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Diffstat (limited to 'docs/LanguageExtensions.html')
| -rw-r--r-- | docs/LanguageExtensions.html | 87 |
1 files changed, 80 insertions, 7 deletions
diff --git a/docs/LanguageExtensions.html b/docs/LanguageExtensions.html index c486562..c855a50 100644 --- a/docs/LanguageExtensions.html +++ b/docs/LanguageExtensions.html @@ -19,6 +19,7 @@ td { <ul> <li><a href="#intro">Introduction</a></li> +<li><a href="#feature_check">Feature 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="#blocks">Blocks</a></li> @@ -45,12 +46,73 @@ td { <!-- ======================================================================= --> <p>This document describes the language extensions provided by Clang. In -addition to the langauge extensions listed here, Clang aims to support a broad +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 two 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 id="__has_builtin">__has_builtin</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 id="__has_feature">__has_feature</h3> +<!-- ======================================================================= --> + +<p>This function-like macro takes a single identifier argument that is the name +of a feature. It evaluates to 1 if the feature is supported or 0 if not. It +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 + +... +#if __has_feature(attribute_overloadable) || \ + __has_feature(blocks) +... +#endif +... +</pre> +</blockquote> + +<p>The feature tag is described along with the language feature below.</p> + + +<!-- ======================================================================= --> <h2 id="builtinmacros">Builtin Macros</h2> <!-- ======================================================================= --> @@ -64,6 +126,8 @@ more information on these extensions.</p> with V.xyzw syntax and other tidbits. See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p> +<p>Query for this feature with __has_feature(attribute_ext_vector_type).</p> + <!-- ======================================================================= --> <h2 id="blocks">Blocks</h2> <!-- ======================================================================= --> @@ -73,6 +137,9 @@ href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI details for the clang implementation are in <a href="BlockImplementation.txt">BlockImplementation.txt</a>.</p> + +<p>Query for this feature with __has_feature(blocks).</p> + <!-- ======================================================================= --> <h2 id="overloading-in-c">Function Overloading in C</h2> <!-- ======================================================================= --> @@ -171,6 +238,9 @@ caveats to this use of name mangling:</p> C.</li> </ul> +<p>Query for this feature with __has_feature(attribute_overloadable).</p> + + <!-- ======================================================================= --> <h2 id="builtins">Builtin Functions</h2> <!-- ======================================================================= --> @@ -306,11 +376,11 @@ 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 intensive 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 +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> @@ -320,7 +390,10 @@ placed at the end of function prototypes:</p> <pre> void foo() <b>__attribute__((analyzer_noreturn))</b>; -</p> +</pre> + +<p>Query for this feature with __has_feature(attribute_analyzer_noreturn).</p> + </div> </body> |
