projects / ceph.git / blame
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| 7c673cae FG |
1 | <html> |
| 2 | <head> | |
| 3 | <title>Functor Parser</title> | |
| 4 | <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> | |
| 5 | <link rel="stylesheet" href="theme/style.css" type="text/css"> | |
| 6 | </head> | |
| 7 | ||
| 8 | <body> | |
| 9 | <table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2"> | |
| 10 | <tr> | |
| 11 | <td width="10"> | |
| 12 | </td> | |
| 13 | <td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Functor | |
| 14 | Parser</b></font> </td> | |
| 15 | <td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" width="112" height="48" align="right" border="0"></a></td> | |
| 16 | </tr> | |
| 17 | </table> | |
| 18 | <br> | |
| 19 | <table border="0"> | |
| 20 | <tr> | |
| 21 | <td width="10"></td> | |
| 22 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> | |
| 23 | <td width="30"><a href="list_parsers.html"><img src="theme/l_arr.gif" border="0"></a></td> | |
| 24 | <td width="30"><a href="refactoring.html"><img src="theme/r_arr.gif" border="0"></a></td> | |
| 25 | </tr> | |
| 26 | </table> | |
| 27 | <p>The simplest way to write your hand coded parser that works well with the rest | |
| 28 | of the Spirit library is to simply write a functor parser.</p> | |
| 29 | <p> A functor parser is expected to have the interface:</p> | |
| 30 | <pre> | |
| 31 | <code><span class=keyword>struct </span><span class=identifier>functor | |
| 32 | </span><span class=special>{ | |
| 33 | </span><span class=keyword>typedef </span><span class=identifier>T </span><span class=identifier>result_t</span><span class=special>; | |
| 34 | ||
| 35 | </span><span class=keyword>template </span><span class=special><</span><span class=keyword>typename </span><span class=identifier>ScannerT</span><span class=special>> | |
| 36 | </span><span class=keyword>std::ptrdiff_t | |
| 37 | </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>; | |
| 38 | </span><span class=special>}; | |
| 39 | </span></code></pre> | |
| 40 | <p> where typedef T result_t; is the attribute type of the parser that will be | |
| 41 | passed back to the match result (see <a href="indepth_the_parser.html">In-depth: | |
| 42 | The Parser</a>). If the parser does not need to return an attribute, this can | |
| 43 | simply be nil_t. The <span class=keyword><tt>std::ptrdiff_t</tt></span> result | |
| 44 | is the number of matching characters matched by your parser. A negative value | |
| 45 | flags an unsucessful match.</p> | |
| 46 | <p> A conforming functor parser can transformed into a well formed Spirit parser | |
| 47 | by wrapping it in the functor_parser template:</p> | |
| 48 | <pre> | |
| 49 | <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>; | |
| 50 | </span></code></pre> | |
| 51 | ||
| 52 | <h2>Example</h2> | |
| 53 | <p> The following example puts the functor_parser into action:</p> | |
| 54 | <pre> | |
| 55 | <code><span class=keyword>struct </span><span class=identifier>number_parser | |
| 56 | </span><span class=special>{ | |
| 57 | </span><span class=keyword>typedef </span><span class=keyword>int </span><span class=identifier>result_t</span><span class=special>; | |
| 58 | </span><span class=keyword>template </span><span class=special><</span><span class=keyword>typename </span><span class=identifier>ScannerT</span><span class=special>> | |
| 59 | </span><span class=keyword>std::ptrdiff_t</span> | |
| 60 | <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 | |
| 61 | </span><span class=special>{ | |
| 62 | </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>()) | |
| 63 | </span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>; | |
| 64 | ||
| 65 | </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>; | |
| 66 | </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>) | |
| 67 | </span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>; | |
| 68 | ||
| 69 | </span><span class=identifier>result </span><span class=special>= </span><span class=number>0</span><span class=special>; | |
| 70 | </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>; | |
| 71 | ||
| 72 | </span><span class=keyword>do | |
| 73 | </span><span class=special>{ | |
| 74 | </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>); | |
| 75 | </span><span class=special>++</span><span class=identifier>len</span><span class=special>; | |
| 76 | </span><span class=special>++</span><span class=identifier>scan</span><span class=special>; | |
| 77 | </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>)); | |
| 78 | ||
| 79 | </span><span class=keyword>return </span><span class=identifier>len</span><span class=special>; | |
| 80 | </span><span class=special>} | |
| 81 | </span><span class=special>}; | |
| 82 | ||
| 83 | </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>; | |
| 84 | </span></code></pre> | |
| 85 | <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> | |
| 86 | <p>To further understand the implementation, see <a href="indepth_the_scanner.html">In-depth: | |
| 87 | 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> | |
| 88 | <pre> | |
| 89 | <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>); | |
| 90 | </span></code></pre> | |
| 91 | <table border="0"> | |
| 92 | <tr> | |
| 93 | <td width="10"></td> | |
| 94 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> | |
| 95 | <td width="30"><a href="list_parsers.html"><img src="theme/l_arr.gif" border="0"></a></td> | |
| 96 | <td width="30"><a href="refactoring.html"><img src="theme/r_arr.gif" border="0"></a></td> | |
| 97 | </tr> | |
| 98 | </table> | |
| 99 | <br> | |
| 100 | <hr size="1"> | |
| 101 | <p class="copyright">Copyright © 1998-2003 Joel de Guzman<br> | |
| 102 | <br> | |
| 103 | <font size="2">Use, modification and distribution is subject to the Boost Software | |
| 104 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
| 105 | http://www.boost.org/LICENSE_1_0.txt)</font></p> | |
| 106 | <p class="copyright"> </p> | |
| 107 | </body> | |
| 108 | </html> |