[jng]

Windows is not written in C++, even if Microsoft did embrace C++ quite a bit with the infamous MFC and so on. Windows was originally written using C and assembly language, using the Pascal calling convention for efficiency. It was originally a layer on top DOS which was written in assembly language. Being a "layer" or not was the subject of a very complex federal antitrust case back in the 90s. You can read "Undocumented DOS" and "Undocumented Windows" for some weird kind of technical investigation thriller which I found weirdly fascinating back in the day.

[pjmlp]

Since Windows Vista, Windows has been transitioning to C++, hence why they don't care much more about ISO C beyond of what is required by ISO C++ standard compliance.

https://herbsutter.com/2012/05/03/reader-qa-what-about-vc-an...

https://www.reddit.com/r/cpp/comments/4oruo1/windows_10_code...