//函数指针void func(void)
{//...
}struct Foo
{void operator()(void){//...
    }
};struct Bar
{using fr_t = void(*)(void);static void func(void){//...
    }operator fr_t(void){return func;}
};struct A
{int mia;void mem_func(void){//...
    }
};int main(void)
{//函数指针void(* func_ptr)(void) = &func;func_ptr();//仿函数
    Foo foo;foo();//被转为指针的类对象
    Bar bar;bar();//类成员函数指针void (A::*mem_func_ptr)(void) = &A::mem_func;//类成员指针int A::*mem_obj_ptr = &A::mia;A aa;(aa.*mem_func_ptr)();aa.*mem_obj_ptr = 123;return 0;
}

#include <iostream>
#include <functional>void func(void)
{std::cout << __FUNCTION__ << std::endl;
}class Foo
{
public:static int foo_func(int a){std::cout << __FUNCTION__ << "(" << a << ")->: ";return a;}
};class Bar
{
public:int operator()(int a){std::cout << __FUNCTION__ << "(" << a << ")->: ";return a;}
};int main(void)
{//绑定一个普通函数std::function<void(void)> fr1 = func;fr1();//绑定一个静态成员函数std::function<int(int)> fr2 = Foo::foo_func;std::cout << fr2(111) << std::endl;//绑定一个仿函数
    Bar bar;fr2 = bar;std::cout << fr2(111) << std::endl;return 0;
}

#include <iostream>
#include <functional>class A
{std::function<void()> callback;
public:A(const std::function<void()> &f) : callback(f){}void notify(void){callback();}
};class Foo
{
public:void operator()(void){std::cout << __FUNCTION__ << std::endl;}
};int main(void)
{Foo foo;A aa(foo);aa.notify();return 0;
}

#include <iostream>
#include <functional>void call_when_event(int x, const std::function<void(int)>& f)
{if(!(x & 1)) //x % 2 == 0
    {f(x);}
}void output(int x)
{std::cout << x << "  ";
}int main(void)
{for(int i = 0; i < 10; i++){call_when_event(i, output);}std::cout << std::endl;return 0;
}

#include <iostream>
#include <functional>void call_when_event(int x, const std::function<void(int)>& f)
{if(!(x & 1)) //x % 2 == 0
    {f(x);}
}void output(int x)
{std::cout << x << "  ";
}void output2(int x)
{std::cout << x + 2 << "  ";
}int main(void)
{{auto fr = std::bind(output, std::placeholders::_1);for(int i = 0; i < 10; i++){call_when_event(i, fr);}std::cout << std::endl;}{auto fr = std::bind(output2, std::placeholders::_1);for(int i = 0; i < 10; i++){call_when_event(i, fr);}std::cout << std::endl;}return 0;
}

#include <iostream>
#include <functional>void output(int x, int y)
{std::cout << x << "  " << y << std::endl;
}int main(void)
{std::bind(output, 1, 2)();                                                 //输出：1 2std::bind(output, std::placeholders::_1, 2)(1);                         //输出：1 2std::bind(output, 2, std::placeholders::_1)(1);                            //输出：2 1//std::bind(output, 2, std::placeholders::_2)(1);                         //error，没有第二个参数std::bind(output, 2, std::placeholders::_2)(1,2);                         //输出：2 2,第一个参数被抛弃std::bind(output, std::placeholders::_1, std::placeholders::_2)(1,2);     //输出：1 2std::bind(output, std::placeholders::_2, std::placeholders::_1)(1,2);     //输出：2 1       return 0;
}

#include <iostream>
#include <functional>class A
{
public:int mi = 0;void output(int x, int y){std::cout << x << "  " << y << std::endl;}
};int main(void)
{A a;std::function<void(int, int)> fr = std::bind(&A::output, &a, std::placeholders::_1, std::placeholders::_2);fr(1, 2);   std::function<int &(void)> fr_i = std::bind(&A::mi, &a);fr_i() = 123;std::cout << a.mi << std::endl;return 0;
}

#include <iostream>
#include <functional>int main()
{std::vector<int> coll;for (int i = 1; i <= 10; ++i){coll.push_back(i);}// 查找元素值大于10的元素的个数// 也就是使得10 < elem成立的元素个数int res = count_if(coll.begin(), coll.end(), std::bind1st(less<int>(), 10));cout << res << endl;// 查找元素值小于10的元素的个数// 也就是使得elem < 10成立的元素个数res = count_if(coll.begin(), coll.end(), std::bind2nd(less<int>(), 10));cout << res << endl;bool b = less<int>(10, 20); // 返回truereturn 0;
}

#include <iostream>
#include <functional>int main()
{using std::placeholders::_1;std::vector<int> coll;//查找元素值大于10的元素个数int count = std::count_if(coll.begin(), coll.end(), std::bind(less<int>(), 10, _1));//查找元素值小于10的元素个数count = std::count_if(coll.begin(), coll.end(), std::bind(less<int>(), _1, 10));return 0;
}

std::bind(std::greater<int>(), std::placeholders::_1, 5);

std::bind(std::less_equal<int>(), std::placeholders::_1, 10);

using std::placeholders::_1;auto f = std::bind(std::logical_and<bool>(),std::bind(std::greater<int>(), std::placeholders::_1, 5),std::bind(std::less_equal<int>(), std::placeholders::_1, 10));int count = std::count_if(coll.begin(), coll.end(), f);