First off, the composite authors name is Lapin, not Laping.
I used this book back around 1990 to develop a large software suite. The first 5 chapters are an excellent intro to portable C coding. We used the beginning chapters to design and develop our common platform headers, libraries and Make system. We did not take their examples unchanged, but used them as starting points for a our needs, which was a somewhat more comprehensive system. My team gives the book credit for helping us get us some of our 10x improvements. Still have not seen the likes of this book even today, in terms of the quality of data to use.
The last half of the book is a summary of different API calls and /bin functions available on different Unixes of the day. Interesting now, from a historical perspective.