queue push() and pop() in C++ STL

Try it on GfG Practice

The std::queue::push() and std::queue::pop() functions in C++ STL are used to push the element at the back of the queue and remove the element from the front of the queue respectively. They are the member functions of the std::queue container defined inside the <queue> header file.

In this article we will learn how to use queue::push() and queue::pop() methods in C++.

queue::push()

The queue::push() function in C++ STL inserts an element at the back of the queue. This operation is called push operation hence the name push() method.

Syntax

q.push(val);

Parameters

• val: Value to insert.

Return Value

• This function does not return any value.

Example of queue::push() Method

// C++ Program to show how to use queue::push()
// to push the element at the back of queue
#include <bits/stdc++.h>
using namespace std;

int main() {
    queue<int> q;

    // Inserting elements at the back of queue
    q.push(0);
    q.push(1);
    q.push(2);

    // Printing queue
    while (!q.empty()) {
        cout << q.front() << " ";
        q.pop();
    }
  	return 0;
}

0 1 2 

Time Complexity: O(1)
Auxiliary Space: O(1)

queue::pop()

The queue::pop() function in C++ STL removes an element from the front of the queue. This operation is called pop operation hence the name. It works according to the FIFO (First-In-First-Out) order of deletion i.e. the element that was inserted first will be removed first.

Syntax

q.pop();

Parameters

• This function does not take any parameter.

Return Value

• This function does not return any value.

Example of queue::pop()

// C++ Program to show how to use queue::pop()
// to remove the element from the front of queue
#include <bits/stdc++.h>
using namespace std;

int main() {
    queue<int> q;

    // Inserting few elements at the back of queue
    q.push(0);
    q.push(1);
    q.push(2);

    // Remove element from the front of queue
    q.pop();

  	// Printing queue
    while (!q.empty()) {
        cout << q.front() << " ";
        q.pop();
    }
  return 0;
}

1 2 

Time Complexity: O(1)
Auxiliary Space: O(1)

Difference Between queue::push() and queue::pop()

The following table list the main differences between queue::push() and queue::pop():