#include<iostream>
#include<functional>
using namespace std;int f_add(int i,int j){return i+j;}auto l_add = [](int i,int j){return i+j;};class c_add{
public:c_add()=default;int operator()(int i,int j){return i+j;}
};int main()
{function<int(int,int)> f1 = f_add;function<int(int,int)> f2 = l_add;function<int(int,int)> f3 = c_add();cout<<"f1 add: "<<f1(3,4)<<endl; 　　cout<<"f2="" add:="" "<<f2(3,4)<<endl; 　　cout<<"f3="" "<<f3(3,4)<<endl;　　cout<<"end="" in="" main\n"; }
//f_add是普通的函数，l_add是lambda表达式，c_add重载了()操作符，都能起到计算两个int和的效果，他们都可以用function对象来“存储”。这东西虽然很方便，但总感觉平时不会用到太多。

#include <iostream>
#include <functional>
using namespace std;// 传统C函数
int c_function(int a, int b)
{return a + b;
}// 函数对象
class Functor
{
public:int operator()(int a, int b){return a + b;}
};int main(int argc, char** argv)
{int(*f)(int, int);    // 声明函数类型，赋值只能是函数指针f = c_function;cout << f(3, 4) << endl;Functor ff = Functor(); // 声明函数对象类型，赋值只能是函数对象cout << ff(3, 4) << endl;
}

#include <iostream>
#include <functional>
using namespace std;// 传统C函数
int c_function(int a, int b)
{return a + b;
}// 函数对象
class Functor
{
public:int operator()(int a, int b){return a + b;}
};int main(int argc, char** argv)
{// 万能可调用对象类型std::function<int(int, int)> callableObject;// 可以赋值为传统C函数指针callableObject = c_function;cout << callableObject(3, 4) << endl;// 可以赋值为函数对象
    Functor functor;callableObject = functor;cout << callableObject(3, 4) << endl;// 可以赋值为lambda表达式（特殊函数对象）callableObject = [](int a, int b){return a + b;};cout << callableObject(3, 4) << endl;
}

#include <iostream>
#include <functional>
#include <list>
using namespace std;// 传统C函数
int c_function(int a, int b)
{return a + b;
}// 函数对象
class Functor
{
public:int operator()(int a, int b){return a + b;}
};int main(int argc, char** argv)
{Functor functor;std::list<std::function<int(int, int)>> callables;callables.push_back(c_function);callables.push_back(functor);callables.push_back([](int x, int y)->int{return x + y;});for (const auto& e : callables){cout << e(3, 4) << endl;}
}