#### 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)
Preface
Free Chapter
Chapter 2: General STL Features
Chapter 7: Strings, Streams, and Formatting
Chapter 10: Using the File System
Chapter 11: A Few More Ideas
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# Create a generator as iterators

A generator is an iterator that generates its own sequence of values. It does not use a container. It creates values on the fly, returning one at a time as needed. A C++ generator stands on its own; it does not need to wrap around another object.

In this recipe, we'll build a generator for a Fibonacci sequence. This is a sequence where each number is the sum of the previous two numbers in the sequence, starting with 0 and 1:

Figure 4.2 – Definition of a Fibonacci sequence

The first ten values of the Fibonacci sequence, not counting zero, are: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55. This is a close approximation of the golden ratio found in nature.

## How to do it…

A Fibonacci sequence is often created with a recursive loop. Recursion in a generator can be difficult and resource-intensive, so instead we'll just save the previous two values in the sequence and add them together. This is more efficient.

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