How to Implement Non-Blocking Console Input in C Using Concurrency?

Non-Blocking Console Input in C

A common requirement in programming is handling user commands while a program continually runs and outputs information. Traditional console input methods in C block the program's execution until the user presses enter, but for non-blocking input, you need an alternative approach.

Solution: Concurrency

C 11 introduces the std::async and std::future library for concurrency. This allows you to spawn a separate thread for non-blocking input without halting the main program.

Implementation

The provided code demonstrates non-blocking console input:

<code class="cpp">#include <iostream>
#include <future>
#include <thread>
#include <chrono>

std::string getAnswer()
{
    std::string answer;
    std::cin >> answer;
    return answer;
}

int main()
{
    std::chrono::seconds timeout(5);
    std::cout << "Do you even lift?" << std::endl << std::flush;
    std::string answer = "maybe"; //default to maybe
    std::future<std::string> future = std::async(getAnswer);
    if (future.wait_for(timeout) == std::future_status::ready)
        answer = future.get();

    std::cout << "the answer was: " << answer << std::endl;
    exit(0);
}</code>

In this code:

• getAnswer() is the function that reads user input in a separate thread.
• The std::async function launches getAnswer() in its own thread.
• The future.wait_for() function checks if getAnswer() has finished in a specified time frame (in this case, 5 seconds).
• If getAnswer() has finished, its result is stored in the answer variable.
• The program continues running and outputting information while the user input thread operates in the background.

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