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# Distributed under the OSI-approved BSD 3-Clause License. See accompanying
# file LICENSE.rst or https://cmake.org/licensing for details.
#[=======================================================================[.rst:
CheckCCompilerFlag
------------------
This module provides a command to check whether the C compiler supports a
given flag.
Load this module in a CMake project with:
.. code-block:: cmake
include(CheckCCompilerFlag)
Commands
^^^^^^^^
This module provides the following command:
.. command:: check_c_compiler_flag
Checks once whether the C compiler supports a given flag:
.. code-block:: cmake
check_c_compiler_flag(<flag> <variable>)
This command checks once that the ``<flag>`` is accepted by the C compiler
without producing a diagnostic message. Multiple flags can be specified
in one argument as a string using a :ref:`semicolon-separated list
<CMake Language Lists>`.
The result of the check is stored in the internal cache variable specified
by ``<variable>``, with boolean true for success and boolean false for
failure.
A successful result only indicates that the compiler did not report an
error when given the flag. Whether the flag has any effect, or the
intended one, is outside the scope of this module.
.. note::
Since the underlying :command:`try_compile` command also uses flags from
variables like :variable:`CMAKE_<LANG>_FLAGS`, unknown or unsupported
flags in those variables may result in a false negative for this check.
.. rubric:: Variables Affecting the Check
The following variables may be set before calling this command to modify
the way the check is run:
.. include:: /module/include/CMAKE_REQUIRED_FLAGS.rst
.. include:: /module/include/CMAKE_REQUIRED_DEFINITIONS.rst
.. include:: /module/include/CMAKE_REQUIRED_INCLUDES.rst
.. include:: /module/include/CMAKE_REQUIRED_LINK_OPTIONS.rst
.. include:: /module/include/CMAKE_REQUIRED_LIBRARIES.rst
.. include:: /module/include/CMAKE_REQUIRED_LINK_DIRECTORIES.rst
.. include:: /module/include/CMAKE_REQUIRED_QUIET.rst
.. include:: /module/include/CMAKE_TRY_COMPILE_TARGET_TYPE.rst
Examples
^^^^^^^^
The following example demonstrates how to use this module to check support
for the C compiler flag ``-fno-optimize-strlen``, which disables
optimizations related to the ``strlen()`` C function in GCC and Clang
compilers. The result of the check is stored in the internal cache
variable ``HAVE_FNO_OPTIMIZE_STRLEN``, and the flag is conditionally enabled
using the :command:`target_compile_options` command. The
:genex:`$<COMPILE_LANGUAGE:...> <COMPILE_LANGUAGE:languages>` generator
expression ensures that the flag is added only to ``C`` source files.
.. code-block:: cmake
include(CheckCCompilerFlag)
check_c_compiler_flag(-fno-optimize-strlen HAVE_FNO_OPTIMIZE_STRLEN)
if(HAVE_FNO_OPTIMIZE_STRLEN)
target_compile_options(
example
PRIVATE $<$<COMPILE_LANGUAGE:C>:-fno-optimize-strlen>
)
endif()
See Also
^^^^^^^^
* The :module:`CheckCompilerFlag` module for a more general command to check
whether a compiler flag is supported.
#]=======================================================================]
include_guard(GLOBAL)
include(Internal/CheckCompilerFlag)
macro (CHECK_C_COMPILER_FLAG _FLAG _RESULT)
cmake_check_compiler_flag(C "${_FLAG}" ${_RESULT})
endmacro ()
# FIXME(#24994): The following module is included only for compatibility
# with projects that accidentally relied on it with CMake 3.26 and below.
include(CheckCSourceCompiles)
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