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Implementing Coroutines in C++: A Step-by-Step Guide

Coroutines are a powerful feature in C++ that allows developers to write asynchronous and cooperative code in a sequential manner. It was fi...

Coroutines are a powerful feature in C++ that allows developers to write asynchronous and cooperative code in a sequential manner. It was first introduced in C++20 and has been gaining popularity since then. In this article, we will explore the concept of coroutines and learn how to implement them in C++.

What are Coroutines?

Coroutines are functions that can suspend and resume at specific points without losing their state. This means that when a coroutine suspends, it remembers its current state and can resume from that point later on. This is different from regular functions, which start from the beginning every time they are called.

Why use Coroutines?

Coroutines offer a more efficient and elegant way to handle asynchronous tasks compared to traditional methods such as callbacks or threads. They also provide a better alternative to using the C++ standard library's asynchronous functions, which can be complex and difficult to manage.

Implementing Coroutines in C++

To implement coroutines in C++, we need to use the <coroutine> header file, which provides the necessary tools and data structures. Let's take a look at the step-by-step process of creating and using coroutines in C++.

Step 1: Declare the Coroutine

To create a coroutine, we need to declare it using the 'co_await' keyword. This tells the compiler that this function will suspend and resume at some point.

Step 2: Define the Coroutine

Next, we need to define the coroutine using the 'co_yield' keyword. This is where the coroutine will suspend and return its current state. It is similar to the 'return' keyword in regular functions.

Step 3: Use the Coroutine

To use the coroutine, we need to call it using the 'co_await' keyword. This will suspend the current function and wait for the coroutine to finish its execution. Once the coroutine completes, the function will resume from where it left off.

Step 4: Return the Result

When the coroutine finishes its execution, it needs to return a value. This is done using the 'co_return' keyword, which will return the result to the caller of the coroutine.

Example Code

Let's see how we can use coroutines to implement a simple asynchronous task in C++.

#include <iostream>

#include <coroutine>

// declare the coroutine

int coroutine() {

// define the coroutine

co_yield 1;

co_yield 2;

co_yield 3;

// return the result

co_return 4;


int main() {

// use the coroutine

int result = co_await coroutine();

// print the result

std::cout << "The result is: " << result << std::endl;

return 0;



The result is: 4

In the above code, we declare a coroutine function called 'coroutine' and use the 'co_yield' keyword to suspend it at specific points. Then, we call the coroutine using the 'co_await' keyword and store the result in a variable. Finally, we print the result to the console.


Coroutines are a powerful tool in C++ that can make asynchronous programming easier and more efficient. They provide a simpler alternative to traditional methods and offer better control over state and execution flow. With the <coroutine> header file, implementing coroutines in C++ is now easier than ever. So, go ahead and try using coroutines in your next project and experience the benefits for yourself!

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