C++ Library - <future>

The <future> header in C++ provides a way to handle asynchronous operations, allowing tasks to be run concurrently and results to be retrieved at a later point. this library is part of the broader concurrency, which enables multi-threaded programming with ease.

It is typically used in combination with std::async, which runs a function asynchronously, or with the std::promise, which manually sets the value for a future object. when the value is ready, it can be accessed using the get() function of the future object. The commonly used C++ <future> copying functions are listed below along with their description.

Including <future> Header

To include the <future> header in your C++ program, you can use the following syntax.

#include <future>

Functions of <future> Header

Below is list of all functions from <future> header.

Waiting for Future to be Ready

In the following example, we are going to use the wait() to block the main thread until the asynchronous operation is complete.

#include <iostream>
#include <future>
#include <thread>
int a(int x, int y) {
   std::this_thread::sleep_for(std::chrono::seconds(2));
   return x + y;
}
int main() {
   std::future < int > b = std::async (std::launch::async, a, 2, 1);
   b.wait();
   std::cout << "Result : " << b.get() << std::endl;
   return 0;
}

Output

Following is the output of the above code −

Result : 3