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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>5. Building C and C++ Extensions on Windows — Python 3.6.7 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="1. Embedding Python in Another Application" href="embedding.html" /> <link rel="prev" title="4. Building C and C++ Extensions" href="building.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/extending/windows.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="embedding.html" title="1. Embedding Python in Another Application" accesskey="N">next</a> |</li> <li class="right" > <a href="building.html" title="4. Building C and C++ Extensions" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.6.7 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Extending and Embedding the Python Interpreter</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="building-c-and-c-extensions-on-windows"> <span id="building-on-windows"></span><h1>5. Building C and C++ Extensions on Windows<a class="headerlink" href="#building-c-and-c-extensions-on-windows" title="Permalink to this headline">¶</a></h1> <p>This chapter briefly explains how to create a Windows extension module for Python using Microsoft Visual C++, and follows with more detailed background information on how it works. The explanatory material is useful for both the Windows programmer learning to build Python extensions and the Unix programmer interested in producing software which can be successfully built on both Unix and Windows.</p> <p>Module authors are encouraged to use the distutils approach for building extension modules, instead of the one described in this section. You will still need the C compiler that was used to build Python; typically Microsoft Visual C++.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">This chapter mentions a number of filenames that include an encoded Python version number. These filenames are represented with the version number shown as <code class="docutils literal notranslate"><span class="pre">XY</span></code>; in practice, <code class="docutils literal notranslate"><span class="pre">'X'</span></code> will be the major version number and <code class="docutils literal notranslate"><span class="pre">'Y'</span></code> will be the minor version number of the Python release you’re working with. For example, if you are using Python 2.2.1, <code class="docutils literal notranslate"><span class="pre">XY</span></code> will actually be <code class="docutils literal notranslate"><span class="pre">22</span></code>.</p> </div> <div class="section" id="a-cookbook-approach"> <span id="win-cookbook"></span><h2>5.1. A Cookbook Approach<a class="headerlink" href="#a-cookbook-approach" title="Permalink to this headline">¶</a></h2> <p>There are two approaches to building extension modules on Windows, just as there are on Unix: use the <a class="reference internal" href="../library/distutils.html#module-distutils" title="distutils: Support for building and installing Python modules into an existing Python installation."><code class="xref py py-mod docutils literal notranslate"><span class="pre">distutils</span></code></a> package to control the build process, or do things manually. The distutils approach works well for most extensions; documentation on using <a class="reference internal" href="../library/distutils.html#module-distutils" title="distutils: Support for building and installing Python modules into an existing Python installation."><code class="xref py py-mod docutils literal notranslate"><span class="pre">distutils</span></code></a> to build and package extension modules is available in <a class="reference internal" href="../distutils/index.html#distutils-index"><span class="std std-ref">Distributing Python Modules (Legacy version)</span></a>. If you find you really need to do things manually, it may be instructive to study the project file for the <a class="reference external" href="https://github.com/python/cpython/tree/3.6/PCbuild/winsound.vcxproj">winsound</a> standard library module.</p> </div> <div class="section" id="differences-between-unix-and-windows"> <span id="dynamic-linking"></span><h2>5.2. Differences Between Unix and Windows<a class="headerlink" href="#differences-between-unix-and-windows" title="Permalink to this headline">¶</a></h2> <p>Unix and Windows use completely different paradigms for run-time loading of code. Before you try to build a module that can be dynamically loaded, be aware of how your system works.</p> <p>In Unix, a shared object (<code class="file docutils literal notranslate"><span class="pre">.so</span></code>) file contains code to be used by the program, and also the names of functions and data that it expects to find in the program. When the file is joined to the program, all references to those functions and data in the file’s code are changed to point to the actual locations in the program where the functions and data are placed in memory. This is basically a link operation.</p> <p>In Windows, a dynamic-link library (<code class="file docutils literal notranslate"><span class="pre">.dll</span></code>) file has no dangling references. Instead, an access to functions or data goes through a lookup table. So the DLL code does not have to be fixed up at runtime to refer to the program’s memory; instead, the code already uses the DLL’s lookup table, and the lookup table is modified at runtime to point to the functions and data.</p> <p>In Unix, there is only one type of library file (<code class="file docutils literal notranslate"><span class="pre">.a</span></code>) which contains code from several object files (<code class="file docutils literal notranslate"><span class="pre">.o</span></code>). During the link step to create a shared object file (<code class="file docutils literal notranslate"><span class="pre">.so</span></code>), the linker may find that it doesn’t know where an identifier is defined. The linker will look for it in the object files in the libraries; if it finds it, it will include all the code from that object file.</p> <p>In Windows, there are two types of library, a static library and an import library (both called <code class="file docutils literal notranslate"><span class="pre">.lib</span></code>). A static library is like a Unix <code class="file docutils literal notranslate"><span class="pre">.a</span></code> file; it contains code to be included as necessary. An import library is basically used only to reassure the linker that a certain identifier is legal, and will be present in the program when the DLL is loaded. So the linker uses the information from the import library to build the lookup table for using identifiers that are not included in the DLL. When an application or a DLL is linked, an import library may be generated, which will need to be used for all future DLLs that depend on the symbols in the application or DLL.</p> <p>Suppose you are building two dynamic-load modules, B and C, which should share another block of code A. On Unix, you would <em>not</em> pass <code class="file docutils literal notranslate"><span class="pre">A.a</span></code> to the linker for <code class="file docutils literal notranslate"><span class="pre">B.so</span></code> and <code class="file docutils literal notranslate"><span class="pre">C.so</span></code>; that would cause it to be included twice, so that B and C would each have their own copy. In Windows, building <code class="file docutils literal notranslate"><span class="pre">A.dll</span></code> will also build <code class="file docutils literal notranslate"><span class="pre">A.lib</span></code>. You <em>do</em> pass <code class="file docutils literal notranslate"><span class="pre">A.lib</span></code> to the linker for B and C. <code class="file docutils literal notranslate"><span class="pre">A.lib</span></code> does not contain code; it just contains information which will be used at runtime to access A’s code.</p> <p>In Windows, using an import library is sort of like using <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">spam</span></code>; it gives you access to spam’s names, but does not create a separate copy. On Unix, linking with a library is more like <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">spam</span> <span class="pre">import</span> <span class="pre">*</span></code>; it does create a separate copy.</p> </div> <div class="section" id="using-dlls-in-practice"> <span id="win-dlls"></span><h2>5.3. Using DLLs in Practice<a class="headerlink" href="#using-dlls-in-practice" title="Permalink to this headline">¶</a></h2> <p>Windows Python is built in Microsoft Visual C++; using other compilers may or may not work (though Borland seems to). The rest of this section is MSVC++ specific.</p> <p>When creating DLLs in Windows, you must pass <code class="file docutils literal notranslate"><span class="pre">pythonXY.lib</span></code> to the linker. To build two DLLs, spam and ni (which uses C functions found in spam), you could use these commands:</p> <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span> <span class="o">/</span><span class="n">LD</span> <span class="o">/</span><span class="n">I</span><span class="o">/</span><span class="n">python</span><span class="o">/</span><span class="n">include</span> <span class="n">spam</span><span class="p">.</span><span class="n">c</span> <span class="p">..</span><span class="o">/</span><span class="n">libs</span><span class="o">/</span><span class="n">pythonXY</span><span class="p">.</span><span class="n">lib</span> <span class="n">cl</span> <span class="o">/</span><span class="n">LD</span> <span class="o">/</span><span class="n">I</span><span class="o">/</span><span class="n">python</span><span class="o">/</span><span class="n">include</span> <span class="n">ni</span><span class="p">.</span><span class="n">c</span> <span class="n">spam</span><span class="p">.</span><span class="n">lib</span> <span class="p">..</span><span class="o">/</span><span class="n">libs</span><span class="o">/</span><span class="n">pythonXY</span><span class="p">.</span><span class="n">lib</span> </pre></div> </div> <p>The first command created three files: <code class="file docutils literal notranslate"><span class="pre">spam.obj</span></code>, <code class="file docutils literal notranslate"><span class="pre">spam.dll</span></code> and <code class="file docutils literal notranslate"><span class="pre">spam.lib</span></code>. <code class="file docutils literal notranslate"><span class="pre">Spam.dll</span></code> does not contain any Python functions (such as <a class="reference internal" href="../c-api/arg.html#c.PyArg_ParseTuple" title="PyArg_ParseTuple"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyArg_ParseTuple()</span></code></a>), but it does know how to find the Python code thanks to <code class="file docutils literal notranslate"><span class="pre">pythonXY.lib</span></code>.</p> <p>The second command created <code class="file docutils literal notranslate"><span class="pre">ni.dll</span></code> (and <code class="file docutils literal notranslate"><span class="pre">.obj</span></code> and <code class="file docutils literal notranslate"><span class="pre">.lib</span></code>), which knows how to find the necessary functions from spam, and also from the Python executable.</p> <p>Not every identifier is exported to the lookup table. If you want any other modules (including Python) to be able to see your identifiers, you have to say <code class="docutils literal notranslate"><span class="pre">_declspec(dllexport)</span></code>, as in <code class="docutils literal notranslate"><span class="pre">void</span> <span class="pre">_declspec(dllexport)</span> <span class="pre">initspam(void)</span></code> or <code class="docutils literal notranslate"><span class="pre">PyObject</span> <span class="pre">_declspec(dllexport)</span> <span class="pre">*NiGetSpamData(void)</span></code>.</p> <p>Developer Studio will throw in a lot of import libraries that you do not really need, adding about 100K to your executable. To get rid of them, use the Project Settings dialog, Link tab, to specify <em>ignore default libraries</em>. Add the correct <code class="file docutils literal notranslate"><span class="pre">msvcrtxx.lib</span></code> to the list of libraries.</p> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">5. Building C and C++ Extensions on Windows</a><ul> <li><a class="reference internal" href="#a-cookbook-approach">5.1. A Cookbook Approach</a></li> <li><a class="reference internal" href="#differences-between-unix-and-windows">5.2. Differences Between Unix and Windows</a></li> <li><a class="reference internal" href="#using-dlls-in-practice">5.3. Using DLLs in Practice</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="building.html" title="previous chapter">4. Building C and C++ Extensions</a></p> <h4>Next topic</h4> <p class="topless"><a href="embedding.html" title="next chapter">1. Embedding Python in Another Application</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.6/Doc/extending/windows.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="embedding.html" title="1. Embedding Python in Another Application" >next</a> |</li> <li class="right" > <a href="building.html" title="4. 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