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Modern C++ For Software Developers Serious C++ Development Karan Singh Garewal Modern C++ For Software Developers Karan Singh Garewal Copyright © 2022+, Karan Singh Garewal This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Trademarked names, logos, and images may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, logo, or image we use the names, logos, and images only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Cover Image Design by Kirill Tonkikh, unsplash.com I Changelog Date Version Notes October 10, 2022 1.3 new chapter on coroutines additions to the GDB Debugger chapter August 30, 2022 1.2 std::format library function Revise threads chapter with additional working examples. Numerous edits to improve readability and improve comprehension. July 30, 2022 1.1 setjmp and longjmp section refactor smart pointers chapter C++ Sanitizers chapter fix errors in some code examples [[maybe_unused]] – C++17 features C++ SonarLint chapter various edits to explain concepts more simply February 28, 2022 1.0 Initial release II Preface This is a book on serious software development with Modern C++. It is my go-to desktop reference when I am developing C++ applications. I hope that you will also consider this book in such an exalted light. This book is divided into eight main sections. The first section is a C language refresher. Knowledge of the C language is presumed. The next section exposes core C++. This is C++ before C++11. This section is followed by four sections that discuss important features of C++11, C++14, C++17 and the latest standard, C++20. This is followed by a section that discusses important functions in the C++ Standard Library. The next section is devoted to the GNU C++ compiler and the GNU debugger. The last section looks at some miscellaneous topics. Every important C++ feature that is discussed in this book is accompanied by a short C++ program to demonstrate how the feature works. You can cut and paste these examples into wandbox (https://wandbox.org) and then compile and execute them. This book can be read sequentially or you can go directly to topics of interest. The reminder of this preface is merely my opinionated meandering on C++ web applications. Is C++ web application development an anachronism? You can safely omit this part of the preface. III A Journey Through C++ Land When I was going to university, I had a friend who was fond of saying “I think in C”. He obviously liked C a lot. Over forty years later, after it’s inception, C still remains very popular. A lot of people really like C. It appears that C imposes very little cognitive load on the brain; C fits easily into the brain. But C has it’s limitations. A few years back I was developing a deep neural network in C. After writing about 30,000 lines I started having difficulty reasoning about the application in it’s entirety. This is not a critique about the language, it is an observation that C does not provide language constructs to architect large applications. This is where C++ comes in. C++ provides constructs to structure and architect extremely large applications. Applications in the multi-million line range are eminently feasible. This is entirely due to constructs such as classes, encapsulation, function overloading, run-time polymorphism and templates. These constructs are remarkably versatile and a very large domain of problems can be modelled with these constructs. But this not to say that C++ is perfect. It is possible that absolutely massive software applications such as the F-35 fighter jet program (up to 30 million C++ Source lines of code) are exposing the deficiencies in C++. In other words, C++ source code is not reliable enough at this scale. The C++ Steering Committee is aware of this issue. Each new release of C++ brings new constructs to improve the correctness of IV C++ programs. Consider for example, const, static_assert, constexpr, consteval, constinit, typed enums, constant templates, auto, type deduction, braced initialization, noexcept, override, [[nodiscard]] and a plethora of other language constructs.. The list of C++ correctness constructs is long and expanding. C++ Is Not A Web Programming Language This is a frequently repeated canard on the Internet. It may have been true in the past but it is not true today. Web frameworks based on dynamically typed languages are invariably held forth as being the best environments to develop web applications. I am alluding to the Python/Django and Ruby/Rails frameworks in particular. I came from a heavy C++ background and migrated to web development. I spent nearly a decade developing Rails applications. Never liked the language or the framework. But it would have been an unforgivable heresy to oppose conventional wisdom. Frameworks based on dynamically typed languages are held out as being suitable for fast web development. I disagree. An experienced C++ programmer can develop web applications just as fast as someone developing in the Ruby and Rails environment for example. If not faster. How can web development in C++ be faster? It all boils down to the compile-link cycle in C++. If your C++ web application compiles and links properly it is almost certain that it will also run on the web. Your main concern will be the “business” logic of your program. In contrast, if the application is developed in a dynamically typed language, you can write the application quickly but you will V spend a lot of time debugging the program at run-time. This is due to the fact that in a dynamically typed language variable types frequently change at run-time. Additionally the debugging tools for dynamically typed languages are mediocre. In the discussion that follows I will use Ruby and Rails as a bete noire. Simply because this is the framework with which I have the most experience and this framework has a huge hype machine behind it. However the discussion applies equally to other frameworks built with dynamically typed languages. Performance There is a dirty little secret concerning web applications built with dynamically typed languages. These applications are very slow and a lot of engineering effort goes into making them run faster. For example, a C++ web application developed in the Drogon framework: ( https://github.com/drogonframework/drogon ) is over fifty times faster than a Ruby/Rails application. See: https://www.techempower.com/benchmarks/#section=data- r19&hw=ph&test=composite The main culprit is the interpreter in these languages which must read each source code statement (or it’s bytecode) before executing the statement. Also see a comparison of the Drogon webserver with the gold standard in webservers: Nginx. https://drogon.docsforge.com/master/benchmarks/#test-plan-and- VI results It is worth-noting that a medium-sized C++ web application will hardly register any CPU usage. An equivalent Ruby/Rails application will stress the CPU and you might end up having to load balance incoming HTTP requests to multiple machines. Libraries vs. Frameworks Using a web framework leads the developer into vendor lock-in. If you develop a web application in Python and Django or Ruby and Rails, your application will for all practical purposes be locked into the vendor’s framework. Migration to another framework will be a major undertaking. Libraries do not produce such a lock-in effect. After all, you can easily switch libraries or develop your own library functions. For example. Drogon is a very thin framework layer wrapped around the drogon webserver. Deployment Deploying Ruby and Rails applications to production servers is complicated. All of the source files and static resources have to be deployed on the production server. In contrast the deployment of a C+ + web application is simple. One or more executable files and the static resources are deployed on the production server. rsync can easily manage this deployment. VII Trying The Theory Out I wanted to confirm my suspicions with a production quality C++ web application. Since I am an Attorney at Law, I developed https://truelawdocs.com as a Drogon C++ application. This is a multi- threaded application for document production. It took about four months of part-time work. The application uses the Cassandra NoSQL database for document storage. This is clearly massive overkill for an application like TrueLawDocs. Cassandra slowed the development cycle since I had zero prior Cassandra experience. I wanted to learn Cassandra on the supposition that I might need this column-oriented NoSQL database in the future. I really liked Cassandra, it’s very well designed. TrueLawDocs has a front-end developed in Bootstrap, Vue, Javascript and CSS. The C++ back-end and the front-end communicate through websockets. As you can surmise TrueLawDocs has a strongly decoupled architecture. Aside from the Drogon framework and the C++ standard library, the only libraries used were nlohmann/json a C++ JSON library, AES.hpp a header only C++ encryption library, the DataStax C driver library for Cassandra, ASAN (address sanitizer) and UBSAN (undefined behaviour sanitizer). That is it for third party libraries. Everything else was hand- coded. For payment integration with Stripe, the LibCurl library was used to interact with the Stripe payment server. Stripe does not support C++ and provides no sample code to integrate C++ applications. The integration of the TrueLawDocs C++ code with the Stripe server VIII exemplifies the raw power of C++. The overall development experience was very pleasant. The Drogon source code is easy to digest; it’s written by a master of Modern C++. TrueLawDocs including Cassandra is running on a seven dollar a month VPS rented from a company In Sharjah. Lessons Learned During my tenure contracting on Rails applications I rarely met developers who had broad experience with other programming languages. They typically only knew their framework. In a decade of contracting, I never met a Rails programmer who was reasonably proficient in C++. One of the reasons that dynamically typed web languages are popular is that they are easy to learn. You can master Rails in less than three months. In contrast one cannot gain reasonable proficiency in C++ unless one has programmed in the language for about two years. The Modern C++ learning curve is very steep. Unfortunately. It’s unavoidable. Another factor is economics. Web applications built in dynamically typed languages rely on cheap labour. Fortune 500 companies use large inputs of foreign contractors and software quality testers to develop and maintain their applications. To my mind, this is a statement on the inadequacy of dynamically typed languages for web development. If these cheap resources were not available, the development model would shift to conserving expensive, high quality IX