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try_compile

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Try building some code.

Try Compiling Whole Projects

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

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 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 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 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:

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 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 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 target_link_options or to set the :prop_tgt:STATIC_LIBRARY_OPTIONS target property in the generated project, depending on the 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, :prop_tgt:OBJC_STANDARD, :prop_tgt:OBJCXX_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, :prop_tgt:OBJC_STANDARD_REQUIRED, :prop_tgt:OBJCXX_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, :prop_tgt:OBJC_EXTENSIONS, :prop_tgt:OBJCXX_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:

If CMP0056 is set to NEW, then CMAKE_EXE_LINKER_FLAGS is passed in as well.

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

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

Set the CMAKE_TRY_COMPILE_CONFIGURATION variable to choose a build configuration.

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

Set the 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 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:

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

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