# try_compile

Try building some code.

## Try Compiling Whole Projects

    try_compile(<resultVar> PROJECT <projectName>
                SOURCE_DIR <srcdir>
                [BINARY_DIR <bindir>]
                [TARGET <targetName>]
                [NO_CACHE]
                [CMAKE_FLAGS <flags>...]
                [OUTPUT_VARIABLE <var>])

New in version 3.25.

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.

Changed in version 3.24: CMake variables describing platform settings, and those listed by the `CMAKE_TRY_COMPILE_PLATFORM_VARIABLES` variable, are propagated into the project's build configuration. See policy `CMP0137`. Previously this was only done by the source file signature.

This command also supports an alternate signature which was present in older versions of CMake:

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

## Try Compiling Source Files

    try_compile(<resultVar>
                <SOURCES <srcfile...>                 |
                 SOURCE_FROM_CONTENT <name> <content> |
                 SOURCE_FROM_VAR <name> <var>         |
                 SOURCE_FROM_FILE <name> <path>       >...
                [NO_CACHE]
                [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>]
                )

New in version 3.25.

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. Additionally, one of `SOURCES` and/or `SOURCE_FROM_*` must precede other keywords.

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})

CMake automatically generates, for each `try_compile` operation, a unique directory under `${CMAKE_BINARY_DIR}/CMakeFiles/CMakeScratch` with an unspecified name. These directories are cleaned automatically unless `--debug-trycompile` is passed to `cmake`. Such directories from previous runs are also unconditionally cleaned at the beginning of any `cmake` execution.

This command also supports an alternate signature which was present in older versions of CMake:

    try_compile(<resultVar> <bindir> <srcfile|SOURCES srcfile...>
                [NO_CACHE]
                [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>]
                )

In this version, `try_compile` will use `<bindir>/CMakeFiles/CMakeTmp` for its operation, and all such files will be cleaned automatically. For debugging, `--debug-trycompile` can be passed to `cmake` to avoid this clean. However, multiple sequential `try_compile` operations, if given the same `<bindir>`, will reuse this single output directory, such that you can only debug one such `try_compile` call at a time. Use of the newer signature is recommended to simplify debugging of multiple `try_compile` operations.

The options are:

`CMAKE_FLAGS <flags>...`

  Specify flags of the form `-DVAR:TYPE=VALUE` to be passed to the `cmake(1)` 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>...`

  New in version 3.14.

  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.

`NO_CACHE`

  New in version 3.25.

  The result will be stored in a normal variable rather than a cache entry.

  The result variable is normally cached so that a simple pattern can be used to avoid repeating the test on subsequent executions of CMake:

      if(NOT DEFINED RESULTVAR)
        # ...(check-specific setup code)...
        try_compile(RESULTVAR ...)
        # ...(check-specific logging and cleanup code)...
      endif()

  If the guard variable and result variable are not the same (for example, if the test is part of a larger inspection), `NO_CACHE` may be useful to avoid leaking the intermediate result variable into the cache.

`OUTPUT_VARIABLE <var>`

  Store the output from the build process in the given variable.

`SOURCE_FROM_CONTENT <name> <content>`

  New in version 3.25.

  Write `<content>` to a file named `<name>` in the operation directory. This can be used to bypass the need to separately write a source file when the contents of the file are dynamically specified. The specified `<name>` is not allowed to contain path components.

  `SOURCE_FROM_CONTENT` may be specified multiple times.

`SOURCE_FROM_FILE <name> <path>`

  New in version 3.25.

  Copy `<path>` to a file named `<name>` in the operation directory. This can be used to consolidate files into the operation directory, which may be useful if a source which already exists (i.e. as a stand-alone file in a project's source repository) needs to refer to other file(s) created by `SOURCE_FROM_*`. (Otherwise, `SOURCES` is usually more convenient.) The specified `<name>` is not allowed to contain path components.

`SOURCE_FROM_VAR <name> <var>`

  New in version 3.25.

  Write the contents of `<var>` to a file named `<name>` in the operation directory. This is the same as `SOURCE_FROM_CONTENT`, but takes the contents from the specified CMake variable, rather than directly, which may be useful when passing arguments through a function which wraps `try_compile`. The specified `<name>` is not allowed to contain path components.

  `SOURCE_FROM_VAR` may be specified multiple times.

`<LANG>_STANDARD <std>`

  New in version 3.8.

  Specify the `C_STANDARD`, `CXX_STANDARD`, `OBJC_STANDARD`, `OBJCXX_STANDARD`, or `CUDA_STANDARD` target property of the generated project.

`<LANG>_STANDARD_REQUIRED <bool>`

  New in version 3.8.

  Specify the `C_STANDARD_REQUIRED`, `CXX_STANDARD_REQUIRED`, `OBJC_STANDARD_REQUIRED`, `OBJCXX_STANDARD_REQUIRED`,or `CUDA_STANDARD_REQUIRED` target property of the generated project.

`<LANG>_EXTENSIONS <bool>`

  New in version 3.8.

  Specify the `C_EXTENSIONS`, `CXX_EXTENSIONS`, `OBJC_EXTENSIONS`, `OBJCXX_EXTENSIONS`, or `CUDA_EXTENSIONS` target property of the generated project.

## Other Behavior Settings

New in version 3.4: If set, the following variables are passed in to the generated try_compile CMakeLists.txt to initialize compile target properties with default values:

- `CMAKE_CUDA_RUNTIME_LIBRARY`

- `CMAKE_ENABLE_EXPORTS`

- `CMAKE_LINK_SEARCH_START_STATIC`

- `CMAKE_LINK_SEARCH_END_STATIC`

- `CMAKE_MSVC_RUNTIME_LIBRARY`

- `CMAKE_POSITION_INDEPENDENT_CODE`

- `CMAKE_WATCOM_RUNTIME_LIBRARY`

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

Changed in version 3.14: 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.

New in version 3.6: Set the `CMAKE_TRY_COMPILE_TARGET_TYPE` variable to specify the type of target used for the source file signature.

New in version 3.6: 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.

Changed in version 3.8: 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_OBJC_STANDARD`

- `CMAKE_OBJC_STANDARD_REQUIRED`

- `CMAKE_OBJC_EXTENSIONS`

- `CMAKE_OBJCXX_STANDARD`

- `CMAKE_OBJCXX_STANDARD_REQUIRED`

- `CMAKE_OBJCXX_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).

Changed in version 3.14: For the `Green Hills MULTI` generator, the GHS toolset and target system customization cache variables are also propagated into the test project.

New in version 3.24: The `CMAKE_TRY_COMPILE_NO_PLATFORM_VARIABLES` variable may be set to disable passing platform variables into the test project.

New in version 3.25: If `CMP0141` is set to `NEW`, one can use `CMAKE_MSVC_DEBUG_INFORMATION_FORMAT` to specify the MSVC debug information format.