how to use argument inside of thread? (C++)

Question

i can't use delay argument inside of thread t

void HelloWorldDelay(int Delay)

{
    cout << "Hello World";
    atomic<bool> abort(false);
    thread t([&abort]() {
        Sleep(Delay);
        abort = true;
    });

    t.join();
    cout << Delay << "Ms ";
}

how to use it inside of thread t?

Sleep(Delay)

Why can't you use it in a thread? It's visible to your local thread variable. — Ron, May 03 '18 at 09:18
Is the error you're getting about not capturing Delay in your lambda, by any chance? — tux3, May 03 '18 at 09:19
Possible duplicate of [Error: variable "cannot be implicitly captured because no default capture mode has been specified"](https://stackoverflow.com/questions/30217956/error-variable-cannot-be-implicitly-captured-because-no-default-capture-mode-h) — tux3, May 03 '18 at 09:22
@kimjaehui See the question I linked above, this has already been answered in details before :) — tux3, May 03 '18 at 09:23

score 0 · Answer 1 · answered May 03 '18 at 09:25

0

void HelloWorldDelay(int Delay) {

  std::cout << "Hello World";
  std::atomic<bool> abort(false);
  std::thread t([&]() {
      std::this_thread::sleep_for(std::chrono::seconds(Delay));
      abort = true;
    });

  t.join();
  std::cout << Delay << "Ms ";
}

will do the capturing

answered May 03 '18 at 09:25

Kaveh Vahedipour

3,412
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Doesn't this capture Delay by reference, which might be out of scope when the thread starts or Delay is used in the thread? – Richard Critten May 03 '18 at 09:35
@RichardCritten it can't get out of scope because of the t.join() that will wait for the thread to exit – Tyker May 03 '18 at 09:36
@kimjaehui Would be kind, if you'd accept the answer then – Kaveh Vahedipour May 03 '18 at 10:31

score 0 · Answer 2 · answered May 03 '18 at 09:38

I think you should invoke like this :

#include <iostream>
#include <fstream>
#include <thread>
#include <atomic>

using namespace std;

void HelloWorldDelay(int Delay)

{
    cout << "Hello World";
    atomic<bool> abort(false);
    thread t([&abort](int delay) {
        //sleep(Delay);
        std::this_thread::sleep_for(std::chrono::milliseconds(delay));

        abort = true;
    }, std::ref(Delay));

    t.join();
    cout << Delay << "Ms ";
}

int main()
{
    HelloWorldDelay(3);
    std::system("pause");
    return 0;
}

how to use argument inside of thread? (C++)

2 Answers2