list crbegin() and crend() function in C++ STL

1. The list::crbegin() is a built-in function in c++ STL that returns a constant reverse iterator which points to the last element of the list i.e reversed beginning of container. The elements cannot be modified or changed as the iterator is a constant one. Syntax:

list_name.crbegin()

1. Parameters: The function does not accept any parameters. Return value: It returns a random access reverse iterator which points to the reverse beginning of the list. Below program illustrates the above function: 

CPP

// C++ program to illustrate the
// list::crbegin() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
 // declaration of the list
 list<int> lis = { 10, 20, 30, 40, 50 };

 // prints the last element
 cout << "The last element is: " << *lis.crbegin();
 cout << "\nList: ";

 for (auto it = lis.crbegin(); it != lis.crend(); ++it)
  cout << *it << " ";

 return 0;
}

Output:

The last element is: 50
List: 50 40 30 20 10

Time Complexity: O(1)

Auxiliary Space: O(1)

1. The list::crend() is a built-in function in C++ STL that returns a constant reverse iterator which points to the theoretical element preceding the first element in the list i.e. the reverse end of the list. The elements cannot be modified or changed as the iterator is a constant one. Syntax:

list_name.crend()

1. Parameters: The function does not accept any parameters. Return value: It returns a constant random reverse iterator which points to the reverse end of the list. Below program illustrates the above function: 

CPP

// C++ program to illustrate the
// list::crend() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
 // declaration of the list
 list<int> lis = { 7, 6, 5, 4, 3, 2 };

 cout << "List: " << endl;

 for (auto it = lis.crbegin(); it != lis.crend(); ++it)
  cout << *it << " ";

 return 0;
}

Output:

List: 
2 3 4 5 6 7

Time Complexity: O(1)

Auxiliary Space: O(1)

Let us see the differences in a tabular form -:

	list crbegin()	list crend()
1.	It is used to return a const_reverse_iterator pointing to the last element in the container	It is used to return a const_reverse_iterator pointing to the theoretical element preceding the first element in the container
2.	Its syntax is -: const_reverse_iterator crbegin();	Its syntax is -: const_reverse_iterator crend();
3.	It does not take any parameters.	It does not take any parameters.
4.	Its complexity is constant.	Its complexity is constant.
5.	Its iterator validity does not changes.	Its iterator validity does not changes.