
928@end
929</pre>
930</blockquote>
931
932<p>and this common initialization pattern</p>
933
934<blockquote>
935<pre>
936NSArray *array = [[NSArray alloc] init];
937</pre>
938</blockquote>
939
940<p>the type of the expression <code>[NSArray alloc]</code> is
941<code>NSArray*</code> because <code>alloc</code> implicitly has a
942related result type. Similarly, the type of the expression
943<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
944<code>init</code> has a related result type and its receiver is known
945to 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>
946
Douglas Gregorbab8a962011-09-08 01:46:34 +0000[diff] [blame]947<p>A method with a related result type can be declared by using the
948type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
949is a contextual keyword that is only permitted in the result type of
950an Objective-C method, e.g.</p>
951
952<pre>
953@interface A
954+ (<b>instancetype</b>)constructAnA;
955@end
956</pre>
957
958<p>The related result type can also be inferred for some methods.
959To determine whether a method has an inferred related result type, the first
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]960word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregorf8b02ca2011-11-03 18:33:01 +0000[diff] [blame]961considered, and the method will have a related result type if its return
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]962type is compatible with the type of its class and if</p>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]963
964<ul>
965
966 <li>the first word is "alloc" or "new", and the method is a class
967 method, or</li>
968
969 <li>the first word is "autorelease", "init", "retain", or "self",
970 and the method is an instance method.</li>
971
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]972</ul>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]973
974<p>If a method with a related result type is overridden by a subclass
975method, the subclass method must also return a type that is compatible
976with the subclass type. For example:</p>
977
978<blockquote>
979<pre>
980@interface NSString : NSObject
981- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
982@end
983</pre>
984</blockquote>
985
986<p>Related result types only affect the type of a message send or
987property access via the given method. In all other respects, a method
Douglas Gregorbab8a962011-09-08 01:46:34 +0000[diff] [blame]988with a related result type is treated the same way as method that
989returns <tt>id</tt>.</p>
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]990
Douglas Gregordc28ba12011-09-08 17:19:31 +0000[diff] [blame]991<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
992the <tt>instancetype</tt> contextual keyword is available.</p>
993
Douglas Gregor33823722011-06-11 01:09:30 +0000[diff] [blame]994<!-- ======================================================================= -->
John McCall31168b02011-06-15 23:02:42 +0000[diff] [blame]995<h2 id="objc_arc">Automatic reference counting </h2>
996<!-- ======================================================================= -->
997
998<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>
999
1000<!-- ======================================================================= -->
Douglas Gregor8b7d4032011-09-08 17:18:35 +0000[diff] [blame]1001<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
1002<!-- ======================================================================= -->
1003
David Blaikie83172452011-10-18 05:49:30 +0000[diff] [blame]1004<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor8b7d4032011-09-08 17:18:35 +0000[diff] [blame]1005underlying type within Objective-C. For example, one can write an
1006enumeration type as:</p>
1007
1008<pre>
1009typedef enum : unsigned char { Red, Green, Blue } Color;
1010</pre>
1011
1012<p>This specifies that the underlying type, which is used to store the
1013enumeration value, is <tt>unsigned char</tt>.</p>
1014
1015<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1016support for fixed underlying types is available in Objective-C.</p>
1017
1018<!-- ======================================================================= -->
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1019<h2 id="overloading-in-c">Function Overloading in C</h2>
1020<!-- ======================================================================= -->
1021
Chris Lattnerb3ef5332009-02-13 21:51:45 +0000[diff] [blame]1022<p>Clang provides support for C++ function overloading in C. Function
1023overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1024example, one might provide several overloaded versions of a <tt>tgsin</tt>
1025function that invokes the appropriate standard function computing the sine of a
1026value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1027precision:</p>
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1028
1029<blockquote>
1030<pre>
1031#include &lt;math.h&gt;
1032float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1033double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1034long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1035</pre>
1036</blockquote>
1037
1038<p>Given these declarations, one can call <tt>tgsin</tt> with a
1039<tt>float</tt> value to receive a <tt>float</tt> result, with a
1040<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1041overloading in C follows the rules of C++ function overloading to pick
1042the best overload given the call arguments, with a few C-specific
1043semantics:</p>
1044<ul>
1045 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1046 double</tt> is ranked as a floating-point promotion (per C99) rather
1047 than as a floating-point conversion (as in C++).</li>
1048
1049 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1050 <tt>U*</tt> is considered a pointer conversion (with conversion
1051 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1052
1053 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1054 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1055 conversion is given "conversion" rank.</li>
1056</ul>
1057
1058<p>The declaration of <tt>overloadable</tt> functions is restricted to
1059function declarations and definitions. Most importantly, if any
1060function with a given name is given the <tt>overloadable</tt>
1061attribute, then all function declarations and definitions with that
1062name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerb3ef5332009-02-13 21:51:45 +0000[diff] [blame]1063attribute. This rule even applies to redeclarations of functions whose original
1064declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1065
1066<blockquote>
1067<pre>
1068int f(int) __attribute__((overloadable));
1069float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1070
1071int g(int) __attribute__((overloadable));
1072int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1073</pre>
1074</blockquote>
1075
Douglas Gregor94349fd2009-02-18 07:07:28 +0000[diff] [blame]1076<p>Functions marked <tt>overloadable</tt> must have
1077prototypes. Therefore, the following code is ill-formed:</p>
1078
1079<blockquote>
1080<pre>
1081int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1082</pre>
1083</blockquote>
1084
1085<p>However, <tt>overloadable</tt> functions are allowed to use a
1086ellipsis 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>
1087
1088<blockquote>
1089<pre>
Chris Lattnerfaca7d92009-02-18 22:27:46 +0000[diff] [blame]1090void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor94349fd2009-02-18 07:07:28 +0000[diff] [blame]1091</pre>
1092</blockquote>
1093
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1094<p>Functions declared with the <tt>overloadable</tt> attribute have
1095their names mangled according to the same rules as C++ function
1096names. For example, the three <tt>tgsin</tt> functions in our
1097motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner19e0fd02010-11-28 18:19:13 +0000[diff] [blame]1098<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1099caveats to this use of name mangling:</p>
1100
1101<ul>
1102
1103 <li>Future versions of Clang may change the name mangling of
1104 functions overloaded in C, so you should not depend on an specific
1105 mangling. To be completely safe, we strongly urge the use of
1106 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1107
1108 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1109 used in C++, because names will already be mangled and functions are
1110 already overloadable. However, when an <tt>overloadable</tt>
1111 function occurs within an <tt>extern "C"</tt> linkage specification,
1112 it's name <i>will</i> be mangled in the same way as it would in
1113 C.</li>
1114</ul>
1115
Peter Collingbourned5d410f2011-05-13 20:54:45 +0000[diff] [blame]1116<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1117
Eli Friedman6b9c41e2011-09-19 23:17:44 +0000[diff] [blame]1118<!-- ======================================================================= -->
1119<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1120<!-- ======================================================================= -->
1121
1122<p>clang supports an extension which allows the following in C:</p>
1123
1124<blockquote>
1125<pre>
1126#include &lt;math.h&gt;
1127#include &lt;complex.h&gt;
1128complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1129</pre>
1130</blockquote>
1131
1132<p>This construct is useful because there is no way to separately
1133initialize the real and imaginary parts of a complex variable in
1134standard C, given that clang does not support <code>_Imaginary</code>.
1135(clang also supports the <code>__real__</code> and <code>__imag__</code>
1136extensions from gcc, which help in some cases, but are not usable in
1137static initializers.)
1138
1139<p>Note that this extension does not allow eliding the braces; the
1140meaning of the following two lines is different:</p>
1141
1142<blockquote>
1143<pre>
1144complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1145complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1146</pre>
1147</blockquote>
1148
1149<p>This extension also works in C++ mode, as far as that goes, but does not
1150 apply to the C++ <code>std::complex</code>. (In C++11, list
1151 initialization allows the same syntax to be used with
1152 <code>std::complex</code> with the same meaning.)
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1153
Douglas Gregor725de572009-02-13 00:57:04 +0000[diff] [blame]1154<!-- ======================================================================= -->
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1155<h2 id="builtins">Builtin Functions</h2>
1156<!-- ======================================================================= -->
1157
1158<p>Clang supports a number of builtin library functions with the same syntax as
1159GCC, including things like <tt>__builtin_nan</tt>,
1160<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1161<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1162addition to the GCC builtins, Clang supports a number of builtins that GCC does
1163not, which are listed here.</p>
1164
1165<p>Please note that Clang does not and will not support all of the GCC builtins
1166for vector operations. Instead of using builtins, you should use the functions
1167defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1168define portable wrappers for these. Many of the Clang versions of these
1169functions are implemented directly in terms of <a href="#vectors">extended
1170vector support</a> instead of builtins, in order to reduce the number of
1171builtins that we need to implement.</p>
1172
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1173<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1174<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1175<!-- ======================================================================= -->
1176
Chris Lattnerc15c2522009-09-16 18:56:12 +0000[diff] [blame]1177<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1178permutation/shuffle/swizzle operations. This builtin is also very important for
1179the implementation of various target-specific header files like
1180<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1181</p>
1182
1183<p><b>Syntax:</b></p>
1184
1185<pre>
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1186__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1187</pre>
1188
1189<p><b>Examples:</b></p>
1190
1191<pre>
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1192 // Identity operation - return 4-element vector V1.
1193 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1194
1195 // "Splat" element 0 of V1 into a 4-element result.
1196 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1197
1198 // Reverse 4-element vector V1.
1199 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1200
1201 // Concatenate every other element of 4-element vectors V1 and V2.
1202 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1203
1204 // Concatenate every other element of 8-element vectors V1 and V2.
1205 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1206</pre>
1207
1208<p><b>Description:</b></p>
1209
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1210<p>The first two arguments to __builtin_shufflevector are vectors that have the
1211same element type. The remaining arguments are a list of integers that specify
1212the elements indices of the first two vectors that should be extracted and
1213returned in a new vector. These element indices are numbered sequentially
1214starting with the first vector, continuing into the second vector. Thus, if
1215vec1 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]1216</p>
1217
Chris Lattner9631dfd2009-02-13 20:00:20 +0000[diff] [blame]1218<p>The result of __builtin_shufflevector is a vector
1219with the same element type as vec1/vec2 but that has an element count equal to
1220the number of indices specified.
1221</p>
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1222
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]1223<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1224
1225<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1226<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]1227<!-- ======================================================================= -->
1228
1229<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1230the program cannot be reached, even if the compiler might otherwise think it
1231can. This is useful to improve optimization and eliminates certain warnings.
1232For example, without the <tt>__builtin_unreachable</tt> in the example below,
1233the compiler assumes that the inline asm can fall through and prints a "function
1234declared 'noreturn' should not return" warning.
1235</p>
1236
1237<p><b>Syntax:</b></p>
1238
1239<pre>
1240__builtin_unreachable()
1241</pre>
1242
1243<p><b>Example of Use:</b></p>
1244
1245<pre>
1246void myabort(void) __attribute__((noreturn));
1247void myabort(void) {
1248 asm("int3");
1249 __builtin_unreachable();
1250}
1251</pre>
1252
1253<p><b>Description:</b></p>
1254
1255<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1256it has undefined behavior, it is a statement that it is never reached and the
1257optimizer can take advantage of this to produce better code. This builtin takes
1258no arguments and produces a void result.
1259</p>
1260
1261<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1262
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]1263<!-- ======================================================================= -->
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1264<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]1265<!-- ======================================================================= -->
1266
1267<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1268memory.
1269</p>
1270
1271<p><b>Syntax:</b></p>
1272
1273<pre>
1274<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1275</pre>
1276
1277<p><b>Example of Use:</b></p>
1278
1279<pre>
Alexis Huntaedbfe42011-06-23 01:21:01 +0000[diff] [blame]1280int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner9cb59fa2011-04-09 03:57:26 +0000[diff] [blame]1281</pre>
1282
1283<p><b>Description:</b></p>
1284
1285<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1286intrinsics to allow code to atomically swap the current value with the new
1287value. More importantly, it helps developers write more efficient and correct
1288code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1289relying on the platform specific implementation details of
1290__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1291</p>
1292
Chris Lattnerbf206382009-09-21 03:09:59 +0000[diff] [blame]1293
Chris Lattnerc86ffc32009-04-09 19:58:15 +0000[diff] [blame]1294<!-- ======================================================================= -->
1295<h2 id="targetspecific">Target-Specific Extensions</h2>
1296<!-- ======================================================================= -->
1297
1298<p>Clang supports some language features conditionally on some targets.</p>
1299
1300<!-- ======================================================================= -->
1301<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1302<!-- ======================================================================= -->
1303
1304<p>The X86 backend has these language extensions:</p>
1305
1306<!-- ======================================================================= -->
1307<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1308<!-- ======================================================================= -->
1309
1310<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnerb7323972009-05-05 18:54:47 +0000[diff] [blame]1311relative to the X86 GS segment register, and address space #257 causes it to be
1312relative to the X86 FS segment. Note that this is a very very low-level
1313feature that should only be used if you know what you're doing (for example in
1314an OS kernel).</p>
Chris Lattnerc86ffc32009-04-09 19:58:15 +0000[diff] [blame]1315
1316<p>Here is an example:</p>
1317
1318<pre>
1319#define GS_RELATIVE __attribute__((address_space(256)))
1320int foo(int GS_RELATIVE *P) {
1321 return *P;
1322}
1323</pre>
1324
1325<p>Which compiles to (on X86-32):</p>
1326
1327<pre>
1328_foo:
1329 movl 4(%esp), %eax
1330 movl %gs:(%eax), %eax
1331 ret
1332</pre>
1333
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1334<!-- ======================================================================= -->
1335<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1336<!-- ======================================================================= -->
1337
1338<p>Clang supports additional attributes that are useful for documenting program
1339invariants and rules for static analysis tools. The extensions documented here
1340are used by the <a
1341href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1342engine</a> that is part of Clang's Analysis library.</p>
1343
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1344<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1345
1346<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek86ee0592009-04-10 05:04:22 +0000[diff] [blame]1347attribute. This attribute, which is typically affixed to a function prototype,
1348indicates that a call to a given function never returns. Function prototypes for
1349common functions like <tt>exit</tt> are typically annotated with this attribute,
1350as well as a variety of common assertion handlers. Users can educate the static
1351analyzer about their own custom assertion handles (thus cutting down on false
1352positives due to false paths) by marking their own &quot;panic&quot; functions
1353with this attribute.</p>
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1354
1355<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewyckybe42c112009-06-14 04:08:08 +0000[diff] [blame]1356there are special functions that for all intents and purposes should be
1357considered panic functions (i.e., they are only called when an internal program
1358error occurs) but may actually return so that the program can fail gracefully.
1359The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1360as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattnerbb72f772009-04-10 05:54:56 +0000[diff] [blame]1361pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1362<tt>noreturn</tt>).</p>
1363
1364<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]1365same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1366placed at the end of function prototypes:</p>
1367
1368<pre>
1369 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1370</pre>
1371
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1372<p>Query for this feature with
1373<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattnerb6f77af2009-06-13 07:13:28 +0000[diff] [blame]1374
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1375<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1376
1377<p>Many methods in Objective-C have conventional meanings determined
1378by their selectors. For the purposes of static analysis, it is
1379sometimes useful to be able to mark a method as having a particular
1380conventional meaning despite not having the right selector, or as not
1381having the conventional meaning that its selector would suggest.
1382For these use cases, we provide an attribute to specifically describe
1383the <q>method family</q> that a method belongs to.</p>
1384
1385<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1386where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1387<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1388can only be placed at the end of a method declaration:</p>
1389
1390<pre>
1391 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1392</pre>
1393
1394<p>Users who do not wish to change the conventional meaning of a
1395method, and who merely want to document its non-standard retain and
1396release semantics, should use the
1397<a href="#attr_retain_release">retaining behavior attributes</a>
1398described below.</p>
1399
1400<p>Query for this feature with
1401<tt>__has_attribute(objc_method_family)</tt>.</p>
1402
1403<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall46669c02011-01-25 04:26:21 +0000[diff] [blame]1404
1405<p>In Objective-C, functions and methods are generally assumed to take
1406and return objects with +0 retain counts, with some exceptions for
1407special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1408there are exceptions, and so Clang provides attributes to allow these
1409exceptions to be documented, which helps the analyzer find leaks (and
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1410ignore non-leaks). Some exceptions may be better described using
1411the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1412attribute instead.</p>
John McCall46669c02011-01-25 04:26:21 +0000[diff] [blame]1413
1414<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1415<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1416and <tt>cf_returns_not_retained</tt> attributes can be placed on
1417methods and functions that return Objective-C or CoreFoundation
1418objects. They are commonly placed at the end of a function prototype
1419or method declaration:</p>
1420
1421<pre>
1422 id foo() <b>__attribute__((ns_returns_retained))</b>;
1423
1424 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1425</pre>
1426
1427<p>The <tt>*_returns_retained</tt> attributes specify that the
1428returned object has a +1 retain count.
1429The <tt>*_returns_not_retained</tt> attributes specify that the return
1430object has a +0 retain count, even if the normal convention for its
1431selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1432returned object is +0, but is guaranteed to live at least as long as the
1433next flush of an autorelease pool.</p>
1434
1435<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1436attributes can be placed on an parameter declaration; they specify
1437that the argument is expected to have a +1 retain count, which will be
1438balanced in some way by the function or method.
1439The <tt>ns_consumes_self</tt> attribute can only be placed on an
1440Objective-C method; it specifies that the method expects
1441its <tt>self</tt> parameter to have a +1 retain count, which it will
1442balance in some way.</p>
1443
1444<pre>
1445 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1446
1447 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1448 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1449</pre>
Ted Kremeneka9deb972009-04-10 05:03:33 +0000[diff] [blame]1450
John McCall6107fc92011-03-18 03:51:49 +0000[diff] [blame]1451<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1452<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1453
Kostya Serebryany9751d342011-11-28 20:51:02 +0000[diff] [blame]1454<!-- ======================================================================= -->
1455<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1456<!-- ======================================================================= -->
1457<h3 id="address_sanitizer">AddressSanitizer</h3>
1458<p> Use <code>__has_feature(address_sanitizer)</code>
1459to check if the code is being built with <a
1460 href="AddressSanitizer.html">AddressSanitizer</a>.
1461</p>
Kostya Serebryany588d6ab2012-01-24 19:25:38 +0000[diff] [blame]1462<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function
1463declaration to specify that address safety instrumentation (e.g.
1464AddressSanitizer) should not be applied to that function.
1465</p>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1466
1467<!-- ======================================================================= -->
Caitlin Sadowski13d44442011-07-28 18:38:36 +0000[diff] [blame]1468<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1469<!-- ======================================================================= -->
1470
1471<p>Clang supports additional attributes for checking basic locking policies in
1472multithreaded programs.
1473Clang currently parses the following list of attributes, although
1474<b>the implementation for these annotations is currently in development.</b>
1475For more details, see the
1476<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1477</p>
1478
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1479<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1480
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1481<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1482declaration to specify that the thread safety analysis should not be run on that
1483function. This attribute provides an escape hatch (e.g. for situations when it
1484is difficult to annotate the locking policy). </p>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1485
1486<h4 id="ts_lockable">lockable</h4>
1487
1488<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1489that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1490used to check consistency.</p>
1491
1492<h4 id="ts_scopedlockable">scoped_lockable</h4>
1493
1494<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1495specify that it has a "scoped" lockable type. Objects of this type will acquire
1496the lock upon construction and release it upon going out of scope.
1497 This annotation is primarily used to check
1498consistency.</p>
1499
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1500<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1501
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1502<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1503specify that the variable must be accessed while holding some lock.</p>
1504
1505<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1506
1507<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1508specify that the pointer must be dereferenced while holding some lock.</p>
1509
1510<h4 id="ts_guardedby">guarded_by(l)</h4>
1511
1512<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1513specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1514
1515<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1516
1517<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1518specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1519
1520<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1521
1522<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1523of a lockable variable to specify that the lock must be acquired before all
1524attribute arguments. Arguments must be lockable type, and there must be at
1525least one argument.</p>
1526
1527<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1528
1529<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1530of a lockable variable to specify that the lock must be acquired after all
1531attribute arguments. Arguments must be lockable type, and there must be at
1532least one argument.</p>
1533
1534<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1535
1536<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1537declaration to specify that the function acquires all listed locks
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1538exclusively. This attribute takes zero or more arguments: either of lockable
1539type or integers indexing into function parameters of lockable type. If no
1540arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1541enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1542
1543<h4 id="ts_slf">shared_lock_function(...)</h4>
1544
1545<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1546declaration to specify that the function acquires all listed locks, although
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1547 the locks may be shared (e.g. read locks). This attribute takes zero or more
1548arguments: either of lockable type or integers indexing into function
1549parameters of lockable type. If no arguments are given, the acquired lock is
1550implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1551
1552<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1553
1554<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1555declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1556all listed locks exclusively. This attribute takes one or more arguments. The
1557first argument is an integer or boolean value specifying the return value of a
1558successful lock acquisition. The remaining arugments are either of lockable type
1559or integers indexing into function parameters of lockable type. If only one
1560argument is given, the acquired lock is implicitly <tt>this</tt> of the
1561enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1562
1563<h4 id="ts_stf">shared_trylock_function(...)</h4>
1564
1565<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1566declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1567all listed locks, although the locks may be shared (e.g. read locks). This
1568attribute takes one or more arguments. The first argument is an integer or
1569boolean value specifying the return value of a successful lock acquisition. The
1570remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1571function parameters of lockable type. If only one argument is given, the
1572acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1573
1574<h4 id="ts_uf">unlock_function(...)</h4>
1575
1576<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1577declaration to specify that the function release all listed locks. This
1578attribute takes zero or more arguments: either of lockable type or integers
1579indexing into function parameters of lockable type. If no arguments are given,
1580the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1581
1582<h4 id="ts_lr">lock_returned(l)</h4>
1583
1584<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1585declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1586must be of lockable type). This annotation is used to aid in resolving lock
1587expressions.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1588
1589<h4 id="ts_le">locks_excluded(...)</h4>
1590
1591<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowski4b1e8392011-08-09 17:59:31 +0000[diff] [blame]1592to specify that the function must not be called with the listed locks. Arguments
1593must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowski63fa6672011-07-28 20:12:35 +0000[diff] [blame]1594
1595<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1596
1597<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1598declaration to specify that the function must be called while holding the listed
1599exclusive locks. Arguments must be lockable type, and there must be at
1600least one argument.</p>
1601
1602<h4 id="ts_slr">shared_locks_required(...)</h4>
1603
1604<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1605declaration to specify that the function must be called while holding the listed
1606shared locks. Arguments must be lockable type, and there must be at
1607least one argument.</p>
Caitlin Sadowskiaac4d212011-07-28 17:21:07 +0000[diff] [blame]1608
Chris Lattnerb8ec6bb2009-02-09 08:46:11 +0000[diff] [blame]1609</div>
1610</body>
1611</html>