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| <td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Functor |
| Parser</b></font> </td> |
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| <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> |
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| <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> |
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