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65 lines
2.5 KiB
65 lines
2.5 KiB
CMAKE_<LANG>_STANDARD_LATEST
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-----------------------------
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.. versionadded:: 3.30
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This variable represents the minimum between the latest version of the
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standard for language ``<LANG>`` which is supported by the current compiler
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and the latest version which is supported by CMake. Its value will be set to
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one of the supported values of the corresponding :prop_tgt:`<LANG>_STANDARD`
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target property; see the documentation of that property for a list of
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supported languages.
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See the :manual:`cmake-compile-features(7)` manual for information on compile
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features and a list of supported compilers.
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.. note::
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``CMAKE_<LANG>_STANDARD_LATEST`` will never be set to a language standard
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which CMake recognizes but provides no support for. Unless explicitly
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stated otherwise, every value which is supported by the corresponding
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:prop_tgt:`<LANG>_STANDARD` target property represents a standard of
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language ``<LANG>`` which is both recognized and supported by CMake.
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Checking for Language Standard Support
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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It is possible to use the value of the ``CMAKE_<LANG>_STANDARD_LATEST``
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variable to check for language standard support. This can be used to, e.g.,
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conditionally enable optional features for a distributed library.
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When doing so, one should be careful to **not** rely on integer value
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comparisons between standard levels. This is because some older standards of
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a given language which are supported by CMake (e.g., C++98, represented as
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``98``) will have a higher numerical value than newer standards of that same
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language.
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The following code sample demonstrates how one might correctly check for
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C++17 support:
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.. code-block:: cmake
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# Careful! We cannot do direct integer comparisons with
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# CMAKE_CXX_STANDARD_LATEST because some earlier C++ standards (e.g.,
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# C++98) will have a higher numerical value than our requirement (C++17).
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#
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# Instead, we keep a list of unsupported C++ standards and check if
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# CMAKE_CXX_STANDARD_LATEST appears in that list.
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set(UNSUPPORTED_CXX_STANDARDS
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98
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11
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14
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)
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list(FIND UNSUPPORTED_CXX_STANDARDS ${CMAKE_CXX_STANDARD_LATEST} UNSUPPORTED_CXX_STANDARDS_INDEX)
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if(UNSUPPORTED_CXX_STANDARDS_INDEX EQUAL -1)
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# We know that the current compiler supports at least C++17. Enabling
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# some optional feature...
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else()
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message(STATUS
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"Feature X is disabled because it requires C++17, but the current "
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"compiler only supports C++${CMAKE_CXX_STANDARD_LATEST}."
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)
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endif()
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