Queue in C++ Function: Syntax, Types And Advantages

What Is a Queue in C++? Explain With Syntax and an Example

The queue in C++ is a large data structure. Queue in C++ uses an encapsulated object of the sequential container class as its principal container. It provides a particular set of member functions that can access its elements.

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Syntax of C++ queue

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

The insertion of queues in C++ takes place at the rear end, and the deletion takes the front. The rear end or rear element is the last element in the queue. The front or the front element is the element at the first position in the queue.

Queue in C++ works in the “first in first out” technique. It means that the element that you insert first is extracted first, and so on. The queues are indicated as the container adaptors in the application areas.

Every container has support for the main operations list that includes size, pop_front, back, front, push_back, and empty. The different template parameters are: 

• Container: This argument defines the internal object of the container where all the queue elements are stored.
• T: This argument defines the type of element that will be held by the container adaptor.

All Queues must allow:

• Enqueue: The addition of an element at the end of the queue.
• Dequeue: The removal of an element from the front of the queue.
• IsEmpty: The checking of the queue if it is empty.
• IsFull: The checking of the queue if it is full.
• Peek: Obtaining the value of the front of the queue without removing the element.

Advantages of Queue C++:

• It is used in applications in which data is transferred asynchronously between two processes. The queue in C++ can be used for obtaining the synchronization.
• The call center systems use queues to hold the incoming calls and to resolve them one by one.
• The queues can handle the interrupts in a real-time system and are ideal for disk scheduling and CPU scheduling.

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Explain the Various Functions of  C++ Queue, With Their Use Cases

The different functions of the queue in C++ are:

• Constructor: It is used for the construction of a queue container.
• Empty: It is used to test the emptiness of a queue in C++. This function returns true if the queue is empty and returns false if the queue is not empty.
• Size: It returns the size of the queue container that is the measure of the number of elements stored in the queue.
• Front: It is used to access the front elements of the queue in C++. It is an important queue function in C++ as it is responsible for deletion operations. Elements are deleted from the front.
• Back: It is used to access the rear element of the queue in C++. It is an important function as it is responsible for the insertion operations. Elements are added from the front.
• Push: It is used to insert a new element at the rear end of the queue in C++.
• Pop: It is used to delete a new element at the front end of the queue in C++.
• Emplace: It is used for the insertion of the new elements in the queue above the current rear element.
• Swap: It is used for interchanging the contents of two containers in the reference.
• Relational Operators: It is a non-member function that specifies the relational operators needed for the queues.
• Uses allocator <queue>: It is a non-member function that uses the allocator for the queues in C++.

Example of Queue C++ Program Showing the Use of Various Functions:

# include <iostream>

# include <queue>

using namespace std;

void showsg (queue <int> sg)

{

  queue <int> ss = sg;

  while (!ss.empty())

  {

  cout << ‘\t’ << ss.front();

  ss.pop();

  }

  cout << ‘\n’;

}

int main()

{

   Queue <int> fquiz;

  fquiz.push(10);

  fquiz.push(20);

  fquiz.push(30);

cout << “The queue fquiz is : “;

showsg(fquiz);

cout << “\nfquiz.size() : “ << fquiz.size();

cout << “\nfquiz.front() : “ << fquiz.front();

cout << “\nfquiz.back() : “ << fquiz.back();

cout << “\nfquiz.pop() : “;

fquiz.pop();

showsg(fquiz);

return 0;

}

Output:

Explain the member types of Queue C++, with their use cases

• container_type: The underlying container type is specified using the container_type member. It is the second template parameter.
• reference: It is a reference type of container member that is usually value_type.
• const_reference: It is a reference type of constant container that is usually const value_type.
• value_type: This member function specifies the types of the elements.
• size_type: This member function specifies the types of the elements.

Example of Queue C++ Program:

# include <iostream>

# include <queue>

using namespace std;

void showsg (queue <int> que)

{

  queue <int> sq = que;

  while (!sq.empty())

  {

  cout << ‘\t’ << sq.front();

  sq.pop();

  }

  cout << ‘\n’;

}

int main()

{

  queue  <int>  fquiz;

  fquiz.push(11);

  fquiz.push(12);

  fquiz.push(13);

cout << “Here is the Queue  :  “;

showQueue(fquiz); 

cout << “\nSize of Queue : “ << fquiz.size();

cout << “\nFront of Queue: “ << fquiz.front();

cout << “\nBack of Queue: “ << fquiz.back();

return 0;

}

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Output:

Wrapping Up

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