priority_queue(3C++) - priority_queue(3C++)
Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.
NAMEpriority_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;
DESCRIPTIONpriority_queue is a container adaptor that allows a container 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
anything 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 imple‐
mentation, x as its standard for determining 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 prior‐
ity, and the allocator alloc for all storage management.
MEMBER FUNCTIONSboolempty () const;
Returns true if the priority_queue is empty, false otherwise.
voidpop();
Removes the item with the highest priority from the queue.
voidpush (const value_type& x);
Adds x to the queue.
size_typesize () 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 Output21aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaWARNINGS
If your compiler does not support default template parameters, 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
Rogue Wave Software 02 Apr 1998 priority_queue(3C++)
