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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.karma.tutorials.num_list"></a><a class="link" href="num_list.html" title="Number List - Printing Numbers From a std::vector">Number List - Printing |
| Numbers From a std::vector</a> |
| </h4></div></div></div> |
| <a name="spirit.karma.tutorials.num_list.using_the_list_operator"></a><h6> |
| <a name="id962940"></a> |
| <a class="link" href="num_list.html#spirit.karma.tutorials.num_list.using_the_list_operator">Using |
| the List Operator</a> |
| </h6> |
| <p> |
| The C++ Standard library lacks an important feature, namely the support |
| for any formatted output of containers. Sure, it's fairly easy to write |
| a custom routine to output a specific container, but doing so over and |
| over again is tedious at best. In this section we will demonstrate some |
| more of the capabilities of <span class="emphasis"><em>Spirit.Karma</em></span> for generating |
| output from arbitrary STL containers. We will build on the example presented |
| in an earlier section (see <a class="link" href="warming_up.html" title="Warming up">Warming |
| Up</a>). |
| </p> |
| <p> |
| The full source code of the example shown in this section can be found |
| here: <a href="../../../../../example/karma/num_list2.cpp" target="_top">num_list2.cpp</a>. |
| </p> |
| <p> |
| This time we take advantage of Karma's <a class="link" href="../reference/operator/list.html" title="Lists (a % b)">List |
| (<code class="computeroutput"><span class="special">%</span></code>)</a> operator. The semantics |
| of the list operator are fully equivalent to the semantics of the sequence |
| we used before. The generator expression |
| </p> |
| <pre class="programlisting"><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> |
| is semantically equivalent to the generator expression |
| </p> |
| <pre class="programlisting"><span class="identifier">double_</span> <span class="special">%</span> <span class="char">','</span> |
| </pre> |
| <p> |
| simplifying the overall code. The list operator's attribute is compatible |
| with any STL container as well. For a change we use 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">double</span><span class="special">></span></code> instead of the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span></code> we used before. Additionally, the routine |
| <code class="computeroutput"><span class="identifier">generate_numbers</span></code> takes |
| the container as a template parameter, so it will now work with any STL |
| container holding <code class="computeroutput"><span class="keyword">double</span></code> numbers. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">OutputIterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">></span> |
| <span class="keyword">bool</span> <span class="identifier">generate_numbers</span><span class="special">(</span><span class="identifier">OutputIterator</span><span class="special">&</span> <span class="identifier">sink</span><span class="special">,</span> <span class="identifier">Container</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</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">karma</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">karma</span><span class="special">::</span><span class="identifier">generate_delimited</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">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">generate_delimited</span><span class="special">(</span> |
| <span class="identifier">sink</span><span class="special">,</span> <span class="comment">// destination: output iterator |
| </span> <span class="identifier">double_</span> <span class="special">%</span> <span class="char">','</span><span class="special">,</span> <span class="comment">// the generator |
| </span> <span class="identifier">space</span><span class="special">,</span> <span class="comment">// the delimiter-generator |
| </span> <span class="identifier">v</span> <span class="comment">// the data to output |
| </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> |
| <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> |
| Despite the container being a template parameter, the <span class="emphasis"><em>Spirit.Karma</em></span> |
| formatting expression (<code class="computeroutput"><span class="identifier">double_</span> |
| <span class="special">%</span> <span class="char">','</span></code>) |
| does not depend on the actual type of the passed container. The only |
| precondition to be met here is that the elements stored in the container |
| have to be convertible to <code class="computeroutput"><span class="keyword">double</span></code>. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.karma.tutorials.num_list.generate_output_from_arbitrary_data"></a><h6> |
| <a name="id963455"></a> |
| <a class="link" href="num_list.html#spirit.karma.tutorials.num_list.generate_output_from_arbitrary_data">Generate |
| Output from Arbitrary Data</a> |
| </h6> |
| <p> |
| The output routine developed above is still not generically usable for |
| all types of STL containers and for arbitrary elements stored in them. |
| In order to be usable the items stored in the container still need to be |
| convertible to a <code class="computeroutput"><span class="keyword">double</span></code>. Fortunately |
| <span class="emphasis"><em>Spirit.Karma</em></span> is capable to output arbitrary data types |
| while using the same format description expression. It implements the |
| <a class="link" href="../reference/stream.html" title="Stream"><code class="computeroutput"><span class="identifier">stream</span></code></a> |
| generators which are able to consume any attribute type as long as a matching |
| standard streaming operator is defined. I.e. for any attribute type <code class="computeroutput"><span class="identifier">Attrib</span></code> a function: |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span><span class="special">&</span> <span class="keyword">operator</span><span class="special"><<</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span><span class="special">&,</span> <span class="identifier">Attrib</span> <span class="keyword">const</span><span class="special">&);</span> |
| </pre> |
| <p> |
| needs to be available. The <a class="link" href="../reference/stream.html" title="Stream"><code class="computeroutput"><span class="identifier">stream</span></code></a> generator will use the |
| standard streaming operator to generate the output. |
| </p> |
| <p> |
| The following example modifies the code shown above to utilize the <a class="link" href="../reference/stream.html" title="Stream"><code class="computeroutput"><span class="identifier">stream</span></code></a> |
| operator, which makes it compatible with almost any data type. We implement |
| a custom data type <code class="computeroutput"><span class="identifier">complex</span></code> |
| to demonstrate this. The example shows how it is possible to integrate |
| this (or any other) custom data type into the <span class="emphasis"><em>Spirit.Karma</em></span> |
| generator framework. |
| </p> |
| <p> |
| This is the custom data structure together with the required standard streaming |
| operator: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="comment">// a simple complex number representation z = a + bi |
| </span><span class="keyword">struct</span> <span class="identifier">complex</span> |
| <span class="special">{</span> |
| <span class="identifier">complex</span> <span class="special">(</span><span class="keyword">double</span> <span class="identifier">a</span><span class="special">,</span> <span class="keyword">double</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">0.0</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">a</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">b</span><span class="special">)</span> <span class="special">{}</span> |
| |
| <span class="keyword">double</span> <span class="identifier">a</span><span class="special">;</span> |
| <span class="keyword">double</span> <span class="identifier">b</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="comment">// the streaming operator for the type complex |
| </span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span><span class="special">&</span> |
| <span class="keyword">operator</span><span class="special"><<</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ostream</span><span class="special">&</span> <span class="identifier">os</span><span class="special">,</span> <span class="identifier">complex</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">z</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="identifier">os</span> <span class="special"><<</span> <span class="string">"{"</span> <span class="special"><<</span> <span class="identifier">z</span><span class="special">.</span><span class="identifier">a</span> <span class="special"><<</span> <span class="string">","</span> <span class="special"><<</span> <span class="identifier">z</span><span class="special">.</span><span class="identifier">b</span> <span class="special"><<</span> <span class="string">"}"</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">os</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| And this is the actual call to generate the output from a vector of those. |
| This time we interleave the generated output with newline breaks (see |
| <a class="link" href="../reference/auxiliary/eol.html" title="End of Line (eol)"><code class="computeroutput"><span class="identifier">eol</span></code></a>), |
| putting each complex number onto a separate line: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">OutputIterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Container</span><span class="special">></span> |
| <span class="keyword">bool</span> <span class="identifier">generate_numbers</span><span class="special">(</span><span class="identifier">OutputIterator</span><span class="special">&</span> <span class="identifier">sink</span><span class="special">,</span> <span class="identifier">Container</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</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">karma</span><span class="special">::</span><span class="identifier">stream</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">karma</span><span class="special">::</span><span class="identifier">generate</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">karma</span><span class="special">::</span><span class="identifier">eol</span><span class="special">;</span> |
| |
| <span class="keyword">bool</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">generate</span><span class="special">(</span> |
| <span class="identifier">sink</span><span class="special">,</span> <span class="comment">// destination: output iterator |
| </span> <span class="identifier">stream</span> <span class="special">%</span> <span class="identifier">eol</span><span class="special">,</span> <span class="comment">// the generator |
| </span> <span class="identifier">v</span> <span class="comment">// the data to output |
| </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 code shown is fully generic and can be used with any STL container |
| as long as the data items stored in that container implement the standard |
| streaming operator. |
| </p> |
| <p> |
| The full source code of the example presented in this section can be found |
| here: <a href="../../../../../example/karma/num_list3.cpp" target="_top">num_list3.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 © 2001-2010 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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