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set::emplace() function in C++ STL

C++ STL set::emplace() function: Here, we are going to learn about the emplace() function of set in C++ STL (Standard Template Library).
Submitted by Radib Kar, on February 16, 2019

C++ STL set::emplace() function

set::emplace() function is a predefined function, it is used to insert a new element to the set, if element is unique.

Syntax

set<T> st; //declaration
st.emplace(T item);

Parameter(s)

This function accepts an "item" of "T" type.

Return value

If it successfully inserts then it returns a pair<Iterator pointer to the inserted value, True>, Else It returns a pair<iterator to the existing value in the set, False>

Sample Input and Output

For a set of integer,
set<int> st;
st.emplace(5);
st.emplace(4);
set content: //sorted always(ordered)
    4
    5

st.emplace(5) //no insertion this time
set content: 
    4
    5

Header file

Header file to be included:

#include <iostream>
#include <set>
OR
#include <bits/stdc++.h>

Example

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

void printSet(set<int> st) {
  set<int>::iterator it;
  cout << "Set contents are:\n";
  if (st.empty()) {
    cout << "empty set\n";
    return;
  }
  for (it = st.begin(); it != st.end(); it++) cout << *it << " ";
  cout << endl;
}

int main() {
  cout << "Example of emplace function\n";
  set<int> st;
  set<int>::iterator it;
  cout << "inserting 4\n";
  st.emplace(4);
  cout << "inserting 6\n";
  st.emplace(6);
  cout << "inserting 10\n";
  st.emplace(10);

  printSet(st);  // printing current set

  return 0;
}

Output

Example of emplace function
inserting 4
inserting 6
inserting 10
Set contents are:
4 6 10