C++ unordered_set - operator=() Function

The C++ unordered_set::operator= function is used to assign new content to the container by replacing the current content.

Syntax

C++11

//copy version - copies all elements
//of x into the container
unordered_set& operator= (const unordered_set& x);

//move version - moves elements of x
//into the container
unordered_set& operator= (unordered_set&& x);

//initializer list version - copies all 
//elements of il into the container
unordered_set& operator= (initializer_list<value_type> il);

Parameters

`x`	Specify a unordered_set object of same type.
`il`	Specify an initializer_list object.

Return Value

Returns *this.

Time Complexity

Linear i.e, Θ(n) for copy version and move version.
On average: Linear i.e, Θ(n). Worst case: quadratic i.e, Θ(n²).

Example: using copy version

In the example below, the unordered_set::operator= function is used to assign new values to the given unordered_set.

#include <iostream>
#include <unordered_set>
using namespace std;
 
int main (){
  unordered_set<int> uSet1{15, 5, 23, 78, 41};
  unordered_set<int>::iterator it;

  //copying all content of uSet1 into uSet2
  unordered_set<int> uSet2;
  uSet2 = uSet1;

  cout<<"uSet1 contains:";
  for(it = uSet1.begin(); it != uSet1.end(); ++it)
    cout<<" "<<*it;

  cout<<"\nuSet2 contains:";
  for(it = uSet2.begin(); it != uSet2.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

uSet1 contains: 41 78 23 5 15
uSet2 contains: 41 78 23 5 15

Example: using move version

Using the move version of operator=, the content of one unordered_set can be moved to another unordered_set. Consider the following example:

#include <iostream>
#include <unordered_set>
using namespace std;
 
int main (){
  unordered_set<int> uSet1{15, 5, 23, 78, 41};
  unordered_set<int>::iterator it;

  cout<<"uSet1 contains:";
  for(it = uSet1.begin(); it != uSet1.end(); ++it)
    cout<<" "<<*it;

  //moving all content of uSet1 into uSet2
  unordered_set<int> uSet2;
  uSet2 = move(uSet1);

  cout<<"\nuSet1 contains:";
  for(it = uSet1.begin(); it != uSet1.end(); ++it)
    cout<<" "<<*it;

  cout<<"\nuSet2 contains:";
  for(it = uSet2.begin(); it != uSet2.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

uSet1 contains: 41 78 23 5 15
uSet1 contains:
uSet2 contains: 41 78 23 5 15

Example: using initializer list version

The initializer list can also be used to assign values into a unordered_set container. Consider the example below:

#include <iostream>
#include <unordered_set>
using namespace std;
 
int main (){
  //creating empty unordered_set
  unordered_set<int> uSet;
  unordered_set<int>::iterator it;

  //creating initializer list
  initializer_list<int> ilist = {15, 5, 23, 78, 41};

  //assigning values of uSet using ilist
  uSet = ilist;

  cout<<"uSet contains:";
  for(it = uSet.begin(); it != uSet.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

uSet contains: 78 23 5 41 15

❮ C++ <unordered_set> Library