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functor_parser.html

functor_parser.html 8.4 KB
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  1. <html>
    2. 

  2. <head>
    3. 

  3. <title>Functor Parser</title>
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  13.     <td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Functor 
    14. 

  14.       Parser</b></font> </td>
    15. 

  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>
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  18. <br>
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  19. <table border="0">
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  21.     <td width="10"></td>
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  22.     <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
    23. 

  23.     <td width="30"><a href="list_parsers.html"><img src="theme/l_arr.gif" border="0"></a></td>
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  24.     <td width="30"><a href="refactoring.html"><img src="theme/r_arr.gif" border="0"></a></td>
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  25.   </tr>
    26. 

  26. </table>
    27. 

  27. <p>The simplest way to write your hand coded parser that works well with the rest 
    28. 

  28.   of the Spirit library is to simply write a functor parser.</p>
    29. 

  29. <p> A functor parser is expected to have the interface:</p>
    30. 

  30. <pre>
    31. 

  31.     <code><span class=keyword>struct </span><span class=identifier>functor
    32. 

  32.     </span><span class=special>{
    33. 

  33.         </span><span class=keyword>typedef </span><span class=identifier>T </span><span class=identifier>result_t</span><span class=special>;
    34. 

  34. 

  35.         </span><span class=keyword>template </span><span class=special>&lt;</span><span class=keyword>typename </span><span class=identifier>ScannerT</span><span class=special>&gt;
    36. 

  36.         </span><span class=keyword>std::ptrdiff_t
    37. 

  37.         </span><span class=keyword>operator</span><span class=special>()(</span><span class=identifier>ScannerT </span><span class=keyword>const</span><span class=special>&amp; </span><span class=identifier>scan</span><span class=special>, </span><span class=identifier>result_t</span><span class=special>&amp; </span><span class=identifier>result</span><span class=special>) </span><span class=keyword>const</span><span class=special>;
    38. 

  38.     </span><span class=special>};
    39. 

  39. </span></code></pre>
    40. 

  40. <p> where typedef T result_t; is the attribute type of the parser that will be 
    41. 

  41.   passed back to the match result (see <a href="indepth_the_parser.html">In-depth: 
    42. 

  42.   The Parser</a>). If the parser does not need to return an attribute, this can 
    43. 

  43.   simply be nil_t. The <span class=keyword><tt>std::ptrdiff_t</tt></span> result 
    44. 

  44.   is the number of matching characters matched by your parser. A negative value 
    45. 

  45.   flags an unsucessful match.</p>
    46. 

  46. <p> A conforming functor parser can transformed into a well formed Spirit parser 
    47. 

  47.   by wrapping it in the functor_parser template:</p>
    48. 

  48. <pre>
    49. 

  49.     <code><span class=identifier>functor_parser</span><span class=special>&lt;</span><span class=identifier>functor</span><span class=special>&gt; </span><span class=identifier>functor_p</span><span class=special>;
    50. 

  50. </span></code></pre>
    51. 

  51. 

  52. <h2>Example</h2>
    53. 

  53. <p> The following example puts the functor_parser into action:</p>
    54. 

  54. <pre>
    55. 

  55.     <code><span class=keyword>struct </span><span class=identifier>number_parser
    56. 

  56.     </span><span class=special>{
    57. 

  57.         </span><span class=keyword>typedef </span><span class=keyword>int </span><span class=identifier>result_t</span><span class=special>;
    58. 

  58.         </span><span class=keyword>template </span><span class=special>&lt;</span><span class=keyword>typename </span><span class=identifier>ScannerT</span><span class=special>&gt;
    59. 

  59.         </span><span class=keyword>std::ptrdiff_t</span>
    60. 

  60.         <span class=keyword>operator</span><span class=special>()(</span><span class=identifier>ScannerT </span><span class=keyword>const</span><span class=special>&amp; </span><span class=identifier>scan</span><span class=special>, </span><span class=identifier>result_t</span><span class=special>&amp; </span><span class=identifier>result</span><span class=special>) </span><span class=keyword>const
    61. 

  61.         </span><span class=special>{
    62. 

  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. 

  63.                 </span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>;
    64. 

  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. 

  66.             </span><span class=keyword>if </span><span class=special>(</span><span class=identifier>ch </span><span class=special>&lt; </span><span class=literal>'0' </span><span class=special>|| </span><span class=identifier>ch </span><span class=special>&gt; </span><span class=literal>'9'</span><span class=special>)
    67. 

  67.                 </span><span class=keyword>return </span><span class=special>-</span><span class=number>1</span><span class=special>;
    68. 

  68. 

  69.             </span><span class=identifier>result </span><span class=special>= </span><span class=number>0</span><span class=special>;
    70. 

  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. 

  71. 

  72.             </span><span class=keyword>do
    73. 

  73.             </span><span class=special>{
    74. 

  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. 

  75.                 </span><span class=special>++</span><span class=identifier>len</span><span class=special>;
    76. 

  76.                 </span><span class=special>++</span><span class=identifier>scan</span><span class=special>;
    77. 

  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>&amp;&amp; </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>&gt;= </span><span class=literal>'0' </span><span class=special>&amp;&amp; </span><span class=identifier>ch </span><span class=special>&lt;= </span><span class=literal>'9'</span><span class=special>));
    78. 

  78. 

  79.             </span><span class=keyword>return </span><span class=identifier>len</span><span class=special>;
    80. 

  80.         </span><span class=special>}
    81. 

  81.     </span><span class=special>};
    82. 

  82. 

  83.     </span><span class=identifier>functor_parser</span><span class=special>&lt;</span><span class=identifier>number_parser</span><span class=special>&gt; </span><span class=identifier>number_parser_p</span><span class=special>;
    84. 

  84. </span></code></pre>
    85. 

  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. 

  86. <p>To further understand the implementation, see <a href="indepth_the_scanner.html">In-depth: 
    87. 

  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. 

  88. <pre>
    89. 

  89.     <code><span class=identifier>r </span><span class=special>= </span><span class=identifier>number_parser_p </span><span class=special>&gt;&gt; </span><span class=special>*(</span><span class=literal>',' </span><span class=special>&gt;&gt; </span><span class=identifier>number_parser_p</span><span class=special>);
    90. 

  90. </span></code></pre>
    91. 

  91. <table border="0">
    92. 

  92.   <tr> 
    93. 

  93.     <td width="10"></td>
    94. 

  94.     <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
    95. 

  95.     <td width="30"><a href="list_parsers.html"><img src="theme/l_arr.gif" border="0"></a></td>
    96. 

  96.     <td width="30"><a href="refactoring.html"><img src="theme/r_arr.gif" border="0"></a></td>
    97. 

  97.   </tr>
    98. 

  98. </table>
    99. 

  99. <br>
    100. 

  100. <hr size="1">
    101. 

  101. <p class="copyright">Copyright &copy; 1998-2003 Joel de Guzman<br>
    102. 

  102.   <br>
    103. 

  103. <font size="2">Use, modification and distribution is subject to the Boost Software
    104. 

  104.     License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
    105. 

  105.     http://www.boost.org/LICENSE_1_0.txt)</font></p>
    106. 

  106. <p class="copyright">&nbsp;</p>
    107. 

  107. </body>
    108. 

  108. </html>
    109.