Book Image

C++20 STL Cookbook

By : Bill Weinman
Book Image

C++20 STL Cookbook

By: Bill Weinman

Overview of this book

Fast, efficient, and flexible, the C++ programming language has come a long way and is used in every area of the industry to solve many problems. The latest version C++20 will see programmers change the way they code as it brings a whole array of features enabling the quick deployment of applications. This book will get you up and running with using the STL in the best way possible. Beginning with new language features in C++20, this book will help you understand the language's mechanics and library features and offer insights into how they work. Unlike other books, the C++20 STL Cookbook takes an implementation-specific, problem-solution approach that will help you overcome hurdles quickly. You'll learn core STL concepts, such as containers, algorithms, utility classes, lambda expressions, iterators, and more, while working on real-world recipes. This book is a reference guide for using the C++ STL with its latest capabilities and exploring the cutting-edge features in functional programming and lambda expressions. By the end of the book C++20 book, you'll be able to leverage the latest C++ features and save time and effort while solving tasks elegantly using the STL.
Table of Contents (13 chapters)

Efficiently modify the keys of map items

A map is an associative container that stores key-value pairs. The container is ordered by the keys. The keys must be unique and they are const-qualified, so they cannot be changed.

For example, if I populate a map and attempt to change the key, I'll get an error at compilation time:

map<int, string> mymap {
    {1, "foo"}, {2, "bar"}, {3, "baz"}
auto it = mymap.begin(); 
it->first = 47;


error: assignment of read-only member ...
    5 |     it->first = 47;
      |     ~~~~~~~~~~^~~~

If you need to re-order a map container, you may do so by swapping keys using the extract() method.

New with C++17, extract() is a member function in the map class and its derivatives. It allows elements of a map to be extracted from the sequence without touching the payload...