C++ <vector> - emplace() Function

The C++ vector::emplace function is used to insert new element at specified position in a vector. Each insertion of element increases the vector container size by one. This may cause a reallocation when the vector size surpasses the vector capacity.

Syntax

C++11

template <class... Args>
iterator emplace (const_iterator position, Args&&... args);

Parameters

`position`	Specify the position in the vector where the new element need to be inserted.
`args`	Arguments forwarded to construct the new element.

Return Value

An iterator that points to the newly emplaced element.

Time Complexity

Linear i.e, Θ(n).

Example:

In the example below, the vector::emplace function is used to insert new element at specified position in a vector MyVector.

#include <iostream>
#include <vector>
using namespace std;
 
int main (){
  vector<int> MyVector{10, 20, 30, 40, 50};
  
  //insert a new element at position = 3
  MyVector.emplace(MyVector.begin()+2, 100);

  //insert a new element at position = 3
  MyVector.emplace(MyVector.begin()+2, 200);

  //insert a new element at the end of the vector
  MyVector.emplace(MyVector.end(), 300);

  cout<<"MyVector contains: ";
  for(int i=0; i< MyVector.size(); i++)
    cout<<MyVector[i]<<" ";   

  return 0;
}

The output of the above code will be:

MyVector contains: 10 20 200 100 30 40 50 300

Example:

Lets see another example where the vector MyVector contains string values.

#include <iostream>
#include <vector>
using namespace std;
 
int main (){
  vector<string> MyVector{"JAN", "APR", "MAY"};
  
  //insert a new element at position = 2
  vector<string>::const_iterator it = MyVector.emplace(MyVector.begin()+1, "MAR");

  //insert a new element at position = 2
  MyVector.emplace(it, "FEB");

  //insert a new element at the end of the vector
  MyVector.emplace(MyVector.end(), "JUN");

  cout<<"MyVector contains: ";
  for(int i=0; i< MyVector.size(); i++)
    cout<<MyVector[i]<<" ";   

  return 0;
}

The output of the above code will be:

MyVector contains: JAN FEB MAR APR MAY JUN

❮ C++ <vector> Library