I have tried to run C++ on the Nspire by replacing gcc with g++ in nspire-gcc, but the linker spams me with error messages then.
I got this to work once (with r349 I guess), so I was able to make a class with a function that prints something to RS232, but I was unable to use functions of libndls. I don't know how I exactly did this anymore (I reinstalled windows), so my question is, how can I get C++ to work again? If there is a chance to do this, wouldn't it be nice to include an nspire-g++ into ndless then?

Perhaps some extern "C" { ... }; blocks would be in order ?

C++ on a Nspire is not really surprising, in fact
C++ code is not necessarily bloated (though the more advanced features can indeed yield significant bloat) and hard to compile for embedded platforms: in the absence of "virtual" stuff, things like inheritance and redefinition of some methods' implementation in derived classes, can be compiled to decent machine code. My team-mate (mostly) and I used such C++ code in the internship at the end of our studies, on a mildly embedded platform (several hundreds of KB of Flash memory).

Wow I didn't realize C++ was possible on it. Isn't C++ OOP btw?

Yes, it is.

By the way shouldn't this be in the calculator help/C sub-forum?

Uhm, I don't know. Feel free to move it

Has C++ been ported to ARM9? If it has, it might be best just to use a dedicated toolchain.

EDIT: Well, obviously C++ has been at least partially ported...