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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>
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]33<li><a href="#availability">Availability attribute</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]34<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]35 <ul>
36 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
37 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]38 </ul></li>
39<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]40 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]41 <li><a href="#cxx0x">C++11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]42 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]43 <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes
44 access control</a></li>
45 <li><a href="#cxx_alias_templates">C++11 alias templates</a></li>
46 <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li>
47 <li><a href="#cxx_attributes">C++11 attributes</a></li>
48 <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li>
49 <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li>
50 <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]51 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]52 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
53 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
54 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
55 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
56 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
57 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
58 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
59 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
60 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
61 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
62 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
63 <li><a href="#cxx_override_control">C++11 override control</a></li>
64 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
65 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
66 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
67 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
68 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
69 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
70 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
71 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
72 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
73 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
74 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
75 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]76 </ul></li>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]77 <li><a href="#c11">C11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]78 <ul>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]79 <li><a href="#c_alignas">C11 alignment specifiers</a></li>
80 <li><a href="#c_generic_selections">C11 generic selections</a></li>
81 <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]82 </ul></li>
83 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]84<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]85<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]86<li><a href="#objc_features">Objective-C Features</a>
87 <ul>
88 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]89 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]90 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]91 <li><a href="#objc_lambdas">Interoperability with C++11 lambdas</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]92 </ul>
93</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]94<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]95<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]96<li><a href="#builtins">Builtin Functions</a>
97 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]98 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]99 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]100 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]101 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]102</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]103<li><a href="#targetspecific">Target-Specific Extensions</a>
104 <ul>
105 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
106 </ul>
107</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]108<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]109<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]110 <ul>
111 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
112 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]113</li>
114<li><a href="#threadsafety">Thread Safety Annotation Checking</a>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]115 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]116 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
117 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
118 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]119 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
120 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]121 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
122 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
123 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
124 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
125 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
126 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
127 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
128 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
129 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
130 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
131 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
132 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
133 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]134 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]135</li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]136</ul>
137
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]138<!-- ======================================================================= -->
139<h2 id="intro">Introduction</h2>
140<!-- ======================================================================= -->
141
142<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]143addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]144range of GCC extensions. Please see the <a
145href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
146more information on these extensions.</p>
147
148<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]149<h2 id="feature_check">Feature Checking Macros</h2>
150<!-- ======================================================================= -->
151
152<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]153on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]154function-like macros. This allows you to directly test for a feature in your
155code without having to resort to something like autoconf or fragile "compiler
156version checks".</p>
157
158<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]159<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]160<!-- ======================================================================= -->
161
162<p>This function-like macro takes a single identifier argument that is the name
163of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
164not. It can be used like this:</p>
165
166<blockquote>
167<pre>
168#ifndef __has_builtin // Optional of course.
169 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
170#endif
171
172...
173#if __has_builtin(__builtin_trap)
174 __builtin_trap();
175#else
176 abort();
177#endif
178...
179</pre>
180</blockquote>
181
182
183<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]184<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]185<!-- ======================================================================= -->
186
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]187<p>These function-like macros take a single identifier argument that is the
188name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
189is both supported by Clang and standardized in the current language standard
190or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
191<code>__has_extension</code> evaluates to 1 if the feature is supported by
192Clang in the current language (either as a language extension or a standard
193language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]194
195<blockquote>
196<pre>
197#ifndef __has_feature // Optional of course.
198 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
199#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]200#ifndef __has_extension
201 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
202#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]203
204...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]205#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]206// This code will only be compiled with the -std=c++11 and -std=gnu++11
207// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]208#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]209
210#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]211// 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]212// and -std=gnu++98 options, because rvalue references are supported as a
213// language extension in C++98.
214#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]215</pre>
216</blockquote>
217
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]218<p id="has_feature_back_compat">For backwards compatibility reasons,
219<code>__has_feature</code> can also be used to test for support for
220non-standardized features, i.e. features not prefixed <code>c_</code>,
221<code>cxx_</code> or <code>objc_</code>.</p>
222
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]223<p id="has_feature_for_non_language_features">
224Another use of <code>__has_feature</code> is to check for compiler features
225not related to the language standard, such as e.g.
226<a href="AddressSanitizer.html">AddressSanitizer</a>.
227
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]228<p>If the <code>-pedantic-errors</code> option is given,
229<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
230
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]231<p>The feature tag is described along with the language feature below.</p>
232
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]233<p>The feature name or extension name can also be specified with a preceding and
234following <code>__</code> (double underscore) to avoid interference from a macro
Richard Smith1d9f4c12012-03-01 02:12:07 +0000[diff] [blame]235with the same name. For instance, <code>__cxx_rvalue_references__</code> can be
236used instead of <code>cxx_rvalue_references</code>.</p>
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]237
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]238<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]239<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]240<!-- ======================================================================= -->
241
242<p>This function-like macro takes a single identifier argument that is the name
243of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
244can be used like this:</p>
245
246<blockquote>
247<pre>
248#ifndef __has_attribute // Optional of course.
249 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
250#endif
251
252...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]253#if __has_attribute(always_inline)
254#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]255#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]256#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]257#endif
258...
259</pre>
260</blockquote>
261
Jean-Daniel Dupas8a5e7fd2012-03-01 14:53:16 +0000[diff] [blame]262<p>The attribute name can also be specified with a preceding and
263following <code>__</code> (double underscore) to avoid interference from a macro
264with the same name. For instance, <code>__always_inline__</code> can be used
265instead of <code>always_inline</code>.</p>
266
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]267<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]268<h2 id="has_include">Include File Checking Macros</h2>
269<!-- ======================================================================= -->
270
271<p>Not all developments systems have the same include files.
272The <a href="#__has_include">__has_include</a> and
273<a href="#__has_include_next">__has_include_next</a> macros allow you to
274check for the existence of an include file before doing
275a possibly failing #include directive.</p>
276
277<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]278<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]279<!-- ======================================================================= -->
280
281<p>This function-like macro takes a single file name string argument that
282is the name of an include file. It evaluates to 1 if the file can
283be found using the include paths, or 0 otherwise:</p>
284
285<blockquote>
286<pre>
287// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]288#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]289# include "myinclude.h"
290#endif
291
292// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]293#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]294# include "myinclude.h"
295#endif
296</pre>
297</blockquote>
298
299<p>To test for this feature, use #if defined(__has_include).</p>
300
301<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]302<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]303<!-- ======================================================================= -->
304
305<p>This function-like macro takes a single file name string argument that
306is the name of an include file. It is like __has_include except that it
307looks for the second instance of the given file found in the include
308paths. It evaluates to 1 if the second instance of the file can
309be found using the include paths, or 0 otherwise:</p>
310
311<blockquote>
312<pre>
313// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]314#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]315# include_next "myinclude.h"
316#endif
317
318// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]319#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]320# include_next "myinclude.h"
321#endif
322</pre>
323</blockquote>
324
325<p>Note that __has_include_next, like the GNU extension
326#include_next directive, is intended for use in headers only,
327and will issue a warning if used in the top-level compilation
328file. A warning will also be issued if an absolute path
329is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]330
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]331
332<!-- ======================================================================= -->
333<h3><a name="__has_warning">__has_warning</a></h3>
334<!-- ======================================================================= -->
335
336<p>This function-like macro takes a string literal that represents a command
337 line option for a warning and returns true if that is a valid warning
338 option.</p>
339
340<blockquote>
341<pre>
342#if __has_warning("-Wformat")
343...
344#endif
345</pre>
346</blockquote>
347
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]348<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]349<h2 id="builtinmacros">Builtin Macros</h2>
350<!-- ======================================================================= -->
351
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]352<dl>
353 <dt><code>__BASE_FILE__</code></dt>
354 <dd>Defined to a string that contains the name of the main input
355 file passed to Clang.</dd>
356
357 <dt><code>__COUNTER__</code></dt>
358 <dd>Defined to an integer value that starts at zero and is
359 incremented each time the <code>__COUNTER__</code> macro is
360 expanded.</dd>
361
362 <dt><code>__INCLUDE_LEVEL__</code></dt>
363 <dd>Defined to an integral value that is the include depth of the
364 file currently being translated. For the main file, this value is
365 zero.</dd>
366
367 <dt><code>__TIMESTAMP__</code></dt>
368 <dd>Defined to the date and time of the last modification of the
369 current source file.</dd>
370
371 <dt><code>__clang__</code></dt>
372 <dd>Defined when compiling with Clang</dd>
373
374 <dt><code>__clang_major__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]375 <dd>Defined to the major marketing version number of Clang (e.g., the
376 2 in 2.0.1). Note that marketing version numbers should not be used to
377 check for language features, as different vendors use different numbering
378 schemes. Instead, use the <a href="#feature_check">feature checking
379 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]380
381 <dt><code>__clang_minor__</code></dt>
382 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]383 2.0.1). Note that marketing version numbers should not be used to
384 check for language features, as different vendors use different numbering
385 schemes. Instead, use the <a href="#feature_check">feature checking
386 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]387
388 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]389 <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]390
391 <dt><code>__clang_version__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]392 <dd>Defined to a string that captures the Clang marketing version, including
393 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]394</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]395
396<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]397<h2 id="vectors">Vectors and Extended Vectors</h2>
398<!-- ======================================================================= -->
399
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]400<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]401
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]402<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
403support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An
404example is:</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]405
406<blockquote>
407<pre>
408typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
409typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
410
411float4 foo(float2 a, float2 b) {
412 float4 c;
413 c.xz = a;
414 c.yw = b;
415 return c;
416}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]417</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]418</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]419
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]420<p>Query for this feature with
421<tt>__has_extension(attribute_ext_vector_type)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]422
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]423<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector
424syntax and functions. For example:</p>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]425
426<blockquote>
427<pre>
428vector float foo(vector int a) {
429 vector int b;
430 b = vec_add(a, a) + a;
431 return (vector float)b;
432}
433</pre>
434</blockquote>
435
436<p>NEON vector types are created using <tt>neon_vector_type</tt> and
437<tt>neon_polyvector_type</tt> attributes. For example:</p>
438
439<blockquote>
440<pre>
441typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
442typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
443
444int8x8_t foo(int8x8_t a) {
445 int8x8_t v;
446 v = a;
447 return v;
448}
449</pre>
450</blockquote>
451
452<!-- ======================================================================= -->
453<h3><a name="vector_literals">Vector Literals</a></h3>
454<!-- ======================================================================= -->
455
456<p>Vector literals can be used to create vectors from a set of scalars, or
457vectors. Either parentheses or braces form can be used. In the parentheses form
458the number of literal values specified must be one, i.e. referring to a scalar
459value, or must match the size of the vector type being created. If a single
460scalar literal value is specified, the scalar literal value will be replicated
461to all the components of the vector type. In the brackets form any number of
462literals can be specified. For example:</p>
463
464<blockquote>
465<pre>
466typedef int v4si __attribute__((__vector_size__(16)));
467typedef float float4 __attribute__((ext_vector_type(4)));
468typedef float float2 __attribute__((ext_vector_type(2)));
469
470v4si vsi = (v4si){1, 2, 3, 4};
471float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
472vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
473vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
474vector int vi3 = (vector int)(1, 2); // error
475vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
476vector int vi5 = (vector int)(1, 2, 3, 4);
477float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
478</pre>
479</blockquote>
480
481<!-- ======================================================================= -->
482<h3><a name="vector_operations">Vector Operations</a></h3>
483<!-- ======================================================================= -->
484
485<p>The table below shows the support for each operation by vector extension.
486A dash indicates that an operation is not accepted according to a corresponding
487specification.</p>
488
489<table width="500" border="1" cellspacing="0">
490 <tr>
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]491 <th>Operator</th>
492 <th>OpenCL</th>
493 <th>AltiVec</th>
494 <th>GCC</th>
495 <th>NEON</th>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]496 </tr>
497 <tr>
498 <td>[]</td>
499 <td align="center">yes</td>
500 <td align="center">yes</td>
501 <td align="center">yes</td>
502 <td align="center">-</td>
503 </tr>
504 <tr>
505 <td>unary operators +, -</td>
506 <td align="center">yes</td>
507 <td align="center">yes</td>
508 <td align="center">yes</td>
509 <td align="center">-</td>
510 </tr>
511 <tr>
512 <td>++, --</td>
513 <td align="center">yes</td>
514 <td align="center">yes</td>
515 <td align="center">-</td>
516 <td align="center">-</td>
517 </tr>
518 <tr>
519 <td>+, -, *, /, %</td>
520 <td align="center">yes</td>
521 <td align="center">yes</td>
522 <td align="center">yes</td>
523 <td align="center">-</td>
524 </tr>
525 <tr>
526 <td>bitwise operators &, |, ^, ~</td>
527 <td align="center">yes</td>
528 <td align="center">yes</td>
529 <td align="center">yes</td>
530 <td align="center">-</td>
531 </tr>
532 <tr>
533 <td>&gt&gt, &lt&lt</td>
534 <td align="center">yes</td>
535 <td align="center">yes</td>
536 <td align="center">yes</td>
537 <td align="center">-</td>
538 </tr>
539 <tr>
540 <td>!, &&,||</td>
541 <td align="center">no</td>
542 <td align="center">-</td>
543 <td align="center">-</td>
544 <td align="center">-</td>
545 </tr>
546 <tr>
547 <td>==,!=, >, <, >=, <=</td>
548 <td align="center">yes</td>
549 <td align="center">yes</td>
550 <td align="center">-</td>
551 <td align="center">-</td>
552 </tr>
553 <tr>
554 <td>=</td>
555 <td align="center">yes</td>
556 <td align="center">yes</td>
557 <td align="center">yes</td>
558 <td align="center">yes</td>
559 </tr>
560 <tr>
561 <td>:?</td>
562 <td align="center">yes</td>
563 <td align="center">-</td>
564 <td align="center">-</td>
565 <td align="center">-</td>
566 </tr>
567 <tr>
568 <td>sizeof</td>
569 <td align="center">yes</td>
570 <td align="center">yes</td>
571 <td align="center">yes</td>
572 <td align="center">yes</td>
573 </tr>
574</table>
575
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]576<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
577
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]578<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]579<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]580<!-- ======================================================================= -->
581
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]582<p>An optional string message can be added to the <tt>deprecated</tt>
583and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]584
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]585<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]586<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]587</blockquote>
588
589<p>If the deprecated or unavailable declaration is used, the message
590will be incorporated into the appropriate diagnostic:</p>
591
592<blockquote>
Benjamin Kramerb4556862012-03-19 19:12:30 +0000[diff] [blame^]593<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!!
594 [-Wdeprecated-declarations]
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]595 explode();
596 ^</pre>
597</blockquote>
598
599<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]600with <tt>__has_extension(attribute_deprecated_with_message)</tt>
601and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]602
603<!-- ======================================================================= -->
604<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
605<!-- ======================================================================= -->
606
607<p>Clang allows attributes to be written on individual enumerators.
608This allows enumerators to be deprecated, made unavailable, etc. The
609attribute must appear after the enumerator name and before any
610initializer, like so:</p>
611
612<blockquote>
613<pre>enum OperationMode {
614 OM_Invalid,
615 OM_Normal,
616 OM_Terrified __attribute__((deprecated)),
617 OM_AbortOnError __attribute__((deprecated)) = 4
618};</pre>
619</blockquote>
620
621<p>Attributes on the <tt>enum</tt> declaration do not apply to
622individual enumerators.</p>
623
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]624<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]625
626<!-- ======================================================================= -->
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]627<h2 id="availability">Availability attribute</h2
628<!-- ======================================================================= -->
629
630<p>Clang introduces the <code>availability</code> attribute, which can
631be placed on declarations to describe the lifecycle of that
632declaration relative to operating system versions. Consider the function declaration for a hypothetical function <code>f</code>:</p>
633
634<pre>
635void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7)));
636</pre>
637
638<p>The availability attribute states that <code>f</code> was introduced in Mac OS X 10.4, deprecated in Mac OS X 10.6, and obsoleted in Mac OS X 10.7. This information is used by Clang to determine when it is safe to use <code>f</code>: for example, if Clang is instructed to compile code for Mac OS X 10.5, a call to <code>f()</code> succeeds. If Clang is instructed to compile code for Mac OS X 10.6, the call succeeds but Clang emits a warning specifying that the function is deprecated. Finally, if Clang is instructed to compile code for Mac OS X 10.7, the call fails because <code>f()</code> is no longer available.</p>
639
640<p>The availablility attribute is a comma-separated list starting with the platform name and then including clauses specifying important milestones in the declaration's lifetime (in any order) along with additional information. Those clauses can be:</p>
641
642<dl>
643 <dt>introduced=<i>version</i></dt>
644 <dd>The first version in which this declaration was introduced.</dd>
645
646 <dt>deprecated=<i>version</i></dt>
647 <dd>The first version in which this declaration was deprecated, meaning that users should migrate away from this API.</dd>
648
649 <dt>obsoleted=<i>version</i></dt>
650 <dd>The first version in which this declaration was obsoleted, meaning that it was removed completely and can no longer be used.</dd>
651
652 <dt>unavailable</dt>
653 <dd>This declaration is never available on this platform.</dd>
654
655 <dt>message=<i>string-literal</i></dt>
656 <dd>Additional message text that Clang will provide when emitting a warning or error about use of a deprecated or obsoleted declaration. Useful to direct users to replacement APIs.</dd>
657</dl>
658
659<p>Multiple availability attributes can be placed on a declaration, which may correspond to different platforms. Only the availability attribute with the platform corresponding to the target platform will be used; any others will be ignored. If no availability attribute specifies availability for the current target platform, the availability attributes are ignored. Supported platforms are:</p>
660
661<dl>
662 <dt>ios</dt>
663 <dd>Apple's iOS operating system. The minimum deployment target is specified by the <code>-mios-version-min=<i>version</i></code> or <code>-miphoneos-version-min=<i>version</i></code> command-line arguments.</dd>
664
665 <dt>macosx</dt>
666 <dd>Apple's Mac OS X operating system. The minimum deployment target is specified by the <code>-mmacosx-version-min=<i>version</i></code> command-line argument.</dd>
667</dl>
668
Douglas Gregor594f8412012-03-11 17:21:03 +0000[diff] [blame]669<p>A declaration can be used even when deploying back to a platform
670version prior to when the declaration was introduced. When this
671happens, the declaration is <a
672 href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly
673linked</a>, as if the <code>weak_import</code> attribute were added to the declaration. A weakly-linked declaration may or may not be present a run-time, and a program can determine whether the declaration is present by checking whether the address of that declaration is non-NULL.</p>
674
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]675<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]676<h2 id="checking_language_features">Checks for Standard Language Features</h2>
677<!-- ======================================================================= -->
678
679<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
680enabled. Those features are listed here.</p>
681
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]682<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]683
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]684<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]685example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]686
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]687<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]688
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]689<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]690compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]691
692<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]693<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
694<!-- ======================================================================= -->
695
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]696<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
697to query if certain upcoming standard language features are enabled. Those
698features are listed here. Features that are not yet implemented will be
699noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]700
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]701<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]702
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]703<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]704C++11 standard. As a result, all these features are enabled
705with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]706
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]707<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]708
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]709<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]710
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]711<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]712
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]713<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
714<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]715C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]716
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]717<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]718
719<p>Use <tt>__has_feature(cxx_alignas)</tt> or
720<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
721specifiers using <tt>alignas</tt> is enabled.</p>
722
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]723<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]724
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]725<p>Use <tt>__has_feature(cxx_attributes)</tt> or
726<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]727parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]728
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]729<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]730
731<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
732for generalized constant expressions (e.g., <tt>constexpr</tt>) is
Richard Smithb5216aa2012-02-14 22:56:17 +0000[diff] [blame]733enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]734
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]735<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]736
737<p>Use <tt>__has_feature(cxx_decltype)</tt> or
738<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
739<tt>decltype()</tt> specifier is enabled.</p>
740
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]741<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]742
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]743<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
744<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
745if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]746
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]747<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
748
749<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
750<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
751defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
752
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]753<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]754
755<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
756support for delegating constructors is enabled.</p>
757
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]758<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]759
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]760<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
761<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]762deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]763
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]764<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]765<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
766
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]767<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]768
769<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
770support for generalized initializers (using braced lists and
Richard Smith88189552012-02-26 07:09:21 +0000[diff] [blame]771<tt>std::initializer_list</tt>) is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]772
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]773<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]774
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]775<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
776implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]777
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]778<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]779
780<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>
781
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]782<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]783
784<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
785<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
786inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]787
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]788<h4 id="cxx_lambdas">C++11 lambdas</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_lambdas)</tt> or
791<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregor46e021e2012-02-23 05:44:09 +0000[diff] [blame]792is enabled. </p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]793
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]794<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]795
796<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
797<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
798exception specifications is enabled.</p>
799
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]800<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]801
802<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]803
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]804<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]805
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]806<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
807<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]808<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]809
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]810<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]811
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]812<p>Use <tt>__has_feature(cxx_override_control)</tt> or
813<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]814the override control keywords is enabled.</p>
815
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]816<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]817<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
818<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
819if support for reference-qualified functions (e.g., member functions with
820<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
821is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]822
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]823<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]824
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]825<p>Use <tt>__has_feature(cxx_range_for)</tt> or
826<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
827range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]828
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]829<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Richard Smith80134582012-03-07 08:57:31 +0000[diff] [blame]830<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support
831for 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]832
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]833<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]834
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]835<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
836<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]837rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]838
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]839<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]840
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]841<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
842<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]843compile-time assertions using <tt>static_assert</tt> is enabled.</p>
844
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]845<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]846
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]847<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]848<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]849supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
850will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]851
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]852<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]853
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]854<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
855<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
856strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]857
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]858<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]859
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]860<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
861<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
862alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]863
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]864<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]865<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
866support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]867
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]868<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]869
Richard Smithec92bc72012-03-03 23:51:05 +0000[diff] [blame]870<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]871
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]872<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]873
Richard Smith9c1dda72012-03-09 08:41:27 +0000[diff] [blame]874<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]875
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]876<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]877
878<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
879<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
880for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]881
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]882<h3 id="c11">C11</h3>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]883
884<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]885C11 standard. As a result, all these features are enabled
886with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]887
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]888<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]889
890<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
891to determine if support for alignment specifiers using <tt>_Alignas</tt>
892is enabled.</p>
893
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]894<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]895
896<p>Use <tt>__has_feature(c_generic_selections)</tt> or
897<tt>__has_extension(c_generic_selections)</tt> to determine if support for
898generic selections is enabled.</p>
899
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]900<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]901languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]902C11 standard.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]903
904<p>In C, type compatibility is decided according to the rules given in the
905appropriate standard, but in C++, which lacks the type compatibility rules
906used in C, types are considered compatible only if they are equivalent.</p>
907
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]908<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]909
910<p>Use <tt>__has_feature(c_static_assert)</tt> or
911<tt>__has_extension(c_static_assert)</tt> to determine if support for
912compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
913
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]914<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]915<h2 id="checking_type_traits">Checks for Type Traits</h2>
916<!-- ======================================================================= -->
917
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]918<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]919<blockquote>
920<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]921#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]922template&lt;typename From, typename To&gt;
923struct is_convertible_to {
924 static const bool value = __is_convertible_to(From, To);
925};
926#else
927// Emulate type trait
928#endif
929</pre>
930</blockquote>
931
932<p>The following type traits are supported by Clang:</p>
933<ul>
934 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
935 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
936 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
937 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
938 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
939 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
940 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
941 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
942 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
943 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
944 <li><code>__is_class</code> (GNU, Microsoft)</li>
945 <li><code>__is_convertible_to</code> (Microsoft)</li>
946 <li><code>__is_empty</code> (GNU, Microsoft)</li>
947 <li><code>__is_enum</code> (GNU, Microsoft)</li>
948 <li><code>__is_pod</code> (GNU, Microsoft)</li>
949 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
950 <li><code>__is_union</code> (GNU, Microsoft)</li>
951 <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]952 <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]953 <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]954 <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>
955 <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]956</ul>
957
958<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]959<h2 id="blocks">Blocks</h2>
960<!-- ======================================================================= -->
961
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]962<p>The syntax and high level language feature description is in <a
963href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
964details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]965href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]966
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]967
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]968<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]969
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]970<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]971<h2 id="objc_features">Objective-C Features</h2>
972<!-- ======================================================================= -->
973
974<h3 id="objc_instancetype">Related result types</h3>
975
976<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>
977
978<blockquote>
979<pre>
980@interface NSObject
981+ (id)alloc;
982- (id)init;
983@end
984
985@interface NSArray : NSObject
986@end
987</pre>
988</blockquote>
989
990<p>and this common initialization pattern</p>
991
992<blockquote>
993<pre>
994NSArray *array = [[NSArray alloc] init];
995</pre>
996</blockquote>
997
998<p>the type of the expression <code>[NSArray alloc]</code> is
999<code>NSArray*</code> because <code>alloc</code> implicitly has a
1000related result type. Similarly, the type of the expression
1001<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
1002<code>init</code> has a related result type and its receiver is known
1003to 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>
1004
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]1005<p>A method with a related result type can be declared by using the
1006type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
1007is a contextual keyword that is only permitted in the result type of
1008an Objective-C method, e.g.</p>
1009
1010<pre>
1011@interface A
1012+ (<b>instancetype</b>)constructAnA;
1013@end
1014</pre>
1015
1016<p>The related result type can also be inferred for some methods.
1017To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1018word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]1019considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1020type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1021
1022<ul>
1023
1024 <li>the first word is "alloc" or "new", and the method is a class
1025 method, or</li>
1026
1027 <li>the first word is "autorelease", "init", "retain", or "self",
1028 and the method is an instance method.</li>
1029
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1030</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1031
1032<p>If a method with a related result type is overridden by a subclass
1033method, the subclass method must also return a type that is compatible
1034with the subclass type. For example:</p>
1035
1036<blockquote>
1037<pre>
1038@interface NSString : NSObject
1039- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
1040@end
1041</pre>
1042</blockquote>
1043
1044<p>Related result types only affect the type of a message send or
1045property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]1046with a related result type is treated the same way as method that
1047returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1048
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]1049<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
1050the <tt>instancetype</tt> contextual keyword is available.</p>
1051
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1052<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]1053<h2 id="objc_arc">Automatic reference counting </h2>
1054<!-- ======================================================================= -->
1055
1056<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>
1057
1058<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1059<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
1060<!-- ======================================================================= -->
1061
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1062<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1063underlying type within Objective-C. For example, one can write an
1064enumeration type as:</p>
1065
1066<pre>
1067typedef enum : unsigned char { Red, Green, Blue } Color;
1068</pre>
1069
1070<p>This specifies that the underlying type, which is used to store the
1071enumeration value, is <tt>unsigned char</tt>.</p>
1072
1073<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1074support for fixed underlying types is available in Objective-C.</p>
1075
1076<!-- ======================================================================= -->
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1077<h2 id="objc_lambdas">Interoperability with C++11 lambdas</h2>
1078<!-- ======================================================================= -->
1079
1080<p>Clang provides interoperability between C++11 lambdas and
1081blocks-based APIs, by permitting a lambda to be implicitly converted
1082to a block pointer with the corresponding signature. For example,
1083consider an API such as <code>NSArray</code>'s array-sorting
1084method:</p>
1085
1086<pre> - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; </pre>
1087
1088<p><code>NSComparator</code> is simply a typedef for the block pointer
1089<code>NSComparisonResult (^)(id, id)</code>, and parameters of this
1090type are generally provided with block literals as arguments. However,
1091one can also use a C++11 lambda so long as it provides the same
1092signature (in this case, accepting two parameters of type
1093<code>id</code> and returning an <code>NSComparisonResult</code>):</p>
1094
1095<pre>
1096 NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11",
1097 @"String 02"];
1098 const NSStringCompareOptions comparisonOptions
1099 = NSCaseInsensitiveSearch | NSNumericSearch |
1100 NSWidthInsensitiveSearch | NSForcedOrderingSearch;
1101 NSLocale *currentLocale = [NSLocale currentLocale];
1102 NSArray *sorted
1103 = [array sortedArrayUsingComparator:<b>[=](id s1, id s2) -&gt; NSComparisonResult {
1104 NSRange string1Range = NSMakeRange(0, [s1 length]);
1105 return [s1 compare:s2 options:comparisonOptions
1106 range:string1Range locale:currentLocale];
1107 }</b>];
1108 NSLog(@"sorted: %@", sorted);
1109</pre>
1110
1111<p>This code relies on an implicit conversion from the type of the
1112lambda expression (an unnamed, local class type called the <i>closure
1113type</i>) to the corresponding block pointer type. The conversion
1114itself is expressed by a conversion operator in that closure type
1115that produces a block pointer with the same signature as the lambda
1116itself, e.g.,</p>
1117
1118<pre>
1119 operator NSComparisonResult (^)(id, id)() const;
1120</pre>
1121
1122<p>This conversion function returns a new block that simply forwards
1123the two parameters to the lambda object (which it captures by copy),
1124then returns the result. The returned block is first copied (with
1125<tt>Block_copy</tt>) and then autoreleased. As an optimization, if a
1126lambda expression is immediately converted to a block pointer (as in
1127the first example, above), then the block is not copied and
1128autoreleased: rather, it is given the same lifetime as a block literal
1129written at that point in the program, which avoids the overhead of
1130copying a block to the heap in the common case.</p>
1131
Douglas Gregorbccda482012-03-10 22:20:11 +0000[diff] [blame]1132<p>The conversion from a lambda to a block pointer is only available
1133in Objective-C++, and not in C++ with blocks, due to its use of
1134Objective-C memory management (autorelease).</p>
1135
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1136<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1137<h2 id="overloading-in-c">Function Overloading in C</h2>
1138<!-- ======================================================================= -->
1139
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1140<p>Clang provides support for C++ function overloading in C. Function
1141overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1142example, one might provide several overloaded versions of a <tt>tgsin</tt>
1143function that invokes the appropriate standard function computing the sine of a
1144value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1145precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1146
1147<blockquote>
1148<pre>
1149#include &lt;math.h&gt;
1150float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1151double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1152long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1153</pre>
1154</blockquote>
1155
1156<p>Given these declarations, one can call <tt>tgsin</tt> with a
1157<tt>float</tt> value to receive a <tt>float</tt> result, with a
1158<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1159overloading in C follows the rules of C++ function overloading to pick
1160the best overload given the call arguments, with a few C-specific
1161semantics:</p>
1162<ul>
1163 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1164 double</tt> is ranked as a floating-point promotion (per C99) rather
1165 than as a floating-point conversion (as in C++).</li>
1166
1167 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1168 <tt>U*</tt> is considered a pointer conversion (with conversion
1169 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1170
1171 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1172 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1173 conversion is given "conversion" rank.</li>
1174</ul>
1175
1176<p>The declaration of <tt>overloadable</tt> functions is restricted to
1177function declarations and definitions. Most importantly, if any
1178function with a given name is given the <tt>overloadable</tt>
1179attribute, then all function declarations and definitions with that
1180name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1181attribute. This rule even applies to redeclarations of functions whose original
1182declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1183
1184<blockquote>
1185<pre>
1186int f(int) __attribute__((overloadable));
1187float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1188
1189int g(int) __attribute__((overloadable));
1190int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1191</pre>
1192</blockquote>
1193
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1194<p>Functions marked <tt>overloadable</tt> must have
1195prototypes. Therefore, the following code is ill-formed:</p>
1196
1197<blockquote>
1198<pre>
1199int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1200</pre>
1201</blockquote>
1202
1203<p>However, <tt>overloadable</tt> functions are allowed to use a
1204ellipsis 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>
1205
1206<blockquote>
1207<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]1208void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1209</pre>
1210</blockquote>
1211
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1212<p>Functions declared with the <tt>overloadable</tt> attribute have
1213their names mangled according to the same rules as C++ function
1214names. For example, the three <tt>tgsin</tt> functions in our
1215motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]1216<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1217caveats to this use of name mangling:</p>
1218
1219<ul>
1220
1221 <li>Future versions of Clang may change the name mangling of
1222 functions overloaded in C, so you should not depend on an specific
1223 mangling. To be completely safe, we strongly urge the use of
1224 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1225
1226 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1227 used in C++, because names will already be mangled and functions are
1228 already overloadable. However, when an <tt>overloadable</tt>
1229 function occurs within an <tt>extern "C"</tt> linkage specification,
1230 it's name <i>will</i> be mangled in the same way as it would in
1231 C.</li>
1232</ul>
1233
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]1234<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1235
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]1236<!-- ======================================================================= -->
1237<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1238<!-- ======================================================================= -->
1239
1240<p>clang supports an extension which allows the following in C:</p>
1241
1242<blockquote>
1243<pre>
1244#include &lt;math.h&gt;
1245#include &lt;complex.h&gt;
1246complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1247</pre>
1248</blockquote>
1249
1250<p>This construct is useful because there is no way to separately
1251initialize the real and imaginary parts of a complex variable in
1252standard C, given that clang does not support <code>_Imaginary</code>.
1253(clang also supports the <code>__real__</code> and <code>__imag__</code>
1254extensions from gcc, which help in some cases, but are not usable in
1255static initializers.)
1256
1257<p>Note that this extension does not allow eliding the braces; the
1258meaning of the following two lines is different:</p>
1259
1260<blockquote>
1261<pre>
1262complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1263complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1264</pre>
1265</blockquote>
1266
1267<p>This extension also works in C++ mode, as far as that goes, but does not
1268 apply to the C++ <code>std::complex</code>. (In C++11, list
1269 initialization allows the same syntax to be used with
1270 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1271
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1272<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1273<h2 id="builtins">Builtin Functions</h2>
1274<!-- ======================================================================= -->
1275
1276<p>Clang supports a number of builtin library functions with the same syntax as
1277GCC, including things like <tt>__builtin_nan</tt>,
1278<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1279<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1280addition to the GCC builtins, Clang supports a number of builtins that GCC does
1281not, which are listed here.</p>
1282
1283<p>Please note that Clang does not and will not support all of the GCC builtins
1284for vector operations. Instead of using builtins, you should use the functions
1285defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1286define portable wrappers for these. Many of the Clang versions of these
1287functions are implemented directly in terms of <a href="#vectors">extended
1288vector support</a> instead of builtins, in order to reduce the number of
1289builtins that we need to implement.</p>
1290
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1291<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1292<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1293<!-- ======================================================================= -->
1294
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1295<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1296permutation/shuffle/swizzle operations. This builtin is also very important for
1297the implementation of various target-specific header files like
1298<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1299</p>
1300
1301<p><b>Syntax:</b></p>
1302
1303<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1304__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1305</pre>
1306
1307<p><b>Examples:</b></p>
1308
1309<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1310 // Identity operation - return 4-element vector V1.
1311 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1312
1313 // "Splat" element 0 of V1 into a 4-element result.
1314 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1315
1316 // Reverse 4-element vector V1.
1317 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1318
1319 // Concatenate every other element of 4-element vectors V1 and V2.
1320 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1321
1322 // Concatenate every other element of 8-element vectors V1 and V2.
1323 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1324</pre>
1325
1326<p><b>Description:</b></p>
1327
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1328<p>The first two arguments to __builtin_shufflevector are vectors that have the
1329same element type. The remaining arguments are a list of integers that specify
1330the elements indices of the first two vectors that should be extracted and
1331returned in a new vector. These element indices are numbered sequentially
1332starting with the first vector, continuing into the second vector. Thus, if
1333vec1 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]1334</p>
1335
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1336<p>The result of __builtin_shufflevector is a vector
1337with the same element type as vec1/vec2 but that has an element count equal to
1338the number of indices specified.
1339</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1340
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1341<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1342
1343<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1344<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1345<!-- ======================================================================= -->
1346
1347<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1348the program cannot be reached, even if the compiler might otherwise think it
1349can. This is useful to improve optimization and eliminates certain warnings.
1350For example, without the <tt>__builtin_unreachable</tt> in the example below,
1351the compiler assumes that the inline asm can fall through and prints a "function
1352declared 'noreturn' should not return" warning.
1353</p>
1354
1355<p><b>Syntax:</b></p>
1356
1357<pre>
1358__builtin_unreachable()
1359</pre>
1360
1361<p><b>Example of Use:</b></p>
1362
1363<pre>
1364void myabort(void) __attribute__((noreturn));
1365void myabort(void) {
1366 asm("int3");
1367 __builtin_unreachable();
1368}
1369</pre>
1370
1371<p><b>Description:</b></p>
1372
1373<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1374it has undefined behavior, it is a statement that it is never reached and the
1375optimizer can take advantage of this to produce better code. This builtin takes
1376no arguments and produces a void result.
1377</p>
1378
1379<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1380
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1381<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1382<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1383<!-- ======================================================================= -->
1384
1385<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1386memory.
1387</p>
1388
1389<p><b>Syntax:</b></p>
1390
1391<pre>
1392<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1393</pre>
1394
1395<p><b>Example of Use:</b></p>
1396
1397<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1398int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1399</pre>
1400
1401<p><b>Description:</b></p>
1402
1403<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1404intrinsics to allow code to atomically swap the current value with the new
1405value. More importantly, it helps developers write more efficient and correct
1406code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1407relying on the platform specific implementation details of
1408__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1409</p>
1410
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1411
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1412<!-- ======================================================================= -->
1413<h2 id="targetspecific">Target-Specific Extensions</h2>
1414<!-- ======================================================================= -->
1415
1416<p>Clang supports some language features conditionally on some targets.</p>
1417
1418<!-- ======================================================================= -->
1419<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1420<!-- ======================================================================= -->
1421
1422<p>The X86 backend has these language extensions:</p>
1423
1424<!-- ======================================================================= -->
1425<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1426<!-- ======================================================================= -->
1427
1428<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1429relative to the X86 GS segment register, and address space #257 causes it to be
1430relative to the X86 FS segment. Note that this is a very very low-level
1431feature that should only be used if you know what you're doing (for example in
1432an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1433
1434<p>Here is an example:</p>
1435
1436<pre>
1437#define GS_RELATIVE __attribute__((address_space(256)))
1438int foo(int GS_RELATIVE *P) {
1439 return *P;
1440}
1441</pre>
1442
1443<p>Which compiles to (on X86-32):</p>
1444
1445<pre>
1446_foo:
1447 movl 4(%esp), %eax
1448 movl %gs:(%eax), %eax
1449 ret
1450</pre>
1451
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1452<!-- ======================================================================= -->
1453<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1454<!-- ======================================================================= -->
1455
1456<p>Clang supports additional attributes that are useful for documenting program
1457invariants and rules for static analysis tools. The extensions documented here
1458are used by the <a
1459href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1460engine</a> that is part of Clang's Analysis library.</p>
1461
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1462<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1463
1464<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1465attribute. This attribute, which is typically affixed to a function prototype,
1466indicates that a call to a given function never returns. Function prototypes for
1467common functions like <tt>exit</tt> are typically annotated with this attribute,
1468as well as a variety of common assertion handlers. Users can educate the static
1469analyzer about their own custom assertion handles (thus cutting down on false
1470positives due to false paths) by marking their own &quot;panic&quot; functions
1471with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1472
1473<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1474there are special functions that for all intents and purposes should be
1475considered panic functions (i.e., they are only called when an internal program
1476error occurs) but may actually return so that the program can fail gracefully.
1477The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1478as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1479pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1480<tt>noreturn</tt>).</p>
1481
1482<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]1483same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1484placed at the end of function prototypes:</p>
1485
1486<pre>
1487 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1488</pre>
1489
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1490<p>Query for this feature with
1491<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1492
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1493<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1494
1495<p>Many methods in Objective-C have conventional meanings determined
1496by their selectors. For the purposes of static analysis, it is
1497sometimes useful to be able to mark a method as having a particular
1498conventional meaning despite not having the right selector, or as not
1499having the conventional meaning that its selector would suggest.
1500For these use cases, we provide an attribute to specifically describe
1501the <q>method family</q> that a method belongs to.</p>
1502
1503<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1504where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1505<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1506can only be placed at the end of a method declaration:</p>
1507
1508<pre>
1509 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1510</pre>
1511
1512<p>Users who do not wish to change the conventional meaning of a
1513method, and who merely want to document its non-standard retain and
1514release semantics, should use the
1515<a href="#attr_retain_release">retaining behavior attributes</a>
1516described below.</p>
1517
1518<p>Query for this feature with
1519<tt>__has_attribute(objc_method_family)</tt>.</p>
1520
1521<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1522
1523<p>In Objective-C, functions and methods are generally assumed to take
1524and return objects with +0 retain counts, with some exceptions for
1525special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1526there are exceptions, and so Clang provides attributes to allow these
1527exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1528ignore non-leaks). Some exceptions may be better described using
1529the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1530attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1531
1532<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1533<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1534and <tt>cf_returns_not_retained</tt> attributes can be placed on
1535methods and functions that return Objective-C or CoreFoundation
1536objects. They are commonly placed at the end of a function prototype
1537or method declaration:</p>
1538
1539<pre>
1540 id foo() <b>__attribute__((ns_returns_retained))</b>;
1541
1542 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1543</pre>
1544
1545<p>The <tt>*_returns_retained</tt> attributes specify that the
1546returned object has a +1 retain count.
1547The <tt>*_returns_not_retained</tt> attributes specify that the return
1548object has a +0 retain count, even if the normal convention for its
1549selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1550returned object is +0, but is guaranteed to live at least as long as the
1551next flush of an autorelease pool.</p>
1552
1553<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1554attributes can be placed on an parameter declaration; they specify
1555that the argument is expected to have a +1 retain count, which will be
1556balanced in some way by the function or method.
1557The <tt>ns_consumes_self</tt> attribute can only be placed on an
1558Objective-C method; it specifies that the method expects
1559its <tt>self</tt> parameter to have a +1 retain count, which it will
1560balance in some way.</p>
1561
1562<pre>
1563 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1564
1565 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1566 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1567</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1568
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1569<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1570<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1571
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1572<!-- ======================================================================= -->
1573<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1574<!-- ======================================================================= -->
1575<h3 id="address_sanitizer">AddressSanitizer</h3>
1576<p> Use <code>__has_feature(address_sanitizer)</code>
1577to check if the code is being built with <a
1578 href="AddressSanitizer.html">AddressSanitizer</a>.
1579</p>
Kostya Serebryany71efba02012-01-24 19:25:38 +0000[diff] [blame]1580<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function
1581declaration to specify that address safety instrumentation (e.g.
1582AddressSanitizer) should not be applied to that function.
1583</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1584
1585<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1586<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1587<!-- ======================================================================= -->
1588
1589<p>Clang supports additional attributes for checking basic locking policies in
1590multithreaded programs.
1591Clang currently parses the following list of attributes, although
1592<b>the implementation for these annotations is currently in development.</b>
1593For more details, see the
1594<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1595</p>
1596
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1597<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1598
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1599<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1600declaration to specify that the thread safety analysis should not be run on that
1601function. This attribute provides an escape hatch (e.g. for situations when it
1602is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1603
1604<h4 id="ts_lockable">lockable</h4>
1605
1606<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1607that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1608used to check consistency.</p>
1609
1610<h4 id="ts_scopedlockable">scoped_lockable</h4>
1611
1612<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1613specify that it has a "scoped" lockable type. Objects of this type will acquire
1614the lock upon construction and release it upon going out of scope.
1615 This annotation is primarily used to check
1616consistency.</p>
1617
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1618<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1619
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1620<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1621specify that the variable must be accessed while holding some lock.</p>
1622
1623<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1624
1625<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1626specify that the pointer must be dereferenced while holding some lock.</p>
1627
1628<h4 id="ts_guardedby">guarded_by(l)</h4>
1629
1630<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1631specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1632
1633<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1634
1635<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1636specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1637
1638<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1639
1640<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1641of a lockable variable to specify that the lock must be acquired before all
1642attribute arguments. Arguments must be lockable type, and there must be at
1643least one argument.</p>
1644
1645<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1646
1647<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1648of a lockable variable to specify that the lock must be acquired after all
1649attribute arguments. Arguments must be lockable type, and there must be at
1650least one argument.</p>
1651
1652<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1653
1654<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1655declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1656exclusively. This attribute takes zero or more arguments: either of lockable
1657type or integers indexing into function parameters of lockable type. If no
1658arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1659enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1660
1661<h4 id="ts_slf">shared_lock_function(...)</h4>
1662
1663<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1664declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1665 the locks may be shared (e.g. read locks). This attribute takes zero or more
1666arguments: either of lockable type or integers indexing into function
1667parameters of lockable type. If no arguments are given, the acquired lock is
1668implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1669
1670<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1671
1672<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1673declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1674all listed locks exclusively. This attribute takes one or more arguments. The
1675first argument is an integer or boolean value specifying the return value of a
1676successful lock acquisition. The remaining arugments are either of lockable type
1677or integers indexing into function parameters of lockable type. If only one
1678argument is given, the acquired lock is implicitly <tt>this</tt> of the
1679enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1680
1681<h4 id="ts_stf">shared_trylock_function(...)</h4>
1682
1683<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1684declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1685all listed locks, although the locks may be shared (e.g. read locks). This
1686attribute takes one or more arguments. The first argument is an integer or
1687boolean value specifying the return value of a successful lock acquisition. The
1688remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1689function parameters of lockable type. If only one argument is given, the
1690acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1691
1692<h4 id="ts_uf">unlock_function(...)</h4>
1693
1694<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1695declaration to specify that the function release all listed locks. This
1696attribute takes zero or more arguments: either of lockable type or integers
1697indexing into function parameters of lockable type. If no arguments are given,
1698the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1699
1700<h4 id="ts_lr">lock_returned(l)</h4>
1701
1702<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1703declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1704must be of lockable type). This annotation is used to aid in resolving lock
1705expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1706
1707<h4 id="ts_le">locks_excluded(...)</h4>
1708
1709<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1710to specify that the function must not be called with the listed locks. Arguments
1711must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1712
1713<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1714
1715<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1716declaration to specify that the function must be called while holding the listed
1717exclusive locks. Arguments must be lockable type, and there must be at
1718least one argument.</p>
1719
1720<h4 id="ts_slr">shared_locks_required(...)</h4>
1721
1722<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1723declaration to specify that the function must be called while holding the listed
1724shared locks. Arguments must be lockable type, and there must be at
1725least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1726
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1727</div>
1728</body>
1729</html>