The complexity of writing C++ is diminishing with each new standard and each new piece of teaching literature. Conferences, blogs, and books abound, and this is a good thing. The world does not have enough engineers of sufficient quality to solve the very real problems we face.
Despite the continuing simplification of the language, there is still much to learn about how to write good C++. Bjarne Stroustrup, the inventor of C++, and Herb Sutter, the convenor of the standards body that maintains C++, have devoted considerable resources to creating teaching materials for both learning C++ and writing better C++. These volumes include The C++ Programming Language1 and A Tour of C++,2 as well as Exceptional C++3 and C++ Coding Standards.4
1. Stroustrup, B, 2013. The C++ Programming Language, Fourth Edition. Boston: Addison-Wesley.
2. Stroustrup, B, 2018. A Tour of C++, Second Edition. Boston: Addison-Wesley.
3. Sutter, H, 1999. Exceptional C++. Reading, MA: Addison-Wesley.
4. Sutter, H, and Alexandrescu, A, 2004. C++ Coding Standards. Boston: Addison-Wesley.
The problem with books, even this modest volume, is that they represent a snapshot in time of the state of affairs, yet C++ is a continuously evolving language. What was good advice in 1998 may no longer be such a smart idea. An evolving language needs an evolving guide.
An online resource, C++ Core Guidelines,5 was launched at the CppCon Conference in 2015 by Bjarne Stroustrup and Herb Sutter during their two6 keynote7 talks. The guidelines provide excellent, simple advice for improving your C++ style such that you can write correct, performant, and efficient code at your first attempt. It is the evolving guide that C++ practitioners need, and the authors will be delighted to review pull requests with corrections and improvements. Everyone, from beginners to veterans, should be able to follow its advisories.
5. Isocpp.github.io. 2021. C++ Core Guidelines. Copyright © Standard C++ Foundation and its contributors. Available at: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines Accessed 16 July 2021.
6. Youtube.com. 2021. CppCon 2015: Bjarne Stroustrup “Writing Good C++14”. Available at: https://www.youtube.com/watch?v=1OEu9C51K2A Accessed 16 July 2021.
7. Youtube.com. 2021. CppCon 2015: Herb Sutter “Writing Good C++14... By Default.” Available at: https://www.youtube.com/watch?v=hEx5DNLWGgA Accessed 16 July 2021.
The guidelines provide excellent, simple advice for improving your C++ style such that you can write correct, performant, and efficient code at your first attempt.
At the end of February 2020, on the #include discord,8 Kate Gregory canvassed interest in producing a book about the Core Guidelines and I cautiously jumped at the chance. Kate gave a talk at CppCon 20179 where she looked at just 10 of the Core Guidelines. I share her enthusiasm for promoting better programming. I am the Head of Engineering Practice at Creative Assembly, Britain’s oldest and largest game development studio, where I have spent a lot of the past 20-plus years helping to turn our fine engineers into even greater engineers. It is our observation that, despite the accessibility and simplicity of the Core Guidelines, many developers are not especially familiar with them. We want to promote their use, and we decided to write this book because there is not enough literature about them.
8. #include <C++>. 2021. #include <C++>. Available at: https://www.includecpp.org/ Accessed 16 July 2021.
9. Youtube.com. 2021. CppCon 2017: Kate Gregory “10 Core Guidelines You Need to Start Using Now.” Available at: https://www.youtube.com/watch?v=XkDEzfpdcSg Accessed 16 July 2021.
The Core Guidelines can be found at https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines. They are absolutely jam-packed with excellent advice: indeed, it is hard to know where to start. Reading from the top to the bottom is feasible, but it is a tall order to grasp the entire set of advisories without repeated reading. They are organized into 22 major sections with titles like “Interfaces,” “Functions,” “Concurrency,” and so on. Each section is composed of individual guidelines, sometimes a few, sometimes dozens. The guidelines are identified by their major section letter, then their number within the section, separated by a period. For example, “F.3: Keep functions short and simple” is the third guideline in section F, “Functions.”
Each guideline is ordered in a similar way. It starts with the title of the guideline, which is presented as an action (do this, don’t do this, avoid this, prefer this) followed by a reason and some examples, and possibly an exception to the guideline. Finally, there is a note on how to enforce the guideline. Enforcement notes range from advice to authors of static analysis tools to hints on how to conduct a code review. There is a skill to reading them, it turns out; deciding which ones to prioritize in your own code is a matter of personal discovery. Let us show you how to start taking advantage of their wisdom.
There are some sharp edges in C++ as well as some dusty corners that are not visited so often in modern C++. We want to steer you away from these. We want to show you that C++ does not have to be difficult, complex, or something that most developers cannot be trusted with.
In this book we offer what we consider to be 30 of the best C++ Core Guidelines. By thoroughly explaining these guidelines we hope that you will at least abide by them, even if you decide against investigating the remainder. The set that we have chosen are not necessarily the most important. However, they are certainly the set that will change your code for the better immediately. Of course, we hope that you will also see that there are many other good guidelines you could also follow. We hope that you will read the remainder and try them out in your code. Just as the Core Guidelines are aimed at all C++ developers with all levels of experience, so is this book aimed at the same set of people. The material does not increase in complexity as the book progresses, nor is there a required order in which to read the chapters. They are independent of one another, although they may explicitly refer to other chapters. We kept each chapter to about three thousand words, so you may decide that this is a bedside volume rather than a textbook. The purpose is not to teach you C++, but to advise you how to improve your style.
We divided the guidelines into five sections of six chapters, following Kate’s original presentation to CppCon in 2017. In Section 1, “Bikeshedding is bad,” we present guidelines that allow you to simply make a decision about when to do A or B, for some particular set of As and Bs, and move on with the minimum of fuss and argument. “Bikeshedding”10 derives from C. Northcote Parkinson’s “law of triviality,” an argument that organization members typically give disproportionate weight to trivial issues, such as the color to paint a bikeshed compared to the testing criteria for the nuclear power station to which it is attached, because it is the one thing everyone knows something about.
10. 2021. Available at: https://exceptionnotfound.net/bikeshedding-the-daily-software-anti-pattern/ Accessed 16 July 2021.
In Section 2, “Don’t hurt yourself,” we present guidelines for preventing personal injury while writing code. One of the problems with the residual complexity of C++ is that there are several places where you can shoot yourself in the foot with ease. For example, while it is legal to populate a constructor initialization list in any order, it is never wise to do so.
Section 3 is named “Stop using that” and deals with parts of the language that are retained for backward compatibility reasons, along with pieces of advice that used to be valuable, but which have been superseded by developments in the language. As C++ evolves, things that seemed like a good idea at the time occasionally reveal themselves as rather less valuable than was originally expected. The standardization process fixes these things, but everyone needs to stay informed about them because you may come across examples if you find yourself working with a legacy codebase. C++ offers a guarantee of backward compatibility: code written 50 years ago in C should still compile today.
Section 4 follows on from this with the title “Use this new thing properly.” Things like concepts, constexpr, structured binding, and so on need care when being deployed. Again, C++ is an evolving standard and new things appear with each release, all of which require some teaching to back them up. Although this text does not aim to teach you the new features of C++20, these guidelines do give you a flavor of how to apprehend novel features.
Section 5, the final section, is titled “Write code well by default.” These are simple guidelines that, if followed, will result in you generating good code without having to think too hard about what is going on. They lead to the production of good idiomatic C++ which will be understood and appreciated by your colleagues.
Throughout the book, as with any good text, themes emerge and are developed. Part of the fun of writing this book, which I hope will translate to the reading of it too, has been seeing what motivates the guidelines and introspecting about the wider application of these motivations. Many of the guidelines, when squinted at carefully with the sun in the right place, restate some of the fundamental truths of software engineering in different ways. Extracting those truths will greatly improve your programming practice.
We truly hope you enjoy and profit from this book.
All of the code is available at the Compiler Explorer website. Matt Godbolt has kindly reserved stable links for each chapter which are formed by joining https://godbolt.org/z/cg30-ch and the chapter number. For example, https://godbolt.org/z/cg30-ch1.3 will take you to the complete code for Chapter 1.3. We recommend you start with https://godbolt.org/z/cg30-ch0.0 for instructions on how to use the website and interact with the code.
—Guy Davidson, @hatcat01 hatcat.com
—Kate Gregory, @gregcons gregcons.com
October 2021
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