Interesting that the manpage claims it conforms to POSIX.1-2001.

https://linux.die.net/man/3/hcreate

POSIX is the standard for Unix, not for C.

I think GP is talking about, e.g., glibc, or any libc you might find on a POSIX system, rather than the abstract C standard library. I agree that as a point of clarity, POSIX isn't standard C and the crappy hashtable described is in POSIX, not standard C.