Library: Containers
Does not inherit
A container adaptor that behaves like a queue (first in, first out)
#include <queue>
namespace std {
template <class T, class Container = deque<T> >
class queue;
}
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.
namespace std {
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 ();
};
// Nonmember 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>&);
}
explicit queue(const Container& = Container());
Creates a queue of zero elements.
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.
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>
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).
//
// queue.cpp
//
#include <deque> // for deque
#include <iostream> // for cout, endl
#include <list> // for list
#include <queue> // for queue
#include <string> // for string
int main ()
{
typedef std::queue<int, std::list<int,
std::allocator<int> > >
IQueue;
// Make a queue using a deque container.
IQueue q;
// Push a couple of values on and retrieve them.
q.push (1);
q.push (2);
std::cout << q.front () << std::endl;
std::cout << q.back () << std::endl;
typedef std::queue<std::string, std::deque<std::string,
std::allocator<std::string> > > SQueue;
// Make a queue of strings using a deque container.
SQueue qs;
// Push on a few strings then pop them back off.
for (int i = 0; i < 10; i++) {
qs.push (std::string (i + 1, 'a'));
std::cout << qs.front () << std::endl;
}
for (int j = 0; j < 10; j++) {
std::cout << qs.front () << std::endl;
qs.pop ();
}
// Return 0 if both containers are empty,
// a non-zero value otherwise.
return !(2 == q.size () && qs.empty ());
}
Program Output:
1 2 a a a a a a a a a a a aa aaa aaaa aaaaa aaaaaa aaaaaaa aaaaaaaa aaaaaaaaa aaaaaaaaaa
allocator, Containers, priority_queue
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 23.2.3.1