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| author | Carlo Zancanaro <carlo@pc-4w14-0.cs.usyd.edu.au> | 2012-10-15 17:10:06 +1100 |
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| committer | Carlo Zancanaro <carlo@pc-4w14-0.cs.usyd.edu.au> | 2012-10-15 17:10:06 +1100 |
| commit | be1de4be954c80875ad4108e0a33e8e131b2f2c0 (patch) | |
| tree | 1fbbecf276bf7c7bdcbb4dd446099d6d90eaa516 /clang/docs/LanguageExtensions.html | |
| parent | c4626a62754862d20b41e8a46a3574264ea80e6d (diff) | |
| parent | f1bd2e48c5324d3f7cda4090c87f8a5b6f463ce2 (diff) | |
Merge branch 'master' of ssh://bitbucket.org/czan/honours
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diff --git a/clang/docs/LanguageExtensions.html b/clang/docs/LanguageExtensions.html new file mode 100644 index 0000000..68f0afc --- /dev/null +++ b/clang/docs/LanguageExtensions.html @@ -0,0 +1,1810 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ --> +<html> +<head> + <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> + <title>Clang Language Extensions</title> + <link type="text/css" rel="stylesheet" href="../menu.css"> + <link type="text/css" rel="stylesheet" href="../content.css"> + <style type="text/css"> + td { + vertical-align: top; + } + th { background-color: #ffddaa; } + </style> +</head> +<body> + +<!--#include virtual="../menu.html.incl"--> + +<div id="content"> + +<h1>Clang Language Extensions</h1> + +<ul> +<li><a href="#intro">Introduction</a></li> +<li><a href="#feature_check">Feature Checking Macros</a></li> +<li><a href="#has_include">Include File Checking Macros</a></li> +<li><a href="#builtinmacros">Builtin Macros</a></li> +<li><a href="#vectors">Vectors and Extended Vectors</a></li> +<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li> +<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li> +<li><a href="#user_specified_system_framework">'User-Specified' System Frameworks</a></li> +<li><a href="#availability">Availability attribute</a></li> +<li><a href="#checking_language_features">Checks for Standard Language Features</a> + <ul> + <li><a href="#cxx98">C++98</a> + <ul> + <li><a href="#cxx_exceptions">C++ exceptions</a></li> + <li><a href="#cxx_rtti">C++ RTTI</a></li> + </ul></li> + <li><a href="#cxx11">C++11</a> + <ul> + <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes access control</a></li> + <li><a href="#cxx_alias_templates">C++11 alias templates</a></li> + <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li> + <li><a href="#cxx_attributes">C++11 attributes</a></li> + <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li> + <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li> + <li><a href="#cxx_default_function_template_args">C++11 default template arguments in function templates</a></li> + <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li> + <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li> + <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li> + <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li> + <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li> + <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li> + <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li> + <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li> + <li><a href="#cxx_lambdas">C++11 lambdas</a></li> + <li><a href="#cxx_local_type_template_args">C++11 local and unnamed types as template arguments</a></li> + <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li> + <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li> + <li><a href="#cxx_nullptr">C++11 nullptr</a></li> + <li><a href="#cxx_override_control">C++11 override control</a></li> + <li><a href="#cxx_range_for">C++11 range-based for loop</a></li> + <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li> + <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li> + <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li> + <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li> + <li><a href="#cxx_auto_type">C++11 type inference</a></li> + <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li> + <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li> + <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li> + <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li> + <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li> + <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li> + </ul></li> + <li><a href="#c11">C11</a> + <ul> + <li><a href="#c_alignas">C11 alignment specifiers</a></li> + <li><a href="#c_atomic">C11 atomic operations</a></li> + <li><a href="#c_generic_selections">C11 generic selections</a></li> + <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li> + </ul></li> +</ul></li> +<li><a href="#checking_type_traits">Checks for Type Traits</a></li> +<li><a href="#blocks">Blocks</a></li> +<li><a href="#objc_features">Objective-C Features</a> + <ul> + <li><a href="#objc_instancetype">Related result types</a></li> + <li><a href="#objc_arc">Automatic reference counting</a></li> + <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li> + <li><a href="#objc_lambdas">Interoperability with C++11 lambdas</a></li> + <li><a href="#object-literals-subscripting">Object Literals and Subscripting</a></li> + </ul> +</li> +<li><a href="#overloading-in-c">Function Overloading in C</a></li> +<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li> +<li><a href="#builtins">Builtin Functions</a> + <ul> + <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li> + <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li> + <li><a href="#__sync_swap">__sync_swap</a></li> + </ul> +</li> +<li><a href="#targetspecific">Target-Specific Extensions</a> + <ul> + <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li> + </ul> +</li> +<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li> +<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a> + <ul> + <li><a href="#address_sanitizer">AddressSanitizer</a></li> + </ul> +</li> +<li><a href="#threadsafety">Thread Safety Annotation Checking</a> + <ul> + <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li> + <li><a href="#ts_lockable"><tt>lockable</tt></a></li> + <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li> + <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li> + <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li> + <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li> + <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li> + <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li> + <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li> + <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li> + <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li> + <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li> + <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li> + <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li> + <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li> + <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li> + <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li> + <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li> + </ul> +</li> +</ul> + +<!-- ======================================================================= --> +<h2 id="intro">Introduction</h2> +<!-- ======================================================================= --> + +<p>This document describes the language extensions provided by Clang. In +addition to the language extensions listed here, Clang aims to support a broad +range of GCC extensions. Please see the <a +href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for +more information on these extensions.</p> + +<!-- ======================================================================= --> +<h2 id="feature_check">Feature Checking Macros</h2> +<!-- ======================================================================= --> + +<p>Language extensions can be very useful, but only if you know you can depend +on them. In order to allow fine-grain features checks, we support three builtin +function-like macros. This allows you to directly test for a feature in your +code without having to resort to something like autoconf or fragile "compiler +version checks".</p> + +<!-- ======================================================================= --> +<h3><a name="__has_builtin">__has_builtin</a></h3> +<!-- ======================================================================= --> + +<p>This function-like macro takes a single identifier argument that is the name +of a builtin function. It evaluates to 1 if the builtin is supported or 0 if +not. It can be used like this:</p> + +<blockquote> +<pre> +#ifndef __has_builtin // Optional of course. + #define __has_builtin(x) 0 // Compatibility with non-clang compilers. +#endif + +... +#if __has_builtin(__builtin_trap) + __builtin_trap(); +#else + abort(); +#endif +... +</pre> +</blockquote> + + +<!-- ======================================================================= --> +<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3> +<!-- ======================================================================= --> + +<p>These function-like macros take a single identifier argument that is the +name of a feature. <code>__has_feature</code> evaluates to 1 if the feature +is both supported by Clang and standardized in the current language standard +or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while +<code>__has_extension</code> evaluates to 1 if the feature is supported by +Clang in the current language (either as a language extension or a standard +language feature) or 0 if not. They can be used like this:</p> + +<blockquote> +<pre> +#ifndef __has_feature // Optional of course. + #define __has_feature(x) 0 // Compatibility with non-clang compilers. +#endif +#ifndef __has_extension + #define __has_extension __has_feature // Compatibility with pre-3.0 compilers. +#endif + +... +#if __has_feature(cxx_rvalue_references) +// This code will only be compiled with the -std=c++11 and -std=gnu++11 +// options, because rvalue references are only standardized in C++11. +#endif + +#if __has_extension(cxx_rvalue_references) +// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98 +// and -std=gnu++98 options, because rvalue references are supported as a +// language extension in C++98. +#endif +</pre> +</blockquote> + +<p id="has_feature_back_compat">For backwards compatibility reasons, +<code>__has_feature</code> can also be used to test for support for +non-standardized features, i.e. features not prefixed <code>c_</code>, +<code>cxx_</code> or <code>objc_</code>.</p> + +<p id="has_feature_for_non_language_features"> +Another use of <code>__has_feature</code> is to check for compiler features +not related to the language standard, such as e.g. +<a href="AddressSanitizer.html">AddressSanitizer</a>. + +<p>If the <code>-pedantic-errors</code> option is given, +<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p> + +<p>The feature tag is described along with the language feature below.</p> + +<p>The feature name or extension name can also be specified with a preceding and +following <code>__</code> (double underscore) to avoid interference from a macro +with the same name. For instance, <code>__cxx_rvalue_references__</code> can be +used instead of <code>cxx_rvalue_references</code>.</p> + +<!-- ======================================================================= --> +<h3><a name="__has_attribute">__has_attribute</a></h3> +<!-- ======================================================================= --> + +<p>This function-like macro takes a single identifier argument that is the name +of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It +can be used like this:</p> + +<blockquote> +<pre> +#ifndef __has_attribute // Optional of course. + #define __has_attribute(x) 0 // Compatibility with non-clang compilers. +#endif + +... +#if __has_attribute(always_inline) +#define ALWAYS_INLINE __attribute__((always_inline)) +#else +#define ALWAYS_INLINE +#endif +... +</pre> +</blockquote> + +<p>The attribute name can also be specified with a preceding and +following <code>__</code> (double underscore) to avoid interference from a macro +with the same name. For instance, <code>__always_inline__</code> can be used +instead of <code>always_inline</code>.</p> + +<!-- ======================================================================= --> +<h2 id="has_include">Include File Checking Macros</h2> +<!-- ======================================================================= --> + +<p>Not all developments systems have the same include files. +The <a href="#__has_include">__has_include</a> and +<a href="#__has_include_next">__has_include_next</a> macros allow you to +check for the existence of an include file before doing +a possibly failing #include directive.</p> + +<!-- ======================================================================= --> +<h3><a name="__has_include">__has_include</a></h3> +<!-- ======================================================================= --> + +<p>This function-like macro takes a single file name string argument that +is the name of an include file. It evaluates to 1 if the file can +be found using the include paths, or 0 otherwise:</p> + +<blockquote> +<pre> +// Note the two possible file name string formats. +#if __has_include("myinclude.h") && __has_include(<stdint.h>) +# include "myinclude.h" +#endif + +// To avoid problem with non-clang compilers not having this macro. +#if defined(__has_include) && __has_include("myinclude.h") +# include "myinclude.h" +#endif +</pre> +</blockquote> + +<p>To test for this feature, use #if defined(__has_include).</p> + +<!-- ======================================================================= --> +<h3><a name="__has_include_next">__has_include_next</a></h3> +<!-- ======================================================================= --> + +<p>This function-like macro takes a single file name string argument that +is the name of an include file. It is like __has_include except that it +looks for the second instance of the given file found in the include +paths. It evaluates to 1 if the second instance of the file can +be found using the include paths, or 0 otherwise:</p> + +<blockquote> +<pre> +// Note the two possible file name string formats. +#if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>) +# include_next "myinclude.h" +#endif + +// To avoid problem with non-clang compilers not having this macro. +#if defined(__has_include_next) && __has_include_next("myinclude.h") +# include_next "myinclude.h" +#endif +</pre> +</blockquote> + +<p>Note that __has_include_next, like the GNU extension +#include_next directive, is intended for use in headers only, +and will issue a warning if used in the top-level compilation +file. A warning will also be issued if an absolute path +is used in the file argument.</p> + + +<!-- ======================================================================= --> +<h3><a name="__has_warning">__has_warning</a></h3> +<!-- ======================================================================= --> + +<p>This function-like macro takes a string literal that represents a command + line option for a warning and returns true if that is a valid warning + option.</p> + +<blockquote> +<pre> +#if __has_warning("-Wformat") +... +#endif +</pre> +</blockquote> + +<!-- ======================================================================= --> +<h2 id="builtinmacros">Builtin Macros</h2> +<!-- ======================================================================= --> + +<dl> + <dt><code>__BASE_FILE__</code></dt> + <dd>Defined to a string that contains the name of the main input + file passed to Clang.</dd> + + <dt><code>__COUNTER__</code></dt> + <dd>Defined to an integer value that starts at zero and is + incremented each time the <code>__COUNTER__</code> macro is + expanded.</dd> + + <dt><code>__INCLUDE_LEVEL__</code></dt> + <dd>Defined to an integral value that is the include depth of the + file currently being translated. For the main file, this value is + zero.</dd> + + <dt><code>__TIMESTAMP__</code></dt> + <dd>Defined to the date and time of the last modification of the + current source file.</dd> + + <dt><code>__clang__</code></dt> + <dd>Defined when compiling with Clang</dd> + + <dt><code>__clang_major__</code></dt> + <dd>Defined to the major marketing version number of Clang (e.g., the + 2 in 2.0.1). Note that marketing version numbers should not be used to + check for language features, as different vendors use different numbering + schemes. Instead, use the <a href="#feature_check">feature checking + macros</a>.</dd> + + <dt><code>__clang_minor__</code></dt> + <dd>Defined to the minor version number of Clang (e.g., the 0 in + 2.0.1). Note that marketing version numbers should not be used to + check for language features, as different vendors use different numbering + schemes. Instead, use the <a href="#feature_check">feature checking + macros</a>.</dd> + + <dt><code>__clang_patchlevel__</code></dt> + <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd> + + <dt><code>__clang_version__</code></dt> + <dd>Defined to a string that captures the Clang marketing version, including + the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd> +</dl> + +<!-- ======================================================================= --> +<h2 id="vectors">Vectors and Extended Vectors</h2> +<!-- ======================================================================= --> + +<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p> + +<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It +support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An +example is:</p> + +<blockquote> +<pre> +typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>; +typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>; + +float4 foo(float2 a, float2 b) { + float4 c; + c.xz = a; + c.yw = b; + return c; +} +</pre> +</blockquote> + +<p>Query for this feature with +<tt>__has_extension(attribute_ext_vector_type)</tt>.</p> + +<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector +syntax and functions. For example:</p> + +<blockquote> +<pre> +vector float foo(vector int a) { + vector int b; + b = vec_add(a, a) + a; + return (vector float)b; +} +</pre> +</blockquote> + +<p>NEON vector types are created using <tt>neon_vector_type</tt> and +<tt>neon_polyvector_type</tt> attributes. For example:</p> + +<blockquote> +<pre> +typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t; +typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t; + +int8x8_t foo(int8x8_t a) { + int8x8_t v; + v = a; + return v; +} +</pre> +</blockquote> + +<!-- ======================================================================= --> +<h3><a name="vector_literals">Vector Literals</a></h3> +<!-- ======================================================================= --> + +<p>Vector literals can be used to create vectors from a set of scalars, or +vectors. Either parentheses or braces form can be used. In the parentheses form +the number of literal values specified must be one, i.e. referring to a scalar +value, or must match the size of the vector type being created. If a single +scalar literal value is specified, the scalar literal value will be replicated +to all the components of the vector type. In the brackets form any number of +literals can be specified. For example:</p> + +<blockquote> +<pre> +typedef int v4si __attribute__((__vector_size__(16))); +typedef float float4 __attribute__((ext_vector_type(4))); +typedef float float2 __attribute__((ext_vector_type(2))); + +v4si vsi = (v4si){1, 2, 3, 4}; +float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f); +vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1). +vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0). +vector int vi3 = (vector int)(1, 2); // error +vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0). +vector int vi5 = (vector int)(1, 2, 3, 4); +float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f)); +</pre> +</blockquote> + +<!-- ======================================================================= --> +<h3><a name="vector_operations">Vector Operations</a></h3> +<!-- ======================================================================= --> + +<p>The table below shows the support for each operation by vector extension. +A dash indicates that an operation is not accepted according to a corresponding +specification.</p> + +<table width="500" border="1" cellspacing="0"> + <tr> + <th>Operator</th> + <th>OpenCL</th> + <th>AltiVec</th> + <th>GCC</th> + <th>NEON</th> + </tr> + <tr> + <td>[]</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + </tr> + <tr> + <td>unary operators +, -</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + </tr> + <tr> + <td>++, --</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + <td align="center">-</td> + </tr> + <tr> + <td>+, -, *, /, %</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + </tr> + <tr> + <td>bitwise operators &, |, ^, ~</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + </tr> + <tr> + <td>>>, <<</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + </tr> + <tr> + <td>!, &&,||</td> + <td align="center">no</td> + <td align="center">-</td> + <td align="center">-</td> + <td align="center">-</td> + </tr> + <tr> + <td>==,!=, >, <, >=, <=</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">-</td> + <td align="center">-</td> + </tr> + <tr> + <td>=</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + </tr> + <tr> + <td>:?</td> + <td align="center">yes</td> + <td align="center">-</td> + <td align="center">-</td> + <td align="center">-</td> + </tr> + <tr> + <td>sizeof</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + <td align="center">yes</td> + </tr> +</table> + +<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p> + +<!-- ======================================================================= --> +<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2> +<!-- ======================================================================= --> + +<p>An optional string message can be added to the <tt>deprecated</tt> +and <tt>unavailable</tt> attributes. For example:</p> + +<blockquote> +<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre> +</blockquote> + +<p>If the deprecated or unavailable declaration is used, the message +will be incorporated into the appropriate diagnostic:</p> + +<blockquote> +<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! + [-Wdeprecated-declarations] + explode(); + ^</pre> +</blockquote> + +<p>Query for this feature +with <tt>__has_extension(attribute_deprecated_with_message)</tt> +and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p> + +<!-- ======================================================================= --> +<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2> +<!-- ======================================================================= --> + +<p>Clang allows attributes to be written on individual enumerators. +This allows enumerators to be deprecated, made unavailable, etc. The +attribute must appear after the enumerator name and before any +initializer, like so:</p> + +<blockquote> +<pre>enum OperationMode { + OM_Invalid, + OM_Normal, + OM_Terrified __attribute__((deprecated)), + OM_AbortOnError __attribute__((deprecated)) = 4 +};</pre> +</blockquote> + +<p>Attributes on the <tt>enum</tt> declaration do not apply to +individual enumerators.</p> + +<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p> + +<!-- ======================================================================= --> +<h2 id="user_specified_system_framework">'User-Specified' System Frameworks</h2> +<!-- ======================================================================= --> + +<p>Clang provides a mechanism by which frameworks can be built in such a way +that they will always be treated as being 'system frameworks', even if they are +not present in a system framework directory. This can be useful to system +framework developers who want to be able to test building other applications +with development builds of their framework, including the manner in which the +compiler changes warning behavior for system headers.</p> + +<p>Framework developers can opt-in to this mechanism by creating a +'.system_framework' file at the top-level of their framework. That is, the +framework should have contents like:</p> + +<pre> + .../TestFramework.framework + .../TestFramework.framework/.system_framework + .../TestFramework.framework/Headers + .../TestFramework.framework/Headers/TestFramework.h + ... +</pre> + +<p>Clang will treat the presence of this file as an indicator that the framework +should be treated as a system framework, regardless of how it was found in the +framework search path. For consistency, we recommend that such files never be +included in installed versions of the framework.</p> + +<!-- ======================================================================= --> +<h2 id="availability">Availability attribute</h2 +<!-- ======================================================================= --> + +<p>Clang introduces the <code>availability</code> attribute, which can +be placed on declarations to describe the lifecycle of that +declaration relative to operating system versions. Consider the function declaration for a hypothetical function <code>f</code>:</p> + +<pre> +void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7))); +</pre> + +<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> + +<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> + +<dl> + <dt>introduced=<i>version</i></dt> + <dd>The first version in which this declaration was introduced.</dd> + + <dt>deprecated=<i>version</i></dt> + <dd>The first version in which this declaration was deprecated, meaning that users should migrate away from this API.</dd> + + <dt>obsoleted=<i>version</i></dt> + <dd>The first version in which this declaration was obsoleted, meaning that it was removed completely and can no longer be used.</dd> + + <dt>unavailable</dt> + <dd>This declaration is never available on this platform.</dd> + + <dt>message=<i>string-literal</i></dt> + <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> +</dl> + +<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> + +<dl> + <dt>ios</dt> + <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> + + <dt>macosx</dt> + <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> +</dl> + +<p>A declaration can be used even when deploying back to a platform +version prior to when the declaration was introduced. When this +happens, the declaration is <a + href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly +linked</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> + +<!-- ======================================================================= --> +<h2 id="checking_language_features">Checks for Standard Language Features</h2> +<!-- ======================================================================= --> + +<p>The <tt>__has_feature</tt> macro can be used to query if certain standard +language features are enabled. The <tt>__has_extension</tt> macro can be used +to query if language features are available as an extension when compiling for +a standard which does not provide them. The features which can be tested are +listed here.</p> + +<h3 id="cxx98">C++98</h3> + +<p>The features listed below are part of the C++98 standard. These features are +enabled by default when compiling C++ code.</p> + +<h4 id="cxx_exceptions">C++ exceptions</h4> + +<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For +example, compiling code with <tt>-fno-exceptions</tt> disables C++ exceptions.</p> + +<h4 id="cxx_rtti">C++ RTTI</h4> + +<p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example, +compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p> + +<h3 id="cxx11">C++11</h3> + +<p>The features listed below are part of the C++11 standard. As a result, all +these features are enabled with the <tt>-std=c++11</tt> or <tt>-std=gnu++11</tt> +option when compiling C++ code.</p> + +<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4> + +<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> + +<h4 id="cxx_alias_templates">C++11 alias templates</h4> + +<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or +<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for +C++11's alias declarations and alias templates is enabled.</p> + +<h4 id="cxx_alignas">C++11 alignment specifiers</h4> + +<p>Use <tt>__has_feature(cxx_alignas)</tt> or +<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment +specifiers using <tt>alignas</tt> is enabled.</p> + +<h4 id="cxx_attributes">C++11 attributes</h4> + +<p>Use <tt>__has_feature(cxx_attributes)</tt> or +<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute +parsing with C++11's square bracket notation is enabled.</p> + +<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4> + +<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support +for generalized constant expressions (e.g., <tt>constexpr</tt>) is +enabled.</p> + +<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4> + +<p>Use <tt>__has_feature(cxx_decltype)</tt> or +<tt>__has_extension(cxx_decltype)</tt> to determine if support for the +<tt>decltype()</tt> specifier is enabled. C++11's <tt>decltype</tt> +does not require type-completeness of a function call expression. +Use <tt>__has_feature(cxx_decltype_incomplete_return_types)</tt> +or <tt>__has_extension(cxx_decltype_incomplete_return_types)</tt> +to determine if support for this feature is enabled.</p> + +<h4 id="cxx_default_function_template_args">C++11 default template arguments in function templates</h4> + +<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or +<tt>__has_extension(cxx_default_function_template_args)</tt> to determine +if support for default template arguments in function templates is enabled.</p> + +<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4> + +<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or +<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for +defaulted function definitions (with <tt>= default</tt>) is enabled.</p> + +<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4> + +<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if +support for delegating constructors is enabled.</p> + +<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4> + +<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or +<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for +deleted function definitions (with <tt>= delete</tt>) is enabled.</p> + +<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4> +<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p> + +<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4> + +<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if +support for generalized initializers (using braced lists and +<tt>std::initializer_list</tt>) is enabled.</p> + +<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4> + +<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will +implicitly generate move constructors and move assignment operators where needed.</p> + +<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4> + +<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> + +<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4> + +<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or +<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for +inline namespaces is enabled.</p> + +<h4 id="cxx_lambdas">C++11 lambdas</h4> + +<p>Use <tt>__has_feature(cxx_lambdas)</tt> or +<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas +is enabled. </p> + +<h4 id="cxx_local_type_template_args">C++11 local and unnamed types as template arguments</h4> + +<p>Use <tt>__has_feature(cxx_local_type_template_args)</tt> or +<tt>__has_extension(cxx_local_type_template_args)</tt> to determine if +support for local and unnamed types as template arguments is enabled.</p> + +<h4 id="cxx_noexcept">C++11 noexcept</h4> + +<p>Use <tt>__has_feature(cxx_noexcept)</tt> or +<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept +exception specifications is enabled.</p> + +<h4 id="cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</h4> + +<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p> + +<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4> + +<p>Use <tt>__has_feature(cxx_nullptr)</tt> or +<tt>__has_extension(cxx_nullptr)</tt> to determine if support for +<tt>nullptr</tt> is enabled.</p> + +<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4> + +<p>Use <tt>__has_feature(cxx_override_control)</tt> or +<tt>__has_extension(cxx_override_control)</tt> to determine if support for +the override control keywords is enabled.</p> + +<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4> +<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or +<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine +if support for reference-qualified functions (e.g., member functions with +<code>&</code> or <code>&&</code> applied to <code>*this</code>) +is enabled.</p> + +<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4> + +<p>Use <tt>__has_feature(cxx_range_for)</tt> or +<tt>__has_extension(cxx_range_for)</tt> to determine if support for the +range-based for loop is enabled. </p> + +<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4> +<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support +for raw string literals (e.g., <tt>R"x(foo\bar)x"</tt>) is enabled.</p> + +<h4 id="cxx_rvalue_references">C++11 rvalue references</h4> + +<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or +<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for +rvalue references is enabled. </p> + +<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4> + +<p>Use <tt>__has_feature(cxx_static_assert)</tt> or +<tt>__has_extension(cxx_static_assert)</tt> to determine if support for +compile-time assertions using <tt>static_assert</tt> is enabled.</p> + +<h4 id="cxx_auto_type">C++11 type inference</h4> + +<p>Use <tt>__has_feature(cxx_auto_type)</tt> or +<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is +supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt> +will instead be a storage class specifier, as in C or C++98.</p> + +<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4> + +<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or +<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for +strongly typed, scoped enumerations is enabled.</p> + +<h4 id="cxx_trailing_return">C++11 trailing return type</h4> + +<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or +<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the +alternate function declaration syntax with trailing return type is enabled.</p> + +<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4> +<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if +support for Unicode string literals is enabled.</p> + +<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4> + +<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled.</p> + +<h4 id="cxx_user_literals">C++11 user-defined literals</h4> + +<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled.</p> + +<h4 id="cxx_variadic_templates">C++11 variadic templates</h4> + +<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or +<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support +for variadic templates is enabled.</p> + +<h3 id="c11">C11</h3> + +<p>The features listed below are part of the C11 standard. As a result, all +these features are enabled with the <tt>-std=c11</tt> or <tt>-std=gnu11</tt> +option when compiling C code. Additionally, because these features are all +backward-compatible, they are available as extensions in all language modes.</p> + +<h4 id="c_alignas">C11 alignment specifiers</h4> + +<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt> +to determine if support for alignment specifiers using <tt>_Alignas</tt> +is enabled.</p> + +<h4 id="c_atomic">C11 atomic operations</h4> + +<p>Use <tt>__has_feature(c_atomic)</tt> or <tt>__has_extension(c_atomic)</tt> +to determine if support for atomic types using <tt>_Atomic</tt> is enabled. +Clang also provides <a href="#__c11_atomic">a set of builtins</a> which can be +used to implement the <tt><stdatomic.h></tt> operations on _Atomic +types.</p> + +<h4 id="c_generic_selections">C11 generic selections</h4> + +<p>Use <tt>__has_feature(c_generic_selections)</tt> or +<tt>__has_extension(c_generic_selections)</tt> to determine if support for +generic selections is enabled.</p> + +<p>As an extension, the C11 generic selection expression is available in all +languages supported by Clang. The syntax is the same as that given in the +C11 standard.</p> + +<p>In C, type compatibility is decided according to the rules given in the +appropriate standard, but in C++, which lacks the type compatibility rules +used in C, types are considered compatible only if they are equivalent.</p> + +<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4> + +<p>Use <tt>__has_feature(c_static_assert)</tt> or +<tt>__has_extension(c_static_assert)</tt> to determine if support for +compile-time assertions using <tt>_Static_assert</tt> is enabled.</p> + +<!-- ======================================================================= --> +<h2 id="checking_type_traits">Checks for Type Traits</h2> +<!-- ======================================================================= --> + +<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: +<blockquote> +<pre> +#if __has_extension(is_convertible_to) +template<typename From, typename To> +struct is_convertible_to { + static const bool value = __is_convertible_to(From, To); +}; +#else +// Emulate type trait +#endif +</pre> +</blockquote> + +<p>The following type traits are supported by Clang:</p> +<ul> + <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li> + <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li> + <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li> + <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li> + <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li> + <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li> + <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li> + <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li> + <li><code>__is_abstract</code> (GNU, Microsoft)</li> + <li><code>__is_base_of</code> (GNU, Microsoft)</li> + <li><code>__is_class</code> (GNU, Microsoft)</li> + <li><code>__is_convertible_to</code> (Microsoft)</li> + <li><code>__is_empty</code> (GNU, Microsoft)</li> + <li><code>__is_enum</code> (GNU, Microsoft)</li> + <li><code>__is_pod</code> (GNU, Microsoft)</li> + <li><code>__is_polymorphic</code> (GNU, Microsoft)</li> + <li><code>__is_union</code> (GNU, Microsoft)</li> + <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li> + <li><code>__is_final</code>: Determines whether the given type is declared with a <code>final</code> class-virt-specifier.</li> + <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> + <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> + <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> +</ul> + +<!-- ======================================================================= --> +<h2 id="blocks">Blocks</h2> +<!-- ======================================================================= --> + +<p>The syntax and high level language feature description is in <a +href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI +details for the clang implementation are in <a +href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p> + + +<p>Query for this feature with __has_extension(blocks).</p> + +<!-- ======================================================================= --> +<h2 id="objc_features">Objective-C Features</h2> +<!-- ======================================================================= --> + +<h3 id="objc_instancetype">Related result types</h3> + +<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> + +<blockquote> +<pre> +@interface NSObject ++ (id)alloc; +- (id)init; +@end + +@interface NSArray : NSObject +@end +</pre> +</blockquote> + +<p>and this common initialization pattern</p> + +<blockquote> +<pre> +NSArray *array = [[NSArray alloc] init]; +</pre> +</blockquote> + +<p>the type of the expression <code>[NSArray alloc]</code> is +<code>NSArray*</code> because <code>alloc</code> implicitly has a +related result type. Similarly, the type of the expression +<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since +<code>init</code> has a related result type and its receiver is known +to 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> + +<p>A method with a related result type can be declared by using the +type <tt>instancetype</tt> as its result type. <tt>instancetype</tt> +is a contextual keyword that is only permitted in the result type of +an Objective-C method, e.g.</p> + +<pre> +@interface A ++ (<b>instancetype</b>)constructAnA; +@end +</pre> + +<p>The related result type can also be inferred for some methods. +To determine whether a method has an inferred related result type, the first +word in the camel-case selector (e.g., "init" in "initWithObjects") is +considered, and the method will have a related result type if its return +type is compatible with the type of its class and if</p> + +<ul> + + <li>the first word is "alloc" or "new", and the method is a class + method, or</li> + + <li>the first word is "autorelease", "init", "retain", or "self", + and the method is an instance method.</li> + +</ul> + +<p>If a method with a related result type is overridden by a subclass +method, the subclass method must also return a type that is compatible +with the subclass type. For example:</p> + +<blockquote> +<pre> +@interface NSString : NSObject +- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString +@end +</pre> +</blockquote> + +<p>Related result types only affect the type of a message send or +property access via the given method. In all other respects, a method +with a related result type is treated the same way as method that +returns <tt>id</tt>.</p> + +<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether +the <tt>instancetype</tt> contextual keyword is available.</p> + +<!-- ======================================================================= --> +<h2 id="objc_arc">Automatic reference counting </h2> +<!-- ======================================================================= --> + +<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> + +<!-- ======================================================================= --> +<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2> +<!-- ======================================================================= --> + +<p>Clang provides support for C++11 enumerations with a fixed +underlying type within Objective-C. For example, one can write an +enumeration type as:</p> + +<pre> +typedef enum : unsigned char { Red, Green, Blue } Color; +</pre> + +<p>This specifies that the underlying type, which is used to store the +enumeration value, is <tt>unsigned char</tt>.</p> + +<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether +support for fixed underlying types is available in Objective-C.</p> + +<!-- ======================================================================= --> +<h2 id="objc_lambdas">Interoperability with C++11 lambdas</h2> +<!-- ======================================================================= --> + +<p>Clang provides interoperability between C++11 lambdas and +blocks-based APIs, by permitting a lambda to be implicitly converted +to a block pointer with the corresponding signature. For example, +consider an API such as <code>NSArray</code>'s array-sorting +method:</p> + +<pre> - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; </pre> + +<p><code>NSComparator</code> is simply a typedef for the block pointer +<code>NSComparisonResult (^)(id, id)</code>, and parameters of this +type are generally provided with block literals as arguments. However, +one can also use a C++11 lambda so long as it provides the same +signature (in this case, accepting two parameters of type +<code>id</code> and returning an <code>NSComparisonResult</code>):</p> + +<pre> + NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11", + @"String 02"]; + const NSStringCompareOptions comparisonOptions + = NSCaseInsensitiveSearch | NSNumericSearch | + NSWidthInsensitiveSearch | NSForcedOrderingSearch; + NSLocale *currentLocale = [NSLocale currentLocale]; + NSArray *sorted + = [array sortedArrayUsingComparator:<b>[=](id s1, id s2) -> NSComparisonResult { + NSRange string1Range = NSMakeRange(0, [s1 length]); + return [s1 compare:s2 options:comparisonOptions + range:string1Range locale:currentLocale]; + }</b>]; + NSLog(@"sorted: %@", sorted); +</pre> + +<p>This code relies on an implicit conversion from the type of the +lambda expression (an unnamed, local class type called the <i>closure +type</i>) to the corresponding block pointer type. The conversion +itself is expressed by a conversion operator in that closure type +that produces a block pointer with the same signature as the lambda +itself, e.g.,</p> + +<pre> + operator NSComparisonResult (^)(id, id)() const; +</pre> + +<p>This conversion function returns a new block that simply forwards +the two parameters to the lambda object (which it captures by copy), +then returns the result. The returned block is first copied (with +<tt>Block_copy</tt>) and then autoreleased. As an optimization, if a +lambda expression is immediately converted to a block pointer (as in +the first example, above), then the block is not copied and +autoreleased: rather, it is given the same lifetime as a block literal +written at that point in the program, which avoids the overhead of +copying a block to the heap in the common case.</p> + +<p>The conversion from a lambda to a block pointer is only available +in Objective-C++, and not in C++ with blocks, due to its use of +Objective-C memory management (autorelease).</p> + +<!-- ======================================================================= --> +<h2 id="object-literals-subscripting">Object Literals and Subscripting</h2> +<!-- ======================================================================= --> + +<p>Clang provides support for <a href="ObjectiveCLiterals.html">Object Literals and Subscripting</a> in Objective-C, which simplifies common Objective-C programming patterns, makes programs more concise, and improves the safety of container creation. There are several feature macros associated with object literals and subscripting: <code>__has_feature(objc_array_literals)</code> tests the availability of array literals; <code>__has_feature(objc_dictionary_literals)</code> tests the availability of dictionary literals; <code>__has_feature(objc_subscripting)</code> tests the availability of object subscripting.</p> + +<!-- ======================================================================= --> +<h2 id="overloading-in-c">Function Overloading in C</h2> +<!-- ======================================================================= --> + +<p>Clang provides support for C++ function overloading in C. Function +overloading in C is introduced using the <tt>overloadable</tt> attribute. For +example, one might provide several overloaded versions of a <tt>tgsin</tt> +function that invokes the appropriate standard function computing the sine of a +value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt> +precision:</p> + +<blockquote> +<pre> +#include <math.h> +float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); } +double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); } +long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); } +</pre> +</blockquote> + +<p>Given these declarations, one can call <tt>tgsin</tt> with a +<tt>float</tt> value to receive a <tt>float</tt> result, with a +<tt>double</tt> to receive a <tt>double</tt> result, etc. Function +overloading in C follows the rules of C++ function overloading to pick +the best overload given the call arguments, with a few C-specific +semantics:</p> +<ul> + <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long + double</tt> is ranked as a floating-point promotion (per C99) rather + than as a floating-point conversion (as in C++).</li> + + <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type + <tt>U*</tt> is considered a pointer conversion (with conversion + rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li> + + <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt> + is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This + conversion is given "conversion" rank.</li> +</ul> + +<p>The declaration of <tt>overloadable</tt> functions is restricted to +function declarations and definitions. Most importantly, if any +function with a given name is given the <tt>overloadable</tt> +attribute, then all function declarations and definitions with that +name (and in that scope) must have the <tt>overloadable</tt> +attribute. This rule even applies to redeclarations of functions whose original +declaration had the <tt>overloadable</tt> attribute, e.g.,</p> + +<blockquote> +<pre> +int f(int) __attribute__((overloadable)); +float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i> + +int g(int) __attribute__((overloadable)); +int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i> +</pre> +</blockquote> + +<p>Functions marked <tt>overloadable</tt> must have +prototypes. Therefore, the following code is ill-formed:</p> + +<blockquote> +<pre> +int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i> +</pre> +</blockquote> + +<p>However, <tt>overloadable</tt> functions are allowed to use a +ellipsis 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> + +<blockquote> +<pre> +void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i> +</pre> +</blockquote> + +<p>Functions declared with the <tt>overloadable</tt> attribute have +their names mangled according to the same rules as C++ function +names. For example, the three <tt>tgsin</tt> functions in our +motivating example get the mangled names <tt>_Z5tgsinf</tt>, +<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two +caveats to this use of name mangling:</p> + +<ul> + + <li>Future versions of Clang may change the name mangling of + functions overloaded in C, so you should not depend on an specific + mangling. To be completely safe, we strongly urge the use of + <tt>static inline</tt> with <tt>overloadable</tt> functions.</li> + + <li>The <tt>overloadable</tt> attribute has almost no meaning when + used in C++, because names will already be mangled and functions are + already overloadable. However, when an <tt>overloadable</tt> + function occurs within an <tt>extern "C"</tt> linkage specification, + it's name <i>will</i> be mangled in the same way as it would in + C.</li> +</ul> + +<p>Query for this feature with __has_extension(attribute_overloadable).</p> + +<!-- ======================================================================= --> +<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2> +<!-- ======================================================================= --> + +<p>clang supports an extension which allows the following in C:</p> + +<blockquote> +<pre> +#include <math.h> +#include <complex.h> +complex float x = { 1.0f, INFINITY }; // Init to (1, Inf) +</pre> +</blockquote> + +<p>This construct is useful because there is no way to separately +initialize the real and imaginary parts of a complex variable in +standard C, given that clang does not support <code>_Imaginary</code>. +(clang also supports the <code>__real__</code> and <code>__imag__</code> +extensions from gcc, which help in some cases, but are not usable in +static initializers.) + +<p>Note that this extension does not allow eliding the braces; the +meaning of the following two lines is different:</p> + +<blockquote> +<pre> +complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1) +complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0) +</pre> +</blockquote> + +<p>This extension also works in C++ mode, as far as that goes, but does not + apply to the C++ <code>std::complex</code>. (In C++11, list + initialization allows the same syntax to be used with + <code>std::complex</code> with the same meaning.) + +<!-- ======================================================================= --> +<h2 id="builtins">Builtin Functions</h2> +<!-- ======================================================================= --> + +<p>Clang supports a number of builtin library functions with the same syntax as +GCC, including things like <tt>__builtin_nan</tt>, +<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>, +<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In +addition to the GCC builtins, Clang supports a number of builtins that GCC does +not, which are listed here.</p> + +<p>Please note that Clang does not and will not support all of the GCC builtins +for vector operations. Instead of using builtins, you should use the functions +defined in target-specific header files like <tt><xmmintrin.h></tt>, which +define portable wrappers for these. Many of the Clang versions of these +functions are implemented directly in terms of <a href="#vectors">extended +vector support</a> instead of builtins, in order to reduce the number of +builtins that we need to implement.</p> + +<!-- ======================================================================= --> +<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3> +<!-- ======================================================================= --> + +<p><tt>__builtin_shufflevector</tt> is used to express generic vector +permutation/shuffle/swizzle operations. This builtin is also very important for +the implementation of various target-specific header files like +<tt><xmmintrin.h></tt>. +</p> + +<p><b>Syntax:</b></p> + +<pre> +__builtin_shufflevector(vec1, vec2, index1, index2, ...) +</pre> + +<p><b>Examples:</b></p> + +<pre> + // Identity operation - return 4-element vector V1. + __builtin_shufflevector(V1, V1, 0, 1, 2, 3) + + // "Splat" element 0 of V1 into a 4-element result. + __builtin_shufflevector(V1, V1, 0, 0, 0, 0) + + // Reverse 4-element vector V1. + __builtin_shufflevector(V1, V1, 3, 2, 1, 0) + + // Concatenate every other element of 4-element vectors V1 and V2. + __builtin_shufflevector(V1, V2, 0, 2, 4, 6) + + // Concatenate every other element of 8-element vectors V1 and V2. + __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14) +</pre> + +<p><b>Description:</b></p> + +<p>The first two arguments to __builtin_shufflevector are vectors that have the +same element type. The remaining arguments are a list of integers that specify +the elements indices of the first two vectors that should be extracted and +returned in a new vector. These element indices are numbered sequentially +starting with the first vector, continuing into the second vector. Thus, if +vec1 is a 4-element vector, index 5 would refer to the second element of vec2. +</p> + +<p>The result of __builtin_shufflevector is a vector +with the same element type as vec1/vec2 but that has an element count equal to +the number of indices specified. +</p> + +<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p> + +<!-- ======================================================================= --> +<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3> +<!-- ======================================================================= --> + +<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in +the program cannot be reached, even if the compiler might otherwise think it +can. This is useful to improve optimization and eliminates certain warnings. +For example, without the <tt>__builtin_unreachable</tt> in the example below, +the compiler assumes that the inline asm can fall through and prints a "function +declared 'noreturn' should not return" warning. +</p> + +<p><b>Syntax:</b></p> + +<pre> +__builtin_unreachable() +</pre> + +<p><b>Example of Use:</b></p> + +<pre> +void myabort(void) __attribute__((noreturn)); +void myabort(void) { + asm("int3"); + __builtin_unreachable(); +} +</pre> + +<p><b>Description:</b></p> + +<p>The __builtin_unreachable() builtin has completely undefined behavior. Since +it has undefined behavior, it is a statement that it is never reached and the +optimizer can take advantage of this to produce better code. This builtin takes +no arguments and produces a void result. +</p> + +<p>Query for this feature with __has_builtin(__builtin_unreachable).</p> + +<!-- ======================================================================= --> +<h3><a name="__sync_swap">__sync_swap</a></h3> +<!-- ======================================================================= --> + +<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in +memory. +</p> + +<p><b>Syntax:</b></p> + +<pre> +<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...) +</pre> + +<p><b>Example of Use:</b></p> + +<pre> +int old_value = __sync_swap(&value, new_value); +</pre> + +<p><b>Description:</b></p> + +<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic +intrinsics to allow code to atomically swap the current value with the new +value. More importantly, it helps developers write more efficient and correct +code by avoiding expensive loops around __sync_bool_compare_and_swap() or +relying on the platform specific implementation details of +__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier. +</p> + +<!-- ======================================================================= --> +<h3><a name="__c11_atomic">__c11_atomic builtins</a></h3> +<!-- ======================================================================= --> + +<p>Clang provides a set of builtins which are intended to be used to implement +C11's <tt><stdatomic.h></tt> header. These builtins provide the semantics +of the <tt>_explicit</tt> form of the corresponding C11 operation, and are named +with a <tt>__c11_</tt> prefix. The supported operations are:</p> + +<ul> + <li><tt>__c11_atomic_init</tt></li> + <li><tt>__c11_atomic_thread_fence</tt></li> + <li><tt>__c11_atomic_signal_fence</tt></li> + <li><tt>__c11_atomic_is_lock_free</tt></li> + <li><tt>__c11_atomic_store</tt></li> + <li><tt>__c11_atomic_load</tt></li> + <li><tt>__c11_atomic_exchange</tt></li> + <li><tt>__c11_atomic_compare_exchange_strong</tt></li> + <li><tt>__c11_atomic_compare_exchange_weak</tt></li> + <li><tt>__c11_atomic_fetch_add</tt></li> + <li><tt>__c11_atomic_fetch_sub</tt></li> + <li><tt>__c11_atomic_fetch_and</tt></li> + <li><tt>__c11_atomic_fetch_or</tt></li> + <li><tt>__c11_atomic_fetch_xor</tt></li> +</ul> + + +<!-- ======================================================================= --> +<h2 id="targetspecific">Target-Specific Extensions</h2> +<!-- ======================================================================= --> + +<p>Clang supports some language features conditionally on some targets.</p> + +<!-- ======================================================================= --> +<h3 id="x86-specific">X86/X86-64 Language Extensions</h3> +<!-- ======================================================================= --> + +<p>The X86 backend has these language extensions:</p> + +<!-- ======================================================================= --> +<h4 id="x86-gs-segment">Memory references off the GS segment</h4> +<!-- ======================================================================= --> + +<p>Annotating a pointer with address space #256 causes it to be code generated +relative to the X86 GS segment register, and address space #257 causes it to be +relative to the X86 FS segment. Note that this is a very very low-level +feature that should only be used if you know what you're doing (for example in +an OS kernel).</p> + +<p>Here is an example:</p> + +<pre> +#define GS_RELATIVE __attribute__((address_space(256))) +int foo(int GS_RELATIVE *P) { + return *P; +} +</pre> + +<p>Which compiles to (on X86-32):</p> + +<pre> +_foo: + movl 4(%esp), %eax + movl %gs:(%eax), %eax + ret +</pre> + +<!-- ======================================================================= --> +<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2> +<!-- ======================================================================= --> + +<p>Clang supports additional attributes that are useful for documenting program +invariants and rules for static analysis tools. The extensions documented here +are used by the <a +href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer +engine</a> that is part of Clang's Analysis library.</p> + +<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3> + +<p>Clang's static analysis engine understands the standard <tt>noreturn</tt> +attribute. This attribute, which is typically affixed to a function prototype, +indicates that a call to a given function never returns. Function prototypes for +common functions like <tt>exit</tt> are typically annotated with this attribute, +as well as a variety of common assertion handlers. Users can educate the static +analyzer about their own custom assertion handles (thus cutting down on false +positives due to false paths) by marking their own "panic" functions +with this attribute.</p> + +<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes +there are special functions that for all intents and purposes should be +considered panic functions (i.e., they are only called when an internal program +error occurs) but may actually return so that the program can fail gracefully. +The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions +as being interpreted as "no return" functions by the analyzer (thus +pruning bogus paths) but will not affect compilation (as in the case of +<tt>noreturn</tt>).</p> + +<p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the +same places where the <tt>noreturn</tt> attribute can be placed. It is commonly +placed at the end of function prototypes:</p> + +<pre> + void foo() <b>__attribute__((analyzer_noreturn))</b>; +</pre> + +<p>Query for this feature with +<tt>__has_attribute(analyzer_noreturn)</tt>.</p> + +<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3> + +<p>Many methods in Objective-C have conventional meanings determined +by their selectors. For the purposes of static analysis, it is +sometimes useful to be able to mark a method as having a particular +conventional meaning despite not having the right selector, or as not +having the conventional meaning that its selector would suggest. +For these use cases, we provide an attribute to specifically describe +the <q>method family</q> that a method belongs to.</p> + +<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>, +where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>, +<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute +can only be placed at the end of a method declaration:</p> + +<pre> + - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>; +</pre> + +<p>Users who do not wish to change the conventional meaning of a +method, and who merely want to document its non-standard retain and +release semantics, should use the +<a href="#attr_retain_release">retaining behavior attributes</a> +described below.</p> + +<p>Query for this feature with +<tt>__has_attribute(objc_method_family)</tt>.</p> + +<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3> + +<p>In Objective-C, functions and methods are generally assumed to take +and return objects with +0 retain counts, with some exceptions for +special methods like <tt>+alloc</tt> and <tt>init</tt>. However, +there are exceptions, and so Clang provides attributes to allow these +exceptions to be documented, which helps the analyzer find leaks (and +ignore non-leaks). Some exceptions may be better described using +the <a href="#attr_method_family"><tt>objc_method_family</tt></a> +attribute instead.</p> + +<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>, +<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>, +and <tt>cf_returns_not_retained</tt> attributes can be placed on +methods and functions that return Objective-C or CoreFoundation +objects. They are commonly placed at the end of a function prototype +or method declaration:</p> + +<pre> + id foo() <b>__attribute__((ns_returns_retained))</b>; + + - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>; +</pre> + +<p>The <tt>*_returns_retained</tt> attributes specify that the +returned object has a +1 retain count. +The <tt>*_returns_not_retained</tt> attributes specify that the return +object has a +0 retain count, even if the normal convention for its +selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the +returned object is +0, but is guaranteed to live at least as long as the +next flush of an autorelease pool.</p> + +<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt> +attributes can be placed on an parameter declaration; they specify +that the argument is expected to have a +1 retain count, which will be +balanced in some way by the function or method. +The <tt>ns_consumes_self</tt> attribute can only be placed on an +Objective-C method; it specifies that the method expects +its <tt>self</tt> parameter to have a +1 retain count, which it will +balance in some way.</p> + +<pre> + void <b>foo(__attribute__((ns_consumed))</b> NSString *string); + + - (void) bar <b>__attribute__((ns_consumes_self))</b>; + - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x; +</pre> + +<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>, +<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p> + +<!-- ======================================================================= --> +<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2> +<!-- ======================================================================= --> +<h3 id="address_sanitizer">AddressSanitizer</h3> +<p> Use <code>__has_feature(address_sanitizer)</code> +to check if the code is being built with <a + href="AddressSanitizer.html">AddressSanitizer</a>. +</p> +<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function +declaration to specify that address safety instrumentation (e.g. +AddressSanitizer) should not be applied to that function. +</p> + +<!-- ======================================================================= --> +<h2 id="threadsafety">Thread-Safety Annotation Checking</h2> +<!-- ======================================================================= --> + +<p>Clang supports additional attributes for checking basic locking policies in +multithreaded programs. +Clang currently parses the following list of attributes, although +<b>the implementation for these annotations is currently in development.</b> +For more details, see the +<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>. +</p> + +<h4 id="ts_noanal">no_thread_safety_analysis</h4> + +<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function +declaration to specify that the thread safety analysis should not be run on that +function. This attribute provides an escape hatch (e.g. for situations when it +is difficult to annotate the locking policy). </p> + +<h4 id="ts_lockable">lockable</h4> + +<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify +that it has a lockable type (e.g. a Mutex class). This annotation is primarily +used to check consistency.</p> + +<h4 id="ts_scopedlockable">scoped_lockable</h4> + +<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to +specify that it has a "scoped" lockable type. Objects of this type will acquire +the lock upon construction and release it upon going out of scope. + This annotation is primarily used to check +consistency.</p> + +<h4 id="ts_guardedvar">guarded_var</h4> + +<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to +specify that the variable must be accessed while holding some lock.</p> + +<h4 id="ts_ptguardedvar">pt_guarded_var</h4> + +<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to +specify that the pointer must be dereferenced while holding some lock.</p> + +<h4 id="ts_guardedby">guarded_by(l)</h4> + +<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to +specify that the variable must be accessed while holding lock <tt>l</tt>.</p> + +<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4> + +<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to +specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p> + +<h4 id="ts_acquiredbefore">acquired_before(...)</h4> + +<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration +of a lockable variable to specify that the lock must be acquired before all +attribute arguments. Arguments must be lockable type, and there must be at +least one argument.</p> + +<h4 id="ts_acquiredafter">acquired_after(...)</h4> + +<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration +of a lockable variable to specify that the lock must be acquired after all +attribute arguments. Arguments must be lockable type, and there must be at +least one argument.</p> + +<h4 id="ts_elf">exclusive_lock_function(...)</h4> + +<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function +declaration to specify that the function acquires all listed locks +exclusively. This attribute takes zero or more arguments: either of lockable +type or integers indexing into function parameters of lockable type. If no +arguments are given, the acquired lock is implicitly <tt>this</tt> of the +enclosing object.</p> + +<h4 id="ts_slf">shared_lock_function(...)</h4> + +<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function +declaration to specify that the function acquires all listed locks, although + the locks may be shared (e.g. read locks). This attribute takes zero or more +arguments: either of lockable type or integers indexing into function +parameters of lockable type. If no arguments are given, the acquired lock is +implicitly <tt>this</tt> of the enclosing object.</p> + +<h4 id="ts_etf">exclusive_trylock_function(...)</h4> + +<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function +declaration to specify that the function will try (without blocking) to acquire +all listed locks exclusively. This attribute takes one or more arguments. The +first argument is an integer or boolean value specifying the return value of a +successful lock acquisition. The remaining arugments are either of lockable type +or integers indexing into function parameters of lockable type. If only one +argument is given, the acquired lock is implicitly <tt>this</tt> of the +enclosing object.</p> + +<h4 id="ts_stf">shared_trylock_function(...)</h4> + +<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function +declaration to specify that the function will try (without blocking) to acquire +all listed locks, although the locks may be shared (e.g. read locks). This +attribute takes one or more arguments. The first argument is an integer or +boolean value specifying the return value of a successful lock acquisition. The +remaining arugments are either of lockable type or integers indexing into +function parameters of lockable type. If only one argument is given, the +acquired lock is implicitly <tt>this</tt> of the enclosing object.</p> + +<h4 id="ts_uf">unlock_function(...)</h4> + +<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function +declaration to specify that the function release all listed locks. This +attribute takes zero or more arguments: either of lockable type or integers +indexing into function parameters of lockable type. If no arguments are given, +the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p> + +<h4 id="ts_lr">lock_returned(l)</h4> + +<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function +declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt> +must be of lockable type). This annotation is used to aid in resolving lock +expressions.</p> + +<h4 id="ts_le">locks_excluded(...)</h4> + +<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration +to specify that the function must not be called with the listed locks. Arguments +must be lockable type, and there must be at least one argument.</p> + +<h4 id="ts_elr">exclusive_locks_required(...)</h4> + +<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function +declaration to specify that the function must be called while holding the listed +exclusive locks. Arguments must be lockable type, and there must be at +least one argument.</p> + +<h4 id="ts_slr">shared_locks_required(...)</h4> + +<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function +declaration to specify that the function must be called while holding the listed +shared locks. Arguments must be lockable type, and there must be at +least one argument.</p> + +</div> +</body> +</html> |