C++ Templates: The Complete Guide

by David Vandevoorde, Nicolai Josuttis, Douglas Gregor

Overview

Templates are among the most powerful features of C++, but they remain misunderstood and under-utilised, even as the C++ language and development community have advanced. In C++ Templates, 2nd Edition, three pioneering C++ experts show why, when, and how to use modern templates to build software that’s cleaner, faster, more efficient, and easier to maintain.

Now extensively updated for the C++11, C++14, and C++17 standards, this new edition presents state-of-the-art techniques for a wider spectrum of applications. The authors provide authoritative explanations of all new language features that either improve templates or interact with them, including variadic templates, generic lambdas, class template argument deduction, compile-time if, forwarding references, and user-defined literals. They also deeply delve into fundamental language concepts (like value categories) and fully cover all standard type traits.

The book starts with an insightful tutorial on basic concepts and relevant language features. The remainder of the book serves as a comprehensive reference, focusing first on language details and then on coding techniques, advanced applications, and sophisticated idioms. Throughout, examples clearly illustrate abstract concepts and demonstrate best practices for exploiting all that C++ templates can do.

• Understand exactly how templates behave, and avoid common pitfalls
• Use templates to write more efficient, flexible, and maintainable software
• Master today’s most effective idioms and techniques
• Reuse source code without compromising performance or safety
• Benefit from utilities for generic programming in the C++ Standard Library
• Preview the upcoming concepts feature

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Product Details

ISBN-13:	9780134778747
Publisher:	Pearson Education
Publication date:	09/14/2017
Sold by:	Barnes & Noble
Format:	eBook
Pages:	832
File size:	67 MB
Note:	This product may take a few minutes to download.
Age Range:	18 Years

About the Author

David Vandevoorde started programming C++ in the late 1980s. After obtaining a PhD from the Rensselaer Polytechnic Institute, he became technical lead of Hewlett-Packard’s C++ compiler team. In 1999 he joined the Edison Design Group (EDG), whose C++ compiler technology is widely recognized as the industry’s most advanced. He is an active member of the C++ Standard Committee and a moderator of the newsgroup comp.lang.c++.moderated (which he co-founded). He is the author of C++ Solutions, the companion to The C++ Programming Language, 3rd Edition.

 

Nicolai M. Josuttis is well known for his best-selling de-facto standard bookThe C++ Standard Library - A Tutorial and Reference. He is an independent technical consultant who designs object-oriented software for the telecommunications, traffic, finance, and manufacturing industries. He is an active member of the C++ Standard Committee and a partner at System Bauhaus, a German group of prominent object-oriented system development experts. Josuttis has written several other books on object-oriented programming and C++.

 

Douglas Gregor is Senior Swift/C++/Objective-C Compiler Engineer at Apple. He holds a PhD in computer science from Rensselaer Polytechnic Institute, and did post-doctoral work at Indiana University.

Read an Excerpt

The idea of templates in C++ is more than ten years old. C++ templates were already documented in 1990 in the Annotated C++ Reference Manual or so-called "ARM" (see EllisStroustrupARM) and they had been described before that in more specialized publications. However, well over a decade later we found a dearth of literature that concentrates on the fundamental concepts and advanced techniques of this fascinating, complex, and powerful C++ feature. We wanted to address this issue and decided to write the book about templates (with perhaps a slight lack of humility).

However, we approached the task with different backgrounds and with different intentions. David, an experienced compiler implementer and member of the C++ Standard Committee Core Language Working Group, was interested in an exact and detailed description of all the power (and problems) of templates. Nico, an "ordinary" application programmer and member of the C++ Standard Committee Library Working Group, was interested in understanding all the techniques of templates in a way that he could use and benefit from them. In addition, we both wanted to share this knowledge with you, the reader, and the whole community to help to avoid further misunderstanding, confusion, or apprehension.

As a consequence, you will see both conceptual introductions with day-to-day examples and detailed descriptions of the exact behavior of templates. Starting from the basic principles of templates and working up to the "art of template programming," you will discover (or rediscover) techniques such as static polymorphism, policy classes, metaprogramming, and expression templates. You will also gain a deeper understanding of the C++standard library, in which almost all code involves templates.

We learned a lot and we had much fun while writing this book. We hope you will have the same experience while reading it. Enjoy!Acknowledgments

This book presents ideas, concepts, solutions, and examples from many sources. In a way it does not seem fair that our names are the only ones on the cover. We'd like to thank all the people and companies who helped and supported us during the past few years. First, we'd like to thank all the reviewers and everyone else who gave us their opinion on early manuscripts. These people endow the book with a quality it would never have had without their input. The reviewers for this book were Kyle Blaney, Thomas Gschwind, Dennis Mancl, Patrick McKillen, and Jan Christiaan van Winkel. Special thanks to Dietmar Kuhl who meticulously reviewed and edited the whole book. His feedback was an incredible contribution to the quality of this book. We'd also like to thank all the people and companies who gave us the opportunity to test our examples on different platforms with different compilers. Many thanks to the Edison Design Groupfor their great compiler and their support. It was a big help during the standardization process and the writing of this book. Many thanks also go to all the developers of the free GNU and egcs compilers (Jason Merrill was especially responsive), and to Microsoft for an evaluation version of Visual C++ (Jonathan Caves, Herb Sutter and Jason Shirk were our contacts there).

Much of the existing "C++ Wisdom" was collectively created by the online C++ community. Most of that comes from the moderated Usenet groups comp.lang.c++.moderated and comp.std.c++. We are therefore especially indebted to the active moderators of those groups, who keep the discussions useful and constructive. We also much appreciate all those who over the years have taken the time to describe and explain their ideas for us all to share.The Addison Wesley team did another great job. We are most indebted to Debbie Lafferty (our editor) for her gentle prodding, good advice, and relentless hard work in support of this book. We're grateful also to Marina Lang who first sponsored this book within Addison Wesley. Susan Winer contributed an early round of editing that helped shape our later work.Nico's Acknowledgments

My first personal thanks goes with a lot kisses to my family: Ulli, Lucas, Anica, and Frederic did support this book with a lot patience, consideration, and spur. In addition, I want to thank David. His expertise turned out to be incredible. But, his patience was even better (sometimes I ask really silly questions). It is a lot of fun to work with him.David's Acknowledgments

My wife Karina has been instrumental in this book coming to a conclusion and I am immensely grateful for the role that she plays in my life. Writing "in your spare time" quickly becomes erratic when many other activities vie for your schedule. Karina helped me to manage that schedule, taught me to say "No" in order to make the time needed to make regular progress in the writing process,and above all was amazingly supportive of this project. I thank God every day for her friendship and love.

I'm also tremendously grateful to have been able to work with Nico. Besides his directly visible contributions to the text, his experience and discipline moved us from my pitiful doodling to a well organized production.John "Mr. Template" Spicer and Steve "Mr. Overload" Adamczyk are wonderful friends and colleagues, but in my opinion they are (together) also the ultimate authority regarding the core C++ language. They clarified many of the trickier issues described in this book, and should you find an error in the description of a C++ language element, it is almost certainly attributable to my failing toconsult with them.

Finally, I want to express my appreciation to those who were supportive of this project without necessarily contributing to it directly (the power of cheer cannot be understated). First are my parents: Their love for me and their encouragements make all the difference. And then, there are the numerous friends constantly asking "How is the book going?"; they too were a source of encouragement: Michael Beckmann, Brett and Julie Beene, Jarran Carr, Simon Chang, Ho and Sarah Cho, Christophe De Dinechin, Peter and Ewa Deelman, Neil and Tammy Eberle, Sassan Hazeghi, Vikram Kumar, Jim and Lindsay Long, Franklin Luk, Richard and Marianna Morgan, Ragu Raghavendra, Jim and Phuong Sharp, Gregg Vaughn, and John Wiegley.

Table of Contents

Preface.
Acknowledgments.
1. About this Book.

What You Should Know Before Reading this Book.
Overall Structure of the Book.
How to Read this Book.
Some Remarks About Programming Style.
The Standard vs. Reality.
Example Code and Additional Information.
Feedback.

I. THE BASICS.

2. Why Templates?
3. Function Templates.

A First Look at Function Templates.

Defining the Template.
Using the Template.

Argument Deduction.
Template Parameters.
Overloading Function Templates.
Summary.

4. Class Templates.

Implementation of Class Template Stack.

Declaration of Class Templates.
Implementation of Member Functions.

Usage of Class Template Stack.
Specializations of Class Templates.
Partial Specialization.
Default Template Parameters.
Summary.

5. Nontype Template Parameters.

Nontype Class Template Parameters.
Nontype Function Template Parameters.
Restrictions for Nontype Template Parameters.
Summary.

6. Tricky Basics.

Keyword typename.

The .template Construct.

Using this-
Member Templates.
TemplateTemplate Parameters.

Template Template Argument Matching.

Zero Initialization.
Summary.

7. Using Templates in Practice.

The Inclusion Model.

Linker Errors.
The Inclusion Mode.

Explicit Instantiation.

Example of Explicit Instantiation.
Combining the Inclusion Model and Explicit Instantiation.

Exporting Templates.

The Keyword export.
Limitations of the Separation Model.
Preparing for the Separation Model.

Templates and inline.
Precompiled Headers.
Debugging Templates.

Decoding the Error Novel.
Shallow Instantiation.
Long Symbols.
Tracers.
Oracles.
Archetypes.

Afternotes.
Summary.

8. Basic Template Terminology.

“Class Template” or “Template Class” ?
Instantiation and Specialization.
Declarations versus Definitions.
The One Definition Rule.
Template Arguments versus Template Parameters.

II. TEMPLATES IN DEPTH.

9. Fundamentals In Depth.

Parameterized Declarations.

Virtual Member Functions.
Linkage Of Templates.
Primary Templates.

Template Parameters.

Template Type Parameters.
Template Nontype Parameters.
Template Template Parameters.
Default Template Arguments.

Template Arguments.

Function Template Arguments.
Template Type Arguments.
Template Nontype Arguments.
Template Template Arguments.
Equivalence.

Friends.

Friend Functions.
Friend Templates.

10. Names in Templates.

Name Taxonomy.
Looking Up Names.

Argument-Dependent Lookup.
Friend Name Injection.
Injected Class Names.

Parsing Templates.

Context Sensitivity in Nontemplates.
Dependent Names of Types.
Dependent Names of Templates.
Dependent Names in Using-Declarations.

Derivation and Class Templates.

Nondependent Base Classes.
Dependent Base Classes.

Afternotes.

11. Instantiation.

On-Demand Instantiation.
Lazy Instantiation.
The C++ Instantiation Model.

Two-Stage Lookup.
Points of Instantiation.
The Inclusion and Separation Models.
Looking Across Translation Units.
Examples.

Implementation Schemes.

Greedy Instantiation.
Queried Instantiation.
Iterated Instantiation.

Explicit Instantiation.

Purpose and Limitations.

Afternotes.

12. Function Template Argument Deduction.

Deduction Process.
Deduced Contexts.
Special Deduction Situations.
Allowable Argument Conversions.
Class Template Parameters.
Default Call Arguments.
Avoiding Deduction: The Barton-Nackman Trick.
Afternotes.

13. Specialization and Overloading.

When “Generic Code” Doesn't Quite Cut It.

Transparent Customization.
Semantic Transparency.

Overloading Function Templates.

Signatures.
Partial Ordering of Overloaded Function Templates.
Formal Ordering Rules.
Templates and Nontemplates.

Explicit Specialization.

Full Class Template Specialization.
Full Function Template Specialization.
Full Member Specialization.

Partial Class Template Specialization.
Afternotes.

14. Future Directions.

The Angle Bracket Hack.
Relaxed typename Rules.
Default Function Template Arguments.
String Literal and Floating-Point Template Arguments.
Relaxed Matching Of Template Template Parameters.
Typedef Templates.
Partial Specialization of Function Templates.
The typeof Operator.
Named Template Arguments.
Static Properties.
Custom Instantiation Diagnostics.
Overloaded Class Templates.
List Parameters.
Layout Control.
Initializer Deduction.
Function Expressions.

III. Templates and Design.

15. The Polymorphic Power Of Templates.

Dynamic Polymorphism.
Static Polymorphism.
Dynamic versus Static Polymorphism.

Combining both Forms.

New Forms of Design Patterns.
Generic Programming.
Afternotes.

16. Traits and Policy Classes.

An Example: Accumulating A Sequence.

Fixed Traits.
Value Traits.
Parameterized Traits.
Policies and Policy Classes.
Traits and Policies: What's The Difference?
Member Templates vs. Template Template Parameters.
Combining Multiple Policies and/or Traits.
Accumulation with General Iterators.

Type Functions.

References and Qualifiers.

Type Classification.

Determining Fundamental Types.
Enumeration Classification With Overload Resolution.
Determining Compound Types.
Identifying Function Types.
Determining Class Types.
Putting it all Together.

Promotion Traits.
Policy Traits.

Read-only Parameter Types.
Copying, Swapping and Moving.

Afternotes.

17. Templates and Inheritance.

Named Template Arguments.
The Empty Base Class Optimization (EBCO).

Layout Principles.
Members as Bases.

The Curiously Recurring Template Pattern (CRTP).
Parameterized Virtuality.
Afternotes.

18. Metaprograms.

A First Example of a Metaprogram.
Enumeration Values versus Static Constants.
A Second Example: Processing the Square Root.

Tracking All Instantiations.

Using Induction Variables.
Computational Completeness.
Recursive Instantiation vs. Recursive Template Arguments.
Using Metaprograms to Unroll Loops.
Expression Templates.

Temporaries and Split Loops.
Encoding Expressions in Template Arguments.
Performance and Limitations of Expression Templates.

Afternotes.

IV. Advanced Applications.

19. Smart Pointers.

Holders and Trules.

Protecting Against Exceptions.
Holders.
Holders as Members.
Resource Acquisition is Initialization.
Holder Limitations.
Copying Holders.
Copying Holders Across Function Calls.
Trules.

Reference Counting.

Where Is The Counter?
Concurrent Counter Access.
Destruction and Deallocation.
The CountingPtr Template.
A Simple Non-Intrusive Counter.
A Simple Intrusive Counter Template.
Constness.
Implicit Conversions.
Comparisons.

Afternotes.

20. Tuples.

Duos.
Recursive Duos.

Number of Fields.
Type of Fields.
Value of Fields.

Tuple Construction.
Afternotes.

21. Function Objects and Callbacks.

Direct, Indirect, and Inlined Calls.
Pointers and References to Functions.
Pointer to Member Functions.
Class Type Functors.

A First Example of Class Type Functors.
Type of Class Type Functors.

Specifying Functors.

Functors as Template Type Arguments.
Functors as Function Call Arguments.
Combining Function Call Parameters and Template Type Parameters.
Functors as Template Nontype Arguments.
Function Pointer Encapsulation.

Introspection.

Analyzing A Functor Type.
Accessing Parameter Types.
Encapsulating Function Pointers.

Composition.

Simple Composition.
Mixed Type Composition.
Reducing the Number of Parameters.

Value Binders.

Selecting the Binding.
Bound Signature.
Argument Selection.
Convenience Functions.

Afternotes.

APPENDIX.

A: The One Definition Rule.

Translation Units.
Declarations and Definitions.
One Definition Rule.

One-Per-Program Constraints.
One-Per-Translation Unit Constraints.
Cross-Translation Unit Equivalence Constraints.

B: Overload Resolution.

When does Overload Resolution Kick in?
Simplified Overload Resolution.

The Implied Argument For Member Functions.
Refining The Perfect Match.

Overloading Details.

Prefer Nontemplates.
Conversion Sequences.
Pointer Conversions.
Functors And Surrogate Functions.
Other Overloading Contexts.

C: Resources.

Newsgroups.
Books and Websites.
Book Recommendations.

Glossary.
Index.

Preface

The idea of templates in C++ is more than ten years old. C++ templates were already documented in 1990 in the Annotated C++ Reference Manual or so-called "ARM" (see EllisStroustrupARM) and they had been described before that in more specialized publications. However, well over a decade later we found a dearth of literature that concentrates on the fundamental concepts and advanced techniques of this fascinating, complex, and powerful C++ feature. We wanted to address this issue and decided to write the book about templates (with perhaps a slight lack of humility).

However, we approached the task with different backgrounds and with different intentions. David, an experienced compiler implementer and member of the C++ Standard Committee Core Language Working Group, was interested in an exact and detailed description of all the power (and problems) of templates. Nico, an "ordinary" application programmer and member of the C++ Standard Committee Library Working Group, was interested in understanding all the techniques of templates in a way that he could use and benefit from them. In addition, we both wanted to share this knowledge with you, the reader, and the whole community to help to avoid further misunderstanding, confusion, or apprehension.

As a consequence, you will see both conceptual introductions with day-to-day examples and detailed descriptions of the exact behavior of templates. Starting from the basic principles of templates and working up to the "art of template programming," you will discover (or rediscover) techniques such as static polymorphism, policy classes, metaprogramming, and expression templates. You will also gain a deeper understanding of the C++standard library, in which almost all code involves templates.

We learned a lot and we had much fun while writing this book. We hope you will have the same experience while reading it. Enjoy!

Acknowledgments

This book presents ideas, concepts, solutions, and examples from many sources. In a way it does not seem fair that our names are the only ones on the cover. We'd like to thank all the people and companies who helped and supported us during the past few years. First, we'd like to thank all the reviewers and everyone else who gave us their opinion on early manuscripts. These people endow the book with a quality it would never have had without their input. The reviewers for this book were Kyle Blaney, Thomas Gschwind, Dennis Mancl, Patrick McKillen, and Jan Christiaan van Winkel. Special thanks to Dietmar Kuhl who meticulously reviewed and edited the whole book. His feedback was an incredible contribution to the quality of this book. We'd also like to thank all the people and companies who gave us the opportunity to test our examples on different platforms with different compilers. Many thanks to the Edison Design Groupfor their great compiler and their support. It was a big help during the standardization process and the writing of this book. Many thanks also go to all the developers of the free GNU and egcs compilers (Jason Merrill was especially responsive), and to Microsoft for an evaluation version of Visual C++ (Jonathan Caves, Herb Sutter and Jason Shirk were our contacts there).

Much of the existing "C++ Wisdom" was collectively created by the online C++ community. Most of that comes from the moderated Usenet groups comp.lang.c++.moderated and comp.std.c++. We are therefore especially indebted to the active moderators of those groups, who keep the discussions useful and constructive. We also much appreciate all those who over the years have taken the time to describe and explain their ideas for us all to share.The Addison Wesley team did another great job. We are most indebted to Debbie Lafferty (our editor) for her gentle prodding, good advice, and relentless hard work in support of this book. We're grateful also to Marina Lang who first sponsored this book within Addison Wesley. Susan Winer contributed an early round of editing that helped shape our later work.

Nico's Acknowledgments

My first personal thanks goes with a lot kisses to my family: Ulli, Lucas, Anica, and Frederic did support this book with a lot patience, consideration, and spur. In addition, I want to thank David. His expertise turned out to be incredible. But, his patience was even better (sometimes I ask really silly questions). It is a lot of fun to work with him.

David's Acknowledgments

My wife Karina has been instrumental in this book coming to a conclusion and I am immensely grateful for the role that she plays in my life. Writing "in your spare time" quickly becomes erratic when many other activities vie for your schedule. Karina helped me to manage that schedule, taught me to say "No" in order to make the time needed to make regular progress in the writing process,and above all was amazingly supportive of this project. I thank God every day for her friendship and love.

I'm also tremendously grateful to have been able to work with Nico. Besides his directly visible contributions to the text, his experience and discipline moved us from my pitiful doodling to a well organized production.John "Mr. Template" Spicer and Steve "Mr. Overload" Adamczyk are wonderful friends and colleagues, but in my opinion they are (together) also the ultimate authority regarding the core C++ language. They clarified many of the trickier issues described in this book, and should you find an error in the description of a C++ language element, it is almost certainly attributable to my failing toconsult with them.

Finally, I want to express my appreciation to those who were supportive of this project without necessarily contributing to it directly (the power of cheer cannot be understated). First are my parents: Their love for me and their encouragements make all the difference. And then, there are the numerous friends constantly asking "How is the book going?"; they too were a source of encouragement: Michael Beckmann, Brett and Julie Beene, Jarran Carr, Simon Chang, Ho and Sarah Cho, Christophe De Dinechin, Peter and Ewa Deelman, Neil and Tammy Eberle, Sassan Hazeghi, Vikram Kumar, Jim and Lindsay Long, Franklin Luk, Richard and Marianna Morgan, Ragu Raghavendra, Jim and Phuong Sharp, Gregg Vaughn, and John Wiegley.

Editorial Reviews

The Barnes & Noble Review
It’s now over a decade since C++ templates were first conceived, yet many C++ programmers still don’t understand them thoroughly and don’t understand just how powerful they can be. Moreover, some developers who try to use templates often find themselves surprised by behavior they would’ve expected if they really understood how C++ supports template-based techniques. In C++ Templates, David Vandevoorde and Nicolai M. Josuttis set out to remedy this -- and they succeed.

The authors begin by introducing function and class templates, nontype template parameters, and several of what they (accurately) call “tricky basics.” They walk through using templates in practice, then move on to in-depth discussions of template naming, instantiation, specialization, overloading, and design issues. The book concludes with an entire section on advanced applications utilizing type classification, smart pointers, tuples, and other techniques.

Vandevoorde, one of the world’s leading C++ compiler experts, co-founded and moderates the comp.lang.c++.moderated newsgroup. Josuttis wrote one of the world’s most widely used C++ books, The C++ Standard Library: A Tutorial and Reference. They’re both on the C++ standards committees. Few people can touch their knowledge of C++ and templates. You’ll really appreciate having that knowledge at your fingertips. Bill Camarda

Bill Camarda is a consultant, writer, and web/multimedia content developer. His 15 books include Special Edition Using Word 2000 and Upgrading & Fixing Networks For Dummies®, Second Edition.