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Edit File: _0023line-Syntax-Details.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.8, https://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <!-- This manual is for GNU Texinfo (version 6.8, 8 June 2021), a documentation system that can produce both online information and a printed manual from a single source using semantic markup. Copyright (C) 1988, 1990-1993, 1995-1999, 2001-2021 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; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". --> <title>#line Syntax Details (GNU Texinfo 6.8)</title> <meta name="description" content="#line Syntax Details (GNU Texinfo 6.8)"> <meta name="keywords" content="#line Syntax Details (GNU Texinfo 6.8)"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="texi2any"> <meta name="viewport" content="width=device-width,initial-scale=1"> <link href="index.html" rel="start" title="Top"> <link href="Command-and-Variable-Index.html" rel="index" title="Command and Variable Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="External-Macro-Processors.html" rel="up" title="External Macro Processors"> <link href="_0023line-and-TeX.html" rel="prev" title="#line and TeX"> <style type="text/css"> <!-- a.copiable-anchor {visibility: hidden; text-decoration: none; line-height: 0em} a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} div.display {margin-left: 3.2em} div.example {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} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} span:hover a.copiable-anchor {visibility: visible} ul.no-bullet {list-style: none} --> </style> </head> <body lang="en"> <div class="subsection" id="g_t_0023line-Syntax-Details"> <div class="header"> <p> Previous: <a href="_0023line-and-TeX.html" accesskey="p" rel="prev">‘<samp>#line</samp>’ and TeX</a>, Up: <a href="External-Macro-Processors.html" accesskey="u" rel="up">External Macro Processors: Line Directives</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p> </div> <hr> <span id="g_t_0023line-Syntax-Details-1"></span><h4 class="subsection">16.6.3 ‘<samp>#line</samp>’ Syntax Details</h4> <span id="index-_0023line-directive-2"></span> <span id="index-Syntax-details_002c-_0023line"></span> <span id="index-Regular-expression_002c-for-_0023line"></span> <p>Syntax details for the ‘<samp>#line</samp>’ directive: the ‘<samp>#</samp>’ character can be preceded or followed by whitespace, the word ‘<samp>line</samp>’ is optional, and the file name can be followed by a whitespace-separated list of integers (these are so-called “flags” output by CPP in some cases). For those who like to know the gory details, the actual (Perl) regular expression which is matched is this: </p> <div class="example"> <pre class="example">/^\s*#\s*(line)? (\d+)(( "([^"]+)")(\s+\d+)*)?\s*$/ </pre></div> <p>As far as we’ve been able to tell, the trailing integer flags only occur in conjunction with a file name, so that is reflected in the regular expression. </p> <p>As an example, the following is a syntactically valid ‘<samp>#line</samp>’ directive, meaning line 1 of <samp>/usr/include/stdio.h</samp>: </p> <div class="example"> <pre class="example"># 1 "/usr/include/stdio.h" 2 3 4 </pre></div> <p>Unfortunately, the quoted file name (‘<samp>"..."</samp>’) has to be optional, because M4 (especially) can often generate ‘<samp>#line</samp>’ directives within a single file. Since the ‘<samp>line</samp>’ is also optional, the result is that lines might match which you wouldn’t expect, e.g., </p> <div class="example"> <pre class="example"># 1 </pre></div> <p>The possible solutions are described above (see <a href="_0023line-Directive.html">‘<samp>#line</samp>’ Directive</a>). </p> </div> </body> </html>