You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
116 lines
5.0 KiB
HTML
116 lines
5.0 KiB
HTML
4 years ago
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>Traditional lexical analysis - The C Preprocessor</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="The C Preprocessor">
|
||
|
|
<meta name="generator" content="makeinfo 4.13">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="up" href="Traditional-Mode.html#Traditional-Mode" title="Traditional Mode">
|
||
|
|
<link rel="next" href="Traditional-macros.html#Traditional-macros" title="Traditional macros">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
Copyright (C) 1987-2015 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.
|
||
|
|
-->
|
||
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
||
|
|
<style type="text/css"><!--
|
||
|
|
pre.display { font-family:inherit }
|
||
|
|
pre.format { font-family:inherit }
|
||
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallexample { font-size:smaller }
|
||
|
|
pre.smalllisp { font-size:smaller }
|
||
|
|
span.sc { font-variant:small-caps }
|
||
|
|
span.roman { font-family:serif; font-weight:normal; }
|
||
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div class="node">
|
||
|
|
<a name="Traditional-lexical-analysis"></a>
|
||
|
|
<p>
|
||
|
|
Next: <a rel="next" accesskey="n" href="Traditional-macros.html#Traditional-macros">Traditional macros</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="Traditional-Mode.html#Traditional-Mode">Traditional Mode</a>
|
||
|
|
<hr>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h3 class="section">10.1 Traditional lexical analysis</h3>
|
||
|
|
|
||
|
|
<p>The traditional preprocessor does not decompose its input into tokens
|
||
|
|
the same way a standards-conforming preprocessor does. The input is
|
||
|
|
simply treated as a stream of text with minimal internal form.
|
||
|
|
|
||
|
|
<p>This implementation does not treat trigraphs (see <a href="trigraphs.html#trigraphs">trigraphs</a>)
|
||
|
|
specially since they were an invention of the standards committee. It
|
||
|
|
handles arbitrarily-positioned escaped newlines properly and splices
|
||
|
|
the lines as you would expect; many traditional preprocessors did not
|
||
|
|
do this.
|
||
|
|
|
||
|
|
<p>The form of horizontal whitespace in the input file is preserved in
|
||
|
|
the output. In particular, hard tabs remain hard tabs. This can be
|
||
|
|
useful if, for example, you are preprocessing a Makefile.
|
||
|
|
|
||
|
|
<p>Traditional CPP only recognizes C-style block comments, and treats the
|
||
|
|
‘<samp><span class="samp">/*</span></samp>’ sequence as introducing a comment only if it lies outside
|
||
|
|
quoted text. Quoted text is introduced by the usual single and double
|
||
|
|
quotes, and also by an initial ‘<samp><span class="samp"><</span></samp>’ in a <code>#include</code>
|
||
|
|
directive.
|
||
|
|
|
||
|
|
<p>Traditionally, comments are completely removed and are not replaced
|
||
|
|
with a space. Since a traditional compiler does its own tokenization
|
||
|
|
of the output of the preprocessor, this means that comments can
|
||
|
|
effectively be used as token paste operators. However, comments
|
||
|
|
behave like separators for text handled by the preprocessor itself,
|
||
|
|
since it doesn't re-lex its input. For example, in
|
||
|
|
|
||
|
|
<pre class="smallexample"> #if foo/**/bar
|
||
|
|
</pre>
|
||
|
|
<p class="noindent">‘<samp><span class="samp">foo</span></samp>’ and ‘<samp><span class="samp">bar</span></samp>’ are distinct identifiers and expanded
|
||
|
|
separately if they happen to be macros. In other words, this
|
||
|
|
directive is equivalent to
|
||
|
|
|
||
|
|
<pre class="smallexample"> #if foo bar
|
||
|
|
</pre>
|
||
|
|
<p class="noindent">rather than
|
||
|
|
|
||
|
|
<pre class="smallexample"> #if foobar
|
||
|
|
</pre>
|
||
|
|
<p>Generally speaking, in traditional mode an opening quote need not have
|
||
|
|
a matching closing quote. In particular, a macro may be defined with
|
||
|
|
replacement text that contains an unmatched quote. Of course, if you
|
||
|
|
attempt to compile preprocessed output containing an unmatched quote
|
||
|
|
you will get a syntax error.
|
||
|
|
|
||
|
|
<p>However, all preprocessing directives other than <code>#define</code>
|
||
|
|
require matching quotes. For example:
|
||
|
|
|
||
|
|
<pre class="smallexample"> #define m This macro's fine and has an unmatched quote
|
||
|
|
"/* This is not a comment. */
|
||
|
|
/* <span class="roman">This is a comment. The following #include directive
|
||
|
|
is ill-formed.</span> */
|
||
|
|
#include <stdio.h
|
||
|
|
</pre>
|
||
|
|
<p>Just as for the ISO preprocessor, what would be a closing quote can be
|
||
|
|
escaped with a backslash to prevent the quoted text from closing.
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|