# vector emplace() function in C++ STL

• Difficulty Level : Basic
• Last Updated : 06 Oct, 2021

The vector::emplace() is an STL in C++ which extends the container by inserting a new element at the position. Reallocation happens only if there is a need for 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.

• element- It specifies the element to be inserted in the vector container.

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

Complexity: Linear
Below programs illustrates the above function:
Program 1:

## CPP

 `// C++ program to illustrate the``// vector::emplace() function``// insertion at thefront``#include ``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:

## CPP

 `// C++ program to illustrate the``// vector::emplace() function``// insertion at the end``#include ``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:

## CPP

 `// C++ program to illustrate the``// vector::emplace() function``// insertion at the middle``#include ``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`

Regular insertion using shift operation in arrays V/s emplace( ) function :

a) If want to insert an element at some specific position between the first and last index, we have to shift all the elements next to that specific index. So, if want to keep our code precise so emplace( ) would be a good choice. In terms of Time Complexity both take the same linear time which is directly dependent on the number of shift operations.

Ex:

## C++

 `#include ``#include ``#include ``using` `namespace` `std;` `int` `main() {``    ``array<``int``,6> a={1,2,4,5};``    ``vector<``int``>  v={1,2,4,5};``  ` `    ``// Insert 3 in the arr at index 2``  ` `    ``for``(``int` `i=3;i>=0;i--)``    ``{``      ``if``(i!=1)``        ``a[i+1]=a[i];``      ``else` `{       ``        ``a[i+1]=3; ``break``;``        ``}``    ``}   ``// Time complexity is high``    ` `    ``cout<<``"Content of a: "``;``    ``for``(``int` `i=0;i<5;i++)``       ``cout<

Output

```Content of a: 1 2 3 4 5
Content of v: 1 2 3 4 5 ```

My Personal Notes arrow_drop_up