C++ FAQs: Frequently Asked Questions

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Preface

FAQ 0.1

What is the purpose of this book?

The purpose of the book is to change the way you think.

Changing the way you think is much more challenging than learning the syntax of a programming language. For example, learning when and why you should use a particular construct is much harder than learning the syntax for that construct. Learning when not to use a particular construct is even harder.

This book gives specific advice and directions to help you properly use C++ for object-oriented programming. If you are new to object-oriented programming, our aim is to convert you to the object-oriented way of thinking. If you are a seasoned veteran, our aim is to have you question some of your ingrained practices and possibly adopt new approaches to using C++ --approaches that will scale better.

FAQ 0.2

What is unique about the style and format of this book?

To achieve the book's goals, we used a novel style and format. Here are the key elements of that style and format.

• A question and answer format: This book contains answers to Frequently Asked Questions (or FAQs) about using C++ for object-oriented programming. These FAQs are the product of several years of teaching others to use C++ effectively, as well as an embarrassingly large number of hours corresponding with the international C++ user community via the Internet news group, comp.lang.c++.
• A focus on principles and concepts rather than syntax: Rather than focusing on the syntax and semantics of various C++ language features, this book shows how to combine features properly and why to combine them.
• A consistent programming and design philosophy: As with any programming language, there are numerous ways to use and combine the various features of C++. Some of these uses and combinations lead to comprehendable, maintainable, extensive, and reusable software; other uses and combinations only work in small examples and are, in reality, abuses of the language. These FAQs identify which uses and combinations are preferred and promote a consistent programming and design philosophy that has good scaling properties.
• Lots of programming examples: This book contains almost 200 programming examples, most of which are complete, runnable programs rather than program fragments. Readers are encouraged to dissect and execute the examples because this will enhance the learning experience.
• Extensive cross referencing: The FAQs in this book are extensively cross referenced to other FAQs, as well as to other C++ books. Since the topic of using C++ for object-oriented programming is too large to be completely covered by one book, we provide you with pointers into other books where complementary material can be found. Three books we selected for cross referencing: Stroustrup's The C++ Programming Language, Second Edition, an excellent description of the language; Ellis and Stroustrup's The Annotated C++ Reference Manual, an authoritative and comprehensive definition of the language; and Lippman's C++ Primer, Second Edition, an excellent introductory book.
• A lighthearted style: We want to change the way you think, so we have to debunk many common assumptions. This leads to the questioning of common practices and --to take the edge off-- humor. Another reason for the lighthearted style is that this book has roots in comp.lang.c++, where the communication style is direct and unforgiving, and where humor is used to calm people's passions and cajole people into seeing your point of view :-)

FAQ 0.3

Where did these FAQs come from?

We made them up.

Surprisingly, most of the FAQs contained in this book are not questions that anyone ever asked us directly. Instead they come from our experience training developers in object-oriented technology and from corresponding with readers on comp.lang.c++. Topics that come up again and again, whether during training sessions or on comp.lang.c++, were coalesced into a series of questions.

FAQ 0.4

Is every topic treated with equal emphasis?

No.

Some topics are covered in greater depth than other topics. We focus more energy on topics that historically have been most difficult for people to get right, and we almost completely ignore placement of semicolons and other issues that the compiler will tell you about. The more subtle the problem, the more we focus on it --especially practices that are accepted by the compiler and appear to function correctly, but which increase the overall cost of the software.

FAQ 0.5

How should you use this book in combination with other books?

It depends on what you're trying to achieve.

This book is not intended to be a tutorial introduction to C++. Each example is meant to illustrate a single idea relevant to that FAQ. Many introductory aspects of the language, such as the syntax of a for loop, are assumed. If you want to cover the fundamentals of C++, we recommend using this book in conjunction with either The C++ Programming Language, Second Edition or C++ Primer, Second Edition. Our FAQs provide extensive cross references into both of these texts.

This book is not intended to be a reference manual for C++. It does not pretend to cover all aspects of the language in encyclopedic detail. If you want such a reference manual, we recommend using this book in conjunction with The Annotated C++ Reference Manual. Our FAQs provide extensive cross references into this text.

FAQ 0.6

How is the book organized?

The FAQs are organized into more than 40 chapters, each of which is organized into ascending complexity.

The FAQs in each chapter all deal with a specific topic. Usually the questions near the beginning of a chapter deal with basic questions and fundamental concepts; later questions deal with advanced issues and complex topics.

The first third of the book deals with object-oriented aspects of C++ such as inheritance, dynamic binding, and polymorphism. The middle portion of the book deals with a variety of C++ facilities ranging from templates to exception handling to the proper management of pointers. The last portion of the book contains chapters that deal with environmental topics such as training, coding standards, and Smalltalk.

FAQ 0.7

Why did we create the electronic FAQ?

To bring order to chaos.

First, the electronic FAQ presents the facts (pun intended) about C++ in a more concise and focused manner than the somewhat chaotic discussions on comp.lang.c++. Second, the number of developers switching to C++ is amazing, and the electronic FAQ answers many basic questions for these new users. Third, without a FAQ list, seasoned veterans would become irritated by answering the same questions over and over; the electronic FAQ encourages the veterans to act more like ambassadors. In the end, the electronic FAQ makes comp.lang.c++ a kinder, gentler news group, where people are less likely to be "flamed" (a technical term for posting a particularly scathing, blistering, and sarcastic response to something that is posted to an electronic bulletin board).

FAQ 0.8

Why did we write this book?

To further spread the good news.

We decided to write this book for several reasons. First, Addison-Wesley expressed interest in such a project. Second, it would make the FAQs available to a wider audience since not everyone has access to Internet and comp.lang.c++. Third, a book permits the material to be presented in a more professional manner than can be easily done with the electronic FAQ. Fourth this project spurred us to expand the material vastly beyond what is provided by the electronic FAQ. In the end, after adding all the new FAQs, examples, and internal and external cross references, the book contains five times more material than the electronic FAQ.

FAQ 0.9

Are Marshall's and Greg's motivations based on language bigotry?

No.

For the record, we are not now --nor have we ever been-- C++ language bigots. We love Smalltalk, Eiffel, C, Lisp, CLOS, Prolog, Simula, Ada, Modula, Pascal, perl, awk, sed, csh, ksh, REXX, COBOL, FORTRAN, RPG, etc. At the same time, we adopted the philosophy that since we're writing a book about C++, we might as well throw ourselves into the project even if it means that we look like C++ fanatics. It certainly has made for more exciting and provocative writing and, we hope, reading.

Our main goal is to get you to think about what you are doing and how you might improve on it. If we accomplish this, then we will be satisfied.

FAQ 0.10

How can you communicate with us?

Email and FTP.

We'd love to hear from you. Our email address is clinefaq@aw.com. Send us your questions. Send us your comments.

You can acquire a free, machine-readable copy of the code sections in this book via FTP (ask your favorite network guru for help on how to access FTP with your software). The code sections will be available via FTP aw.com in the directory aw.computer.science/clinefaq. Use anonymous as your user ID, and use your email address as your password.

Enjoy!

0201589583P04062001

Table of Contents

Introduction.


Fundamentals of Object-Oriented Technology.


Fundamentals of Extensibility.


Fundamentals of C++.


Designing Classes and Objects.


Designing Good Interfaces.


Fundamentals of Inheritance.


Dynamic Binding.


Specifying Observable Behavior.


Proper Inheritance.


Correcting Improper Inheritance.


Edge-Effects of Inheritance.


Static and Dynamic Typing.


Constructors and Destructors.


Initialization Lists.


The Big Three.


User-Defined Assignment Operators.


Designing for Testability.


Friend Classes and Friend Functions.


Strategic Advice for Exception Handling.


Tactical Advice for Exception Handling.


Templates.


References.


New and Delete.


Preventing Memory Leaks.


Preventing Wild Pointers.


Const Correctness.


Operator Overloading.


Exploring Inline Functions.


Reference and Value Semantics.


Performance Tuning.


Input/Output.


Static Class Members.


Inter-Language Linkage with C.


Training.


Coding Standards.


Leaf Classes.


C++ and Smalltalk.


Private and Protected Inheritance.


Pointers to Member Functions.


Source Code.


Miscellaneous.


Getting More Information on C++. 0201589583T04062001

Errata

Errata for "C++ Frequently Asked Questions"
Marshall Cline/Greg Lomow
0-201-58958-3

Table of contents (pg vi): title of FAQ 50:
old: ... help beat the speed/safety tradeoff?
new: ... help beat the performance/encapsulation tradeoff?

Table of contents (pg xv): title of FAQ 316:
old: ... an object to manage a resource and also perform ...
new: ... a resource manager object's constructor to perform ...

Acknowledgments (pg xxi):
old: Steve Clammage
new: Steve Clamage

FAQ 10 (page 5): Add after the sentence ending "have an explicit return type.":
add: Also, we exploit the new C++ feature that requires the compiler to insert an implicit return 0; at 

end of main().

FAQ 88 (pg 66):
old: virtual nStack() { }
new: virtual ~Stack() { }

FAQ 117
old: Substitutablility
new: Substitutability

FAQ 141 (pg 128): Program output:
old: Derived::g(float)
 Derived::g(float)
new: Base::g(float)
 Base::g(float)

FAQ 142 (pg 129): Program output:
old: Derived::f(float)
 Derived::f(float)
new: Base::f(float)
 Base::f(float)

FAQ 180 (pg 171): Add at the very end of the answer:
add: If you use this technique, do not access the static object from the destructor of another static 

object.

FAQ 206 (pg 203):
old: systhesized
new: synthesized

FAQ 226 (pg 229): remove the line:  --numElems_;

FAQ 227 (pg 230):
old: ... must re-verify the object's state and its transitions there ...
new: ... must continually re-verify the object's state and its transitions, but there ...

FAQ 228 (pg 231): "friend DataBase;" should be private in class DataBaseCursor:
old: protected:
new: private:

FAQ 240 (pg 243):
old: friend Fraction operator*(const Fraction&,const Fraction&)
new: friend Fraction operator*(const Fraction& a,const Fraction& b)

FAQ 240 (pg 243): change "ostr" to "o" (in BOTTOM example on this page):
old: ostr << f.num_
new: o << f.num_

FAQ 245: contents of pgs 248 and 249 are swapped.

FAQ 265 (pg 270):
old: ...living dead -- object's that aren't quite alive but aren't quite...
new: ...living dead -- an object that isn't quite alive but isn't quite...

FAQ 266 (pg 272):
old: A() throw(int)  : x(), y() { cout << "A ctor\n"; }
new: A() throw(int)  : x_(), y_() { cout << "A ctor\n"; }

FAQ 271 (pg 276):
old: #include 
new: #include   //or  ...

FAQ 272 (pg 278): first line:
old: The unexpected function...
new: The unexpected() function...

FAQ 282 (pg 288):
old: //BAD FORM: manipulates (i.e., "manipulates") the bits of
 //the T objects:
new: //BAD FORM: manipulates the bits of the T objects:

FAQ 282 (pg 288):
old: #if 1s
new: #if 1

FAQ 302 (pg 304): In the "Flexibility:" paragraph
old: overridden
new: overloaded

FAQ 311 (pg 310):
old: protected:
new: private:

FAQ 313 (pg 312):
old: unsigned chk(unsigned i)          //checks index i
new: unsigned chk(unsigned i) const    //checks index i

FAQ 313 (pg 312): Change "T" to "int":
old: T*       arr_;
new: int*     arr_;

FAQ 342 (pg 340):
old: operator* (Number a, Number a)
new: operator* (Number a, Number b)

FAQ 380 (pg 376): In default ctor init list:
old: serial_(num)
new: serial_(num_)

FAQ 425 (pg 408): Paragraph that starts "Member function names":
old: ...class names are introduced with...
new: ...member function names are introduced with...

FAQ 425 (pg 409): Paragraph that starts "Data member names":
old: ...in multi-word class names...
new: ...in multi-word data member names...

FAQ 456 (pg 432):
old: #include 
new: #include 

Index (pg 453): Under "Evil things:"
old: evaluating inheritance via "specification"
new: evaluating inheritance via "specialization"



---
Marshall P. Cline, Ph.D.
President, Paradigm Shift, Inc.
P.O. Box 5108 / Potsdam, NY  13676
cline@parashift.com / 315-353-6100(voice) / 315-353-6110(fax)