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| <div class="section" id="cmp0120"> |
| <span id="policy:CMP0120"></span><h1>CMP0120<a class="headerlink" href="#cmp0120" title="Permalink to this headline">ΒΆ</a></h1> |
| <div class="versionadded"> |
| <p><span class="versionmodified added">New in version 3.20.</span></p> |
| </div> |
| <p>The <span class="target" id="index-0-module:WriteCompilerDetectionHeader"></span><a class="reference internal" href="../module/WriteCompilerDetectionHeader.html#module:WriteCompilerDetectionHeader" title="WriteCompilerDetectionHeader"><code class="xref cmake cmake-module docutils literal notranslate"><span class="pre">WriteCompilerDetectionHeader</span></code></a> module is removed.</p> |
| <p>CMake versions 3.1 through 3.19 provide this module to generate a |
| C++ compatibility layer by re-using information from CMake's table of |
| preprocessor checks for <span class="target" id="index-0-manual:cmake-compile-features(7)"></span><a class="reference internal" href="../manual/cmake-compile-features.7.html#manual:cmake-compile-features(7)" title="cmake-compile-features(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">cmake-compile-features(7)</span></code></a>. However:</p> |
| <ul class="simple"> |
| <li><p>Those granular features have been superseded by meta-features for |
| <a class="reference internal" href="../manual/cmake-compile-features.7.html#requiring-language-standards"><span class="std std-ref">Requiring Language Standards</span></a> such as <code class="docutils literal notranslate"><span class="pre">cxx_std_11</span></code>. Therefore |
| no new granular feature checks will be added and projects will need to |
| use other means to conditionally use new C++ features.</p></li> |
| <li><p>The module exposes some of CMake's implementation details directly |
| to C++ translation units.</p></li> |
| <li><p>The module's approach effectively provides a header file with CMake, |
| thus tying the version of the header to the version of CMake. |
| Many projects found that the <span class="target" id="index-1-module:WriteCompilerDetectionHeader"></span><a class="reference internal" href="../module/WriteCompilerDetectionHeader.html#module:WriteCompilerDetectionHeader" title="WriteCompilerDetectionHeader"><code class="xref cmake cmake-module docutils literal notranslate"><span class="pre">WriteCompilerDetectionHeader</span></code></a> was |
| best used by manually generating its header locally with a recent version |
| of CMake and then bundling it with the project source so that it could |
| be used with older CMake versions.</p></li> |
| </ul> |
| <p>For reasons including the above, CMake 3.20 and above prefer to not |
| provide the <span class="target" id="index-2-module:WriteCompilerDetectionHeader"></span><a class="reference internal" href="../module/WriteCompilerDetectionHeader.html#module:WriteCompilerDetectionHeader" title="WriteCompilerDetectionHeader"><code class="xref cmake cmake-module docutils literal notranslate"><span class="pre">WriteCompilerDetectionHeader</span></code></a> module. This policy |
| provides compatibility for projects that have not been ported away from |
| it. Projects using the module should be updated to stop using it. |
| Alternatives include:</p> |
| <ul class="simple"> |
| <li><p>Bundle a copy of the generated header in the project's source.</p></li> |
| <li><p>Use a third-party alternative, such as the CC0-licensed <a class="reference external" href="https://nemequ.github.io/hedley/">Hedley</a>.</p></li> |
| <li><p>Drop support for compilers too old to provide the features natively.</p></li> |
| </ul> |
| <p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of this policy is for inclusion of the deprecated |
| <span class="target" id="index-3-module:WriteCompilerDetectionHeader"></span><a class="reference internal" href="../module/WriteCompilerDetectionHeader.html#module:WriteCompilerDetectionHeader" title="WriteCompilerDetectionHeader"><code class="xref cmake cmake-module docutils literal notranslate"><span class="pre">WriteCompilerDetectionHeader</span></code></a> module to work. The <code class="docutils literal notranslate"><span class="pre">NEW</span></code> |
| behavior is for inclusion of the module to fail as if it does not exist.</p> |
| <p>This policy was introduced in CMake version 3.20. CMake version 3.23.1 |
| warns when the policy is not set and uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior. Use the |
| <span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> command to set it to <code class="docutils literal notranslate"><span class="pre">OLD</span></code> or <code class="docutils literal notranslate"><span class="pre">NEW</span></code> explicitly.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is |
| <span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a> |
| and may be removed in a future version of CMake.</p> |
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| title="previous chapter">CMP0121</a></p> |
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