C++ set operator=

There are following three uses of operator = in set:

• ✅ Operator = is used to assign new content to the set container by replacing its old content (or copy the content ) and modifies size if necessary.
• ✅ Operator = is used to move the content of one set container into another and modifies size if necessary.
• ✅ Operator = is used to copy the elements from initializer list to set container.

Syntax

Example
Copy
copy(1)               set& operator= (const set& x);                             //until C++ 11
copy (1) 	set& operator= (const set& x);		            //since C++ 11
move (2)	set& operator= (set&& x);                                   //since C++ 11
initializer list (3)	set& operator= (initializer_list<value_type> il);      //since C++ 11
Try it Yourself

copy (1) :- Copies all the elements from x into the set container.

move (2) :- Moves the content of x into the set container.

initializer_list (3) :- Copies the elements of il into the set container.

Parameter

x : A set object with the same type.

il : An initializer list object.

Return value

this pointer.

Complexity

Copy assignment : Linear in sizes.

Move assignment : Linear in current container size.

Initializer list assignment : Up to logarithmic in sizes.

Iterator validity

All references, iterators and pointers related to this set are invalidated.

Data Races

All copied elements are accessed.

The move assignment modifies x.

The set container and all its elements are modified.

Exception Safety

If an exception is thrown, the container is in a valid state.

Example 1

Let's see the simple example to copy the content of one set to another:

#include <iostream>
#include <set>

using namespace std;

int main(void) {

   set<int> s1 = {10,20,30};

   cout << "Set s1 contains following elements" << endl;
    for (auto it = s1.begin(); it != s1.end(); ++it)
      cout << *it << endl;
      
    set<int> s2 = s1;  
    cout<<"\nAfter Copying the elements from s1 to s2... \n";  
    
    cout << "\nSet s2 contains following elements" << endl;
    for (auto it = s2.begin(); it != s2.end(); ++it)
      cout << *it<< endl; 

   return 0;
}

Output:

Set s1 contains following elements
10
20
30

After copying the elements from s1 to s2... 

Set s2 contains following elements
10
20
30

In the above example, operator = is used to copy the content of one set s1 to another set s2.

Example 2

Let's see a simple example to move the elements of one set to another:

#include <iostream> 
#include <set>

using namespace std;

int main(void) {
   
   set<char> s1 = {'a','e','i','o','u'};

      cout << "Set m1 contains following elements" << endl;
    for (auto it = s1.begin(); it != s1.end(); ++it)
      cout << *it << ", ";
      
    set<char> s2 = move(s1); 
    cout<<"\n\nAfter moving the elements from s1 to s2... \n";  
    
    cout << "\nSet s2 contains following elements" << endl;
    for (auto it = s2.begin(); it != s2.end(); ++it)
      cout << *it << ", ";

   return 0;
}

Output:

Set m1 contains following elements
a, e, i, o, u, 

After moving the elements from s1 to s2?

Set s2 contains following elements
a, e, i, o, u,

In the above example, operator = is used to move the content of one set s1 to another set s2.

Example 3

Let's see a simple example to copy the content from initializer list to set:

#include <iostream>
#include <set>

using namespace std;

int main(void) {
   set<int> s;

   s = {100, 200, 300, 400, 500};  //initializer list

   cout << "Set contains the following elements" << endl;

   for (auto it = s.begin(); it != s.end(); ++it)
      cout << *it << endl;

   return 0;
}

Output:

Set contains the following elements
100
200
300
400
500

In the above example, operator = is used to copy the content from initializer list to set m.

Example 4

Let's see a simple example:

#include <iostream>
#include <set>

using namespace std;

int  main () 
{ 
  int  values []  =  {  5 ,  2 ,  4 ,  1 ,  0 ,  0 ,  9  }; 
  set < int >  c1 ( values ,  values  +  7 ); 
  set < int >  c2 ;

  c2  =  c1 ; 
  c1  =  set < int > ();

  cout<<  "Size Of c1:"  <<  c1 . size ()  << endl ; 
  cout<< "Size Of c2:"  <<  c2 . size ()  << endl ; 
}

Output:

Size Of c1:0
Size Of c2:6

In the above example, there are two sets c1 and c2. c1 has 7 elements and c2 is empty, but after assigning c1 to c2, size of c1 become 0 and size of c2 become 7.