No, I'm perfectly well-versed in the differences between C and C++, having written in one or the other for a long time. A trivial look-alike implementation of std::string can be written in C, and would look a lot like the RString class.

Your argument is actually, essentially mine. The need to use the platforms' string functions heavily swings (but does not force) the choice of null-terminating the RString members. As I mentioned, it would be really stupid but entirely possible to simply clone the non-null-terminated string into a temporary null-terminated char array every time you want to use a function that takes standard "C strings" if you really, truly, madly wanted to have an RString implementation that was one byte smaller to store. But that would be insane.