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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/Stringizing.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
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diff --git a/share/doc/cpp/Stringizing.html b/share/doc/cpp/Stringizing.html new file mode 100644 index 0000000..e97c519 --- /dev/null +++ b/share/doc/cpp/Stringizing.html @@ -0,0 +1,167 @@ +<!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: Stringizing</title> + +<meta name="description" content="The C Preprocessor: Stringizing"> +<meta name="keywords" content="The C Preprocessor: Stringizing"> +<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="Concatenation.html#Concatenation" rel="next" title="Concatenation"> +<link href="Macro-Arguments.html#Macro-Arguments" rel="previous" title="Macro Arguments"> +<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="Stringizing"></a> +<div class="header"> +<p> +Next: <a href="Concatenation.html#Concatenation" accesskey="n" rel="next">Concatenation</a>, Previous: <a href="Macro-Arguments.html#Macro-Arguments" accesskey="p" rel="previous">Macro Arguments</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="Stringizing-1"></a> +<h3 class="section">3.4 Stringizing</h3> +<a name="index-stringizing"></a> +<a name="index-_0023-operator"></a> + +<p>Sometimes you may want to convert a macro argument into a string +constant. Parameters are not replaced inside string constants, but you +can use the ‘<samp>#</samp>’ preprocessing operator instead. When a macro +parameter is used with a leading ‘<samp>#</samp>’, the preprocessor replaces it +with the literal text of the actual argument, converted to a string +constant. Unlike normal parameter replacement, the argument is not +macro-expanded first. This is called <em>stringizing</em>. +</p> +<p>There is no way to combine an argument with surrounding text and +stringize it all together. Instead, you can write a series of adjacent +string constants and stringized arguments. The preprocessor +replaces the stringized arguments with string constants. The C +compiler then combines all the adjacent string constants into one +long string. +</p> +<p>Here is an example of a macro definition that uses stringizing: +</p> +<div class="smallexample"> +<pre class="smallexample">#define WARN_IF(EXP) \ +do { if (EXP) \ + fprintf (stderr, "Warning: " #EXP "\n"); } \ +while (0) +WARN_IF (x == 0); + → do { if (x == 0) + fprintf (stderr, "Warning: " "x == 0" "\n"); } while (0); +</pre></div> + +<p>The argument for <code>EXP</code> is substituted once, as-is, into the +<code>if</code> statement, and once, stringized, into the argument to +<code>fprintf</code>. If <code>x</code> were a macro, it would be expanded in the +<code>if</code> statement, but not in the string. +</p> +<p>The <code>do</code> and <code>while (0)</code> are a kludge to make it possible to +write <code>WARN_IF (<var>arg</var>);</code>, which the resemblance of +<code>WARN_IF</code> to a function would make C programmers want to do; see +<a href="Swallowing-the-Semicolon.html#Swallowing-the-Semicolon">Swallowing the Semicolon</a>. +</p> +<p>Stringizing in C involves more than putting double-quote characters +around the fragment. The preprocessor backslash-escapes the quotes +surrounding embedded string constants, and all backslashes within string and +character constants, in order to get a valid C string constant with the +proper contents. Thus, stringizing <code>p = "foo\n";<!-- /@w --></code> results in +<tt>"p = \"foo\\n\";"<!-- /@w --></tt>. However, backslashes that are not inside string +or character constants are not duplicated: ‘<samp>\n</samp>’ by itself +stringizes to <tt>"\n"</tt>. +</p> +<p>All leading and trailing whitespace in text being stringized is +ignored. Any sequence of whitespace in the middle of the text is +converted to a single space in the stringized result. Comments are +replaced by whitespace long before stringizing happens, so they +never appear in stringized text. +</p> +<p>There is no way to convert a macro argument into a character constant. +</p> +<p>If you want to stringize the result of expansion of a macro argument, +you have to use two levels of macros. +</p> +<div class="smallexample"> +<pre class="smallexample">#define xstr(s) str(s) +#define str(s) #s +#define foo 4 +str (foo) + → "foo" +xstr (foo) + → xstr (4) + → str (4) + → "4" +</pre></div> + +<p><code>s</code> is stringized when it is used in <code>str</code>, so it is not +macro-expanded first. But <code>s</code> is an ordinary argument to +<code>xstr</code>, so it is completely macro-expanded before <code>xstr</code> +itself is expanded (see <a href="Argument-Prescan.html#Argument-Prescan">Argument Prescan</a>). Therefore, by the time +<code>str</code> gets to its argument, it has already been macro-expanded. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Concatenation.html#Concatenation" accesskey="n" rel="next">Concatenation</a>, Previous: <a href="Macro-Arguments.html#Macro-Arguments" accesskey="p" rel="previous">Macro Arguments</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> + + + +</body> +</html> |