queue(3C++)
Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
queue
- A container adaptor that behaves like a queue (first in, first out).
SYNOPSIS
#include <queue>
template <class T, class Container = deque<T> >
class queue ;
DESCRIPTION
The queue container adaptor lets a container act as a queue. In a queue, items are pushed into the back of the container and removed from the front. The first items pushed into the queue are the first items to be popped off of the queue (first in, first out, or "FIFO").
queue can adapt any container that supports the front(), back(), push_back(), and pop_front() operations. In particular, deque and list can be used.
INTERFACE
template <class T, class Container = deque<T> >
class queue {
public:
// typedefs
typedef typename Container::value_type value_type;
typedef typename Container::size_type size_type;
typedef Container container_type;
// Construct/Copy/Destroy
explicit queue (const Container& = Container());
// Accessors
bool empty () const;
size_type size () const;
value_type& front ();
const value_type& front () const;
value_type& back ();
const value_type& back () const;
void push (const value_type&);
void pop ();
};
// Non-member Operators
template <class T, class Container>
bool operator== (const queue<T, Container>&,
const queue<T, Container>&);
template <class T, class Container>
bool operator!= (const queue<T, Container>&,
const queue<T, Container>&);
template <class T, class Container>
bool operator< (const queue<T, Container>&,
const queue<T, Container>&);
template <class T, class Container>
bool operator> (const queue<T, Container>&,
const queue<T, Container>&);
template <class T, class Container>
bool operator<= (const queue<T, Container>&,
const queue<T, Container>&);
template <class T, class Container>
bool operator>= (const queue<T, Container>&,
const queue<T, Container>&);
CONSTRUCTORS
explicit queue (const Container& = Container());
Creates a queue of zero elements. The queue uses the allocator Allocator() for all storage management.
MEMBER FUNCTIONS
value_type&
back ();
Returns a reference to the item at the back of the queue (the last item pushed into the queue).
const value_type&
back() const;
Returns a constant reference to the item at the back of the queue as a const_value_type.
bool
empty () const;
Returns true if the queue is empty, otherwise false.
value_type&
front ();
Returns a reference to the item at the front of the queue. This is the first item pushed onto the queue unless pop() has been called since then.
const value_type&
front () const;
Returns a constant reference to the item at the front of the queue as a const_value_type.
void
pop ();
Removes the item at the front of the queue.
void
push (const value_type& x);
Pushes x onto the back of the queue.
size_type
size () const;
Returns the number of elements on the queue.
NON-MEMBER OPERATORS
template <class T, class Container>
bool operator== (const queue<T, Container>& x,
const queue<T, Container>& y);
Returns true if x is the same as y.
template <class T, class Container>
bool operator!= (const queue<T, Container>& x,
const queue<T, Container>& y);
Returns !(x==y).
template <class T, class Container>
bool operator< (const queue<T, Container>& x,
const queue<T, Container>& y);
Returns true if the queue defined by the elements contained in x is lexicographically less than the queue defined by the elements contained in y.
template <class T, class Container>
bool operator> (const queue<T, Container>& x,
const queue<T, Container>& y);
Returns y < x.
template <class T, class Container>
bool operator< (const queue<T, Container>& x,
const queue<T, Container>& y);
Returns !(y < x).
template <class T, class Container>
bool operator< (const queue<T, Container>& x,
const queue<T, Container>& y);
Returns !(x < y).
EXAMPLE
//
// queue.cpp
//
#include <queue>
#include <string>
#include <deque>
#include <list>
#include <iostream>
using namespace std;
int main(void)
{
// Make a queue using a list container
queue<int, list<int>> q;
// Push a couple of values on then pop them off
q.push(1);
q.push(2);
cout << q.front() << endl;
q.pop();
cout << q.front() << endl;
q.pop();
// Make a queue of strings using a deque container
queue<string,deque<string>> qs;
// Push on a few strings then pop them back off
int i;
for (i = 0; i < 10; i++)
{
qs.push(string(i+1,’a’));
cout << qs.front() << endl;
}
for (i = 0; i < 10; i++)
{
cout << qs.front() << endl;
qs.pop();
}
return 0;
}
Program Output
1
2
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 parameters, you must always include a Container template parameter. For example you would not be able to write:
queue<int> var;
rather, you would have to write,
queue<int, deque<int> > var;
If your compiler does not support namespaces, then you do not need the using declaration for std.
SEE ALSO
allocator, Containers, priority_queue
Rogue Wave Software — Last change: 02 Apr 1998