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# Distributed under the OSI-approved BSD 3-Clause License. See accompanying
# file Copyright.txt or https://cmake.org/licensing for details.
#[=======================================================================[.rst:
CheckCXXCompilerFlag
------------------------
Check whether the CXX compiler supports a given flag.
.. command:: check_cxx_compiler_flag
::
check_cxx_compiler_flag(<flag> <var>)
Check that the ``<flag>`` is accepted by the compiler without
a diagnostic. Stores the result in an internal cache entry
named ``<var>``.
This command temporarily sets the ``CMAKE_REQUIRED_DEFINITIONS`` variable
and calls the ``check_cxx_source_compiles`` macro from the
:module:`CheckCXXSourceCompiles` module. See documentation of that
module for a listing of variables that can otherwise modify the build.
A positive result from this check indicates only that the compiler did not
issue a diagnostic message when given the flag. Whether the flag has any
effect or even a specific one is beyond the scope of this module.
.. note::
Since the :command:`try_compile` command forwards flags from variables
like :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>`, unknown flags
in such variables may cause a false negative for this check.
#]=======================================================================]
include(CheckCXXSourceCompiles)
include(CMakeCheckCompilerFlagCommonPatterns)
macro (CHECK_CXX_COMPILER_FLAG _FLAG _RESULT)
set(SAFE_CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}")
set(CMAKE_REQUIRED_DEFINITIONS "${_FLAG}")
# Normalize locale during test compilation.
set(_CheckCXXCompilerFlag_LOCALE_VARS LC_ALL LC_MESSAGES LANG)
foreach(v ${_CheckCXXCompilerFlag_LOCALE_VARS})
set(_CheckCXXCompilerFlag_SAVED_${v} "$ENV{${v}}")
set(ENV{${v}} C)
endforeach()
CHECK_COMPILER_FLAG_COMMON_PATTERNS(_CheckCXXCompilerFlag_COMMON_PATTERNS)
CHECK_CXX_SOURCE_COMPILES("int main() { return 0; }" ${_RESULT}
# Some compilers do not fail with a bad flag
FAIL_REGEX "command line option .* is valid for .* but not for C\\\\+\\\\+" # GNU
${_CheckCXXCompilerFlag_COMMON_PATTERNS}
)
foreach(v ${_CheckCXXCompilerFlag_LOCALE_VARS})
set(ENV{${v}} ${_CheckCXXCompilerFlag_SAVED_${v}})
unset(_CheckCXXCompilerFlag_SAVED_${v})
endforeach()
unset(_CheckCXXCompilerFlag_LOCALE_VARS)
unset(_CheckCXXCompilerFlag_COMMON_PATTERNS)
set (CMAKE_REQUIRED_DEFINITIONS "${SAFE_CMAKE_REQUIRED_DEFINITIONS}")
endmacro ()
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