diff options
| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
|---|---|---|
| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/cpp/Initial-processing.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
Diffstat (limited to 'share/doc/cpp/Initial-processing.html')
| -rw-r--r-- | share/doc/cpp/Initial-processing.html | 243 |
1 files changed, 243 insertions, 0 deletions
diff --git a/share/doc/cpp/Initial-processing.html b/share/doc/cpp/Initial-processing.html new file mode 100644 index 0000000..b69d1d7 --- /dev/null +++ b/share/doc/cpp/Initial-processing.html @@ -0,0 +1,243 @@ +<!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: Initial processing</title> + +<meta name="description" content="The C Preprocessor: Initial processing"> +<meta name="keywords" content="The C Preprocessor: Initial processing"> +<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="Overview.html#Overview" rel="up" title="Overview"> +<link href="Tokenization.html#Tokenization" rel="next" title="Tokenization"> +<link href="Character-sets.html#Character-sets" rel="previous" title="Character sets"> +<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="Initial-processing"></a> +<div class="header"> +<p> +Next: <a href="Tokenization.html#Tokenization" accesskey="n" rel="next">Tokenization</a>, Previous: <a href="Character-sets.html#Character-sets" accesskey="p" rel="previous">Character sets</a>, Up: <a href="Overview.html#Overview" accesskey="u" rel="up">Overview</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="Initial-processing-1"></a> +<h3 class="section">1.2 Initial processing</h3> + +<p>The preprocessor performs a series of textual transformations on its +input. These happen before all other processing. Conceptually, they +happen in a rigid order, and the entire file is run through each +transformation before the next one begins. CPP actually does them +all at once, for performance reasons. These transformations correspond +roughly to the first three “phases of translation” described in the C +standard. +</p> +<ol> +<li> <a name="index-line-endings"></a> +The input file is read into memory and broken into lines. + +<p>Different systems use different conventions to indicate the end of a +line. GCC accepts the ASCII control sequences <kbd>LF</kbd>, <kbd>CR LF<!-- /@w --></kbd> and <kbd>CR</kbd> as end-of-line markers. These are the canonical +sequences used by Unix, DOS and VMS, and the classic Mac OS (before +OSX) respectively. You may therefore safely copy source code written +on any of those systems to a different one and use it without +conversion. (GCC may lose track of the current line number if a file +doesn’t consistently use one convention, as sometimes happens when it +is edited on computers with different conventions that share a network +file system.) +</p> +<p>If the last line of any input file lacks an end-of-line marker, the end +of the file is considered to implicitly supply one. The C standard says +that this condition provokes undefined behavior, so GCC will emit a +warning message. +</p> +</li><li> <a name="index-trigraphs"></a> +<a name="trigraphs"></a>If trigraphs are enabled, they are replaced by their +corresponding single characters. By default GCC ignores trigraphs, +but if you request a strictly conforming mode with the <samp>-std</samp> +option, or you specify the <samp>-trigraphs</samp> option, then it +converts them. + +<p>These are nine three-character sequences, all starting with ‘<samp>??</samp>’, +that are defined by ISO C to stand for single characters. They permit +obsolete systems that lack some of C’s punctuation to use C. For +example, ‘<samp>??/</samp>’ stands for ‘<samp>\</samp>’, so <tt>'??/n'</tt> is a character +constant for a newline. +</p> +<p>Trigraphs are not popular and many compilers implement them +incorrectly. Portable code should not rely on trigraphs being either +converted or ignored. With <samp>-Wtrigraphs</samp> GCC will warn you +when a trigraph may change the meaning of your program if it were +converted. See <a href="Invocation.html#Wtrigraphs">Wtrigraphs</a>. +</p> +<p>In a string constant, you can prevent a sequence of question marks +from being confused with a trigraph by inserting a backslash between +the question marks, or by separating the string literal at the +trigraph and making use of string literal concatenation. <tt>"(??\?)"</tt> +is the string ‘<samp>(???)</samp>’, not ‘<samp>(?]</samp>’. Traditional C compilers +do not recognize these idioms. +</p> +<p>The nine trigraphs and their replacements are +</p> +<div class="smallexample"> +<pre class="smallexample">Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- +Replacement: [ ] { } # \ ^ | ~ +</pre></div> + +</li><li> <a name="index-continued-lines"></a> +<a name="index-backslash_002dnewline"></a> +Continued lines are merged into one long line. + +<p>A continued line is a line which ends with a backslash, ‘<samp>\</samp>’. The +backslash is removed and the following line is joined with the current +one. No space is inserted, so you may split a line anywhere, even in +the middle of a word. (It is generally more readable to split lines +only at white space.) +</p> +<p>The trailing backslash on a continued line is commonly referred to as a +<em>backslash-newline</em>. +</p> +<p>If there is white space between a backslash and the end of a line, that +is still a continued line. However, as this is usually the result of an +editing mistake, and many compilers will not accept it as a continued +line, GCC will warn you about it. +</p> +</li><li> <a name="index-comments"></a> +<a name="index-line-comments"></a> +<a name="index-block-comments"></a> +All comments are replaced with single spaces. + +<p>There are two kinds of comments. <em>Block comments</em> begin with +‘<samp>/*</samp>’ and continue until the next ‘<samp>*/</samp>’. Block comments do not +nest: +</p> +<div class="smallexample"> +<pre class="smallexample">/* <span class="roman">this is</span> /* <span class="roman">one comment</span> */ <span class="roman">text outside comment</span> +</pre></div> + +<p><em>Line comments</em> begin with ‘<samp>//</samp>’ and continue to the end of the +current line. Line comments do not nest either, but it does not matter, +because they would end in the same place anyway. +</p> +<div class="smallexample"> +<pre class="smallexample">// <span class="roman">this is</span> // <span class="roman">one comment</span> +<span class="roman">text outside comment</span> +</pre></div> +</li></ol> + +<p>It is safe to put line comments inside block comments, or vice versa. +</p> +<div class="smallexample"> +<pre class="smallexample">/* <span class="roman">block comment</span> + // <span class="roman">contains line comment</span> + <span class="roman">yet more comment</span> + */ <span class="roman">outside comment</span> + +// <span class="roman">line comment</span> /* <span class="roman">contains block comment</span> */ +</pre></div> + +<p>But beware of commenting out one end of a block comment with a line +comment. +</p> +<div class="smallexample"> +<pre class="smallexample"> // <span class="roman">l.c.</span> /* <span class="roman">block comment begins</span> + <span class="roman">oops! this isn’t a comment anymore</span> */ +</pre></div> + +<p>Comments are not recognized within string literals. +<tt>"/* blah */"<!-- /@w --></tt> is the string constant ‘<samp>/* blah */<!-- /@w --></samp>’, not +an empty string. +</p> +<p>Line comments are not in the 1989 edition of the C standard, but they +are recognized by GCC as an extension. In C++ and in the 1999 edition +of the C standard, they are an official part of the language. +</p> +<p>Since these transformations happen before all other processing, you can +split a line mechanically with backslash-newline anywhere. You can +comment out the end of a line. You can continue a line comment onto the +next line with backslash-newline. You can even split ‘<samp>/*</samp>’, +‘<samp>*/</samp>’, and ‘<samp>//</samp>’ onto multiple lines with backslash-newline. +For example: +</p> +<div class="smallexample"> +<pre class="smallexample">/\ +* +*/ # /* +*/ defi\ +ne FO\ +O 10\ +20 +</pre></div> + +<p>is equivalent to <code>#define FOO 1020<!-- /@w --></code>. All these tricks are +extremely confusing and should not be used in code intended to be +readable. +</p> +<p>There is no way to prevent a backslash at the end of a line from being +interpreted as a backslash-newline. This cannot affect any correct +program, however. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Tokenization.html#Tokenization" accesskey="n" rel="next">Tokenization</a>, Previous: <a href="Character-sets.html#Character-sets" accesskey="p" rel="previous">Character sets</a>, Up: <a href="Overview.html#Overview" accesskey="u" rel="up">Overview</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> |