Queues

Variations include

• deque - (pronounced deck) double-ended queue. One of the basic containers.

• queues - items are pushed into the back of the container and removed from the front. The underlying container can be vector or a deque. The items can be whatever you like. For instance you could create a queue of messages

  // create a message structure
  struct Message{ ... }
  
  // wait until an item appears on the queue, then process it.
  void server(queue<Message> &q)
  {
    while(!q.empty()) {
      Message& m = q.front();
      m.service();q.pop();
    }
  }
  

• priority queues - items are pushed into the back of the container and removed from the front in order of priority. The underlying container can be vector, amongst other things. In the following example the priority is determined by comparing the value of the integers in the queue using less.

  [fontsize=\small,frame=single,formatcom=\color{progcolor}]
   #include <queue>
   #include <vector>
   #include <iostream>
   using namespace std;
  
   int main()
   {
     // Make a priority queue of int using a vector container
     priority_queue<int, vector<int>, less<int> > pq;
   
     // Push a couple of values
     pq.push(1);
     pq.push(7);
     pq.push(2);
     pq.push(2);
     pq.push(3);
     // Pop all the values off
     while(!pq.empty()) {
       cout << pq.top() << endl;
       pq.pop();
     }
   return 0;
   }