The point is that you are telling people to use C instead of C++ and that the best way to do that is by using a library that is written in C++. I completely understand that it's invisible, but it's not irrelevant -- it's not eating your own dog food (given that you are the author of ZeroMQ).
ZeroMQ is a community of many projects. The old core library is libzmq, written in C++ by hundreds of people, led originally by Martin Sustrik. The library I'm explaining in this book is CZMQ, a high level C binding for libzmq that offers such things as actors, pollers, certificate management, beacons, and containers. CZMQ of course uses libzmq to send messages between processes and threads. In fact libzmq exposes only a C API, not C++ at all.
