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diff --git a/share/doc/cpp/_005f_005fhas_005finclude.html b/share/doc/cpp/_005f_005fhas_005finclude.html new file mode 100644 index 0000000..f386b51 --- /dev/null +++ b/share/doc/cpp/_005f_005fhas_005finclude.html @@ -0,0 +1,120 @@ +<!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. The Front-Cover Texts are +(a) (see below), and the Back-Cover Texts are (b) (see below). + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. 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_include</title> + +<meta name="description" content="The C Preprocessor: __has_include"> +<meta name="keywords" content="The C Preprocessor: __has_include"> +<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="Deleted-Code.html#Deleted-Code" rel="next" title="Deleted Code"> +<link href="_005f_005fhas_005fbuiltin.html#g_t_005f_005fhas_005fbuiltin" rel="previous" title="__has_builtin"> +<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_005finclude"></a> +<div class="header"> +<p> +Previous: <a href="_005f_005fhas_005fbuiltin.html#g_t_005f_005fhas_005fbuiltin" accesskey="p" rel="previous"><code>__has_builtin</code></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_005finclude-1"></a> +<h4 class="subsection">4.2.10 <code>__has_include</code></h4> +<a name="index-_005f_005fhas_005finclude"></a> + +<p>The special operator <code>__has_include (<var>operand</var>)</code> may be used in +‘<samp>#if</samp>’ and ‘<samp>#elif</samp>’ expressions to test whether the header referenced +by its <var>operand</var> can be included using the ‘<samp>#include</samp>’ directive. Using +the operator in other contexts is not valid. The <var>operand</var> takes +the same form as the file in the ‘<samp>#include</samp>’ directive (see <a href="Include-Syntax.html#Include-Syntax">Include Syntax</a>) and evaluates to a nonzero value if the header can be included and +to zero otherwise. Note that that the ability to include a header doesn’t +imply that the header doesn’t contain invalid constructs or ‘<samp>#error</samp>’ +directives that would cause the preprocessor to fail. +</p> +<p>The <code>__has_include</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_include +# if __has_include (<stdatomic.h>) +# include <stdatomic.h> +# 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_include</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_include && __has_include ("header.h") /* not portable */ +… +#endif +</pre></div> + + + + +</body> +</html> |