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155 lines
6.6 KiB
HTML
155 lines
6.6 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1987-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation. A copy of
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the license is included in the
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section entitled "GNU Free Documentation License".
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This manual contains no Invariant Sections. The Front-Cover Texts are
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(a) (see below), and the Back-Cover Texts are (b) (see below).
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Traditional lexical analysis (The C Preprocessor)</title>
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<meta name="description" content="Traditional lexical analysis (The C Preprocessor)">
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<meta name="keywords" content="Traditional lexical analysis (The C Preprocessor)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Traditional-Mode.html#Traditional-Mode" rel="up" title="Traditional Mode">
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<link href="Traditional-macros.html#Traditional-macros" rel="next" title="Traditional macros">
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<link href="Traditional-Mode.html#Traditional-Mode" rel="prev" title="Traditional Mode">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Traditional-lexical-analysis"></a>
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<div class="header">
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<p>
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Next: <a href="Traditional-macros.html#Traditional-macros" accesskey="n" rel="next">Traditional macros</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>
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</div>
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<hr>
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<a name="Traditional-lexical-analysis-1"></a>
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<h3 class="section">10.1 Traditional lexical analysis</h3>
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<p>The traditional preprocessor does not decompose its input into tokens
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the same way a standards-conforming preprocessor does. The input is
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simply treated as a stream of text with minimal internal form.
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</p>
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<p>This implementation does not treat trigraphs (see <a href="Initial-processing.html#trigraphs">trigraphs</a>)
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specially since they were an invention of the standards committee. It
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handles arbitrarily-positioned escaped newlines properly and splices
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the lines as you would expect; many traditional preprocessors did not
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do this.
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</p>
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<p>The form of horizontal whitespace in the input file is preserved in
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the output. In particular, hard tabs remain hard tabs. This can be
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useful if, for example, you are preprocessing a Makefile.
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</p>
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<p>Traditional CPP only recognizes C-style block comments, and treats the
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‘<samp>/*</samp>’ sequence as introducing a comment only if it lies outside
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quoted text. Quoted text is introduced by the usual single and double
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quotes, and also by an initial ‘<samp><</samp>’ in a <code>#include</code>
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directive.
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</p>
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<p>Traditionally, comments are completely removed and are not replaced
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with a space. Since a traditional compiler does its own tokenization
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of the output of the preprocessor, this means that comments can
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effectively be used as token paste operators. However, comments
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behave like separators for text handled by the preprocessor itself,
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since it doesn’t re-lex its input. For example, in
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</p>
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<div class="smallexample">
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<pre class="smallexample">#if foo/**/bar
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</pre></div>
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<p>‘<samp>foo</samp>’ and ‘<samp>bar</samp>’ are distinct identifiers and expanded
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separately if they happen to be macros. In other words, this
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directive is equivalent to
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</p>
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<div class="smallexample">
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<pre class="smallexample">#if foo bar
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</pre></div>
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<p>rather than
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</p>
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<div class="smallexample">
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<pre class="smallexample">#if foobar
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</pre></div>
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<p>Generally speaking, in traditional mode an opening quote need not have
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a matching closing quote. In particular, a macro may be defined with
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replacement text that contains an unmatched quote. Of course, if you
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attempt to compile preprocessed output containing an unmatched quote
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you will get a syntax error.
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</p>
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<p>However, all preprocessing directives other than <code>#define</code>
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require matching quotes. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">#define m This macro's fine and has an unmatched quote
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"/* This is not a comment. */
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/* <span class="roman">This is a comment. The following #include directive
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is ill-formed.</span> */
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#include <stdio.h
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</pre></div>
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<p>Just as for the ISO preprocessor, what would be a closing quote can be
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escaped with a backslash to prevent the quoted text from closing.
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</p>
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<hr>
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|
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<div class="header">
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|
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<p>
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Next: <a href="Traditional-macros.html#Traditional-macros" accesskey="n" rel="next">Traditional macros</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>
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</div>
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</body>
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</html>
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