C++ Queue Library - front() Function

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Description

The C++ function std::queue::front() returns a reference to the first element of the queue. This element will be removed after performing pop operation on queue.

This member function effectively calls the front member function of underlying container.

Declaration

Following is the declaration for std::queue::front() function form std::queue header.

C++98

value_type& front();
const value_type& front() const;

C++11

reference& front();
const_reference& front() const;

Parameters

None

Return value

Returns reference to the first element of the queue.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::queue::front() function.

#include <iostream>
#include <queue>

using namespace std;

int main(void) {
   queue<int> q;

   for (int i = 0; i < 5; ++i)
      q.emplace(i + 1);

   cout << "First element of queue = " << q.front() << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

First element of queue = 1