This is fun and impressive, but it feel the author kind of misses out on explaining in the intro why it would be wrong to just ... use C's regex library [1]?

I guess the entire post could be seen as an exercise in wrapping C++ to C with nice memory-handling properties and so on, but it would also be fine to be open and upfront about that, in my opinion.

1: https://www.man7.org/linux/man-pages/man3/regex.3.html