unordered_set swap() in C++ STL

The swap() method of “unordered_set” swaps the contents of two containers. It is public member function. This function:

• Exchanges the content of the container by the content of variable, which is another unordered_set object containing elements of the same type but the sizes may differ.
• After the call to this member function, the elements in this container are those which were in variable before the call, and the elements of variable are those which were in this.

Syntax:

void swap(unordered_set &another_unordered_set);

Parameters: It receives another_unordered_set container object of the same type as this container with which it is to be swapped.

Returns: It does not return any value.

Below program illustrate the unordered_set swap() function :-

Example 1:

#include <iostream>
#include <string>
#include <unordered_set>

using namespace std;

int main()
{

    // sets the values in two container
    unordered_set<string>
        first = { "FOR GEEKS" },
        second = { "GEEKS" };

    // before swap values
    cout << "before swap :- \n";

    cout << "1st container : ";
    for (const string& x : first)
        cout << x << endl;

    cout << "2nd container : ";
    for (const string& x : second)
        cout << x << endl;

    // call swap

    first.swap(second);

    // after swap values
    cout << "\nafter swap :- \n";

    // displaying 1st container
    cout << "1st container : ";
    for (const string& x : first)
        cout << x << endl;

    // displaying 2nd container
    cout << "2nd container : ";
    for (const string& x : second)
        cout << x << endl;

    return 0;
}

Output:

before swap :- 
1st container : FOR GEEKS
2nd container : GEEKS

after swap :- 
1st container : GEEKS
2nd container : FOR GEEKS

Example 2:

#include <iostream>
#include <string>
#include <unordered_set>

using namespace std;

int main()
{

    // sets the values in two container
    unordered_set<int>
        first = { 1, 2, 3 },
        second = { 4, 5, 6 };

    // before swap values
    cout << "before swap :- \n";

    cout << "1st container : ";
    for (const int& x : first)
        cout << x << " ";
    cout << endl;

    cout << "2nd container : ";
    for (const int& x : second)
        cout << x << " ";
    cout << endl;

    // call swap

    first.swap(second);

    // after swap values
    cout << "\nafter swap :- \n";

    // displaying 1st container
    cout << "1st container : ";
    for (const int& x : first)
        cout << x << " ";
    cout << endl;

    // displaying 2nd container
    cout << "2nd container : ";
    for (const int& x : second)
        cout << x << " ";
    cout << endl;

    return 0;
}

Output:

before swap :- 
1st container : 3 2 1 
2nd container : 6 5 4 

after swap :- 
1st container : 6 5 4 
2nd container : 3 2 1