This document is by far the best out there on the net explaining step by step how argp works!
Download actual file here
If you have ever wondered where to find the text “Give this help list”, it is contained in the file argp_parse.c
This file is in the argp folder in the package eglibc-2.19.
You can get hold of this package by running: apt-get source libc6.
All of this is within the glibc or ebligc binaries on your Ubuntu/Debian systems of course. But just in case you wondered.