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The C++ std::unordered_set::operator=() function is used to replace the content of the unordered_set container or to copy or move an unordered_set to another unordered_set container.

The assignment operator is only defined for objects of the same type; if we try to attempt the assignment operator with different types, it will result in a compilation error.

This function has 3 polymorphic variants: with using the copy assignment operator, move assignment operator and initializer list(you can find the syntaxes of all the variants below).

Syntax

Following is the syntax of std::operators=() function.

unordered_set& operator= ( const unordered_set& ust );
or	
unordered_set& operator= ( unordered_set&& ust );
or
unordered_set& operator= ( intitializer_list<value_type> il );

Parameters

• ust − It indicates the unordered_set object of the same type.
• il − It indicates an initializer_list object.

Return Value

This function returns the (*this) unordered_set container.

Example 1

In the following example, we are going to use the unordered_set::operator=() function to copy the elements of the current unordered_set into the other unordered_set.

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

int main() {
   unordered_set<int> uSet, myUset;
   uSet = {1, 2, 3 ,4, 5};
   //assigning the current unordered_set into another unordrer_set
   myUset = uSet;
   cout<<"Elements of myUset: ";
   for(auto it: myUset){
      cout<<it<<" ";
   }
   cout<<endl;
   return 0;
}

Output

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

Elements of myUset: 5 4 3 2 1

Example 2

Consider the following example, where we are going to use the move version of the std::unordered_map::operator=() function.

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

int main() {
   unordered_set<int> uSet, myUset;
   uSet = {1, 2, 3 ,4, 5};
   //assigning the current unordered_set into another unordrer_set
   myUset = move(uSet);
   cout<<"Elements of myUset: ";
   for(auto it: myUset){
      cout<<it<<" ";
   }
   cout<<endl;
   return 0;
}

Output

Following is the output of the above code −

Elements of myUset: 5 4 3 2 1 

Example 3

Let's look at the following example, where we are going to replace the content of ilist in the current unordered_set.

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

int main(void) {
   unordered_set<char> uSet = { 'a', 'b', 'c', 'd', 'e'};
   auto ilist = {'A', 'B', 'C'};
   cout<<"uSet content before the assignment operator= operation: "<<endl;
   for(auto&it : uSet){
      cout<<it<<endl;
   }
   cout<<"The ilist content before the assignment operator = operation: "<<endl;
   for(auto & i : ilist){
      cout<<i<<endl;
   }
   //using operator = function
   uSet = ilist;
   cout<<"uSet content after the assignment operator = operation: "<<endl;
   for(auto& it : uSet){
      cout<<it<<endl;
   }
   return 0;
}

Output

Output of the above code is as follows −

uSet content before the assignment operator= operation: 
e
d
c
b
a
The ilist content before the assignment operator = operation: 
A
B
C
uSet content after the assignment operator = operation: 
C
B
A