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Developing a large-scale software system in C++ requires more than just a sound understanding of the logical design issues covered in most books on C++ programming. To be successful, you will also need a grasp of physical design concepts that, while closely tied to the technical aspects of development, include a dimension with which even expert software developers may have little or no experience.
This is the definitive book for all C++ software professionals involved in large development efforts such as databases, operating systems, compilers, and frameworks. It is the first C++ book that actually demonstrates how to design large systems, and one of the few books on object-oriented design specifically geared to practical aspects of the C++ programming language.
In this book, Lakos explains the process of decomposing large systems into physical (not inheritance) hierarchies of smaller, more manageable components. Such systems with their acyclic physical dependencies are fundamentally easier and more economical to maintain, test, and reuse than tightly interdependent systems. In addition to explaining the motivation for following good physical as well as logical design practices, Lakos provides you with a catalog of specific techniques designed to eliminate cyclic, compile-time, and link-time (physical) dependencies. He then extends these concepts from large to very large systems. The book concludes with a comprehensive top-down approach to the logical design of individual components. Appendices include a valuable design pattern "Protocol Hierarchy" designed to avoid fat interfaces while minimizing physical dependencies; the details of implementing an ANSI C compatible C++ procedural interface; and a complete specification for a suite of UNIX-like tools to extract and analyze physical dependencies. Practical design rules, guidelines, and principles are also collected in an appendix and indexed for quick reference.
From C to C++.
Using C++ to Develop Large Projects.
Software Development Tools.
I. BASICS.1. Preliminaries.
Multi-File C++ Programs.
A Few Matters of Style.
Logical Design Notation.
Inheritance versus Layering.
Summary.2. Ground Rules.
Member Data Access.
The Global Name Space.
Redundant Include Guards.
II. PHYSICAL DESIGN CONCEPTS.3. Components.
Components versus Classes.
Physical Design Rules.
The DependsOn Relation.
Extracting Actual Dependencies.
Summary.4. Physical Hierarchy.
A Metaphor for Software Testing.
A Complex Subsystem.
The Difficulty in Testing “Good” Interfaces.
Design for Testability.
Testing in Isolation.
Acyclic Physical Dependencies.
Hierarchical and Incremental Testing.
Testing a Complex Subsystem.
Testing versus Tested.
Cyclic Physical Dependencies.
Cumulative Component Dependency (CCD).
Physical Design Quality.
Some Causes of Cyclic Physical Dependencies.
From Encapsulation to Insulation.
C++ Constructs and Compile-Time Coupling.
Partial Insulation Techniques.
Total Insulation Techniques.
The Procedural Interface.
To Insulate or Not to Insulate.
From Components to Packages.
Registered Package Prefixes.
The Release Process.
The main Program.
III. LOGICAL DESIGN ISSUES.8. Architecting a Component.
Abstractions and Components.
Component Interface Design.
Degrees of Encapsulation.
Auxiliary Implementation Classes.
Summary.9. Designing a Function.
Fundamental Types Used in the Interface.
Special Case Functions.
Summary.10. Implementing an Object.
Using C++ Templates in Large Projects.
Summary.Appendix A. Protocol Hierarchy.
As a member of the IC Division at Mentor Graphics Corporation, I am fortunate to have worked with many bright, talented software engineers, developing very large systems.
Back in 1985, Mentor Graphics became one of the first companies to attempt a truly large project in C++. Back then no one knew how to do that, and no one could have anticipated the cost overruns, slipped schedules, huge executables, poor performance, and incredibly expensive build times that a naive approach would inevitably produce.
Many valuable lessons were learned along the way - knowledge obtained through bitter experience. There were no books to help guide the design process; object-oriented designs on this scale had never before been attempted.
Ten years later, with a wealth of valuable experience under its belt, Mentor Graphics has produced several large software systems written in C++, and in doing so has paved the way for others to do the same without having to pay such a high price for the privilege.
During my 13 years as a C (turned C++) Computer-Aided Design (CAD) software developer, I have seen over and over again that planning ahead invariably produces a higher-quality, more maintainable product. My emphasis at Mentor Graphics has been on helping to ensure that quality is an integral part of the design process from the very start.
In 1990 I developed the graduate course "Object-Oriented Design and Programming" at Columbia University. As the instructor of this course since 1991, I have had the opportunity to share many of the insights that we at Mentor Graphics gained during our industrial-strength software development efforts. Questions and feedback from literally hundreds of graduate students and professional programmers have helped me to crystallize many important concepts. This book is a direct result of that experience. To my knowledge, this is the first text that identifies development and quality issues that arise only in large C++ projects. I hope that this information will be as useful in your work as it is in mine.
Developing a large-scale software system in C++ requires more than just a sound understanding of the logical design issues covered in most books on C++ programming. Effective design also requires a grasp of physical design concepts that, although closely tied to the technical aspects of development, include a dimension with which even expert professional software developers may have little or no experience.
Yet most of the advice presented in this book also applies to small projects. It is typical for a person to start with a small project and then begin to take on larger and more challenging enterprises. Often the scope of a particular project will expand, and what starts out as a small project becomes a major undertaking. The immediate consequences of disregarding good practice in a large project, however, are far more severe than they are for disregarding good practice in a smaller project.
This book unites high-level design concepts with specific C++ programming details to satisfy two needs:
In short, if you feel that you know C++ well, but would like to understand more about how to use the language effectively on large projects, this book is for you.
Except where otherwise indicated, all examples in this text are intended to represent "good design." Examples presented in earlier chapters are therefore consistent with all practices recommended throughout the book. A disadvantage of this approach is that you may see code that is written differently from the code you are used to seeing, without yet knowing exactly why. I feel that being able to use all of the examples in the book for reference compensates for this drawback.
There are two notable exceptions to this practice: comments and package prefixes. Comments for many of the examples in this text have simply been omitted for lack of space. Where they are presented, they are at best minimal. Unfortunately, this is one place where the reader is asked to "do as I say, not as I do" -- at least in this book. Let the reader be assured that in practice I am scrupulous about commenting all interfaces as I write them (not after).
The second exception is the inconsistent use of package prefixes in the early examples of the book. In a large project environment package prefixes are required, but they are awkward at first and take some getting used to. I have elected to omit the consistent use of registered package prefixes until after they are formally presented in Chapter 7, so as not to detract from the presentation of other important fundamental material.
Many texts note that inline functions are used in examples for textual brevity when illustrating intended functionality. Since much of this book is directly related to organizational issues such as when to inline, my tendency will be to avoid inline functions in examples. If a function is declared
inline, there is a justification for it beyond notational convenience.
Developing large systems in C++ is a constant series of engineering trade-offs. There are almost no absolutes. It is tempting to make statements using words such as never and always. Such statements allow for a simplified presentation of the material. For the level of C++ programmers whom I expect will read this book, such sweeping statements would be challenged - and rightly so. To avoid getting side-tracked in such situations, I will state what is (almost) always true, and then provide a footnote or a pointer to the exceptional case.
There are a variety of popular file name extensions used to distinguish C++ header files and C++ implementation files. For example:
Header File Extensions:Throughout the examples we consistently use the
.h .hxx .H .h++ .hh .hpp
Implementation File Extensions:
.c .cxx .C .c++ .cc .cpp
.hextension to identify C++ header files and the
.cextension to identify C++ implementation files. In the text, we will frequently refer to header files as
.hfiles and to implementation files as
.cfiles. Finally, all of the examples in this text have been compiled and are syntactically correct using SUN's version of CFRONT 3.0 running on SUN SPARC stations, as well as on HP700 series machines running their native C++ compiler. Of course, any errors are the sole responsibility of the author.
Chapter 0: Introduction. An overview of what lies in wait for the large-scale C++ software developer.
PART I: BASICS
Chapter 1: Preliminaries. A review of basic language information, common design patterns, and style conventions used in this book.
Chapter 2: Ground Rules. Important design practices that should be followed in any C++ project.
The remainder of the text is divided into two main sections. The first, entitled "Physical Design Concepts," presents a sequence of important topics related to the physical structure of large systems. The material in these chapters (3 through 7) focuses on aspects of programming that will be entirely new to many readers, and cuts right to the bone of large program design. This section is presented "bottom up," with each chapter drawing on information developed in previous chapters.
PART II: PHYSICAL DESIGN CONCEPTS
Chapter 3: Components. The fundamental physical building blocks of a system.
Chapter 4: Physical Hierarchy. The importance of creating a hierarchy of components with acyclic physical dependencies for testing, maintainability, and reuse.
Chapter 5: Levelization. Specific techniques for reducing link-time dependencies.
Chapter 6: Insulation. Specific techniques for reducing compile-time dependencies.
Chapter 7: Packages. Extending the above techniques to yet larger systems.
The final section, entitled "Logical Design Issues," addresses the conventional discipline of logical design in conjunction with physical design. These chapters (8 through 10) address the design of a component as a whole, summarize the myriad issues surrounding sensible interface design, and address implementation issues in the context of a large-project environment.
PART III: LOGICAL DESIGN ISSUES
Chapter 8: Architecting a Component. An overview of considerations important to the overall design of components.
Chapter 9: Designing a Function. A detailed survey of the issues involved in creating a component's functional interface.
Chapter 10: Implementing an Object. Several organizational issues specific to the implementation of objects in a large-project environment.
Topics found in the appendixes are referenced throughout the text.
First and foremost, I would like to recognize the contributions of my friend, colleague, and former college classmate Franklin Klein, who reviewed virtually every page of the manuscript in its raw form. Franklin provided a sounding board for presenting many concepts that will be new to most software developers. The depth of Franklin's wisdom, intelligence, knowledge, diplomacy, and grasp of the nuances of effective communication is unprecedented in my experience. His detailed comments are responsible for countless revisions in the content, flow, and demeanor of the presentation.
Several dedicated and gifted software professionals reviewed all or most of the material in this book during its formative stages. I consider myself fortunate that they agreed to invest their valuable time reviewing this book. I would like to thank Brad Appleton, Rick Cohen, Mindy Garber, Matt Greenwood, Amy Katriel, Tom O'Rourke, Ann Sera, Charles Thayer, and Chris Van Wyk for the enormous energy they spent helping to make this book as valuable as it could be. In particular, I would like to thank Rick Eesley for many fertile discussions and practical recommendations - especially his plea for a summary at the end of each chapter.
Several expert software developers and quality assurance engineers reviewed individual chapters. I would like to thank Samir Agarwal, Jim Anderson, Dave Arnone, Robert Brazile, Tom Cargill, Joe Cicchiello, Brad Cox, Brian Dalio, Shawn Edwards, Gad Gruenstein, William Hopkins, Curt Horkey, Ajay Kamdar, Reid Madsen, Jason Ng, Pete Papamichael, Mahesh Ragavan, Vojislav Stojkovic, Clovis Tondo, Glenn Wikle, Steve Unger, and John Vlissides for their technical contributions. I would also like to thank Lisa Cavaliere-Kaytes and Tom Matheson of Mentor Graphics for their suggestions regarding some of the figures in this text. In addition I would like to acknowledge the contributions of Eugene Lakos and Laura Mengel.
This book might never have been written were it not for a promotional letter I received at Columbia University offering me a complimentary review copy of Rob Murray's book. Since I teach only during the Spring semester, I returned the enclosed form, but requested that the book be sent to Mentor Graphics instead of Columbia. Soon after that, I received a call from Pradeepa Siva (of Addison-Wesley's Corporate & Professional Publishing Group) determined to get to the bottom of this unusual request. After convincing her of its legitimacy (and some perhaps gratuitous self aggrandizement) she remarked, "I think my boss would like to talk with you." A few days after that, I met with her boss - the publisher. I had always revered the excellence of the Professional Computing Series produced by this group, and it is that reputation that ultimately compelled me to commit to writing this book for that series.
I owe a great deal to the members of the Corporate & Professional Publishing Group at Addison-Wesley. John Wait, its publisher, has patiently provided me with insights into people and communication that I will forever cherish. From relentlessly reading books and reviews, to direct discussions with individual software professionals, to standing in bookstores and discretely observing the buying habits of potential readers, John Wait has his fingers on the pulse of the industry.
The production staff headed by Marty Rabinowitz is dedicated to excellence in all its respects. Despite apprehension expressed to me by authors in academia (associated with other publishers), I was delighted with the tremendous importance placed by Marty on delivering a technically accurate, readily usable, and aesthetically appealing rendering of the author's ideas. I especially want to thank Frances Scanlon for her tireless and seemingly endless efforts in typesetting this entire book.
Brian Kernighan, the technical editor of this series, provided valuable contributions on both style and substance, as well as finding many typographical errors and inconsistencies that no one else caught. The depth and breadth of his knowledge coupled with his concise writing style has in no small way contributed to the success of this series.
Finally, I would like to thank the other authors in this series for documenting fundamental logical concepts and design practices that this book takes for granted.