165 lines
7.8 KiB
HTML
165 lines
7.8 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1987-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>The C Preprocessor: Preprocessor Output</title>
|
|
|
|
<meta name="description" content="The C Preprocessor: Preprocessor Output">
|
|
<meta name="keywords" content="The C Preprocessor: Preprocessor Output">
|
|
<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="index.html#Top" rel="up" title="Top">
|
|
<link href="Traditional-Mode.html#Traditional-Mode" rel="next" title="Traditional Mode">
|
|
<link href="Other-Directives.html#Other-Directives" rel="prev" title="Other Directives">
|
|
<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="Preprocessor-Output"></a>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="n" rel="next">Traditional Mode</a>, Previous: <a href="Other-Directives.html#Other-Directives" accesskey="p" rel="prev">Other Directives</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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="Preprocessor-Output-1"></a>
|
|
<h2 class="chapter">9 Preprocessor Output</h2>
|
|
|
|
<p>When the C preprocessor is used with the C, C++, or Objective-C
|
|
compilers, it is integrated into the compiler and communicates a stream
|
|
of binary tokens directly to the compiler’s parser. However, it can
|
|
also be used in the more conventional standalone mode, where it produces
|
|
textual output.
|
|
</p>
|
|
<a name="index-output-format"></a>
|
|
<p>The output from the C preprocessor looks much like the input, except
|
|
that all preprocessing directive lines have been replaced with blank
|
|
lines and all comments with spaces. Long runs of blank lines are
|
|
discarded.
|
|
</p>
|
|
<p>The ISO standard specifies that it is implementation defined whether a
|
|
preprocessor preserves whitespace between tokens, or replaces it with
|
|
e.g. a single space. In GNU CPP, whitespace between tokens is collapsed
|
|
to become a single space, with the exception that the first token on a
|
|
non-directive line is preceded with sufficient spaces that it appears in
|
|
the same column in the preprocessed output that it appeared in the
|
|
original source file. This is so the output is easy to read.
|
|
See <a href="Differences-from-previous-versions.html#Differences-from-previous-versions">Differences from previous versions</a>. CPP does not insert any
|
|
whitespace where there was none in the original source, except where
|
|
necessary to prevent an accidental token paste.
|
|
</p>
|
|
<a name="index-linemarkers"></a>
|
|
<p>Source file name and line number information is conveyed by lines
|
|
of the form
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample"># <var>linenum</var> <var>filename</var> <var>flags</var>
|
|
</pre></div>
|
|
|
|
<p>These are called <em>linemarkers</em>. They are inserted as needed into
|
|
the output (but never within a string or character constant). They mean
|
|
that the following line originated in file <var>filename</var> at line
|
|
<var>linenum</var>. <var>filename</var> will never contain any non-printing
|
|
characters; they are replaced with octal escape sequences.
|
|
</p>
|
|
<p>After the file name comes zero or more flags, which are ‘<samp>1</samp>’,
|
|
‘<samp>2</samp>’, ‘<samp>3</samp>’, or ‘<samp>4</samp>’. If there are multiple flags, spaces
|
|
separate them. Here is what the flags mean:
|
|
</p>
|
|
<dl compact="compact">
|
|
<dt>‘<samp>1</samp>’</dt>
|
|
<dd><p>This indicates the start of a new file.
|
|
</p></dd>
|
|
<dt>‘<samp>2</samp>’</dt>
|
|
<dd><p>This indicates returning to a file (after having included another file).
|
|
</p></dd>
|
|
<dt>‘<samp>3</samp>’</dt>
|
|
<dd><p>This indicates that the following text comes from a system header file,
|
|
so certain warnings should be suppressed.
|
|
</p></dd>
|
|
<dt>‘<samp>4</samp>’</dt>
|
|
<dd><p>This indicates that the following text should be treated as being
|
|
wrapped in an implicit <code>extern "C"</code> block.
|
|
</p></dd>
|
|
</dl>
|
|
|
|
<p>As an extension, the preprocessor accepts linemarkers in non-assembler
|
|
input files. They are treated like the corresponding ‘<samp>#line</samp>’
|
|
directive, (see <a href="Line-Control.html#Line-Control">Line Control</a>), except that trailing flags are
|
|
permitted, and are interpreted with the meanings described above. If
|
|
multiple flags are given, they must be in ascending order.
|
|
</p>
|
|
<p>Some directives may be duplicated in the output of the preprocessor.
|
|
These are ‘<samp>#ident</samp>’ (always), ‘<samp>#pragma</samp>’ (only if the
|
|
preprocessor does not handle the pragma itself), and ‘<samp>#define</samp>’ and
|
|
‘<samp>#undef</samp>’ (with certain debugging options). If this happens, the
|
|
‘<samp>#</samp>’ of the directive will always be in the first column, and there
|
|
will be no space between the ‘<samp>#</samp>’ and the directive name. If macro
|
|
expansion happens to generate tokens which might be mistaken for a
|
|
duplicated directive, a space will be inserted between the ‘<samp>#</samp>’ and
|
|
the directive name.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="n" rel="next">Traditional Mode</a>, Previous: <a href="Other-Directives.html#Other-Directives" accesskey="p" rel="prev">Other Directives</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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>
|