A nitpick: please don't conflate C and C++. They're separate languages, this article is exclusively about C, and C++ is an instance of one of the languages that "speaks C". C++ has its own symbol mangling and ABI, which has not historically been nearly as stable or universal.
Virtually every language has a mode to make calls into the C ABI. That's exactly the point of the article.
To switch in to C ABI mode in C++ you have to wrap the declarations in 'extern "C" { ... }' blocks, otherwise you get the C++ ABI, not the C ABI. It's done similarly in many other languages.
