Human languges have great ambiguities. For the same words, people may have different understandings.

Indeed, the global variables are still available in the file in which they are defined, after a "static" key word is applied.
However, they are no longer available in other C++ source files even we claim they are "extern".

Such things sounds trivial to C++ veterans, but not all C++ gurus can explain them elegantly. Thank you for discussions.