109 lines
8.4 KiB
HTML
109 lines
8.4 KiB
HTML
<html>
|
|
<head>
|
|
<title>Functor Parser</title>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<link rel="stylesheet" href="theme/style.css" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
<table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2">
|
|
<tr>
|
|
<td width="10">
|
|
</td>
|
|
<td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Functor
|
|
Parser</b></font> </td>
|
|
<td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" width="112" height="48" align="right" border="0"></a></td>
|
|
</tr>
|
|
</table>
|
|
<br>
|
|
<table border="0">
|
|
<tr>
|
|
<td width="10"></td>
|
|
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
|
|
<td width="30"><a href="list_parsers.html"><img src="theme/l_arr.gif" border="0"></a></td>
|
|
<td width="30"><a href="refactoring.html"><img src="theme/r_arr.gif" border="0"></a></td>
|
|
</tr>
|
|
</table>
|
|
<p>The simplest way to write your hand coded parser that works well with the rest
|
|
of the Spirit library is to simply write a functor parser.</p>
|
|
<p> A functor parser is expected to have the interface:</p>
|
|
<pre>
|
|
<code><span class=keyword>struct </span><span class=identifier>functor
|
|
</span><span class=special>{
|
|
</span><span class=keyword>typedef </span><span class=identifier>T </span><span class=identifier>result_t</span><span class=special>;
|
|
|
|
</span><span class=keyword>template </span><span class=special><</span><span class=keyword>typename </span><span class=identifier>ScannerT</span><span class=special>>
|
|
</span><span class=keyword>std::ptrdiff_t
|
|
</span><span class=keyword>operator</span><span class=special>()(</span><span class=identifier>ScannerT </span><span class=keyword>const</span><span class=special>& </span><span class=identifier>scan</span><span class=special>, </span><span class=identifier>result_t</span><span class=special>& </span><span class=identifier>result</span><span class=special>) </span><span class=keyword>const</span><span class=special>;
|
|
</span><span class=special>};
|
|
</span></code></pre>
|
|
<p> where typedef T result_t; is the attribute type of the parser that will be
|
|
passed back to the match result (see <a href="indepth_the_parser.html">In-depth:
|
|
The Parser</a>). If the parser does not need to return an attribute, this can
|
|
simply be nil_t. The <span class=keyword><tt>std::ptrdiff_t</tt></span> result
|
|
is the number of matching characters matched by your parser. A negative value
|
|
flags an unsucessful match.</p>
|
|
<p> A conforming functor parser can transformed into a well formed Spirit parser
|
|
by wrapping it in the functor_parser template:</p>
|
|
<pre>
|
|
<code><span class=identifier>functor_parser</span><span class=special><</span><span class=identifier>functor</span><span class=special>> </span><span class=identifier>functor_p</span><span class=special>;
|
|
</span></code></pre>
|
|
|
|
<h2>Example</h2>
|
|
<p> The following example puts the functor_parser into action:</p>
|
|
<pre>
|
|
<code><span class=keyword>struct </span><span class=identifier>number_parser
|
|
</span><span class=special>{
|
|
</span><span class=keyword>typedef </span><span class=keyword>int </span><span class=identifier>result_t</span><span class=special>;
|
|
</span><span class=keyword>template </span><span class=special><</span><span class=keyword>typename </span><span class=identifier>ScannerT</span><span class=special>>
|
|
</span><span class=keyword>std::ptrdiff_t</span>
|
|
<span class=keyword>operator</span><span class=special>()(</span><span class=identifier>ScannerT </span><span class=keyword>const</span><span class=special>& </span><span class=identifier>scan</span><span class=special>, </span><span class=identifier>result_t</span><span class=special>& </span><span class=identifier>result</span><span class=special>) </span><span class=keyword>const
|
|
</span><span class=special>{
|
|
</span><span class=keyword>if </span><span class=special>(</span><span class=identifier>scan</span><span class=special>.</span><span class=identifier>at_end</span><span class=special>())
|
|
</span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>;
|
|
|
|
</span><span class=keyword>char </span><span class=identifier>ch </span><span class=special>= </span><span class=special>*</span><span class=identifier>scan</span><span class=special>;
|
|
</span><span class=keyword>if </span><span class=special>(</span><span class=identifier>ch </span><span class=special>< </span><span class=literal>'0' </span><span class=special>|| </span><span class=identifier>ch </span><span class=special>> </span><span class=literal>'9'</span><span class=special>)
|
|
</span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>;
|
|
|
|
</span><span class=identifier>result </span><span class=special>= </span><span class=number>0</span><span class=special>;
|
|
</span><span class=keyword>std::ptrdiff_t</span> <span class=identifier>len </span><span class=special>= </span><span class=number>0</span><span class=special>;
|
|
|
|
</span><span class=keyword>do
|
|
</span><span class=special>{
|
|
</span><span class=identifier>result </span><span class=special>= </span><span class=identifier>result</span><span class=special>*</span><span class=number>10 </span><span class=special>+ </span><span class=keyword>int</span><span class=special>(</span><span class=identifier>ch </span><span class=special>- </span><span class=literal>'0'</span><span class=special>);
|
|
</span><span class=special>++</span><span class=identifier>len</span><span class=special>;
|
|
</span><span class=special>++</span><span class=identifier>scan</span><span class=special>;
|
|
</span><span class=special>} </span><span class=keyword>while </span><span class=special>(!</span><span class=identifier>scan</span><span class=special>.</span><span class=identifier>at_end</span><span class=special>() </span><span class=special>&& </span><span class=special>(</span><span class=identifier>ch </span><span class=special>= </span><span class=special>*</span><span class=identifier>scan</span><span class=special>, </span><span class=identifier>ch </span><span class=special>>= </span><span class=literal>'0' </span><span class=special>&& </span><span class=identifier>ch </span><span class=special><= </span><span class=literal>'9'</span><span class=special>));
|
|
|
|
</span><span class=keyword>return </span><span class=identifier>len</span><span class=special>;
|
|
</span><span class=special>}
|
|
</span><span class=special>};
|
|
|
|
</span><span class=identifier>functor_parser</span><span class=special><</span><span class=identifier>number_parser</span><span class=special>> </span><span class=identifier>number_parser_p</span><span class=special>;
|
|
</span></code></pre>
|
|
<p> <img src="theme/lens.gif" width="15" height="16"> The full source code can be <a href="../example/fundamental/functor_parser.cpp">viewed here</a>. This is part of the Spirit distribution. </p>
|
|
<p>To further understand the implementation, see <a href="indepth_the_scanner.html">In-depth:
|
|
The Scanner</a> for the scanner API details. We now have a parser <tt>number_parser_p</tt> that we can use just like any other Spirit parser. Example:</p>
|
|
<pre>
|
|
<code><span class=identifier>r </span><span class=special>= </span><span class=identifier>number_parser_p </span><span class=special>>> </span><span class=special>*(</span><span class=literal>',' </span><span class=special>>> </span><span class=identifier>number_parser_p</span><span class=special>);
|
|
</span></code></pre>
|
|
<table border="0">
|
|
<tr>
|
|
<td width="10"></td>
|
|
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
|
|
<td width="30"><a href="list_parsers.html"><img src="theme/l_arr.gif" border="0"></a></td>
|
|
<td width="30"><a href="refactoring.html"><img src="theme/r_arr.gif" border="0"></a></td>
|
|
</tr>
|
|
</table>
|
|
<br>
|
|
<hr size="1">
|
|
<p class="copyright">Copyright © 1998-2003 Joel de Guzman<br>
|
|
<br>
|
|
<font size="2">Use, modification and distribution is subject to the Boost Software
|
|
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
|
|
http://www.boost.org/LICENSE_1_0.txt)</font></p>
|
|
<p class="copyright"> </p>
|
|
</body>
|
|
</html>
|