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51 lines
2.1 KiB
51 lines
2.1 KiB
Step 10: Selecting Static or Shared Libraries
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=============================================
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In this section we will show how the :variable:`BUILD_SHARED_LIBS` variable can
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be used to control the default behavior of :command:`add_library`,
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and allow control over how libraries without an explicit type (``STATIC``,
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``SHARED``, ``MODULE`` or ``OBJECT``) are built.
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To accomplish this we need to add :variable:`BUILD_SHARED_LIBS` to the
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top-level ``CMakeLists.txt``. We use the :command:`option` command as it allows
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users to optionally select if the value should be ``ON`` or ``OFF``.
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.. literalinclude:: Step11/CMakeLists.txt
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-option-BUILD_SHARED_LIBS
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:language: cmake
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:start-after: set(CMAKE_RUNTIME_OUTPUT_DIRECTORY
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:end-before: # configure a header file to pass the version number only
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Next, we need to specify output directories for our static and shared
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libraries.
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.. literalinclude:: Step11/CMakeLists.txt
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:caption: CMakeLists.txt
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:name: CMakeLists.txt-cmake-output-directories
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:language: cmake
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:start-after: # we don't need to tinker with the path to run the executable
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:end-before: # configure a header file to pass the version number only
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Finally, update ``MathFunctions/MathFunctions.h`` to use dll export defines:
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.. literalinclude:: Step11/MathFunctions/MathFunctions.h
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:caption: MathFunctions/MathFunctions.h
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:name: MathFunctions/MathFunctions.h
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:language: c++
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At this point, if you build everything, you may notice that linking fails
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as we are combining a static library without position independent code with a
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library that has position independent code. The solution to this is to
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explicitly set the :prop_tgt:`POSITION_INDEPENDENT_CODE` target property of
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SqrtLibrary to be ``True`` when building shared libraries.
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.. literalinclude:: Step11/MathFunctions/CMakeLists.txt
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:caption: MathFunctions/CMakeLists.txt
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:name: MathFunctions/CMakeLists.txt-POSITION_INDEPENDENT_CODE
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:language: cmake
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:lines: 37-42
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**Exercise**: We modified ``MathFunctions.h`` to use dll export defines.
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Using CMake documentation can you find a helper module to simplify this?
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