C++ <deque> - rbegin() Function

The C++ deque::rbegin function returns the reverse iterator pointing to the last element of the deque. A reverse iterator iterates in backward direction and increasing it results into moving to the beginning of the deque container. Similarly, decreasing a reverse iterator results into moving to the end of the deque container. Please note that, Unlike the deque::back function, which returns a direct reference to the last element, it returns the reverse iterator pointing to the same element of the deque.

Syntax

• C++98
• C++11

reverse_iterator rbegin();
const_reverse_iterator rbegin() const;

reverse_iterator rbegin() noexcept;
const_reverse_iterator rbegin() const noexcept;

Parameters

No parameter is required.

Return Value

A reverse iterator to the reverse beginning of the sequence container. If the sequence object is constant qualified, the function returns a const_reverse_iterator, else returns an reverse_iterator.

Time Complexity

Constant i.e, Θ(1).

Example:

In the example below, the deque::rbegin function returns the reverse iterator pointing to the last element of the deque MyDeque.

#include <iostream>
#include <deque>
using namespace std;
 
int main (){
  deque<string> MyDeque{"Alpha","Coding","Skills"};
  deque<string>::reverse_iterator rit;

  rit = MyDeque.rbegin();
  cout<<*rit<<" ";
  rit++;
  cout<<*rit<<" ";
  rit++;
  cout<<*rit<<" ";
  return 0;
}

The output of the above code will be:

Skills Coding Alpha 

Example:

Lets see another example where the deque called MyDeque contains integer values and deque::rbegin function is used with deque::rend function to specify a range including all elements of the deque container.

#include <iostream>
#include <deque>
using namespace std;
 
int main (){
  deque<int> MyDeque{10, 20, 30, 40, 50};
  deque<int>::reverse_iterator rit;

  for(rit = MyDeque.rbegin(); rit != MyDeque.rend(); ++rit)
    cout<<*rit<<" ";

  return 0;
}

The output of the above code will be:

50 40 30 20 10