/usr/share/doc/flex-doc/html/Bison-Bridge.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- 
The flex manual is placed under the same licensing conditions as the
rest of flex:

Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2012
The Flex Project.

Copyright (C) 1990, 1997 The Regents of the University of California.
All rights reserved.

This code is derived from software contributed to Berkeley by
Vern Paxson.

The United States Government has rights in this work pursuant
to contract no. DE-AC03-76SF00098 between the United States
Department of Energy and the University of California.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.

THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. -->
<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Bison Bridge (Lexical Analysis With Flex, for Flex 2.6.4)</title>

<meta name="description" content="Bison Bridge (Lexical Analysis With Flex, for Flex 2.6.4)">
<meta name="keywords" content="Bison Bridge (Lexical Analysis With Flex, for Flex 2.6.4)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="Indices.html#Indices" rel="index" title="Indices">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Appendices.html#Appendices" rel="up" title="Appendices">
<link href="M4-Dependency.html#M4-Dependency" rel="next" title="M4 Dependency">
<link href="Makefiles-and-Flex.html#Makefiles-and-Flex" rel="prev" title="Makefiles and Flex">
<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="Bison-Bridge"></a>
<div class="header">
<p>
Next: <a href="M4-Dependency.html#M4-Dependency" accesskey="n" rel="next">M4 Dependency</a>, Previous: <a href="Makefiles-and-Flex.html#Makefiles-and-Flex" accesskey="p" rel="prev">Makefiles and Flex</a>, Up: <a href="Appendices.html#Appendices" accesskey="u" rel="up">Appendices</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="C-Scanners-with-Bison-Parsers"></a>
<h3 class="section">A.2 C Scanners with Bison Parsers</h3>

<a name="index-bison_002c-bridging-with-flex"></a>
<a name="index-yylval"></a>
<a name="index-yylloc"></a>
<a name="index-YYLTYPE"></a>
<a name="index-YYSTYPE"></a>

<p>This section describes the <code>flex</code> features useful when integrating
<code>flex</code> with <code>GNU bison</code><a name="DOCF7" href="#FOOT7"><sup>7</sup></a>.
Skip this section if you are not using
<code>bison</code> with your scanner.  Here we discuss only the <code>flex</code>
half of the <code>flex</code> and <code>bison</code> pair.  We do not discuss
<code>bison</code> in any detail.  For more information about generating
<code>bison</code> parsers, see <cite><a href="http://www.gnu.org/software/bison/manual/html_node/index.html#Top">the GNU Bison Manual</a></cite>.
</p>
<p>A compatible <code>bison</code> scanner is generated by declaring &lsquo;<samp>%option
bison-bridge</samp>&rsquo; or by supplying &lsquo;<samp>--bison-bridge</samp>&rsquo; when invoking <code>flex</code>
from the command line.  This instructs <code>flex</code> that the macro
<code>yylval</code> may be used. The data type for
<code>yylval</code>, <code>YYSTYPE</code>,
is typically defined in a header file, included in section 1 of the
<code>flex</code> input file.  For a list of functions and macros
available, See <a href="Reentrant-Functions.html#bison_002dfunctions">bison-functions</a>.
</p>
<p>The declaration of yylex becomes,
</p>
<a name="index-yylex-_0028reentrant-version_0029"></a>
<div class="example">
<pre class="verbatim">      int yylex ( YYSTYPE * lvalp, yyscan_t scanner );
</pre></div>

<p>If <code>%option bison-locations</code> is specified, then the declaration
becomes,
</p>
<a name="index-yylex-_0028reentrant-version_0029-1"></a>
<div class="example">
<pre class="verbatim">      int yylex ( YYSTYPE * lvalp, YYLTYPE * llocp, yyscan_t scanner );
</pre></div>

<p>Note that the macros <code>yylval</code> and <code>yylloc</code> evaluate to pointers.
Support for <code>yylloc</code> is optional in <code>bison</code>, so it is optional in
<code>flex</code> as well. The following is an example of a <code>flex</code> scanner that
is compatible with <code>bison</code>.
</p>
<a name="index-bison_002c-scanner-to-be-called-from-bison"></a>
<div class="example">
<pre class="verbatim">    /* Scanner for &quot;C&quot; assignment statements... sort of. */
    %{
    #include &quot;y.tab.h&quot;  /* Generated by bison. */
    %}

    %option bison-bridge bison-locations
    %

    [[:digit:]]+  { yylval-&gt;num = atoi(yytext);   return NUMBER;}
    [[:alnum:]]+  { yylval-&gt;str = strdup(yytext); return STRING;}
    &quot;=&quot;|&quot;;&quot;       { return yytext[0];}
    .  {}
    %
</pre></div>

<p>As you can see, there really is no magic here. We just use
<code>yylval</code> as we would any other variable. The data type of
<code>yylval</code> is generated by <code>bison</code>, and included in the file
<samp>y.tab.h</samp>. Here is the corresponding <code>bison</code> parser:
</p>
<a name="index-bison_002c-parser"></a>
<div class="example">
<pre class="verbatim">    /* Parser to convert &quot;C&quot; assignments to lisp. */
    %{
    /* Pass the argument to yyparse through to yylex. */
    #define YYPARSE_PARAM scanner
    #define YYLEX_PARAM   scanner
    %}
    %locations
    %pure_parser
    %union {
        int num;
        char* str;
    }
    %token &lt;str&gt; STRING
    %token &lt;num&gt; NUMBER
    %%
    assignment:
        STRING '=' NUMBER ';' {
            printf( &quot;(setf %s %d)&quot;, $1, $3 );
       }
    ;
</pre></div>

<div class="footnote">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>

<h3><a name="FOOT7" href="#DOCF7">(7)</a></h3>
<p>The features described here are
purely optional, and are by no means the only way to use flex with bison.
We merely provide some glue to ease development of your parser-scanner pair.</p>
</div>
<hr>
<div class="header">
<p>
Next: <a href="M4-Dependency.html#M4-Dependency" accesskey="n" rel="next">M4 Dependency</a>, Previous: <a href="Makefiles-and-Flex.html#Makefiles-and-Flex" accesskey="p" rel="prev">Makefiles and Flex</a>, Up: <a href="Appendices.html#Appendices" accesskey="u" rel="up">Appendices</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
</div>



</body>
</html>
flex-doc 2.6.4-6 / usr / share / doc / flex-doc / html / Bison-Bridge.html
