unordered_set end() in C++ STL

The unordered_set::end() function is a built-in function in C++ STL which returns an iterator pointing to the past-the-end-element. This iterator does not directly point to an element, rather it points to the location just after the last element.

Syntax

umap_name.end()

or,

umap_name.end(int i)

Parameters: This function takes a single integer parameter i which is optional.

Return value:

  • If the parameter i is not passed then the function returns an iterator pointing to the past-the-end element. Actually, it does not point to any element of the set, but it points to the position following the last element of the container.
  • If the parameter i is passed then the function returns an iterator pointing to the past-the-end element of i-th bucket. As in the previous case, it does not point to any element of the set, but it points to the position following the last element of i-th bucket.
    So the iterator returned by unordered_set::end() cannot be dereferenced.

Below programs illustrate the unordered_set::end() function:

Program 1:

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// CPP program to illustrate the unordered_set::end() 
// function
  
#include <iostream>
#include <unordered_set>
  
using namespace std;
  
int main()
{
    unordered_set<int> sampleSet = 
            { 5, 10, 15, 4, 2, 7, 8, 6 };
  
    // Continue the loop until it points to the
    // past-the-end position returned by sampleSet.end()
    for (auto it = sampleSet.begin(); it != sampleSet.end(); 
                                                        it++) 
    {
        cout << *it << " ";
    }
  
    return 0;
}

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Output:

6 8 7 2 4 15 10 5

Program 2:

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// CPP program to illustrate the
// unordered_set::end() function
  
#include <iostream>
#include <unordered_set>
  
using namespace std;
  
int main()
{
    unordered_set<int> sampleSet = 
                { 5, 10, 15, 4, 2, 7, 8, 6 };
  
    // displaying all the buckets of the set.
    // Continue the loop until it points to the 
    // past-the-end position returned by sampleset.end(i)
    for (unsigned i = 0; i < sampleSet.bucket_count(); ++i) 
    {
        cout << "Bucket " << i << " Contains: ";
        for (auto it1 = sampleSet.begin(i); 
                        it1 != sampleSet.end(i); ++it1)
            cout << " " << *it1;
        cout << endl;
    }
      
    return 0;
}

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Output:

Bucket 0 Contains: 
Bucket 1 Contains: 
Bucket 2 Contains:  2
Bucket 3 Contains: 
Bucket 4 Contains:  4 15
Bucket 5 Contains:  5
Bucket 6 Contains:  6
Bucket 7 Contains:  7
Bucket 8 Contains:  8
Bucket 9 Contains: 
Bucket 10 Contains:  10


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