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<title>Sum - adding numbers</title>
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<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="spirit.qi.tutorials.sum___adding_numbers"></a><a class="link" href="sum___adding_numbers.html" title="Sum - adding numbers">Sum - adding
numbers</a>
</h4></div></div></div>
<p>
Here's a parser that sums a comma-separated list of numbers.
</p>
<p>
Ok we've glossed over some details in our previous examples. First, our
includes:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</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">include</span><span class="special">/</span><span class="identifier">qi</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</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">include</span><span class="special">/</span><span class="identifier">phoenix_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</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">include</span><span class="special">/</span><span class="identifier">phoenix_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span>
</pre>
<p>
</p>
<p>
Then some using directives:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">qi</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">qi</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">ascii</span><span class="special">;</span>
<span class="keyword">namespace</span> <span class="identifier">phoenix</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">;</span>
<span class="keyword">using</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">qi</span><span class="special">::</span><span class="identifier">_1</span><span class="special">;</span>
<span class="keyword">using</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">phoenix</span><span class="special">::</span><span class="identifier">ref</span><span class="special">;</span>
</pre>
<p>
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
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<thead><tr>
<th>
<p>
Namespace
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
boost::phoenix
</p>
</td>
<td>
<p>
All of phoenix
</p>
</td>
</tr>
<tr>
<td>
<p>
boost::spirit
</p>
</td>
<td>
<p>
All of spirit
</p>
</td>
</tr>
<tr>
<td>
<p>
boost::spirit::qi
</p>
</td>
<td>
<p>
All of spirit.qi
</p>
</td>
</tr>
<tr>
<td>
<p>
boost::spirit::ascii
</p>
</td>
<td>
<p>
ASCII version of <code class="computeroutput"><span class="identifier">char_</span></code>
and all char related parsers. Other encodings are also provided
(e.g. also an ISO8859.1)
</p>
</td>
</tr>
<tr>
<td>
<p>
boost::spirit::arg_names
</p>
</td>
<td>
<p>
Special phoenix placeholders for spirit
</p>
</td>
</tr>
</tbody>
</table></div>
<div class="note"><table border="0" summary="Note">
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<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 feel uneasy with using whole namespaces, feel free to qualify
your code, use namespace aliases, etc. For the purpose of this tutorial,
we will be presenting unqualified names for both Spirit and <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a>.
No worries, we will always present the full working code, so you won't
get lost. In fact, all examples in this tutorial have a corresponding
cpp file that QuickBook (the documentation tool we are using) imports
in here as code snippets.
</p></td></tr>
</table></div>
<p>
Now the actual parser:
</p>
<p>
</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">bool</span> <span class="identifier">adder</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="keyword">double</span><span class="special">&</span> <span class="identifier">n</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">bool</span> <span class="identifier">r</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="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="identifier">double_</span><span class="special">[</span><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><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">n</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="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">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="keyword">return</span> <span class="identifier">r</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/sum.cpp" target="_top">../../example/qi/sum.cpp</a>
</p>
<p>
This is almost like our original numbers list example. We're incrementally
building on top of our examples. This time though, like in the complex
number example, we'll be adding the smarts. There's an accumulator (<code class="computeroutput"><span class="keyword">double</span><span class="special">&</span> <span class="identifier">n</span></code>) that adds the numbers parsed. On a
successful parse, this number is the sum of all the parsed numbers.
</p>
<p>
The first <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 <code class="computeroutput"><span class="identifier">n</span></code>.
<code class="computeroutput"><span class="identifier">ref</span><span class="special">(</span><span class="identifier">n</span><span class="special">)</span></code> tells
<a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> 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 <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a>
placeholder for the parsed result attribute.
</p>
<p>
The second <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>
So, subsequent numbers add into <code class="computeroutput"><span class="identifier">n</span></code>.
</p>
<p>
That wasn't too bad, was it :-) ?
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2011 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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