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  <section id="step-3-adding-usage-requirements-for-a-library">
<span id="guide:tutorial/Adding Usage Requirements for a Library"></span><h1>Step 3: Adding Usage Requirements for a Library<a class="headerlink" href="#step-3-adding-usage-requirements-for-a-library" title="Permalink to this heading">¶</a></h1>
<section id="exercise-1-adding-usage-requirements-for-a-library">
<h2>Exercise 1 - Adding Usage Requirements for a Library<a class="headerlink" href="#exercise-1-adding-usage-requirements-for-a-library" title="Permalink to this heading">¶</a></h2>
<p><a class="reference internal" href="../../manual/cmake-buildsystem.7.html#target-usage-requirements"><span class="std std-ref">Usage requirements</span></a> of a target parameters
allow for far better control over a library or executable's link and include
line while also giving more control over the transitive property of targets
inside CMake. The primary commands that
leverage usage requirements are:</p>
<ul class="simple">
<li><p><span class="target" id="index-0-command:target_compile_definitions"></span><a class="reference internal" href="../../command/target_compile_definitions.html#command:target_compile_definitions" title="target_compile_definitions"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_compile_definitions()</span></code></a></p></li>
<li><p><span class="target" id="index-0-command:target_compile_options"></span><a class="reference internal" href="../../command/target_compile_options.html#command:target_compile_options" title="target_compile_options"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_compile_options()</span></code></a></p></li>
<li><p><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></p></li>
<li><p><span class="target" id="index-0-command:target_link_directories"></span><a class="reference internal" href="../../command/target_link_directories.html#command:target_link_directories" title="target_link_directories"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_link_directories()</span></code></a></p></li>
<li><p><span class="target" id="index-0-command:target_link_options"></span><a class="reference internal" href="../../command/target_link_options.html#command:target_link_options" title="target_link_options"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_link_options()</span></code></a></p></li>
<li><p><span class="target" id="index-0-command:target_precompile_headers"></span><a class="reference internal" href="../../command/target_precompile_headers.html#command:target_precompile_headers" title="target_precompile_headers"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_precompile_headers()</span></code></a></p></li>
<li><p><span class="target" id="index-0-command:target_sources"></span><a class="reference internal" href="../../command/target_sources.html#command:target_sources" title="target_sources"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_sources()</span></code></a></p></li>
</ul>
<section id="goal">
<h3>Goal<a class="headerlink" href="#goal" title="Permalink to this heading">¶</a></h3>
<p>Add usage requirements for a library.</p>
</section>
<section id="helpful-materials">
<h3>Helpful Materials<a class="headerlink" href="#helpful-materials" title="Permalink to this heading">¶</a></h3>
<ul class="simple">
<li><p><span class="target" id="index-0-variable:CMAKE_CURRENT_SOURCE_DIR"></span><a class="reference internal" href="../../variable/CMAKE_CURRENT_SOURCE_DIR.html#variable:CMAKE_CURRENT_SOURCE_DIR" title="CMAKE_CURRENT_SOURCE_DIR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_CURRENT_SOURCE_DIR</span></code></a></p></li>
</ul>
</section>
<section id="files-to-edit">
<h3>Files to Edit<a class="headerlink" href="#files-to-edit" title="Permalink to this heading">¶</a></h3>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">MathFunctions/CMakeLists.txt</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code></p></li>
</ul>
</section>
<section id="getting-started">
<h3>Getting Started<a class="headerlink" href="#getting-started" title="Permalink to this heading">¶</a></h3>
<p>In this exercise, we will refactor our code from
<a class="reference internal" href="Adding%20a%20Library.html#guide:tutorial/Adding a Library" title="tutorial/Adding a Library"><code class="xref cmake cmake-guide docutils literal notranslate"><span class="pre">Adding</span> <span class="pre">a</span> <span class="pre">Library</span></code></a> to use the modern CMake approach. We will
let our library define its own usage requirements so they are passed
transitively to other targets as necessary. In this case, <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code>
will specify any needed include directories itself. Then, the consuming target
<code class="docutils literal notranslate"><span class="pre">Tutorial</span></code> simply needs to link to <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> and not worry about
any additional include directories.</p>
<p>The starting source code is provided in the <code class="docutils literal notranslate"><span class="pre">Step3</span></code> directory. In this
exercise, complete <code class="docutils literal notranslate"><span class="pre">TODO</span> <span class="pre">1</span></code> through <code class="docutils literal notranslate"><span class="pre">TODO</span> <span class="pre">3</span></code>.</p>
<p>First, add a call to <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> in
<code class="docutils literal notranslate"><span class="pre">MathFunctions/CMakeLists</span></code>. Remember that
<span class="target" id="index-1-variable:CMAKE_CURRENT_SOURCE_DIR"></span><a class="reference internal" href="../../variable/CMAKE_CURRENT_SOURCE_DIR.html#variable:CMAKE_CURRENT_SOURCE_DIR" title="CMAKE_CURRENT_SOURCE_DIR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_CURRENT_SOURCE_DIR</span></code></a> is the path to the source directory
currently being processed.</p>
<p>Then, update (and simplify!) the call to
<span class="target" id="index-2-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> in the top-level <code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code>.</p>
</section>
<section id="build-and-run">
<h3>Build and Run<a class="headerlink" href="#build-and-run" title="Permalink to this heading">¶</a></h3>
<p>Make a new directory called <code class="docutils literal notranslate"><span class="pre">Step3_build</span></code>, run the <span class="target" id="index-0-manual:cmake(1)"></span><a class="reference internal" href="../../manual/cmake.1.html#manual:cmake(1)" title="cmake(1)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">cmake</span></code></a> executable or the <span class="target" id="index-0-manual:cmake-gui(1)"></span><a class="reference internal" href="../../manual/cmake-gui.1.html#manual:cmake-gui(1)" title="cmake-gui(1)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">cmake-gui</span></code></a> to
configure the project and then build it with your chosen build tool or by
using <a class="reference internal" href="../../manual/cmake.1.html#cmdoption-cmake-build"><code class="xref std std-option docutils literal notranslate"><span class="pre">cmake</span> <span class="pre">--build</span> <span class="pre">.</span></code></a> from the build directory.
Here's a refresher of what that looks like from the command line:</p>
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="go">mkdir Step3_build</span>
<span class="go">cd Step3_build</span>
<span class="go">cmake ../Step3</span>
<span class="go">cmake --build .</span>
</pre></div>
</div>
<p>Next, use the newly built <code class="docutils literal notranslate"><span class="pre">Tutorial</span></code> and verify that it is working as
expected.</p>
</section>
<section id="solution">
<h3>Solution<a class="headerlink" href="#solution" title="Permalink to this heading">¶</a></h3>
<p>Let's update the code from the previous step to use the modern CMake
approach of usage requirements.</p>
<p>We want to state that anybody linking to <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> needs to include
the current source directory, while <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> itself doesn't. This
can be expressed with an <code class="docutils literal notranslate"><span class="pre">INTERFACE</span></code> usage requirement. Remember
<code class="docutils literal notranslate"><span class="pre">INTERFACE</span></code> means things that consumers require but the producer doesn't.</p>
<p>At the end of <code class="docutils literal notranslate"><span class="pre">MathFunctions/CMakeLists.txt</span></code>, use
<span class="target" id="index-3-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> with the <code class="docutils literal notranslate"><span class="pre">INTERFACE</span></code> keyword, as
follows:</p>
<details><summary>TODO 1: Click to show/hide answer</summary><div class="literal-block-wrapper docutils container" id="mathfunctions-cmakelists-txt-target-include-directories-interface">
<div class="code-block-caption"><span class="caption-text">TODO 1: MathFunctions/CMakeLists.txt</span><a class="headerlink" href="#mathfunctions-cmakelists-txt-target-include-directories-interface" 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="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>
</pre></div>
</div>
</div>
</details><p>Now that we've specified usage requirements for <code class="docutils literal notranslate"><span class="pre">MathFunctions</span></code> we can
safely remove our uses of the <code class="docutils literal notranslate"><span class="pre">EXTRA_INCLUDES</span></code> variable from the top-level
<code class="docutils literal notranslate"><span class="pre">CMakeLists.txt</span></code>, here:</p>
<details><summary>TODO 2: Click to show/hide answer</summary><div class="literal-block-wrapper docutils container" id="cmakelists-txt-remove-extra-includes">
<div class="code-block-caption"><span class="caption-text">TODO 2: CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-remove-extra-includes" title="Permalink to this code">¶</a></div>
<div class="highlight-cmake notranslate"><div class="highlight"><pre><span></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">add_subdirectory(</span><span class="nb">MathFunctions</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="no">EXTRA_LIBS</span><span class="w"> </span><span class="nb">MathFunctions</span><span class="nf">)</span><span class="w"></span>
<span class="nf">endif()</span><span class="w"></span>
</pre></div>
</div>
</div>
</details><p>And here:</p>
<details><summary>TODO 3: Click to show/hide answer</summary><div class="literal-block-wrapper docutils container" id="cmakelists-txt-target-include-directories-remove-extra-includes">
<div class="code-block-caption"><span class="caption-text">TODO 3: CMakeLists.txt</span><a class="headerlink" href="#cmakelists-txt-target-include-directories-remove-extra-includes" 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">Tutorial</span><span class="w"> </span><span class="no">PUBLIC</span><span class="w"></span>
<span class="w">                           </span><span class="s">&quot;${PROJECT_BINARY_DIR}&quot;</span><span class="w"></span>
<span class="w">                           </span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
</div>
</details><p>Notice that with this technique, the only thing our executable target does to
use our library is call <span class="target" id="index-0-command:target_link_libraries"></span><a class="reference internal" href="../../command/target_link_libraries.html#command:target_link_libraries" title="target_link_libraries"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_link_libraries()</span></code></a> with the name
of the library target. In larger projects, the classic method of specifying
library dependencies manually becomes very complicated very quickly.</p>
</section>
</section>
</section>

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    <h3><a href="../../index.html">Table of Contents</a></h3>
    <ul>
<li><a class="reference internal" href="#">Step 3: Adding Usage Requirements for a Library</a><ul>
<li><a class="reference internal" href="#exercise-1-adding-usage-requirements-for-a-library">Exercise 1 - Adding Usage Requirements for a Library</a><ul>
<li><a class="reference internal" href="#goal">Goal</a></li>
<li><a class="reference internal" href="#helpful-materials">Helpful Materials</a></li>
<li><a class="reference internal" href="#files-to-edit">Files to Edit</a></li>
<li><a class="reference internal" href="#getting-started">Getting Started</a></li>
<li><a class="reference internal" href="#build-and-run">Build and Run</a></li>
<li><a class="reference internal" href="#solution">Solution</a></li>
</ul>
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