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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<title>Bison 3.0.4: Calc++ Scanner</title>

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<body lang="en">
<a name="Calc_002b_002b-Scanner"></a>
<div class="header">
<p>
Next: <a href="Calc_002b_002b-Top-Level.html#Calc_002b_002b-Top-Level" accesskey="n" rel="next">Calc++ Top Level</a>, Previous: <a href="Calc_002b_002b-Parser.html#Calc_002b_002b-Parser" accesskey="p" rel="prev">Calc++ Parser</a>, Up: <a href="A-Complete-C_002b_002b-Example.html#A-Complete-C_002b_002b-Example" accesskey="u" rel="up">A Complete C++ Example</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Terms.html#Index-of-Terms" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Calc_002b_002b-Scanner-1"></a>
<h4 class="subsubsection">10.1.6.4 Calc++ Scanner</h4>

<p>The Flex scanner first includes the driver declaration, then the
parser&rsquo;s to get the set of defined tokens.
</p>
<div class="example">
<pre class="example">%{ /* -*- C++ -*- */
# include &lt;cerrno&gt;
# include &lt;climits&gt;
# include &lt;cstdlib&gt;
# include &lt;string&gt;
# include &quot;calc++-driver.hh&quot;
# include &quot;calc++-parser.hh&quot;

// Work around an incompatibility in flex (at least versions
// 2.5.31 through 2.5.33): it generates code that does
// not conform to C89.  See Debian bug 333231
// &lt;http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=333231&gt;.
# undef yywrap
# define yywrap() 1

// The location of the current token.
static yy::location loc;
%}
</pre></div>

<p>Because there is no <code>#include</code>-like feature we don&rsquo;t need
<code>yywrap</code>, we don&rsquo;t need <code>unput</code> either, and we parse an
actual file, this is not an interactive session with the user.
Finally, we enable scanner tracing.
</p>
<div class="example">
<pre class="example">%option noyywrap nounput batch debug noinput
</pre></div>

<p>Abbreviations allow for more readable rules.
</p>
<div class="example">
<pre class="example">id    [a-zA-Z][a-zA-Z_0-9]*
int   [0-9]+
blank [ \t]
</pre></div>

<p>The following paragraph suffices to track locations accurately.  Each
time <code>yylex</code> is invoked, the begin position is moved onto the end
position.  Then when a pattern is matched, its width is added to the end
column.  When matching ends of lines, the end
cursor is adjusted, and each time blanks are matched, the begin cursor
is moved onto the end cursor to effectively ignore the blanks
preceding tokens.  Comments would be treated equally.
</p>
<div class="example">
<pre class="example">%{
  // Code run each time a pattern is matched.
  # define YY_USER_ACTION  loc.columns (yyleng);
%}
</pre><pre class="example">%%
</pre><pre class="example">%{
  // Code run each time yylex is called.
  loc.step ();
%}
</pre><pre class="example">{blank}+   loc.step ();
[\n]+      loc.lines (yyleng); loc.step ();
</pre></div>

<p>The rules are simple.  The driver is used to report errors.
</p>
<div class="example">
<pre class="example">&quot;-&quot;      return yy::calcxx_parser::make_MINUS(loc);
&quot;+&quot;      return yy::calcxx_parser::make_PLUS(loc);
&quot;*&quot;      return yy::calcxx_parser::make_STAR(loc);
&quot;/&quot;      return yy::calcxx_parser::make_SLASH(loc);
&quot;(&quot;      return yy::calcxx_parser::make_LPAREN(loc);
&quot;)&quot;      return yy::calcxx_parser::make_RPAREN(loc);
&quot;:=&quot;     return yy::calcxx_parser::make_ASSIGN(loc);

</pre><pre class="example">{int}      {
  errno = 0;
  long n = strtol (yytext, NULL, 10);
  if (! (INT_MIN &lt;= n &amp;&amp; n &lt;= INT_MAX &amp;&amp; errno != ERANGE))
    driver.error (loc, &quot;integer is out of range&quot;);
  return yy::calcxx_parser::make_NUMBER(n, loc);
}
</pre><pre class="example">{id}       return yy::calcxx_parser::make_IDENTIFIER(yytext, loc);
.          driver.error (loc, &quot;invalid character&quot;);
&lt;&lt;EOF&gt;&gt;    return yy::calcxx_parser::make_END(loc);
%%
</pre></div>

<p>Finally, because the scanner-related driver&rsquo;s member-functions depend
on the scanner&rsquo;s data, it is simpler to implement them in this file.
</p>
<div class="example">
<pre class="example">void
calcxx_driver::scan_begin ()
{
  yy_flex_debug = trace_scanning;
  if (file.empty () || file == &quot;-&quot;)
    yyin = stdin;
  else if (!(yyin = fopen (file.c_str (), &quot;r&quot;)))
    {
      error (&quot;cannot open &quot; + file + &quot;: &quot; + strerror(errno));
      exit (EXIT_FAILURE);
    }
}
</pre><pre class="example">
</pre><pre class="example">void
calcxx_driver::scan_end ()
{
  fclose (yyin);
}
</pre></div>

<hr>
<div class="header">
<p>
Next: <a href="Calc_002b_002b-Top-Level.html#Calc_002b_002b-Top-Level" accesskey="n" rel="next">Calc++ Top Level</a>, Previous: <a href="Calc_002b_002b-Parser.html#Calc_002b_002b-Parser" accesskey="p" rel="prev">Calc++ Parser</a>, Up: <a href="A-Complete-C_002b_002b-Example.html#A-Complete-C_002b_002b-Example" accesskey="u" rel="up">A Complete C++ Example</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Terms.html#Index-of-Terms" title="Index" rel="index">Index</a>]</p>
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