原型：

template< class R, class F, class... Args > 

bind( F&& f, Args&&... args );

bind函数模板的作用是：

The function template bind generates a forwarding call wrapper for f. Calling this wrapper is equivalent to invoking f with some of its arguments bound to args.

不怎么好翻译，尝试解释一下：我们为某个函数做一个bind，然后调用该bind和调用函数是一样的，跟函数指针有点像。

#include 
     
      #include 
      
       #include 
       
        #include 
        
          void f(int n1, int n2, int n3, const int& n4, int n5){    std::cout << n1 << ' ' << n2 << ' ' << n3 << ' ' << n4 << ' ' << n5 << '\n';} int g(int n1){    return n1;} struct Foo {    void print_sum(int n1, int n2)    {        std::cout << n1+n2 << '\n';    }    int data = 10;}; int main(){    using namespace std::placeholders;  // for _1, _2, _3...     // demonstrates argument reordering and pass-by-reference    int n = 7;    // (_1 and _2 are from std::placeholders, and represent future    // arguments that will be passed to f1)    auto f1 = std::bind(f, _2, _1, 42, std::cref(n), n);    n = 10;    f1(1, 2, 1001); // 1 is bound by _1, 2 is bound by _2, 1001 is unused     // nested bind subexpressions share the placeholders    auto f2 = std::bind(f, _3, std::bind(g, _3), _3, 4, 5);    f2(10, 11, 12);     // bind to a member function    Foo foo;    auto f3 = std::bind(&Foo::print_sum, &foo, 95, _1);    f3(5);     // bind to member data    auto f4 = std::bind(&Foo::data, _1);    std::cout << f4(foo) << '\n';