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# Distributed under the OSI-approved BSD 3-Clause License. See accompanying
# file Copyright.txt or for details.
Check whether the C compiler supports a given flag.
.. command:: check_c_compiler_flag
.. code-block:: cmake
check_c_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_c_source_compiles`` macro from the
:module:`CheckCSourceCompiles` 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_C_FLAGS <CMAKE_<LANG>_FLAGS>`, unknown flags
in such variables may cause a false negative for this check.
function(check_c_compiler_flag _flag _var)
# Normalize locale during test compilation.
set(_locale_vars LC_ALL LC_MESSAGES LANG)
foreach(v IN LISTS _locale_vars)
set(_locale_vars_saved_${v} "$ENV{${v}}")
set(ENV{${v}} C)
check_c_source_compiles("int main(void) { return 0; }" ${_var}
# Some compilers do not fail with a bad flag
FAIL_REGEX "command line option .* is valid for .* but not for C" # GNU
foreach(v IN LISTS _locale_vars)
set(ENV{${v}} ${_locale_vars_saved_${v}})
set(${_var} "${${_var}}" PARENT_SCOPE)