c++ map 官方样例

#include <iostream>
#include <string>
#include <iomanip>
#include <map>

template<typename Map>
void print_map(Map& m)
{
    std::cout << '{';
    for(auto& p : m)
        std::cout << p.first << ":" << p.second << ' ';
    std::cout << '}'<<std::endl;
}
struct Point
{
        double x, y;
};
struct PointCmp
{
        bool operator()(const Point& lhs, const Point& rhs) const
        {
            return lhs.x < rhs.x;
        }
};

int main()
{
    using namespace std;
    //freopen("d://1.text", "r", stdin);
    //default constructor
    std::map<std::string, int> map1;
    map1["something"] = 69;
    map1["anything"] = 199;
    map1["that thing"] = 50;
    std::cout << "map1= ";
    print_map(map1);

     //range constructor
    //从anything到结尾
     map<string, int> iter(map1.find("anything"), map1.end());
     cout << "
iter= ";
     print_map(iter);
     cout << "map1= ";
     print_map(map1);

     //copy construct
     map<string, int> copied(map1);
     cout << "
copied= ";
     print_map(copied);
     cout << "map1 = ";
     print_map(map1);

     //move construct
     map<string, int> moved(std::move(map1));
     cout<<endl<<"moved = "; print_map(moved);
     cout<<"map1 = ";print_map(map1);

     //initalizer list constructor
     const map<string,int> init{
         {"this",100},
         {"can",100},
         {"be",100},
         {"const",100},
     };
     cout<<"
init = ";print_map(init);

     //custom key class option 1;
     //use a comparison struct
     map<Point,double,PointCmp>mag =
     {
             {{5,-12},13},
             {{3,4},5},
             {{8,-15},17}
     };
     for(auto p:mag)
         cout<<"The magnitude of("<<p.first.x
         <<", "<<p.first.y<<") is "
         <<p.second<<endl;

     //Custom Key class option 2:
     //use a comparison lambda
     //This lambda sorts points according to their magnitudes, where note that
     // these magnitudes are taken from the local variable mag
     //声明一个比较器
     auto cmplambda =
             [&mag](const Point &lhs,const Point& rhs){return mag[lhs] < mag[rhs];};
     //you could also use a lambda that is not dependent on local variables,like this:
     //auto cmpLambda= [](const Point& lhs,const Point& rhs){return lhs.y < rhs.y;};
     map<Point,double,decltype(cmplambda)>magy(cmplambda);

     //various ways of inserting elements:
     magy.insert(pair<Point,double>({5,-12},13));
     magy.insert({{3,4},5});
     magy.insert({Point{-8.0,-15.0},17});
     cout<<"
";
     for(auto p :magy)
     {
         cout<<"The magnitude of {"<<p.first.x
                 <<". "<<p.first.y<<") is "
                 <<p.second<<"
";
     }
     map<Point,double>::iterator it;
     //use iterator
     cout<<'
';
     for(it=magy.begin();it!=magy.end();it++)
     {
         cout<<"The magnitude of {"<<it->first.x
                         <<". "<<it->first.y<<") is "
                         <<it->second<<"
";
     }

    return 0;
}

 原文地址：https://en.cppreference.com/w/cpp/container/map/map