C++ <deque> - crbegin() Function

The C++ deque::crbegin function returns the constant reverse iterator (const_reverse_iterator) pointing to the last element of the deque. Please note that, Unlike the deque::back function, which returns a direct reference to the last element, it returns the const_reverse_iterator pointing to the same element of the deque.

Note: A const_reverse_iterator is an iterator that points to constant value and iterates in backward direction. Increasing a const_reverse_iterator results into moving to the beginning of the deque container and decreasing it results into moving to the end of the deque container. Along with this, it cannot be used to modify the contents it points to, even if the deque element is not itself constant.

Syntax

C++11

const_reverse_iterator crbegin() const noexcept;

Parameters

No parameter is required.

Return Value

A const_reverse_iterator to the reverse beginning of the sequence container.

Time Complexity

Constant i.e, Θ(1).

Example:

In the example below, the deque::crbegin function returns the const_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>::const_reverse_iterator crit;

  crit = MyDeque.crbegin();
  cout<<*crit<<" ";
  crit++;
  cout<<*crit<<" ";
  crit++;
  cout<<*crit<<" ";
  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::crbegin function is used with deque::crend 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>::const_reverse_iterator crit;

  for(crit = MyDeque.crbegin(); crit != MyDeque.crend(); ++crit)
    cout<<*crit<<" ";

  return 0;
}

The output of the above code will be:

50 40 30 20 10

❮ C++ <deque> Library