Except you can perfectly well link together a C89 and a C++11 object file compiled with the same compiler. All compilers let you specify the exact standard you'

Except you can perfectly well link together a C89 and a C++11 object file compiled with the same compiler. All compilers let you specify the exact standard you're compiling, so even if tomorrow C++2x adds "frob" as a keyword, you can opt out of it in most of your code and only compile a few of your .cpp files as C++2x and they will still link together just fine because the ABI is stable. Which means you're never in the position that "this update broke our code", barring of course compiler bugs and switches to a new ABI, both of which are extremely rare.