C++ set - operator=() Function

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

Syntax

C++98
C++11

//copies all elements of x into the container
set& operator= (const set& x);

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

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

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

Parameters

`x`	Specify a 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.
Up to logarithmic i.e, Θ(nlog(n)). Linear i.e, Θ(n) if il is already sorted.

Example: using copy version

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

#include <iostream>
#include <set>
using namespace std;
 
int main (){
  set<int> set1{15, 5, 23, 78, 41};
  set<int>::iterator it;

  //copying all content of set1 into set2
  set<int> set2;
  set2 = set1;

  cout<<"The set1 contains:";
  for(it = set1.begin(); it != set1.end(); ++it)
    cout<<" "<<*it;

  cout<<"\nThe set2 contains:";
  for(it = set2.begin(); it != set2.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

The set1 contains: 5 15 23 41 78
The set2 contains: 5 15 23 41 78

Example: using move version

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

#include <iostream>
#include <set>
using namespace std;
 
int main (){
  set<int> set1{15, 5, 23, 78, 41};
  set<int>::iterator it;

  cout<<"The set1 contains:";
  for(it = set1.begin(); it != set1.end(); ++it)
    cout<<" "<<*it;

  //moving all content of set1 into set2
  set<int> set2;
  set2 = move(set1);

  cout<<"\nThe set1 contains:";
  for(it = set1.begin(); it != set1.end(); ++it)
    cout<<" "<<*it;

  cout<<"\nThe set2 contains:";
  for(it = set2.begin(); it != set2.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

The set1 contains: 5 15 23 41 78
The set1 contains:
The set2 contains: 5 15 23 41 78

Example: using initializer list version

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

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

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

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

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

  return 0;
}

The output of the above code will be:

MySet contains: 5 15 23 41 78

❮ C++ <set> Library