set operator= in C++ STL

Difficulty Level : Medium
Last Updated : 02 Jun, 2020

The ‘=’ is an operator in C++ STL which copies (or moves) a set to another set and set::operator= is the corresponding operator function. There are three versions of this function:

The first version takes reference of an set as an argument and copies it to an set.
Syntax:
```
ums1.operator=(set &set2)
```
Parameters: The first version takes the reference of an set as argument.
The second version performs a move assignment i.e it moves the content of an set to another set.
Syntax:
```
ums1.operator=(set &&set2)
```
Parameters: The second version takes the r-value reference of an set as argument

The third version assigns contents of an initializer list to an set.

Syntax:

ums1.operator=(initializer list)

Parameters: The third version takes an initializer list as argument.

Return Value: All of them return the value of this pointer(*this).

The following programs illustrates set::operator= :

// C++ code to illustrate the method
// set::operator=()
  
#include <iostream>
#include <set>
using namespace std;
  
// merge function
template <class T>
T merge(T a, T b)
{
    T t(a);
    t.insert(b.begin(), b.end());
    return t;
}
  
int main()
{
    set<int> sample1, sample2, sample3;
  
    // List initialization
    sample1 = { 1, 2, 3, 4, 5 };
    sample2 = { 6, 7, 8, 1 };
  
    // Merge both sets and
    // move the result to sample3
    sample3 = merge(sample1, sample2);
  
    // copy assignment
    sample1 = sample3;
  
    // Print the sets
    for (auto it = sample1.begin(); it != sample1.end(); ++it) {
        cout << *it << " ";
    }
  
    cout << endl;
  
    for (auto it = sample2.begin(); it != sample2.end(); ++it) {
        cout << *it << " ";
    }
  
    cout << endl;
  
    for (auto it = sample3.begin(); it != sample3.end(); ++it) {
        cout << *it << " ";
    }
  
    cout << endl;
  
    return 0;
}

Output:

1 2 3 4 5 6 7 8 
1 6 7 8 
1 2 3 4 5 6 7 8

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set operator= in C++ STL