std::<int, std::string>map,删除key（first）小于20的元素。

c++ map

#include <map>
#include <string>

void print(const std::map<int, std::string> &map)
{
    for (auto it=map.begin(); it!=map.end(); it++) {
        printf("key = %d, value=%s\n", it->first, it->second.c_str());
    }
}

void mothed1(const std::map<int, std::string> &m)
{
    printf("***********MOTHED 1*************\n");
    print(m);
    auto map = m;
    for (auto it=map.begin(); it!=map.end();) {
         if (it->first < 20 ) {
             map.erase(it++);
          } else {
              break;
          }
    }
    printf("************************\n");
    print(map);
}

void mothed2(const std::map<int, std::string> &m)
{
    printf("***********MOTHED 2*************\n");
    print(m);
    auto map = m;
    for (auto it=map.begin(); it!=map.end();) {
          if (it->first < 20 ) {
              it = map.erase(it);
          } else {
              break;
          }
    }
    printf("************************\n");
    print(map);
}

void mothed3(const std::map<int, std::string> &m)
{
    printf("***********MOTHED 3*************\n");
    print(m);
    auto map = m;
    auto it = std::find_if(map.begin(), map.end(), [](std::pair<int, std::string> t){return t.first>=20;});
    if (it != map.end()) {
        map.erase(map.begin(), it);
    } else {
        map.clear(); //remove all
    }
    printf("************************\n");
    print(map);
}

void func()
{
    srand(time(0));
    std::map<int, std::string> map;
    for (int i=0; i<16; i++) {
        map.insert(std::make_pair(rand()%30, "value1"));
    }
    
    //删除key小于20的元素
    mothed1(map);
    mothed2(map);
    mothed3(map);
}