创建 STL 最小堆优先级队列？

Question

My task is to implement a min heap priority queue sorting each queue object with the m_time member variable. My problem is that I can't manage the queue to sort smallest first instead of largest.

I have a struct in the .h file called Event that includes three variables:

struct Event
{ 
 Event(int time=-1, int grind=-1, bool val=false) 
 { m_time=time;m_grindNr=grind; m_value=val;}

    int  m_time;
    int  m_grindNr;
    bool m_value;
};

The code below is what's inside the .cpp file:

struct compare
{
    bool operator()(const Event& a, const Event& b)
    {
        return a.m_time < b.m_time;
    }
};


void main()
{
    priority_queue <Event,vector<Event>, compare> Que;

    Event firstEvent;
    firstEvent.m_time = 2;
    firstEvent.m_grindNr = 0;
    firstEvent.m_value = 0;
    Que.push(firstEvent);

    Event secondEvent;
    secondEvent.m_time = 5;
    secondEvent.m_grindNr = 0;
    secondEvent.m_value = 0;
    Que.push(secondEvent);

    Event tempEvent = Que.top(); //Takes the top value
    Que.pop();
    cout << tempEvent.m_time << " "; //Should print number 2, but prints 5

    tempEvent = Que.top(); //Takes the top value
    Que.pop();
    cout << tempEvent.m_time << endl; //Should print number 5, but prints 2
}

I have also tried using the std::less in the priority queue parameter but its the same result.

I hope you understand my question, thanks in advance.

Answer 1

You have to use greater , as priority_queue take largest first.

So change your compare to

return b.m_time < a.m_time;