C++ multiset rend
The C++ multiset rend function is employed to retrieve an iterator pointing to the end of the multiset in reverse order, which is not the last element but rather the one past the last element. This behavior is analogous to the element that comes before the first element of the container when it is not reversed.
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() nothrow; //since C++ 11
const_reverse_iterator rend() const nothrow; //since C++ 11
Parameter
Return value
It provides a reverse iterator pointing to the element after the final element of the reversed container.
Complexity
Constant.
Iterator validity
No changes.
Data Races
The container is retrieved. Both the constant and non-constant variants do not alter the container.
Simultaneously accessing the elements of a multiset container is secure.
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 () {
multiset<int> mymultiset = {30,40,20,10,20};
cout << "Elements are :";
for (auto rit = mymultiset.rbegin(); rit != mymultiset.rend(); ++rit)
cout << ' ' << *rit;
cout << '\n';
return 0;
}
Output:
Elements are : 40 30 20 20 10
In the previous instance, the rend method is employed to provide a reverse iterator pointing to the element after the last element of the reversed container.
Since multisets arrange elements based on the keys in sorted order, iterating through a multiset will produce the same order, which is the sorted sequence of keys.
Example 2
Let's explore a basic illustration of iterating over the multiset in reverse sequence utilizing a while loop:
#include <iostream>
#include <set>
#include <string>
#include <iterator>
using namespace std;
int main() {
// Creating & Initializing a multiset of String & Ints
multiset<string> multisetEx = {"aaa", "bbb", "ccc", "ddd", "ccc"};
// Create a multiset iterator and point to the end of multiset
multiset<string>::reverse_iterator it = multisetEx.rbegin();
// Iterate over the multiset using Iterator till beginning.
while (it != multisetEx.rend()) {
// Accessing KEY from elemencpp tutorialed by it.
string word = *it;
cout << word << endl;
// Increment the Iterator to point to next entry
it++;
}
return 0;
}
Output:
ddd
ccc
ccc
bbb
aaa
In the example provided, we utilize a while loop to traverse the multiset in reverse. Multisets maintain elements in a sorted order based on keys. Consequently, iterating through a multiset will yield the aforementioned sequence, which corresponds to the sorted order of keys.
Example 3
Let's see a simple example:
#include <set>
#include <iostream>
int main() {
using namespace std;
multiset <int> s1;
multiset <int>::iterator s1_Iter;
multiset <int>::reverse_iterator s1_rIter;
s1.insert( 10 );
s1.insert( 20 );
s1.insert( 30 );
s1.insert( 10 );
s1_rIter = s1.rend( );
s1_rIter--;
cout << "The last element in the reversed multiset is "
<< *s1_rIter << "." << endl;
// end can be used to terminate an iteration
// throught a multiset in a forward order
cout << "The multiset 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 multiset in a reverse order
cout << "The reversed multiset 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 multiset is " << *s1_rIter << "." << endl;
}
Output:
The last element in the reversed multiset is 10.
The multiset is: 10 10 20 30 .
The reversed multiset is: 30 20 10 10 .
After erase, the last element in the reversed multiset is 20.
In the example provided, the items of the multiset are returned in reverse sequence.
Example 4
Let's explore a basic illustration for arranging and determining the top score:
#include <iostream>
#include <string>
#include <set>
using namespace std;
int main ()
{
multiset<int> emp = {1000,2500,4500,5000,3000,4500};
cout << "Salary" << '\n';
cout<<"______________________\n";
multiset<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
4500
3000
2500
1000
Highest salary: 5000
In the scenario mentioned, a multiset named emp is utilized to store salaries as values. This allows us to benefit from the automatic sorting feature in multisets and helps us determine the highest salary present.
