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| <span class="target" id="manual:cmake-compile-features(7)"></span><div class="section" id="cmake-compile-features-7"> |
| <h1><a class="toc-backref" href="#id1">cmake-compile-features(7)</a><a class="headerlink" href="#cmake-compile-features-7" title="Permalink to this headline">¶</a></h1> |
| <div class="contents topic" id="contents"> |
| <p class="topic-title first">Contents</p> |
| <ul class="simple"> |
| <li><a class="reference internal" href="#cmake-compile-features-7" id="id1">cmake-compile-features(7)</a><ul> |
| <li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li> |
| <li><a class="reference internal" href="#compile-feature-requirements" id="id3">Compile Feature Requirements</a><ul> |
| <li><a class="reference internal" href="#requiring-language-standards" id="id4">Requiring Language Standards</a></li> |
| <li><a class="reference internal" href="#availability-of-compiler-extensions" id="id5">Availability of Compiler Extensions</a></li> |
| </ul> |
| </li> |
| <li><a class="reference internal" href="#optional-compile-features" id="id6">Optional Compile Features</a></li> |
| <li><a class="reference internal" href="#conditional-compilation-options" id="id7">Conditional Compilation Options</a></li> |
| <li><a class="reference internal" href="#supported-compilers" id="id8">Supported Compilers</a></li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| <div class="section" id="introduction"> |
| <h2><a class="toc-backref" href="#id2">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2> |
| <p>Project source code may depend on, or be conditional on, the availability |
| of certain features of the compiler. There are three use-cases which arise: |
| <a class="reference internal" href="#compile-feature-requirements">Compile Feature Requirements</a>, <a class="reference internal" href="#optional-compile-features">Optional Compile Features</a> |
| and <a class="reference internal" href="#conditional-compilation-options">Conditional Compilation Options</a>.</p> |
| <p>While features are typically specified in programming language standards, |
| CMake provides a primary user interface based on granular handling of |
| the features, not the language standard that introduced the feature.</p> |
| <p>The <span class="target" id="index-0-prop_gbl:CMAKE_C_KNOWN_FEATURES"></span><a class="reference internal" href="../prop_gbl/CMAKE_C_KNOWN_FEATURES.html#prop_gbl:CMAKE_C_KNOWN_FEATURES" title="CMAKE_C_KNOWN_FEATURES"><code class="xref cmake cmake-prop_gbl docutils literal"><span class="pre">CMAKE_C_KNOWN_FEATURES</span></code></a> and |
| <span class="target" id="index-0-prop_gbl:CMAKE_CXX_KNOWN_FEATURES"></span><a class="reference internal" href="../prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html#prop_gbl:CMAKE_CXX_KNOWN_FEATURES" title="CMAKE_CXX_KNOWN_FEATURES"><code class="xref cmake cmake-prop_gbl docutils literal"><span class="pre">CMAKE_CXX_KNOWN_FEATURES</span></code></a> global properties contain all the |
| features known to CMake, regardless of compiler support for the feature. |
| The <span class="target" id="index-0-variable:CMAKE_C_COMPILE_FEATURES"></span><a class="reference internal" href="../variable/CMAKE_C_COMPILE_FEATURES.html#variable:CMAKE_C_COMPILE_FEATURES" title="CMAKE_C_COMPILE_FEATURES"><code class="xref cmake cmake-variable docutils literal"><span class="pre">CMAKE_C_COMPILE_FEATURES</span></code></a> and |
| <span class="target" id="index-0-variable:CMAKE_CXX_COMPILE_FEATURES"></span><a class="reference internal" href="../variable/CMAKE_CXX_COMPILE_FEATURES.html#variable:CMAKE_CXX_COMPILE_FEATURES" title="CMAKE_CXX_COMPILE_FEATURES"><code class="xref cmake cmake-variable docutils literal"><span class="pre">CMAKE_CXX_COMPILE_FEATURES</span></code></a> variables contain all features |
| CMake knows are known to the compiler, regardless of language standard |
| or compile flags needed to use them.</p> |
| <p>Features known to CMake are named mostly following the same convention |
| as the Clang feature test macros. The are some exceptions, such as |
| CMake using <code class="docutils literal"><span class="pre">cxx_final</span></code> and <code class="docutils literal"><span class="pre">cxx_override</span></code> instead of the single |
| <code class="docutils literal"><span class="pre">cxx_override_control</span></code> used by Clang.</p> |
| </div> |
| <div class="section" id="compile-feature-requirements"> |
| <h2><a class="toc-backref" href="#id3">Compile Feature Requirements</a><a class="headerlink" href="#compile-feature-requirements" title="Permalink to this headline">¶</a></h2> |
| <p>Compile feature requirements may be specified with the |
| <span class="target" id="index-0-command:target_compile_features"></span><a class="reference internal" href="../command/target_compile_features.html#command:target_compile_features" title="target_compile_features"><code class="xref cmake cmake-command docutils literal"><span class="pre">target_compile_features()</span></code></a> command. For example, if a target must |
| be compiled with compiler support for the |
| <span class="target" id="index-1-prop_gbl:CMAKE_CXX_KNOWN_FEATURES"></span><a class="reference internal" href="../prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html#prop_gbl:CMAKE_CXX_KNOWN_FEATURES" title="CMAKE_CXX_KNOWN_FEATURES"><code class="xref cmake cmake-prop_gbl docutils literal"><span class="pre">cxx_constexpr</span></code></a> feature:</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">add_library</span><span class="p">(</span><span class="s">mylib</span> <span class="s">requires_constexpr.cpp</span><span class="p">)</span> |
| <span class="nb">target_compile_features</span><span class="p">(</span><span class="s">mylib</span> <span class="s">PRIVATE</span> <span class="s">cxx_constexpr</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>In processing the requirement for the <code class="docutils literal"><span class="pre">cxx_constexpr</span></code> feature, |
| <span class="target" id="index-0-manual:cmake(1)"></span><a class="reference internal" href="cmake.1.html#manual:cmake(1)" title="cmake(1)"><code class="xref cmake cmake-manual docutils literal"><span class="pre">cmake(1)</span></code></a> will ensure that the in-use C++ compiler is capable |
| of the feature, and will add any necessary flags such as <code class="docutils literal"><span class="pre">-std=gnu++11</span></code> |
| to the compile lines of C++ files in the <code class="docutils literal"><span class="pre">mylib</span></code> target. A |
| <code class="docutils literal"><span class="pre">FATAL_ERROR</span></code> is issued if the compiler is not capable of the |
| feature.</p> |
| <p>The exact compile flags and language standard are deliberately not part |
| of the user interface for this use-case. CMake will compute the |
| appropriate compile flags to use by considering the features specified |
| for each target.</p> |
| <p>Such compile flags are added even if the compiler supports the |
| particular feature without the flag. For example, the GNU compiler |
| supports variadic templates (with a warning) even if <code class="docutils literal"><span class="pre">-std=gnu++98</span></code> is |
| used. CMake adds the <code class="docutils literal"><span class="pre">-std=gnu++11</span></code> flag if <code class="docutils literal"><span class="pre">cxx_variadic_templates</span></code> |
| is specified as a requirement.</p> |
| <p>In the above example, <code class="docutils literal"><span class="pre">mylib</span></code> requires <code class="docutils literal"><span class="pre">cxx_constexpr</span></code> when it |
| is built itself, but consumers of <code class="docutils literal"><span class="pre">mylib</span></code> are not required to use a |
| compiler which supports <code class="docutils literal"><span class="pre">cxx_constexpr</span></code>. If the interface of |
| <code class="docutils literal"><span class="pre">mylib</span></code> does require the <code class="docutils literal"><span class="pre">cxx_constexpr</span></code> feature (or any other |
| known feature), that may be specified with the <code class="docutils literal"><span class="pre">PUBLIC</span></code> or |
| <code class="docutils literal"><span class="pre">INTERFACE</span></code> signatures of <span class="target" id="index-1-command:target_compile_features"></span><a class="reference internal" href="../command/target_compile_features.html#command:target_compile_features" title="target_compile_features"><code class="xref cmake cmake-command docutils literal"><span class="pre">target_compile_features()</span></code></a>:</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">add_library</span><span class="p">(</span><span class="s">mylib</span> <span class="s">requires_constexpr.cpp</span><span class="p">)</span> |
| <span class="c"># cxx_constexpr is a usage-requirement</span> |
| <span class="nb">target_compile_features</span><span class="p">(</span><span class="s">mylib</span> <span class="s">PUBLIC</span> <span class="s">cxx_constexpr</span><span class="p">)</span> |
| |
| <span class="c"># main.cpp will be compiled with -std=gnu++11 on GNU for cxx_constexpr.</span> |
| <span class="nb">add_executable</span><span class="p">(</span><span class="s">myexe</span> <span class="s">main.cpp</span><span class="p">)</span> |
| <span class="nb">target_link_libraries</span><span class="p">(</span><span class="s">myexe</span> <span class="s">mylib</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>Feature requirements are evaluated transitively by consuming the link |
| implementation. See <span class="target" id="index-0-manual:cmake-buildsystem(7)"></span><a class="reference internal" href="cmake-buildsystem.7.html#manual:cmake-buildsystem(7)" title="cmake-buildsystem(7)"><code class="xref cmake cmake-manual docutils literal"><span class="pre">cmake-buildsystem(7)</span></code></a> for more on |
| transitive behavior of build properties and usage requirements.</p> |
| <div class="section" id="requiring-language-standards"> |
| <h3><a class="toc-backref" href="#id4">Requiring Language Standards</a><a class="headerlink" href="#requiring-language-standards" title="Permalink to this headline">¶</a></h3> |
| <p>In projects that use a large number of commonly available features from |
| a particular language standard (e.g. C++ 11) one may specify a |
| meta-feature (e.g. <code class="docutils literal"><span class="pre">cxx_std_11</span></code>) that requires use of a compiler mode |
| aware of that standard. This is simpler than specifying all the |
| features individually, but does not guarantee the existence of any |
| particular feature. Diagnosis of use of unsupported features will be |
| delayed until compile time.</p> |
| <p>For example, if C++ 11 features are used extensively in a project’s |
| header files, then clients must use a compiler mode aware of C++ 11 |
| or above. This can be requested with the code:</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">target_compile_features</span><span class="p">(</span><span class="s">mylib</span> <span class="s">PUBLIC</span> <span class="s">cxx_std_11</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>In this example, CMake will ensure the compiler is invoked in a mode |
| that is aware of C++ 11 (or above), adding flags such as |
| <code class="docutils literal"><span class="pre">-std=gnu++11</span></code> if necessary. This applies to sources within <code class="docutils literal"><span class="pre">mylib</span></code> |
| as well as any dependents (that may include headers from <code class="docutils literal"><span class="pre">mylib</span></code>).</p> |
| </div> |
| <div class="section" id="availability-of-compiler-extensions"> |
| <h3><a class="toc-backref" href="#id5">Availability of Compiler Extensions</a><a class="headerlink" href="#availability-of-compiler-extensions" title="Permalink to this headline">¶</a></h3> |
| <p>Because the <span class="target" id="index-0-prop_tgt:CXX_EXTENSIONS"></span><a class="reference internal" href="../prop_tgt/CXX_EXTENSIONS.html#prop_tgt:CXX_EXTENSIONS" title="CXX_EXTENSIONS"><code class="xref cmake cmake-prop_tgt docutils literal"><span class="pre">CXX_EXTENSIONS</span></code></a> target property is <code class="docutils literal"><span class="pre">ON</span></code> by default, |
| CMake uses extended variants of language dialects by default, such as |
| <code class="docutils literal"><span class="pre">-std=gnu++11</span></code> instead of <code class="docutils literal"><span class="pre">-std=c++11</span></code>. That target property may be |
| set to <code class="docutils literal"><span class="pre">OFF</span></code> to use the non-extended variant of the dialect flag. Note |
| that because most compilers enable extensions by default, this could |
| expose cross-platform bugs in user code or in the headers of third-party |
| dependencies.</p> |
| </div> |
| </div> |
| <div class="section" id="optional-compile-features"> |
| <h2><a class="toc-backref" href="#id6">Optional Compile Features</a><a class="headerlink" href="#optional-compile-features" title="Permalink to this headline">¶</a></h2> |
| <p>Compile features may be preferred if available, without creating a hard |
| requirement. For example, a library may provides alternative |
| implementations depending on whether the <code class="docutils literal"><span class="pre">cxx_variadic_templates</span></code> |
| feature is available:</p> |
| <div class="highlight-c++"><div class="highlight"><pre><span></span><span class="cp">#if Foo_COMPILER_CXX_VARIADIC_TEMPLATES</span> |
| <span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I</span><span class="p">,</span> <span class="kt">int</span><span class="p">...</span> <span class="n">Is</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span><span class="p">;</span> |
| |
| <span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span><span class="o"><</span><span class="n">I</span><span class="o">></span> |
| <span class="p">{</span> |
| <span class="k">static</span> <span class="kt">int</span> <span class="n">accumulate</span><span class="p">()</span> |
| <span class="p">{</span> |
| <span class="k">return</span> <span class="n">I</span><span class="p">;</span> |
| <span class="p">}</span> |
| <span class="p">};</span> |
| |
| <span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I</span><span class="p">,</span> <span class="kt">int</span><span class="p">...</span> <span class="n">Is</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span> |
| <span class="p">{</span> |
| <span class="k">static</span> <span class="kt">int</span> <span class="n">accumulate</span><span class="p">()</span> |
| <span class="p">{</span> |
| <span class="k">return</span> <span class="n">I</span> <span class="o">+</span> <span class="n">Interface</span><span class="o"><</span><span class="n">Is</span><span class="p">...</span><span class="o">>::</span><span class="n">accumulate</span><span class="p">();</span> |
| <span class="p">}</span> |
| <span class="p">};</span> |
| <span class="cp">#else</span> |
| <span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I1</span><span class="p">,</span> <span class="kt">int</span> <span class="n">I2</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="kt">int</span> <span class="n">I3</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="kt">int</span> <span class="n">I4</span> <span class="o">=</span> <span class="mi">0</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span> |
| <span class="p">{</span> |
| <span class="k">static</span> <span class="kt">int</span> <span class="n">accumulate</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">I1</span> <span class="o">+</span> <span class="n">I2</span> <span class="o">+</span> <span class="n">I3</span> <span class="o">+</span> <span class="n">I4</span><span class="p">;</span> <span class="p">}</span> |
| <span class="p">};</span> |
| <span class="cp">#endif</span> |
| </pre></div> |
| </div> |
| <p>Such an interface depends on using the correct preprocessor defines for the |
| compiler features. CMake can generate a header file containing such |
| defines using 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"><span class="pre">WriteCompilerDetectionHeader</span></code></a> module. The |
| module contains the <code class="docutils literal"><span class="pre">write_compiler_detection_header</span></code> function which |
| accepts parameters to control the content of the generated header file:</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">write_compiler_detection_header</span><span class="p">(</span> |
| <span class="s">FILE</span> <span class="s2">"${CMAKE_CURRENT_BINARY_DIR}/foo_compiler_detection.h"</span> |
| <span class="s">PREFIX</span> <span class="s">Foo</span> |
| <span class="s">COMPILERS</span> <span class="s">GNU</span> |
| <span class="s">FEATURES</span> |
| <span class="s">cxx_variadic_templates</span> |
| <span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>Such a header file may be used internally in the source code of a project, |
| and it may be installed and used in the interface of library code.</p> |
| <p>For each feature listed in <code class="docutils literal"><span class="pre">FEATURES</span></code>, a preprocessor definition |
| is created in the header file, and defined to either <code class="docutils literal"><span class="pre">1</span></code> or <code class="docutils literal"><span class="pre">0</span></code>.</p> |
| <p>Additionally, some features call for additional defines, such as the |
| <code class="docutils literal"><span class="pre">cxx_final</span></code> and <code class="docutils literal"><span class="pre">cxx_override</span></code> features. Rather than being used in |
| <code class="docutils literal"><span class="pre">#ifdef</span></code> code, the <code class="docutils literal"><span class="pre">final</span></code> keyword is abstracted by a symbol |
| which is defined to either <code class="docutils literal"><span class="pre">final</span></code>, a compiler-specific equivalent, or |
| to empty. That way, C++ code can be written to unconditionally use the |
| symbol, and compiler support determines what it is expanded to:</p> |
| <div class="highlight-c++"><div class="highlight"><pre><span></span><span class="k">struct</span> <span class="n">Interface</span> <span class="p">{</span> |
| <span class="k">virtual</span> <span class="kt">void</span> <span class="n">Execute</span><span class="p">()</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> |
| <span class="p">};</span> |
| |
| <span class="k">struct</span> <span class="n">Concrete</span> <span class="n">Foo_FINAL</span> <span class="p">{</span> |
| <span class="kt">void</span> <span class="n">Execute</span><span class="p">()</span> <span class="n">Foo_OVERRIDE</span><span class="p">;</span> |
| <span class="p">};</span> |
| </pre></div> |
| </div> |
| <p>In this case, <code class="docutils literal"><span class="pre">Foo_FINAL</span></code> will expand to <code class="docutils literal"><span class="pre">final</span></code> if the |
| compiler supports the keyword, or to empty otherwise.</p> |
| <p>In this use-case, the CMake code will wish to enable a particular language |
| standard if available from the compiler. The <span class="target" id="index-0-prop_tgt:CXX_STANDARD"></span><a class="reference internal" href="../prop_tgt/CXX_STANDARD.html#prop_tgt:CXX_STANDARD" title="CXX_STANDARD"><code class="xref cmake cmake-prop_tgt docutils literal"><span class="pre">CXX_STANDARD</span></code></a> |
| target property variable may be set to the desired language standard |
| for a particular target, and the <span class="target" id="index-0-variable:CMAKE_CXX_STANDARD"></span><a class="reference internal" href="../variable/CMAKE_CXX_STANDARD.html#variable:CMAKE_CXX_STANDARD" title="CMAKE_CXX_STANDARD"><code class="xref cmake cmake-variable docutils literal"><span class="pre">CMAKE_CXX_STANDARD</span></code></a> may be |
| set to influence all following targets:</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">write_compiler_detection_header</span><span class="p">(</span> |
| <span class="s">FILE</span> <span class="s2">"${CMAKE_CURRENT_BINARY_DIR}/foo_compiler_detection.h"</span> |
| <span class="s">PREFIX</span> <span class="s">Foo</span> |
| <span class="s">COMPILERS</span> <span class="s">GNU</span> |
| <span class="s">FEATURES</span> |
| <span class="s">cxx_final</span> <span class="s">cxx_override</span> |
| <span class="p">)</span> |
| |
| <span class="c"># Includes foo_compiler_detection.h and uses the Foo_FINAL symbol</span> |
| <span class="c"># which will expand to 'final' if the compiler supports the requested</span> |
| <span class="c"># CXX_STANDARD.</span> |
| <span class="nb">add_library</span><span class="p">(</span><span class="s">foo</span> <span class="s">foo.cpp</span><span class="p">)</span> |
| <span class="nb">set_property</span><span class="p">(</span><span class="s">TARGET</span> <span class="s">foo</span> <span class="s">PROPERTY</span> <span class="s">CXX_STANDARD</span> <span class="s">11</span><span class="p">)</span> |
| |
| <span class="c"># Includes foo_compiler_detection.h and uses the Foo_FINAL symbol</span> |
| <span class="c"># which will expand to 'final' if the compiler supports the feature,</span> |
| <span class="c"># even though CXX_STANDARD is not set explicitly. The requirement of</span> |
| <span class="c"># cxx_constexpr causes CMake to set CXX_STANDARD internally, which</span> |
| <span class="c"># affects the compile flags.</span> |
| <span class="nb">add_library</span><span class="p">(</span><span class="s">foo_impl</span> <span class="s">foo_impl.cpp</span><span class="p">)</span> |
| <span class="nb">target_compile_features</span><span class="p">(</span><span class="s">foo_impl</span> <span class="s">PRIVATE</span> <span class="s">cxx_constexpr</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>The <code class="docutils literal"><span class="pre">write_compiler_detection_header</span></code> function also creates compatibility |
| code for other features which have standard equivalents. For example, the |
| <code class="docutils literal"><span class="pre">cxx_static_assert</span></code> feature is emulated with a template and abstracted |
| via the <code class="docutils literal"><span class="pre"><PREFIX>_STATIC_ASSERT</span></code> and <code class="docutils literal"><span class="pre"><PREFIX>_STATIC_ASSERT_MSG</span></code> |
| function-macros.</p> |
| </div> |
| <div class="section" id="conditional-compilation-options"> |
| <h2><a class="toc-backref" href="#id7">Conditional Compilation Options</a><a class="headerlink" href="#conditional-compilation-options" title="Permalink to this headline">¶</a></h2> |
| <p>Libraries may provide entirely different header files depending on |
| requested compiler features.</p> |
| <p>For example, a header at <code class="docutils literal"><span class="pre">with_variadics/interface.h</span></code> may contain:</p> |
| <div class="highlight-c++"><div class="highlight"><pre><span></span><span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I</span><span class="p">,</span> <span class="kt">int</span><span class="p">...</span> <span class="n">Is</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span><span class="p">;</span> |
| |
| <span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span><span class="o"><</span><span class="n">I</span><span class="o">></span> |
| <span class="p">{</span> |
| <span class="k">static</span> <span class="kt">int</span> <span class="n">accumulate</span><span class="p">()</span> |
| <span class="p">{</span> |
| <span class="k">return</span> <span class="n">I</span><span class="p">;</span> |
| <span class="p">}</span> |
| <span class="p">};</span> |
| |
| <span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I</span><span class="p">,</span> <span class="kt">int</span><span class="p">...</span> <span class="n">Is</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span> |
| <span class="p">{</span> |
| <span class="k">static</span> <span class="kt">int</span> <span class="n">accumulate</span><span class="p">()</span> |
| <span class="p">{</span> |
| <span class="k">return</span> <span class="n">I</span> <span class="o">+</span> <span class="n">Interface</span><span class="o"><</span><span class="n">Is</span><span class="p">...</span><span class="o">>::</span><span class="n">accumulate</span><span class="p">();</span> |
| <span class="p">}</span> |
| <span class="p">};</span> |
| </pre></div> |
| </div> |
| <p>while a header at <code class="docutils literal"><span class="pre">no_variadics/interface.h</span></code> may contain:</p> |
| <div class="highlight-c++"><div class="highlight"><pre><span></span><span class="k">template</span><span class="o"><</span><span class="kt">int</span> <span class="n">I1</span><span class="p">,</span> <span class="kt">int</span> <span class="n">I2</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="kt">int</span> <span class="n">I3</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="kt">int</span> <span class="n">I4</span> <span class="o">=</span> <span class="mi">0</span><span class="o">></span> |
| <span class="k">struct</span> <span class="n">Interface</span> |
| <span class="p">{</span> |
| <span class="k">static</span> <span class="kt">int</span> <span class="n">accumulate</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">I1</span> <span class="o">+</span> <span class="n">I2</span> <span class="o">+</span> <span class="n">I3</span> <span class="o">+</span> <span class="n">I4</span><span class="p">;</span> <span class="p">}</span> |
| <span class="p">};</span> |
| </pre></div> |
| </div> |
| <p>It would be possible to write a abstraction <code class="docutils literal"><span class="pre">interface.h</span></code> header |
| containing something like:</p> |
| <div class="highlight-c++"><div class="highlight"><pre><span></span><span class="cp">#include</span> <span class="cpf">"foo_compiler_detection.h"</span><span class="cp"></span> |
| <span class="cp">#if Foo_COMPILER_CXX_VARIADIC_TEMPLATES</span> |
| <span class="cp">#include</span> <span class="cpf">"with_variadics/interface.h"</span><span class="cp"></span> |
| <span class="cp">#else</span> |
| <span class="cp">#include</span> <span class="cpf">"no_variadics/interface.h"</span><span class="cp"></span> |
| <span class="cp">#endif</span> |
| </pre></div> |
| </div> |
| <p>However this could be unmaintainable if there are many files to |
| abstract. What is needed is to use alternative include directories |
| depending on the compiler capabilities.</p> |
| <p>CMake provides a <code class="docutils literal"><span class="pre">COMPILE_FEATURES</span></code> |
| <span class="target" id="index-0-manual:cmake-generator-expressions(7)"></span><a class="reference internal" href="cmake-generator-expressions.7.html#manual:cmake-generator-expressions(7)" title="cmake-generator-expressions(7)"><code class="xref cmake cmake-manual docutils literal"><span class="pre">generator</span> <span class="pre">expression</span></code></a> to implement |
| such conditions. This may be used with the build-property commands such as |
| <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"><span class="pre">target_include_directories()</span></code></a> and <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"><span class="pre">target_link_libraries()</span></code></a> |
| to set the appropriate <span class="target" id="index-1-manual:cmake-buildsystem(7)"></span><a class="reference internal" href="cmake-buildsystem.7.html#manual:cmake-buildsystem(7)" title="cmake-buildsystem(7)"><code class="xref cmake cmake-manual docutils literal"><span class="pre">buildsystem</span></code></a> |
| properties:</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">add_library</span><span class="p">(</span><span class="s">foo</span> <span class="s">INTERFACE</span><span class="p">)</span> |
| <span class="nb">set</span><span class="p">(</span><span class="s">with_variadics</span> <span class="o">${</span><span class="nv">CMAKE_CURRENT_SOURCE_DIR</span><span class="o">}</span><span class="s">/with_variadics</span><span class="p">)</span> |
| <span class="nb">set</span><span class="p">(</span><span class="s">no_variadics</span> <span class="o">${</span><span class="nv">CMAKE_CURRENT_SOURCE_DIR</span><span class="o">}</span><span class="s">/no_variadics</span><span class="p">)</span> |
| <span class="nb">target_include_directories</span><span class="p">(</span><span class="s">foo</span> |
| <span class="s">INTERFACE</span> |
| <span class="s2">"$<$<COMPILE_FEATURES:cxx_variadic_templates>:${with_variadics}>"</span> |
| <span class="s2">"$<$<NOT:$<COMPILE_FEATURES:cxx_variadic_templates>>:${no_variadics}>"</span> |
| <span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>Consuming code then simply links to the <code class="docutils literal"><span class="pre">foo</span></code> target as usual and uses |
| the feature-appropriate include directory</p> |
| <div class="highlight-cmake"><div class="highlight"><pre><span></span><span class="nb">add_executable</span><span class="p">(</span><span class="s">consumer_with</span> <span class="s">consumer_with.cpp</span><span class="p">)</span> |
| <span class="nb">target_link_libraries</span><span class="p">(</span><span class="s">consumer_with</span> <span class="s">foo</span><span class="p">)</span> |
| <span class="nb">set_property</span><span class="p">(</span><span class="s">TARGET</span> <span class="s">consumer_with</span> <span class="s">CXX_STANDARD</span> <span class="s">11</span><span class="p">)</span> |
| |
| <span class="nb">add_executable</span><span class="p">(</span><span class="s">consumer_no</span> <span class="s">consumer_no.cpp</span><span class="p">)</span> |
| <span class="nb">target_link_libraries</span><span class="p">(</span><span class="s">consumer_no</span> <span class="s">foo</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="supported-compilers"> |
| <h2><a class="toc-backref" href="#id8">Supported Compilers</a><a class="headerlink" href="#supported-compilers" title="Permalink to this headline">¶</a></h2> |
| <p>CMake is currently aware of the <span class="target" id="index-1-prop_tgt:CXX_STANDARD"></span><a class="reference internal" href="../prop_tgt/CXX_STANDARD.html#prop_tgt:CXX_STANDARD" title="CXX_STANDARD"><code class="xref cmake cmake-prop_tgt docutils literal"><span class="pre">C++</span> <span class="pre">standards</span></code></a> |
| and <span class="target" id="index-2-prop_gbl:CMAKE_CXX_KNOWN_FEATURES"></span><a class="reference internal" href="../prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html#prop_gbl:CMAKE_CXX_KNOWN_FEATURES" title="CMAKE_CXX_KNOWN_FEATURES"><code class="xref cmake cmake-prop_gbl docutils literal"><span class="pre">compile</span> <span class="pre">features</span></code></a> available from |
| the following <span class="target" id="index-0-variable:CMAKE_<LANG>_COMPILER_ID"></span><a class="reference internal" href="../variable/CMAKE_LANG_COMPILER_ID.html#variable:CMAKE_<LANG>_COMPILER_ID" title="CMAKE_<LANG>_COMPILER_ID"><code class="xref cmake cmake-variable docutils literal"><span class="pre">compiler</span> <span class="pre">ids</span></code></a> as of the |
| versions specified for each:</p> |
| <ul class="simple"> |
| <li><code class="docutils literal"><span class="pre">AppleClang</span></code>: Apple Clang for Xcode versions 4.4 though 6.2.</li> |
| <li><code class="docutils literal"><span class="pre">Clang</span></code>: Clang compiler versions 2.9 through 3.4.</li> |
| <li><code class="docutils literal"><span class="pre">GNU</span></code>: GNU compiler versions 4.4 through 5.0.</li> |
| <li><code class="docutils literal"><span class="pre">MSVC</span></code>: Microsoft Visual Studio versions 2010 through 2015.</li> |
| <li><code class="docutils literal"><span class="pre">SunPro</span></code>: Oracle SolarisStudio version 12.4.</li> |
| <li><code class="docutils literal"><span class="pre">Intel</span></code>: Intel compiler versions 12.1 through 17.0.</li> |
| </ul> |
| <p>CMake is currently aware of the <span class="target" id="index-0-prop_tgt:C_STANDARD"></span><a class="reference internal" href="../prop_tgt/C_STANDARD.html#prop_tgt:C_STANDARD" title="C_STANDARD"><code class="xref cmake cmake-prop_tgt docutils literal"><span class="pre">C</span> <span class="pre">standards</span></code></a> |
| and <span class="target" id="index-1-prop_gbl:CMAKE_C_KNOWN_FEATURES"></span><a class="reference internal" href="../prop_gbl/CMAKE_C_KNOWN_FEATURES.html#prop_gbl:CMAKE_C_KNOWN_FEATURES" title="CMAKE_C_KNOWN_FEATURES"><code class="xref cmake cmake-prop_gbl docutils literal"><span class="pre">compile</span> <span class="pre">features</span></code></a> available from |
| the following <span class="target" id="index-1-variable:CMAKE_<LANG>_COMPILER_ID"></span><a class="reference internal" href="../variable/CMAKE_LANG_COMPILER_ID.html#variable:CMAKE_<LANG>_COMPILER_ID" title="CMAKE_<LANG>_COMPILER_ID"><code class="xref cmake cmake-variable docutils literal"><span class="pre">compiler</span> <span class="pre">ids</span></code></a> as of the |
| versions specified for each:</p> |
| <ul class="simple"> |
| <li>all compilers and versions listed above for C++</li> |
| <li><code class="docutils literal"><span class="pre">GNU</span></code>: GNU compiler versions 3.4 through 5.0.</li> |
| </ul> |
| <p>CMake is currently aware of the <span class="target" id="index-0-prop_tgt:CUDA_STANDARD"></span><a class="reference internal" href="../prop_tgt/CUDA_STANDARD.html#prop_tgt:CUDA_STANDARD" title="CUDA_STANDARD"><code class="xref cmake cmake-prop_tgt docutils literal"><span class="pre">CUDA</span> <span class="pre">standards</span></code></a> |
| from the following <span class="target" id="index-2-variable:CMAKE_<LANG>_COMPILER_ID"></span><a class="reference internal" href="../variable/CMAKE_LANG_COMPILER_ID.html#variable:CMAKE_<LANG>_COMPILER_ID" title="CMAKE_<LANG>_COMPILER_ID"><code class="xref cmake cmake-variable docutils literal"><span class="pre">compiler</span> <span class="pre">ids</span></code></a> as of the |
| versions specified for each:</p> |
| <ul class="simple"> |
| <li><code class="docutils literal"><span class="pre">NVIDIA</span></code>: NVIDIA nvcc compiler 7.5 though 8.0.</li> |
| </ul> |
| </div> |
| </div> |
| |
| |
| </div> |
| </div> |
| </div> |
| <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> |
| <div class="sphinxsidebarwrapper"> |
| <h3><a href="../index.html">Table Of Contents</a></h3> |
| <ul> |
| <li><a class="reference internal" href="#">cmake-compile-features(7)</a><ul> |
| <li><a class="reference internal" href="#introduction">Introduction</a></li> |
| <li><a class="reference internal" href="#compile-feature-requirements">Compile Feature Requirements</a><ul> |
| <li><a class="reference internal" href="#requiring-language-standards">Requiring Language Standards</a></li> |
| <li><a class="reference internal" href="#availability-of-compiler-extensions">Availability of Compiler Extensions</a></li> |
| </ul> |
| </li> |
| <li><a class="reference internal" href="#optional-compile-features">Optional Compile Features</a></li> |
| <li><a class="reference internal" href="#conditional-compilation-options">Conditional Compilation Options</a></li> |
| <li><a class="reference internal" href="#supported-compilers">Supported Compilers</a></li> |
| </ul> |
| </li> |
| </ul> |
| |
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