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.
S.N. |
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
S.N. |
Method & Description |
1 |
queue::queue default constructorConstructs an empty queue object, with zero elements. |
2 |
queue::queue initialize constructorConstructs a queue object and assigns internal container by a copy of ctnr. |
3 |
queue::queue move constructorConstructs 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
S.N. |
Method & Description |
1 |
queue::~queue
Destroys queue by deallocating container memory. |
Member functions
S.N. |
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 versionAssigns new contents to the queue by replacing old ones. |
6 |
queue::operator= move versionAssigns new contents to the queue by replacing old ones. |
7 |
queue::pop
Removes front element of the queue. |
8 |
queue::push copy versionInserts new element at the end of queue. |
9 |
queue::push move versionInserts 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
S.N. |
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.
Definition
Below is definition of std::priority_queue from <queue> header file
template <class T, class Container = vector<T>,
class Compare = less<typename Container::value_type> < class priority_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.
- Compare − Comparison object to be used to order the priority_queue.
This may be a function pointer or function object that can compare its two arguments.
Member types
Following member types can be used as parameters or return type by member functions.
S.N. |
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
Destructor
Member functions
Non-member overloaded functions
S.N. |
Method & Description |
1 |
swap
Exchanges the contents of priority_queue with contents of another priority_queue. |
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