C ++ 11线程，它是有效的代码吗？

Question

I am playing around with threads features of C++11. But the following code does not compile under both clang (3.5) and gcc (4.9.2).

#include <iostream>
#include <thread>

void add(int& x) {
    x += 1;
}

int main (int argc, char const *argv[])
{
    int x{ 5 };
    int y{ 8 };

    std::thread my_thread_1{ add, x };
    std::thread my_thread_2{ add, y };
    my_thread_1.join();
    my_thread_2.join();

    std::cout << x << " " << y << std::endl;

    return 0;
}

Is it valid C++11?

Answer 1

It's valid, but the thread class copies its arguments, so you can't use references directly. You have to use std::ref to make it work:

std::thread my_thread_1{ add, std::ref(x) };