unordered_set emplace() in C++

emplace(): This function is available in the File: unordered_set.h

Syntax:

template<class... _Args> std::pair<std::__detail::_Node_iterator<int, true, false>, bool> std::unordered_set<int>::emplace(_Args &&...__args).

This functions takes one argument as its parameter. This function attempts to build and insert an element into the unordered_set. This function inserts a new element in the unordered_set if its value is unique.

Note: If inserted, this effectively increases the container size by one.

Parameters: One parameter is required for this function.

__args – Arguments used to generate an element.

Returns: 

A pair, of which the first element is an iterator that points to the possibly inserted element, and the second is a bool that is true if the element was actually inserted. This function attempts to build and insert an element into the unordered_set.

Note: Insertion requires amortized constant time.

File: unordered_set.h

Approach

C++

#include <bits/stdc++.h>
using namespace std;

int main()
{
    unordered_set<int> st = {9, 4};

    st.emplace(10);
    cout << st.size() << "\n";

    return 0;
}

Output:

3