# CheckCXXCompilerFlag

Check whether the CXX compiler supports a given flag.

`check_cxx_compiler_flag`

      check_cxx_compiler_flag(<flag> <var>)

  Check that the `<flag>` is accepted by the compiler without a diagnostic. Stores the result in an internal cache entry named `<var>`.

This command temporarily sets the `CMAKE_REQUIRED_DEFINITIONS` variable and calls the `check_cxx_source_compiles` macro from the `CheckCXXSourceCompiles` module. See documentation of that module for a listing of variables that can otherwise modify the build.

A positive result from this check indicates only that the compiler did not issue a diagnostic message when given the flag. Whether the flag has any effect or even a specific one is beyond the scope of this module.

Note

Since the `try_compile()` command forwards flags from variables like `CMAKE_CXX_FLAGS`, unknown flags in such variables may cause a false negative for this check.