#include <iostream>       // std::cout

#include <functional>     // std::ref

#include <thread>         // std::thread

#include <future>         // std::promise, std::future

void print_int1(int& value) {

    std::cout << "value1: " << value << '\n'; // 打印 value: 10.

    value = ;

}

void print_int2(int value) {

    std::cout << "value2: " << value << '\n'; // 打印 value: 10.

    value = ;

}

int main ()

{

    int value1 = ;

    int value2 = ;

    std::thread t1(print_int1, std::ref(value1));

    t1.join();

    std::thread t2(print_int2, value2);

    t2.join();

    std::cout << "value1: " << value1 << '\n'; // 打印 value: 10.

    std::cout << "value2: " << value2 << '\n'; // 打印 value: 10.

    return ;

}

g++ future.cpp -std=c++1y -g -pthread

.输出：

value1:

value2:

value1:

value2:

可见，当函数 print_int1(int&),且std::ref(value1) 时，是传递的引用。

#include <functional>

#include <iostream>

 

void f(int& n1, int& n2, const int& n3)

{

    std::cout << "In function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';

    ++n1; // increments the copy of n1 stored in the function object

    ++n2; // increments the main()'s n2

    // ++n3; // compile error

}

 

int main()

{

    int n1 = 1, n2 = 2, n3 = 3;

    std::function<void()> bound_f = std::bind(f, n1, std::ref(n2), std::cref(n3));

    n1 = 10;

    n2 = 11;

    n3 = 12;

    std::cout << "Before function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';

    bound_f();

    std::cout << "After function: " << n1 << ' ' << n2 << ' ' << n3 << '\n';

}

输出：

Before function: 10 11 12

In function: 1 11 12

After function: 10 12 12

http://zh.cppreference.com/w/cpp/utility/functional/ref

#include <thread>

#include <iostream>

using namespace std;

void func1(int& a)

{

    a++;

}

void func2(int a)

{

    a++;

}

int main()

{

    int a = ;

    std::thread t1(func1, std::ref(a));

    std::thread t2(func2, a);

    std::thread t3(func2, std::ref(a));

    //std::thread t4(func1, a); 编译错误

    t1.join();

    t2.join();

    t3.join();

    std::cout << a << std::endl; return ;

}