C++ Queue Library - back() Function

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Description

The C++ function std::queue::back() returns a reference to the last element of queue. This is the most recently enqueued element.

Declaration

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

C++98

value_type& back();
const value_type& back() const;

C++11

reference& back();
const_reference& back() const;

Parameters

None

Return value

Returns reference to the last element of the queue.

Exceptions

No-throw guarantee for standard non-empty containers.

Time complexity

Constant i.e. O(1)

Example

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

#include <iostream>
#include <queue>

using namespace std;

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

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

   cout << "Last element of queue q is = " << q.back() << endl;

   return 0;
}

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

Last element of queue q is = 5