All well and good until you find out half of it is written in C or something like that. I like to go out and find the most starred repos on github or just ask around for a library that people think highly of and read that.
C itself is actually a pretty good example of where this fails as well. Its standard library is usually more macros than code. It's necessary if you are going to ship portable code that deals with every conceivable architecture and endianness and permutation of toolchain from 1976 until now, but it's not how most C code looks.
K&R is a much more meaningful guide than unistd.h.
K&R is a much more meaningful guide than unistd.h.