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diff --git a/share/doc/cpp/_005f_005fhas_005fattribute.html b/share/doc/cpp/_005f_005fhas_005fattribute.html new file mode 100644 index 0000000..67e5b17 --- /dev/null +++ b/share/doc/cpp/_005f_005fhas_005fattribute.html @@ -0,0 +1,121 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1987-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation. A copy of +the license is included in the +section entitled "GNU Free Documentation License". + +This manual contains no Invariant Sections. 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Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The C Preprocessor: __has_attribute</title> + +<meta name="description" content="The C Preprocessor: __has_attribute"> +<meta name="keywords" content="The C Preprocessor: __has_attribute"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Conditional-Syntax.html#Conditional-Syntax" rel="up" title="Conditional Syntax"> +<link href="_005f_005fhas_005fcpp_005fattribute.html#g_t_005f_005fhas_005fcpp_005fattribute" rel="next" title="__has_cpp_attribute"> +<link href="Elif.html#Elif" rel="previous" title="Elif"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="g_t_005f_005fhas_005fattribute"></a> +<div class="header"> +<p> +Next: <a href="_005f_005fhas_005fcpp_005fattribute.html#g_t_005f_005fhas_005fcpp_005fattribute" accesskey="n" rel="next"><code>__has_cpp_attribute</code></a>, Previous: <a href="Elif.html#Elif" accesskey="p" rel="previous">Elif</a>, Up: <a href="Conditional-Syntax.html#Conditional-Syntax" accesskey="u" rel="up">Conditional Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="g_t_005f_005fhas_005fattribute-1"></a> +<h4 class="subsection">4.2.6 <code>__has_attribute</code></h4> +<a name="index-_005f_005fhas_005fattribute"></a> + +<p>The special operator <code>__has_attribute (<var>operand</var>)</code> may be used +in ‘<samp>#if</samp>’ and ‘<samp>#elif</samp>’ expressions to test whether the attribute +referenced by its <var>operand</var> is recognized by GCC. Using the operator +in other contexts is not valid. In C code, if compiling for strict +conformance to standards before C2x, <var>operand</var> must be +a valid identifier. Otherwise, <var>operand</var> may be optionally +introduced by the <code><var>attribute-scope</var>::</code> prefix. +The <var>attribute-scope</var> prefix identifies the “namespace” within +which the attribute is recognized. The scope of GCC attributes is +‘<samp>gnu</samp>’ or ‘<samp>__gnu__</samp>’. The <code>__has_attribute</code> operator by +itself, without any <var>operand</var> or parentheses, acts as a predefined +macro so that support for it can be tested in portable code. Thus, +the recommended use of the operator is as follows: +</p> +<div class="smallexample"> +<pre class="smallexample">#if defined __has_attribute +# if __has_attribute (nonnull) +# define ATTR_NONNULL __attribute__ ((nonnull)) +# endif +#endif +</pre></div> + +<p>The first ‘<samp>#if</samp>’ test succeeds only when the operator is supported +by the version of GCC (or another compiler) being used. Only when that +test succeeds is it valid to use <code>__has_attribute</code> as a preprocessor +operator. As a result, combining the two tests into a single expression as +shown below would only be valid with a compiler that supports the operator +but not with others that don’t. +</p> +<div class="smallexample"> +<pre class="smallexample">#if defined __has_attribute && __has_attribute (nonnull) /* not portable */ +… +#endif +</pre></div> + + + + +</body> +</html> |