unordered_multimap swap() function in C++ STL

The unordered_multimap::swap() is a built-in function in C++ STL which swaps the contents of two unordered_multimap containers. The sizes can differ of both the containers.

Syntax:

unordered_multimap_name1.swap(unordered_multimap_name2)

Parameters: The function accepts a single mandatory parameter unordered_multimap_name2 which specifies the unordered_multimap with which the swapping of unordered_multimap_name1 is to be done.

Return Value: It does not return anything.

Below programs illustrates the above function:

Program 1:

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

int main()
{

    // declaration
    unordered_multimap<int, int> sample1, sample2;

    // inserts key and element
    // in sample1
    sample1.insert({ 10, 100 });
    sample1.insert({ 50, 500 });

    // inserts key and element
    // in sample1
    sample2.insert({ 20, 200 });
    sample2.insert({ 30, 300 });
    sample2.insert({ 30, 150 });

    cout << "Key and Elements of Sample1 before swap are:";
    for (auto it = sample1.begin(); it != sample1.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    cout << "\nKey and Elements of Sample2 before swap are:";
    for (auto it = sample2.begin(); it != sample2.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    // performs swap of two
    // unordered_multimaps
    sample1.swap(sample2);

    cout << "\n\nKey and Elements of Sample1 after swap are:";
    for (auto it = sample1.begin(); it != sample1.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    cout << "\nKey and Elements of Sample2 after swap are:";
    for (auto it = sample2.begin(); it != sample2.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    return 0;
}

Output:

Key and Elements of Sample1 before swap are:{50, 500} {10, 100} 
Key and Elements of Sample2 before swap are:{20, 200} {30, 150} {30, 300} 

Key and Elements of Sample1 after swap are:{20, 200} {30, 150} {30, 300} 
Key and Elements of Sample2 after swap are:{50, 500} {10, 100}

Program 2:

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

int main()
{

    // declaration
    unordered_multimap<char, char> sample1, sample2;

    // inserts key and element
    // in sample1
    sample1.insert({ 'a', 'A' });
    sample1.insert({ 'g', 'G' });

    // inserts key and element
    // in sample1
    sample2.insert({ 'b', 'B' });
    sample2.insert({ 'c', 'C' });
    sample2.insert({ 'd', 'D' });

    cout << "Key and Elements of Sample1 before swap are:";
    for (auto it = sample1.begin(); it != sample1.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    cout << "\nKey and Elements of Sample2 before swap are:";
    for (auto it = sample2.begin(); it != sample2.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    // performs swap of two
    // unordered_multimaps
    sample1.swap(sample2);

    cout << "\n\nKey and Elements of Sample1 after swap are:";
    for (auto it = sample1.begin(); it != sample1.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    cout << "\nKey and Elements of Sample2 after swap are:";
    for (auto it = sample2.begin(); it != sample2.end(); it++) {
        cout << "{" << it->first << ", " << it->second << "} ";
    }

    return 0;
}

Output:

Key and Elements of Sample1 before swap are:{g, G} {a, A} 
Key and Elements of Sample2 before swap are:{d, D} {b, B} {c, C} 

Key and Elements of Sample1 after swap are:{d, D} {b, B} {c, C} 
Key and Elements of Sample2 after swap are:{g, G} {a, A}