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  4. <title>Employee - Parsing into structs</title>
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  24. </div>
  25. <div class="section">
  26. <div class="titlepage"><div><div><h3 class="title">
  27. <a name="spirit_x3.tutorials.employee"></a><a class="link" href="employee.html" title="Employee - Parsing into structs">Employee - Parsing into
  28. structs</a>
  29. </h3></div></div></div>
  30. <p>
  31. It's a common question in the <a href="https://lists.sourceforge.net/lists/listinfo/spirit-general" target="_top">Spirit
  32. Mailing List</a>: How do I parse and place the results into a C++ struct?
  33. Of course, at this point, you already know various ways to do it, using semantic
  34. actions. There are many ways to skin a cat. Spirit X3, being fully attributed,
  35. makes it even easier. The next example demonstrates some features of Spirit
  36. X3 that make this easy. In the process, you'll learn about:
  37. </p>
  38. <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  39. <li class="listitem">
  40. More about attributes
  41. </li>
  42. <li class="listitem">
  43. Auto rules
  44. </li>
  45. <li class="listitem">
  46. Some more built-in parsers
  47. </li>
  48. <li class="listitem">
  49. Directives
  50. </li>
  51. </ul></div>
  52. <p>
  53. First, let's create a struct representing an employee:
  54. </p>
  55. <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">client</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">ast</span>
  56. <span class="special">{</span>
  57. <span class="keyword">struct</span> <span class="identifier">employee</span>
  58. <span class="special">{</span>
  59. <span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span>
  60. <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">forename</span><span class="special">;</span>
  61. <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">surname</span><span class="special">;</span>
  62. <span class="keyword">double</span> <span class="identifier">salary</span><span class="special">;</span>
  63. <span class="special">};</span>
  64. <span class="special">}}</span>
  65. </pre>
  66. <p>
  67. Then, we need to tell <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a>
  68. about our employee struct to make it a first-class fusion citizen that the
  69. grammar can utilize. If you don't know fusion yet, it is a <a href="http://www.boost.org/" target="_top">Boost</a>
  70. library for working with heterogeneous collections of data, commonly referred
  71. to as tuples. Spirit uses fusion extensively as part of its infrastructure.
  72. </p>
  73. <p>
  74. In fusion's view, a struct is just a form of a tuple. You can adapt any struct
  75. to be a fully conforming fusion tuple:
  76. </p>
  77. <pre class="programlisting"><span class="identifier">BOOST_FUSION_ADAPT_STRUCT</span><span class="special">(</span>
  78. <span class="identifier">client</span><span class="special">::</span><span class="identifier">ast</span><span class="special">::</span><span class="identifier">employee</span><span class="special">,</span>
  79. <span class="identifier">age</span><span class="special">,</span> <span class="identifier">forename</span><span class="special">,</span> <span class="identifier">surname</span><span class="special">,</span> <span class="identifier">salary</span>
  80. <span class="special">)</span>
  81. </pre>
  82. <p>
  83. Now we'll write a parser for our employee. Inputs will be of the form:
  84. </p>
  85. <pre class="programlisting"><span class="identifier">employee</span><span class="special">{</span> <span class="identifier">age</span><span class="special">,</span> <span class="string">"forename"</span><span class="special">,</span> <span class="string">"surname"</span><span class="special">,</span> <span class="identifier">salary</span> <span class="special">}</span>
  86. </pre>
  87. <p>
  88. <a name="__tutorial_employee_parser__"></a>Here goes:
  89. </p>
  90. <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">parser</span>
  91. <span class="special">{</span>
  92. <span class="keyword">namespace</span> <span class="identifier">x3</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">x3</span><span class="special">;</span>
  93. <span class="keyword">namespace</span> <span class="identifier">ascii</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">x3</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">;</span>
  94. <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span>
  95. <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span>
  96. <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span>
  97. <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">lexeme</span><span class="special">;</span>
  98. <span class="keyword">using</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span>
  99. <span class="identifier">x3</span><span class="special">::</span><span class="identifier">rule</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">employee</span><span class="special">,</span> <span class="identifier">ast</span><span class="special">::</span><span class="identifier">employee</span><span class="special">&gt;</span> <span class="keyword">const</span> <span class="identifier">employee</span> <span class="special">=</span> <span class="string">"employee"</span><span class="special">;</span>
  100. <span class="keyword">auto</span> <span class="keyword">const</span> <span class="identifier">quoted_string</span> <span class="special">=</span> <span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">&gt;&gt;</span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">&gt;&gt;</span> <span class="char">'"'</span><span class="special">];</span>
  101. <span class="keyword">auto</span> <span class="keyword">const</span> <span class="identifier">employee_def</span> <span class="special">=</span>
  102. <span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span>
  103. <span class="special">&gt;&gt;</span> <span class="char">'{'</span>
  104. <span class="special">&gt;&gt;</span> <span class="identifier">int_</span> <span class="special">&gt;&gt;</span> <span class="char">','</span>
  105. <span class="special">&gt;&gt;</span> <span class="identifier">quoted_string</span> <span class="special">&gt;&gt;</span> <span class="char">','</span>
  106. <span class="special">&gt;&gt;</span> <span class="identifier">quoted_string</span> <span class="special">&gt;&gt;</span> <span class="char">','</span>
  107. <span class="special">&gt;&gt;</span> <span class="identifier">double_</span>
  108. <span class="special">&gt;&gt;</span> <span class="char">'}'</span>
  109. <span class="special">;</span>
  110. <span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">employee</span><span class="special">);</span>
  111. <span class="special">}</span>
  112. </pre>
  113. <p>
  114. The full cpp file for this example can be found here: <a href="../../../../../example/x3/employee.cpp" target="_top">employee.cpp</a>
  115. </p>
  116. <p>
  117. Let's walk through this one step at a time (not necessarily from top to bottom).
  118. </p>
  119. <h5>
  120. <a name="spirit_x3.tutorials.employee.h0"></a>
  121. <span class="phrase"><a name="spirit_x3.tutorials.employee.rule_declaration"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.rule_declaration">Rule
  122. Declaration</a>
  123. </h5>
  124. <p>
  125. We are assuming that you already know about rules. We introduced rules in
  126. the previous <a class="link" href="roman.html" title="Roman Numerals">Roman Numerals example</a>.
  127. Please go back and review the previous tutorial if you have to.
  128. </p>
  129. <pre class="programlisting"><span class="identifier">x3</span><span class="special">::</span><span class="identifier">rule</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">employee</span><span class="special">,</span> <span class="identifier">ast</span><span class="special">::</span><span class="identifier">employee</span><span class="special">&gt;</span> <span class="identifier">employee</span> <span class="special">=</span> <span class="string">"employee"</span><span class="special">;</span>
  130. </pre>
  131. <h5>
  132. <a name="spirit_x3.tutorials.employee.h1"></a>
  133. <span class="phrase"><a name="spirit_x3.tutorials.employee.lexeme"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.lexeme">Lexeme</a>
  134. </h5>
  135. <pre class="programlisting"><span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">&gt;&gt;</span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">&gt;&gt;</span> <span class="char">'"'</span><span class="special">];</span>
  136. </pre>
  137. <p>
  138. <code class="computeroutput"><span class="identifier">lexeme</span></code> inhibits space skipping
  139. from the open brace to the closing brace. The expression parses quoted strings.
  140. </p>
  141. <pre class="programlisting"><span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span>
  142. </pre>
  143. <p>
  144. parses one or more chars, except the double quote. It stops when it sees
  145. a double quote.
  146. </p>
  147. <h5>
  148. <a name="spirit_x3.tutorials.employee.h2"></a>
  149. <span class="phrase"><a name="spirit_x3.tutorials.employee.difference"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.difference">Difference</a>
  150. </h5>
  151. <p>
  152. The expression:
  153. </p>
  154. <pre class="programlisting"><span class="identifier">a</span> <span class="special">-</span> <span class="identifier">b</span>
  155. </pre>
  156. <p>
  157. parses <code class="computeroutput"><span class="identifier">a</span></code> but not <code class="computeroutput"><span class="identifier">b</span></code>. Its attribute is just <code class="computeroutput"><span class="identifier">A</span></code>; the attribute of <code class="computeroutput"><span class="identifier">a</span></code>.
  158. <code class="computeroutput"><span class="identifier">b</span></code>'s attribute is ignored.
  159. Hence, the attribute of:
  160. </p>
  161. <pre class="programlisting"><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span>
  162. </pre>
  163. <p>
  164. is just <code class="computeroutput"><span class="keyword">char</span></code>.
  165. </p>
  166. <h5>
  167. <a name="spirit_x3.tutorials.employee.h3"></a>
  168. <span class="phrase"><a name="spirit_x3.tutorials.employee.plus"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.plus">Plus</a>
  169. </h5>
  170. <pre class="programlisting"><span class="special">+</span><span class="identifier">a</span>
  171. </pre>
  172. <p>
  173. is similar to Kleene star. Rather than match everything, <code class="computeroutput"><span class="special">+</span><span class="identifier">a</span></code> matches one or more. Like it's related
  174. function, the Kleene star, its attribute is a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span></code>
  175. where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute
  176. of <code class="computeroutput"><span class="identifier">a</span></code>. So, putting all these
  177. together, the attribute of
  178. </p>
  179. <pre class="programlisting"><span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span>
  180. </pre>
  181. <p>
  182. is then:
  183. </p>
  184. <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span>
  185. </pre>
  186. <h5>
  187. <a name="spirit_x3.tutorials.employee.h4"></a>
  188. <span class="phrase"><a name="spirit_x3.tutorials.employee.sequence_attribute"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.sequence_attribute">Sequence
  189. Attribute</a>
  190. </h5>
  191. <p>
  192. Now what's the attribute of
  193. </p>
  194. <pre class="programlisting"><span class="char">'"'</span> <span class="special">&gt;&gt;</span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">&gt;&gt;</span> <span class="char">'"'</span>
  195. </pre>
  196. <p>
  197. ?
  198. </p>
  199. <p>
  200. Well, typically, the attribute of:
  201. </p>
  202. <pre class="programlisting"><span class="identifier">a</span> <span class="special">&gt;&gt;</span> <span class="identifier">b</span> <span class="special">&gt;&gt;</span> <span class="identifier">c</span>
  203. </pre>
  204. <p>
  205. is:
  206. </p>
  207. <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">,</span> <span class="identifier">C</span><span class="special">&gt;</span>
  208. </pre>
  209. <p>
  210. where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute
  211. of <code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">B</span></code>
  212. is the attribute of <code class="computeroutput"><span class="identifier">b</span></code> and
  213. <code class="computeroutput"><span class="identifier">C</span></code> is the attribute of <code class="computeroutput"><span class="identifier">c</span></code>. What is <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>?
  214. - a tuple.
  215. </p>
  216. <div class="note"><table border="0" summary="Note">
  217. <tr>
  218. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
  219. <th align="left">Note</th>
  220. </tr>
  221. <tr><td align="left" valign="top"><p>
  222. If you don't know what I am talking about, see: <a href="http://tinyurl.com/6xun4j" target="_top">Fusion
  223. Vector</a>. It might be a good idea to have a look into <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a>
  224. at this point. You'll definitely see more of it in the coming pages.
  225. </p></td></tr>
  226. </table></div>
  227. <h5>
  228. <a name="spirit_x3.tutorials.employee.h5"></a>
  229. <span class="phrase"><a name="spirit_x3.tutorials.employee.attribute_collapsing"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.attribute_collapsing">Attribute
  230. Collapsing</a>
  231. </h5>
  232. <p>
  233. Some parsers, especially those very little literal parsers you see, like
  234. <code class="computeroutput"><span class="char">'"'</span></code>, do not have attributes.
  235. </p>
  236. <p>
  237. Nodes without attributes are disregarded. In a sequence, like above, all
  238. nodes with no attributes are filtered out of the <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>.
  239. So, since <code class="computeroutput"><span class="char">'"'</span></code> has no attribute,
  240. and <code class="computeroutput"><span class="special">+(</span><span class="identifier">char_</span>
  241. <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span></code> has a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span></code>
  242. attribute, the whole expression's attribute should have been:
  243. </p>
  244. <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span> <span class="special">&gt;</span>
  245. </pre>
  246. <p>
  247. But wait, there's one more collapsing rule: If the attribute is followed
  248. by a single element <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>,
  249. The element is stripped naked from its container. To make a long story short,
  250. the attribute of the expression:
  251. </p>
  252. <pre class="programlisting"><span class="char">'"'</span> <span class="special">&gt;&gt;</span> <span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span> <span class="special">&gt;&gt;</span> <span class="char">'"'</span>
  253. </pre>
  254. <p>
  255. is:
  256. </p>
  257. <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;</span>
  258. </pre>
  259. <h5>
  260. <a name="spirit_x3.tutorials.employee.h6"></a>
  261. <span class="phrase"><a name="spirit_x3.tutorials.employee.rule_definition"></a></span><a class="link" href="employee.html#spirit_x3.tutorials.employee.rule_definition">Rule
  262. Definition</a>
  263. </h5>
  264. <p>
  265. Again, we are assuming that you already know about rules and rule definitions.
  266. We introduced rules in the previous <a class="link" href="roman.html" title="Roman Numerals">Roman
  267. Numerals example</a>. Please go back and review the previous tutorial
  268. if you have to.
  269. </p>
  270. <pre class="programlisting"><span class="identifier">employee</span> <span class="special">=</span>
  271. <span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span>
  272. <span class="special">&gt;&gt;</span> <span class="char">'{'</span>
  273. <span class="special">&gt;&gt;</span> <span class="identifier">int_</span> <span class="special">&gt;&gt;</span> <span class="char">','</span>
  274. <span class="special">&gt;&gt;</span> <span class="identifier">quoted_string</span> <span class="special">&gt;&gt;</span> <span class="char">','</span>
  275. <span class="special">&gt;&gt;</span> <span class="identifier">quoted_string</span> <span class="special">&gt;&gt;</span> <span class="char">','</span>
  276. <span class="special">&gt;&gt;</span> <span class="identifier">double_</span>
  277. <span class="special">&gt;&gt;</span> <span class="char">'}'</span>
  278. <span class="special">;</span>
  279. <span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">employee</span><span class="special">);</span>
  280. </pre>
  281. <p>
  282. Applying our collapsing rules above, the RHS has an attribute of:
  283. </p>
  284. <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">double</span><span class="special">&gt;</span>
  285. </pre>
  286. <p>
  287. These nodes do not have an attribute:
  288. </p>
  289. <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  290. <li class="listitem">
  291. <code class="computeroutput"><span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span></code>
  292. </li>
  293. <li class="listitem">
  294. <code class="computeroutput"><span class="char">'{'</span></code>
  295. </li>
  296. <li class="listitem">
  297. <code class="computeroutput"><span class="char">','</span></code>
  298. </li>
  299. <li class="listitem">
  300. <code class="computeroutput"><span class="char">'}'</span></code>
  301. </li>
  302. </ul></div>
  303. <div class="note"><table border="0" summary="Note">
  304. <tr>
  305. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
  306. <th align="left">Note</th>
  307. </tr>
  308. <tr><td align="left" valign="top"><p>
  309. In case you are wondering, <code class="computeroutput"><span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span></code> is the same as "employee". We
  310. had to wrap it inside <code class="computeroutput"><span class="identifier">lit</span></code>
  311. because immediately after it is <code class="computeroutput"><span class="special">&gt;&gt;</span>
  312. <span class="char">'{'</span></code>. You can't right-shift a <code class="computeroutput"><span class="keyword">char</span><span class="special">[]</span></code> and
  313. a <code class="computeroutput"><span class="keyword">char</span></code> - you know, C++ syntax
  314. rules.
  315. </p></td></tr>
  316. </table></div>
  317. <p>
  318. Recall that the attribute of <code class="computeroutput"><span class="identifier">parser</span><span class="special">::</span><span class="identifier">employee</span></code>
  319. is the <code class="computeroutput"><span class="identifier">ast</span><span class="special">::</span><span class="identifier">employee</span></code> struct.
  320. </p>
  321. <p>
  322. Now everything is clear, right? The <code class="computeroutput"><span class="keyword">struct</span>
  323. <span class="identifier">employee</span></code> <span class="bold"><strong>IS</strong></span>
  324. compatible with <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">double</span><span class="special">&gt;</span></code>.
  325. So, the RHS of <code class="computeroutput"><span class="identifier">start</span></code> uses
  326. start's attribute (a <code class="computeroutput"><span class="keyword">struct</span> <span class="identifier">employee</span></code>) in-situ when it does its work.
  327. </p>
  328. </div>
  329. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  330. <td align="left"></td>
  331. <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2018 Joel de Guzman,
  332. Hartmut Kaiser<p>
  333. Distributed under the Boost Software License, Version 1.0. (See accompanying
  334. file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
  335. </p>
  336. </div></td>
  337. </tr></table>
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