unordered_multimap cbegin() function in C++ STL

Last Updated : 08 Aug, 2018

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

unordered_multimap_name.cbegin(n)

Parameters: The function accepts one parameter. If a parameter is passed, it returns a constant iterator pointing to the first element in the bucket. If no parameter is passed, then it returns a constant iterator pointing to the first element in the unordered_multimap container. Return Value: It returns a constant iterator. It cannot be used to change the value of the unordered_multimap element. Below programs illustrates the above function: Program 1:

CPP

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

int main()
{

    // declaration
    unordered_multimap<int, int> sample;

    // inserts key and element
    sample.insert({ 1, 2 });
    sample.insert({ 3, 4 });
    sample.insert({ 3, 4 });
    sample.insert({ 2, 3 });
    sample.insert({ 2, 3 });

    // prints all key and element
    cout << "Key and Elements : \n";
    for (auto it = sample.begin(); it != sample.end(); it++)
        cout << "   " << it->first << "\t      " 
             << it->second << endl;

    auto it = sample.begin();

    // print the first element
    cout << "\nThe first element and key: " 
         << it->first << " ";
    cout << it->second;

    return 0;
}

Output:

Key and Elements : 
   2          3
   2          3
   1          2
   3          4
   3          4

The first element and key: 2 3

Program 2:

CPP

// C++ program to illustrate the
// unordered_multimap::cbegin(bucket) 
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<int, int> sample;

    // inserts element
    sample.insert({ 1, 2 });
    sample.insert({ 3, 4 });
    sample.insert({ 3, 4 });
    sample.insert({ 2, 3 });
    sample.insert({ 2, 3 });

    // prints all element
    cout << "Key and Elements of first bucket: \n";
    for (auto it = sample.cbegin(1); it != sample.cend(1); it++)
        cout << "   " << it->first << "\t      " 
             << it->second << endl;

    auto it = sample.cbegin(1);

    // print the first element
    cout << "\nThe first element and key in first bucket: "
         << it->first << " ";
    cout << it->second;

    return 0;
}

Output:

Key and Elements of first bucket: 
   1          2

The first element and key in first bucket: 1 2

unordered_multimap bucket_size() function in C++ STL

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