标准库function类型的使用

#include<iostream>
#include<map>
#include<functional>
#include<string>
using namespace std;

int add(int a,int b)
{
    return a+b;
}

struct divide{
    int operator()(int denominator,int divisor)
    {
        return denominator/divisor;
    }
};

auto mode=[](int i,int j) { return i%j;};

int main()
{
    int (*pf)(int,int)=add;
    map<string,function<int(int,int)>> binops;
    binops.insert({"+",add});
    binops.insert({"+",pf});
    binops.insert({"-",minus<int>()});
    binops.insert({"*",[](int i,int j) {return i*j;}});
    binops.insert({"/",divide()});
    binops.insert({"%",mode});
    cout<<binops["+"](1,3)<<endl;
    cout<<binops["-"](2,5)<<endl;
    cout<<binops["*"](1,2)<<endl;
    cout<<binops["/"](4,2)<<endl;
    cout<<binops["%"](4,2)<<endl;
    return 0;
}