std heap sorting using custom > comparator

Question

I'm trying to sort an integer array using std heap.

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

using namespace std;

struct compare {
    bool operator() (const int& s1, const int& s2) const{
        if (s1 < s2) return true;
        return false;
    }
};

int main() {
    vector<int> v;
    v.push_back(8);
    v.push_back(1);
    v.push_back(3);
    v.push_back(2);
    v.push_back(4);
    make_heap(v.begin(), v.end(), compare());
    for (int i=0; i<5; i++) {
        int t = v.front();
        pop_heap(v.begin(), v.end()); v.pop_back();
        cout << t << ' ';
    }
    cout << endl;
}

Now this sort outputs 8, 4, 3, 2, 1, which is correct.

But if I change s1 < s2 to s1 > s2 in the comparator function, the result becomes 1, 4, 8, 3, 2.

What am I doing wrong here?

Answer 1

Ahh I figured out, I have to include that comparator in pop_heap too.