Insert an element at the beginning of a vector in C++

This post will discuss how to insert an element at the beginning of a vector in C++.

1. Using `std::vector::insert` function

The standard solution to insert an element to a vector is with the std::vector::insert function. It takes an iterator to the position where the element needs to be inserted. To insert an element at the beginning of a vector, pass an iterator pointing to the first element in the vector. For example,

#include <iostream>

#include <vector>

#include <iterator>

int main()

{

std::vector<int> v = {2, 3, 4, 5};

int target = 1;

// add target at beginning

v.insert(v.begin(), target);

// print vector

std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));

return 0;

}

Download Run Code

Output:

1 2 3 4 5

2. Using `std::rotate` function

Alternatively, we can append the element at the vector’s end and then rotate the vector to the right by 1 position. A typical implementation of this approach would look like this:

#include <iostream>

#include <vector>

#include <algorithm>

#include <iterator>

int main()

{

std::vector<int> v = {2, 3, 4, 5};

int target = 1;

// add target at beginning

v.push_back(target);

std::rotate(v.rbegin(), v.rbegin() + 1, v.rend());

// print vector

std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));

return 0;

}

Download Run Code

Output:

1 2 3 4 5

3. Using `std::deque`

To add and remove elements from both the front and the end of a container, consider using a std::deque. It implements a Double-ended queue that can expand or shrink on both ends. To insert an element at the beginning, use the push_front member function of std::deque, as shown below:

#include <iostream>

#include <deque>

#include <iterator>

int main()

{

std::deque<int> d = {2, 3, 4, 5};

int target = 1;

// add target at beginning

d.push_front(target);

// print vector

std::copy(d.begin(), d.end(), std::ostream_iterator<int>(std::cout, " "));

return 0;

}

Download Run Code

Output:

1 2 3 4 5

That’s all about inserting an element at the beginning of a vector in C++.

Insert an element at the beginning of a vector in C++

1. Using std::vector::insert function

2. Using std::rotate function

3. Using std::deque

Share this:

1. Using `std::vector::insert` function

2. Using `std::rotate` function

3. Using `std::deque`