C++ Library - <queue>

Introduction to queue

Queue is a data structure designed to operate in FIFO (First in First out) context. In queue elements are inserted from rear end and get removed from front end.

Queue class is container adapter. Container is an objects that hold data of same type. Queue can be created from different sequence containers. Container adapters do not support iterators therefore we cannot use them for data manipulation. However they support push() and pop() member functions for data insertion and deletion respectively.

Definition

Below is definition of std::queuer from <queue> header file

template <class T, class Container = deque<T> > class queue;

Parameters

T − Type of the element contained.

T may be substituted by any other data type including user-defined type.
Container − Type of the underlying container object.

Member types

Following member types can be used as parameters or return type by member functions.

Sr.No.	Member types	Definition
1	value_type	T (First parameter of the template)
2	container_type	Second parameter of the template
3	size_type	size_t
4	reference	value_type&
5	const_reference	const value_type&
6	difference_type	ptrdiff_t

Functions from <queue>

Below is list of all methods from <queue> header.

Constructors

Sr.No.	Method & Description
1	queue::queue `default constructor` Constructs an empty queue object, with zero elements.
2	queue::queue `initialize constructor` Constructs a queue object and assigns internal container by a copy of `ctnr`.
3	queue::queue `move constructor` Constructs the queue with the contents of other using move semantics.
4	queue::queue `copy constructor` Constructs a queue with copy of each elements present in existing queue `other`.

Destructor

Sr.No.	Method & Description
1	queue::~queue Destroys queue by deallocating container memory.

Member functions

Sr.No.	Method & Description
1	queue::back Returns a reference to the last element of queue.
2	queue::emplace Constructs and inserts new element at the end of queue.
3	queue::empty Tests whether queue is empty or not.
4	queue::front Returns a reference to the first element of the queue.
5	queue::operator= `copy version` Assigns new contents to the queue by replacing old ones.
6	queue::operator= `move version` Assigns new contents to the queue by replacing old ones.
7	queue::pop Removes front element of the queue.
8	queue::push `copy version` Inserts new element at the end of queue.
9	queue::push `move version` Inserts new element at the end of queue.
10	queue::size Returns the total number of elements present in the queue.
11	queue::swap Exchanges the contents of queue with contents of another queue.

Non-member overloaded functions

Sr.No.	Method & Description
1	operator== Tests whether two queues are equal or not.
2	operator!= Tests whether two queues are equal or not.
3	operator< Tests whether first queue is less than other or not.
4	operator<= Tests whether first queue is less than or equal to other or not.
5	operator> Tests whether first queue is greater than other or not.
6	operator>= Tests whether first queue is greater than or equal to other or not.
7	swap Exchanges the contents of two queues.

Introduction to priority_queue

Priority queue is queue data structure that holds priority. Priority queue is analogous to heap data structure where element can be inserted in any order and always max heap element is retrieved first.