Book Image

Modern C++ Programming Cookbook - Third Edition

By : Marius Bancila
Book Image

Modern C++ Programming Cookbook - Third Edition

By: Marius Bancila

Overview of this book

The updated third edition of Modern C++ Programming Cookbook addresses the latest features of C++23, such as the stack library, the expected and mdspan types, span buffers, formatting library improvements, and updates to the ranges library. It also gets into more C++20 topics not previously covered, such as sync output streams and source_location. The book is organized in the form of practical recipes covering a wide range of real-world problems. It gets into the details of all the core concepts of modern C++ programming, such as functions and classes, iterators and algorithms, streams and the file system, threading and concurrency, smart pointers and move semantics, and many others. You will cover the performance aspects of programming in depth, and learning to write fast and lean code with the help of best practices. You will explore useful patterns and the implementation of many idioms, including pimpl, named parameter, attorney-client, and the factory pattern. A chapter dedicated to unit testing introduces you to three of the most widely used libraries for C++: Boost.Test, Google Test, and Catch2. By the end of this modern C++ programming book, you will be able to effectively leverage the features and techniques of C++11/14/17/20/23 programming to enhance the performance, scalability, and efficiency of your applications.
Table of Contents (15 chapters)
13
Other Books You May Enjoy
14
Index

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 that 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...