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                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.


NAME
     priority_queue

      - A container adapter that behaves like a  priority  queue.
     Items  popped  from the queue are in order with respect to a
     "priority."



SYNOPSIS
     #include <queue>
     template <class T,
              class Container = vector<T>,
              class Compare = less<Container::value_type> >
     class priority_queue;



DESCRIPTION
     priority_queue is a container adaptor  that  allows  a  con-
     tainer  to act as a priority queue. This means that the item
     with the highest  priority,  as  determined  by  either  the
     default  comparison  operator (operator <) or the comparison
     Compare, is brought to the front of the queue whenever  any-
     thing is pushed onto or popped off the queue.

     priority_queue adapts  any  container  that  gives  front(),
     push_back(), and pop_back(). In particular, deque and vector
     can be used.



INTERFACE
     template <class T, class Container = vector<T>,
              class Compare = less<typename
                              Container::value_type> >
     class priority_queue {
     public:

     // typedefs
       typedef typename Container::value_type value_type;
       typedef typename Container::size_type size_type;
       typedef Container container_type;

     //  Construct
       explicit priority_queue (const Compare& = Compare(),
                                const Container& = Container());
       template <class InputIterator>
         priority_queue (InputIterator first,
                         InputIterator last,
                         const Compare& = Compare(),
                         const Container& = Container());
       bool empty () const;
       size_type size () const;
       const value_type& top () const;
       void push (const value_type&);
       void pop();
     };



CONSTRUCTORS
     explicit priority_queue (const Compare& x = Compare(),
                             const Container& = Container());


        Constructs a priority queue that uses Container  for  its
        underlying  implementation,  x as its standard for deter-
        mining priority, and the allocator  Allocator()  for  all
        storage management.



     template <class InputIterator>
     priority_queue (InputIterator first, InputIterator last,
                    const Compare& x = Compare(),
                    const allocator_type& alloc =
                    allocator_type());


        Constructs a new priority queue and places into it  every
        entity  in  the  range  [first, last). The priority_queue
        uses x for determining the priority,  and  the  allocator
        alloc for all storage management.



MEMBER FUNCTIONS
     bool
     empty () const;


        Returns true if the priority_queue is empty, false other-
        wise.

     void
     pop();


        Removes the item  with  the  highest  priority  from  the
        queue.



     void
     push (const value_type& x);


        Adds x to the queue.



     size_type
     size () const;


        Returns the number of elements in the priority_queue.



     const value_type&
     top () const;


        Returns a constant reference to the element in the  queue
        with the highest priority.



EXAMPLE
     //
     // p_queue.cpp
     //
      #include <queue>
      #include <deque>
      #include <vector>
      #include <string>
      #include <iostream>
     using namespace std;

     int main(void)
      {
        // 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(2);

        // Pop a couple of values and examine the ends
       cout << pq.top() << endl;
       pq.pop();
       cout << pq.top() << endl;
       pq.pop();

        // Make a priority queue of strings using
        // a deque container
        priority_queue<string, deque<string>, less<string> >
          pqs;

        // Push on a few strings then pop them back off
       int i;
       for (i = 0; i < 10; i++)
        {
         pqs.push(string(i+1,'a'));
         cout << pqs.top() << endl;
        }
       for (i = 0; i < 10; i++)
        {
         cout << pqs.top() << endl;
         pqs.pop();
        }

        // Make a priority queue of strings using a deque
        // container, and greater as the compare operation
        priority_queue<string,deque<string>, greater<string> >
          pgqs;

        // Push on a few strings then pop them back off
       for (i = 0; i < 10; i++)
        {
         pgqs.push(string(i+1,'a'));
         cout << pgqs.top() << endl;
        }

       for (i = 0; i < 10; i++)
        {
         cout << pgqs.top() << endl;
         pgqs.pop();
        }

       return 0;
      }

     Program Output


     2
     1
     a
     aa
     aaa
     aaaa
     aaaaa
     aaaaaa
     aaaaaaa
     aaaaaaaa
     aaaaaaaaa
     aaaaaaaaaa
     aaaaaaaaa
     aaaaaaaa
     aaaaaaa
     aaaaaa
     aaaaa
     aaaa
     aaa
     aa
     a
     a
     a
     a
     a
     a
     a
     a
     a
     a
     a
     a
     aa
     aaa
     aaaa
     aaaaa
     aaaaaa
     aaaaaaa
     aaaaaaaa
     aaaaaaaaa
     aaaaaaaaaa



WARNINGS
     If your compiler does not support default  template  parame-
     ters, you must always include a Container template parameter
     and a Compare template parameter when declaring an  instance
     of  priority_queue.  For  example,  you would not be able to
     write:

     priority_queue<int> var;

     Instead, you would have to write:


     priority_queue<int, vector<int>,
       less<typename vector<int>::value_type> > var;

     If your compiler does not support namespaces,  then  you  do
     not need the using declaration for std.



SEE ALSO
     Containers, queue

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