# CheckSourceCompiles

Added in version 3.19.

Check once if source code can be built for a given language.

check_source_compiles

      check_source_compiles(<lang> <code> <resultVar>
                            [FAIL_REGEX <regex1> [<regex2>...]]
                            [SRC_EXT <extension>])

  Check once that the source supplied in `<code>` can be built for code language `<lang>`. The result is stored in the internal cache variable specified by `<resultVar>`, with boolean `true` for success and boolean `false` for failure.

  If `FAIL_REGEX` is provided, then failure is determined by checking if anything in the compiler output matches any of the specified regular expressions.

  By default, the test source file will be given a file extension that matches the requested language. The `SRC_EXT` option can be used to override this with `.<extension>` instead.

  The C example checks if the compiler supports the `noreturn` attribute:

      set(CMAKE_TRY_COMPILE_TARGET_TYPE "STATIC_LIBRARY")

      check_source_compiles(C
      "#if !__has_c_attribute(noreturn)
      #error \"No noreturn attribute\"
      #endif"
      HAVE_NORETURN)

  The Fortran example checks if the compiler supports the `pure` procedure attribute:

      set(CMAKE_TRY_COMPILE_TARGET_TYPE "STATIC_LIBRARY")

      check_source_compiles(Fortran
      "pure subroutine foo()
      end subroutine"
      HAVE_PURE)

  Internally, `try_compile()` is used to compile the source. If `CMAKE_TRY_COMPILE_TARGET_TYPE` is set to `EXECUTABLE` (default), the source is compiled and linked as an executable program. If set to `STATIC_LIBRARY`, the source is compiled but not linked. In any case, all functions must be declared as usual.

  See also `check_source_runs()` to run compiled source.

  The compile and link commands can be influenced by setting any of the following variables prior to calling `check_source_compiles()`:

> `CMAKE_REQUIRED_FLAGS`

>   String of additional flags to pass to the compiler. The string must be space-delimited--a ;-list will not work. The contents of `CMAKE_<LANG>_FLAGS` and its associated configuration-specific variable are automatically added to the compiler command before the contents of `CMAKE_REQUIRED_FLAGS`.

> `CMAKE_REQUIRED_DEFINITIONS`

>   A ;-list of compiler definitions of the form `-DFOO` or `-DFOO=bar`. A definition for the name specified by `<resultVar>` will also be added automatically.

> `CMAKE_REQUIRED_INCLUDES`

>   A ;-list of header search paths to pass to the compiler. These will be the only header search paths used--the contents of the `INCLUDE_DIRECTORIES` directory property will be ignored.

> `CMAKE_REQUIRED_LINK_OPTIONS`

>   Added in version 3.14.

>   A ;-list of options to add to the link command (see `try_compile()` for further details).

> `CMAKE_REQUIRED_LIBRARIES`

>   A ;-list of libraries to add to the link command. These can be the name of system libraries or they can be Imported Targets (see `try_compile()` for further details).

> `CMAKE_REQUIRED_LINK_DIRECTORIES`

>   Added in version 3.31.

>   A ;-list of libraries search paths to pass to the linker (see `try_compile()` for further details).

> `CMAKE_REQUIRED_QUIET`

>   Added in version 3.1.

>   If this variable evaluates to a boolean true value, all status messages associated with the check will be suppressed.