set::swap() in C++ STL

Sets are a type of associative containers in which each element has to be unique, because the value of the element identifies it. The value of the element cannot be modified once it is added to the set, though it is possible to remove and add the modified value of that element.

set::swap()
This function is used to exchange the contents of two sets but the sets must be of same type, although sizes may differ.

Syntax:

set1.swap(set2)

Return value: None

Examples:

Input  : set1 = {1, 2, 3, 4}
         set2 = {5, 6, 7, 8}
         set1.swap(set2);
Output : set1 = {5, 6, 7, 8}
         set2 = {1, 2, 3, 4}

Input  : set1 = {'a', 'b', 'c', 'd'}
         set2 = {'w', 'x', 'y', 'z'}
         set1.swap(set2);
Output : set1 = {'w', 'x', 'y', 'z'}
         set2 = {'a', 'b', 'c', 'd'}

// CPP program to illustrate
// Implementation of swap() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Take any two sets
    set<int> set1{ 1, 2, 3, 4 };
    set<int> set2{ 5, 6, 7, 8 };

    // Swap elements of sets
    set1.swap(set2);

    // Print the first set
    cout << "set1 = ";
    for (auto it = set1.begin();
         it != set1.end(); ++it)
        cout << ' ' << *it;

    // Print the second set
    cout << endl
         << "set2 = ";
    for (auto it = set2.begin();
         it != set2.end(); ++it)
        cout << ' ' << *it;

    return 0;
}

Output:

set1 =  5 6 7 8
set2 =  1 2 3 4

Time complexity: Constant