The target property overrides the global setting, so you can set CMAKE_CXX_STANDARD as the default and then set the target property if you really need a differe

The target property overrides the global setting, so you can set CMAKE_CXX_STANDARD as the default and then set the target property if you really need a different standard for some reason. And if you have a whole sub-project that needs a specific version, you can set CMAKE_CXX_STANDARD before calling add_subdirectory to have it apply to only the targets in that directory.