unordered_set operator= in C++ STL

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

• The first version takes reference of an unordered_set as an argument and copies it to an unordered_set.
• The second version performs a move assignment i.e it moves the content of an unordered_set to another unordered_set.
• The third version assigns contents of an initializer list to an unordered_set.

Syntax

uset.operator= ( unordered_set& us )
uset.operator= ( unordered_set&& us )
uset.operator= ( initializer list )

Parameters:

• The first version takes the reference of an unordered_set as argument.
• The second version takes the r-value reference of an unordered_set as argument.
• The third version takes an initializer list as argument.

Return value: All of them returns the value of this pointer(*this) . Below program illustrates the unordered_set::operator= in C++. 

Program:

CPP

// C++ code to illustrate the method
// unordered_set::operator=()
#include <iostream>
#include <unordered_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()
{
    unordered_set<int> sample1, sample2, sample3;

    // List initialization
    sample1 = { 7, 8, 9 };
    sample2 = { 9, 10, 11, 12 };

    // Merge both lists
    sample3 = merge(sample1, sample2);

    // copy assignment
    sample1 = sample3;

    // Print the unordered_set list
    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;
}

Output:

10 11 12 7 8 9 
12 11 10 9 
10 11 12 7 8 9

Time complexity: O(n)
Auxiliary Space: O(n)