I got on very well with Van der Linden's Deep C Secrets. It's from 1994, so misses out on the newer versions, but aside from that it's aged well, IMHO.

And good news: it's been open sourced: https://freecomputerbooks.com/Expert-C-Programming-Deep-C-Se... and its well regarded on Hacker News https://hackernewsbooks.com/book/expert-c-programming-deep-c... .

Are you sure it's been open sourced? I'm reasonably sure you've linked to a site offering pirated copies.

There are several links to PDF versions of the book. None of them include either a copyright page or a statement that it's been released as open source.

The author's own website <https://afu.com/> includes errata for the book, but doesn't provide or mention a free copy.

A free sample of the Kindle version of the book does include a copyright notice. A book published in 1994 is not public domain unless it's been explicitly released.

Something that appears to be a legitimate PDF sample (not the while book) is here:

https://ptgmedia.pearsoncmg.com/images/9780131774292/samplep...