How should I solve this c++ sorting problem

Question

#include<iostream>
#include<cstdio>
#include<vector>
#include<algorithm>
#include<string.h>
#include<map>
#include<functional>
using namespace std;
map<string, int> m;
vector<pair<pair<string, int>, int>> v;
vector<pair<pair<string, int>,int>> v3;
vector<pair<pair<string, int>, int>> v2[1001];
int N;
int idx;
bool cmp(const pair<pair<string, int>,int>& n1, pair<pair<string, int>, int>& n2)
{
    return n1.first.first < n2.first.first;
}
bool cmp2(const pair<pair<string, int>, int>& n1, pair<pair<string, int>, int>& n2)
{
    if(n1.first.first==n2.first.first)
        return n1.first.second > n2.first.second;
}
bool cmp3(const pair<pair<string, int>, int>& n1, pair<pair<string, int>, int>& n2)
{
    if(n1.first.first==n2.first.first)
        if (n1.first.second == n2.first.second)
            return n1.second > n2.second;
}

int main(void)
{
    int N;
    string s;
    int num;
    cin >> N;
    for (int i = 0; i < N; i++)
    {
        cin >> s >> num;
        m[s]+= num;
        v.push_back(make_pair(make_pair(s, num), i));
    }
    sort(v.begin(), v.end(), cmp);
    sort(v.begin(), v.end(), cmp2);
    sort(v.begin(), v.end(), cmp3);
    //for (auto it = v.begin(); it != v.end(); it++)
    //{
    //  cout << "first: " << it->first.first << " second: " << it->first.second << " " << it->second << endl;
    //}
    for (int i = 0; i < v.size(); i++)
    {
        v3.push_back(v[i]);
    }
    for (auto it = v3.begin(); it != v3.end(); it++)
    {
        cout << "first: " << it->first.first << " second: " << it->first.second << " third: " << it->second << endl;
    }
}

I have a sorting problem and don't know y cmp3 is kept getting error... trying to sort the third element descending(while the second element is the same) how should I fix it?

the input data is

8

classic 1000

classic 500

pop 300

classic 1000

classic 600

pop 100

classic 1000

classic 1000

Answer 1

The comparison functions cmp2 and cmp3 have undefined behavior - they don't return a value for every input. So, they won't really sort the vector.

I suspect you might be trying to use all three comparison functions together, but they are actually completely re-sorting it 3 different times. You need to put the entire behavior in one sorting function:

bool cmp3(const pair<pair<string, int>, int>& n1, pair<pair<string, int>, int>& n2)
{
    if (n1.first.first != n2.first.first) {
        return n1.first.first < n2.first.first;
    }
    if (n1.first.second != n2.first.second) {
        return n1.first.second < n2.first.second;
    }
    return n2.second < n1.second; // descending
}