Use priority_queue::(push, pop, empty, top) STL functions in Visual C++

This article helps you resolve the problem where how to use the priority_queue::push, priority_queue::pop, priority_queue::empty, priority_queue::top, and priority_queue::size STL functions in Visual C++.

Original product version:   Visual C++
Original KB number:   157623

Summary

The sample code below illustrates how to use the priority_queue::push, priority_queue::pop, priority_queue::empty, priority_queue::top, and priority_queue::size STL functions in Visual C++.

The priority_queue adapter holds objects of the type defined by the type of container supported by the priority_queue. The two containers supported are the vector and the deque. Objects are inserted by push() and removed by pop(). top() returns the top item in the priority_queue.

Since adapters do not support iteration, a priority_queue has no associated iterator.

Priority_queue allows you to maintain a sorted collection of items determined by an associated comparator function, such as less, greater, etc. The top item therefore becomes the candidate of choice, lowest or highest based on the function chosen.

Required header

<queue>

Prototype

priority_queue::push();
priority_queue::pop();
priority_queue::empty();
priority_queue::top();
priority_queue::size();

Sample code

The sample shows priority_queueimplementation using deque and vector containers.

//////////////////////////////////////////////////////////////////////
// Compile options needed: /GX
// <filename> : priority_queue.cpp
// Functions:
// priority_queue::push(), priority_queue::pop(),
// priority_queue::empty(), priority_queue::top(), queue::size()
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
//////////////////////////////////////////////////////////////////////

#include <iostream>
#include <queue>
#include <deque>
#include <vector>
#include <functional>
using namespace std;

#if _MSC_VER > 1020 // if VC++ version is > 4.2
    using namespace std; // std c++ libs implemented in std
#endif

// Using priority_queue with deque
// Use of function greater sorts the items in ascending order
typedef deque<int, allocator<int> > INTDQU;
typedef priority_queue<int,INTDQU, greater<int> > INTPRQUE;

// Using priority_queue with vector
// Use of function less sorts the items in descending order
typedef vector<char, allocator<char> > CHVECTOR;
typedef priority_queue<char,CHVECTOR,less<char> > CHPRQUE;

void main(void)
{
    int size_q;
    INTPRQUE q;
    CHPRQUE p;

    // Insert items in the priority_queue(uses deque)
    q.push(42);
    q.push(100);
    q.push(49);
    q.push(201);

    // Output the item at the top using top()
    cout << q.top() << endl;
    // Output the size of priority_queue
    size_q = q.size();
    cout << "size of q is:" << size_q << endl;
    // Output items in priority_queue using top()
    // and use pop() to get to next item until
    // priority_queue is empty
    while (!q.empty())
    {
        cout << q.top() << endl;
        q.pop();
    }

    // Insert items in the priority_queue(uses vector)
    p.push('c');
    p.push('a');
    p.push('d');
    p.push('m');
    p.push('h');

    // Output the item at the top using top()
    cout << p.top() << endl;

    // Output the size of priority_queue
    size_q = p.size();
    cout << "size of p is:" << size_q << endl;

    // Output items in `priority_queue`using top()
    // and use pop() to get to next item until
    // `priority_queue`is empty
    while (!p.empty())
    {
        cout << p.top() << endl;
        p.pop();
    }
}

Program output:

4
size of q is:4
42
49
100
201
m
size of p is:5
m
h
d
c
a