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- </div>
- <div class="section">
- <div class="titlepage"><div><div><h3 class="title">
- <a name="spirit_x3.tutorials.roman"></a><a class="link" href="roman.html" title="Roman Numerals">Roman Numerals</a>
- </h3></div></div></div>
- <p>
- This example demonstrates:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- The Symbol Table
- </li>
- <li class="listitem">
- Non-terminal rules
- </li>
- </ul></div>
- <h5>
- <a name="spirit_x3.tutorials.roman.h0"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.symbol_table"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.symbol_table">Symbol
- Table</a>
- </h5>
- <p>
- The symbol table holds a dictionary of symbols where each symbol is a sequence
- of characters. The template class, can work efficiently with 8, 16, 32 and
- even 64 bit characters. Mutable data of type T are associated with each symbol.
- </p>
- <p>
- Traditionally, symbol table management is maintained separately outside the
- BNF grammar through semantic actions. Contrary to standard practice, the
- Spirit symbol table class <code class="computeroutput"><span class="identifier">symbols</span></code>
- is a parser. An object of which may be used anywhere in the EBNF grammar
- specification. It is an example of a dynamic parser. A dynamic parser is
- characterized by its ability to modify its behavior at run time. Initially,
- an empty symbols object matches nothing. At any time, symbols may be added
- or removed, thus, dynamically altering its behavior.
- </p>
- <p>
- Each entry in a symbol table may have an associated mutable data slot. In
- this regard, one can view the symbol table as an associative container (or
- map) of key-value pairs where the keys are strings.
- </p>
- <p>
- The symbols class expects one template parameter to specify the data type
- associated with each symbol: its attribute. There are a couple of namespaces
- in X3 where you can find various versions of the symbols class for handling
- different character encoding including ascii, standard, standard_wide, iso8859_1,
- and unicode. The default symbol parser type in the main x3 namespace is standard.
- </p>
- <p>
- Here's a parser for roman hundreds (100..900) using the symbol table. Keep
- in mind that the data associated with each slot is the parser's attribute
- (which is passed to attached semantic actions).
- </p>
- <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">hundreds_</span> <span class="special">:</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span>
- <span class="special">{</span>
- <span class="identifier">hundreds_</span><span class="special">()</span>
- <span class="special">{</span>
- <span class="identifier">add</span>
- <span class="special">(</span><span class="string">"C"</span> <span class="special">,</span> <span class="number">100</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"CC"</span> <span class="special">,</span> <span class="number">200</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"CCC"</span> <span class="special">,</span> <span class="number">300</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"CD"</span> <span class="special">,</span> <span class="number">400</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"D"</span> <span class="special">,</span> <span class="number">500</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"DC"</span> <span class="special">,</span> <span class="number">600</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"DCC"</span> <span class="special">,</span> <span class="number">700</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"DCCC"</span> <span class="special">,</span> <span class="number">800</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"CM"</span> <span class="special">,</span> <span class="number">900</span><span class="special">)</span>
- <span class="special">;</span>
- <span class="special">}</span>
- <span class="special">}</span> <span class="identifier">hundreds</span><span class="special">;</span>
- </pre>
- <p>
- Here's a parser for roman tens (10..90):
- </p>
- <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">tens_</span> <span class="special">:</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span>
- <span class="special">{</span>
- <span class="identifier">tens_</span><span class="special">()</span>
- <span class="special">{</span>
- <span class="identifier">add</span>
- <span class="special">(</span><span class="string">"X"</span> <span class="special">,</span> <span class="number">10</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"XX"</span> <span class="special">,</span> <span class="number">20</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"XXX"</span> <span class="special">,</span> <span class="number">30</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"XL"</span> <span class="special">,</span> <span class="number">40</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"L"</span> <span class="special">,</span> <span class="number">50</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"LX"</span> <span class="special">,</span> <span class="number">60</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"LXX"</span> <span class="special">,</span> <span class="number">70</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"LXXX"</span> <span class="special">,</span> <span class="number">80</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"XC"</span> <span class="special">,</span> <span class="number">90</span><span class="special">)</span>
- <span class="special">;</span>
- <span class="special">}</span>
- <span class="special">}</span> <span class="identifier">tens</span><span class="special">;</span>
- </pre>
- <p>
- and, finally, for ones (1..9):
- </p>
- <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">ones_</span> <span class="special">:</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">unsigned</span><span class="special">></span>
- <span class="special">{</span>
- <span class="identifier">ones_</span><span class="special">()</span>
- <span class="special">{</span>
- <span class="identifier">add</span>
- <span class="special">(</span><span class="string">"I"</span> <span class="special">,</span> <span class="number">1</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"II"</span> <span class="special">,</span> <span class="number">2</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"III"</span> <span class="special">,</span> <span class="number">3</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"IV"</span> <span class="special">,</span> <span class="number">4</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"V"</span> <span class="special">,</span> <span class="number">5</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"VI"</span> <span class="special">,</span> <span class="number">6</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"VII"</span> <span class="special">,</span> <span class="number">7</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"VIII"</span> <span class="special">,</span> <span class="number">8</span><span class="special">)</span>
- <span class="special">(</span><span class="string">"IX"</span> <span class="special">,</span> <span class="number">9</span><span class="special">)</span>
- <span class="special">;</span>
- <span class="special">}</span>
- <span class="special">}</span> <span class="identifier">ones</span><span class="special">;</span>
- </pre>
- <p>
- Now we can use <code class="computeroutput"><span class="identifier">hundreds</span></code>,
- <code class="computeroutput"><span class="identifier">tens</span></code> and <code class="computeroutput"><span class="identifier">ones</span></code>
- anywhere in our parser expressions. They are all parsers.
- </p>
- <h5>
- <a name="spirit_x3.tutorials.roman.h1"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.rules"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.rules">Rules</a>
- </h5>
- <p>
- Up until now, we've been inlining our parser expressions, passing them directly
- to the <code class="computeroutput"><span class="identifier">phrase_parse</span></code> function.
- The expression evaluates into a temporary, unnamed parser which is passed
- into the <code class="computeroutput"><span class="identifier">phrase_parse</span></code> function,
- used, and then destroyed. This is fine for small parsers. When the expressions
- get complicated, you'd want to break the expressions into smaller easier-to-understand
- pieces, name them, and refer to them from other parser expressions by name.
- </p>
- <p>
- A parser expression can be assigned to what is called a "rule".
- There are various ways to declare rules. The simplest form is:
- </p>
- <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">ID</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">r</span> <span class="special">=</span> <span class="string">"some-name"</span><span class="special">;</span>
- </pre>
- <h5>
- <a name="spirit_x3.tutorials.roman.h2"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.rule_id"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.rule_id">Rule
- ID</a>
- </h5>
- <p>
- At the very least, the rule needs an identification tag. This ID can be any
- struct or class type and need not be defined. Forward declaration would suffice.
- In subsequent tutorials, we will see that the rule ID can have additional
- functionalities for error handling and annotation.
- </p>
- <h5>
- <a name="spirit_x3.tutorials.roman.h3"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.rule_name"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.rule_name">Rule
- Name</a>
- </h5>
- <p>
- The name is optional, but is useful for debugging and error handling, as
- we'll see later. Notice that rule <code class="computeroutput"><span class="identifier">r</span></code>
- is declared <code class="computeroutput"><span class="keyword">const</span></code>. Rules are
- immutable and are best declared as <code class="computeroutput"><span class="keyword">const</span></code>.
- Rules are lightweight and can be passed around by value. Its only member
- variable is a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>: its name.
- </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>
- Unlike Qi (Spirit V2), X3 rules can be used with both <code class="computeroutput"><span class="identifier">phrase_parse</span></code>
- and <code class="computeroutput"><span class="identifier">parse</span></code> without having
- to specify the skip parser
- </p></td></tr>
- </table></div>
- <h5>
- <a name="spirit_x3.tutorials.roman.h4"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.rule_attributes"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.rule_attributes">Rule
- Attributes</a>
- </h5>
- <p>
- For our next example, there's one more rule form you should know about:
- </p>
- <pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">ID</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">r</span> <span class="special">=</span> <span class="string">"some-name"</span><span class="special">;</span>
- </pre>
- <p>
- The Attribute parameter specifies the attribute type of the rule. You've
- seen that our parsers can have an attribute. Recall that the <code class="computeroutput"><span class="identifier">double_</span></code> parser has an attribute of <code class="computeroutput"><span class="keyword">double</span></code>. To be precise, these are <span class="emphasis"><em>synthesized</em></span>
- attributes. The parser "synthesizes" the attribute value. If the
- parser is a function, think of them as function return values.
- </p>
- <h5>
- <a name="spirit_x3.tutorials.roman.h5"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.rule_definition"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.rule_definition">Rule
- Definition</a>
- </h5>
- <p>
- After having declared a rule, you need a definition for the rule. Example:
- </p>
- <pre class="programlisting"><span class="keyword">auto</span> <span class="keyword">const</span> <span class="identifier">r_def</span> <span class="special">=</span> <span class="identifier">double_</span> <span class="special">>></span> <span class="special">*(</span><span class="char">','</span> <span class="special">>></span> <span class="identifier">double_</span><span class="special">);</span>
- </pre>
- <p>
- By convention, rule definitions have a _def suffix. Like rules, rule definitions
- are immutable and are best declared as <code class="computeroutput"><span class="keyword">const</span></code>.
- </p>
- <a name="__tutorial_spirit_define__"></a><h5>
- <a name="spirit_x3.tutorials.roman.h6"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.boost_spirit_define"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.boost_spirit_define">BOOST_SPIRIT_DEFINE</a>
- </h5>
- <p>
- Now that we have a rule and its definition, we tie the rule with a rule definition
- using the <code class="computeroutput"><span class="identifier">BOOST_SPIRIT_DEFINE</span></code>
- macro:
- </p>
- <pre class="programlisting"><span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">r</span><span class="special">);</span>
- </pre>
- <p>
- Behind the scenes, what's actually happening is that we are defining a <code class="computeroutput"><span class="identifier">parse_rule</span></code> function in the client namespace
- that tells X3 how to invoke the rule. For example, given a rule named <code class="computeroutput"><span class="identifier">my_rule</span></code> and a corresponding definition
- named <code class="computeroutput"><span class="identifier">my_rule_def</span></code>, <code class="computeroutput"><span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">my_rule</span><span class="special">)</span></code>
- expands to this code:
- </p>
- <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span>
- <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="identifier">parse_rule</span><span class="special">(</span>
- <span class="keyword">decltype</span><span class="special">(</span><span class="identifier">my_rule</span><span class="special">)</span>
- <span class="special">,</span> <span class="identifier">Iterator</span><span class="special">&</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">last</span>
- <span class="special">,</span> <span class="identifier">Context</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">context</span><span class="special">,</span> <span class="keyword">decltype</span><span class="special">(</span><span class="identifier">my_rule</span><span class="special">)::</span><span class="identifier">attribute_type</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="keyword">using</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">unused</span><span class="special">;</span>
- <span class="keyword">static</span> <span class="keyword">auto</span> <span class="keyword">const</span> <span class="identifier">def_</span> <span class="special">=</span> <span class="identifier">my_rule_def</span><span class="special">;</span>
- <span class="keyword">return</span> <span class="identifier">def_</span><span class="special">.</span><span class="identifier">parse</span><span class="special">(</span><span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">context</span><span class="special">,</span> <span class="identifier">unused</span><span class="special">,</span> <span class="identifier">attr</span><span class="special">);</span>
- <span class="special">}</span>
- </pre>
- <p>
- And so for each rule defined using <code class="computeroutput"><span class="identifier">BOOST_SPIRIT_DEFINE</span></code>,
- there is an overloaded <code class="computeroutput"><span class="identifier">parse_rule</span></code>
- function. At parse time, Spirit X3 recursively calls the appropriate <code class="computeroutput"><span class="identifier">parse_rule</span></code> function.
- </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>
- <code class="computeroutput"><span class="identifier">BOOST_SPIRIT_DEFINE</span></code> is
- variadic and may be used for one or more rules. Example: <code class="computeroutput"><span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">r1</span><span class="special">,</span> <span class="identifier">r2</span><span class="special">,</span> <span class="identifier">r3</span><span class="special">);</span></code>
- </p></td></tr>
- </table></div>
- <h5>
- <a name="spirit_x3.tutorials.roman.h7"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.grammars"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.grammars">Grammars</a>
- </h5>
- <p>
- Unlike Qi (Spirit V2), X3 discards the notion of a grammar as a concrete
- entity for encapsulating rules. In X3, a grammar is simply a logical group
- of rules that work together, typically with a single top-level start rule
- which serves as the main entry point. X3 grammars are grouped using namespaces.
- The roman numeral grammar is a very nice and simple example of a grammar:
- </p>
- <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">parser</span>
- <span class="special">{</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">eps</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">_val</span><span class="special">;</span>
- <span class="keyword">using</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">_attr</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="keyword">auto</span> <span class="identifier">set_zero</span> <span class="special">=</span> <span class="special">[&](</span><span class="keyword">auto</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">){</span> <span class="identifier">_val</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="special">};</span>
- <span class="keyword">auto</span> <span class="identifier">add1000</span> <span class="special">=</span> <span class="special">[&](</span><span class="keyword">auto</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">){</span> <span class="identifier">_val</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span> <span class="special">+=</span> <span class="number">1000</span><span class="special">;</span> <span class="special">};</span>
- <span class="keyword">auto</span> <span class="identifier">add</span> <span class="special">=</span> <span class="special">[&](</span><span class="keyword">auto</span><span class="special">&</span> <span class="identifier">ctx</span><span class="special">){</span> <span class="identifier">_val</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span> <span class="special">+=</span> <span class="identifier">_attr</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</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">roman</span><span class="special">,</span> <span class="keyword">unsigned</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">roman</span> <span class="special">=</span> <span class="string">"roman"</span><span class="special">;</span>
- <span class="keyword">auto</span> <span class="keyword">const</span> <span class="identifier">roman_def</span> <span class="special">=</span>
- <span class="identifier">eps</span> <span class="special">[</span><span class="identifier">set_zero</span><span class="special">]</span>
- <span class="special">>></span>
- <span class="special">(</span>
- <span class="special">-(+</span><span class="identifier">lit</span><span class="special">(</span><span class="char">'M'</span><span class="special">)</span> <span class="special">[</span><span class="identifier">add1000</span><span class="special">])</span>
- <span class="special">>></span> <span class="special">-</span><span class="identifier">hundreds</span> <span class="special">[</span><span class="identifier">add</span><span class="special">]</span>
- <span class="special">>></span> <span class="special">-</span><span class="identifier">tens</span> <span class="special">[</span><span class="identifier">add</span><span class="special">]</span>
- <span class="special">>></span> <span class="special">-</span><span class="identifier">ones</span> <span class="special">[</span><span class="identifier">add</span><span class="special">]</span>
- <span class="special">)</span>
- <span class="special">;</span>
- <span class="identifier">BOOST_SPIRIT_DEFINE</span><span class="special">(</span><span class="identifier">roman</span><span class="special">);</span>
- <span class="special">}</span>
- </pre>
- <p>
- Things to take notice of:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- The start rule's attribute is <code class="computeroutput"><span class="keyword">unsigned</span></code>.
- </li>
- <li class="listitem">
- <code class="computeroutput"><span class="identifier">_val</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code>
- gets a reference to the rule's synthesized attribute.
- </li>
- <li class="listitem">
- <code class="computeroutput"><span class="identifier">_attr</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code>
- gets a reference to the parser's synthesized attribute.
- </li>
- <li class="listitem">
- <code class="computeroutput"><span class="identifier">eps</span></code> is a special spirit
- parser that consumes no input but is always successful. We use it to
- initialize the rule's synthesized attribute, to zero before anything
- else. The actual parser starts at <code class="computeroutput"><span class="special">+</span><span class="identifier">lit</span><span class="special">(</span><span class="char">'M'</span><span class="special">)</span></code>, parsing
- roman thousands. Using <code class="computeroutput"><span class="identifier">eps</span></code>
- this way is good for doing pre and post initializations.
- </li>
- <li class="listitem">
- The rule <code class="computeroutput"><span class="identifier">roman</span></code> and the
- definition <code class="computeroutput"><span class="identifier">roman_def</span></code>
- are const objects.
- </li>
- <li class="listitem">
- The rule's ID is <code class="computeroutput"><span class="keyword">class</span> <span class="identifier">roman</span></code>. C++ allows you to declare the
- class in the actual template declaration as you can see in the example:
- </li>
- </ul></div>
- <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">roman</span><span class="special">,</span> <span class="keyword">unsigned</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">roman</span> <span class="special">=</span> <span class="string">"roman"</span><span class="special">;</span>
- </pre>
- <h5>
- <a name="spirit_x3.tutorials.roman.h8"></a>
- <span class="phrase"><a name="spirit_x3.tutorials.roman.let_s_parse_"></a></span><a class="link" href="roman.html#spirit_x3.tutorials.roman.let_s_parse_">Let's
- Parse!</a>
- </h5>
- <pre class="programlisting"><span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">parse</span><span class="special">(</span><span class="identifier">iter</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span> <span class="identifier">roman</span><span class="special">,</span> <span class="identifier">result</span><span class="special">);</span>
- <span class="keyword">if</span> <span class="special">(</span><span class="identifier">r</span> <span class="special">&&</span> <span class="identifier">iter</span> <span class="special">==</span> <span class="identifier">end</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------\n"</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing succeeded\n"</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"result = "</span> <span class="special"><<</span> <span class="identifier">result</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------\n"</span><span class="special">;</span>
- <span class="special">}</span>
- <span class="keyword">else</span>
- <span class="special">{</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">rest</span><span class="special">(</span><span class="identifier">iter</span><span class="special">,</span> <span class="identifier">end</span><span class="special">);</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------\n"</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Parsing failed\n"</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"stopped at: \": "</span> <span class="special"><<</span> <span class="identifier">rest</span> <span class="special"><<</span> <span class="string">"\"\n"</span><span class="special">;</span>
- <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"-------------------------\n"</span><span class="special">;</span>
- <span class="special">}</span>
- </pre>
- <p>
- <code class="computeroutput"><span class="identifier">roman</span></code> is our roman numeral
- parser. This time around we are using the no-skipping version of the parse
- functions. We do not want to skip any spaces! We are also passing in an attribute,
- <code class="computeroutput"><span class="keyword">unsigned</span> <span class="identifier">result</span></code>,
- which will receive the parsed value.
- </p>
- <p>
- The full cpp file for this example can be found here: <a href="../../../../../example/x3/roman.cpp" target="_top">roman.cpp</a>
- </p>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <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>)
- </p>
- </div></td>
- </tr></table>
- <hr>
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