Working with C APIs with Swift can get frustrating, and with C going to new platforms such as Linux this is becoming even more important.
Umberto Raimondi has written an excellent an in-depth guide to working with C going further than the official documentation and provides a playground for exploring things within Xcode.
The guide is very complete provides a number of nice examples especially on more complicated topics such as the different ways of working with C pointers.
You can find the tutorial over on the Uraimo blog.
A nice guide on working with C APIs in Swift.