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gerrit-public.fairphone.software / platform / external / clang / aebb653a28b142b570596e45cb31b1d5fce1710c / . / docs / LanguageExtensions.html
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19
20<div id="content">
21
22<h1>Clang Language Extensions</h1>
23
24<ul>
25<li><a href="#intro">Introduction</a></li>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]26<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]27<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]28<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]29<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]30<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
31<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]32<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]33 <ul>
34 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
35 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]36 </ul></li>
37<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]38 <ul>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]39 <li><a href="#cxx0x">C++0x</a>
40 <ul>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]41 <li><a href="#cxx_access_control_sfinae">C++0x SFINAE includes access control</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]42 <li><a href="#cxx_alias_templates">C++0x alias templates</a></li>
43 <li><a href="#cxx_attributes">C++0x attributes</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]44 <li><a href="#cxx_constexpr">C++0x generalized constant expressions</a></li>
45 <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]46 <li><a href="#cxx_default_function_template_args">C++0x default template arguments in function templates</a></li>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]47 <li><a href="#cxx_delegating_constructor">C++0x delegating constructors</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]48 <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]49 <li><a href="#cxx_explicit_conversions">C++0x explicit conversion functions</a></li>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]50 <li><a href="#cxx_generalized_initializers">C++0x generalized initializers</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]51 <li><a href="#cxx_implicit_moves">C++0x implicit move constructors/assignment operators</a></li>
52 <li><a href="#cxx_inheriting_constructors">C++0x inheriting constructors</a></li>
53 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]54 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]55 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
56 <li><a href="#cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]57 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
58 <li><a href="#cxx_override_control">C++0x override control</a></li>
59 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]60 <li><a href="#cxx_raw_string_literals">C++0x raw string literals</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]61 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
62 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
63 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
64 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]65 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]66 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]67 <li><a href="#cxx_unicode_literals">C++0x Unicode string literals</a></li>
68 <li><a href="#cxx_unrestricted_unions">C++0x unrestricted unions</a></li>
69 <li><a href="#cxx_user_literals">C++0x user-defined literals</a></li>
70 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
71 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]72 <li><a href="#c1x">C1X</a>
73 <ul>
74 <li><a href="#c_generic_selections">C1X generic selections</a></li>
75 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]76 </ul></li>
77 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]78<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]79<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]80<li><a href="#objc_features">Objective-C Features</a>
81 <ul>
82 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]83 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]84 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]85 </ul>
86</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]87<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]88<li><a href="#builtins">Builtin Functions</a>
89 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]90 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]91 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]92 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]93 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]94</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]95<li><a href="#targetspecific">Target-Specific Extensions</a>
96 <ul>
97 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
98 </ul>
99</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]100<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]101<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
102 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]103 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
104 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
105 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]106 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
107 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]108 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
109 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
110 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
111 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
112 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
113 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
114 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
115 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
116 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
117 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
118 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
119 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
120 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]121 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]122</ul>
123
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]124<!-- ======================================================================= -->
125<h2 id="intro">Introduction</h2>
126<!-- ======================================================================= -->
127
128<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]129addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]130range of GCC extensions. Please see the <a
131href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
132more information on these extensions.</p>
133
134<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]135<h2 id="feature_check">Feature Checking Macros</h2>
136<!-- ======================================================================= -->
137
138<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]139on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]140function-like macros. This allows you to directly test for a feature in your
141code without having to resort to something like autoconf or fragile "compiler
142version checks".</p>
143
144<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]145<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]146<!-- ======================================================================= -->
147
148<p>This function-like macro takes a single identifier argument that is the name
149of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
150not. It can be used like this:</p>
151
152<blockquote>
153<pre>
154#ifndef __has_builtin // Optional of course.
155 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
156#endif
157
158...
159#if __has_builtin(__builtin_trap)
160 __builtin_trap();
161#else
162 abort();
163#endif
164...
165</pre>
166</blockquote>
167
168
169<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]170<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]171<!-- ======================================================================= -->
172
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]173<p>These function-like macros take a single identifier argument that is the
174name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
175is both supported by Clang and standardized in the current language standard
176or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
177<code>__has_extension</code> evaluates to 1 if the feature is supported by
178Clang in the current language (either as a language extension or a standard
179language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]180
181<blockquote>
182<pre>
183#ifndef __has_feature // Optional of course.
184 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
185#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]186#ifndef __has_extension
187 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
188#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]189
190...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]191#if __has_feature(cxx_rvalue_references)
192// This code will only be compiled with the -std=c++0x and -std=gnu++0x
193// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]194#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]195
196#if __has_extension(cxx_rvalue_references)
197// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
198// and -std=gnu++98 options, because rvalue references are supported as a
199// language extension in C++98.
200#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]201</pre>
202</blockquote>
203
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]204<p id="has_feature_back_compat">For backwards compatibility reasons,
205<code>__has_feature</code> can also be used to test for support for
206non-standardized features, i.e. features not prefixed <code>c_</code>,
207<code>cxx_</code> or <code>objc_</code>.</p>
208
209<p>If the <code>-pedantic-errors</code> option is given,
210<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
211
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]212<p>The feature tag is described along with the language feature below.</p>
213
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]214<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]215<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]216<!-- ======================================================================= -->
217
218<p>This function-like macro takes a single identifier argument that is the name
219of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
220can be used like this:</p>
221
222<blockquote>
223<pre>
224#ifndef __has_attribute // Optional of course.
225 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
226#endif
227
228...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]229#if __has_attribute(always_inline)
230#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]231#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]232#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]233#endif
234...
235</pre>
236</blockquote>
237
238<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]239<h2 id="has_include">Include File Checking Macros</h2>
240<!-- ======================================================================= -->
241
242<p>Not all developments systems have the same include files.
243The <a href="#__has_include">__has_include</a> and
244<a href="#__has_include_next">__has_include_next</a> macros allow you to
245check for the existence of an include file before doing
246a possibly failing #include directive.</p>
247
248<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]249<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]250<!-- ======================================================================= -->
251
252<p>This function-like macro takes a single file name string argument that
253is the name of an include file. It evaluates to 1 if the file can
254be found using the include paths, or 0 otherwise:</p>
255
256<blockquote>
257<pre>
258// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]259#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]260# include "myinclude.h"
261#endif
262
263// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]264#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]265# include "myinclude.h"
266#endif
267</pre>
268</blockquote>
269
270<p>To test for this feature, use #if defined(__has_include).</p>
271
272<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]273<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]274<!-- ======================================================================= -->
275
276<p>This function-like macro takes a single file name string argument that
277is the name of an include file. It is like __has_include except that it
278looks for the second instance of the given file found in the include
279paths. It evaluates to 1 if the second instance of the file can
280be found using the include paths, or 0 otherwise:</p>
281
282<blockquote>
283<pre>
284// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]285#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]286# include_next "myinclude.h"
287#endif
288
289// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]290#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]291# include_next "myinclude.h"
292#endif
293</pre>
294</blockquote>
295
296<p>Note that __has_include_next, like the GNU extension
297#include_next directive, is intended for use in headers only,
298and will issue a warning if used in the top-level compilation
299file. A warning will also be issued if an absolute path
300is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]301
302<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]303<h2 id="builtinmacros">Builtin Macros</h2>
304<!-- ======================================================================= -->
305
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]306<dl>
307 <dt><code>__BASE_FILE__</code></dt>
308 <dd>Defined to a string that contains the name of the main input
309 file passed to Clang.</dd>
310
311 <dt><code>__COUNTER__</code></dt>
312 <dd>Defined to an integer value that starts at zero and is
313 incremented each time the <code>__COUNTER__</code> macro is
314 expanded.</dd>
315
316 <dt><code>__INCLUDE_LEVEL__</code></dt>
317 <dd>Defined to an integral value that is the include depth of the
318 file currently being translated. For the main file, this value is
319 zero.</dd>
320
321 <dt><code>__TIMESTAMP__</code></dt>
322 <dd>Defined to the date and time of the last modification of the
323 current source file.</dd>
324
325 <dt><code>__clang__</code></dt>
326 <dd>Defined when compiling with Clang</dd>
327
328 <dt><code>__clang_major__</code></dt>
329 <dd>Defined to the major version number of Clang (e.g., the 2 in
330 2.0.1).</dd>
331
332 <dt><code>__clang_minor__</code></dt>
333 <dd>Defined to the minor version number of Clang (e.g., the 0 in
334 2.0.1).</dd>
335
336 <dt><code>__clang_patchlevel__</code></dt>
337 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
338
339 <dt><code>__clang_version__</code></dt>
340 <dd>Defined to a string that captures the Clang version, including
341 the Subversion tag or revision number, e.g., "1.5 (trunk
342 102332)".</dd>
343</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]344
345<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]346<h2 id="vectors">Vectors and Extended Vectors</h2>
347<!-- ======================================================================= -->
348
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]349<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
350
351<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
352syntax and other tidbits as seen in OpenCL. An example is:</p>
353
354<blockquote>
355<pre>
356typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
357typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
358
359float4 foo(float2 a, float2 b) {
360 float4 c;
361 c.xz = a;
362 c.yw = b;
363 return c;
364}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]365</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]366</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]367
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]368<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]369
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]370<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
371
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]372<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]373<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]374<!-- ======================================================================= -->
375
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]376<p>An optional string message can be added to the <tt>deprecated</tt>
377and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]378
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]379<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]380<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]381</blockquote>
382
383<p>If the deprecated or unavailable declaration is used, the message
384will be incorporated into the appropriate diagnostic:</p>
385
386<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]387<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! [-Wdeprecated-declarations]
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]388 explode();
389 ^</pre>
390</blockquote>
391
392<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]393with <tt>__has_extension(attribute_deprecated_with_message)</tt>
394and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]395
396<!-- ======================================================================= -->
397<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
398<!-- ======================================================================= -->
399
400<p>Clang allows attributes to be written on individual enumerators.
401This allows enumerators to be deprecated, made unavailable, etc. The
402attribute must appear after the enumerator name and before any
403initializer, like so:</p>
404
405<blockquote>
406<pre>enum OperationMode {
407 OM_Invalid,
408 OM_Normal,
409 OM_Terrified __attribute__((deprecated)),
410 OM_AbortOnError __attribute__((deprecated)) = 4
411};</pre>
412</blockquote>
413
414<p>Attributes on the <tt>enum</tt> declaration do not apply to
415individual enumerators.</p>
416
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]417<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]418
419<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]420<h2 id="checking_language_features">Checks for Standard Language Features</h2>
421<!-- ======================================================================= -->
422
423<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
424enabled. Those features are listed here.</p>
425
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]426<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]427
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]428<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]429example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]430
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]431<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]432
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]433<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]434compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]435
436<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]437<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
438<!-- ======================================================================= -->
439
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]440<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
441to query if certain upcoming standard language features are enabled. Those
442features are listed here. Features that are not yet implemented will be
443noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]444
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]445<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]446
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]447<p>The features listed below are slated for inclusion in the upcoming
448C++0x standard. As a result, all these features are enabled
449with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]450
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]451<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]452
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]453<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]454
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]455<h4 id="cxx_alias_templates">C++0x alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]456
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]457<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
458<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]459C++0x's alias declarations and alias templates is enabled.</p>
460
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]461<h4 id="cxx_attributes">C++0x attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]462
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]463<p>Use <tt>__has_feature(cxx_attributes)</tt> or
464<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
465parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]466
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]467<h4 id="cxx_constexpr">C++0x generalized constant expressions</h4>
468
469<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
470for generalized constant expressions (e.g., <tt>constexpr</tt>) is
471enabled. Clang does not currently implement this feature.</p>
472
473<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h4>
474
475<p>Use <tt>__has_feature(cxx_decltype)</tt> or
476<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
477<tt>decltype()</tt> specifier is enabled.</p>
478
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]479<h4 id="cxx_default_function_template_args">C++0x default template arguments in function templates</h4>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]480
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]481<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
482<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
483if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]484
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]485<h4 id="cxx_delegating_constructors">C++0x delegating constructors</h4>
486
487<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
488support for delegating constructors is enabled.</p>
489
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]490<h4 id="cxx_deleted_functions">C++0x <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]491
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]492<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
493<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]494deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]495
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]496<h4 id="cxx_explicit_conversions">C++0x explicit conversion functions</h3>
497<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
498
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]499<h4 id="cxx_generalized_initializers">C++0x generalized initializers</h4>
500
501<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
502support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]503<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
504this feature.</p>
505
506<h4 id="cxx_implicit_moves">C++0x implicit move constructors/assignment operators</h4>
507
508<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will implicitly generate move constructors and move assignment operators where needed. Clang does not currently implement this feature.</p>
509
510<h4 id="cxx_inheriting_constructors">C++0x inheriting constructors</h4>
511
512<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>
513
514<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h4>
515
516<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
517<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
518inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]519
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]520<h4 id="cxx_lambdas">C++0x lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]521
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]522<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
523<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]524is enabled. Clang does not currently implement this feature.</p>
525
526<h4 id="cxx_noexcept">C++0x noexcept</h4>
527
528<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
529<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
530exception specifications is enabled.</p>
531
532<h4 id="cxx_nonstatic_member_init">C++0x in-class non-static data member initialization</h4>
533
534<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]535
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]536<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]537
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]538<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
539<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]540<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]541
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]542<h4 id="cxx_override_control">C++0x <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]543
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]544<p>Use <tt>__has_feature(cxx_override_control)</tt> or
545<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]546the override control keywords is enabled.</p>
547
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]548<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]549<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
550<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
551if support for reference-qualified functions (e.g., member functions with
552<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
553is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]554
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]555<h4 id="cxx_range_for">C++0x range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]556
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]557<p>Use <tt>__has_feature(cxx_range_for)</tt> or
558<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
559range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]560
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]561<h4 id="cxx_raw_string_literals">C++0x raw string literals</h4>
562<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support for raw string literals (e.g., <tt>R"foo\bar"</tt>) is enabled.</p>
563
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]564<h4 id="cxx_rvalue_references">C++0x rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]565
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]566<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
567<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]568rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]569
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]570<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]571
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]572<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
573<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]574compile-time assertions using <tt>static_assert</tt> is enabled.</p>
575
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]576<h4 id="cxx_auto_type">C++0x type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]577
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]578<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
579<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
580supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
581will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]582
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]583<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]584
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]585<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
586<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
587strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]588
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]589<h4 id="cxx_trailing_return">C++0x trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]590
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]591<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
592<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
593alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]594
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]595<h4 id="cxx_unicode_literals">C++0x Unicode string literals</h4>
596<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
597support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]598
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]599<h4 id="cxx_unrestricted_unions">C++0x unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]600
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]601<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled. Clang does not currently support this feature.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]602
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]603<h4 id="cxx_user_literals">C++0x user-defined literals</h4>
604
605<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled. Clang does not currently support this feature.</p>
606
607<h4 id="cxx_variadic_templates">C++0x variadic templates</h4>
608
609<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
610<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
611for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]612
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]613<h3 id="c1x">C1X</h3>
614
615<p>The features listed below are slated for inclusion in the upcoming
616C1X standard. As a result, all these features are enabled
617with the <tt>-std=c1x</tt> option when compiling C code.</p>
618
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]619<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]620
621<p>Use <tt>__has_feature(c_generic_selections)</tt> or
622<tt>__has_extension(c_generic_selections)</tt> to determine if support for
623generic selections is enabled.</p>
624
625<p>As an extension, the C1X generic selection expression is available in all
626languages supported by Clang. The syntax is the same as that given in the
627C1X draft standard.</p>
628
629<p>In C, type compatibility is decided according to the rules given in the
630appropriate standard, but in C++, which lacks the type compatibility rules
631used in C, types are considered compatible only if they are equivalent.</p>
632
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]633<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]634
635<p>Use <tt>__has_feature(c_static_assert)</tt> or
636<tt>__has_extension(c_static_assert)</tt> to determine if support for
637compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
638
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]639<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]640<h2 id="checking_type_traits">Checks for Type Traits</h2>
641<!-- ======================================================================= -->
642
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]643<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]644<blockquote>
645<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]646#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]647template&lt;typename From, typename To&gt;
648struct is_convertible_to {
649 static const bool value = __is_convertible_to(From, To);
650};
651#else
652// Emulate type trait
653#endif
654</pre>
655</blockquote>
656
657<p>The following type traits are supported by Clang:</p>
658<ul>
659 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
660 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
661 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
662 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
663 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
664 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
665 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
666 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
667 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
668 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
669 <li><code>__is_class</code> (GNU, Microsoft)</li>
670 <li><code>__is_convertible_to</code> (Microsoft)</li>
671 <li><code>__is_empty</code> (GNU, Microsoft)</li>
672 <li><code>__is_enum</code> (GNU, Microsoft)</li>
673 <li><code>__is_pod</code> (GNU, Microsoft)</li>
674 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
675 <li><code>__is_union</code> (GNU, Microsoft)</li>
676 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
Sean Hunt1fba8282011-07-18 17:22:33 +0000[diff] [blame]677 <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++0x standard library.</li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]678</ul>
679
680<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]681<h2 id="blocks">Blocks</h2>
682<!-- ======================================================================= -->
683
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]684<p>The syntax and high level language feature description is in <a
685href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
686details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]687href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]688
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]689
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]690<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]691
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]692<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]693<h2 id="objc_features">Objective-C Features</h2>
694<!-- ======================================================================= -->
695
696<h3 id="objc_instancetype">Related result types</h3>
697
698<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>
699
700<blockquote>
701<pre>
702@interface NSObject
703+ (id)alloc;
704- (id)init;
705@end
706
707@interface NSArray : NSObject
708@end
709</pre>
710</blockquote>
711
712<p>and this common initialization pattern</p>
713
714<blockquote>
715<pre>
716NSArray *array = [[NSArray alloc] init];
717</pre>
718</blockquote>
719
720<p>the type of the expression <code>[NSArray alloc]</code> is
721<code>NSArray*</code> because <code>alloc</code> implicitly has a
722related result type. Similarly, the type of the expression
723<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
724<code>init</code> has a related result type and its receiver is known
725to 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>
726
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]727<p>A method with a related result type can be declared by using the
728type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
729is a contextual keyword that is only permitted in the result type of
730an Objective-C method, e.g.</p>
731
732<pre>
733@interface A
734+ (<b>instancetype</b>)constructAnA;
735@end
736</pre>
737
738<p>The related result type can also be inferred for some methods.
739To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]740word in the camel-case selector (e.g., "init" in "initWithObjects") is
741considered, and the method will a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]742type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]743
744<ul>
745
746 <li>the first word is "alloc" or "new", and the method is a class
747 method, or</li>
748
749 <li>the first word is "autorelease", "init", "retain", or "self",
750 and the method is an instance method.</li>
751
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]752</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]753
754<p>If a method with a related result type is overridden by a subclass
755method, the subclass method must also return a type that is compatible
756with the subclass type. For example:</p>
757
758<blockquote>
759<pre>
760@interface NSString : NSObject
761- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
762@end
763</pre>
764</blockquote>
765
766<p>Related result types only affect the type of a message send or
767property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]768with a related result type is treated the same way as method that
769returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]770
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame^]771<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
772the <tt>instancetype</tt> contextual keyword is available.</p>
773
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]774<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]775<h2 id="objc_arc">Automatic reference counting </h2>
776<!-- ======================================================================= -->
777
778<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>
779
780<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]781<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
782<!-- ======================================================================= -->
783
784<p>Clang provides support for C++0x enumerations with a fixed
785underlying type within Objective-C. For example, one can write an
786enumeration type as:</p>
787
788<pre>
789typedef enum : unsigned char { Red, Green, Blue } Color;
790</pre>
791
792<p>This specifies that the underlying type, which is used to store the
793enumeration value, is <tt>unsigned char</tt>.</p>
794
795<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
796support for fixed underlying types is available in Objective-C.</p>
797
798<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]799<h2 id="overloading-in-c">Function Overloading in C</h2>
800<!-- ======================================================================= -->
801
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]802<p>Clang provides support for C++ function overloading in C. Function
803overloading in C is introduced using the <tt>overloadable</tt> attribute. For
804example, one might provide several overloaded versions of a <tt>tgsin</tt>
805function that invokes the appropriate standard function computing the sine of a
806value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
807precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]808
809<blockquote>
810<pre>
811#include &lt;math.h&gt;
812float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
813double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
814long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
815</pre>
816</blockquote>
817
818<p>Given these declarations, one can call <tt>tgsin</tt> with a
819<tt>float</tt> value to receive a <tt>float</tt> result, with a
820<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
821overloading in C follows the rules of C++ function overloading to pick
822the best overload given the call arguments, with a few C-specific
823semantics:</p>
824<ul>
825 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
826 double</tt> is ranked as a floating-point promotion (per C99) rather
827 than as a floating-point conversion (as in C++).</li>
828
829 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
830 <tt>U*</tt> is considered a pointer conversion (with conversion
831 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
832
833 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
834 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
835 conversion is given "conversion" rank.</li>
836</ul>
837
838<p>The declaration of <tt>overloadable</tt> functions is restricted to
839function declarations and definitions. Most importantly, if any
840function with a given name is given the <tt>overloadable</tt>
841attribute, then all function declarations and definitions with that
842name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]843attribute. This rule even applies to redeclarations of functions whose original
844declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]845
846<blockquote>
847<pre>
848int f(int) __attribute__((overloadable));
849float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
850
851int g(int) __attribute__((overloadable));
852int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
853</pre>
854</blockquote>
855
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]856<p>Functions marked <tt>overloadable</tt> must have
857prototypes. Therefore, the following code is ill-formed:</p>
858
859<blockquote>
860<pre>
861int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
862</pre>
863</blockquote>
864
865<p>However, <tt>overloadable</tt> functions are allowed to use a
866ellipsis 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>
867
868<blockquote>
869<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]870void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]871</pre>
872</blockquote>
873
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]874<p>Functions declared with the <tt>overloadable</tt> attribute have
875their names mangled according to the same rules as C++ function
876names. For example, the three <tt>tgsin</tt> functions in our
877motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]878<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]879caveats to this use of name mangling:</p>
880
881<ul>
882
883 <li>Future versions of Clang may change the name mangling of
884 functions overloaded in C, so you should not depend on an specific
885 mangling. To be completely safe, we strongly urge the use of
886 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
887
888 <li>The <tt>overloadable</tt> attribute has almost no meaning when
889 used in C++, because names will already be mangled and functions are
890 already overloadable. However, when an <tt>overloadable</tt>
891 function occurs within an <tt>extern "C"</tt> linkage specification,
892 it's name <i>will</i> be mangled in the same way as it would in
893 C.</li>
894</ul>
895
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]896<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]897
898
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]899<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]900<h2 id="builtins">Builtin Functions</h2>
901<!-- ======================================================================= -->
902
903<p>Clang supports a number of builtin library functions with the same syntax as
904GCC, including things like <tt>__builtin_nan</tt>,
905<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
906<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
907addition to the GCC builtins, Clang supports a number of builtins that GCC does
908not, which are listed here.</p>
909
910<p>Please note that Clang does not and will not support all of the GCC builtins
911for vector operations. Instead of using builtins, you should use the functions
912defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
913define portable wrappers for these. Many of the Clang versions of these
914functions are implemented directly in terms of <a href="#vectors">extended
915vector support</a> instead of builtins, in order to reduce the number of
916builtins that we need to implement.</p>
917
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]918<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]919<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]920<!-- ======================================================================= -->
921
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]922<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]923permutation/shuffle/swizzle operations. This builtin is also very important for
924the implementation of various target-specific header files like
925<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]926</p>
927
928<p><b>Syntax:</b></p>
929
930<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]931__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]932</pre>
933
934<p><b>Examples:</b></p>
935
936<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]937 // Identity operation - return 4-element vector V1.
938 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
939
940 // "Splat" element 0 of V1 into a 4-element result.
941 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
942
943 // Reverse 4-element vector V1.
944 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
945
946 // Concatenate every other element of 4-element vectors V1 and V2.
947 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
948
949 // Concatenate every other element of 8-element vectors V1 and V2.
950 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]951</pre>
952
953<p><b>Description:</b></p>
954
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]955<p>The first two arguments to __builtin_shufflevector are vectors that have the
956same element type. The remaining arguments are a list of integers that specify
957the elements indices of the first two vectors that should be extracted and
958returned in a new vector. These element indices are numbered sequentially
959starting with the first vector, continuing into the second vector. Thus, if
960vec1 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]961</p>
962
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]963<p>The result of __builtin_shufflevector is a vector
964with the same element type as vec1/vec2 but that has an element count equal to
965the number of indices specified.
966</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]967
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]968<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
969
970<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]971<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]972<!-- ======================================================================= -->
973
974<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
975the program cannot be reached, even if the compiler might otherwise think it
976can. This is useful to improve optimization and eliminates certain warnings.
977For example, without the <tt>__builtin_unreachable</tt> in the example below,
978the compiler assumes that the inline asm can fall through and prints a "function
979declared 'noreturn' should not return" warning.
980</p>
981
982<p><b>Syntax:</b></p>
983
984<pre>
985__builtin_unreachable()
986</pre>
987
988<p><b>Example of Use:</b></p>
989
990<pre>
991void myabort(void) __attribute__((noreturn));
992void myabort(void) {
993 asm("int3");
994 __builtin_unreachable();
995}
996</pre>
997
998<p><b>Description:</b></p>
999
1000<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1001it has undefined behavior, it is a statement that it is never reached and the
1002optimizer can take advantage of this to produce better code. This builtin takes
1003no arguments and produces a void result.
1004</p>
1005
1006<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1007
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1008<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1009<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1010<!-- ======================================================================= -->
1011
1012<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1013memory.
1014</p>
1015
1016<p><b>Syntax:</b></p>
1017
1018<pre>
1019<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1020</pre>
1021
1022<p><b>Example of Use:</b></p>
1023
1024<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1025int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1026</pre>
1027
1028<p><b>Description:</b></p>
1029
1030<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1031intrinsics to allow code to atomically swap the current value with the new
1032value. More importantly, it helps developers write more efficient and correct
1033code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1034relying on the platform specific implementation details of
1035__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1036</p>
1037
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1038
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1039<!-- ======================================================================= -->
1040<h2 id="targetspecific">Target-Specific Extensions</h2>
1041<!-- ======================================================================= -->
1042
1043<p>Clang supports some language features conditionally on some targets.</p>
1044
1045<!-- ======================================================================= -->
1046<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1047<!-- ======================================================================= -->
1048
1049<p>The X86 backend has these language extensions:</p>
1050
1051<!-- ======================================================================= -->
1052<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1053<!-- ======================================================================= -->
1054
1055<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1056relative to the X86 GS segment register, and address space #257 causes it to be
1057relative to the X86 FS segment. Note that this is a very very low-level
1058feature that should only be used if you know what you're doing (for example in
1059an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1060
1061<p>Here is an example:</p>
1062
1063<pre>
1064#define GS_RELATIVE __attribute__((address_space(256)))
1065int foo(int GS_RELATIVE *P) {
1066 return *P;
1067}
1068</pre>
1069
1070<p>Which compiles to (on X86-32):</p>
1071
1072<pre>
1073_foo:
1074 movl 4(%esp), %eax
1075 movl %gs:(%eax), %eax
1076 ret
1077</pre>
1078
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1079<!-- ======================================================================= -->
1080<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1081<!-- ======================================================================= -->
1082
1083<p>Clang supports additional attributes that are useful for documenting program
1084invariants and rules for static analysis tools. The extensions documented here
1085are used by the <a
1086href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1087engine</a> that is part of Clang's Analysis library.</p>
1088
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1089<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1090
1091<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1092attribute. This attribute, which is typically affixed to a function prototype,
1093indicates that a call to a given function never returns. Function prototypes for
1094common functions like <tt>exit</tt> are typically annotated with this attribute,
1095as well as a variety of common assertion handlers. Users can educate the static
1096analyzer about their own custom assertion handles (thus cutting down on false
1097positives due to false paths) by marking their own &quot;panic&quot; functions
1098with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1099
1100<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1101there are special functions that for all intents and purposes should be
1102considered panic functions (i.e., they are only called when an internal program
1103error occurs) but may actually return so that the program can fail gracefully.
1104The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1105as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1106pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1107<tt>noreturn</tt>).</p>
1108
1109<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]1110same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1111placed at the end of function prototypes:</p>
1112
1113<pre>
1114 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1115</pre>
1116
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1117<p>Query for this feature with
1118<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1119
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1120<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1121
1122<p>Many methods in Objective-C have conventional meanings determined
1123by their selectors. For the purposes of static analysis, it is
1124sometimes useful to be able to mark a method as having a particular
1125conventional meaning despite not having the right selector, or as not
1126having the conventional meaning that its selector would suggest.
1127For these use cases, we provide an attribute to specifically describe
1128the <q>method family</q> that a method belongs to.</p>
1129
1130<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1131where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1132<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1133can only be placed at the end of a method declaration:</p>
1134
1135<pre>
1136 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1137</pre>
1138
1139<p>Users who do not wish to change the conventional meaning of a
1140method, and who merely want to document its non-standard retain and
1141release semantics, should use the
1142<a href="#attr_retain_release">retaining behavior attributes</a>
1143described below.</p>
1144
1145<p>Query for this feature with
1146<tt>__has_attribute(objc_method_family)</tt>.</p>
1147
1148<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1149
1150<p>In Objective-C, functions and methods are generally assumed to take
1151and return objects with +0 retain counts, with some exceptions for
1152special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1153there are exceptions, and so Clang provides attributes to allow these
1154exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1155ignore non-leaks). Some exceptions may be better described using
1156the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1157attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1158
1159<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1160<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1161and <tt>cf_returns_not_retained</tt> attributes can be placed on
1162methods and functions that return Objective-C or CoreFoundation
1163objects. They are commonly placed at the end of a function prototype
1164or method declaration:</p>
1165
1166<pre>
1167 id foo() <b>__attribute__((ns_returns_retained))</b>;
1168
1169 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1170</pre>
1171
1172<p>The <tt>*_returns_retained</tt> attributes specify that the
1173returned object has a +1 retain count.
1174The <tt>*_returns_not_retained</tt> attributes specify that the return
1175object has a +0 retain count, even if the normal convention for its
1176selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1177returned object is +0, but is guaranteed to live at least as long as the
1178next flush of an autorelease pool.</p>
1179
1180<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1181attributes can be placed on an parameter declaration; they specify
1182that the argument is expected to have a +1 retain count, which will be
1183balanced in some way by the function or method.
1184The <tt>ns_consumes_self</tt> attribute can only be placed on an
1185Objective-C method; it specifies that the method expects
1186its <tt>self</tt> parameter to have a +1 retain count, which it will
1187balance in some way.</p>
1188
1189<pre>
1190 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1191
1192 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1193 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1194</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1195
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1196<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1197<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1198
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1199
1200<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1201<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1202<!-- ======================================================================= -->
1203
1204<p>Clang supports additional attributes for checking basic locking policies in
1205multithreaded programs.
1206Clang currently parses the following list of attributes, although
1207<b>the implementation for these annotations is currently in development.</b>
1208For more details, see the
1209<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1210</p>
1211
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1212<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1213
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1214<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1215declaration to specify that the thread safety analysis should not be run on that
1216function. This attribute provides an escape hatch (e.g. for situations when it
1217is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1218
1219<h4 id="ts_lockable">lockable</h4>
1220
1221<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1222that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1223used to check consistency.</p>
1224
1225<h4 id="ts_scopedlockable">scoped_lockable</h4>
1226
1227<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1228specify that it has a "scoped" lockable type. Objects of this type will acquire
1229the lock upon construction and release it upon going out of scope.
1230 This annotation is primarily used to check
1231consistency.</p>
1232
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1233<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1234
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1235<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1236specify that the variable must be accessed while holding some lock.</p>
1237
1238<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1239
1240<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1241specify that the pointer must be dereferenced while holding some lock.</p>
1242
1243<h4 id="ts_guardedby">guarded_by(l)</h4>
1244
1245<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1246specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1247
1248<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1249
1250<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1251specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1252
1253<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1254
1255<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1256of a lockable variable to specify that the lock must be acquired before all
1257attribute arguments. Arguments must be lockable type, and there must be at
1258least one argument.</p>
1259
1260<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1261
1262<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1263of a lockable variable to specify that the lock must be acquired after all
1264attribute arguments. Arguments must be lockable type, and there must be at
1265least one argument.</p>
1266
1267<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1268
1269<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1270declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1271exclusively. This attribute takes zero or more arguments: either of lockable
1272type or integers indexing into function parameters of lockable type. If no
1273arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1274enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1275
1276<h4 id="ts_slf">shared_lock_function(...)</h4>
1277
1278<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1279declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1280 the locks may be shared (e.g. read locks). This attribute takes zero or more
1281arguments: either of lockable type or integers indexing into function
1282parameters of lockable type. If no arguments are given, the acquired lock is
1283implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1284
1285<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1286
1287<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1288declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1289all listed locks exclusively. This attribute takes one or more arguments. The
1290first argument is an integer or boolean value specifying the return value of a
1291successful lock acquisition. The remaining arugments are either of lockable type
1292or integers indexing into function parameters of lockable type. If only one
1293argument is given, the acquired lock is implicitly <tt>this</tt> of the
1294enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1295
1296<h4 id="ts_stf">shared_trylock_function(...)</h4>
1297
1298<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1299declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1300all listed locks, although the locks may be shared (e.g. read locks). This
1301attribute takes one or more arguments. The first argument is an integer or
1302boolean value specifying the return value of a successful lock acquisition. The
1303remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1304function parameters of lockable type. If only one argument is given, the
1305acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1306
1307<h4 id="ts_uf">unlock_function(...)</h4>
1308
1309<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1310declaration to specify that the function release all listed locks. This
1311attribute takes zero or more arguments: either of lockable type or integers
1312indexing into function parameters of lockable type. If no arguments are given,
1313the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1314
1315<h4 id="ts_lr">lock_returned(l)</h4>
1316
1317<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1318declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1319must be of lockable type). This annotation is used to aid in resolving lock
1320expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1321
1322<h4 id="ts_le">locks_excluded(...)</h4>
1323
1324<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1325to specify that the function must not be called with the listed locks. Arguments
1326must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1327
1328<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1329
1330<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1331declaration to specify that the function must be called while holding the listed
1332exclusive locks. Arguments must be lockable type, and there must be at
1333least one argument.</p>
1334
1335<h4 id="ts_slr">shared_locks_required(...)</h4>
1336
1337<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1338declaration to specify that the function must be called while holding the listed
1339shared locks. Arguments must be lockable type, and there must be at
1340least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1341
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1342</div>
1343</body>
1344</html>