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diff --git a/share/doc/gcc/Variadic-Macros.html b/share/doc/gcc/Variadic-Macros.html new file mode 100644 index 0000000..897ab88 --- /dev/null +++ b/share/doc/gcc/Variadic-Macros.html @@ -0,0 +1,152 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 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; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). 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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>Using the GNU Compiler Collection (GCC): Variadic Macros</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Variadic Macros"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Variadic 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="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions"> +<link href="Escaped-Newlines.html#Escaped-Newlines" rel="next" title="Escaped Newlines"> +<link href="Variable-Length.html#Variable-Length" rel="previous" title="Variable Length"> +<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_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Variadic-Macros"></a> +<div class="header"> +<p> +Next: <a href="Escaped-Newlines.html#Escaped-Newlines" accesskey="n" rel="next">Escaped Newlines</a>, Previous: <a href="Variable-Length.html#Variable-Length" accesskey="p" rel="previous">Variable Length</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Macros-with-a-Variable-Number-of-Arguments_002e"></a> +<h3 class="section">6.21 Macros with a Variable Number of Arguments.</h3> +<a name="index-variable-number-of-arguments"></a> +<a name="index-macro-with-variable-arguments"></a> +<a name="index-rest-argument-_0028in-macro_0029"></a> +<a name="index-variadic-macros"></a> + +<p>In the ISO C standard of 1999, a macro can be declared to accept a +variable number of arguments much as a function can. The syntax for +defining the macro is similar to that of a function. Here is an +example: +</p> +<div class="smallexample"> +<pre class="smallexample">#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__) +</pre></div> + +<p>Here ‘<samp>…</samp>’ is a <em>variable argument</em>. In the invocation of +such a macro, it represents the zero or more tokens until the closing +parenthesis that ends the invocation, including any commas. This set of +tokens replaces the identifier <code>__VA_ARGS__</code> in the macro body +wherever it appears. See the CPP manual for more information. +</p> +<p>GCC has long supported variadic macros, and used a different syntax that +allowed you to give a name to the variable arguments just like any other +argument. Here is an example: +</p> +<div class="smallexample"> +<pre class="smallexample">#define debug(format, args...) fprintf (stderr, format, args) +</pre></div> + +<p>This is in all ways equivalent to the ISO C example above, but arguably +more readable and descriptive. +</p> +<p>GNU CPP has two further variadic macro extensions, and permits them to +be used with either of the above forms of macro definition. +</p> +<p>In standard C, you are not allowed to leave the variable argument out +entirely; but you are allowed to pass an empty argument. For example, +this invocation is invalid in ISO C, because there is no comma after +the string: +</p> +<div class="smallexample"> +<pre class="smallexample">debug ("A message") +</pre></div> + +<p>GNU CPP permits you to completely omit the variable arguments in this +way. In the above examples, the compiler would complain, though since +the expansion of the macro still has the extra comma after the format +string. +</p> +<p>To help solve this problem, CPP behaves specially for variable arguments +used with the token paste operator, ‘<samp>##</samp>’. If instead you write +</p> +<div class="smallexample"> +<pre class="smallexample">#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__) +</pre></div> + +<p>and if the variable arguments are omitted or empty, the ‘<samp>##</samp>’ +operator causes the preprocessor to remove the comma before it. If you +do provide some variable arguments in your macro invocation, GNU CPP +does not complain about the paste operation and instead places the +variable arguments after the comma. Just like any other pasted macro +argument, these arguments are not macro expanded. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Escaped-Newlines.html#Escaped-Newlines" accesskey="n" rel="next">Escaped Newlines</a>, Previous: <a href="Variable-Length.html#Variable-Length" accesskey="p" rel="previous">Variable Length</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |