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<section id="step-11-adding-export-configuration">
<span id="guide:tutorial/Adding Export Configuration"></span><h1>Step 11: Adding Export Configuration<a class="headerlink" href="#step-11-adding-export-configuration" title="Permalink to this heading">¶</a></h1>
<p>During <a class="reference internal" href="Installing%20and%20Testing.html#guide:tutorial/Installing and Testing" title="tutorial/Installing and Testing"><code class="xref cmake cmake-guide docutils literal notranslate"><span class="pre">Installing</span> <span class="pre">and</span> <span class="pre">Testing</span></code></a> of the tutorial we added the
ability for CMake to install the library and headers of the project. During
<a class="reference internal" href="Packaging%20an%20Installer.html#guide:tutorial/Packaging an Installer" title="tutorial/Packaging an Installer"><code class="xref cmake cmake-guide docutils literal notranslate"><span class="pre">Packaging</span> <span class="pre">an</span> <span class="pre">Installer</span></code></a> we added the ability to package up
this information so it could be distributed to other people.</p>
<p>The next step is to add the necessary information so that other CMake projects
can use our project, be it from a build directory, a local install or when
packaged.</p>
<p>The first step is to update our <span class="target" id="index-0-command:install"></span><a class="reference internal" href="../../command/install.html#command:install" title="install"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">install(TARGETS)</span></code></a> commands to not
only specify a <code class="docutils literal notranslate"><span class="pre">DESTINATION</span></code> but also an <code class="docutils literal notranslate"><span class="pre">EXPORT</span></code>. The <code class="docutils literal notranslate"><span class="pre">EXPORT</span></code> keyword
generates a CMake file containing code to import all targets listed in the
install command from the installation tree. So let's go ahead and explicitly
<code class="docutils literal notranslate"><span class="pre">EXPORT</span></code> the <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> library by updating the <code class="docutils literal notranslate"><span class="pre">install</span></code> command
in <code class="docutils literal notranslate"><span class="pre">MathFunctions/CMakeLists.txt</span></code> to look like:</p>
<div class="literal-block-wrapper docutils container" id="mathfunctions-cmakelists-txt-install-targets-export">
<div class="code-block-caption"><span class="caption-text">MathFunctions/CMakeLists.txt</span><a class="headerlink" href="#mathfunctions-cmakelists-txt-install-targets-export" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">set(</span><span class="nb">installable_libs</span><span class="w"> </span><span class="nb">MathFunctions</span><span class="w"> </span><span class="nb">tutorial_compiler_flags</span><span class="nf">)</span><span class="w"></span>
<span class="nf">if(</span><span class="no">TARGET</span><span class="w"> </span><span class="nb">SqrtLibrary</span><span class="nf">)</span><span class="w"></span>
<span class="w"> </span><span class="nf">list(</span><span class="no">APPEND</span><span class="w"> </span><span class="nb">installable_libs</span><span class="w"> </span><span class="nb">SqrtLibrary</span><span class="nf">)</span><span class="w"></span>
<span class="nf">endif()</span><span class="w"></span>
<span class="nf">install(</span><span class="no">TARGETS</span><span class="w"> </span><span class="o">${</span><span class="nt">installable_libs</span><span class="o">}</span><span class="w"></span>
<span class="w"> </span><span class="no">EXPORT</span><span class="w"> </span><span class="nb">MathFunctionsTargets</span><span class="w"></span>
<span class="w"> </span><span class="no">DESTINATION</span><span class="w"> </span><span class="nb">lib</span><span class="nf">)</span><span class="w"></span>
<span class="c"># install include headers</span>
<span class="nf">install(</span><span class="no">FILES</span><span class="w"> </span><span class="nb">MathFunctions.h</span><span class="w"> </span><span class="no">DESTINATION</span><span class="w"> </span><span class="nb">include</span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>Now that we have <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> being exported, we also need to explicitly
install the generated <code class="docutils literal notranslate"><span class="pre">MathFunctionsTargets.cmake</span></code> file. This is done by
adding the following to the bottom of the top-level <code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code>:</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-install-export">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-install-export" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">install(</span><span class="no">EXPORT</span><span class="w"> </span><span class="nb">MathFunctionsTargets</span><span class="w"></span>
<span class="w"> </span><span class="no">FILE</span><span class="w"> </span><span class="nb">MathFunctionsTargets.cmake</span><span class="w"></span>
<span class="w"> </span><span class="no">DESTINATION</span><span class="w"> </span><span class="na">lib/cmake/MathFunctions</span><span class="w"></span>
<span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>At this point you should try and run CMake. If everything is setup properly
you will see that CMake will generate an error that looks like:</p>
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="go">Target "MathFunctions" INTERFACE_INCLUDE_DIRECTORIES property contains</span>
<span class="go">path:</span>
<span class="go"> "/Users/robert/Documents/CMakeClass/Tutorial/Step11/MathFunctions"</span>
<span class="go">which is prefixed in the source directory.</span>
</pre></div>
</div>
<p>What CMake is trying to say is that during generating the export information
it will export a path that is intrinsically tied to the current machine and
will not be valid on other machines. The solution to this is to update the
<code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> <span class="target" id="index-0-command:target_include_directories"></span><a class="reference internal" href="../../command/target_include_directories.html#command:target_include_directories" title="target_include_directories"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_include_directories()</span></code></a> to understand that it
needs different <code class="docutils literal notranslate"><span class="pre">INTERFACE</span></code> locations when being used from within the build
directory and from an install / package. This means converting the
<span class="target" id="index-1-command:target_include_directories"></span><a class="reference internal" href="../../command/target_include_directories.html#command:target_include_directories" title="target_include_directories"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_include_directories()</span></code></a> call for <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> to look like:</p>
<div class="literal-block-wrapper docutils container" id="mathfunctions-cmakelists-txt-target-include-directories">
<div class="code-block-caption"><span class="caption-text">MathFunctions/CMakeLists.txt</span><a class="headerlink" href="#mathfunctions-cmakelists-txt-target-include-directories" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">target_include_directories(</span><span class="nb">MathFunctions</span><span class="w"></span>
<span class="w"> </span><span class="no">INTERFACE</span><span class="w"></span>
<span class="w"> </span><span class="o">$<</span><span class="no">BUILD_INTERFACE</span><span class="o">:${</span><span class="nt">CMAKE_CURRENT_SOURCE_DIR</span><span class="o">}></span><span class="w"></span>
<span class="w"> </span><span class="o">$<</span><span class="no">INSTALL_INTERFACE</span><span class="o">:</span><span class="nb">include</span><span class="o">></span><span class="w"></span>
<span class="w"> </span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>Once this has been updated, we can re-run CMake and verify that it doesn't
warn anymore.</p>
<p>At this point, we have CMake properly packaging the target information that is
required but we will still need to generate a <code class="docutils literal notranslate"><span class="pre">MathFunctionsConfig.cmake</span></code> so
that the CMake <span class="target" id="index-0-command:find_package"></span><a class="reference internal" href="../../command/find_package.html#command:find_package" title="find_package"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">find_package()</span></code></a> command can find our project. So let's go
ahead and add a new file to the top-level of the project called
<code class="docutils literal notranslate"><span class="pre">Config.cmake.in</span></code> with the following contents:</p>
<div class="literal-block-wrapper docutils container" id="config-cmake-in">
<div class="code-block-caption"><span class="caption-text">Config.cmake.in</span><a class="headerlink" href="#config-cmake-in" title="Permalink to this code">¶</a></div>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>
@PACKAGE_INIT@
include ( "${CMAKE_CURRENT_LIST_DIR}/MathFunctionsTargets.cmake" )
</pre></div>
</div>
</div>
<p>Then, to properly configure and install that file, add the following to the
bottom of the top-level <code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code>:</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-install-config-cmake">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-install-config-cmake" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">install(</span><span class="no">EXPORT</span><span class="w"> </span><span class="nb">MathFunctionsTargets</span><span class="w"></span>
<span class="w"> </span><span class="no">FILE</span><span class="w"> </span><span class="nb">MathFunctionsTargets.cmake</span><span class="w"></span>
<span class="w"> </span><span class="no">DESTINATION</span><span class="w"> </span><span class="na">lib/cmake/MathFunctions</span><span class="w"></span>
<span class="nf">)</span><span class="w"></span>
<span class="nf">include(</span><span class="nb">CMakePackageConfigHelpers</span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>Next, we execute the <span class="target" id="index-0-command:configure_package_config_file"></span><a class="reference internal" href="../../module/CMakePackageConfigHelpers.html#command:configure_package_config_file" title="configure_package_config_file"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">configure_package_config_file()</span></code></a>. This command
will configure a provided file but with a few specific differences from the
standard <span class="target" id="index-0-command:configure_file"></span><a class="reference internal" href="../../command/configure_file.html#command:configure_file" title="configure_file"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">configure_file()</span></code></a> way.
To properly utilize this function, the input file should have a single line
with the text <code class="docutils literal notranslate"><span class="pre">@PACKAGE_INIT@</span></code> in addition to the content that is desired.
That variable will be replaced with a block of code which turns set values into
relative paths. These values which are new can be referenced by the same name
but prepended with a <code class="docutils literal notranslate"><span class="pre">PACKAGE_</span></code> prefix.</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-configure-package-config-cmake">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-configure-package-config-cmake" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">install(</span><span class="no">EXPORT</span><span class="w"> </span><span class="nb">MathFunctionsTargets</span><span class="w"></span>
<span class="w"> </span><span class="no">FILE</span><span class="w"> </span><span class="nb">MathFunctionsTargets.cmake</span><span class="w"></span>
<span class="w"> </span><span class="no">DESTINATION</span><span class="w"> </span><span class="na">lib/cmake/MathFunctions</span><span class="w"></span>
<span class="nf">)</span><span class="w"></span>
<span class="nf">include(</span><span class="nb">CMakePackageConfigHelpers</span><span class="nf">)</span><span class="w"></span>
<span class="c"># generate the config file that includes the exports</span>
<span class="nf">configure_package_config_file(</span><span class="o">${</span><span class="nt">CMAKE_CURRENT_SOURCE_DIR</span><span class="o">}</span><span class="na">/Config.cmake.in</span><span class="w"></span>
<span class="w"> </span><span class="s">"${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfig.cmake"</span><span class="w"></span>
<span class="w"> </span><span class="no">INSTALL_DESTINATION</span><span class="w"> </span><span class="s">"lib/cmake/example"</span><span class="w"></span>
<span class="w"> </span><span class="no">NO_SET_AND_CHECK_MACRO</span><span class="w"></span>
<span class="w"> </span><span class="no">NO_CHECK_REQUIRED_COMPONENTS_MACRO</span><span class="w"></span>
<span class="w"> </span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>The <span class="target" id="index-0-command:write_basic_package_version_file"></span><a class="reference internal" href="../../module/CMakePackageConfigHelpers.html#command:write_basic_package_version_file" title="write_basic_package_version_file"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">write_basic_package_version_file()</span></code></a> is next. This command writes
a file which is used by <span class="target" id="index-1-command:find_package"></span><a class="reference internal" href="../../command/find_package.html#command:find_package" title="find_package"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">find_package()</span></code></a>, documenting the version and
compatibility of the desired package. Here, we use the <code class="docutils literal notranslate"><span class="pre">Tutorial_VERSION_*</span></code>
variables and say that it is compatible with <code class="docutils literal notranslate"><span class="pre">AnyNewerVersion</span></code>, which
denotes that this version or any higher one are compatible with the requested
version.</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-basic-version-file-cmake">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-basic-version-file-cmake" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">write_basic_package_version_file(</span><span class="w"></span>
<span class="w"> </span><span class="s">"${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsConfigVersion.cmake"</span><span class="w"></span>
<span class="w"> </span><span class="no">VERSION</span><span class="w"> </span><span class="s">"${Tutorial_VERSION_MAJOR}.${Tutorial_VERSION_MINOR}"</span><span class="w"></span>
<span class="w"> </span><span class="no">COMPATIBILITY</span><span class="w"> </span><span class="nb">AnyNewerVersion</span><span class="w"></span>
<span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>Finally, set both generated files to be installed:</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-install-configured-files-cmake">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-install-configured-files-cmake" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">install(</span><span class="no">FILES</span><span class="w"></span>
<span class="w"> </span><span class="o">${</span><span class="nt">CMAKE_CURRENT_BINARY_DIR</span><span class="o">}</span><span class="na">/MathFunctionsConfig.cmake</span><span class="w"></span>
<span class="w"> </span><span class="o">${</span><span class="nt">CMAKE_CURRENT_BINARY_DIR</span><span class="o">}</span><span class="na">/MathFunctionsConfigVersion.cmake</span><span class="w"></span>
<span class="w"> </span><span class="no">DESTINATION</span><span class="w"> </span><span class="na">lib/cmake/MathFunctions</span><span class="w"></span>
<span class="w"> </span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>At this point, we have generated a relocatable CMake Configuration for our
project that can be used after the project has been installed or packaged. If
we want our project to also be used from a build directory we only have to add
the following to the bottom of the top level <code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code>:</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-export">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-export" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">export(</span><span class="no">EXPORT</span><span class="w"> </span><span class="nb">MathFunctionsTargets</span><span class="w"></span>
<span class="w"> </span><span class="no">FILE</span><span class="w"> </span><span class="s">"${CMAKE_CURRENT_BINARY_DIR}/MathFunctionsTargets.cmake"</span><span class="w"></span>
<span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>With this export call we now generate a <code class="docutils literal notranslate"><span class="pre">MathFunctionsTargets.cmake</span></code>, allowing the
configured <code class="docutils literal notranslate"><span class="pre">MathFunctionsConfig.cmake</span></code> in the build directory to be used by
other projects, without needing it to be installed.</p>
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