Nicolai M. Josuttis - C++20 - The Complete Guide

C++20 is the next evolution in modern C++ programming,which is already (partially) supported by the latest version of gcc, clang, and Visual C++.The move to C++20 is at least as big a step as the move to C++11.C++20 contains a significant number of new language features and librariesthat again will change the way we program in C++.This applies to both application programmers and programmerswho provide foundation libraries.

This book is an experiment in two ways:

• I am writing an in-depth book covering a complex new features provided by different authors and C++ working groups. However, I can ask questions and I do.
• I am publishing the book myself on Leanpub and for printing on demand. That is, this book is written step by step and I will publish new versions as soon there is a significant improvement that makes the publication of a new version worthwhile.

The good thing is:

• You get the view of the language features from an experienced application programmersomebody who feels the pain a feature might cause and asks the relevant questions to be able to motivate and explain the design and its consequences for programming in practice.
• You can benefit from my experience with C++20 while I am still learning and writing.
• This book and all readers can benefit from your early feedback.

This means that you are also part of the experiment.So help me out:give about flaws, errors,features that are not explained well, or gaps,so that we all can benefit from these improvements.

Because this book is written incrementally,the following is a history of the major updates(newest first):

• 2021-12-31: Describe where typename is no longer required for type members of template parameters
• 2021-12-30: Describe new bit operations (including bit_cast<>())
• 2021-12-29: Describe all improvements for string types (including std::u8string and using strings at compile time)
• 2021-12-28: Describe the unseq execution policy for algorithms
• 2021-12-25: Describe all other missing lambda features
• 2021-12-11: Describe consteval lambdas
• 2021-12-06: Describe std::endian
• 2021-12-06: Describe synchronized output streams
• 2021-12-04: Describe header
• 2021-11-21: Describe compile-time use of vectors and constexpr extensions
• 2021-10-25: Describe designated initializers
• 2021-10-14: Describe severe compatibility issues with operator==
• 2021-10-14: Describe mathematical constants
• 2021-10-12: Describe constinit, consteval, and std::is_constant_evaluated()
• 2021-10-07: Describe char8_t for UTF-8 (and its compatibility issues)
• 2021-10-02: Clarify over which const views you cannot iterate
• 2021-10-01: Details about the formatting library
• 2021-09-21: Updates and fixes according to several reviews
• 2021-09-20: First description of features for modules
• 2021-09-11: const issues of ranges and views
• 2021-08-30: All concepts documented
• 2021-08-30: All concepts documented
• 2021-08-28: Document all new type traits
• 2021-08-27: Document iterator utility functions for ranges.
• 2021-08-26: Document lazy_split_view<> added to C++20 with a defect.
• 2021-08-25: Document all missing views of C++20 and all_t<>
• 2021-08-20: Document all new iterator types (counted_iterator, common_iterator, default_sentinel, unreachable_sentinel)
• 2021-08-20: Document all primary range adaptors (counted(), all(), and common())
• 2021-08-19: Document common_view
• 2021-08-16: Document how to deal with semantic constraints of concepts
• 2021-08-15: Document type_identity
• 2021-07-31: Document empty_view, ref_view, and view_interface
• 2021-07-29: Generic code for range has to use universal/forwarding references
• 2021-07-28: Document iota_view and unreached_sentinel
• 2021-07-27: Extend and reorganize chapters about ranges and views
• 2021-07-17: Document subrange
• 2021-07-15: Fix wrong website for the book
• 2021-07-09: Document
• 2021-06-29: The initial published version of the book. The following features are more or less completely described or provide at least a full conceptual introduction:
  • Comparisons and the spaceship operator <=>
  • Generic functions
  • Concepts and requirements (details open)
  • Ranges and views (details open)
  • Spans
  • Non-type template parameter extensions
  • Formatted output (overview only)
  • Dates and time zones for
  • Coroutines (first examples)
  • std::thread and stop tokens
  • New concurrency features

First of all, I would like to thank you, the C++ community,for making this book possible.The incredible design of all the features of C++20, thehelpful feedback, and your curiosity are thebasis for the evolution of a successful language.In particular, thanks for all the issues youtold me about and explained and for the feedback you gave.

I would especially like to thank everyone who reviewed drafts of this bookor corresponding slidesand provided valuable feedback and clarification.These reviews increased the quality of the book significantly,again proving that good things are usually the result of many people.Therefore, so far (this list is still growing)huge thanks toCarlos Buchart,Javier Estrada,Howard Hinnant,Paul Ranson,Thomas Symalla,Steve VinoskiandVictor Zverovich.

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In addition, I would like to thank everyoneon the C++ standards committee.In addition to all the work involved in adding new language and library features,these experts spent many, many hours explaining and discussing their work with me, andthey did so with patience and enthusiasm.Special thanks here go toHoward Hinnant,Tomasz Kaminski,Arthur ODwyer,Peter Sommerlad,Tim Song,Barry Revzin,Ville Voutilainen,andJonathan Wakely.