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  <section id="step-10-selecting-static-or-shared-libraries">
<span id="guide:tutorial/Selecting Static or Shared Libraries"></span><h1>Step 10: Selecting Static or Shared Libraries<a class="headerlink" href="#step-10-selecting-static-or-shared-libraries" title="Permalink to this heading">¶</a></h1>
<p>In this section we will show how the <span class="target" id="index-0-variable:BUILD_SHARED_LIBS"></span><a class="reference internal" href="../../variable/BUILD_SHARED_LIBS.html#variable:BUILD_SHARED_LIBS" title="BUILD_SHARED_LIBS"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">BUILD_SHARED_LIBS</span></code></a> variable can
be used to control the default behavior of <span class="target" id="index-0-command:add_library"></span><a class="reference internal" href="../../command/add_library.html#command:add_library" title="add_library"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">add_library()</span></code></a>,
and allow control over how libraries without an explicit type (<code class="docutils literal notranslate"><span class="pre">STATIC</span></code>,
<code class="docutils literal notranslate"><span class="pre">SHARED</span></code>, <code class="docutils literal notranslate"><span class="pre">MODULE</span></code> or <code class="docutils literal notranslate"><span class="pre">OBJECT</span></code>) are built.</p>
<p>To accomplish this we need to add <span class="target" id="index-1-variable:BUILD_SHARED_LIBS"></span><a class="reference internal" href="../../variable/BUILD_SHARED_LIBS.html#variable:BUILD_SHARED_LIBS" title="BUILD_SHARED_LIBS"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">BUILD_SHARED_LIBS</span></code></a> to the
top-level <code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code>. We use the <span class="target" id="index-0-command:option"></span><a class="reference internal" href="../../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command as it allows
users to optionally select if the value should be <code class="docutils literal notranslate"><span class="pre">ON</span></code> or <code class="docutils literal notranslate"><span class="pre">OFF</span></code>.</p>
<p>Next we are going to refactor <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> to become a real library that
encapsulates using <code class="docutils literal notranslate"><span class="pre">mysqrt</span></code> or <code class="docutils literal notranslate"><span class="pre">sqrt</span></code>, instead of requiring the calling
code to do this logic. This will also mean that <code class="docutils literal notranslate"><span class="pre">USE_MYMATH</span></code> will not control
building <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code>, but instead will control the behavior of this
library.</p>
<p>The first step is to update the starting section of the top-level
<code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code> to look like:</p>
<div class="literal-block-wrapper docutils container" id="cmakelists-txt-option-build-shared-libs">
<div class="code-block-caption"><span class="caption-text">CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-option-build-shared-libs" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">cmake_minimum_required(</span><span class="no">VERSION</span><span class="w"> </span><span class="m">3.15</span><span class="nf">)</span><span class="w"></span>

<span class="c"># set the project name and version</span>
<span class="nf">project(</span><span class="nb">Tutorial</span><span class="w"> </span><span class="no">VERSION</span><span class="w"> </span><span class="m">1.0</span><span class="nf">)</span><span class="w"></span>

<span class="c"># specify the C++ standard</span>
<span class="nf">add_library(</span><span class="nb">tutorial_compiler_flags</span><span class="w"> </span><span class="no">INTERFACE</span><span class="nf">)</span><span class="w"></span>
<span class="nf">target_compile_features(</span><span class="nb">tutorial_compiler_flags</span><span class="w"> </span><span class="no">INTERFACE</span><span class="w"> </span><span class="nb">cxx_std_11</span><span class="nf">)</span><span class="w"></span>

<span class="c"># add compiler warning flags just when building this project via</span>
<span class="c"># the BUILD_INTERFACE genex</span>
<span class="nf">set(</span><span class="nb">gcc_like_cxx</span><span class="w"> </span><span class="s">&quot;$&lt;COMPILE_LANG_AND_ID:CXX,ARMClang,AppleClang,Clang,GNU,LCC&gt;&quot;</span><span class="nf">)</span><span class="w"></span>
<span class="nf">set(</span><span class="nb">msvc_cxx</span><span class="w"> </span><span class="s">&quot;$&lt;COMPILE_LANG_AND_ID:CXX,MSVC&gt;&quot;</span><span class="nf">)</span><span class="w"></span>
<span class="nf">target_compile_options(</span><span class="nb">tutorial_compiler_flags</span><span class="w"> </span><span class="no">INTERFACE</span><span class="w"></span>
<span class="w">  </span><span class="s">&quot;$&lt;${gcc_like_cxx}:$&lt;BUILD_INTERFACE:-Wall;-Wextra;-Wshadow;-Wformat=2;-Wunused&gt;&gt;&quot;</span><span class="w"></span>
<span class="w">  </span><span class="s">&quot;$&lt;${msvc_cxx}:$&lt;BUILD_INTERFACE:-W3&gt;&gt;&quot;</span><span class="w"></span>
<span class="nf">)</span><span class="w"></span>

<span class="c"># control where the static and shared libraries are built so that on windows</span>
<span class="c"># we don&#39;t need to tinker with the path to run the executable</span>
<span class="nf">set(</span><span class="no">CMAKE_ARCHIVE_OUTPUT_DIRECTORY</span><span class="w"> </span><span class="s">&quot;${PROJECT_BINARY_DIR}&quot;</span><span class="nf">)</span><span class="w"></span>
<span class="nf">set(</span><span class="no">CMAKE_LIBRARY_OUTPUT_DIRECTORY</span><span class="w"> </span><span class="s">&quot;${PROJECT_BINARY_DIR}&quot;</span><span class="nf">)</span><span class="w"></span>
<span class="nf">set(</span><span class="no">CMAKE_RUNTIME_OUTPUT_DIRECTORY</span><span class="w"> </span><span class="s">&quot;${PROJECT_BINARY_DIR}&quot;</span><span class="nf">)</span><span class="w"></span>

<span class="nf">option(</span><span class="no">BUILD_SHARED_LIBS</span><span class="w"> </span><span class="s">&quot;Build using shared libraries&quot;</span><span class="w"> </span><span class="no">ON</span><span class="nf">)</span><span class="w"></span>

<span class="c"># configure a header file to pass the version number only</span>
<span class="nf">configure_file(</span><span class="nb">TutorialConfig.h.in</span><span class="w"> </span><span class="nb">TutorialConfig.h</span><span class="nf">)</span><span class="w"></span>

<span class="c"># add the MathFunctions library</span>
<span class="nf">add_subdirectory(</span><span class="nb">MathFunctions</span><span class="nf">)</span><span class="w"></span>

<span class="c"># add the executable</span>
<span class="nf">add_executable(</span><span class="nb">Tutorial</span><span class="w"> </span><span class="nb">tutorial.cxx</span><span class="nf">)</span><span class="w"></span>
<span class="nf">target_link_libraries(</span><span class="nb">Tutorial</span><span class="w"> </span><span class="no">PUBLIC</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>
</pre></div>
</div>
</div>
<p>Now that we have made <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> always be used, we will need to update
the logic of that library. So, in <code class="docutils literal notranslate"><span class="pre">MathFunctions/CMakeLists.txt</span></code> we need to
create a SqrtLibrary that will conditionally be built and installed when
<code class="docutils literal notranslate"><span class="pre">USE_MYMATH</span></code> is enabled. Now, since this is a tutorial, we are going to
explicitly require that SqrtLibrary is built statically.</p>
<p>The end result is that <code class="docutils literal notranslate"><span class="pre">MathFunctions/CMakeLists.txt</span></code> should look like:</p>
<div class="literal-block-wrapper docutils container" id="mathfunctions-cmakelists-txt-add-library-static">
<div class="code-block-caption"><span class="caption-text">MathFunctions/CMakeLists.txt</span><a class="headerlink" href="#mathfunctions-cmakelists-txt-add-library-static" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="c"># add the library that runs</span>
<span class="nf">add_library(</span><span class="nb">MathFunctions</span><span class="w"> </span><span class="nb">MathFunctions.cxx</span><span class="nf">)</span><span class="w"></span>

<span class="c"># state that anybody linking to us needs to include the current source dir</span>
<span class="c"># to find MathFunctions.h, while we don&#39;t.</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="o">${</span><span class="nt">CMAKE_CURRENT_SOURCE_DIR</span><span class="o">}</span><span class="w"></span>
<span class="w">                           </span><span class="nf">)</span><span class="w"></span>

<span class="c"># should we use our own math functions</span>
<span class="nf">option(</span><span class="no">USE_MYMATH</span><span class="w"> </span><span class="s">&quot;Use tutorial provided math implementation&quot;</span><span class="w"> </span><span class="no">ON</span><span class="nf">)</span><span class="w"></span>
<span class="nf">if(</span><span class="no">USE_MYMATH</span><span class="nf">)</span><span class="w"></span>

<span class="w">  </span><span class="nf">target_compile_definitions(</span><span class="nb">MathFunctions</span><span class="w"> </span><span class="no">PRIVATE</span><span class="w"> </span><span class="s">&quot;USE_MYMATH&quot;</span><span class="nf">)</span><span class="w"></span>

<span class="w">  </span><span class="c"># first we add the executable that generates the table</span>
<span class="w">  </span><span class="nf">add_executable(</span><span class="nb">MakeTable</span><span class="w"> </span><span class="nb">MakeTable.cxx</span><span class="nf">)</span><span class="w"></span>
<span class="w">  </span><span class="nf">target_link_libraries(</span><span class="nb">MakeTable</span><span class="w"> </span><span class="no">PRIVATE</span><span class="w"> </span><span class="nb">tutorial_compiler_flags</span><span class="nf">)</span><span class="w"></span>

<span class="w">  </span><span class="c"># add the command to generate the source code</span>
<span class="w">  </span><span class="nf">add_custom_command(</span><span class="w"></span>
<span class="w">    </span><span class="no">OUTPUT</span><span class="w"> </span><span class="o">${</span><span class="nt">CMAKE_CURRENT_BINARY_DIR</span><span class="o">}</span><span class="na">/Table.h</span><span class="w"></span>
<span class="w">    </span><span class="no">COMMAND</span><span class="w"> </span><span class="nb">MakeTable</span><span class="w"> </span><span class="o">${</span><span class="nt">CMAKE_CURRENT_BINARY_DIR</span><span class="o">}</span><span class="na">/Table.h</span><span class="w"></span>
<span class="w">    </span><span class="no">DEPENDS</span><span class="w"> </span><span class="nb">MakeTable</span><span class="w"></span>
<span class="w">    </span><span class="nf">)</span><span class="w"></span>

<span class="w">  </span><span class="c"># library that just does sqrt</span>
<span class="w">  </span><span class="nf">add_library(</span><span class="nb">SqrtLibrary</span><span class="w"> </span><span class="no">STATIC</span><span class="w"></span>
<span class="w">              </span><span class="nb">mysqrt.cxx</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">/Table.h</span><span class="w"></span>
<span class="w">              </span><span class="nf">)</span><span class="w"></span>

<span class="w">  </span><span class="c"># state that we depend on our binary dir to find Table.h</span>
<span class="w">  </span><span class="nf">target_include_directories(</span><span class="nb">SqrtLibrary</span><span class="w"> </span><span class="no">PRIVATE</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="w"></span>
<span class="w">                             </span><span class="nf">)</span><span class="w"></span>

<span class="w">  </span><span class="nf">target_link_libraries(</span><span class="nb">SqrtLibrary</span><span class="w"> </span><span class="no">PUBLIC</span><span class="w"> </span><span class="nb">tutorial_compiler_flags</span><span class="nf">)</span><span class="w"></span>
<span class="w">  </span><span class="nf">target_link_libraries(</span><span class="nb">MathFunctions</span><span class="w"> </span><span class="no">PRIVATE</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">target_link_libraries(</span><span class="nb">MathFunctions</span><span class="w"> </span><span class="no">PUBLIC</span><span class="w"> </span><span class="nb">tutorial_compiler_flags</span><span class="nf">)</span><span class="w"></span>

<span class="c"># define the symbol stating we are using the declspec(dllexport) when</span>
<span class="c"># building on windows</span>
<span class="nf">target_compile_definitions(</span><span class="nb">MathFunctions</span><span class="w"> </span><span class="no">PRIVATE</span><span class="w"> </span><span class="s">&quot;EXPORTING_MYMATH&quot;</span><span class="nf">)</span><span class="w"></span>

<span class="c"># install libs</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="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>Next, update <code class="docutils literal notranslate"><span class="pre">MathFunctions/mysqrt.cxx</span></code> to use the <code class="docutils literal notranslate"><span class="pre">mathfunctions</span></code> and
<code class="docutils literal notranslate"><span class="pre">detail</span></code> namespaces:</p>
<div class="literal-block-wrapper docutils container" id="mathfunctions-mysqrt-cxx-namespace">
<div class="code-block-caption"><span class="caption-text">MathFunctions/mysqrt.cxx</span><a class="headerlink" href="#mathfunctions-mysqrt-cxx-namespace" title="Permalink to this code">¶</a></div>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">&lt;iostream&gt;</span><span class="cp"></span>

<span class="cp">#include</span><span class="w"> </span><span class="cpf">&quot;MathFunctions.h&quot;</span><span class="cp"></span>

<span class="c1">// include the generated table</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf">&quot;Table.h&quot;</span><span class="cp"></span>

<span class="k">namespace</span><span class="w"> </span><span class="nn">mathfunctions</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="k">namespace</span><span class="w"> </span><span class="nn">detail</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="c1">// a hack square root calculation using simple operations</span>
<span class="kt">double</span><span class="w"> </span><span class="nf">mysqrt</span><span class="p">(</span><span class="kt">double</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"></span>
<span class="p">{</span><span class="w"></span>
<span class="w">  </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">x</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w">    </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"></span>
<span class="w">  </span><span class="p">}</span><span class="w"></span>

<span class="w">  </span><span class="c1">// use the table to help find an initial value</span>
<span class="w">  </span><span class="kt">double</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">x</span><span class="p">;</span><span class="w"></span>
<span class="w">  </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">x</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">&amp;&amp;</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">10</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w">    </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;Use the table to help find an initial value &quot;</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span><span class="w"></span>
<span class="w">    </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">sqrtTable</span><span class="p">[</span><span class="k">static_cast</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="p">(</span><span class="n">x</span><span class="p">)];</span><span class="w"></span>
<span class="w">  </span><span class="p">}</span><span class="w"></span>

<span class="w">  </span><span class="c1">// do ten iterations</span>
<span class="w">  </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w">    </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">result</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w">      </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0.1</span><span class="p">;</span><span class="w"></span>
<span class="w">    </span><span class="p">}</span><span class="w"></span>
<span class="w">    </span><span class="kt">double</span><span class="w"> </span><span class="n">delta</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="p">(</span><span class="n">result</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">result</span><span class="p">);</span><span class="w"></span>
<span class="w">    </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mf">0.5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">delta</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">result</span><span class="p">;</span><span class="w"></span>
<span class="w">    </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;Computing sqrt of &quot;</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot; to be &quot;</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span><span class="w"></span>
<span class="w">  </span><span class="p">}</span><span class="w"></span>

<span class="w">  </span><span class="k">return</span><span class="w"> </span><span class="n">result</span><span class="p">;</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>We also need to make some changes in <code class="docutils literal notranslate"><span class="pre">tutorial.cxx</span></code>, so that it no longer
uses <code class="docutils literal notranslate"><span class="pre">USE_MYMATH</span></code>:</p>
<ol class="arabic simple">
<li><p>Always include <code class="docutils literal notranslate"><span class="pre">MathFunctions.h</span></code></p></li>
<li><p>Always use <code class="docutils literal notranslate"><span class="pre">mathfunctions::sqrt</span></code></p></li>
<li><p>Don't include <code class="docutils literal notranslate"><span class="pre">cmath</span></code></p></li>
</ol>
<p>Finally, update <code class="docutils literal notranslate"><span class="pre">MathFunctions/MathFunctions.h</span></code> to use dll export defines:</p>
<div class="literal-block-wrapper docutils container" id="mathfunctions-mathfunctions-h">
<div class="code-block-caption"><span class="caption-text">MathFunctions/MathFunctions.h</span><a class="headerlink" href="#mathfunctions-mathfunctions-h" title="Permalink to this code">¶</a></div>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#if defined(_WIN32)</span>
<span class="cp">#  if defined(EXPORTING_MYMATH)</span>
<span class="cp">#    define DECLSPEC __declspec(dllexport)</span>
<span class="cp">#  else</span>
<span class="cp">#    define DECLSPEC __declspec(dllimport)</span>
<span class="cp">#  endif</span>
<span class="cp">#else </span><span class="c1">// non windows</span>
<span class="cp">#  define DECLSPEC</span>
<span class="cp">#endif</span>

<span class="k">namespace</span><span class="w"> </span><span class="nn">mathfunctions</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="kt">double</span><span class="w"> </span><span class="n">DECLSPEC</span><span class="w"> </span><span class="nf">sqrt</span><span class="p">(</span><span class="kt">double</span><span class="w"> </span><span class="n">x</span><span class="p">);</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</pre></div>
</div>
</div>
<p>At this point, if you build everything, you may notice that linking fails
as we are combining a static library without position independent code with a
library that has position independent code. The solution to this is to
explicitly set the <span class="target" id="index-0-prop_tgt:POSITION_INDEPENDENT_CODE"></span><a class="reference internal" href="../../prop_tgt/POSITION_INDEPENDENT_CODE.html#prop_tgt:POSITION_INDEPENDENT_CODE" title="POSITION_INDEPENDENT_CODE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">POSITION_INDEPENDENT_CODE</span></code></a> target property of
SqrtLibrary to be <code class="docutils literal notranslate"><span class="pre">True</span></code> when building shared libraries.</p>
<div class="literal-block-wrapper docutils container" id="mathfunctions-cmakelists-txt-position-independent-code">
<div class="code-block-caption"><span class="caption-text">MathFunctions/CMakeLists.txt</span><a class="headerlink" href="#mathfunctions-cmakelists-txt-position-independent-code" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="w">  </span><span class="c"># state that SqrtLibrary need PIC when the default is shared libraries</span>
<span class="w">  </span><span class="nf">set_target_properties(</span><span class="nb">SqrtLibrary</span><span class="w"> </span><span class="no">PROPERTIES</span><span class="w"></span>
<span class="w">                        </span><span class="no">POSITION_INDEPENDENT_CODE</span><span class="w"> </span><span class="o">${</span><span class="nt">BUILD_SHARED_LIBS</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><strong>Exercise</strong>: We modified <code class="docutils literal notranslate"><span class="pre">MathFunctions.h</span></code> to use dll export defines.
Using CMake documentation can you find a helper module to simplify this?</p>
</section>


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