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C++ Unordered Set Swap

The C++ std::unordered_set::swap() function is used to exchange the contents of the unordered_set with others. If both the unordered_sets have the same contents, it does nothing; otherwise, exchange the contents of the unordered_sets with another unordered_set. The return type of this function is void which implies that it does not return any value.

Following is the syntax of std::unordered_set::swap() function −

void swap ( unordered_set& other);

• other − It is another container to exchange the contents with.

This function does not return any value.

Let's look at the following example, where we are going to exchange the contents of the num_set1 with the contents of the num_set2.

#include<iostream>
#include<string>
#include<unordered_set>
using namespace std;

int main () {
   //create unordered_sets
   unordered_set<int> num_set1 = {1, 2, 3, 4, 5};
   unordered_set<int> num_set2 = {6, 7, 8, 9, 10};
   cout<<"Contents of the num_set1 before swap operation: "<<endl;
   for(int n1 : num_set1){
      cout<<n1<<endl;
   }
   cout<<"Contents of the num_set2 before swap operation: "<<endl;
   for(int n2 : num_set2){
      cout<<n2<<endl;
   }
   //using the swap() function
   num_set1.swap(num_set2);
   cout<<"Contents of the num_set1 after swap operation: "<<endl;
   for(int n1 : num_set1){
      cout<<n1<<endl;
   }
   cout<<"Contents of the num_set2 after swap operation: "<<endl;
   for(int n2 : num_set2){
      cout<<n2<<endl;
   }
}

If we run the above code it will generate the following output −

Contents of the num_set1 before swap operation: 
5
4
3
2
1
Contents of the num_set2 before swap operation: 
10
9
8
7
6
Contents of the num_set1 after swap operation: 
10
9
8
7
6
Contents of the num_set2 after swap operation: 
5
4
3
2
1

Consider the another scenario, where we are going to consider the unordered_sets of char type and applying the swap() function.

#include<iostream>
#include<string>
#include<unordered_set>
using namespace std;

int main () {
   //create unordered_sets
   unordered_set<char> char_set1 = {};
   unordered_set<char> char_set2 = {'a', 'b', 'c', 'd'};
   cout<<"Size of the char_set1 before swap operation: "<<char_set1.size()<<endl;
   cout<<"Contents of the char_set2 before swap operation: "<<endl;
   for(char c2 : char_set2){
      cout<<c2<<endl;
   }
   //using the swap() function
   char_set1.swap(char_set2);
   cout<<"Contents of the char_set1 after swap operation: "<<endl;
   for(char c1 : char_set1){
      cout<<c1<<endl;
   }
   cout<<"Size of the char_set2 after the swap operation: "<<char_set2.size();
}

Following is the output of the above code −

Size of the char_set1 before swap operation: 0
Contents of the char_set2 before swap operation: 
d
c
b
a
Contents of the char_set1 after swap operation: 
d
c
b
a
Size of the char_set2 after the swap operation: 0

In the following example, we are going to consider the unordered_set of string type and applying the swap() function to exchange the contents of the unordered_set.

#include<iostream>
#include<string>
#include<unordered_set>
using namespace std;

int main () {
   //create unordered_sets
   unordered_set<string> str_set1 = {"Red", "Blue", "Yellow", "White"};
   unordered_set<string> str_set2 = {"Apple", "Banana", "Mango", "Orange"};
   cout<<"Contents of the str_set1 before swap operation: "<<endl;
   for(string s1 : str_set1){
      cout<<s1<<endl;
   }
   cout<<"Content of the str_set2 before swap operation: "<<endl;
   for(string s2 : str_set2){
      cout<<s2<<endl;
   }
   //using swap() operation
   str_set1.swap(str_set2);
   cout<<"Contents of the str_set1 after swap operation: "<<endl;
   for(string s1 : str_set1){
      cout<<s1<<endl;
   }
   cout<<"Content of the str_set2 after swap operation: "<<endl;
   for(string s2 : str_set2){
      cout<<s2<<endl;
   }
}

Output of the above code is as follows −

Contents of the str_set1 before swap operation: 
White
Yellow
Blue
Red
Content of the str_set2 before swap operation: 
Mango
Banana
Orange
Apple
Contents of the str_set1 after swap operation: 
Mango
Banana
Orange
Apple
Content of the str_set2 after swap operation: 
White
Yellow
Blue
Red

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