https://www.amazon.com/21st-Century-Tips-New-School/dp/14919...
As mentioned in another post, David Hanson's "C Interfaces and Implementations - Techniques for Creating Reusable Software" [1] is a great book, stressing the design of good APIs. This book in particular might help you in your goal to become a better engineer.
On the free side, there's an excellent PDF by Jens Gustedt, "Modern C" [2]. I've not read the whole thing but it seems like an in-depth look at C11.
John Regehr's blog "Embedded in Academia" [3] is a good resource for C programming. You'll learn a lot about weird edge cases and undefined behavior. He also has a recent post about teaching C, with suggestions for resources [4].
[0] https://www.amazon.com/21st-Century-Tips-New-School/dp/14919...
[1] https://www.amazon.com/Interfaces-Implementations-Techniques...
[2] http://icube-icps.unistra.fr/img_auth.php/d/db/ModernC.pdf
http://www.amazon.com/21st-Century-Tips-New-School/dp/149190...
http://www.amazon.com/Interfaces-Implementations-Techniques-...
It uses Donald Knuth's literate programming which takes getting used to, however, it's a great case study of how to make a good library.
There is a new book on "21st Century C" which I haven't read. It has mixed reviews, however.
http://www.amazon.com/21st-Century-Tips-New-School/dp/144932...
http://www.amazon.com/21st-Century-Tips-New-School/dp/144932...
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