c++11: bind用法

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 <random>
#include <iostream>
#include <memory>
#include <functional>

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 = ;
};

int main()
{
    using namespace std::placeholders;  // for _1, _2, _3...

    // demonstrates argument reordering and pass-by-reference
    int n = ;
    // (_1 and _2 are from std::placeholders, and represent future
    // arguments that will be passed to f1)
    auto f1 = std::bind(f, _2, _1, , std::cref(n), n);
    n = ;
    f1(, , ); // 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, , );
    f2(, , );

    // bind to a member function
    Foo foo;
    auto f3 = std::bind(&Foo::print_sum, &foo, , _1);
    f3();

    // bind to member data
    auto f4 = std::bind(&Foo::data, _1);
    std::cout << f4(foo) << '\n';