I guess people mostly take source compatibility to mean that you can write the headers for your C library so that it can be used from C++. That's not the same t

I guess people mostly take source compatibility to mean that you can write the headers for your C library so that it can be used from C++. That's not the same thing as C being a proper subset of C++ or whatever, but it's still a vast enough advantage of C++ over most competitors that it might as well be.