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50 lines
2.4 KiB
50 lines
2.4 KiB
CMP0091
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-------
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MSVC runtime library flags are selected by an abstraction.
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Compilers targeting the MSVC ABI have flags to select the MSVC runtime library.
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Runtime library selection typically varies with build configuration because
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there is a separate runtime library for Debug builds.
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In CMake 3.14 and below, MSVC runtime library selection flags are added to
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the default :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` cache entries by CMake
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automatically. This allows users to edit their cache entries to adjust the
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flags. However, the presence of such default flags is problematic for
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projects that want to choose a different runtime library programmatically.
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In particular, it requires string editing of the
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:variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` variables with knowledge of the
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CMake builtin defaults so they can be replaced.
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CMake 3.15 and above prefer to leave the MSVC runtime library selection flags
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out of the default :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` values and instead
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offer a first-class abstraction. The :variable:`CMAKE_MSVC_RUNTIME_LIBRARY`
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variable and :prop_tgt:`MSVC_RUNTIME_LIBRARY` target property may be set to
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select the MSVC runtime library. If they are not set then CMake uses the
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default value ``MultiThreaded$<$<CONFIG:Debug>:Debug>DLL`` which is
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equivalent to the original flags.
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This policy provides compatibility with projects that have not been updated
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to be aware of the abstraction. The policy setting takes effect as of the
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first :command:`project` or :command:`enable_language` command that enables
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a language whose compiler targets the MSVC ABI.
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.. note::
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Once the policy has taken effect at the top of a project, that choice
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must be used throughout the tree. In projects that have nested projects
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in subdirectories, be sure to convert everything together.
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The ``OLD`` behavior for this policy is to place MSVC runtime library
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flags in the default :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` cache
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entries and ignore the :variable:`CMAKE_MSVC_RUNTIME_LIBRARY` abstraction.
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The ``NEW`` behavior for this policy is to *not* place MSVC runtime
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library flags in the default cache entries and use the abstraction instead.
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This policy was introduced in CMake version 3.15. Use the
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:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
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Unlike many policies, CMake version |release| does *not* warn
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when this policy is not set and simply uses ``OLD`` behavior.
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.. include:: DEPRECATED.txt
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