Book Image

Modern C++ Programming Cookbook

By : Marius Bancila
Book Image

Modern C++ Programming Cookbook

By: Marius Bancila

Overview of this book

C++ is one of the most widely used programming languages. Fast, efficient, and flexible, it is used to solve many problems. The latest versions of C++ have seen programmers change the way they code, giving up on the old-fashioned C-style programming and adopting modern C++ instead. Beginning with the modern language features, each recipe addresses a specific problem, with a discussion that explains the solution and offers insight into how it works. You will learn major concepts about the core programming language as well as common tasks faced while building a wide variety of software. You will learn about concepts such as concurrency, performance, meta-programming, lambda expressions, regular expressions, testing, and many more in the form of recipes. These recipes will ensure you can make your applications robust and fast. By the end of the book, you will understand the newer aspects of C++11/14/17 and will be able to overcome tasks that are time-consuming or would break your stride while developing.
Table of Contents (19 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Using promises and futures to return values from threads


In the first recipe of this chapter, we discussed how to work with threads. You also learned that thread functions cannot return values, and threads should use other means, such as shared data, to do so; however, for this, synchronization is required. An alternative to communicating a return value or an exception with either the main or another thread is using std::promise. This recipe will explain how this mechanism works.

Getting ready

The promise and future classes used in this recipe are available in the std namespace in the <future> header.

How to do it...

To communicate a value from one thread to another through promises and futures, do this:

  1. Make a promise available to the thread function through a parameter, for example:
        void produce_value(std::promise<int>& p)
        {
          // simulate long running operation
          {
            using namespace std::chrono_literals;
            std::this_thread:...