There's no common C++ build system. That means (among other things) that there's no way to turn features you don't use into compile-time errors. There's no project configuration to select an allowed subset of features. All the difficulty goes onto the programmers, and in a multi-person project into the code review process. In practice, you end up using the combined set of C++ sublanguages each contributor chooses to use. You have to know about all of C++'s features to use C++ in a large enough team.