Does comparators in priority Queue works in reverse than normal comparators in c++?

Question

I tried making the same comparator for vector and priority queue, but they give reverse results. Why is it so?

Code:

struct cmp {
    bool operator()(int a, int b)
    {
        return a<b;
    }
};

bool compare(int a, int b)
{
    return a<b;
}
int main()
{
  priority_queue<int,vector<int>, cmp> numbers;

  vector<int>v;
  v.push_back(1);
  v.push_back(20);
  v.push_back(7);
  sort(v.begin(), v.end(), compare);

  numbers.push(1);
  numbers.push(20);
  numbers.push(7);

  cout << "Priority Queue: ";

  while(!numbers.empty()) {
    cout << numbers.top() << ", ";   
    numbers.pop();
  }

  cout << endl;

 cout<<"Vector: "; 
 int i=0;
while(i<v.size()) {
    cout << v[i] << ", ";   
    i++;
  }

  cout << endl;
    return 0;
}

//Output:
Priority Queue: 20, 7, 1, 
Vector: 1, 7, 20, 

//Output: Priority Queue: 20, 7, 1, Vector: 1, 7, 20,

Please clarify the confusion. Thanks

Answer 1

Yes, they work in reverse. For one possible reference, see cppreference's description of std::priority_queue:

Template parameters

[...]

Compare - A Compare type providing a strict weak ordering.

Note that the Compare parameter is defined such that it returns true if its first argument comes before its second argument in a weak ordering. But because the priority queue outputs largest elements first, the elements that "come before" are actually output last. That is, the front of the queue contains the "last" element according to the weak ordering imposed by Compare.