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.
139 lines
6.4 KiB
HTML
139 lines
6.4 KiB
HTML
4 years ago
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1987-2018 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 6.4, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Line Control (The C Preprocessor)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Line Control (The C Preprocessor)">
|
||
|
|
<meta name="keywords" content="Line Control (The C Preprocessor)">
|
||
|
|
<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="Pragmas.html#Pragmas" rel="next" title="Pragmas">
|
||
|
|
<link href="Diagnostics.html#Diagnostics" rel="prev" title="Diagnostics">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
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.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<a name="Line-Control"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Pragmas.html#Pragmas" accesskey="n" rel="next">Pragmas</a>, Previous: <a href="Diagnostics.html#Diagnostics" accesskey="p" rel="prev">Diagnostics</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="Line-Control-1"></a>
|
||
|
|
<h2 class="chapter">6 Line Control</h2>
|
||
|
|
<a name="index-line-control"></a>
|
||
|
|
|
||
|
|
<p>The C preprocessor informs the C compiler of the location in your source
|
||
|
|
code where each token came from. Presently, this is just the file name
|
||
|
|
and line number. All the tokens resulting from macro expansion are
|
||
|
|
reported as having appeared on the line of the source file where the
|
||
|
|
outermost macro was used. We intend to be more accurate in the future.
|
||
|
|
</p>
|
||
|
|
<p>If you write a program which generates source code, such as the
|
||
|
|
<code>bison</code> parser generator, you may want to adjust the preprocessor’s
|
||
|
|
notion of the current file name and line number by hand. Parts of the
|
||
|
|
output from <code>bison</code> are generated from scratch, other parts come
|
||
|
|
from a standard parser file. The rest are copied verbatim from
|
||
|
|
<code>bison</code>’s input. You would like compiler error messages and
|
||
|
|
symbolic debuggers to be able to refer to <code>bison</code>’s input file.
|
||
|
|
</p>
|
||
|
|
<a name="index-_0023line"></a>
|
||
|
|
<p><code>bison</code> or any such program can arrange this by writing
|
||
|
|
‘<samp>#line</samp>’ directives into the output file. ‘<samp>#line</samp>’ is a
|
||
|
|
directive that specifies the original line number and source file name
|
||
|
|
for subsequent input in the current preprocessor input file.
|
||
|
|
‘<samp>#line</samp>’ has three variants:
|
||
|
|
</p>
|
||
|
|
<dl compact="compact">
|
||
|
|
<dt><code>#line <var>linenum</var></code></dt>
|
||
|
|
<dd><p><var>linenum</var> is a non-negative decimal integer constant. It specifies
|
||
|
|
the line number which should be reported for the following line of
|
||
|
|
input. Subsequent lines are counted from <var>linenum</var>.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
<dt><code>#line <var>linenum</var> <var>filename</var></code></dt>
|
||
|
|
<dd><p><var>linenum</var> is the same as for the first form, and has the same
|
||
|
|
effect. In addition, <var>filename</var> is a string constant. The
|
||
|
|
following line and all subsequent lines are reported to come from the
|
||
|
|
file it specifies, until something else happens to change that.
|
||
|
|
<var>filename</var> is interpreted according to the normal rules for a string
|
||
|
|
constant: backslash escapes are interpreted. This is different from
|
||
|
|
‘<samp>#include</samp>’.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
<dt><code>#line <var>anything else</var></code></dt>
|
||
|
|
<dd><p><var>anything else</var> is checked for macro calls, which are expanded.
|
||
|
|
The result should match one of the above two forms.
|
||
|
|
</p></dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<p>‘<samp>#line</samp>’ directives alter the results of the <code>__FILE__</code> and
|
||
|
|
<code>__LINE__</code> predefined macros from that point on. See <a href="Standard-Predefined-Macros.html#Standard-Predefined-Macros">Standard Predefined Macros</a>. They do not have any effect on ‘<samp>#include</samp>’’s
|
||
|
|
idea of the directory containing the current file.
|
||
|
|
</p>
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Pragmas.html#Pragmas" accesskey="n" rel="next">Pragmas</a>, Previous: <a href="Diagnostics.html#Diagnostics" accesskey="p" rel="prev">Diagnostics</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>
|