function adapter bind(C++11)

1.头文件

    #include<functional>

2.绑定

    std::bind可以绑定

    [1]functions

    [2]function objects

    [3]member functions,_1必须是某个object地址

    [4]data members,_1必须是某个object地址

    返回一个function object ret，调用ret相当于调用上述1,2,3，或相当于去除4

    http://www.cplusplus.com/reference/functional/bind/?kw=bind

// bind example
#include <iostream>     // std::cout
#include <functional>   // std::bind
#include <vector>
#include <algorithm>
using namespace std;
// a function: (also works with function object: std::divides<double> my_divide;)
double my_divide (double x, double y) {return x/y;}

struct MyPair {
double a,b;
double multiply() {return a*b;}
};

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

// binding functions:
auto fn_five = std::bind (my_divide,10,2);               // returns 10/2
std::cout << fn_five() << '\n';                          // 5

auto fn_half = std::bind (my_divide,_1,2);               // returns x/2
std::cout << fn_half(10) << '\n';                        // 5

auto fn_invert = std::bind (my_divide,_2,_1);            // returns y/x
std::cout << fn_invert(10,2) << '\n';                    // 0.2

auto fn_rounding = std::bind<int> (my_divide,_1,_2);     // returns int(x/y)
std::cout << fn_rounding(10,3) << '\n';                  // 3

MyPair ten_two {10,2};

// binding members:
auto bound_member_fn = std::bind (&MyPair::multiply,_1); // returns x.multiply()
std::cout << bound_member_fn(ten_two) << '\n';           // 20

auto bound_member_data = std::bind (&MyPair::a,ten_two); // returns ten_two.a
std::cout << bound_member_data() << '\n';                // 10

vector<int> v{15, 37, 94, 50, 73, 58, 28, 98};
int n = count_if(v.cbegin(), v.cend(), not1(bind2nd(less<int>(), 50)));
cout << "n=" << n << endl; // 5

auto fn_ = bind(less<int>(), _1, 50);
cout << count_if(v.cbegin(), v.cend(), fn_) << endl;  // 3
cout << count_if(v.begin(), v.end(), bind(less<int>(), _1, 50)) << endl;  //3
cout << count_if(v.begin(), v.end(), bind(less<int>(), _1, 50)) << endl;
return 0;
}