Well, I got the book on the 5th, and read it and entered the code listings and worked through the exercises. My overall take on this book is this. I am a C++ programmer kinda new to DarkBASIC Pro and new to DarkGDK.
DarkGDK coverage
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This book contained almost everything I was expecting learn about DarkGDK. Given the sad state of the documentation at hand (the .chm file especially), it answered alot of questions I had about using the various db functions. It definately jumpstarted my ability to apply what I am learning in DBPro to DarkGDK. So for me personally, this aspect of the book made it, well, not fully worth the price tag, let's say justified the purchase.
C++ coverage
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This aspect leaves much to be desired. The book is 12 chapters long. You don't get to Arrays until chapter 10, and Strings and Files in chapter 11. So you pretty much learn the basics of procedural C using C++ for the first 11 chapters, since the strings in chapter 11 you cover are char arrays! A little ways into chapter 11 there is a section called, "Using Standard C++ Library Functions to Work with Strings." Here you learn the C string functions, ie. strlen, strcat, etc. You need to learn this since you are learning char arrays here, but you are instructed to #include <string.h> instead of the C++ <cstring>. So much for namespacing. References are only mentioned in function calls, pass by reference, and nowhere in the book are pointers discussed. Pointers are not even in the index. I don't know about you but I say they should drop $50 off the price tag for this, specifically for beginners new to C++ and the book's advertising does say "Learn C++", even on the back cover!
So, to existing C++ programmers completely new to DarkGDK, this book will suit you well, you can pretty much focus on the DarkGDK aspect.
To programmers wanting to learn C++, I would suggest a C++ book either before or after this book. This book pretty much teaches you what you will find in the first 4-5 chapters of the more popular beginner books. I would suggest "Beginning C++ Through Game Programming - Second Edition." It is not a "Game Programming" book, but rather a pretty good C++ beginner book that uses game analogies to get the point across, ie. Players and Enemies rather than Teachers and Students, Character Profiles rather than Employee records. And it uses Standard C++ from the modern perspective from the beginning, std::string, containers, etc.
Anyway, this is my personal opinion. Gonna put this review on amazon, and give the book 3 stars. Hope this answers some of your questions.
MFC Coder