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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.qi.tutorials.complex___our_first_complex_parser"></a><a class="link" href="complex___our_first_complex_parser.html" title="Complex - Our first complex parser">Complex |
| - Our first complex parser</a> |
| </h4></div></div></div> |
| <p> |
| Well, not really a complex parser, but a parser that parses complex numbers. |
| This time, we're using <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> |
| to do the semantic actions. |
| </p> |
| <p> |
| Here's a simple parser expression for complex numbers: |
| </p> |
| <pre class="programlisting"> <span class="char">'('</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> <span class="special">>></span> <span class="char">')'</span> |
| <span class="special">|</span> <span class="identifier">double_</span> |
| </pre> |
| <p> |
| What's new? Well, we have: |
| </p> |
| <div class="orderedlist"><ol class="orderedlist" type="1"> |
| <li class="listitem"> |
| Alternates: e.g. <code class="computeroutput"><span class="identifier">a</span> <span class="special">|</span> <span class="identifier">b</span></code>. |
| Try <code class="computeroutput"><span class="identifier">a</span></code> first. If it |
| succeeds, good. If not, try the next alternative, <code class="computeroutput"><span class="identifier">b</span></code>. |
| </li> |
| <li class="listitem"> |
| Optionals: e.g. -p. Match the parser p zero or one time. |
| </li> |
| </ol></div> |
| <p> |
| The complex parser presented above reads as: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| One or two real numbers in parentheses, separated by comma (the second |
| number is optional) |
| </li> |
| <li class="listitem"> |
| <span class="bold"><strong>OR</strong></span> a single real number. |
| </li> |
| </ul></div> |
| <p> |
| This parser can parse complex numbers of the form: |
| </p> |
| <pre class="programlisting"><span class="special">(</span><span class="number">123.45</span><span class="special">,</span> <span class="number">987.65</span><span class="special">)</span> |
| <span class="special">(</span><span class="number">123.45</span><span class="special">)</span> |
| <span class="number">123.45</span> |
| </pre> |
| <p> |
| Here goes, this time with actions: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">client</span> |
| <span class="special">{</span> |
| <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">bool</span> <span class="identifier">parse_complex</span><span class="special">(</span><span class="identifier">Iterator</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">Iterator</span> <span class="identifier">last</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">>&</span> <span class="identifier">c</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">qi</span><span class="special">::</span><span class="identifier">double_</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">qi</span><span class="special">::</span><span class="identifier">_1</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">qi</span><span class="special">::</span><span class="identifier">phrase_parse</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">ascii</span><span class="special">::</span><span class="identifier">space</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">ref</span><span class="special">;</span> |
| |
| <span class="keyword">double</span> <span class="identifier">rN</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">;</span> |
| <span class="keyword">double</span> <span class="identifier">iN</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">;</span> |
| <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">phrase_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="comment">// Begin grammar |
| </span> <span class="special">(</span> |
| <span class="char">'('</span> <span class="special">>></span> <span class="identifier">double_</span><span class="special">[</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">rN</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</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><span class="identifier">ref</span><span class="special">(</span><span class="identifier">iN</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">_1</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><span class="identifier">ref</span><span class="special">(</span><span class="identifier">rN</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> |
| <span class="special">),</span> |
| <span class="comment">// End grammar |
| </span> |
| <span class="identifier">space</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">first</span> <span class="special">!=</span> <span class="identifier">last</span><span class="special">)</span> <span class="comment">// fail if we did not get a full match |
| </span> <span class="keyword">return</span> <span class="keyword">false</span><span class="special">;</span> |
| <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">>(</span><span class="identifier">rN</span><span class="special">,</span> <span class="identifier">iN</span><span class="special">);</span> |
| <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| The full cpp file for this example can be found here: <a href="../../../../../example/qi/complex_number.cpp" target="_top">../../example/qi/complex_number.cpp</a> |
| </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> |
| Those with experience using <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> |
| might be confused with the placeholders that we are using (i.e. <code class="computeroutput"><span class="identifier">_1</span></code>, <code class="computeroutput"><span class="identifier">_2</span></code>, |
| etc.). Please be aware that we are not using the same placeholders supplied |
| by Phoenix. Take note that we are pulling in the placeholders from namespace |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span></code>. These placeholders are specifically |
| tailored for Spirit. |
| </p></td></tr> |
| </table></div> |
| <p> |
| The <code class="computeroutput"><span class="identifier">double_</span></code> parser attaches |
| this action: |
| </p> |
| <pre class="programlisting"><span class="identifier">ref</span><span class="special">(</span><span class="identifier">n</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">_1</span> |
| </pre> |
| <p> |
| This assigns the parsed result (actually, the attribute of <code class="computeroutput"><span class="identifier">double_</span></code>) to n. <code class="computeroutput"><span class="identifier">ref</span><span class="special">(</span><span class="identifier">n</span><span class="special">)</span></code> |
| tells Phoenix that <code class="computeroutput"><span class="identifier">n</span></code> is |
| a mutable reference. <code class="computeroutput"><span class="identifier">_1</span></code> |
| is a Phoenix placeholder for the parsed result attribute. |
| </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 © 2001-2010 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> |
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