C++ uppper_bound 使用

map 的key，默认按照从小到达排序；

upper_bound(4)，

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>

using namespace std;

int main()
{
    map<int, string>  mapA;   //默认从小到大排序（升序）

    for(int i=0;i<10;++i)
    {
        string str;
        str ="henry" + std::to_string(10-i);
        mapA[i]=str;
        cout <<"key:"<<i<<",val:"<<mapA[i]<<endl;
    }

 
    auto upIt = mapA.upper_bound(4);
    auto lowIt = mapA.lower_bound(4);

    cout <<"---------out put upper_bound(4) :"<<endl;
    for(auto it = mapA.begin(); it!=upIt; ++it)
    {
        cout <<"key:"<< it->first<<",val:"<<it->second<<endl;// 0,1,2,3,4
    }
    cout <<endl;

    cout <<"---------out put lower_bound(4):"<<endl;
    for(auto it = lowIt; it!=mapA.end(); ++it)
    {
        cout <<"key:"<< it->first<<",val:"<<it->second<<endl;//4,5,6,7,8,9
    }
    cout <<endl;

    cout <<"-----finished -----"<<endl;
    return 0;
}