What are futures and promises in C++?

What are futures and promises in C++?

Futures and promises in C++ are used for asynchronous programming. A promise is a way to set a value that will be available in the future, while a future is a way to retrieve that value once it's ready.

How do I create a promise in C++?

You can create a promise using the std::promise class. Here's a simple example:

#include <iostream>
#include <future>

int main() {
    std::promise<int> promise;
    std::future<int> future = promise.get_future();
    
    // Set the value in a separate thread
    std::thread([&promise]() {
        promise.set_value(42);
    }).detach();
    
    std::cout << "Value from promise: " << future.get() << std::endl;
    return 0;
}

What about futures? How do I use them?

Futures are created from promises. You can use std::async to run a function asynchronously and get a future. Here's an example:

#include <iostream>
#include <future>

int compute() {
    return 42;
}

int main() {
    std::future<int> future = std::async(std::launch::async, compute);
    std::cout << "Value from future: " << future.get() << std::endl;
    return 0;
}