[silentbicycle]

Author of the top post, here. Two of my favorite C books are David Hanson's _C Interfaces and Implementations_ and Peter van der Linden's _Expert C Programming: Deep C Secrets_.

The former is ostensibly about designing reusable modules for data structures (e.g. ring buffers), but also contains a lot of wisdom about API design, particularly how to make the most of what little API design tools C gives you. The latter is all over the place, from funny anecdotes about compiler bugs and programming contests to all kinds of useful C information that is too advanced for an intro book on C-the-language, but way too practical for most books on a specific domain: valuable details about linkers, symbol visibility, different kinds of allocation, and the memory hierarchy. Also, it's called "Deep C Secrets" and has a giant fish on the cover. What more do you need to know?

I skimmed "21st Century C" briefly a couple months back and didn't have strong feelings about it one way or the other.