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19<!--#include virtual="../menu.html.incl"-->
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21<div id="content">
22
23<h1>Clang Language Extensions</h1>
24
25<ul>
26<li><a href="#intro">Introduction</a></li>
Chris 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>
Daniel Dunbar85ff9692012-04-05 17:10:06 +0000[diff] [blame]33<li><a href="#user_specified_system_framework">'User-Specified' System Frameworks</a></li>
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]34<li><a href="#availability">Availability attribute</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]35<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]36 <ul>
37 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
38 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]39 </ul></li>
40<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]41 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]42 <li><a href="#cxx0x">C++11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]43 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]44 <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes
45 access control</a></li>
46 <li><a href="#cxx_alias_templates">C++11 alias templates</a></li>
47 <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li>
48 <li><a href="#cxx_attributes">C++11 attributes</a></li>
49 <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li>
50 <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li>
51 <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]52 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]53 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
54 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
55 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
56 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
57 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
58 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
59 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
60 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
Douglas Gregor7b156dd2012-04-04 00:48:39 +0000[diff] [blame]61 <li><a href="#cxx_local_type_template_args">C++11 local and unnamed types as template arguments</a></li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]62 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
63 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
64 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
65 <li><a href="#cxx_override_control">C++11 override control</a></li>
66 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
67 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
68 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
69 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
70 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
71 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
72 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
73 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
74 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
75 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
76 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
77 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]78 </ul></li>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]79 <li><a href="#c11">C11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]80 <ul>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]81 <li><a href="#c_alignas">C11 alignment specifiers</a></li>
82 <li><a href="#c_generic_selections">C11 generic selections</a></li>
83 <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]84 </ul></li>
85 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]86<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]87<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]88<li><a href="#objc_features">Objective-C Features</a>
89 <ul>
90 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]91 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]92 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]93 <li><a href="#objc_lambdas">Interoperability with C++11 lambdas</a></li>
Patrick Beard62f12342012-03-20 21:51:03 +0000[diff] [blame]94 <li><a href="#object-literals-subscripting">Object Literals and Subscripting</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]95 </ul>
96</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]97<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]98<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]99<li><a href="#builtins">Builtin Functions</a>
100 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]101 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]102 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]103 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]104 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]105</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]106<li><a href="#targetspecific">Target-Specific Extensions</a>
107 <ul>
108 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
109 </ul>
110</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]111<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]112<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]113 <ul>
114 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
115 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]116</li>
117<li><a href="#threadsafety">Thread Safety Annotation Checking</a>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]118 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]119 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
120 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
121 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]122 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
123 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]124 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
125 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
126 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
127 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
128 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
129 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
130 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
131 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
132 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
133 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
134 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
135 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
136 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]137 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]138</li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]139</ul>
140
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]141<!-- ======================================================================= -->
142<h2 id="intro">Introduction</h2>
143<!-- ======================================================================= -->
144
145<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]146addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]147range of GCC extensions. Please see the <a
148href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
149more information on these extensions.</p>
150
151<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]152<h2 id="feature_check">Feature Checking Macros</h2>
153<!-- ======================================================================= -->
154
155<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]156on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]157function-like macros. This allows you to directly test for a feature in your
158code without having to resort to something like autoconf or fragile "compiler
159version checks".</p>
160
161<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]162<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]163<!-- ======================================================================= -->
164
165<p>This function-like macro takes a single identifier argument that is the name
166of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
167not. It can be used like this:</p>
168
169<blockquote>
170<pre>
171#ifndef __has_builtin // Optional of course.
172 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
173#endif
174
175...
176#if __has_builtin(__builtin_trap)
177 __builtin_trap();
178#else
179 abort();
180#endif
181...
182</pre>
183</blockquote>
184
185
186<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]187<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]188<!-- ======================================================================= -->
189
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]190<p>These function-like macros take a single identifier argument that is the
191name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
192is both supported by Clang and standardized in the current language standard
193or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
194<code>__has_extension</code> evaluates to 1 if the feature is supported by
195Clang in the current language (either as a language extension or a standard
196language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]197
198<blockquote>
199<pre>
200#ifndef __has_feature // Optional of course.
201 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
202#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]203#ifndef __has_extension
204 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
205#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]206
207...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]208#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]209// This code will only be compiled with the -std=c++11 and -std=gnu++11
210// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]211#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]212
213#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]214// 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]215// and -std=gnu++98 options, because rvalue references are supported as a
216// language extension in C++98.
217#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]218</pre>
219</blockquote>
220
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]221<p id="has_feature_back_compat">For backwards compatibility reasons,
222<code>__has_feature</code> can also be used to test for support for
223non-standardized features, i.e. features not prefixed <code>c_</code>,
224<code>cxx_</code> or <code>objc_</code>.</p>
225
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]226<p id="has_feature_for_non_language_features">
227Another use of <code>__has_feature</code> is to check for compiler features
228not related to the language standard, such as e.g.
229<a href="AddressSanitizer.html">AddressSanitizer</a>.
230
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]231<p>If the <code>-pedantic-errors</code> option is given,
232<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
233
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]234<p>The feature tag is described along with the language feature below.</p>
235
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]236<p>The feature name or extension name can also be specified with a preceding and
237following <code>__</code> (double underscore) to avoid interference from a macro
Richard Smith1d9f4c12012-03-01 02:12:07 +0000[diff] [blame]238with the same name. For instance, <code>__cxx_rvalue_references__</code> can be
239used instead of <code>cxx_rvalue_references</code>.</p>
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]240
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]241<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]242<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]243<!-- ======================================================================= -->
244
245<p>This function-like macro takes a single identifier argument that is the name
246of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
247can be used like this:</p>
248
249<blockquote>
250<pre>
251#ifndef __has_attribute // Optional of course.
252 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
253#endif
254
255...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]256#if __has_attribute(always_inline)
257#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]258#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]259#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]260#endif
261...
262</pre>
263</blockquote>
264
Jean-Daniel Dupas8a5e7fd2012-03-01 14:53:16 +0000[diff] [blame]265<p>The attribute name can also be specified with a preceding and
266following <code>__</code> (double underscore) to avoid interference from a macro
267with the same name. For instance, <code>__always_inline__</code> can be used
268instead of <code>always_inline</code>.</p>
269
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]270<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]271<h2 id="has_include">Include File Checking Macros</h2>
272<!-- ======================================================================= -->
273
274<p>Not all developments systems have the same include files.
275The <a href="#__has_include">__has_include</a> and
276<a href="#__has_include_next">__has_include_next</a> macros allow you to
277check for the existence of an include file before doing
278a possibly failing #include directive.</p>
279
280<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]281<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]282<!-- ======================================================================= -->
283
284<p>This function-like macro takes a single file name string argument that
285is the name of an include file. It evaluates to 1 if the file can
286be found using the include paths, or 0 otherwise:</p>
287
288<blockquote>
289<pre>
290// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]291#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]292# include "myinclude.h"
293#endif
294
295// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]296#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]297# include "myinclude.h"
298#endif
299</pre>
300</blockquote>
301
302<p>To test for this feature, use #if defined(__has_include).</p>
303
304<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]305<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]306<!-- ======================================================================= -->
307
308<p>This function-like macro takes a single file name string argument that
309is the name of an include file. It is like __has_include except that it
310looks for the second instance of the given file found in the include
311paths. It evaluates to 1 if the second instance of the file can
312be found using the include paths, or 0 otherwise:</p>
313
314<blockquote>
315<pre>
316// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]317#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]318# include_next "myinclude.h"
319#endif
320
321// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]322#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]323# include_next "myinclude.h"
324#endif
325</pre>
326</blockquote>
327
328<p>Note that __has_include_next, like the GNU extension
329#include_next directive, is intended for use in headers only,
330and will issue a warning if used in the top-level compilation
331file. A warning will also be issued if an absolute path
332is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]333
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]334
335<!-- ======================================================================= -->
336<h3><a name="__has_warning">__has_warning</a></h3>
337<!-- ======================================================================= -->
338
339<p>This function-like macro takes a string literal that represents a command
340 line option for a warning and returns true if that is a valid warning
341 option.</p>
342
343<blockquote>
344<pre>
345#if __has_warning("-Wformat")
346...
347#endif
348</pre>
349</blockquote>
350
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]351<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]352<h2 id="builtinmacros">Builtin Macros</h2>
353<!-- ======================================================================= -->
354
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]355<dl>
356 <dt><code>__BASE_FILE__</code></dt>
357 <dd>Defined to a string that contains the name of the main input
358 file passed to Clang.</dd>
359
360 <dt><code>__COUNTER__</code></dt>
361 <dd>Defined to an integer value that starts at zero and is
362 incremented each time the <code>__COUNTER__</code> macro is
363 expanded.</dd>
364
365 <dt><code>__INCLUDE_LEVEL__</code></dt>
366 <dd>Defined to an integral value that is the include depth of the
367 file currently being translated. For the main file, this value is
368 zero.</dd>
369
370 <dt><code>__TIMESTAMP__</code></dt>
371 <dd>Defined to the date and time of the last modification of the
372 current source file.</dd>
373
374 <dt><code>__clang__</code></dt>
375 <dd>Defined when compiling with Clang</dd>
376
377 <dt><code>__clang_major__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]378 <dd>Defined to the major marketing version number of Clang (e.g., the
379 2 in 2.0.1). Note that marketing version numbers should not be used to
380 check for language features, as different vendors use different numbering
381 schemes. Instead, use the <a href="#feature_check">feature checking
382 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]383
384 <dt><code>__clang_minor__</code></dt>
385 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]386 2.0.1). Note that marketing version numbers should not be used to
387 check for language features, as different vendors use different numbering
388 schemes. Instead, use the <a href="#feature_check">feature checking
389 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]390
391 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]392 <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]393
394 <dt><code>__clang_version__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]395 <dd>Defined to a string that captures the Clang marketing version, including
396 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]397</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]398
399<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]400<h2 id="vectors">Vectors and Extended Vectors</h2>
401<!-- ======================================================================= -->
402
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]403<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]404
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]405<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
406support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An
407example is:</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]408
409<blockquote>
410<pre>
411typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
412typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
413
414float4 foo(float2 a, float2 b) {
415 float4 c;
416 c.xz = a;
417 c.yw = b;
418 return c;
419}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]420</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]421</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]422
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]423<p>Query for this feature with
424<tt>__has_extension(attribute_ext_vector_type)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]425
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]426<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector
427syntax and functions. For example:</p>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]428
429<blockquote>
430<pre>
431vector float foo(vector int a) {
432 vector int b;
433 b = vec_add(a, a) + a;
434 return (vector float)b;
435}
436</pre>
437</blockquote>
438
439<p>NEON vector types are created using <tt>neon_vector_type</tt> and
440<tt>neon_polyvector_type</tt> attributes. For example:</p>
441
442<blockquote>
443<pre>
444typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
445typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
446
447int8x8_t foo(int8x8_t a) {
448 int8x8_t v;
449 v = a;
450 return v;
451}
452</pre>
453</blockquote>
454
455<!-- ======================================================================= -->
456<h3><a name="vector_literals">Vector Literals</a></h3>
457<!-- ======================================================================= -->
458
459<p>Vector literals can be used to create vectors from a set of scalars, or
460vectors. Either parentheses or braces form can be used. In the parentheses form
461the number of literal values specified must be one, i.e. referring to a scalar
462value, or must match the size of the vector type being created. If a single
463scalar literal value is specified, the scalar literal value will be replicated
464to all the components of the vector type. In the brackets form any number of
465literals can be specified. For example:</p>
466
467<blockquote>
468<pre>
469typedef int v4si __attribute__((__vector_size__(16)));
470typedef float float4 __attribute__((ext_vector_type(4)));
471typedef float float2 __attribute__((ext_vector_type(2)));
472
473v4si vsi = (v4si){1, 2, 3, 4};
474float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
475vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
476vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
477vector int vi3 = (vector int)(1, 2); // error
478vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
479vector int vi5 = (vector int)(1, 2, 3, 4);
480float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
481</pre>
482</blockquote>
483
484<!-- ======================================================================= -->
485<h3><a name="vector_operations">Vector Operations</a></h3>
486<!-- ======================================================================= -->
487
488<p>The table below shows the support for each operation by vector extension.
489A dash indicates that an operation is not accepted according to a corresponding
490specification.</p>
491
492<table width="500" border="1" cellspacing="0">
493 <tr>
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]494 <th>Operator</th>
495 <th>OpenCL</th>
496 <th>AltiVec</th>
497 <th>GCC</th>
498 <th>NEON</th>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]499 </tr>
500 <tr>
501 <td>[]</td>
502 <td align="center">yes</td>
503 <td align="center">yes</td>
504 <td align="center">yes</td>
505 <td align="center">-</td>
506 </tr>
507 <tr>
508 <td>unary operators +, -</td>
509 <td align="center">yes</td>
510 <td align="center">yes</td>
511 <td align="center">yes</td>
512 <td align="center">-</td>
513 </tr>
514 <tr>
515 <td>++, --</td>
516 <td align="center">yes</td>
517 <td align="center">yes</td>
518 <td align="center">-</td>
519 <td align="center">-</td>
520 </tr>
521 <tr>
522 <td>+, -, *, /, %</td>
523 <td align="center">yes</td>
524 <td align="center">yes</td>
525 <td align="center">yes</td>
526 <td align="center">-</td>
527 </tr>
528 <tr>
529 <td>bitwise operators &, |, ^, ~</td>
530 <td align="center">yes</td>
531 <td align="center">yes</td>
532 <td align="center">yes</td>
533 <td align="center">-</td>
534 </tr>
535 <tr>
536 <td>&gt&gt, &lt&lt</td>
537 <td align="center">yes</td>
538 <td align="center">yes</td>
539 <td align="center">yes</td>
540 <td align="center">-</td>
541 </tr>
542 <tr>
543 <td>!, &&,||</td>
544 <td align="center">no</td>
545 <td align="center">-</td>
546 <td align="center">-</td>
547 <td align="center">-</td>
548 </tr>
549 <tr>
550 <td>==,!=, >, <, >=, <=</td>
551 <td align="center">yes</td>
552 <td align="center">yes</td>
553 <td align="center">-</td>
554 <td align="center">-</td>
555 </tr>
556 <tr>
557 <td>=</td>
558 <td align="center">yes</td>
559 <td align="center">yes</td>
560 <td align="center">yes</td>
561 <td align="center">yes</td>
562 </tr>
563 <tr>
564 <td>:?</td>
565 <td align="center">yes</td>
566 <td align="center">-</td>
567 <td align="center">-</td>
568 <td align="center">-</td>
569 </tr>
570 <tr>
571 <td>sizeof</td>
572 <td align="center">yes</td>
573 <td align="center">yes</td>
574 <td align="center">yes</td>
575 <td align="center">yes</td>
576 </tr>
577</table>
578
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]579<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
580
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]581<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]582<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]583<!-- ======================================================================= -->
584
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]585<p>An optional string message can be added to the <tt>deprecated</tt>
586and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]587
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]588<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]589<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]590</blockquote>
591
592<p>If the deprecated or unavailable declaration is used, the message
593will be incorporated into the appropriate diagnostic:</p>
594
595<blockquote>
Benjamin Kramerb4556862012-03-19 19:12:30 +0000[diff] [blame]596<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!!
597 [-Wdeprecated-declarations]
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]598 explode();
599 ^</pre>
600</blockquote>
601
602<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]603with <tt>__has_extension(attribute_deprecated_with_message)</tt>
604and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]605
606<!-- ======================================================================= -->
607<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
608<!-- ======================================================================= -->
609
610<p>Clang allows attributes to be written on individual enumerators.
611This allows enumerators to be deprecated, made unavailable, etc. The
612attribute must appear after the enumerator name and before any
613initializer, like so:</p>
614
615<blockquote>
616<pre>enum OperationMode {
617 OM_Invalid,
618 OM_Normal,
619 OM_Terrified __attribute__((deprecated)),
620 OM_AbortOnError __attribute__((deprecated)) = 4
621};</pre>
622</blockquote>
623
624<p>Attributes on the <tt>enum</tt> declaration do not apply to
625individual enumerators.</p>
626
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]627<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]628
629<!-- ======================================================================= -->
Daniel Dunbar85ff9692012-04-05 17:10:06 +0000[diff] [blame]630<h2 id="user_specified_system_framework">'User-Specified' System Frameworks</h2>
631<!-- ======================================================================= -->
632
633<p>Clang provides a mechanism by which frameworks can be built in such a way
634that they will always be treated as being 'system frameworks', even if they are
635not present in a system framework directory. This can be useful to system
636framework developers who want to be able to test building other applications
637with development builds of their framework, including the manner in which the
638compiler changes warning behavior for system headers.</p>
639
640<p>Framework developers can opt-in to this mechanism by creating a
641'.system_framework' file at the top-level of their framework. That is, the
642framework should have contents like:</p>
643
644<pre>
645 .../TestFramework.framework
646 .../TestFramework.framework/.system_framework
647 .../TestFramework.framework/Headers
648 .../TestFramework.framework/Headers/TestFramework.h
649 ...
650</pre>
651
652<p>Clang will treat the presence of this file as an indicator that the framework
653should be treated as a system framework, regardless of how it was found in the
654framework search path. For consistency, we recommend that such files never be
655included in installed versions of the framework.</p>
656
657<!-- ======================================================================= -->
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]658<h2 id="availability">Availability attribute</h2
659<!-- ======================================================================= -->
660
661<p>Clang introduces the <code>availability</code> attribute, which can
662be placed on declarations to describe the lifecycle of that
663declaration relative to operating system versions. Consider the function declaration for a hypothetical function <code>f</code>:</p>
664
665<pre>
666void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7)));
667</pre>
668
669<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>
670
671<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>
672
673<dl>
674 <dt>introduced=<i>version</i></dt>
675 <dd>The first version in which this declaration was introduced.</dd>
676
677 <dt>deprecated=<i>version</i></dt>
678 <dd>The first version in which this declaration was deprecated, meaning that users should migrate away from this API.</dd>
679
680 <dt>obsoleted=<i>version</i></dt>
681 <dd>The first version in which this declaration was obsoleted, meaning that it was removed completely and can no longer be used.</dd>
682
683 <dt>unavailable</dt>
684 <dd>This declaration is never available on this platform.</dd>
685
686 <dt>message=<i>string-literal</i></dt>
687 <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>
688</dl>
689
690<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>
691
692<dl>
693 <dt>ios</dt>
694 <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>
695
696 <dt>macosx</dt>
697 <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>
698</dl>
699
Douglas Gregor594f8412012-03-11 17:21:03 +0000[diff] [blame]700<p>A declaration can be used even when deploying back to a platform
701version prior to when the declaration was introduced. When this
702happens, the declaration is <a
703 href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly
704linked</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>
705
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]706<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]707<h2 id="checking_language_features">Checks for Standard Language Features</h2>
708<!-- ======================================================================= -->
709
710<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
711enabled. Those features are listed here.</p>
712
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]713<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]714
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]715<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]716example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]717
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]718<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]719
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]720<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]721compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]722
723<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]724<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
725<!-- ======================================================================= -->
726
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]727<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
728to query if certain upcoming standard language features are enabled. Those
729features are listed here. Features that are not yet implemented will be
730noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]731
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]732<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]733
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]734<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]735C++11 standard. As a result, all these features are enabled
736with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]737
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]738<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]739
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]740<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]741
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]742<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]743
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]744<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
745<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]746C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]747
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]748<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]749
750<p>Use <tt>__has_feature(cxx_alignas)</tt> or
751<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
752specifiers using <tt>alignas</tt> is enabled.</p>
753
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]754<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]755
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]756<p>Use <tt>__has_feature(cxx_attributes)</tt> or
757<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]758parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]759
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]760<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]761
762<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
763for generalized constant expressions (e.g., <tt>constexpr</tt>) is
Richard Smithb5216aa2012-02-14 22:56:17 +0000[diff] [blame]764enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]765
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]766<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]767
768<p>Use <tt>__has_feature(cxx_decltype)</tt> or
769<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
Douglas Gregor316551f2012-04-10 20:00:33 +0000[diff] [blame^]770<tt>decltype()</tt> specifier is enabled. C++11's <tt>decltype</tt>
771does not require type-completeness of a function call expression.
772Use <tt>__has_feature(cxx_decltype_incomplete_return_types)</tt>
773or <tt>__has_extension(cxx_decltype_incomplete_return_types)</tt>
774to determine if support for this feature is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]775
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]776<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]777
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]778<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
779<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
780if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]781
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]782<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
783
784<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
785<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
786defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
787
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]788<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]789
790<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
791support for delegating constructors is enabled.</p>
792
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]793<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]794
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]795<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
796<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]797deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]798
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]799<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]800<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
801
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]802<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]803
804<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
805support for generalized initializers (using braced lists and
Richard Smith88189552012-02-26 07:09:21 +0000[diff] [blame]806<tt>std::initializer_list</tt>) is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]807
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]808<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]809
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]810<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
811implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]812
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]813<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]814
815<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>
816
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]817<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]818
819<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
820<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
821inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]822
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]823<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]824
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]825<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
826<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregor46e021e2012-02-23 05:44:09 +0000[diff] [blame]827is enabled. </p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]828
Douglas Gregor7b156dd2012-04-04 00:48:39 +0000[diff] [blame]829<h4 id="cxx_local_type_template_args">C++11 local and unnamed types as template arguments</h4>
830
831<p>Use <tt>__has_feature(cxx_local_type_template_args)</tt> or
832<tt>__has_extension(cxx_local_type_template_args)</tt> to determine if
833support for local and unnamed types as template arguments is enabled.</p>
834
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]835<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]836
837<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
838<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
839exception specifications is enabled.</p>
840
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]841<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]842
843<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]844
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]845<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></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_nullptr)</tt> or
848<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]849<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]850
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]851<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]852
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]853<p>Use <tt>__has_feature(cxx_override_control)</tt> or
854<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]855the override control keywords is enabled.</p>
856
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]857<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]858<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
859<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
860if support for reference-qualified functions (e.g., member functions with
861<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
862is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]863
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]864<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]865
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]866<p>Use <tt>__has_feature(cxx_range_for)</tt> or
867<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
868range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]869
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]870<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Richard Smith80134582012-03-07 08:57:31 +0000[diff] [blame]871<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support
872for 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]873
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]874<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]875
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]876<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
877<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]878rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]879
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]880<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]881
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]882<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
883<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]884compile-time assertions using <tt>static_assert</tt> is enabled.</p>
885
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]886<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]887
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]888<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]889<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]890supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
891will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]892
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]893<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]894
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]895<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
896<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
897strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]898
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]899<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]900
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]901<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
902<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
903alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]904
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]905<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]906<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
907support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]908
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]909<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]910
Richard Smithec92bc72012-03-03 23:51:05 +0000[diff] [blame]911<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]912
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]913<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]914
Richard Smith9c1dda72012-03-09 08:41:27 +0000[diff] [blame]915<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]916
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]917<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]918
919<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
920<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
921for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]922
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]923<h3 id="c11">C11</h3>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]924
925<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]926C11 standard. As a result, all these features are enabled
927with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]928
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]929<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]930
931<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
932to determine if support for alignment specifiers using <tt>_Alignas</tt>
933is enabled.</p>
934
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]935<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]936
937<p>Use <tt>__has_feature(c_generic_selections)</tt> or
938<tt>__has_extension(c_generic_selections)</tt> to determine if support for
939generic selections is enabled.</p>
940
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]941<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]942languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]943C11 standard.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]944
945<p>In C, type compatibility is decided according to the rules given in the
946appropriate standard, but in C++, which lacks the type compatibility rules
947used in C, types are considered compatible only if they are equivalent.</p>
948
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]949<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]950
951<p>Use <tt>__has_feature(c_static_assert)</tt> or
952<tt>__has_extension(c_static_assert)</tt> to determine if support for
953compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
954
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]955<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]956<h2 id="checking_type_traits">Checks for Type Traits</h2>
957<!-- ======================================================================= -->
958
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]959<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]960<blockquote>
961<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]962#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]963template&lt;typename From, typename To&gt;
964struct is_convertible_to {
965 static const bool value = __is_convertible_to(From, To);
966};
967#else
968// Emulate type trait
969#endif
970</pre>
971</blockquote>
972
973<p>The following type traits are supported by Clang:</p>
974<ul>
975 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
976 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
977 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
978 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
979 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
980 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
981 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
982 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
983 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
984 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
985 <li><code>__is_class</code> (GNU, Microsoft)</li>
986 <li><code>__is_convertible_to</code> (Microsoft)</li>
987 <li><code>__is_empty</code> (GNU, Microsoft)</li>
988 <li><code>__is_enum</code> (GNU, Microsoft)</li>
989 <li><code>__is_pod</code> (GNU, Microsoft)</li>
990 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
991 <li><code>__is_union</code> (GNU, Microsoft)</li>
992 <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]993 <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]994 <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]995 <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>
996 <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]997</ul>
998
999<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1000<h2 id="blocks">Blocks</h2>
1001<!-- ======================================================================= -->
1002
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]1003<p>The syntax and high level language feature description is in <a
1004href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
1005details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]1006href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1007
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1008
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]1009<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1010
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1011<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1012<h2 id="objc_features">Objective-C Features</h2>
1013<!-- ======================================================================= -->
1014
1015<h3 id="objc_instancetype">Related result types</h3>
1016
1017<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>
1018
1019<blockquote>
1020<pre>
1021@interface NSObject
1022+ (id)alloc;
1023- (id)init;
1024@end
1025
1026@interface NSArray : NSObject
1027@end
1028</pre>
1029</blockquote>
1030
1031<p>and this common initialization pattern</p>
1032
1033<blockquote>
1034<pre>
1035NSArray *array = [[NSArray alloc] init];
1036</pre>
1037</blockquote>
1038
1039<p>the type of the expression <code>[NSArray alloc]</code> is
1040<code>NSArray*</code> because <code>alloc</code> implicitly has a
1041related result type. Similarly, the type of the expression
1042<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
1043<code>init</code> has a related result type and its receiver is known
1044to 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>
1045
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]1046<p>A method with a related result type can be declared by using the
1047type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
1048is a contextual keyword that is only permitted in the result type of
1049an Objective-C method, e.g.</p>
1050
1051<pre>
1052@interface A
1053+ (<b>instancetype</b>)constructAnA;
1054@end
1055</pre>
1056
1057<p>The related result type can also be inferred for some methods.
1058To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1059word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]1060considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1061type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1062
1063<ul>
1064
1065 <li>the first word is "alloc" or "new", and the method is a class
1066 method, or</li>
1067
1068 <li>the first word is "autorelease", "init", "retain", or "self",
1069 and the method is an instance method.</li>
1070
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1071</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1072
1073<p>If a method with a related result type is overridden by a subclass
1074method, the subclass method must also return a type that is compatible
1075with the subclass type. For example:</p>
1076
1077<blockquote>
1078<pre>
1079@interface NSString : NSObject
1080- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
1081@end
1082</pre>
1083</blockquote>
1084
1085<p>Related result types only affect the type of a message send or
1086property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]1087with a related result type is treated the same way as method that
1088returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1089
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]1090<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
1091the <tt>instancetype</tt> contextual keyword is available.</p>
1092
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1093<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]1094<h2 id="objc_arc">Automatic reference counting </h2>
1095<!-- ======================================================================= -->
1096
1097<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>
1098
1099<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1100<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
1101<!-- ======================================================================= -->
1102
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1103<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1104underlying type within Objective-C. For example, one can write an
1105enumeration type as:</p>
1106
1107<pre>
1108typedef enum : unsigned char { Red, Green, Blue } Color;
1109</pre>
1110
1111<p>This specifies that the underlying type, which is used to store the
1112enumeration value, is <tt>unsigned char</tt>.</p>
1113
1114<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1115support for fixed underlying types is available in Objective-C.</p>
1116
1117<!-- ======================================================================= -->
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1118<h2 id="objc_lambdas">Interoperability with C++11 lambdas</h2>
1119<!-- ======================================================================= -->
1120
1121<p>Clang provides interoperability between C++11 lambdas and
1122blocks-based APIs, by permitting a lambda to be implicitly converted
1123to a block pointer with the corresponding signature. For example,
1124consider an API such as <code>NSArray</code>'s array-sorting
1125method:</p>
1126
1127<pre> - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; </pre>
1128
1129<p><code>NSComparator</code> is simply a typedef for the block pointer
1130<code>NSComparisonResult (^)(id, id)</code>, and parameters of this
1131type are generally provided with block literals as arguments. However,
1132one can also use a C++11 lambda so long as it provides the same
1133signature (in this case, accepting two parameters of type
1134<code>id</code> and returning an <code>NSComparisonResult</code>):</p>
1135
1136<pre>
1137 NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11",
1138 @"String 02"];
1139 const NSStringCompareOptions comparisonOptions
1140 = NSCaseInsensitiveSearch | NSNumericSearch |
1141 NSWidthInsensitiveSearch | NSForcedOrderingSearch;
1142 NSLocale *currentLocale = [NSLocale currentLocale];
1143 NSArray *sorted
1144 = [array sortedArrayUsingComparator:<b>[=](id s1, id s2) -&gt; NSComparisonResult {
1145 NSRange string1Range = NSMakeRange(0, [s1 length]);
1146 return [s1 compare:s2 options:comparisonOptions
1147 range:string1Range locale:currentLocale];
1148 }</b>];
1149 NSLog(@"sorted: %@", sorted);
1150</pre>
1151
1152<p>This code relies on an implicit conversion from the type of the
1153lambda expression (an unnamed, local class type called the <i>closure
1154type</i>) to the corresponding block pointer type. The conversion
1155itself is expressed by a conversion operator in that closure type
1156that produces a block pointer with the same signature as the lambda
1157itself, e.g.,</p>
1158
1159<pre>
1160 operator NSComparisonResult (^)(id, id)() const;
1161</pre>
1162
1163<p>This conversion function returns a new block that simply forwards
1164the two parameters to the lambda object (which it captures by copy),
1165then returns the result. The returned block is first copied (with
1166<tt>Block_copy</tt>) and then autoreleased. As an optimization, if a
1167lambda expression is immediately converted to a block pointer (as in
1168the first example, above), then the block is not copied and
1169autoreleased: rather, it is given the same lifetime as a block literal
1170written at that point in the program, which avoids the overhead of
1171copying a block to the heap in the common case.</p>
1172
Douglas Gregorbccda482012-03-10 22:20:11 +0000[diff] [blame]1173<p>The conversion from a lambda to a block pointer is only available
1174in Objective-C++, and not in C++ with blocks, due to its use of
1175Objective-C memory management (autorelease).</p>
1176
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1177<!-- ======================================================================= -->
Patrick Beard62f12342012-03-20 21:51:03 +0000[diff] [blame]1178<h2 id="object-literals-subscripting">Object Literals and Subscripting</h2>
1179<!-- ======================================================================= -->
1180
Patrick Beard1526f542012-03-21 16:22:53 +0000[diff] [blame]1181<p>Clang provides support for <a href="ObjectiveCLiterals.html">Object Literals and Subscripting</a> in Objective-C, which simplifies common Objective-C programming patterns, makes programs more concise, and improves the safety of container creation. There are several feature macros associated with object literals and subscripting: <code>__has_feature(objc_array_literals)</code> tests the availability of array literals; <code>__has_feature(objc_dictionary_literals)</code> tests the availability of dictionary literals; <code>__has_feature(objc_subscripting)</code> tests the availability of object subscripting.</p>
Patrick Beard62f12342012-03-20 21:51:03 +0000[diff] [blame]1182
1183<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1184<h2 id="overloading-in-c">Function Overloading in C</h2>
1185<!-- ======================================================================= -->
1186
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1187<p>Clang provides support for C++ function overloading in C. Function
1188overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1189example, one might provide several overloaded versions of a <tt>tgsin</tt>
1190function that invokes the appropriate standard function computing the sine of a
1191value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1192precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1193
1194<blockquote>
1195<pre>
1196#include &lt;math.h&gt;
1197float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1198double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1199long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1200</pre>
1201</blockquote>
1202
1203<p>Given these declarations, one can call <tt>tgsin</tt> with a
1204<tt>float</tt> value to receive a <tt>float</tt> result, with a
1205<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1206overloading in C follows the rules of C++ function overloading to pick
1207the best overload given the call arguments, with a few C-specific
1208semantics:</p>
1209<ul>
1210 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1211 double</tt> is ranked as a floating-point promotion (per C99) rather
1212 than as a floating-point conversion (as in C++).</li>
1213
1214 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1215 <tt>U*</tt> is considered a pointer conversion (with conversion
1216 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1217
1218 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1219 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1220 conversion is given "conversion" rank.</li>
1221</ul>
1222
1223<p>The declaration of <tt>overloadable</tt> functions is restricted to
1224function declarations and definitions. Most importantly, if any
1225function with a given name is given the <tt>overloadable</tt>
1226attribute, then all function declarations and definitions with that
1227name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1228attribute. This rule even applies to redeclarations of functions whose original
1229declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1230
1231<blockquote>
1232<pre>
1233int f(int) __attribute__((overloadable));
1234float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1235
1236int g(int) __attribute__((overloadable));
1237int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1238</pre>
1239</blockquote>
1240
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1241<p>Functions marked <tt>overloadable</tt> must have
1242prototypes. Therefore, the following code is ill-formed:</p>
1243
1244<blockquote>
1245<pre>
1246int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1247</pre>
1248</blockquote>
1249
1250<p>However, <tt>overloadable</tt> functions are allowed to use a
1251ellipsis 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>
1252
1253<blockquote>
1254<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]1255void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1256</pre>
1257</blockquote>
1258
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1259<p>Functions declared with the <tt>overloadable</tt> attribute have
1260their names mangled according to the same rules as C++ function
1261names. For example, the three <tt>tgsin</tt> functions in our
1262motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]1263<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1264caveats to this use of name mangling:</p>
1265
1266<ul>
1267
1268 <li>Future versions of Clang may change the name mangling of
1269 functions overloaded in C, so you should not depend on an specific
1270 mangling. To be completely safe, we strongly urge the use of
1271 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1272
1273 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1274 used in C++, because names will already be mangled and functions are
1275 already overloadable. However, when an <tt>overloadable</tt>
1276 function occurs within an <tt>extern "C"</tt> linkage specification,
1277 it's name <i>will</i> be mangled in the same way as it would in
1278 C.</li>
1279</ul>
1280
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]1281<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1282
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]1283<!-- ======================================================================= -->
1284<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1285<!-- ======================================================================= -->
1286
1287<p>clang supports an extension which allows the following in C:</p>
1288
1289<blockquote>
1290<pre>
1291#include &lt;math.h&gt;
1292#include &lt;complex.h&gt;
1293complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1294</pre>
1295</blockquote>
1296
1297<p>This construct is useful because there is no way to separately
1298initialize the real and imaginary parts of a complex variable in
1299standard C, given that clang does not support <code>_Imaginary</code>.
1300(clang also supports the <code>__real__</code> and <code>__imag__</code>
1301extensions from gcc, which help in some cases, but are not usable in
1302static initializers.)
1303
1304<p>Note that this extension does not allow eliding the braces; the
1305meaning of the following two lines is different:</p>
1306
1307<blockquote>
1308<pre>
1309complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1310complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1311</pre>
1312</blockquote>
1313
1314<p>This extension also works in C++ mode, as far as that goes, but does not
1315 apply to the C++ <code>std::complex</code>. (In C++11, list
1316 initialization allows the same syntax to be used with
1317 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1318
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1319<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1320<h2 id="builtins">Builtin Functions</h2>
1321<!-- ======================================================================= -->
1322
1323<p>Clang supports a number of builtin library functions with the same syntax as
1324GCC, including things like <tt>__builtin_nan</tt>,
1325<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1326<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1327addition to the GCC builtins, Clang supports a number of builtins that GCC does
1328not, which are listed here.</p>
1329
1330<p>Please note that Clang does not and will not support all of the GCC builtins
1331for vector operations. Instead of using builtins, you should use the functions
1332defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1333define portable wrappers for these. Many of the Clang versions of these
1334functions are implemented directly in terms of <a href="#vectors">extended
1335vector support</a> instead of builtins, in order to reduce the number of
1336builtins that we need to implement.</p>
1337
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1338<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1339<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1340<!-- ======================================================================= -->
1341
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1342<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1343permutation/shuffle/swizzle operations. This builtin is also very important for
1344the implementation of various target-specific header files like
1345<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1346</p>
1347
1348<p><b>Syntax:</b></p>
1349
1350<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1351__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1352</pre>
1353
1354<p><b>Examples:</b></p>
1355
1356<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1357 // Identity operation - return 4-element vector V1.
1358 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1359
1360 // "Splat" element 0 of V1 into a 4-element result.
1361 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1362
1363 // Reverse 4-element vector V1.
1364 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1365
1366 // Concatenate every other element of 4-element vectors V1 and V2.
1367 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1368
1369 // Concatenate every other element of 8-element vectors V1 and V2.
1370 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1371</pre>
1372
1373<p><b>Description:</b></p>
1374
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1375<p>The first two arguments to __builtin_shufflevector are vectors that have the
1376same element type. The remaining arguments are a list of integers that specify
1377the elements indices of the first two vectors that should be extracted and
1378returned in a new vector. These element indices are numbered sequentially
1379starting with the first vector, continuing into the second vector. Thus, if
1380vec1 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]1381</p>
1382
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1383<p>The result of __builtin_shufflevector is a vector
1384with the same element type as vec1/vec2 but that has an element count equal to
1385the number of indices specified.
1386</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1387
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1388<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1389
1390<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1391<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1392<!-- ======================================================================= -->
1393
1394<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1395the program cannot be reached, even if the compiler might otherwise think it
1396can. This is useful to improve optimization and eliminates certain warnings.
1397For example, without the <tt>__builtin_unreachable</tt> in the example below,
1398the compiler assumes that the inline asm can fall through and prints a "function
1399declared 'noreturn' should not return" warning.
1400</p>
1401
1402<p><b>Syntax:</b></p>
1403
1404<pre>
1405__builtin_unreachable()
1406</pre>
1407
1408<p><b>Example of Use:</b></p>
1409
1410<pre>
1411void myabort(void) __attribute__((noreturn));
1412void myabort(void) {
1413 asm("int3");
1414 __builtin_unreachable();
1415}
1416</pre>
1417
1418<p><b>Description:</b></p>
1419
1420<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1421it has undefined behavior, it is a statement that it is never reached and the
1422optimizer can take advantage of this to produce better code. This builtin takes
1423no arguments and produces a void result.
1424</p>
1425
1426<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1427
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1428<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1429<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1430<!-- ======================================================================= -->
1431
1432<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1433memory.
1434</p>
1435
1436<p><b>Syntax:</b></p>
1437
1438<pre>
1439<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1440</pre>
1441
1442<p><b>Example of Use:</b></p>
1443
1444<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1445int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1446</pre>
1447
1448<p><b>Description:</b></p>
1449
1450<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1451intrinsics to allow code to atomically swap the current value with the new
1452value. More importantly, it helps developers write more efficient and correct
1453code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1454relying on the platform specific implementation details of
1455__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1456</p>
1457
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1458
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1459<!-- ======================================================================= -->
1460<h2 id="targetspecific">Target-Specific Extensions</h2>
1461<!-- ======================================================================= -->
1462
1463<p>Clang supports some language features conditionally on some targets.</p>
1464
1465<!-- ======================================================================= -->
1466<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1467<!-- ======================================================================= -->
1468
1469<p>The X86 backend has these language extensions:</p>
1470
1471<!-- ======================================================================= -->
1472<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1473<!-- ======================================================================= -->
1474
1475<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1476relative to the X86 GS segment register, and address space #257 causes it to be
1477relative to the X86 FS segment. Note that this is a very very low-level
1478feature that should only be used if you know what you're doing (for example in
1479an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1480
1481<p>Here is an example:</p>
1482
1483<pre>
1484#define GS_RELATIVE __attribute__((address_space(256)))
1485int foo(int GS_RELATIVE *P) {
1486 return *P;
1487}
1488</pre>
1489
1490<p>Which compiles to (on X86-32):</p>
1491
1492<pre>
1493_foo:
1494 movl 4(%esp), %eax
1495 movl %gs:(%eax), %eax
1496 ret
1497</pre>
1498
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1499<!-- ======================================================================= -->
1500<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1501<!-- ======================================================================= -->
1502
1503<p>Clang supports additional attributes that are useful for documenting program
1504invariants and rules for static analysis tools. The extensions documented here
1505are used by the <a
1506href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1507engine</a> that is part of Clang's Analysis library.</p>
1508
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1509<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1510
1511<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1512attribute. This attribute, which is typically affixed to a function prototype,
1513indicates that a call to a given function never returns. Function prototypes for
1514common functions like <tt>exit</tt> are typically annotated with this attribute,
1515as well as a variety of common assertion handlers. Users can educate the static
1516analyzer about their own custom assertion handles (thus cutting down on false
1517positives due to false paths) by marking their own &quot;panic&quot; functions
1518with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1519
1520<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1521there are special functions that for all intents and purposes should be
1522considered panic functions (i.e., they are only called when an internal program
1523error occurs) but may actually return so that the program can fail gracefully.
1524The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1525as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1526pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1527<tt>noreturn</tt>).</p>
1528
1529<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]1530same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1531placed at the end of function prototypes:</p>
1532
1533<pre>
1534 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1535</pre>
1536
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1537<p>Query for this feature with
1538<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1539
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1540<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1541
1542<p>Many methods in Objective-C have conventional meanings determined
1543by their selectors. For the purposes of static analysis, it is
1544sometimes useful to be able to mark a method as having a particular
1545conventional meaning despite not having the right selector, or as not
1546having the conventional meaning that its selector would suggest.
1547For these use cases, we provide an attribute to specifically describe
1548the <q>method family</q> that a method belongs to.</p>
1549
1550<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1551where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1552<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1553can only be placed at the end of a method declaration:</p>
1554
1555<pre>
1556 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1557</pre>
1558
1559<p>Users who do not wish to change the conventional meaning of a
1560method, and who merely want to document its non-standard retain and
1561release semantics, should use the
1562<a href="#attr_retain_release">retaining behavior attributes</a>
1563described below.</p>
1564
1565<p>Query for this feature with
1566<tt>__has_attribute(objc_method_family)</tt>.</p>
1567
1568<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1569
1570<p>In Objective-C, functions and methods are generally assumed to take
1571and return objects with +0 retain counts, with some exceptions for
1572special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1573there are exceptions, and so Clang provides attributes to allow these
1574exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1575ignore non-leaks). Some exceptions may be better described using
1576the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1577attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1578
1579<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1580<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1581and <tt>cf_returns_not_retained</tt> attributes can be placed on
1582methods and functions that return Objective-C or CoreFoundation
1583objects. They are commonly placed at the end of a function prototype
1584or method declaration:</p>
1585
1586<pre>
1587 id foo() <b>__attribute__((ns_returns_retained))</b>;
1588
1589 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1590</pre>
1591
1592<p>The <tt>*_returns_retained</tt> attributes specify that the
1593returned object has a +1 retain count.
1594The <tt>*_returns_not_retained</tt> attributes specify that the return
1595object has a +0 retain count, even if the normal convention for its
1596selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1597returned object is +0, but is guaranteed to live at least as long as the
1598next flush of an autorelease pool.</p>
1599
1600<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1601attributes can be placed on an parameter declaration; they specify
1602that the argument is expected to have a +1 retain count, which will be
1603balanced in some way by the function or method.
1604The <tt>ns_consumes_self</tt> attribute can only be placed on an
1605Objective-C method; it specifies that the method expects
1606its <tt>self</tt> parameter to have a +1 retain count, which it will
1607balance in some way.</p>
1608
1609<pre>
1610 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1611
1612 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1613 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1614</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1615
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1616<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1617<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1618
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1619<!-- ======================================================================= -->
1620<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1621<!-- ======================================================================= -->
1622<h3 id="address_sanitizer">AddressSanitizer</h3>
1623<p> Use <code>__has_feature(address_sanitizer)</code>
1624to check if the code is being built with <a
1625 href="AddressSanitizer.html">AddressSanitizer</a>.
1626</p>
Kostya Serebryany71efba02012-01-24 19:25:38 +0000[diff] [blame]1627<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function
1628declaration to specify that address safety instrumentation (e.g.
1629AddressSanitizer) should not be applied to that function.
1630</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1631
1632<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1633<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1634<!-- ======================================================================= -->
1635
1636<p>Clang supports additional attributes for checking basic locking policies in
1637multithreaded programs.
1638Clang currently parses the following list of attributes, although
1639<b>the implementation for these annotations is currently in development.</b>
1640For more details, see the
1641<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1642</p>
1643
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1644<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1645
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1646<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1647declaration to specify that the thread safety analysis should not be run on that
1648function. This attribute provides an escape hatch (e.g. for situations when it
1649is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1650
1651<h4 id="ts_lockable">lockable</h4>
1652
1653<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1654that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1655used to check consistency.</p>
1656
1657<h4 id="ts_scopedlockable">scoped_lockable</h4>
1658
1659<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1660specify that it has a "scoped" lockable type. Objects of this type will acquire
1661the lock upon construction and release it upon going out of scope.
1662 This annotation is primarily used to check
1663consistency.</p>
1664
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1665<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1666
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1667<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1668specify that the variable must be accessed while holding some lock.</p>
1669
1670<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1671
1672<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1673specify that the pointer must be dereferenced while holding some lock.</p>
1674
1675<h4 id="ts_guardedby">guarded_by(l)</h4>
1676
1677<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1678specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1679
1680<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1681
1682<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1683specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1684
1685<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1686
1687<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1688of a lockable variable to specify that the lock must be acquired before all
1689attribute arguments. Arguments must be lockable type, and there must be at
1690least one argument.</p>
1691
1692<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1693
1694<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1695of a lockable variable to specify that the lock must be acquired after all
1696attribute arguments. Arguments must be lockable type, and there must be at
1697least one argument.</p>
1698
1699<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1700
1701<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1702declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1703exclusively. This attribute takes zero or more arguments: either of lockable
1704type or integers indexing into function parameters of lockable type. If no
1705arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1706enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1707
1708<h4 id="ts_slf">shared_lock_function(...)</h4>
1709
1710<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1711declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1712 the locks may be shared (e.g. read locks). This attribute takes zero or more
1713arguments: either of lockable type or integers indexing into function
1714parameters of lockable type. If no arguments are given, the acquired lock is
1715implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1716
1717<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1718
1719<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1720declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1721all listed locks exclusively. This attribute takes one or more arguments. The
1722first argument is an integer or boolean value specifying the return value of a
1723successful lock acquisition. The remaining arugments are either of lockable type
1724or integers indexing into function parameters of lockable type. If only one
1725argument is given, the acquired lock is implicitly <tt>this</tt> of the
1726enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1727
1728<h4 id="ts_stf">shared_trylock_function(...)</h4>
1729
1730<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1731declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1732all listed locks, although the locks may be shared (e.g. read locks). This
1733attribute takes one or more arguments. The first argument is an integer or
1734boolean value specifying the return value of a successful lock acquisition. The
1735remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1736function parameters of lockable type. If only one argument is given, the
1737acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1738
1739<h4 id="ts_uf">unlock_function(...)</h4>
1740
1741<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1742declaration to specify that the function release all listed locks. This
1743attribute takes zero or more arguments: either of lockable type or integers
1744indexing into function parameters of lockable type. If no arguments are given,
1745the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1746
1747<h4 id="ts_lr">lock_returned(l)</h4>
1748
1749<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1750declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1751must be of lockable type). This annotation is used to aid in resolving lock
1752expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1753
1754<h4 id="ts_le">locks_excluded(...)</h4>
1755
1756<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1757to specify that the function must not be called with the listed locks. Arguments
1758must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1759
1760<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1761
1762<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1763declaration to specify that the function must be called while holding the listed
1764exclusive locks. Arguments must be lockable type, and there must be at
1765least one argument.</p>
1766
1767<h4 id="ts_slr">shared_locks_required(...)</h4>
1768
1769<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1770declaration to specify that the function must be called while holding the listed
1771shared locks. Arguments must be lockable type, and there must be at
1772least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1773
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1774</div>
1775</body>
1776</html>