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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 Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]27<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]28<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]29<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]30<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 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>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]33<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 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>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]37 </ul></li>
38<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]39 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]40 <li><a href="#cxx0x">C++11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]41 <ul>
David Blaikie5090e9f2011-10-18 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 Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]50 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie5090e9f2011-10-18 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 Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]75 </ul></li>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]76 <li><a href="#c11">C11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]77 <ul>
Benjamin Kramerffbe9b92011-12-23 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>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]81 </ul></li>
82 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]83<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]84<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 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 McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]88 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]89 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]90 <li><a href="#objc_lambdas">Interoperability with C++11 lambdas</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]91 </ul>
92</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]93<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]94<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]95<li><a href="#builtins">Builtin Functions</a>
96 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]97 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]98 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]99 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]100 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]101</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]102<li><a href="#targetspecific">Target-Specific Extensions</a>
103 <ul>
104 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
105 </ul>
106</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]107<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]108<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]109 <ul>
110 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
111 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]112</li>
113<li><a href="#threadsafety">Thread Safety Annotation Checking</a>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]114 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]115 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
116 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
117 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]118 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
119 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]120 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
121 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
122 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
123 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
124 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
125 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
126 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
127 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
128 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
129 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
130 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
131 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
132 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]133 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]134</li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]135</ul>
136
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]137<!-- ======================================================================= -->
138<h2 id="intro">Introduction</h2>
139<!-- ======================================================================= -->
140
141<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]142addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]143range of GCC extensions. Please see the <a
144href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
145more information on these extensions.</p>
146
147<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]148<h2 id="feature_check">Feature Checking Macros</h2>
149<!-- ======================================================================= -->
150
151<p>Language extensions can be very useful, but only if you know you can depend
Chris Lattnerc70e1932011-03-21 16:25:11 +0000[diff] [blame]152on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]153function-like macros. This allows you to directly test for a feature in your
154code without having to resort to something like autoconf or fragile "compiler
155version checks".</p>
156
157<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]158<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]159<!-- ======================================================================= -->
160
161<p>This function-like macro takes a single identifier argument that is the name
162of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
163not. It can be used like this:</p>
164
165<blockquote>
166<pre>
167#ifndef __has_builtin // Optional of course.
168 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
169#endif
170
171...
172#if __has_builtin(__builtin_trap)
173 __builtin_trap();
174#else
175 abort();
176#endif
177...
178</pre>
179</blockquote>
180
181
182<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]183<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]184<!-- ======================================================================= -->
185
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]186<p>These function-like macros take a single identifier argument that is the
187name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
188is both supported by Clang and standardized in the current language standard
189or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
190<code>__has_extension</code> evaluates to 1 if the feature is supported by
191Clang in the current language (either as a language extension or a standard
192language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]193
194<blockquote>
195<pre>
196#ifndef __has_feature // Optional of course.
197 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
198#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]199#ifndef __has_extension
200 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
201#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]202
203...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]204#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]205// This code will only be compiled with the -std=c++11 and -std=gnu++11
206// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]207#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]208
209#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]210// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]211// and -std=gnu++98 options, because rvalue references are supported as a
212// language extension in C++98.
213#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]214</pre>
215</blockquote>
216
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]217<p id="has_feature_back_compat">For backwards compatibility reasons,
218<code>__has_feature</code> can also be used to test for support for
219non-standardized features, i.e. features not prefixed <code>c_</code>,
220<code>cxx_</code> or <code>objc_</code>.</p>
221
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]222<p id="has_feature_for_non_language_features">
223Another use of <code>__has_feature</code> is to check for compiler features
224not related to the language standard, such as e.g.
225<a href="AddressSanitizer.html">AddressSanitizer</a>.
226
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]227<p>If the <code>-pedantic-errors</code> option is given,
228<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
229
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]230<p>The feature tag is described along with the language feature below.</p>
231
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]232<p>The feature name or extension name can also be specified with a preceding and
233following <code>__</code> (double underscore) to avoid interference from a macro
Richard Smith1d9f4c12012-03-01 02:12:07 +0000[diff] [blame]234with the same name. For instance, <code>__cxx_rvalue_references__</code> can be
235used instead of <code>cxx_rvalue_references</code>.</p>
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]236
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]237<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]238<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]239<!-- ======================================================================= -->
240
241<p>This function-like macro takes a single identifier argument that is the name
242of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
243can be used like this:</p>
244
245<blockquote>
246<pre>
247#ifndef __has_attribute // Optional of course.
248 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
249#endif
250
251...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]252#if __has_attribute(always_inline)
253#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]254#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]255#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]256#endif
257...
258</pre>
259</blockquote>
260
Jean-Daniel Dupas8a5e7fd2012-03-01 14:53:16 +0000[diff] [blame]261<p>The attribute name can also be specified with a preceding and
262following <code>__</code> (double underscore) to avoid interference from a macro
263with the same name. For instance, <code>__always_inline__</code> can be used
264instead of <code>always_inline</code>.</p>
265
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]266<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]267<h2 id="has_include">Include File Checking Macros</h2>
268<!-- ======================================================================= -->
269
270<p>Not all developments systems have the same include files.
271The <a href="#__has_include">__has_include</a> and
272<a href="#__has_include_next">__has_include_next</a> macros allow you to
273check for the existence of an include file before doing
274a possibly failing #include directive.</p>
275
276<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]277<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]278<!-- ======================================================================= -->
279
280<p>This function-like macro takes a single file name string argument that
281is the name of an include file. It evaluates to 1 if the file can
282be found using the include paths, or 0 otherwise:</p>
283
284<blockquote>
285<pre>
286// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]287#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]288# include "myinclude.h"
289#endif
290
291// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]292#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]293# include "myinclude.h"
294#endif
295</pre>
296</blockquote>
297
298<p>To test for this feature, use #if defined(__has_include).</p>
299
300<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]301<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]302<!-- ======================================================================= -->
303
304<p>This function-like macro takes a single file name string argument that
305is the name of an include file. It is like __has_include except that it
306looks for the second instance of the given file found in the include
307paths. It evaluates to 1 if the second instance of the file can
308be found using the include paths, or 0 otherwise:</p>
309
310<blockquote>
311<pre>
312// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]313#if __has_include_next("myinclude.h") &amp;&amp; __has_include_next(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]314# include_next "myinclude.h"
315#endif
316
317// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]318#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]319# include_next "myinclude.h"
320#endif
321</pre>
322</blockquote>
323
324<p>Note that __has_include_next, like the GNU extension
325#include_next directive, is intended for use in headers only,
326and will issue a warning if used in the top-level compilation
327file. A warning will also be issued if an absolute path
328is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]329
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]330
331<!-- ======================================================================= -->
332<h3><a name="__has_warning">__has_warning</a></h3>
333<!-- ======================================================================= -->
334
335<p>This function-like macro takes a string literal that represents a command
336 line option for a warning and returns true if that is a valid warning
337 option.</p>
338
339<blockquote>
340<pre>
341#if __has_warning("-Wformat")
342...
343#endif
344</pre>
345</blockquote>
346
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]347<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]348<h2 id="builtinmacros">Builtin Macros</h2>
349<!-- ======================================================================= -->
350
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]351<dl>
352 <dt><code>__BASE_FILE__</code></dt>
353 <dd>Defined to a string that contains the name of the main input
354 file passed to Clang.</dd>
355
356 <dt><code>__COUNTER__</code></dt>
357 <dd>Defined to an integer value that starts at zero and is
358 incremented each time the <code>__COUNTER__</code> macro is
359 expanded.</dd>
360
361 <dt><code>__INCLUDE_LEVEL__</code></dt>
362 <dd>Defined to an integral value that is the include depth of the
363 file currently being translated. For the main file, this value is
364 zero.</dd>
365
366 <dt><code>__TIMESTAMP__</code></dt>
367 <dd>Defined to the date and time of the last modification of the
368 current source file.</dd>
369
370 <dt><code>__clang__</code></dt>
371 <dd>Defined when compiling with Clang</dd>
372
373 <dt><code>__clang_major__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]374 <dd>Defined to the major marketing version number of Clang (e.g., the
375 2 in 2.0.1). Note that marketing version numbers should not be used to
376 check for language features, as different vendors use different numbering
377 schemes. Instead, use the <a href="#feature_check">feature checking
378 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]379
380 <dt><code>__clang_minor__</code></dt>
381 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]382 2.0.1). Note that marketing version numbers should not be used to
383 check for language features, as different vendors use different numbering
384 schemes. Instead, use the <a href="#feature_check">feature checking
385 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]386
387 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]388 <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]389
390 <dt><code>__clang_version__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]391 <dd>Defined to a string that captures the Clang marketing version, including
392 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]393</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]394
395<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]396<h2 id="vectors">Vectors and Extended Vectors</h2>
397<!-- ======================================================================= -->
398
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]399<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]400
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]401<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
402support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An
403example is:</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]404
405<blockquote>
406<pre>
407typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
408typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
409
410float4 foo(float2 a, float2 b) {
411 float4 c;
412 c.xz = a;
413 c.yw = b;
414 return c;
415}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]416</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]417</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]418
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]419<p>Query for this feature with
420<tt>__has_extension(attribute_ext_vector_type)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]421
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]422<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector
423syntax and functions. For example:</p>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]424
425<blockquote>
426<pre>
427vector float foo(vector int a) {
428 vector int b;
429 b = vec_add(a, a) + a;
430 return (vector float)b;
431}
432</pre>
433</blockquote>
434
435<p>NEON vector types are created using <tt>neon_vector_type</tt> and
436<tt>neon_polyvector_type</tt> attributes. For example:</p>
437
438<blockquote>
439<pre>
440typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
441typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
442
443int8x8_t foo(int8x8_t a) {
444 int8x8_t v;
445 v = a;
446 return v;
447}
448</pre>
449</blockquote>
450
451<!-- ======================================================================= -->
452<h3><a name="vector_literals">Vector Literals</a></h3>
453<!-- ======================================================================= -->
454
455<p>Vector literals can be used to create vectors from a set of scalars, or
456vectors. Either parentheses or braces form can be used. In the parentheses form
457the number of literal values specified must be one, i.e. referring to a scalar
458value, or must match the size of the vector type being created. If a single
459scalar literal value is specified, the scalar literal value will be replicated
460to all the components of the vector type. In the brackets form any number of
461literals can be specified. For example:</p>
462
463<blockquote>
464<pre>
465typedef int v4si __attribute__((__vector_size__(16)));
466typedef float float4 __attribute__((ext_vector_type(4)));
467typedef float float2 __attribute__((ext_vector_type(2)));
468
469v4si vsi = (v4si){1, 2, 3, 4};
470float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
471vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
472vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
473vector int vi3 = (vector int)(1, 2); // error
474vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
475vector int vi5 = (vector int)(1, 2, 3, 4);
476float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
477</pre>
478</blockquote>
479
480<!-- ======================================================================= -->
481<h3><a name="vector_operations">Vector Operations</a></h3>
482<!-- ======================================================================= -->
483
484<p>The table below shows the support for each operation by vector extension.
485A dash indicates that an operation is not accepted according to a corresponding
486specification.</p>
487
488<table width="500" border="1" cellspacing="0">
489 <tr>
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]490 <th>Operator</th>
491 <th>OpenCL</th>
492 <th>AltiVec</th>
493 <th>GCC</th>
494 <th>NEON</th>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]495 </tr>
496 <tr>
497 <td>[]</td>
498 <td align="center">yes</td>
499 <td align="center">yes</td>
500 <td align="center">yes</td>
501 <td align="center">-</td>
502 </tr>
503 <tr>
504 <td>unary operators +, -</td>
505 <td align="center">yes</td>
506 <td align="center">yes</td>
507 <td align="center">yes</td>
508 <td align="center">-</td>
509 </tr>
510 <tr>
511 <td>++, --</td>
512 <td align="center">yes</td>
513 <td align="center">yes</td>
514 <td align="center">-</td>
515 <td align="center">-</td>
516 </tr>
517 <tr>
518 <td>+, -, *, /, %</td>
519 <td align="center">yes</td>
520 <td align="center">yes</td>
521 <td align="center">yes</td>
522 <td align="center">-</td>
523 </tr>
524 <tr>
525 <td>bitwise operators &, |, ^, ~</td>
526 <td align="center">yes</td>
527 <td align="center">yes</td>
528 <td align="center">yes</td>
529 <td align="center">-</td>
530 </tr>
531 <tr>
532 <td>&gt&gt, &lt&lt</td>
533 <td align="center">yes</td>
534 <td align="center">yes</td>
535 <td align="center">yes</td>
536 <td align="center">-</td>
537 </tr>
538 <tr>
539 <td>!, &&,||</td>
540 <td align="center">no</td>
541 <td align="center">-</td>
542 <td align="center">-</td>
543 <td align="center">-</td>
544 </tr>
545 <tr>
546 <td>==,!=, >, <, >=, <=</td>
547 <td align="center">yes</td>
548 <td align="center">yes</td>
549 <td align="center">-</td>
550 <td align="center">-</td>
551 </tr>
552 <tr>
553 <td>=</td>
554 <td align="center">yes</td>
555 <td align="center">yes</td>
556 <td align="center">yes</td>
557 <td align="center">yes</td>
558 </tr>
559 <tr>
560 <td>:?</td>
561 <td align="center">yes</td>
562 <td align="center">-</td>
563 <td align="center">-</td>
564 <td align="center">-</td>
565 </tr>
566 <tr>
567 <td>sizeof</td>
568 <td align="center">yes</td>
569 <td align="center">yes</td>
570 <td align="center">yes</td>
571 <td align="center">yes</td>
572 </tr>
573</table>
574
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]575<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
576
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]577<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]578<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]579<!-- ======================================================================= -->
580
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]581<p>An optional string message can be added to the <tt>deprecated</tt>
582and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]583
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]584<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]585<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]586</blockquote>
587
588<p>If the deprecated or unavailable declaration is used, the message
589will be incorporated into the appropriate diagnostic:</p>
590
591<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]592<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! [-Wdeprecated-declarations]
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]593 explode();
594 ^</pre>
595</blockquote>
596
597<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]598with <tt>__has_extension(attribute_deprecated_with_message)</tt>
599and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]600
601<!-- ======================================================================= -->
602<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
603<!-- ======================================================================= -->
604
605<p>Clang allows attributes to be written on individual enumerators.
606This allows enumerators to be deprecated, made unavailable, etc. The
607attribute must appear after the enumerator name and before any
608initializer, like so:</p>
609
610<blockquote>
611<pre>enum OperationMode {
612 OM_Invalid,
613 OM_Normal,
614 OM_Terrified __attribute__((deprecated)),
615 OM_AbortOnError __attribute__((deprecated)) = 4
616};</pre>
617</blockquote>
618
619<p>Attributes on the <tt>enum</tt> declaration do not apply to
620individual enumerators.</p>
621
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]622<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]623
624<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]625<h2 id="checking_language_features">Checks for Standard Language Features</h2>
626<!-- ======================================================================= -->
627
628<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
629enabled. Those features are listed here.</p>
630
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]631<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]632
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]633<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For
Sean Hunt647ba1b2011-06-23 00:42:53 +0000[diff] [blame]634example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]635
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]636<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]637
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]638<p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example,
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]639compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]640
641<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]642<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
643<!-- ======================================================================= -->
644
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]645<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
646to query if certain upcoming standard language features are enabled. Those
647features are listed here. Features that are not yet implemented will be
648noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]649
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]650<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]651
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]652<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]653C++11 standard. As a result, all these features are enabled
654with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]655
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]656<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]657
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]658<p>Use <tt>__has_feature(cxx_access_control_sfinae)</tt> or <tt>__has_extension(cxx_access_control_sfinae)</tt> to determine whether access-control errors (e.g., calling a private constructor) are considered to be template argument deduction errors (aka SFINAE errors), per <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170">C++ DR1170</a>.</p>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]659
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]660<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]661
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]662<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
663<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]664C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]665
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]666<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]667
668<p>Use <tt>__has_feature(cxx_alignas)</tt> or
669<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
670specifiers using <tt>alignas</tt> is enabled.</p>
671
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]672<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]673
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]674<p>Use <tt>__has_feature(cxx_attributes)</tt> or
675<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]676parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]677
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]678<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]679
680<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
681for generalized constant expressions (e.g., <tt>constexpr</tt>) is
Richard Smithb5216aa2012-02-14 22:56:17 +0000[diff] [blame]682enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]683
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]684<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]685
686<p>Use <tt>__has_feature(cxx_decltype)</tt> or
687<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
688<tt>decltype()</tt> specifier is enabled.</p>
689
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]690<h4 id="cxx_default_function_template_args">C++11 default template arguments in function templates</h4>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]691
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]692<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
693<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
694if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]695
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]696<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
697
698<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
699<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
700defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
701
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]702<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]703
704<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
705support for delegating constructors is enabled.</p>
706
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]707<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]708
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]709<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
710<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]711deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]712
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]713<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]714<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
715
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]716<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]717
718<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
719support for generalized initializers (using braced lists and
Richard Smith88189552012-02-26 07:09:21 +0000[diff] [blame]720<tt>std::initializer_list</tt>) is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]721
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]722<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]723
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]724<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
725implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]726
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]727<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]728
729<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>
730
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]731<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]732
733<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
734<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
735inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]736
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]737<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]738
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]739<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
740<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregor46e021e2012-02-23 05:44:09 +0000[diff] [blame]741is enabled. </p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]742
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]743<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]744
745<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
746<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
747exception specifications is enabled.</p>
748
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]749<h4 id="cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]750
751<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]752
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]753<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]754
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]755<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
756<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]757<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]758
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]759<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]760
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]761<p>Use <tt>__has_feature(cxx_override_control)</tt> or
762<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]763the override control keywords is enabled.</p>
764
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]765<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]766<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
767<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
768if support for reference-qualified functions (e.g., member functions with
769<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
770is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]771
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]772<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]773
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]774<p>Use <tt>__has_feature(cxx_range_for)</tt> or
775<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
776range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]777
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]778<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Richard Smith80134582012-03-07 08:57:31 +0000[diff] [blame]779<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support
780for raw string literals (e.g., <tt>R"x(foo\bar)x"</tt>) is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]781
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]782<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]783
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]784<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
785<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]786rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]787
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]788<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]789
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]790<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
791<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]792compile-time assertions using <tt>static_assert</tt> is enabled.</p>
793
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]794<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]795
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]796<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]797<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]798supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
799will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]800
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]801<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]802
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]803<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
804<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
805strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]806
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]807<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]808
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]809<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
810<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
811alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]812
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]813<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]814<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
815support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]816
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]817<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]818
Richard Smithec92bc72012-03-03 23:51:05 +0000[diff] [blame]819<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]820
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]821<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]822
Richard Smith9c1dda72012-03-09 08:41:27 +0000[diff] [blame]823<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]824
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]825<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]826
827<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
828<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
829for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]830
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]831<h3 id="c11">C11</h3>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]832
833<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]834C11 standard. As a result, all these features are enabled
835with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]836
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]837<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]838
839<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
840to determine if support for alignment specifiers using <tt>_Alignas</tt>
841is enabled.</p>
842
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]843<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]844
845<p>Use <tt>__has_feature(c_generic_selections)</tt> or
846<tt>__has_extension(c_generic_selections)</tt> to determine if support for
847generic selections is enabled.</p>
848
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]849<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]850languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]851C11 standard.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]852
853<p>In C, type compatibility is decided according to the rules given in the
854appropriate standard, but in C++, which lacks the type compatibility rules
855used in C, types are considered compatible only if they are equivalent.</p>
856
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]857<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]858
859<p>Use <tt>__has_feature(c_static_assert)</tt> or
860<tt>__has_extension(c_static_assert)</tt> to determine if support for
861compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
862
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]863<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]864<h2 id="checking_type_traits">Checks for Type Traits</h2>
865<!-- ======================================================================= -->
866
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]867<p>Clang supports the <a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html">GNU C++ type traits</a> and a subset of the <a href="http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx">Microsoft Visual C++ Type traits</a>. For each supported type trait <code>__X</code>, <code>__has_extension(X)</code> indicates the presence of the type trait. For example:
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]868<blockquote>
869<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]870#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]871template&lt;typename From, typename To&gt;
872struct is_convertible_to {
873 static const bool value = __is_convertible_to(From, To);
874};
875#else
876// Emulate type trait
877#endif
878</pre>
879</blockquote>
880
881<p>The following type traits are supported by Clang:</p>
882<ul>
883 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
884 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
885 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
886 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
887 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
888 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
889 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
890 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
891 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
892 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
893 <li><code>__is_class</code> (GNU, Microsoft)</li>
894 <li><code>__is_convertible_to</code> (Microsoft)</li>
895 <li><code>__is_empty</code> (GNU, Microsoft)</li>
896 <li><code>__is_enum</code> (GNU, Microsoft)</li>
897 <li><code>__is_pod</code> (GNU, Microsoft)</li>
898 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
899 <li><code>__is_union</code> (GNU, Microsoft)</li>
900 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
Douglas Gregor5e9392b2011-12-03 18:14:24 +0000[diff] [blame]901 <li><code>__is_final</code>: Determines whether the given type is declared with a <code>final</code> class-virt-specifier.</li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]902 <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 Gregor4ca8ac22012-02-24 07:38:34 +0000[diff] [blame]903 <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>
904 <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 Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]905</ul>
906
907<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]908<h2 id="blocks">Blocks</h2>
909<!-- ======================================================================= -->
910
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]911<p>The syntax and high level language feature description is in <a
912href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
913details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]914href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]915
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]916
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]917<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]918
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]919<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]920<h2 id="objc_features">Objective-C Features</h2>
921<!-- ======================================================================= -->
922
923<h3 id="objc_instancetype">Related result types</h3>
924
925<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>
926
927<blockquote>
928<pre>
929@interface NSObject
930+ (id)alloc;
931- (id)init;
932@end
933
934@interface NSArray : NSObject
935@end
936</pre>
937</blockquote>
938
939<p>and this common initialization pattern</p>
940
941<blockquote>
942<pre>
943NSArray *array = [[NSArray alloc] init];
944</pre>
945</blockquote>
946
947<p>the type of the expression <code>[NSArray alloc]</code> is
948<code>NSArray*</code> because <code>alloc</code> implicitly has a
949related result type. Similarly, the type of the expression
950<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
951<code>init</code> has a related result type and its receiver is known
952to 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>
953
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]954<p>A method with a related result type can be declared by using the
955type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
956is a contextual keyword that is only permitted in the result type of
957an Objective-C method, e.g.</p>
958
959<pre>
960@interface A
961+ (<b>instancetype</b>)constructAnA;
962@end
963</pre>
964
965<p>The related result type can also be inferred for some methods.
966To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]967word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]968considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]969type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]970
971<ul>
972
973 <li>the first word is "alloc" or "new", and the method is a class
974 method, or</li>
975
976 <li>the first word is "autorelease", "init", "retain", or "self",
977 and the method is an instance method.</li>
978
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]979</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]980
981<p>If a method with a related result type is overridden by a subclass
982method, the subclass method must also return a type that is compatible
983with the subclass type. For example:</p>
984
985<blockquote>
986<pre>
987@interface NSString : NSObject
988- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
989@end
990</pre>
991</blockquote>
992
993<p>Related result types only affect the type of a message send or
994property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]995with a related result type is treated the same way as method that
996returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]997
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]998<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
999the <tt>instancetype</tt> contextual keyword is available.</p>
1000
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1001<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]1002<h2 id="objc_arc">Automatic reference counting </h2>
1003<!-- ======================================================================= -->
1004
1005<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>
1006
1007<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1008<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
1009<!-- ======================================================================= -->
1010
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1011<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1012underlying type within Objective-C. For example, one can write an
1013enumeration type as:</p>
1014
1015<pre>
1016typedef enum : unsigned char { Red, Green, Blue } Color;
1017</pre>
1018
1019<p>This specifies that the underlying type, which is used to store the
1020enumeration value, is <tt>unsigned char</tt>.</p>
1021
1022<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1023support for fixed underlying types is available in Objective-C.</p>
1024
1025<!-- ======================================================================= -->
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1026<h2 id="objc_lambdas">Interoperability with C++11 lambdas</h2>
1027<!-- ======================================================================= -->
1028
1029<p>Clang provides interoperability between C++11 lambdas and
1030blocks-based APIs, by permitting a lambda to be implicitly converted
1031to a block pointer with the corresponding signature. For example,
1032consider an API such as <code>NSArray</code>'s array-sorting
1033method:</p>
1034
1035<pre> - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; </pre>
1036
1037<p><code>NSComparator</code> is simply a typedef for the block pointer
1038<code>NSComparisonResult (^)(id, id)</code>, and parameters of this
1039type are generally provided with block literals as arguments. However,
1040one can also use a C++11 lambda so long as it provides the same
1041signature (in this case, accepting two parameters of type
1042<code>id</code> and returning an <code>NSComparisonResult</code>):</p>
1043
1044<pre>
1045 NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11",
1046 @"String 02"];
1047 const NSStringCompareOptions comparisonOptions
1048 = NSCaseInsensitiveSearch | NSNumericSearch |
1049 NSWidthInsensitiveSearch | NSForcedOrderingSearch;
1050 NSLocale *currentLocale = [NSLocale currentLocale];
1051 NSArray *sorted
1052 = [array sortedArrayUsingComparator:<b>[=](id s1, id s2) -&gt; NSComparisonResult {
1053 NSRange string1Range = NSMakeRange(0, [s1 length]);
1054 return [s1 compare:s2 options:comparisonOptions
1055 range:string1Range locale:currentLocale];
1056 }</b>];
1057 NSLog(@"sorted: %@", sorted);
1058</pre>
1059
1060<p>This code relies on an implicit conversion from the type of the
1061lambda expression (an unnamed, local class type called the <i>closure
1062type</i>) to the corresponding block pointer type. The conversion
1063itself is expressed by a conversion operator in that closure type
1064that produces a block pointer with the same signature as the lambda
1065itself, e.g.,</p>
1066
1067<pre>
1068 operator NSComparisonResult (^)(id, id)() const;
1069</pre>
1070
1071<p>This conversion function returns a new block that simply forwards
1072the two parameters to the lambda object (which it captures by copy),
1073then returns the result. The returned block is first copied (with
1074<tt>Block_copy</tt>) and then autoreleased. As an optimization, if a
1075lambda expression is immediately converted to a block pointer (as in
1076the first example, above), then the block is not copied and
1077autoreleased: rather, it is given the same lifetime as a block literal
1078written at that point in the program, which avoids the overhead of
1079copying a block to the heap in the common case.</p>
1080
Douglas Gregorbccda482012-03-10 22:20:11 +0000[diff] [blame^]1081<p>The conversion from a lambda to a block pointer is only available
1082in Objective-C++, and not in C++ with blocks, due to its use of
1083Objective-C memory management (autorelease).</p>
1084
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1085<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1086<h2 id="overloading-in-c">Function Overloading in C</h2>
1087<!-- ======================================================================= -->
1088
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1089<p>Clang provides support for C++ function overloading in C. Function
1090overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1091example, one might provide several overloaded versions of a <tt>tgsin</tt>
1092function that invokes the appropriate standard function computing the sine of a
1093value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1094precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1095
1096<blockquote>
1097<pre>
1098#include &lt;math.h&gt;
1099float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1100double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1101long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1102</pre>
1103</blockquote>
1104
1105<p>Given these declarations, one can call <tt>tgsin</tt> with a
1106<tt>float</tt> value to receive a <tt>float</tt> result, with a
1107<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1108overloading in C follows the rules of C++ function overloading to pick
1109the best overload given the call arguments, with a few C-specific
1110semantics:</p>
1111<ul>
1112 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1113 double</tt> is ranked as a floating-point promotion (per C99) rather
1114 than as a floating-point conversion (as in C++).</li>
1115
1116 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1117 <tt>U*</tt> is considered a pointer conversion (with conversion
1118 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1119
1120 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1121 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1122 conversion is given "conversion" rank.</li>
1123</ul>
1124
1125<p>The declaration of <tt>overloadable</tt> functions is restricted to
1126function declarations and definitions. Most importantly, if any
1127function with a given name is given the <tt>overloadable</tt>
1128attribute, then all function declarations and definitions with that
1129name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1130attribute. This rule even applies to redeclarations of functions whose original
1131declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1132
1133<blockquote>
1134<pre>
1135int f(int) __attribute__((overloadable));
1136float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1137
1138int g(int) __attribute__((overloadable));
1139int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1140</pre>
1141</blockquote>
1142
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1143<p>Functions marked <tt>overloadable</tt> must have
1144prototypes. Therefore, the following code is ill-formed:</p>
1145
1146<blockquote>
1147<pre>
1148int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1149</pre>
1150</blockquote>
1151
1152<p>However, <tt>overloadable</tt> functions are allowed to use a
1153ellipsis 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>
1154
1155<blockquote>
1156<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]1157void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1158</pre>
1159</blockquote>
1160
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1161<p>Functions declared with the <tt>overloadable</tt> attribute have
1162their names mangled according to the same rules as C++ function
1163names. For example, the three <tt>tgsin</tt> functions in our
1164motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]1165<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1166caveats to this use of name mangling:</p>
1167
1168<ul>
1169
1170 <li>Future versions of Clang may change the name mangling of
1171 functions overloaded in C, so you should not depend on an specific
1172 mangling. To be completely safe, we strongly urge the use of
1173 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1174
1175 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1176 used in C++, because names will already be mangled and functions are
1177 already overloadable. However, when an <tt>overloadable</tt>
1178 function occurs within an <tt>extern "C"</tt> linkage specification,
1179 it's name <i>will</i> be mangled in the same way as it would in
1180 C.</li>
1181</ul>
1182
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]1183<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1184
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]1185<!-- ======================================================================= -->
1186<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1187<!-- ======================================================================= -->
1188
1189<p>clang supports an extension which allows the following in C:</p>
1190
1191<blockquote>
1192<pre>
1193#include &lt;math.h&gt;
1194#include &lt;complex.h&gt;
1195complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1196</pre>
1197</blockquote>
1198
1199<p>This construct is useful because there is no way to separately
1200initialize the real and imaginary parts of a complex variable in
1201standard C, given that clang does not support <code>_Imaginary</code>.
1202(clang also supports the <code>__real__</code> and <code>__imag__</code>
1203extensions from gcc, which help in some cases, but are not usable in
1204static initializers.)
1205
1206<p>Note that this extension does not allow eliding the braces; the
1207meaning of the following two lines is different:</p>
1208
1209<blockquote>
1210<pre>
1211complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1212complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1213</pre>
1214</blockquote>
1215
1216<p>This extension also works in C++ mode, as far as that goes, but does not
1217 apply to the C++ <code>std::complex</code>. (In C++11, list
1218 initialization allows the same syntax to be used with
1219 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1220
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1221<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1222<h2 id="builtins">Builtin Functions</h2>
1223<!-- ======================================================================= -->
1224
1225<p>Clang supports a number of builtin library functions with the same syntax as
1226GCC, including things like <tt>__builtin_nan</tt>,
1227<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1228<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1229addition to the GCC builtins, Clang supports a number of builtins that GCC does
1230not, which are listed here.</p>
1231
1232<p>Please note that Clang does not and will not support all of the GCC builtins
1233for vector operations. Instead of using builtins, you should use the functions
1234defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1235define portable wrappers for these. Many of the Clang versions of these
1236functions are implemented directly in terms of <a href="#vectors">extended
1237vector support</a> instead of builtins, in order to reduce the number of
1238builtins that we need to implement.</p>
1239
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1240<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1241<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1242<!-- ======================================================================= -->
1243
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1244<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1245permutation/shuffle/swizzle operations. This builtin is also very important for
1246the implementation of various target-specific header files like
1247<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1248</p>
1249
1250<p><b>Syntax:</b></p>
1251
1252<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1253__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1254</pre>
1255
1256<p><b>Examples:</b></p>
1257
1258<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1259 // Identity operation - return 4-element vector V1.
1260 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1261
1262 // "Splat" element 0 of V1 into a 4-element result.
1263 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1264
1265 // Reverse 4-element vector V1.
1266 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1267
1268 // Concatenate every other element of 4-element vectors V1 and V2.
1269 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1270
1271 // Concatenate every other element of 8-element vectors V1 and V2.
1272 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1273</pre>
1274
1275<p><b>Description:</b></p>
1276
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1277<p>The first two arguments to __builtin_shufflevector are vectors that have the
1278same element type. The remaining arguments are a list of integers that specify
1279the elements indices of the first two vectors that should be extracted and
1280returned in a new vector. These element indices are numbered sequentially
1281starting with the first vector, continuing into the second vector. Thus, if
1282vec1 is a 4-element vector, index 5 would refer to the second element of vec2.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1283</p>
1284
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1285<p>The result of __builtin_shufflevector is a vector
1286with the same element type as vec1/vec2 but that has an element count equal to
1287the number of indices specified.
1288</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1289
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1290<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1291
1292<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1293<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1294<!-- ======================================================================= -->
1295
1296<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1297the program cannot be reached, even if the compiler might otherwise think it
1298can. This is useful to improve optimization and eliminates certain warnings.
1299For example, without the <tt>__builtin_unreachable</tt> in the example below,
1300the compiler assumes that the inline asm can fall through and prints a "function
1301declared 'noreturn' should not return" warning.
1302</p>
1303
1304<p><b>Syntax:</b></p>
1305
1306<pre>
1307__builtin_unreachable()
1308</pre>
1309
1310<p><b>Example of Use:</b></p>
1311
1312<pre>
1313void myabort(void) __attribute__((noreturn));
1314void myabort(void) {
1315 asm("int3");
1316 __builtin_unreachable();
1317}
1318</pre>
1319
1320<p><b>Description:</b></p>
1321
1322<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1323it has undefined behavior, it is a statement that it is never reached and the
1324optimizer can take advantage of this to produce better code. This builtin takes
1325no arguments and produces a void result.
1326</p>
1327
1328<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1329
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1330<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1331<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1332<!-- ======================================================================= -->
1333
1334<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1335memory.
1336</p>
1337
1338<p><b>Syntax:</b></p>
1339
1340<pre>
1341<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1342</pre>
1343
1344<p><b>Example of Use:</b></p>
1345
1346<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1347int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1348</pre>
1349
1350<p><b>Description:</b></p>
1351
1352<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1353intrinsics to allow code to atomically swap the current value with the new
1354value. More importantly, it helps developers write more efficient and correct
1355code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1356relying on the platform specific implementation details of
1357__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1358</p>
1359
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1360
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1361<!-- ======================================================================= -->
1362<h2 id="targetspecific">Target-Specific Extensions</h2>
1363<!-- ======================================================================= -->
1364
1365<p>Clang supports some language features conditionally on some targets.</p>
1366
1367<!-- ======================================================================= -->
1368<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1369<!-- ======================================================================= -->
1370
1371<p>The X86 backend has these language extensions:</p>
1372
1373<!-- ======================================================================= -->
1374<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1375<!-- ======================================================================= -->
1376
1377<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1378relative to the X86 GS segment register, and address space #257 causes it to be
1379relative to the X86 FS segment. Note that this is a very very low-level
1380feature that should only be used if you know what you're doing (for example in
1381an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1382
1383<p>Here is an example:</p>
1384
1385<pre>
1386#define GS_RELATIVE __attribute__((address_space(256)))
1387int foo(int GS_RELATIVE *P) {
1388 return *P;
1389}
1390</pre>
1391
1392<p>Which compiles to (on X86-32):</p>
1393
1394<pre>
1395_foo:
1396 movl 4(%esp), %eax
1397 movl %gs:(%eax), %eax
1398 ret
1399</pre>
1400
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1401<!-- ======================================================================= -->
1402<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1403<!-- ======================================================================= -->
1404
1405<p>Clang supports additional attributes that are useful for documenting program
1406invariants and rules for static analysis tools. The extensions documented here
1407are used by the <a
1408href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1409engine</a> that is part of Clang's Analysis library.</p>
1410
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1411<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1412
1413<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1414attribute. This attribute, which is typically affixed to a function prototype,
1415indicates that a call to a given function never returns. Function prototypes for
1416common functions like <tt>exit</tt> are typically annotated with this attribute,
1417as well as a variety of common assertion handlers. Users can educate the static
1418analyzer about their own custom assertion handles (thus cutting down on false
1419positives due to false paths) by marking their own &quot;panic&quot; functions
1420with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1421
1422<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1423there are special functions that for all intents and purposes should be
1424considered panic functions (i.e., they are only called when an internal program
1425error occurs) but may actually return so that the program can fail gracefully.
1426The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1427as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1428pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1429<tt>noreturn</tt>).</p>
1430
1431<p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1432same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1433placed at the end of function prototypes:</p>
1434
1435<pre>
1436 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1437</pre>
1438
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1439<p>Query for this feature with
1440<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1441
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1442<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1443
1444<p>Many methods in Objective-C have conventional meanings determined
1445by their selectors. For the purposes of static analysis, it is
1446sometimes useful to be able to mark a method as having a particular
1447conventional meaning despite not having the right selector, or as not
1448having the conventional meaning that its selector would suggest.
1449For these use cases, we provide an attribute to specifically describe
1450the <q>method family</q> that a method belongs to.</p>
1451
1452<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1453where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1454<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1455can only be placed at the end of a method declaration:</p>
1456
1457<pre>
1458 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1459</pre>
1460
1461<p>Users who do not wish to change the conventional meaning of a
1462method, and who merely want to document its non-standard retain and
1463release semantics, should use the
1464<a href="#attr_retain_release">retaining behavior attributes</a>
1465described below.</p>
1466
1467<p>Query for this feature with
1468<tt>__has_attribute(objc_method_family)</tt>.</p>
1469
1470<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1471
1472<p>In Objective-C, functions and methods are generally assumed to take
1473and return objects with +0 retain counts, with some exceptions for
1474special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1475there are exceptions, and so Clang provides attributes to allow these
1476exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1477ignore non-leaks). Some exceptions may be better described using
1478the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1479attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1480
1481<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1482<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1483and <tt>cf_returns_not_retained</tt> attributes can be placed on
1484methods and functions that return Objective-C or CoreFoundation
1485objects. They are commonly placed at the end of a function prototype
1486or method declaration:</p>
1487
1488<pre>
1489 id foo() <b>__attribute__((ns_returns_retained))</b>;
1490
1491 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1492</pre>
1493
1494<p>The <tt>*_returns_retained</tt> attributes specify that the
1495returned object has a +1 retain count.
1496The <tt>*_returns_not_retained</tt> attributes specify that the return
1497object has a +0 retain count, even if the normal convention for its
1498selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1499returned object is +0, but is guaranteed to live at least as long as the
1500next flush of an autorelease pool.</p>
1501
1502<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1503attributes can be placed on an parameter declaration; they specify
1504that the argument is expected to have a +1 retain count, which will be
1505balanced in some way by the function or method.
1506The <tt>ns_consumes_self</tt> attribute can only be placed on an
1507Objective-C method; it specifies that the method expects
1508its <tt>self</tt> parameter to have a +1 retain count, which it will
1509balance in some way.</p>
1510
1511<pre>
1512 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1513
1514 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1515 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1516</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1517
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1518<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1519<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1520
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1521<!-- ======================================================================= -->
1522<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1523<!-- ======================================================================= -->
1524<h3 id="address_sanitizer">AddressSanitizer</h3>
1525<p> Use <code>__has_feature(address_sanitizer)</code>
1526to check if the code is being built with <a
1527 href="AddressSanitizer.html">AddressSanitizer</a>.
1528</p>
Kostya Serebryany71efba02012-01-24 19:25:38 +0000[diff] [blame]1529<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function
1530declaration to specify that address safety instrumentation (e.g.
1531AddressSanitizer) should not be applied to that function.
1532</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1533
1534<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1535<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1536<!-- ======================================================================= -->
1537
1538<p>Clang supports additional attributes for checking basic locking policies in
1539multithreaded programs.
1540Clang currently parses the following list of attributes, although
1541<b>the implementation for these annotations is currently in development.</b>
1542For more details, see the
1543<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1544</p>
1545
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1546<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1547
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1548<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1549declaration to specify that the thread safety analysis should not be run on that
1550function. This attribute provides an escape hatch (e.g. for situations when it
1551is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1552
1553<h4 id="ts_lockable">lockable</h4>
1554
1555<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1556that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1557used to check consistency.</p>
1558
1559<h4 id="ts_scopedlockable">scoped_lockable</h4>
1560
1561<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1562specify that it has a "scoped" lockable type. Objects of this type will acquire
1563the lock upon construction and release it upon going out of scope.
1564 This annotation is primarily used to check
1565consistency.</p>
1566
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1567<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1568
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1569<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1570specify that the variable must be accessed while holding some lock.</p>
1571
1572<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1573
1574<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1575specify that the pointer must be dereferenced while holding some lock.</p>
1576
1577<h4 id="ts_guardedby">guarded_by(l)</h4>
1578
1579<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1580specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1581
1582<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1583
1584<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1585specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1586
1587<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1588
1589<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1590of a lockable variable to specify that the lock must be acquired before all
1591attribute arguments. Arguments must be lockable type, and there must be at
1592least one argument.</p>
1593
1594<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1595
1596<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1597of a lockable variable to specify that the lock must be acquired after all
1598attribute arguments. Arguments must be lockable type, and there must be at
1599least one argument.</p>
1600
1601<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1602
1603<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1604declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1605exclusively. This attribute takes zero or more arguments: either of lockable
1606type or integers indexing into function parameters of lockable type. If no
1607arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1608enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1609
1610<h4 id="ts_slf">shared_lock_function(...)</h4>
1611
1612<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1613declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1614 the locks may be shared (e.g. read locks). This attribute takes zero or more
1615arguments: either of lockable type or integers indexing into function
1616parameters of lockable type. If no arguments are given, the acquired lock is
1617implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1618
1619<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1620
1621<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1622declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1623all listed locks exclusively. This attribute takes one or more arguments. The
1624first argument is an integer or boolean value specifying the return value of a
1625successful lock acquisition. The remaining arugments are either of lockable type
1626or integers indexing into function parameters of lockable type. If only one
1627argument is given, the acquired lock is implicitly <tt>this</tt> of the
1628enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1629
1630<h4 id="ts_stf">shared_trylock_function(...)</h4>
1631
1632<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1633declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1634all listed locks, although the locks may be shared (e.g. read locks). This
1635attribute takes one or more arguments. The first argument is an integer or
1636boolean value specifying the return value of a successful lock acquisition. The
1637remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1638function parameters of lockable type. If only one argument is given, the
1639acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1640
1641<h4 id="ts_uf">unlock_function(...)</h4>
1642
1643<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1644declaration to specify that the function release all listed locks. This
1645attribute takes zero or more arguments: either of lockable type or integers
1646indexing into function parameters of lockable type. If no arguments are given,
1647the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1648
1649<h4 id="ts_lr">lock_returned(l)</h4>
1650
1651<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1652declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1653must be of lockable type). This annotation is used to aid in resolving lock
1654expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1655
1656<h4 id="ts_le">locks_excluded(...)</h4>
1657
1658<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1659to specify that the function must not be called with the listed locks. Arguments
1660must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1661
1662<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1663
1664<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1665declaration to specify that the function must be called while holding the listed
1666exclusive locks. Arguments must be lockable type, and there must be at
1667least one argument.</p>
1668
1669<h4 id="ts_slr">shared_locks_required(...)</h4>
1670
1671<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1672declaration to specify that the function must be called while holding the listed
1673shared locks. Arguments must be lockable type, and there must be at
1674least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1675
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1676</div>
1677</body>
1678</html>