Container Adaptor
A container adaptor that behaves like a queue (first in, first out).
#include <queue>
template <class T, class Container = deque<T>,
class Allocator = allocator> class queue ;
The queue container adaptor lets a container function 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, list, and vector can be used.
template <class T, class Container = deque<T>,
class Allocator = allocator>
class queue {
public:
// typedefs
typedef typename Container::value_type value_type;
typedef typename Container::size_type size_type;
typedef Allocator allocator_type;
// Construct/Copy/Destroy
explicit queue (const Allocator& = Allocator());
allocator_type get_allocator () const;
// 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, class Allocator>
bool operator== (const queue<T, Container, Allocator>&,
const queue<T, Container, Allocator>&);
template <class T, class Container, class Allocator>
bool operator< (const queue<T, Container, Allocator>&,
const queue<T, Container, Allocator>&);
explicit queue (const Allocator& alloc= Allocator());
Creates a queue of zero elements. The queue will use the allocator alloc for all storage management.
allocator_type get_allocator () const;
Returns a copy of the allocator used by self for storage management.
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 will be 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.
template <class T, class Container, class Allocator>
bool operator== (const queue<T, Container, Allocator>& x,
const queue<T, Container, Allocator>& y);
Equality operator. Returns true if x is the same as y.
template <class T, class Container, class Allocator>
bool operator< (const queue<T, Container, Allocator>& x,
const queue<T, Container, Allocator>& 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.
//
// queue.cpp
//
#include <queue>
#include <string>
#include <deque>
#include <list>
#include <iostream.h>
int main(void)
{
// Make a queue using a list container
queue<int, list<int>, allocator> 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>, allocator> 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;
}
Output :
1
2
a
a
a
a
a
a
a
a
a
a
a
aa
aaa
aaaa
aaaaa
aaaaaa
aaaaaaa
aaaaaaaa
aaaaaaaaa
aaaaaaaaaa
If your compiler does not support default template parameters, you must always provide a Container template parameter and an Allocator template parameter. For example you would not be able to write:
queue<int> var;
rather, you would have to write,
queue<int, deque<int>, allocator> var;
allocator, Containers, priority_queue