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- <title>Employee - Parsing into structs</title>
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- </div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="spirit_x3.tutorials.employee"></a><a class="link" href="employee.html" title="Employee - Parsing into structs">Employee - Parsing into
- structs</a>
- </h3></div></div></div>
- <p>
- It's a common question in the <a href="https://lists.sourceforge.net/lists/listinfo/spirit-general" target="_top">Spirit
- Mailing List</a>: How do I parse and place the results into a C++ struct?
- Of course, at this point, you already know various ways to do it, using semantic
- actions. There are many ways to skin a cat. Spirit X3, being fully attributed,
- makes it even easier. The next example demonstrates some features of Spirit
- X3 that make this easy. In the process, you'll learn about:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- More about attributes
- </li>
- <li class="listitem">
- Auto rules
- </li>
- <li class="listitem">
- Some more built-in parsers
- </li>
- <li class="listitem">
- Directives
- </li>
- </ul></div>
- <p>
- First, let's create a struct representing an employee:
- </p>
- <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>
- <span class="special">{</span>
- <span class="keyword">struct</span> <span class="identifier">employee</span>
- <span class="special">{</span>
- <span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">forename</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">surname</span><span class="special">;</span>
- <span class="keyword">double</span> <span class="identifier">salary</span><span class="special">;</span>
- <span class="special">};</span>
- <span class="special">}}</span>
- </pre>
- <p>
- Then, we need to tell <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a>
- about our employee struct to make it a first-class fusion citizen that the
- grammar can utilize. If you don't know fusion yet, it is a <a href="http://www.boost.org/" target="_top">Boost</a>
- library for working with heterogeneous collections of data, commonly referred
- to as tuples. Spirit uses fusion extensively as part of its infrastructure.
- </p>
- <p>
- In fusion's view, a struct is just a form of a tuple. You can adapt any struct
- to be a fully conforming fusion tuple:
- </p>
- <pre class="programlisting"><span class="identifier">BOOST_FUSION_ADAPT_STRUCT</span><span class="special">(</span>
- <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>
- <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>
- <span class="special">)</span>
- </pre>
- <p>
- Now we'll write a parser for our employee. Inputs will be of the form:
- </p>
- <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>
- </pre>
- <p>
- <a name="__tutorial_employee_parser__"></a>Here goes:
- </p>
- <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">parser</span>
- <span class="special">{</span>
- <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>
- <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>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">lexeme</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span>
- <span class="identifier">x3</span><span class="special">::</span><span class="identifier">rule</span><span class="special"><</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">></span> <span class="keyword">const</span> <span class="identifier">employee</span> <span class="special">=</span> <span class="string">"employee"</span><span class="special">;</span>
- <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">>></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">>></span> <span class="char">'"'</span><span class="special">];</span>
- <span class="keyword">auto</span> <span class="keyword">const</span> <span class="identifier">employee_def</span> <span class="special">=</span>
- <span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span>
- <span class="special">>></span> <span class="char">'{'</span>
- <span class="special">>></span> <span class="identifier">int_</span> <span class="special">>></span> <span class="char">','</span>
- <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span>
- <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span>
- <span class="special">>></span> <span class="identifier">double_</span>
- <span class="special">>></span> <span class="char">'}'</span>
- <span class="special">;</span>
- <span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">employee</span><span class="special">);</span>
- <span class="special">}</span>
- </pre>
- <p>
- The full cpp file for this example can be found here: <a href="../../../../../example/x3/employee.cpp" target="_top">employee.cpp</a>
- </p>
- <p>
- Let's walk through this one step at a time (not necessarily from top to bottom).
- </p>
- <h5>
- <a name="spirit_x3.tutorials.employee.h0"></a>
- <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
- Declaration</a>
- </h5>
- <p>
- We are assuming that you already know about rules. We introduced rules in
- the previous <a class="link" href="roman.html" title="Roman Numerals">Roman Numerals example</a>.
- Please go back and review the previous tutorial if you have to.
- </p>
- <pre class="programlisting"><span class="identifier">x3</span><span class="special">::</span><span class="identifier">rule</span><span class="special"><</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">></span> <span class="identifier">employee</span> <span class="special">=</span> <span class="string">"employee"</span><span class="special">;</span>
- </pre>
- <h5>
- <a name="spirit_x3.tutorials.employee.h1"></a>
- <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>
- </h5>
- <pre class="programlisting"><span class="identifier">lexeme</span><span class="special">[</span><span class="char">'"'</span> <span class="special">>></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">>></span> <span class="char">'"'</span><span class="special">];</span>
- </pre>
- <p>
- <code class="computeroutput"><span class="identifier">lexeme</span></code> inhibits space skipping
- from the open brace to the closing brace. The expression parses quoted strings.
- </p>
- <pre class="programlisting"><span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span>
- </pre>
- <p>
- parses one or more chars, except the double quote. It stops when it sees
- a double quote.
- </p>
- <h5>
- <a name="spirit_x3.tutorials.employee.h2"></a>
- <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>
- </h5>
- <p>
- The expression:
- </p>
- <pre class="programlisting"><span class="identifier">a</span> <span class="special">-</span> <span class="identifier">b</span>
- </pre>
- <p>
- 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>.
- <code class="computeroutput"><span class="identifier">b</span></code>'s attribute is ignored.
- Hence, the attribute of:
- </p>
- <pre class="programlisting"><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span>
- </pre>
- <p>
- is just <code class="computeroutput"><span class="keyword">char</span></code>.
- </p>
- <h5>
- <a name="spirit_x3.tutorials.employee.h3"></a>
- <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>
- </h5>
- <pre class="programlisting"><span class="special">+</span><span class="identifier">a</span>
- </pre>
- <p>
- 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
- 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"><</span><span class="identifier">A</span><span class="special">></span></code>
- where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute
- of <code class="computeroutput"><span class="identifier">a</span></code>. So, putting all these
- together, the attribute of
- </p>
- <pre class="programlisting"><span class="special">+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'"'</span><span class="special">)</span>
- </pre>
- <p>
- is then:
- </p>
- <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span>
- </pre>
- <h5>
- <a name="spirit_x3.tutorials.employee.h4"></a>
- <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
- Attribute</a>
- </h5>
- <p>
- Now what's the attribute of
- </p>
- <pre class="programlisting"><span class="char">'"'</span> <span class="special">>></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">>></span> <span class="char">'"'</span>
- </pre>
- <p>
- ?
- </p>
- <p>
- Well, typically, the attribute of:
- </p>
- <pre class="programlisting"><span class="identifier">a</span> <span class="special">>></span> <span class="identifier">b</span> <span class="special">>></span> <span class="identifier">c</span>
- </pre>
- <p>
- is:
- </p>
- <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</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">></span>
- </pre>
- <p>
- where <code class="computeroutput"><span class="identifier">A</span></code> is the attribute
- of <code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">B</span></code>
- is the attribute of <code class="computeroutput"><span class="identifier">b</span></code> and
- <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>?
- - a tuple.
- </p>
- <div class="note"><table border="0" summary="Note">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
- <th align="left">Note</th>
- </tr>
- <tr><td align="left" valign="top"><p>
- If you don't know what I am talking about, see: <a href="http://tinyurl.com/6xun4j" target="_top">Fusion
- 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>
- at this point. You'll definitely see more of it in the coming pages.
- </p></td></tr>
- </table></div>
- <h5>
- <a name="spirit_x3.tutorials.employee.h5"></a>
- <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
- Collapsing</a>
- </h5>
- <p>
- Some parsers, especially those very little literal parsers you see, like
- <code class="computeroutput"><span class="char">'"'</span></code>, do not have attributes.
- </p>
- <p>
- Nodes without attributes are disregarded. In a sequence, like above, all
- 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>.
- So, since <code class="computeroutput"><span class="char">'"'</span></code> has no attribute,
- and <code class="computeroutput"><span class="special">+(</span><span class="identifier">char_</span>
- <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"><</span><span class="keyword">char</span><span class="special">></span></code>
- attribute, the whole expression's attribute should have been:
- </p>
- <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="special">></span>
- </pre>
- <p>
- But wait, there's one more collapsing rule: If the attribute is followed
- by a single element <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span></code>,
- The element is stripped naked from its container. To make a long story short,
- the attribute of the expression:
- </p>
- <pre class="programlisting"><span class="char">'"'</span> <span class="special">>></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">>></span> <span class="char">'"'</span>
- </pre>
- <p>
- is:
- </p>
- <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span>
- </pre>
- <h5>
- <a name="spirit_x3.tutorials.employee.h6"></a>
- <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
- Definition</a>
- </h5>
- <p>
- Again, we are assuming that you already know about rules and rule definitions.
- We introduced rules in the previous <a class="link" href="roman.html" title="Roman Numerals">Roman
- Numerals example</a>. Please go back and review the previous tutorial
- if you have to.
- </p>
- <pre class="programlisting"><span class="identifier">employee</span> <span class="special">=</span>
- <span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span>
- <span class="special">>></span> <span class="char">'{'</span>
- <span class="special">>></span> <span class="identifier">int_</span> <span class="special">>></span> <span class="char">','</span>
- <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span>
- <span class="special">>></span> <span class="identifier">quoted_string</span> <span class="special">>></span> <span class="char">','</span>
- <span class="special">>></span> <span class="identifier">double_</span>
- <span class="special">>></span> <span class="char">'}'</span>
- <span class="special">;</span>
- <span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">employee</span><span class="special">);</span>
- </pre>
- <p>
- Applying our collapsing rules above, the RHS has an attribute of:
- </p>
- <pre class="programlisting"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</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">></span>
- </pre>
- <p>
- These nodes do not have an attribute:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- <code class="computeroutput"><span class="identifier">lit</span><span class="special">(</span><span class="string">"employee"</span><span class="special">)</span></code>
- </li>
- <li class="listitem">
- <code class="computeroutput"><span class="char">'{'</span></code>
- </li>
- <li class="listitem">
- <code class="computeroutput"><span class="char">','</span></code>
- </li>
- <li class="listitem">
- <code class="computeroutput"><span class="char">'}'</span></code>
- </li>
- </ul></div>
- <div class="note"><table border="0" summary="Note">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../images/note.png"></td>
- <th align="left">Note</th>
- </tr>
- <tr><td align="left" valign="top"><p>
- 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
- had to wrap it inside <code class="computeroutput"><span class="identifier">lit</span></code>
- because immediately after it is <code class="computeroutput"><span class="special">>></span>
- <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
- a <code class="computeroutput"><span class="keyword">char</span></code> - you know, C++ syntax
- rules.
- </p></td></tr>
- </table></div>
- <p>
- Recall that the attribute of <code class="computeroutput"><span class="identifier">parser</span><span class="special">::</span><span class="identifier">employee</span></code>
- is the <code class="computeroutput"><span class="identifier">ast</span><span class="special">::</span><span class="identifier">employee</span></code> struct.
- </p>
- <p>
- Now everything is clear, right? The <code class="computeroutput"><span class="keyword">struct</span>
- <span class="identifier">employee</span></code> <span class="bold"><strong>IS</strong></span>
- compatible with <code class="computeroutput"><span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</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">></span></code>.
- So, the RHS of <code class="computeroutput"><span class="identifier">start</span></code> uses
- 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.
- </p>
- </div>
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- <td align="right"><div class="copyright-footer">Copyright © 2001-2018 Joel de Guzman,
- Hartmut Kaiser<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- 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>)
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