Gitiles
Code Review Sign In
gerrit-public.fairphone.software / fp2-dev / platform / external / clang / 594f8419349d4131216e9296bfba0c5e8d2be950 / . / docs / LanguageExtensions.html
blob: cbdebe12deadc5b8a60a2e4a47a9282611ae0c16 [file] [log] [blame]
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]4<html>
5<head>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]6 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]7 <title>Clang Language Extensions</title>
Sean Hunt64f857b2011-06-23 01:22:53 +0000[diff] [blame]8 <link type="text/css" rel="stylesheet" href="../menu.css">
9 <link type="text/css" rel="stylesheet" href="../content.css">
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]10 <style type="text/css">
11 td {
12 vertical-align: top;
13 }
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]14 th { background-color: #ffddaa; }
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]15 </style>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]16</head>
17<body>
18
19<!--#include virtual="../menu.html.incl"-->
20
21<div id="content">
22
23<h1>Clang Language Extensions</h1>
24
25<ul>
26<li><a href="#intro">Introduction</a></li>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]27<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]28<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]29<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]30<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]31<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
32<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]33<li><a href="#availability">Availability attribute</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]34<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]35 <ul>
36 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
37 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]38 </ul></li>
39<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]40 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]41 <li><a href="#cxx0x">C++11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]42 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]43 <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes
44 access control</a></li>
45 <li><a href="#cxx_alias_templates">C++11 alias templates</a></li>
46 <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li>
47 <li><a href="#cxx_attributes">C++11 attributes</a></li>
48 <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li>
49 <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li>
50 <li><a href="#cxx_default_function_template_args">C++11 default template arguments in function templates</a></li>
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]51 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]52 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
53 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
54 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
55 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
56 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
57 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
58 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
59 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
60 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
61 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
62 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
63 <li><a href="#cxx_override_control">C++11 override control</a></li>
64 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
65 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
66 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
67 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
68 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
69 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
70 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
71 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
72 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
73 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
74 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
75 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]76 </ul></li>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]77 <li><a href="#c11">C11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]78 <ul>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]79 <li><a href="#c_alignas">C11 alignment specifiers</a></li>
80 <li><a href="#c_generic_selections">C11 generic selections</a></li>
81 <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]82 </ul></li>
83 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]84<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]85<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]86<li><a href="#objc_features">Objective-C Features</a>
87 <ul>
88 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]89 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]90 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]91 <li><a href="#objc_lambdas">Interoperability with C++11 lambdas</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]92 </ul>
93</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]94<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]95<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]96<li><a href="#builtins">Builtin Functions</a>
97 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]98 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]99 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]100 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]101 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]102</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]103<li><a href="#targetspecific">Target-Specific Extensions</a>
104 <ul>
105 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
106 </ul>
107</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]108<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]109<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]110 <ul>
111 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
112 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]113</li>
114<li><a href="#threadsafety">Thread Safety Annotation Checking</a>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]115 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]116 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
117 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
118 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]119 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
120 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]121 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
122 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
123 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
124 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
125 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
126 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
127 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
128 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
129 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
130 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
131 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
132 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
133 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]134 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]135</li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]136</ul>
137
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]138<!-- ======================================================================= -->
139<h2 id="intro">Introduction</h2>
140<!-- ======================================================================= -->
141
142<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]143addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]144range of GCC extensions. Please see the <a
145href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
146more information on these extensions.</p>
147
148<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]149<h2 id="feature_check">Feature Checking Macros</h2>
150<!-- ======================================================================= -->
151
152<p>Language extensions can be very useful, but only if you know you can depend
Chris Lattnerc70e1932011-03-21 16:25:11 +0000[diff] [blame]153on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]154function-like macros. This allows you to directly test for a feature in your
155code without having to resort to something like autoconf or fragile "compiler
156version checks".</p>
157
158<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]159<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]160<!-- ======================================================================= -->
161
162<p>This function-like macro takes a single identifier argument that is the name
163of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
164not. It can be used like this:</p>
165
166<blockquote>
167<pre>
168#ifndef __has_builtin // Optional of course.
169 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
170#endif
171
172...
173#if __has_builtin(__builtin_trap)
174 __builtin_trap();
175#else
176 abort();
177#endif
178...
179</pre>
180</blockquote>
181
182
183<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]184<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]185<!-- ======================================================================= -->
186
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]187<p>These function-like macros take a single identifier argument that is the
188name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
189is both supported by Clang and standardized in the current language standard
190or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
191<code>__has_extension</code> evaluates to 1 if the feature is supported by
192Clang in the current language (either as a language extension or a standard
193language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]194
195<blockquote>
196<pre>
197#ifndef __has_feature // Optional of course.
198 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
199#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]200#ifndef __has_extension
201 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
202#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]203
204...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]205#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]206// This code will only be compiled with the -std=c++11 and -std=gnu++11
207// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]208#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]209
210#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]211// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]212// and -std=gnu++98 options, because rvalue references are supported as a
213// language extension in C++98.
214#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]215</pre>
216</blockquote>
217
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]218<p id="has_feature_back_compat">For backwards compatibility reasons,
219<code>__has_feature</code> can also be used to test for support for
220non-standardized features, i.e. features not prefixed <code>c_</code>,
221<code>cxx_</code> or <code>objc_</code>.</p>
222
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]223<p id="has_feature_for_non_language_features">
224Another use of <code>__has_feature</code> is to check for compiler features
225not related to the language standard, such as e.g.
226<a href="AddressSanitizer.html">AddressSanitizer</a>.
227
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]228<p>If the <code>-pedantic-errors</code> option is given,
229<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
230
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]231<p>The feature tag is described along with the language feature below.</p>
232
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]233<p>The feature name or extension name can also be specified with a preceding and
234following <code>__</code> (double underscore) to avoid interference from a macro
Richard Smith1d9f4c12012-03-01 02:12:07 +0000[diff] [blame]235with the same name. For instance, <code>__cxx_rvalue_references__</code> can be
236used instead of <code>cxx_rvalue_references</code>.</p>
Richard Smith5297d712012-02-25 10:41:10 +0000[diff] [blame]237
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]238<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]239<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]240<!-- ======================================================================= -->
241
242<p>This function-like macro takes a single identifier argument that is the name
243of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
244can be used like this:</p>
245
246<blockquote>
247<pre>
248#ifndef __has_attribute // Optional of course.
249 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
250#endif
251
252...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]253#if __has_attribute(always_inline)
254#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]255#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]256#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]257#endif
258...
259</pre>
260</blockquote>
261
Jean-Daniel Dupas8a5e7fd2012-03-01 14:53:16 +0000[diff] [blame]262<p>The attribute name can also be specified with a preceding and
263following <code>__</code> (double underscore) to avoid interference from a macro
264with the same name. For instance, <code>__always_inline__</code> can be used
265instead of <code>always_inline</code>.</p>
266
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]267<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]268<h2 id="has_include">Include File Checking Macros</h2>
269<!-- ======================================================================= -->
270
271<p>Not all developments systems have the same include files.
272The <a href="#__has_include">__has_include</a> and
273<a href="#__has_include_next">__has_include_next</a> macros allow you to
274check for the existence of an include file before doing
275a possibly failing #include directive.</p>
276
277<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]278<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]279<!-- ======================================================================= -->
280
281<p>This function-like macro takes a single file name string argument that
282is the name of an include file. It evaluates to 1 if the file can
283be found using the include paths, or 0 otherwise:</p>
284
285<blockquote>
286<pre>
287// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]288#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]289# include "myinclude.h"
290#endif
291
292// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]293#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]294# include "myinclude.h"
295#endif
296</pre>
297</blockquote>
298
299<p>To test for this feature, use #if defined(__has_include).</p>
300
301<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]302<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]303<!-- ======================================================================= -->
304
305<p>This function-like macro takes a single file name string argument that
306is the name of an include file. It is like __has_include except that it
307looks for the second instance of the given file found in the include
308paths. It evaluates to 1 if the second instance of the file can
309be found using the include paths, or 0 otherwise:</p>
310
311<blockquote>
312<pre>
313// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]314#if __has_include_next("myinclude.h") &amp;&amp; __has_include_next(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]315# include_next "myinclude.h"
316#endif
317
318// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]319#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]320# include_next "myinclude.h"
321#endif
322</pre>
323</blockquote>
324
325<p>Note that __has_include_next, like the GNU extension
326#include_next directive, is intended for use in headers only,
327and will issue a warning if used in the top-level compilation
328file. A warning will also be issued if an absolute path
329is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]330
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]331
332<!-- ======================================================================= -->
333<h3><a name="__has_warning">__has_warning</a></h3>
334<!-- ======================================================================= -->
335
336<p>This function-like macro takes a string literal that represents a command
337 line option for a warning and returns true if that is a valid warning
338 option.</p>
339
340<blockquote>
341<pre>
342#if __has_warning("-Wformat")
343...
344#endif
345</pre>
346</blockquote>
347
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]348<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]349<h2 id="builtinmacros">Builtin Macros</h2>
350<!-- ======================================================================= -->
351
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]352<dl>
353 <dt><code>__BASE_FILE__</code></dt>
354 <dd>Defined to a string that contains the name of the main input
355 file passed to Clang.</dd>
356
357 <dt><code>__COUNTER__</code></dt>
358 <dd>Defined to an integer value that starts at zero and is
359 incremented each time the <code>__COUNTER__</code> macro is
360 expanded.</dd>
361
362 <dt><code>__INCLUDE_LEVEL__</code></dt>
363 <dd>Defined to an integral value that is the include depth of the
364 file currently being translated. For the main file, this value is
365 zero.</dd>
366
367 <dt><code>__TIMESTAMP__</code></dt>
368 <dd>Defined to the date and time of the last modification of the
369 current source file.</dd>
370
371 <dt><code>__clang__</code></dt>
372 <dd>Defined when compiling with Clang</dd>
373
374 <dt><code>__clang_major__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]375 <dd>Defined to the major marketing version number of Clang (e.g., the
376 2 in 2.0.1). Note that marketing version numbers should not be used to
377 check for language features, as different vendors use different numbering
378 schemes. Instead, use the <a href="#feature_check">feature checking
379 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]380
381 <dt><code>__clang_minor__</code></dt>
382 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]383 2.0.1). Note that marketing version numbers should not be used to
384 check for language features, as different vendors use different numbering
385 schemes. Instead, use the <a href="#feature_check">feature checking
386 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]387
388 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]389 <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]390
391 <dt><code>__clang_version__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]392 <dd>Defined to a string that captures the Clang marketing version, including
393 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]394</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]395
396<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]397<h2 id="vectors">Vectors and Extended Vectors</h2>
398<!-- ======================================================================= -->
399
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]400<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]401
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]402<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
403support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An
404example is:</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]405
406<blockquote>
407<pre>
408typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
409typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
410
411float4 foo(float2 a, float2 b) {
412 float4 c;
413 c.xz = a;
414 c.yw = b;
415 return c;
416}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]417</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]418</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]419
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]420<p>Query for this feature with
421<tt>__has_extension(attribute_ext_vector_type)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]422
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]423<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector
424syntax and functions. For example:</p>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]425
426<blockquote>
427<pre>
428vector float foo(vector int a) {
429 vector int b;
430 b = vec_add(a, a) + a;
431 return (vector float)b;
432}
433</pre>
434</blockquote>
435
436<p>NEON vector types are created using <tt>neon_vector_type</tt> and
437<tt>neon_polyvector_type</tt> attributes. For example:</p>
438
439<blockquote>
440<pre>
441typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
442typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
443
444int8x8_t foo(int8x8_t a) {
445 int8x8_t v;
446 v = a;
447 return v;
448}
449</pre>
450</blockquote>
451
452<!-- ======================================================================= -->
453<h3><a name="vector_literals">Vector Literals</a></h3>
454<!-- ======================================================================= -->
455
456<p>Vector literals can be used to create vectors from a set of scalars, or
457vectors. Either parentheses or braces form can be used. In the parentheses form
458the number of literal values specified must be one, i.e. referring to a scalar
459value, or must match the size of the vector type being created. If a single
460scalar literal value is specified, the scalar literal value will be replicated
461to all the components of the vector type. In the brackets form any number of
462literals can be specified. For example:</p>
463
464<blockquote>
465<pre>
466typedef int v4si __attribute__((__vector_size__(16)));
467typedef float float4 __attribute__((ext_vector_type(4)));
468typedef float float2 __attribute__((ext_vector_type(2)));
469
470v4si vsi = (v4si){1, 2, 3, 4};
471float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
472vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
473vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
474vector int vi3 = (vector int)(1, 2); // error
475vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
476vector int vi5 = (vector int)(1, 2, 3, 4);
477float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
478</pre>
479</blockquote>
480
481<!-- ======================================================================= -->
482<h3><a name="vector_operations">Vector Operations</a></h3>
483<!-- ======================================================================= -->
484
485<p>The table below shows the support for each operation by vector extension.
486A dash indicates that an operation is not accepted according to a corresponding
487specification.</p>
488
489<table width="500" border="1" cellspacing="0">
490 <tr>
Benjamin Kramer3419d7c2012-01-15 16:42:14 +0000[diff] [blame]491 <th>Operator</th>
492 <th>OpenCL</th>
493 <th>AltiVec</th>
494 <th>GCC</th>
495 <th>NEON</th>
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame]496 </tr>
497 <tr>
498 <td>[]</td>
499 <td align="center">yes</td>
500 <td align="center">yes</td>
501 <td align="center">yes</td>
502 <td align="center">-</td>
503 </tr>
504 <tr>
505 <td>unary operators +, -</td>
506 <td align="center">yes</td>
507 <td align="center">yes</td>
508 <td align="center">yes</td>
509 <td align="center">-</td>
510 </tr>
511 <tr>
512 <td>++, --</td>
513 <td align="center">yes</td>
514 <td align="center">yes</td>
515 <td align="center">-</td>
516 <td align="center">-</td>
517 </tr>
518 <tr>
519 <td>+, -, *, /, %</td>
520 <td align="center">yes</td>
521 <td align="center">yes</td>
522 <td align="center">yes</td>
523 <td align="center">-</td>
524 </tr>
525 <tr>
526 <td>bitwise operators &, |, ^, ~</td>
527 <td align="center">yes</td>
528 <td align="center">yes</td>
529 <td align="center">yes</td>
530 <td align="center">-</td>
531 </tr>
532 <tr>
533 <td>&gt&gt, &lt&lt</td>
534 <td align="center">yes</td>
535 <td align="center">yes</td>
536 <td align="center">yes</td>
537 <td align="center">-</td>
538 </tr>
539 <tr>
540 <td>!, &&,||</td>
541 <td align="center">no</td>
542 <td align="center">-</td>
543 <td align="center">-</td>
544 <td align="center">-</td>
545 </tr>
546 <tr>
547 <td>==,!=, >, <, >=, <=</td>
548 <td align="center">yes</td>
549 <td align="center">yes</td>
550 <td align="center">-</td>
551 <td align="center">-</td>
552 </tr>
553 <tr>
554 <td>=</td>
555 <td align="center">yes</td>
556 <td align="center">yes</td>
557 <td align="center">yes</td>
558 <td align="center">yes</td>
559 </tr>
560 <tr>
561 <td>:?</td>
562 <td align="center">yes</td>
563 <td align="center">-</td>
564 <td align="center">-</td>
565 <td align="center">-</td>
566 </tr>
567 <tr>
568 <td>sizeof</td>
569 <td align="center">yes</td>
570 <td align="center">yes</td>
571 <td align="center">yes</td>
572 <td align="center">yes</td>
573 </tr>
574</table>
575
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]576<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
577
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]578<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]579<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]580<!-- ======================================================================= -->
581
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]582<p>An optional string message can be added to the <tt>deprecated</tt>
583and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]584
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]585<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]586<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]587</blockquote>
588
589<p>If the deprecated or unavailable declaration is used, the message
590will be incorporated into the appropriate diagnostic:</p>
591
592<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]593<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]594 explode();
595 ^</pre>
596</blockquote>
597
598<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]599with <tt>__has_extension(attribute_deprecated_with_message)</tt>
600and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]601
602<!-- ======================================================================= -->
603<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
604<!-- ======================================================================= -->
605
606<p>Clang allows attributes to be written on individual enumerators.
607This allows enumerators to be deprecated, made unavailable, etc. The
608attribute must appear after the enumerator name and before any
609initializer, like so:</p>
610
611<blockquote>
612<pre>enum OperationMode {
613 OM_Invalid,
614 OM_Normal,
615 OM_Terrified __attribute__((deprecated)),
616 OM_AbortOnError __attribute__((deprecated)) = 4
617};</pre>
618</blockquote>
619
620<p>Attributes on the <tt>enum</tt> declaration do not apply to
621individual enumerators.</p>
622
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]623<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]624
625<!-- ======================================================================= -->
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]626<h2 id="availability">Availability attribute</h2
627<!-- ======================================================================= -->
628
629<p>Clang introduces the <code>availability</code> attribute, which can
630be placed on declarations to describe the lifecycle of that
631declaration relative to operating system versions. Consider the function declaration for a hypothetical function <code>f</code>:</p>
632
633<pre>
634void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7)));
635</pre>
636
637<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>
638
639<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>
640
641<dl>
642 <dt>introduced=<i>version</i></dt>
643 <dd>The first version in which this declaration was introduced.</dd>
644
645 <dt>deprecated=<i>version</i></dt>
646 <dd>The first version in which this declaration was deprecated, meaning that users should migrate away from this API.</dd>
647
648 <dt>obsoleted=<i>version</i></dt>
649 <dd>The first version in which this declaration was obsoleted, meaning that it was removed completely and can no longer be used.</dd>
650
651 <dt>unavailable</dt>
652 <dd>This declaration is never available on this platform.</dd>
653
654 <dt>message=<i>string-literal</i></dt>
655 <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>
656</dl>
657
658<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>
659
660<dl>
661 <dt>ios</dt>
662 <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>
663
664 <dt>macosx</dt>
665 <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>
666</dl>
667
Douglas Gregor594f8412012-03-11 17:21:03 +0000[diff] [blame^]668<p>A declaration can be used even when deploying back to a platform
669version prior to when the declaration was introduced. When this
670happens, the declaration is <a
671 href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly
672linked</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>
673
Douglas Gregor93a70672012-03-11 04:53:21 +0000[diff] [blame]674<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]675<h2 id="checking_language_features">Checks for Standard Language Features</h2>
676<!-- ======================================================================= -->
677
678<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
679enabled. Those features are listed here.</p>
680
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]681<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]682
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]683<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]684example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]685
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]686<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]687
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]688<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]689compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]690
691<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]692<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
693<!-- ======================================================================= -->
694
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]695<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
696to query if certain upcoming standard language features are enabled. Those
697features are listed here. Features that are not yet implemented will be
698noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]699
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]700<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]701
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]702<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]703C++11 standard. As a result, all these features are enabled
704with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]705
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]706<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]707
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]708<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]709
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]710<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]711
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]712<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
713<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]714C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]715
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]716<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]717
718<p>Use <tt>__has_feature(cxx_alignas)</tt> or
719<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
720specifiers using <tt>alignas</tt> is enabled.</p>
721
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]722<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]723
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]724<p>Use <tt>__has_feature(cxx_attributes)</tt> or
725<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]726parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]727
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]728<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]729
730<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
731for generalized constant expressions (e.g., <tt>constexpr</tt>) is
Richard Smithb5216aa2012-02-14 22:56:17 +0000[diff] [blame]732enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]733
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]734<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]735
736<p>Use <tt>__has_feature(cxx_decltype)</tt> or
737<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
738<tt>decltype()</tt> specifier is enabled.</p>
739
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]740<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]741
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]742<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
743<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
744if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]745
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]746<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
747
748<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
749<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
750defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
751
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]752<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]753
754<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
755support for delegating constructors is enabled.</p>
756
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]757<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]758
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]759<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
760<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]761deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]762
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]763<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]764<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
765
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]766<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]767
768<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
769support for generalized initializers (using braced lists and
Richard Smith88189552012-02-26 07:09:21 +0000[diff] [blame]770<tt>std::initializer_list</tt>) is enabled.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]771
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]772<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]773
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]774<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
775implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]776
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]777<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]778
779<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>
780
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]781<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]782
783<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
784<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
785inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]786
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]787<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]788
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]789<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
790<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregor46e021e2012-02-23 05:44:09 +0000[diff] [blame]791is enabled. </p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]792
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]793<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]794
795<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
796<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
797exception specifications is enabled.</p>
798
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]799<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]800
801<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]802
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]803<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]804
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]805<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
806<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]807<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]808
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]809<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]810
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]811<p>Use <tt>__has_feature(cxx_override_control)</tt> or
812<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]813the override control keywords is enabled.</p>
814
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]815<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]816<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
817<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
818if support for reference-qualified functions (e.g., member functions with
819<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
820is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]821
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]822<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]823
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]824<p>Use <tt>__has_feature(cxx_range_for)</tt> or
825<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
826range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]827
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]828<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Richard Smith80134582012-03-07 08:57:31 +0000[diff] [blame]829<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support
830for 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]831
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]832<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]833
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]834<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
835<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]836rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]837
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]838<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]839
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]840<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
841<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]842compile-time assertions using <tt>static_assert</tt> is enabled.</p>
843
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]844<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]845
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]846<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]847<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]848supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
849will instead be a storage class specifier, as in C or C++98.</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_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]852
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]853<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
854<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
855strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]856
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]857<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]858
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]859<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
860<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
861alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]862
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]863<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]864<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
865support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]866
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]867<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]868
Richard Smithec92bc72012-03-03 23:51:05 +0000[diff] [blame]869<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]870
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]871<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]872
Richard Smith9c1dda72012-03-09 08:41:27 +0000[diff] [blame]873<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]874
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]875<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]876
877<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
878<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
879for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]880
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]881<h3 id="c11">C11</h3>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]882
883<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]884C11 standard. As a result, all these features are enabled
885with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]886
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]887<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]888
889<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
890to determine if support for alignment specifiers using <tt>_Alignas</tt>
891is enabled.</p>
892
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]893<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]894
895<p>Use <tt>__has_feature(c_generic_selections)</tt> or
896<tt>__has_extension(c_generic_selections)</tt> to determine if support for
897generic selections is enabled.</p>
898
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]899<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]900languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]901C11 standard.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]902
903<p>In C, type compatibility is decided according to the rules given in the
904appropriate standard, but in C++, which lacks the type compatibility rules
905used in C, types are considered compatible only if they are equivalent.</p>
906
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]907<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]908
909<p>Use <tt>__has_feature(c_static_assert)</tt> or
910<tt>__has_extension(c_static_assert)</tt> to determine if support for
911compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
912
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]913<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]914<h2 id="checking_type_traits">Checks for Type Traits</h2>
915<!-- ======================================================================= -->
916
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]917<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]918<blockquote>
919<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]920#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]921template&lt;typename From, typename To&gt;
922struct is_convertible_to {
923 static const bool value = __is_convertible_to(From, To);
924};
925#else
926// Emulate type trait
927#endif
928</pre>
929</blockquote>
930
931<p>The following type traits are supported by Clang:</p>
932<ul>
933 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
934 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
935 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
936 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
937 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
938 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
939 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
940 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
941 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
942 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
943 <li><code>__is_class</code> (GNU, Microsoft)</li>
944 <li><code>__is_convertible_to</code> (Microsoft)</li>
945 <li><code>__is_empty</code> (GNU, Microsoft)</li>
946 <li><code>__is_enum</code> (GNU, Microsoft)</li>
947 <li><code>__is_pod</code> (GNU, Microsoft)</li>
948 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
949 <li><code>__is_union</code> (GNU, Microsoft)</li>
950 <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]951 <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]952 <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]953 <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>
954 <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]955</ul>
956
957<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]958<h2 id="blocks">Blocks</h2>
959<!-- ======================================================================= -->
960
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]961<p>The syntax and high level language feature description is in <a
962href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
963details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]964href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]965
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]966
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]967<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]968
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]969<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]970<h2 id="objc_features">Objective-C Features</h2>
971<!-- ======================================================================= -->
972
973<h3 id="objc_instancetype">Related result types</h3>
974
975<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>
976
977<blockquote>
978<pre>
979@interface NSObject
980+ (id)alloc;
981- (id)init;
982@end
983
984@interface NSArray : NSObject
985@end
986</pre>
987</blockquote>
988
989<p>and this common initialization pattern</p>
990
991<blockquote>
992<pre>
993NSArray *array = [[NSArray alloc] init];
994</pre>
995</blockquote>
996
997<p>the type of the expression <code>[NSArray alloc]</code> is
998<code>NSArray*</code> because <code>alloc</code> implicitly has a
999related result type. Similarly, the type of the expression
1000<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
1001<code>init</code> has a related result type and its receiver is known
1002to 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>
1003
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]1004<p>A method with a related result type can be declared by using the
1005type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
1006is a contextual keyword that is only permitted in the result type of
1007an Objective-C method, e.g.</p>
1008
1009<pre>
1010@interface A
1011+ (<b>instancetype</b>)constructAnA;
1012@end
1013</pre>
1014
1015<p>The related result type can also be inferred for some methods.
1016To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1017word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]1018considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1019type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1020
1021<ul>
1022
1023 <li>the first word is "alloc" or "new", and the method is a class
1024 method, or</li>
1025
1026 <li>the first word is "autorelease", "init", "retain", or "self",
1027 and the method is an instance method.</li>
1028
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1029</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1030
1031<p>If a method with a related result type is overridden by a subclass
1032method, the subclass method must also return a type that is compatible
1033with the subclass type. For example:</p>
1034
1035<blockquote>
1036<pre>
1037@interface NSString : NSObject
1038- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
1039@end
1040</pre>
1041</blockquote>
1042
1043<p>Related result types only affect the type of a message send or
1044property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]1045with a related result type is treated the same way as method that
1046returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1047
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]1048<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
1049the <tt>instancetype</tt> contextual keyword is available.</p>
1050
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]1051<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]1052<h2 id="objc_arc">Automatic reference counting </h2>
1053<!-- ======================================================================= -->
1054
1055<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>
1056
1057<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1058<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
1059<!-- ======================================================================= -->
1060
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]1061<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]1062underlying type within Objective-C. For example, one can write an
1063enumeration type as:</p>
1064
1065<pre>
1066typedef enum : unsigned char { Red, Green, Blue } Color;
1067</pre>
1068
1069<p>This specifies that the underlying type, which is used to store the
1070enumeration value, is <tt>unsigned char</tt>.</p>
1071
1072<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1073support for fixed underlying types is available in Objective-C.</p>
1074
1075<!-- ======================================================================= -->
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1076<h2 id="objc_lambdas">Interoperability with C++11 lambdas</h2>
1077<!-- ======================================================================= -->
1078
1079<p>Clang provides interoperability between C++11 lambdas and
1080blocks-based APIs, by permitting a lambda to be implicitly converted
1081to a block pointer with the corresponding signature. For example,
1082consider an API such as <code>NSArray</code>'s array-sorting
1083method:</p>
1084
1085<pre> - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; </pre>
1086
1087<p><code>NSComparator</code> is simply a typedef for the block pointer
1088<code>NSComparisonResult (^)(id, id)</code>, and parameters of this
1089type are generally provided with block literals as arguments. However,
1090one can also use a C++11 lambda so long as it provides the same
1091signature (in this case, accepting two parameters of type
1092<code>id</code> and returning an <code>NSComparisonResult</code>):</p>
1093
1094<pre>
1095 NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11",
1096 @"String 02"];
1097 const NSStringCompareOptions comparisonOptions
1098 = NSCaseInsensitiveSearch | NSNumericSearch |
1099 NSWidthInsensitiveSearch | NSForcedOrderingSearch;
1100 NSLocale *currentLocale = [NSLocale currentLocale];
1101 NSArray *sorted
1102 = [array sortedArrayUsingComparator:<b>[=](id s1, id s2) -&gt; NSComparisonResult {
1103 NSRange string1Range = NSMakeRange(0, [s1 length]);
1104 return [s1 compare:s2 options:comparisonOptions
1105 range:string1Range locale:currentLocale];
1106 }</b>];
1107 NSLog(@"sorted: %@", sorted);
1108</pre>
1109
1110<p>This code relies on an implicit conversion from the type of the
1111lambda expression (an unnamed, local class type called the <i>closure
1112type</i>) to the corresponding block pointer type. The conversion
1113itself is expressed by a conversion operator in that closure type
1114that produces a block pointer with the same signature as the lambda
1115itself, e.g.,</p>
1116
1117<pre>
1118 operator NSComparisonResult (^)(id, id)() const;
1119</pre>
1120
1121<p>This conversion function returns a new block that simply forwards
1122the two parameters to the lambda object (which it captures by copy),
1123then returns the result. The returned block is first copied (with
1124<tt>Block_copy</tt>) and then autoreleased. As an optimization, if a
1125lambda expression is immediately converted to a block pointer (as in
1126the first example, above), then the block is not copied and
1127autoreleased: rather, it is given the same lifetime as a block literal
1128written at that point in the program, which avoids the overhead of
1129copying a block to the heap in the common case.</p>
1130
Douglas Gregorbccda482012-03-10 22:20:11 +0000[diff] [blame]1131<p>The conversion from a lambda to a block pointer is only available
1132in Objective-C++, and not in C++ with blocks, due to its use of
1133Objective-C memory management (autorelease).</p>
1134
Douglas Gregor8a4e1822012-03-09 23:24:48 +0000[diff] [blame]1135<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1136<h2 id="overloading-in-c">Function Overloading in C</h2>
1137<!-- ======================================================================= -->
1138
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1139<p>Clang provides support for C++ function overloading in C. Function
1140overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1141example, one might provide several overloaded versions of a <tt>tgsin</tt>
1142function that invokes the appropriate standard function computing the sine of a
1143value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1144precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1145
1146<blockquote>
1147<pre>
1148#include &lt;math.h&gt;
1149float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1150double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1151long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1152</pre>
1153</blockquote>
1154
1155<p>Given these declarations, one can call <tt>tgsin</tt> with a
1156<tt>float</tt> value to receive a <tt>float</tt> result, with a
1157<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1158overloading in C follows the rules of C++ function overloading to pick
1159the best overload given the call arguments, with a few C-specific
1160semantics:</p>
1161<ul>
1162 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1163 double</tt> is ranked as a floating-point promotion (per C99) rather
1164 than as a floating-point conversion (as in C++).</li>
1165
1166 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1167 <tt>U*</tt> is considered a pointer conversion (with conversion
1168 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1169
1170 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1171 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1172 conversion is given "conversion" rank.</li>
1173</ul>
1174
1175<p>The declaration of <tt>overloadable</tt> functions is restricted to
1176function declarations and definitions. Most importantly, if any
1177function with a given name is given the <tt>overloadable</tt>
1178attribute, then all function declarations and definitions with that
1179name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1180attribute. This rule even applies to redeclarations of functions whose original
1181declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1182
1183<blockquote>
1184<pre>
1185int f(int) __attribute__((overloadable));
1186float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1187
1188int g(int) __attribute__((overloadable));
1189int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1190</pre>
1191</blockquote>
1192
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1193<p>Functions marked <tt>overloadable</tt> must have
1194prototypes. Therefore, the following code is ill-formed:</p>
1195
1196<blockquote>
1197<pre>
1198int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1199</pre>
1200</blockquote>
1201
1202<p>However, <tt>overloadable</tt> functions are allowed to use a
1203ellipsis 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>
1204
1205<blockquote>
1206<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]1207void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1208</pre>
1209</blockquote>
1210
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1211<p>Functions declared with the <tt>overloadable</tt> attribute have
1212their names mangled according to the same rules as C++ function
1213names. For example, the three <tt>tgsin</tt> functions in our
1214motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]1215<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1216caveats to this use of name mangling:</p>
1217
1218<ul>
1219
1220 <li>Future versions of Clang may change the name mangling of
1221 functions overloaded in C, so you should not depend on an specific
1222 mangling. To be completely safe, we strongly urge the use of
1223 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1224
1225 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1226 used in C++, because names will already be mangled and functions are
1227 already overloadable. However, when an <tt>overloadable</tt>
1228 function occurs within an <tt>extern "C"</tt> linkage specification,
1229 it's name <i>will</i> be mangled in the same way as it would in
1230 C.</li>
1231</ul>
1232
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]1233<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1234
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]1235<!-- ======================================================================= -->
1236<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1237<!-- ======================================================================= -->
1238
1239<p>clang supports an extension which allows the following in C:</p>
1240
1241<blockquote>
1242<pre>
1243#include &lt;math.h&gt;
1244#include &lt;complex.h&gt;
1245complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1246</pre>
1247</blockquote>
1248
1249<p>This construct is useful because there is no way to separately
1250initialize the real and imaginary parts of a complex variable in
1251standard C, given that clang does not support <code>_Imaginary</code>.
1252(clang also supports the <code>__real__</code> and <code>__imag__</code>
1253extensions from gcc, which help in some cases, but are not usable in
1254static initializers.)
1255
1256<p>Note that this extension does not allow eliding the braces; the
1257meaning of the following two lines is different:</p>
1258
1259<blockquote>
1260<pre>
1261complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1262complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1263</pre>
1264</blockquote>
1265
1266<p>This extension also works in C++ mode, as far as that goes, but does not
1267 apply to the C++ <code>std::complex</code>. (In C++11, list
1268 initialization allows the same syntax to be used with
1269 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1270
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1271<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1272<h2 id="builtins">Builtin Functions</h2>
1273<!-- ======================================================================= -->
1274
1275<p>Clang supports a number of builtin library functions with the same syntax as
1276GCC, including things like <tt>__builtin_nan</tt>,
1277<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1278<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1279addition to the GCC builtins, Clang supports a number of builtins that GCC does
1280not, which are listed here.</p>
1281
1282<p>Please note that Clang does not and will not support all of the GCC builtins
1283for vector operations. Instead of using builtins, you should use the functions
1284defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1285define portable wrappers for these. Many of the Clang versions of these
1286functions are implemented directly in terms of <a href="#vectors">extended
1287vector support</a> instead of builtins, in order to reduce the number of
1288builtins that we need to implement.</p>
1289
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1290<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1291<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1292<!-- ======================================================================= -->
1293
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1294<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1295permutation/shuffle/swizzle operations. This builtin is also very important for
1296the implementation of various target-specific header files like
1297<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1298</p>
1299
1300<p><b>Syntax:</b></p>
1301
1302<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1303__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1304</pre>
1305
1306<p><b>Examples:</b></p>
1307
1308<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1309 // Identity operation - return 4-element vector V1.
1310 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1311
1312 // "Splat" element 0 of V1 into a 4-element result.
1313 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1314
1315 // Reverse 4-element vector V1.
1316 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1317
1318 // Concatenate every other element of 4-element vectors V1 and V2.
1319 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1320
1321 // Concatenate every other element of 8-element vectors V1 and V2.
1322 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1323</pre>
1324
1325<p><b>Description:</b></p>
1326
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1327<p>The first two arguments to __builtin_shufflevector are vectors that have the
1328same element type. The remaining arguments are a list of integers that specify
1329the elements indices of the first two vectors that should be extracted and
1330returned in a new vector. These element indices are numbered sequentially
1331starting with the first vector, continuing into the second vector. Thus, if
1332vec1 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]1333</p>
1334
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1335<p>The result of __builtin_shufflevector is a vector
1336with the same element type as vec1/vec2 but that has an element count equal to
1337the number of indices specified.
1338</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1339
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1340<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1341
1342<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1343<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1344<!-- ======================================================================= -->
1345
1346<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1347the program cannot be reached, even if the compiler might otherwise think it
1348can. This is useful to improve optimization and eliminates certain warnings.
1349For example, without the <tt>__builtin_unreachable</tt> in the example below,
1350the compiler assumes that the inline asm can fall through and prints a "function
1351declared 'noreturn' should not return" warning.
1352</p>
1353
1354<p><b>Syntax:</b></p>
1355
1356<pre>
1357__builtin_unreachable()
1358</pre>
1359
1360<p><b>Example of Use:</b></p>
1361
1362<pre>
1363void myabort(void) __attribute__((noreturn));
1364void myabort(void) {
1365 asm("int3");
1366 __builtin_unreachable();
1367}
1368</pre>
1369
1370<p><b>Description:</b></p>
1371
1372<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1373it has undefined behavior, it is a statement that it is never reached and the
1374optimizer can take advantage of this to produce better code. This builtin takes
1375no arguments and produces a void result.
1376</p>
1377
1378<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1379
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1380<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1381<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1382<!-- ======================================================================= -->
1383
1384<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1385memory.
1386</p>
1387
1388<p><b>Syntax:</b></p>
1389
1390<pre>
1391<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1392</pre>
1393
1394<p><b>Example of Use:</b></p>
1395
1396<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1397int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1398</pre>
1399
1400<p><b>Description:</b></p>
1401
1402<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1403intrinsics to allow code to atomically swap the current value with the new
1404value. More importantly, it helps developers write more efficient and correct
1405code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1406relying on the platform specific implementation details of
1407__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1408</p>
1409
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1410
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1411<!-- ======================================================================= -->
1412<h2 id="targetspecific">Target-Specific Extensions</h2>
1413<!-- ======================================================================= -->
1414
1415<p>Clang supports some language features conditionally on some targets.</p>
1416
1417<!-- ======================================================================= -->
1418<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1419<!-- ======================================================================= -->
1420
1421<p>The X86 backend has these language extensions:</p>
1422
1423<!-- ======================================================================= -->
1424<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1425<!-- ======================================================================= -->
1426
1427<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1428relative to the X86 GS segment register, and address space #257 causes it to be
1429relative to the X86 FS segment. Note that this is a very very low-level
1430feature that should only be used if you know what you're doing (for example in
1431an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1432
1433<p>Here is an example:</p>
1434
1435<pre>
1436#define GS_RELATIVE __attribute__((address_space(256)))
1437int foo(int GS_RELATIVE *P) {
1438 return *P;
1439}
1440</pre>
1441
1442<p>Which compiles to (on X86-32):</p>
1443
1444<pre>
1445_foo:
1446 movl 4(%esp), %eax
1447 movl %gs:(%eax), %eax
1448 ret
1449</pre>
1450
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1451<!-- ======================================================================= -->
1452<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1453<!-- ======================================================================= -->
1454
1455<p>Clang supports additional attributes that are useful for documenting program
1456invariants and rules for static analysis tools. The extensions documented here
1457are used by the <a
1458href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1459engine</a> that is part of Clang's Analysis library.</p>
1460
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1461<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1462
1463<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1464attribute. This attribute, which is typically affixed to a function prototype,
1465indicates that a call to a given function never returns. Function prototypes for
1466common functions like <tt>exit</tt> are typically annotated with this attribute,
1467as well as a variety of common assertion handlers. Users can educate the static
1468analyzer about their own custom assertion handles (thus cutting down on false
1469positives due to false paths) by marking their own &quot;panic&quot; functions
1470with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1471
1472<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1473there are special functions that for all intents and purposes should be
1474considered panic functions (i.e., they are only called when an internal program
1475error occurs) but may actually return so that the program can fail gracefully.
1476The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1477as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1478pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1479<tt>noreturn</tt>).</p>
1480
1481<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]1482same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1483placed at the end of function prototypes:</p>
1484
1485<pre>
1486 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1487</pre>
1488
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1489<p>Query for this feature with
1490<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1491
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1492<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1493
1494<p>Many methods in Objective-C have conventional meanings determined
1495by their selectors. For the purposes of static analysis, it is
1496sometimes useful to be able to mark a method as having a particular
1497conventional meaning despite not having the right selector, or as not
1498having the conventional meaning that its selector would suggest.
1499For these use cases, we provide an attribute to specifically describe
1500the <q>method family</q> that a method belongs to.</p>
1501
1502<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1503where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1504<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1505can only be placed at the end of a method declaration:</p>
1506
1507<pre>
1508 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1509</pre>
1510
1511<p>Users who do not wish to change the conventional meaning of a
1512method, and who merely want to document its non-standard retain and
1513release semantics, should use the
1514<a href="#attr_retain_release">retaining behavior attributes</a>
1515described below.</p>
1516
1517<p>Query for this feature with
1518<tt>__has_attribute(objc_method_family)</tt>.</p>
1519
1520<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1521
1522<p>In Objective-C, functions and methods are generally assumed to take
1523and return objects with +0 retain counts, with some exceptions for
1524special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1525there are exceptions, and so Clang provides attributes to allow these
1526exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1527ignore non-leaks). Some exceptions may be better described using
1528the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1529attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1530
1531<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1532<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1533and <tt>cf_returns_not_retained</tt> attributes can be placed on
1534methods and functions that return Objective-C or CoreFoundation
1535objects. They are commonly placed at the end of a function prototype
1536or method declaration:</p>
1537
1538<pre>
1539 id foo() <b>__attribute__((ns_returns_retained))</b>;
1540
1541 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1542</pre>
1543
1544<p>The <tt>*_returns_retained</tt> attributes specify that the
1545returned object has a +1 retain count.
1546The <tt>*_returns_not_retained</tt> attributes specify that the return
1547object has a +0 retain count, even if the normal convention for its
1548selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1549returned object is +0, but is guaranteed to live at least as long as the
1550next flush of an autorelease pool.</p>
1551
1552<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1553attributes can be placed on an parameter declaration; they specify
1554that the argument is expected to have a +1 retain count, which will be
1555balanced in some way by the function or method.
1556The <tt>ns_consumes_self</tt> attribute can only be placed on an
1557Objective-C method; it specifies that the method expects
1558its <tt>self</tt> parameter to have a +1 retain count, which it will
1559balance in some way.</p>
1560
1561<pre>
1562 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1563
1564 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1565 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1566</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1567
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1568<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1569<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1570
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1571<!-- ======================================================================= -->
1572<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1573<!-- ======================================================================= -->
1574<h3 id="address_sanitizer">AddressSanitizer</h3>
1575<p> Use <code>__has_feature(address_sanitizer)</code>
1576to check if the code is being built with <a
1577 href="AddressSanitizer.html">AddressSanitizer</a>.
1578</p>
Kostya Serebryany71efba02012-01-24 19:25:38 +0000[diff] [blame]1579<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function
1580declaration to specify that address safety instrumentation (e.g.
1581AddressSanitizer) should not be applied to that function.
1582</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1583
1584<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1585<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1586<!-- ======================================================================= -->
1587
1588<p>Clang supports additional attributes for checking basic locking policies in
1589multithreaded programs.
1590Clang currently parses the following list of attributes, although
1591<b>the implementation for these annotations is currently in development.</b>
1592For more details, see the
1593<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1594</p>
1595
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1596<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1597
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1598<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1599declaration to specify that the thread safety analysis should not be run on that
1600function. This attribute provides an escape hatch (e.g. for situations when it
1601is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1602
1603<h4 id="ts_lockable">lockable</h4>
1604
1605<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1606that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1607used to check consistency.</p>
1608
1609<h4 id="ts_scopedlockable">scoped_lockable</h4>
1610
1611<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1612specify that it has a "scoped" lockable type. Objects of this type will acquire
1613the lock upon construction and release it upon going out of scope.
1614 This annotation is primarily used to check
1615consistency.</p>
1616
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1617<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1618
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1619<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1620specify that the variable must be accessed while holding some lock.</p>
1621
1622<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1623
1624<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1625specify that the pointer must be dereferenced while holding some lock.</p>
1626
1627<h4 id="ts_guardedby">guarded_by(l)</h4>
1628
1629<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1630specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1631
1632<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1633
1634<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1635specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1636
1637<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1638
1639<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1640of a lockable variable to specify that the lock must be acquired before all
1641attribute arguments. Arguments must be lockable type, and there must be at
1642least one argument.</p>
1643
1644<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1645
1646<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1647of a lockable variable to specify that the lock must be acquired after all
1648attribute arguments. Arguments must be lockable type, and there must be at
1649least one argument.</p>
1650
1651<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1652
1653<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1654declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1655exclusively. This attribute takes zero or more arguments: either of lockable
1656type or integers indexing into function parameters of lockable type. If no
1657arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1658enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1659
1660<h4 id="ts_slf">shared_lock_function(...)</h4>
1661
1662<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1663declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1664 the locks may be shared (e.g. read locks). This attribute takes zero or more
1665arguments: either of lockable type or integers indexing into function
1666parameters of lockable type. If no arguments are given, the acquired lock is
1667implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1668
1669<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1670
1671<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1672declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1673all listed locks exclusively. This attribute takes one or more arguments. The
1674first argument is an integer or boolean value specifying the return value of a
1675successful lock acquisition. The remaining arugments are either of lockable type
1676or integers indexing into function parameters of lockable type. If only one
1677argument is given, the acquired lock is implicitly <tt>this</tt> of the
1678enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1679
1680<h4 id="ts_stf">shared_trylock_function(...)</h4>
1681
1682<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1683declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1684all listed locks, although the locks may be shared (e.g. read locks). This
1685attribute takes one or more arguments. The first argument is an integer or
1686boolean value specifying the return value of a successful lock acquisition. The
1687remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1688function parameters of lockable type. If only one argument is given, the
1689acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1690
1691<h4 id="ts_uf">unlock_function(...)</h4>
1692
1693<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1694declaration to specify that the function release all listed locks. This
1695attribute takes zero or more arguments: either of lockable type or integers
1696indexing into function parameters of lockable type. If no arguments are given,
1697the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1698
1699<h4 id="ts_lr">lock_returned(l)</h4>
1700
1701<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1702declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1703must be of lockable type). This annotation is used to aid in resolving lock
1704expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1705
1706<h4 id="ts_le">locks_excluded(...)</h4>
1707
1708<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1709to specify that the function must not be called with the listed locks. Arguments
1710must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1711
1712<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1713
1714<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1715declaration to specify that the function must be called while holding the listed
1716exclusive locks. Arguments must be lockable type, and there must be at
1717least one argument.</p>
1718
1719<h4 id="ts_slr">shared_locks_required(...)</h4>
1720
1721<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1722declaration to specify that the function must be called while holding the listed
1723shared locks. Arguments must be lockable type, and there must be at
1724least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1725
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1726</div>
1727</body>
1728</html>