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Language: C++
Expertise: Intermediate

Mar 4, 1999

The Standard Template Library defines a specialized form of the queue<> container called priority_queue<>. A priority_queue is a queue whose elements are internally sorted according to their priority. Thus, an element with the highest priority is located at the top. To qualify as an element of priority_queue<>, an object has to define the < operator. For example:

 
#include <functional> // definition of less<> 
#include <queue>  // definition of priority_queue<>
#include <iostream>
using namespace std;

struct Task
{
  int priority;
  friend bool operator < (const Task& t1, const Task& t2);
  Task(int p=0) : priority(p) {}  
};

bool operator < (const Task& t1, const Task& t2) 
{ 
	return t1.priority < t2.priority;
}

int main()
{
  priority_queue<Task> scheduler;
  scheduler.push(Task(3));
  scheduler.push(Task(5));
  scheduler.push(Task(1));

  cout<< scheduler.top().priority <<endl;   // output 5
}