【STL容器】multiset的比较规则

#include <iostream>
#include <string>
#include <set>
#include <cmath>
using namespace std;
class Member
{
public:
    int id, power;
public:
    Member(int _id, int _power) : id(_id), power(_power) {}
    friend bool operator<(const Member &ls, const Member &rs)
    {
        return ls.power < rs.power;
    }
    friend ostream &operator<<(ostream &os, const Member &m)
    {
        os << m.id;
        return os;
    }
    bool operator==(const Member &rs)
    {
        return this->id == rs.id;
    }
};
int main(int argc, char const *argv[])
{
    multiset<Member> mem_set;
    mem_set.insert({1, 1000000000});
    int n;
    cin >> n;
    while (n--)
    {
        int id, power;
        cin >> id >> power;
        Member new_mem{id, power};
        mem_set.insert(new_mem);
        auto lower_iter = mem_set.lower_bound(new_mem);
        auto upper_iter = mem_set.upper_bound(new_mem);
        if (lower_iter == mem_set.begin()) // if this mem's power is the lowest
            cout << new_mem << " " << *upper_iter << endl;
        else if (upper_iter == mem_set.end()) // if no mem's power is higher than this mem
            cout << new_mem << " " << *(--lower_iter) << endl;
        else
        {
            if (new_mem == *lower_iter)
                --lower_iter;
            if ((new_mem.power - lower_iter->power) > (upper_iter->power - new_mem.power))
                cout << new_mem << " " << *upper_iter << endl;
            else
                cout << new_mem << " " << *lower_iter << endl;
        }
    }
    return 0;
}

• lower_bound 和 upper_bound 两个方法返回的迭代器的值域要搞清楚
• 代码中要重载Member这个类的“<”运算符，一定要声明为友元或者是const函数
  • 如果重载为普通的成员函数，在g++下面编译不过，原因目前为止