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)

Use unordered_map with custom keys

With an ordered map, the type of the key must be sortable, which means it must at least support the less-than < comparison operator. Suppose you want to use an associative container with a custom type that is not sortable. For example, a vector where (0, 1) is not smaller or larger than (1, 0), it simply points in a different direction. In such cases, you may still use the unordered_map type. Let's look at how to do this.

How to do it…

For this recipe we'll create an unordered_map object that uses x/y coordinates for the key. We will need a few support functions for this.

  • First, we'll define a structure for the coordinates:
    struct Coord {
        int x{};
        int y{};

This is a simple structure with two members, x and y, for the coordinates.

  • Our map will use the Coord structure for the key, and an int for the value:
    using Coordmap = unordered_map<Coord, int...