try_compile
-----------

.. only:: html

   .. contents::

Try building some code.

Try Compiling Whole Projects
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: cmake

  try_compile(<resultVar> <bindir> <srcdir>
              <projectName> [<targetName>] [CMAKE_FLAGS <flags>...]
              [OUTPUT_VARIABLE <var>])

Try building a project.  The success or failure of the ``try_compile``,
i.e. ``TRUE`` or ``FALSE`` respectively, is returned in ``<resultVar>``.

In this form, ``<srcdir>`` should contain a complete CMake project with a
``CMakeLists.txt`` file and all sources.  The ``<bindir>`` and ``<srcdir>``
will not be deleted after this command is run.  Specify ``<targetName>`` to
build a specific target instead of the ``all`` or ``ALL_BUILD`` target.  See
below for the meaning of other options.

Try Compiling Source Files
^^^^^^^^^^^^^^^^^^^^^^^^^^

.. code-block:: cmake

  try_compile(<resultVar> <bindir> <srcfile|SOURCES srcfile...>
              [CMAKE_FLAGS <flags>...]
              [COMPILE_DEFINITIONS <defs>...]
              [LINK_OPTIONS <options>...]
              [LINK_LIBRARIES <libs>...]
              [OUTPUT_VARIABLE <var>]
              [COPY_FILE <fileName> [COPY_FILE_ERROR <var>]]
              [<LANG>_STANDARD <std>]
              [<LANG>_STANDARD_REQUIRED <bool>]
              [<LANG>_EXTENSIONS <bool>]
              )

Try building an executable or static library from one or more source files
(which one is determined by the :variable:`CMAKE_TRY_COMPILE_TARGET_TYPE`
variable).  The success or failure of the ``try_compile``, i.e. ``TRUE`` or
``FALSE`` respectively, is returned in ``<resultVar>``.

In this form, one or more source files must be provided.  If
:variable:`CMAKE_TRY_COMPILE_TARGET_TYPE` is unset or is set to ``EXECUTABLE``,
the sources must include a definition for ``main`` and CMake will create a
``CMakeLists.txt`` file to build the source(s) as an executable.
If :variable:`CMAKE_TRY_COMPILE_TARGET_TYPE` is set to ``STATIC_LIBRARY``,
a static library will be built instead and no definition for ``main`` is
required.  For an executable, the generated ``CMakeLists.txt`` file would
contain something like the following:

.. code-block:: cmake

  add_definitions(<expanded COMPILE_DEFINITIONS from caller>)
  include_directories(${INCLUDE_DIRECTORIES})
  link_directories(${LINK_DIRECTORIES})
  add_executable(cmTryCompileExec <srcfile>...)
  target_link_options(cmTryCompileExec PRIVATE <LINK_OPTIONS from caller>)
  target_link_libraries(cmTryCompileExec ${LINK_LIBRARIES})

The options are:

``CMAKE_FLAGS <flags>...``
  Specify flags of the form ``-DVAR:TYPE=VALUE`` to be passed to
  the ``cmake`` command-line used to drive the test build.
  The above example shows how values for variables
  ``INCLUDE_DIRECTORIES``, ``LINK_DIRECTORIES``, and ``LINK_LIBRARIES``
  are used.

``COMPILE_DEFINITIONS <defs>...``
  Specify ``-Ddefinition`` arguments to pass to :command:`add_definitions`
  in the generated test project.

``COPY_FILE <fileName>``
  Copy the built executable or static library to the given ``<fileName>``.

``COPY_FILE_ERROR <var>``
  Use after ``COPY_FILE`` to capture into variable ``<var>`` any error
  message encountered while trying to copy the file.

``LINK_LIBRARIES <libs>...``
  Specify libraries to be linked in the generated project.
  The list of libraries may refer to system libraries and to
  :ref:`Imported Targets <Imported Targets>` from the calling project.

  If this option is specified, any ``-DLINK_LIBRARIES=...`` value
  given to the ``CMAKE_FLAGS`` option will be ignored.

``LINK_OPTIONS <options>...``
  Specify link step options to pass to :command:`target_link_options` or to
  set the :prop_tgt:`STATIC_LIBRARY_OPTIONS` target property in the generated
  project, depending on the :variable:`CMAKE_TRY_COMPILE_TARGET_TYPE` variable.

``OUTPUT_VARIABLE <var>``
  Store the output from the build process in the given variable.

``<LANG>_STANDARD <std>``
  Specify the :prop_tgt:`C_STANDARD`, :prop_tgt:`CXX_STANDARD`,
  or :prop_tgt:`CUDA_STANDARD` target property of the generated project.

``<LANG>_STANDARD_REQUIRED <bool>``
  Specify the :prop_tgt:`C_STANDARD_REQUIRED`,
  :prop_tgt:`CXX_STANDARD_REQUIRED`, or :prop_tgt:`CUDA_STANDARD_REQUIRED`
  target property of the generated project.

``<LANG>_EXTENSIONS <bool>``
  Specify the :prop_tgt:`C_EXTENSIONS`, :prop_tgt:`CXX_EXTENSIONS`,
  or :prop_tgt:`CUDA_EXTENSIONS` target property of the generated project.

In this version all files in ``<bindir>/CMakeFiles/CMakeTmp`` will be
cleaned automatically.  For debugging, ``--debug-trycompile`` can be
passed to ``cmake`` to avoid this clean.  However, multiple sequential
``try_compile`` operations reuse this single output directory.  If you use
``--debug-trycompile``, you can only debug one ``try_compile`` call at a time.
The recommended procedure is to protect all ``try_compile`` calls in your
project by ``if(NOT DEFINED <resultVar>)`` logic, configure with cmake
all the way through once, then delete the cache entry associated with
the try_compile call of interest, and then re-run cmake again with
``--debug-trycompile``.

Other Behavior Settings
^^^^^^^^^^^^^^^^^^^^^^^

If set, the following variables are passed in to the generated
try_compile CMakeLists.txt to initialize compile target properties with
default values:

* :variable:`CMAKE_ENABLE_EXPORTS`
* :variable:`CMAKE_LINK_SEARCH_START_STATIC`
* :variable:`CMAKE_LINK_SEARCH_END_STATIC`
* :variable:`CMAKE_MSVC_RUNTIME_LIBRARY`
* :variable:`CMAKE_POSITION_INDEPENDENT_CODE`

If :policy:`CMP0056` is set to ``NEW``, then
:variable:`CMAKE_EXE_LINKER_FLAGS` is passed in as well.

If :policy:`CMP0083` is set to ``NEW``, then in order to obtain correct
behavior at link time, the ``check_pie_supported()`` command from the
:module:`CheckPIESupported` module must be called before using the
:command:`try_compile` command.

The current settings of :policy:`CMP0065` and :policy:`CMP0083` are propagated
through to the generated test project.

Set the :variable:`CMAKE_TRY_COMPILE_CONFIGURATION` variable to choose
a build configuration.

Set the :variable:`CMAKE_TRY_COMPILE_TARGET_TYPE` variable to specify
the type of target used for the source file signature.

Set the :variable:`CMAKE_TRY_COMPILE_PLATFORM_VARIABLES` variable to specify
variables that must be propagated into the test project.  This variable is
meant for use only in toolchain files and is only honored by the
``try_compile()`` command for the source files form, not when given a whole
project.

If :policy:`CMP0067` is set to ``NEW``, or any of the ``<LANG>_STANDARD``,
``<LANG>_STANDARD_REQUIRED``, or ``<LANG>_EXTENSIONS`` options are used,
then the language standard variables are honored:

* :variable:`CMAKE_C_STANDARD`
* :variable:`CMAKE_C_STANDARD_REQUIRED`
* :variable:`CMAKE_C_EXTENSIONS`
* :variable:`CMAKE_CXX_STANDARD`
* :variable:`CMAKE_CXX_STANDARD_REQUIRED`
* :variable:`CMAKE_CXX_EXTENSIONS`
* :variable:`CMAKE_CUDA_STANDARD`
* :variable:`CMAKE_CUDA_STANDARD_REQUIRED`
* :variable:`CMAKE_CUDA_EXTENSIONS`

Their values are used to set the corresponding target properties in
the generated project (unless overridden by an explicit option).

For the :generator:`Green Hills MULTI` generator the GHS toolset and target
system customization cache variables are also propagated into the test project.
