unordered_multiset begin() function in C++ STL

The unordered_multiset::begin() is a built-in function in C++ STL which returns an iterator pointing to the first element in the container or to the first element in one of its bucket.

Syntax:

unordered_multiset_name.begin(n)

Parameters: The function accepts one parameter. If a parameter is passed, it returns an iterator pointing to the first element in the bucket. If no parameter is passed, then it returns an iterator pointing to the first element in the unordered_multiset container.

Return Value: It returns an iterator.

Below programs illustrates the above function:

Program 1:

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

int main()
{

    // declaration
    unordered_multiset<int> sample;

    // inserts element
    sample.insert(10);
    sample.insert(11);
    sample.insert(15);
    sample.insert(13);
    sample.insert(14);

    // print the first element
    cout << "The first element: " << *sample.begin();

    cout << "\nElements: ";

    // prints all element
    for (auto it = sample.begin(); it != sample.end(); it++)
        cout << *it << " ";
    return 0;
}

Output:

The first element: 14
Elements: 14 13 15 10 11

Program 2:

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

int main()
{

    // declaration
    unordered_multiset<char> sample;

    // inserts element
    sample.insert('a');
    sample.insert('b');
    sample.insert('c');
    sample.insert('x');
    sample.insert('z');

    // print the first element

    auto it = sample.begin();
    cout << "The first element: " << *it;

    it++;
    cout << "\nThe second element: " << *it;

    cout << "\nElements: ";

    // prints all element
    for (auto it = sample.begin(); it != sample.end(); it++)
        cout << *it << " ";
    return 0;
}

Output:

The first element: z
The second element: x
Elements: z x c a b

Program 3:

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

int main()
{

    // declaration
    unordered_multiset<char> sample;

    // inserts element
    sample.insert('a');
    sample.insert('b');
    sample.insert('c');
    sample.insert('x');
    sample.insert('z');

    // print the first element
    cout << "The first element in first bucket : " << *sample.begin(1);

    cout << "\nElements in first bucket: ";

    // prints all element
    for (auto it = sample.begin(1); it != sample.end(1); it++)
        cout << *it << " ";
    return 0;
}

Output:

The first element in first bucket : x
Elements in first bucket: x c