#include <functional>
#include <iostream>
#include<cstring>
#include<string.h>
#include<memory>
#include<atomic>
#include<unordered_map>
#include<mutex>
#include <thread>
#include <string>
void method(int & a){ a += 5;}

using namespace std;
int main(){

    int a = 0;
    // each reference used by the threads would refer to the same object.
    thread th(method,ref(a));
    th.join();
    cout << a <<endl;
    /*
     *
I could compile your code successfully with MSVC2013. However, thread() works passing copies of its argument to the new thread. This means that if your code would compile on your compiler, each thread wourd run with its own copy of ht, so that at the end, main's a would be empty.
GCC doesn't compile with this weird message.
     */
    /*thread th2(method, a);  //浅拷贝
    th2.join();
    cout << a <<endl;*/
    return 0;
}

/** @file  bindRefT.cpp
*  @note   
*  @brief
*  @author 
*  @date   2019-8-8
*  @note   
*  @history
*  @warning
*/
#include <functional>
#include <iostream>
//std::ref主要是考虑函数式编程（如std::bind）在使用时，是对参数直接拷贝，而不是引用
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';
}