1、函數語言程式設計如std::bind、std::thread傳引數等使用時，是對引數直接拷貝而不是引用

如：

#include <functional>
#include <iostream>

void f(int& n1, int& n2, const int& n3)
{
    std::cout << "In function: n1[" << n1 << "]    n2[" << n2 << "]    n3[" << n3 << "]" << std::endl;
    
 
++n1; // 增加儲存於函式物件的 n1 副本
    ++n2; // 增加 main() 的 n2
    //++n3; // 編譯錯誤
    std::cout << "In function end: n1[" << n1 << "]     n2[" << n2 << "]     n3[" << n3 << "]" << std::endl;
}

int main()
{
    int n1 = 1, n2 = 1, n3 = 1;
    std::cout << "Before function: n1[
 
" << n1 << "]     n2[" << n2 << "]     n3[" << n3 << "]" << std::endl;
    std::function<void()> bound_f = std::bind(f, n1, std::ref(n2), std::cref(n3));
    bound_f();
    std::cout << "After function: n1[" << n1 << "]     n2[" << n2 << "
 
]     n3[" << n3 << "]" << std::endl;
}

結果：

Before function: n1[1]     n2[1]     n3[1]
In function: n1[1]    n2[1]    n3[1]
In function end: n1[2]     n2[2]     n3[1]
After function: n1[1]     n2[2]     n3[1]

n1是普通值傳遞；n2是引用傳遞；n3是const引用傳遞

參考：https://blog.csdn.net/lmb1612977696/article/details/81543802