C++ set rend()

C++ set rend() function is used to return an iterator to the end of the set (not the last element but the past last element) in reverse order. This is similar to the element preceding the first element of the non-reversed container.

Note:- This is a placeholder. No element exists in this location and attempting to access is undefined behavior.

Syntax

      reverse_iterator rend();                             //until C++ 11
const_reverse_iterator rend() const;                 //until C++ 11
      reverse_iterator rend() noexcept;               //since C++ 11
const_reverse_iterator rend() const noexcept;   //since C++ 11

Parameter

None

Return value

It returns a reverse iterator to the element following the last element of the reversed container.

Complexity

Constant.

Iterator validity

No changes.

Data Races

The container is accessed. Neither the const nor the non-const versions modify the container.

Concurrently accessing the elements of a set is safe.

Exception Safety

This function never throws exception.

Example 1

Let's see the simple example for rend() function:

#include <iostream>
#include <set>

using namespace std;

int main () {
   set<int> myset = {40,50,20,10,30};

   cout << "Elements are :";
   for (auto rit = myset.rbegin(); rit != myset.rend(); ++rit)
      cout << ' ' << *rit;
      cout << '\n';

   return 0;
}

Output:

Elements are : 50 40 30 20 10

In the above example, rend() function is used to return a reverse iterator to the element following the last element of the reversed container.

Because set stores the elements in sorted order of keys therefore, iterating over a set will result in above order i.e. sorted order of keys.

Example 2

Let's see a simple example to iterate over the set in reverse order using while loop:

#include <iostream>
#include <set>
#include <string>
#include <iterator>

using namespace std;
 
int main() {
 
	// Creating & Initializing a set of String & Ints
	set<string> setEx = {"aaa", "bbb", "ccc", "ddd"};
 
	// Create a set iterator and point to the end of set
	set<string>::reverse_iterator it = setEx.rbegin();
 
	// Iterate over the set using Iterator till beginning.
	while (it != setEx.rend()) {
		// Accessing KEY from element pointed by it.
		string word = *it;
 
		cout << word << endl;
 
		// Increment the Iterator to point to next entry
		it++;
	}
	return 0;
}

Output:

ddd
ccc
bbb
aaa

In the above example, we are using while loop to iterate over the set in reverse order.

Because set stores the elements in sorted order of keys therefore, iterating over a set will result in above order i.e. sorted order of keys.

Example 3

Let's see a simple example:

#include <set>  
#include <iostream>  
  
int main() {  
   using namespace std;     
   set <int> s1;  
   set <int>::iterator s1_Iter;  
   set <int>::reverse_iterator s1_rIter;  

   s1.insert( 10 );  
   s1.insert( 20 );  
   s1.insert( 30 );  
  
   s1_rIter = s1.rend( );  
   s1_rIter--;  
   cout << "The last element in the reversed set is "  
        << *s1_rIter << "." << endl;  
  
   // end can be used to terminate an iteration   
   // throught a set in a forward order  
   cout << "The set is: ";  
   for ( s1_Iter = s1.begin( ) ; s1_Iter != s1.end( ); s1_Iter++ )  
      cout << *s1_Iter << " ";  
   cout << "." << endl;  
  
   // rend can be used to terminate an iteration   
   // throught a set in a reverse order  
   cout << "The reversed set is: ";  
   for ( s1_rIter = s1.rbegin( ) ; s1_rIter != s1.rend( ); s1_rIter++ )  
      cout << *s1_rIter << " ";  
   cout << "." << endl;  
  
   s1_rIter = s1.rend( );  
   s1_rIter--;  
   s1.erase ( *s1_rIter );  
  
   s1_rIter = s1.rend( );  
   --s1_rIter;  
   cout << "After erase, the last element in the "  
        << "reversed set is " << *s1_rIter << "." << endl;  
}  

Output:

The last element in the reversed set is 10.
The set is: 10 20 30 .
The reversed set is: 30 20 10 .
After erase, the last element in the reversed set is 20.

In the above example, elements of set returned in reverse order.

Example 4

Let's see a simple example to sort and calculate the highest marks:

#include <iostream>
#include <string>
#include <set>

using namespace std;

int main ()
{
  set<int> emp = {1000,2500,4500,5000,3000};

   cout << "Salary" << '\n';
   cout<<"______________________\n";
   
  set<int>::reverse_iterator rit;
    for (rit=emp.rbegin(); rit!=emp.rend(); ++rit)
    cout << *rit<< '\n';

    auto ite = emp.rbegin();
 
    cout << "\nHighest salary: "<< *ite <<" \n";

  return 0;
  }

Output:

Salary
______________________
5000
4500
3000
2500
1000

Highest salary: 5000

In the above example, a set emp is implemented where the ID is being stored as value and salary as key. This enables us to take advantage of the auto sorting in sets and lets us to identify the ID of the element with the highest salary.

Next TopicSet crbegin() Function

← prev next →