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53 lines
2.0 KiB
53 lines
2.0 KiB
3 years ago
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Step 3: Adding Usage Requirements for a Library
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===============================================
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Usage requirements allow for far better control over a library or executable's
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link and include line while also giving more control over the transitive
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property of targets inside CMake. The primary commands that leverage usage
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requirements are:
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- :command:`target_compile_definitions`
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- :command:`target_compile_options`
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- :command:`target_include_directories`
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- :command:`target_link_libraries`
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Let's refactor our code from :guide:`tutorial/Adding a Library` to use the
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modern CMake approach of usage requirements. We first state that anybody
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linking to ``MathFunctions`` needs to include the current source directory,
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while ``MathFunctions`` itself doesn't. So this can become an ``INTERFACE``
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usage requirement.
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Remember ``INTERFACE`` means things that consumers require but the producer
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doesn't. Add the following lines to the end of
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``MathFunctions/CMakeLists.txt``:
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.. literalinclude:: Step4/MathFunctions/CMakeLists.txt
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:caption: MathFunctions/CMakeLists.txt
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:name: MathFunctions/CMakeLists.txt-target_include_directories-INTERFACE
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:language: cmake
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:start-after: # to find MathFunctions.h
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Now that we've specified usage requirements for ``MathFunctions`` we can safely
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remove our uses of the ``EXTRA_INCLUDES`` variable from the top-level
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``CMakeLists.txt``, here:
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.. literalinclude:: Step4/CMakeLists.txt
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-remove-EXTRA_INCLUDES
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:language: cmake
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:start-after: # add the MathFunctions library
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:end-before: # add the executable
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And here:
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.. literalinclude:: Step4/CMakeLists.txt
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-target_include_directories-remove-EXTRA_INCLUDES
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:language: cmake
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:start-after: # so that we will find TutorialConfig.h
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Once this is done, run the :manual:`cmake <cmake(1)>` executable or the
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:manual:`cmake-gui <cmake-gui(1)>` to configure the project and then build it
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with your chosen build tool or by using ``cmake --build .`` from the build
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directory.
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