list emplace() function in C++ STL

The list::emplace() is a built-in function in C++ STL which extends list by inserting new element at a given position.

Syntax:

list_name.emplace(position, element)

Parameters: The function accepts two mandatory parameters which are described below:

• position – it specifies the iterator which points to the position in the list where the new element is to be inserted.
• args – it specifies the elements to be inserted in the list container.

Return value: It returns a random access iterator which points to the newly inserted element.

Below programs illustrate the above function:

Program 1:

CPP

// C++ program to illustrate the
// list::emplace() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
 // declaration of list
 list<int> lis = { 5, 6, 7, 8, 9, 10 };

 auto it = lis.emplace(lis.begin(), 2);

 // inserts at the beginning of the list
 lis.emplace(it, 1);

 cout << "List: ";
 for (auto it = lis.begin(); it != lis.end(); ++it)
  cout << *it << " ";

 return 0;
}

Output

List: 1 2 5 6 7 8 9 10

Time Complexity: O(n)
Auxiliary Space: O(1)

Program 2:

CPP

// C++ program to illustrate the
// list::emplace() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
 // declaration of list
 list<pair<int, char> > lis;

 // inserts at the beginning of the list
 auto it = lis.emplace(lis.begin(), 4, 'a');

 // inserts at the beginning of the list
 lis.emplace(it, 3, 'b');

 cout << "List: ";

 for (auto it : lis)
  cout << "(" << it.first << ", " << it.second << ") ";

 return 0;
}

Output

List: (3, b) (4, a)

Time Complexity: O(n)
Auxiliary Space: O(1)