C++ <list> - emplace() Function

The C++ list::emplace function is used to insert new element at specified position in a list. Each insertion of element increases the list container size by one.

Syntax

C++11

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

Parameters

`position`	Specify the position in the list 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

Constant i.e, Θ(1).

Example:

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

#include <iostream>
#include <list>
using namespace std;
 
int main (){
  list<int> MyList{10, 20, 30, 40, 50};
  list<int>::iterator it;
  
  it = MyList.begin();
  advance(it, 2);
  //insert a new element at position = 3
  MyList.emplace(it, 100);

  it = MyList.end();
  //insert a new element at the end of the list
  MyList.emplace(it, 200);

  //insert a another new element at the end of the list
  MyList.emplace(it, 300);

  cout<<"MyList contains: ";
  for(it = MyList.begin(); it != MyList.end(); it++)
    cout<<*it<<" ";   

  return 0;
}

The output of the above code will be:

MyList contains: 10 20 100 30 40 50 200 300

Example:

Lets see another example where the list MyList contains string values.

#include <iostream>
#include <list>
using namespace std;
 
int main (){
  list<string> MyList{"JAN", "MAR", "APR", "MAY"};
  list<string>::iterator it;

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

  it = MyList.end();
  //insert a new element at the end of the list
  MyList.emplace(MyList.end(), "JUN");

  cout<<"MyList contains: ";
  for(it = MyList.begin(); it != MyList.end(); it++)
  {
   cout<<*it<<" ";   
  }
  return 0;
}

The output of the above code will be:

MyList contains: JAN FEB MAR APR MAY JUN

Example:

Lets see another example where the list MyList contains paired values.

#include <iostream>
#include <list>
using namespace std;
 
int main (){
  list<pair<int,string>> MyList;
  list<pair<int,string>>::iterator it;
  
  it = MyList.begin();
  //insert a new elements in the list
  MyList.emplace(it, 1, "JAN");
  MyList.emplace(it, 2, "FEB");
  MyList.emplace(it, 3, "MAR");

  cout<<"MyList contains: ";
  for(it = MyList.begin(); it != MyList.end(); it++)
  {
   cout<<"("<<it->first<<","<<it->second<<") ";   
  }
  return 0;
}

The output of the above code will be:

MyList contains: (1,JAN) (2,FEB) (3,MAR)

❮ C++ <list> Library