This book is an introduction to how the object-oriented methodology works and how it can be implemented in both C and C++. Topics not treated in other books on the subject include: how to use C in an object-oriented fashion; presents problems that are likely to arise in C++ applications and how C++ in some object-oriented applications; the final chapter shows how to do real object-oriented programming in a C or C++ environment. C++ is not a full object-oriented language like Smalltalk-it only gets you about two-thirds of the way there. The last chapter shows you how to work around this deficiency in the language. It uses significant real world examples throughout rather than resorting to tivial examples which skirt the deficiencies of the language. The book relates difficult to understand C++ concepts directly to C,usually by showing how a C++ feature could be implemented in C by presenting code in both languages.
This was the book I used to learn C++. Holub takes a very unique approach. Some would call it the "C first" approach, but he goes beyond the typical "C first" way of doing things. The book assumes the reader doesn't know C. So the first third of the book teaches the C language. The rest of the book teaches about the structures of C++ from the perspective of C, and actually illustrates some C++ concepts using real C code, and then in the last part teaches actual C++. The idea being to familiarize the reader with what's going on under the "covers" of the language, and then to finally show the language itself. I much preferred this approach to the way many books of the time attempted to teach C++. As with C, it is very important to understand the semantics of your code in C++, not just in how your code will execute, but what your code is doing at the level "beneath" it, because "appearances" in the language are probably deceiving to the beginner.
A big part that's missing from this book is a discussion of templates. They didn't exist in the language at the time this book was written, in 1991. No updated edition has come out since then. So in that sense it's outdated. However, I would still recommend this book to anyone who wants to learn C++, with the aforementioned caveat.