queue::front() and queue::back() in C++ STL

In this article we will be discussing the working, syntax and examples of queue::front() and queue::back() functions in C++ STL.

What is a queue in C++ STL?

Queue is a simple sequence or data structure defined in the C++ STL which does insertion and deletion of the data in FIFO(First In First Out) fashion. The data in a queue is stored in continuous manner. The elements are inserted at the end and removed from the starting of the queue. In C++ STL there is already a predefined template of queue, which inserts and removes the data in the similar fashion of a queue.

What is queue::front()?

queue::front() is an inbuilt function in C++ STL which is declared in  header file. queue::front() returns a reference to the first element which is inserted in the queue container associated with it. Also in other words we can state that front() directly refers to the element which is oldest in a queue container.

Like in the above given figure, head i.e. 1 is the first element which has been entered in the queue and tail i.e. -4 is the last or the most recent element which is entered in the queue

Syntax

myqueue.front();

This function accepts no parameter

Return value

This function returns a reference to the element which is first inserted in the queue container.

Example

Input: queue<int> myqueue = {10, 20, 30, 40};
      myqueue.front();
Output:
      Front element of the queue = 10

Example

 Live Demo

#include <iostream>
#include <queue>
using namespace std;
int main(){
   queue<int> Queue;
   Queue.push(10);
   Queue.push(20);
   Queue.push(30);
   Queue.push(40);
   Queue.push(40);
      cout<<"Element in front of a queue is: "<<Queue.front();
   return 0;
}

Output

If we run the above code it will generate the following output −

Element in front of a queue is: 10

What is queue::back()?

queue::back() is an inbuilt function in C++ STL which is declared in  header file. queue::back() returns a reference to the last element which is inserted in the queue container associated with it. Also in other words we can state that back() directly refers to the element which is newest in a queue container.

Syntax

myqueue.back();

This function accepts no parameter

Return value

This function returns a reference to the element which is last inserted in the queue container.

Example

Input: queue<int> myqueue = {10, 20 30, 40};
      myqueue.back();
Output:
      Back element of the queue = 40

Example

 Live Demo

#include <iostream>
#include <queue>
using namespace std;
int main(){
   queue<int> Queue;
   Queue.push(10);
   Queue.push(20);
   Queue.push(30);
   Queue.push(40);
   Queue.push(50);
      cout<<"Elements at the back of the queue is: "<<Queue.back();
   return 0;
}

Output

If we run the above code it will generate the following output −

Elements at the back of the queue is: 50