# CheckCXXSourceCompiles

This module provides a command to check whether a C++ source can be built.

Load this module in a CMake project with:

    include(CheckCXXSourceCompiles)

## Commands

This module provides the following command:

check_cxx_source_compiles

  Checks once whether the given C++ source code can be built:

      check_cxx_source_compiles(<code> <variable> [FAIL_REGEX <regexes>...])

  This command checks once that the source supplied in `<code>` can be compiled (and linked into an executable). The result of the check is stored in the internal cache variable specified by `<variable>`.

  The arguments are:

  `<code>`

    C++ source code to check. This must be an entire program, as written in a file containing the body block. All symbols used in the source code are expected to be declared as usual in their corresponding headers.

  `<variable>`

    Variable name of an internal cache variable to store the result of the check, with boolean true for success and boolean false for failure.

  `FAIL_REGEX <regexes>...`

    If one or more regular expression patterns are provided, then failure is determined by checking if anything in the compiler output matches any of the specified regular expressions.

  Variables Affecting the Check

  The following variables may be set before calling this command to modify the way the check is run:

  `CMAKE_REQUIRED_FLAGS`

    A space-separated string of additional flags to pass to the compiler. A semicolon-separated list will not work. The contents of `CMAKE_<LANG>_FLAGS` and its associated configuration-specific `CMAKE_<LANG>_FLAGS_<CONFIG>` variables are automatically prepended to the compiler command before the contents of this variable.

  `CMAKE_REQUIRED_DEFINITIONS`

    A semicolon-separated list of compiler definitions, each of the form `-DFOO` or `-DFOO=bar`. A definition for the name specified by the result variable argument of the check command is also added automatically.

  `CMAKE_REQUIRED_INCLUDES`

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

  `CMAKE_REQUIRED_LIBRARIES`

    A semicolon-separated list of libraries to add to the link command. These can be the names 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 semicolon-separated list of library 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.

  `CMAKE_TRY_COMPILE_TARGET_TYPE`

    Internally, the `try_compile()` command is used to perform the check, and this variable controls the type of target it creates. If this variable is set to `EXECUTABLE` (the default), the check compiles and links the test source code as an executable program. If set to `STATIC_LIBRARY`, the test source code is compiled but not linked.

## Examples

The following example demonstrates how to check whether the C++ compiler supports a specific language feature. In this case, the check verifies if the compiler supports `C++11` lambda expressions. The result is stored in the internal cache variable `HAVE_CXX11_LAMBDAS`:

    include(CheckCXXSourceCompiles)

    check_cxx_source_compiles("
      int main()
      {
        auto lambda = []() { return 42; };
        return lambda();
      }
    " HAVE_CXX11_LAMBDAS)

## See Also

- The `CheckSourceCompiles` module for a more general command to check whether source can be built.

- The `CheckSourceRuns` module to check whether source can be built and run.