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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/cpp/Traditional-macros.html | |
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diff --git a/share/doc/cpp/Traditional-macros.html b/share/doc/cpp/Traditional-macros.html new file mode 100644 index 0000000..1175aba --- /dev/null +++ b/share/doc/cpp/Traditional-macros.html @@ -0,0 +1,180 @@ +<!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: Traditional macros</title> + +<meta name="description" content="The C Preprocessor: Traditional macros"> +<meta name="keywords" content="The C Preprocessor: Traditional 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="Traditional-Mode.html#Traditional-Mode" rel="up" title="Traditional Mode"> +<link href="Traditional-miscellany.html#Traditional-miscellany" rel="next" title="Traditional miscellany"> +<link href="Traditional-lexical-analysis.html#Traditional-lexical-analysis" rel="previous" title="Traditional lexical analysis"> +<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="Traditional-macros"></a> +<div class="header"> +<p> +Next: <a href="Traditional-miscellany.html#Traditional-miscellany" accesskey="n" rel="next">Traditional miscellany</a>, Previous: <a href="Traditional-lexical-analysis.html#Traditional-lexical-analysis" accesskey="p" rel="previous">Traditional lexical analysis</a>, Up: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="u" rel="up">Traditional Mode</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="Traditional-macros-1"></a> +<h3 class="section">10.2 Traditional macros</h3> + +<p>The major difference between traditional and ISO macros is that the +former expand to text rather than to a token sequence. CPP removes +all leading and trailing horizontal whitespace from a macro’s +replacement text before storing it, but preserves the form of internal +whitespace. +</p> +<p>One consequence is that it is legitimate for the replacement text to +contain an unmatched quote (see <a href="Traditional-lexical-analysis.html#Traditional-lexical-analysis">Traditional lexical analysis</a>). An +unclosed string or character constant continues into the text +following the macro call. Similarly, the text at the end of a macro’s +expansion can run together with the text after the macro invocation to +produce a single token. +</p> +<p>Normally comments are removed from the replacement text after the +macro is expanded, but if the <samp>-CC</samp> option is passed on the +command-line comments are preserved. (In fact, the current +implementation removes comments even before saving the macro +replacement text, but it careful to do it in such a way that the +observed effect is identical even in the function-like macro case.) +</p> +<p>The ISO stringizing operator ‘<samp>#</samp>’ and token paste operator +‘<samp>##</samp>’ have no special meaning. As explained later, an effect +similar to these operators can be obtained in a different way. Macro +names that are embedded in quotes, either from the main file or after +macro replacement, do not expand. +</p> +<p>CPP replaces an unquoted object-like macro name with its replacement +text, and then rescans it for further macros to replace. Unlike +standard macro expansion, traditional macro expansion has no provision +to prevent recursion. If an object-like macro appears unquoted in its +replacement text, it will be replaced again during the rescan pass, +and so on <em>ad infinitum</em>. GCC detects when it is expanding +recursive macros, emits an error message, and continues after the +offending macro invocation. +</p> +<div class="smallexample"> +<pre class="smallexample">#define PLUS + +#define INC(x) PLUS+x +INC(foo); + → ++foo; +</pre></div> + +<p>Function-like macros are similar in form but quite different in +behavior to their ISO counterparts. Their arguments are contained +within parentheses, are comma-separated, and can cross physical lines. +Commas within nested parentheses are not treated as argument +separators. Similarly, a quote in an argument cannot be left +unclosed; a following comma or parenthesis that comes before the +closing quote is treated like any other character. There is no +facility for handling variadic macros. +</p> +<p>This implementation removes all comments from macro arguments, unless +the <samp>-C</samp> option is given. The form of all other horizontal +whitespace in arguments is preserved, including leading and trailing +whitespace. In particular +</p> +<div class="smallexample"> +<pre class="smallexample">f( ) +</pre></div> + +<p>is treated as an invocation of the macro ‘<samp>f</samp>’ with a single +argument consisting of a single space. If you want to invoke a +function-like macro that takes no arguments, you must not leave any +whitespace between the parentheses. +</p> +<p>If a macro argument crosses a new line, the new line is replaced with +a space when forming the argument. If the previous line contained an +unterminated quote, the following line inherits the quoted state. +</p> +<p>Traditional preprocessors replace parameters in the replacement text +with their arguments regardless of whether the parameters are within +quotes or not. This provides a way to stringize arguments. For +example +</p> +<div class="smallexample"> +<pre class="smallexample">#define str(x) "x" +str(/* <span class="roman">A comment</span> */some text ) + → "some text " +</pre></div> + +<p>Note that the comment is removed, but that the trailing space is +preserved. Here is an example of using a comment to effect token +pasting. +</p> +<div class="smallexample"> +<pre class="smallexample">#define suffix(x) foo_/**/x +suffix(bar) + → foo_bar +</pre></div> + +<hr> +<div class="header"> +<p> +Next: <a href="Traditional-miscellany.html#Traditional-miscellany" accesskey="n" rel="next">Traditional miscellany</a>, Previous: <a href="Traditional-lexical-analysis.html#Traditional-lexical-analysis" accesskey="p" rel="previous">Traditional lexical analysis</a>, Up: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="u" rel="up">Traditional Mode</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> + + + +</body> +</html> |