unordered_multimap empty() function in C++ STL

The unordered_multimap::empty() is a built-in function in C++ STL which returns a boolean value. It returns true if the unordered_multimap container is empty. Otherwise, it returns false.

Syntax:

unordered_multimap_name.empty()

Parameters: The function does not accept any parameter.

Return Value: It returns a boolean value which denotes whether a unordered_multimap is empty or not.

Below programs illustrates the above function:

Program 1:

// C++ program to illustrate the
// unordered_multimap::empty() function
#include <iostream>
#include <unordered_map>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<int, int> sample;

    // inserts key and element
    sample.insert({ 1, 2 });
    sample.insert({ 1, 2 });
    sample.insert({ 2, 3 });
    sample.insert({ 3, 4 });
    sample.insert({ 5, 6 });

    // if not empty then print the elements
    if (sample.empty() == false) {
        cout << "Key and Elements: ";

        for (auto it = sample.begin(); it != sample.end(); it++) {
            cout << "{" << it->first << ":" << it->second << "} ";
        }
    }

    // container is erased completely
    sample.clear();

    if (sample.empty() == true)
        cout << "\nContainer is empty";

    return 0;
}

Output:

Key and Elements: {5:6} {3:4} {2:3} {1:2} {1:2} 
Container is empty

Program 2:

// C++ program to illustrate the
// unordered_multimap::empty()
#include <iostream>
#include <unordered_map>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<char, char> sample;

    // inserts element
    sample.insert({ 'a', 'b' });
    sample.insert({ 'a', 'b' });
    sample.insert({ 'g', 'd' });
    sample.insert({ 'r', 'e' });
    sample.insert({ 'g', 'd' });

    // if not empty then print the elements
    if (sample.empty() == false) {
        cout << "Key and elements: ";

        for (auto it = sample.begin(); it != sample.end(); it++) {
            cout << "{" << it->first << ":" << it->second << "} ";
        }
    }

    // container is erased completely
    sample.clear();

    if (sample.empty() == true)
        cout << "\nContainer is empty";

    return 0;
}

Output:

Key and elements: {r:e} {g:d} {g:d} {a:b} {a:b} 
Container is empty