Top products from r/Cprog

• Redis is a very popular key:value store written entirely in very readable C. However if you were to expand your list to just "popular software written in C" (such as MariaDB) it would probably be very long, and not too useful. I would advise you to not do this, and focus on C specific stuff.
  
  
• ZeroMQ is a pretty nice networking library for high performance message passing.
  
  
• Jannson is apparently pretty popular for working with JSON. I haven't used it myself.
  
  
• Ragel is a DSL for finite state machines that compiles to C amongst other languages. You can also use it to parse text, by describing your tokens with regex like syntax, and wiring token detection to state transitions. It sounds complex, but its actually really straightforward, and I have found it to output parsing code much faster and safer than I could write it, and it worked fine in embedded too. Zed Shaw sings its praises here.
  
  
• Expert C Programming: Deep C Secrets is a very good book, which should certainly not be your first or maybe second C book, but really digs into the innards in a very interesting and entertaining way.
  
  

There-in lies the flaw in your reasoning; you're looking online for an educational resource for an authoritatively defined programming language... and any moron can post rubbish online. To be clear on that, I'm also a moron... but I at least strive not to mislead people, where-as the author of this website doesn't give a crap. It seem he'll publish any nonsense, without learning, probably just to make himself look credible (even if the rubbish is misleading and the publishing of it is possibly illegal). I think maybe he's a sociopath, grooming his image as an educator at a university who has taken it upon himself to needlessly (and horrifically) reinvent the wheel of education.

Over the decades, K&R2E has taught many thousands of people the bulk of what we know as C without serious problems. Save yourself many headaches, request a copy at your library if you can't afford it... read through it, do the exercises as you stumble across them, and feel free to ask the people here if you have any problems with those exercises (don't skip exercises in this textbook). I have confidence that everyone here (except perhaps u/WesternLong) will honestly try to help you if they can. What they won't do is needlessly reinvent the wheel of education (or at least, so I hope), for like me, many of these people likely see no significant improvement that can be made upon the authoritative resources we used to learn.

The way you're going about it now, though, you'll stumble across this problem again and again: the idiots of the internet who assume the role of an educator without properly learning C, presumably in order to groom their own self esteem...

Two books to checkout could be:

1. File Structures : The C++ sample isn't all that great but it does teach you how to create on disk B+-Trees.
   
   
2. Database Systems : The entire book is mostly about Relational Databases. First half is mostly theory related stuff (like relational algebra etc) and the second half talks about implementation related stuff like indexes / storage / query engine.
   
   I'm not sure if these recommendations would be of much help. I'm not an expert either. However, though I'd put the names out there just in case.