diff options
Diffstat (limited to 'share/doc/cpp/Function_002dlike-Macros.html')
| -rw-r--r-- | share/doc/cpp/Function_002dlike-Macros.html | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/share/doc/cpp/Function_002dlike-Macros.html b/share/doc/cpp/Function_002dlike-Macros.html new file mode 100644 index 0000000..a0b0786 --- /dev/null +++ b/share/doc/cpp/Function_002dlike-Macros.html @@ -0,0 +1,130 @@ +<!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: Function-like Macros</title> + +<meta name="description" content="The C Preprocessor: Function-like Macros"> +<meta name="keywords" content="The C Preprocessor: Function-like Macros"> +<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="Macros.html#Macros" rel="up" title="Macros"> +<link href="Macro-Arguments.html#Macro-Arguments" rel="next" title="Macro Arguments"> +<link href="Object_002dlike-Macros.html#Object_002dlike-Macros" rel="previous" title="Object-like Macros"> +<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="Function_002dlike-Macros"></a> +<div class="header"> +<p> +Next: <a href="Macro-Arguments.html#Macro-Arguments" accesskey="n" rel="next">Macro Arguments</a>, Previous: <a href="Object_002dlike-Macros.html#Object_002dlike-Macros" accesskey="p" rel="previous">Object-like Macros</a>, Up: <a href="Macros.html#Macros" accesskey="u" rel="up">Macros</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="Function_002dlike-Macros-1"></a> +<h3 class="section">3.2 Function-like Macros</h3> +<a name="index-function_002dlike-macros"></a> + +<p>You can also define macros whose use looks like a function call. These +are called <em>function-like macros</em>. To define a function-like macro, +you use the same ‘<samp>#define</samp>’ directive, but you put a pair of +parentheses immediately after the macro name. For example, +</p> +<div class="smallexample"> +<pre class="smallexample">#define lang_init() c_init() +lang_init() + → c_init() +</pre></div> + +<p>A function-like macro is only expanded if its name appears with a pair +of parentheses after it. If you write just the name, it is left alone. +This can be useful when you have a function and a macro of the same +name, and you wish to use the function sometimes. +</p> +<div class="smallexample"> +<pre class="smallexample">extern void foo(void); +#define foo() /* <span class="roman">optimized inline version</span> */ +… + foo(); + funcptr = foo; +</pre></div> + +<p>Here the call to <code>foo()</code> will use the macro, but the function +pointer will get the address of the real function. If the macro were to +be expanded, it would cause a syntax error. +</p> +<p>If you put spaces between the macro name and the parentheses in the +macro definition, that does not define a function-like macro, it defines +an object-like macro whose expansion happens to begin with a pair of +parentheses. +</p> +<div class="smallexample"> +<pre class="smallexample">#define lang_init () c_init() +lang_init() + → () c_init()() +</pre></div> + +<p>The first two pairs of parentheses in this expansion come from the +macro. The third is the pair that was originally after the macro +invocation. Since <code>lang_init</code> is an object-like macro, it does not +consume those parentheses. +</p> + + + +</body> +</html> |