What are two or three C codebases that are elegantly and cleanly written, and that every mid-level C programmer should read for sake of knowledge?
Mbed TLS, since I have it in mind from another thread, is also a pretty clean C library for the problem it tries to solve; it's a testament to its design that we (TrustInSoft, who had not participated to its development) were able to verify that some uses of the library were free of Undefined Behavior: https://tls.mbed.org
Opened a random part of musl out of sheer boredom. Here's what I see:
https://git.musl-libc.org/cgit/musl/tree/include/aio.h
A bunch of return codes #defined like so (see https://git.musl-libc.org/cgit/musl/tree/src/aio/aio.c):
#define AIO_CANCELED 0 #define AIO_NOTCANCELED 1 #define AIO_ALLDONE 2
#define LIO_READ 0 #define LIO_WRITE 1 #define LIO_NOP 2
#define LIO_WAIT 0 #define LIO_NOWAIT 1
Why weren't they using an enum instead? I wouldn't sign off on this code (and I don't think it lives up to best practices).