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- <title>How can I wrap functions which take C++ containers as arguments?</title>
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- <div class="titlepage"><div><div><h3 class="title">
- <a name="faq.how_can_i_wrap_functions_which_t"></a><a class="link" href="how_can_i_wrap_functions_which_t.html" title="How can I wrap functions which take C++ containers as arguments?">How can I wrap
- functions which take C++ containers as arguments?</a>
- </h3></div></div></div>
- <p>
- Ralf W. Grosse-Kunstleve provides these notes:
- </p>
- <div class="orderedlist"><ol class="orderedlist" type="1">
- <li class="listitem">
- <p class="simpara">
- Using the regular <code class="computeroutput"><span class="identifier">class_</span><span class="special"><></span></code> wrapper:
- </p>
- <pre class="programlisting"><span class="identifier">class_</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">double</span><span class="special">></span> <span class="special">>(</span><span class="string">"std_vector_double"</span><span class="special">)</span>
- <span class="special">.</span><span class="identifier">def</span><span class="special">(...)</span>
- <span class="special">...</span>
- <span class="special">;</span>
- </pre>
- <p class="simpara">
- This can be moved to a template so that several types (<code class="computeroutput"><span class="keyword">double</span></code>, <code class="computeroutput"><span class="keyword">int</span></code>,
- <code class="computeroutput"><span class="keyword">long</span></code>, etc.) can be wrapped
- with the same code. This technique is used in the file <code class="computeroutput"><span class="identifier">scitbx</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">scitbx</span><span class="special">/</span><span class="identifier">array_family</span><span class="special">/</span><span class="identifier">boost_python</span><span class="special">/</span><span class="identifier">flex_wrapper</span><span class="special">.</span><span class="identifier">h</span></code> in the "scitbx" package.
- The file could easily be modified for wrapping <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><></span></code> instantiations. This type of
- C++/Python binding is most suitable for containers that may contain a
- large number of elements (>10000).
- </p>
- </li>
- <li class="listitem">
- <p class="simpara">
- Using custom rvalue converters. Boost.Python "rvalue converters"
- match function signatures such as:
- </p>
- <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</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">double</span><span class="special">></span> <span class="keyword">const</span> <span class="special">&</span><span class="identifier">array</span><span class="special">);</span> <span class="comment">// pass by const-reference</span>
- <span class="keyword">void</span> <span class="identifier">foo</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">double</span><span class="special">></span> <span class="identifier">array</span><span class="special">);</span> <span class="comment">// pass by value</span>
- </pre>
- <p class="simpara">
- Some custom rvalue converters are implemented in the file <code class="computeroutput"><span class="identifier">scitbx</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">scitbx</span><span class="special">/</span><span class="identifier">boost_python</span><span class="special">/</span><span class="identifier">container_conversions</span><span class="special">.</span><span class="identifier">h</span></code> This code can be used to convert
- from C++ container types such as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><></span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special"><></span></code> to Python tuples and vice versa.
- A few simple examples can be found in the file <code class="computeroutput"><span class="identifier">scitbx</span><span class="special">/</span><span class="identifier">array_family</span><span class="special">/</span><span class="identifier">boost_python</span><span class="special">/</span><span class="identifier">regression_test_module</span><span class="special">.</span><span class="identifier">cpp</span></code>
- Automatic C++ container <-> Python tuple conversions are most suitable
- for containers of moderate size. These converters generate significantly
- less object code compared to alternative 1 above.
- </p>
- </li>
- </ol></div>
- <p>
- A disadvantage of using alternative 2 is that operators such as arithmetic
- +,-,*,/,% are not available. It would be useful to have custom rvalue converters
- that convert to a "math_array" type instead of tuples. This is
- currently not implemented but is possible within the framework of Boost.Python
- V2 as it will be released in the next couple of weeks. [ed.: this was posted
- on 2002/03/10]
- </p>
- <p>
- It would also be useful to also have "custom lvalue converters"
- such as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><></span></code>
- <-> Python list. These converters would support the modification of
- the Python list from C++. For example:
- </p>
- <p>
- C++:
- </p>
- <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</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">double</span><span class="special">></span> <span class="special">&</span><span class="identifier">array</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="keyword">for</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span><span class="special">=</span><span class="number">0</span><span class="special">;</span><span class="identifier">i</span><span class="special">&</span><span class="identifier">lt</span><span class="special">;</span><span class="identifier">array</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span><span class="identifier">i</span><span class="special">++)</span> <span class="special">{</span>
- <span class="identifier">array</span><span class="special">[</span><span class="identifier">i</span><span class="special">]</span> <span class="special">*=</span> <span class="number">2</span><span class="special">;</span>
- <span class="special">}</span>
- <span class="special">}</span>
- </pre>
- <p>
- Python:
- </p>
- <pre class="programlisting"><span class="special">>>></span> <span class="identifier">l</span> <span class="special">=</span> <span class="special">[</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">]</span>
- <span class="special">>>></span> <span class="identifier">foo</span><span class="special">(</span><span class="identifier">l</span><span class="special">)</span>
- <span class="special">>>></span> <span class="keyword">print</span> <span class="identifier">l</span>
- <span class="special">[</span><span class="number">2</span><span class="special">,</span> <span class="number">4</span><span class="special">,</span> <span class="number">6</span><span class="special">]</span>
- </pre>
- <p>
- Custom lvalue converters require changes to the Boost.Python core library
- and are currently not available.
- </p>
- <p>
- P.S.:
- </p>
- <p>
- The "scitbx" files referenced above are available via anonymous
- CVS:
- </p>
- <pre class="programlisting"><span class="identifier">cvs</span> <span class="special">-</span><span class="identifier">d</span><span class="special">:</span><span class="identifier">pserver</span><span class="special">:</span><span class="identifier">anonymous</span><span class="error">@</span><span class="identifier">cvs</span><span class="special">.</span><span class="identifier">cctbx</span><span class="special">.</span><span class="identifier">sourceforge</span><span class="special">.</span><span class="identifier">net</span><span class="special">:/</span><span class="identifier">cvsroot</span><span class="special">/</span><span class="identifier">cctbx</span> <span class="identifier">login</span>
- <span class="identifier">cvs</span> <span class="special">-</span><span class="identifier">d</span><span class="special">:</span><span class="identifier">pserver</span><span class="special">:</span><span class="identifier">anonymous</span><span class="error">@</span><span class="identifier">cvs</span><span class="special">.</span><span class="identifier">cctbx</span><span class="special">.</span><span class="identifier">sourceforge</span><span class="special">.</span><span class="identifier">net</span><span class="special">:/</span><span class="identifier">cvsroot</span><span class="special">/</span><span class="identifier">cctbx</span> <span class="identifier">co</span> <span class="identifier">scitbx</span>
- </pre>
- </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 © 2002-2015 David
- Abrahams, Stefan Seefeld<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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