# try_compile

Contents

- try_compile
  - Try Compiling Whole Projects
  - Try Compiling Source Files
  - Other Behavior Settings

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 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 `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 `C_STANDARD`, `CXX_STANDARD`, or `CUDA_STANDARD` target property of the generated project.
`<LANG>_STANDARD_REQUIRED <bool>`
  Specify the `C_STANDARD_REQUIRED`, `CXX_STANDARD_REQUIRED`, or `CUDA_STANDARD_REQUIRED` target property of the generated project.
`<LANG>_EXTENSIONS <bool>`
  Specify the `C_EXTENSIONS`, `CXX_EXTENSIONS`, or `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:

- `CMAKE_ENABLE_EXPORTS`
- `CMAKE_LINK_SEARCH_START_STATIC`
- `CMAKE_LINK_SEARCH_END_STATIC`
- `CMAKE_POSITION_INDEPENDENT_CODE`

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:

- `CMAKE_C_STANDARD`
- `CMAKE_C_STANDARD_REQUIRED`
- `CMAKE_C_EXTENSIONS`
- `CMAKE_CXX_STANDARD`
- `CMAKE_CXX_STANDARD_REQUIRED`
- `CMAKE_CXX_EXTENSIONS`
- `CMAKE_CUDA_STANDARD`
- `CMAKE_CUDA_STANDARD_REQUIRED`
- `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 `Green Hills MULTI` generator the GHS toolset and target system customization cache variables are also propagated into the test project.