vector emplace() function in C++ STL

The vector::emplace() is an STL in C++ which extends container by inserting new element at position. Reallocation happens only if there is a need of more space. Here the container size increases by one.

Syntax:

template 
iterator vector_name.emplace (const_iterator position, element);

Parameter:
The function accepts two mandatory parameters which are specified as below:

position – It specifies the iterator pointing to the position in the container where the new element is to be inserted.
args – It specifies the element to be inserted to be inserted in the vector container.

Return value: The function returns an iterator which points to the newly inserted element.

Below programs illustrates the above function:

Program 1:

// C++ program to illustrate the 
// vector::emplace() function 
// insertion at thefront 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vec = { 10, 20, 30 }; 
  
    // insert element by emplace function 
    // at front 
    auto it = vec.emplace(vec.begin(), 15); 
  
    // print the elements of the vector 
cout << "The vector elements are: ";  
    for (auto it = vec.begin(); it != vec.end(); ++it) 
        cout << *it << " "; 
  
    return 0; 
} 

Output:

The vector elements are: 15 10 20 30

Program 2:

// C++ program to illustrate the 
// vector::emplace() function 
// insertion at the end 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vec = { 10, 20, 30 }; 
  
    // insert element by emplace function 
    // at the end 
    auto it = vec.emplace(vec.end(), 16); 
  
    // print the elements of the vector 
cout << "The vector elements are: ";  
    for (auto it = vec.begin(); it != vec.end(); ++it) 
        cout << *it << " "; 
  
    return 0; 
} 

Output:

The vector elements are: 10 20 30 16

Program 3:

// C++ program to illustrate the 
// vector::emplace() function 
// insertion at the middle 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vec = { 10, 20, 30 }; 
  
    // insert element by emplace function 
    // in the middle 
    auto it = vec.emplace(vec.begin() + 2, 16); 
  
    // print the elements of the vector 
cout << "The vector elements are: ";  
    for (auto it = vec.begin(); it != vec.end(); ++it) 
        cout << *it << " "; 
  
    return 0; 
} 

Output:

The vector elements are: 10 20 16 30

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