How to Insert Elements into 2D Vector in C++? (original) (raw)

Last Updated : 23 Jul, 2025

In C++, 2D vectors provide several built-in methods to insert elements. The efficiency of the insertion depends on where the insertion occurs. In this article, we will explore different ways to insert elements into a 2D vector in C++ and their specific use cases.

The simplest way to add elements to a 2D vector is by appending the rows of elements (1D vectors) to the end using the **vector push_back() method. Let's take a look at an example:

C++ `

#include <bits/stdc++.h> using namespace std;

int main() { vector<vector> v = {{1, 2, 3}, {4, 5, 6}};

// Adding a new row at the end
v.push_back({7, 8, 9});

// Adding an element to the last row
v[2].push_back(10);

for (const auto& i : v) {
    for (int j : i)
        cout << j << " ";
    cout << endl;
}
return 0;

}

Output

1 2 3 4 5 6 7 8 9 10

Inserting elements in the middle is an expensive operation in a vector because all elements after the insertion point need to be shifted.

Using Vector insert()

The vector insert() method is versatile and can insert elements at any position in a 2D vector. It can also insert multiple elements simultaneously.

C++ `

#include <bits/stdc++.h> using namespace std;

int main() { vector<vector> v = {{1, 3, 5}, {7, 9, 11}};

// Inserting a new row at position 1
v.insert(v.begin() + 1, {4, 6, 8});

// Inserting a value into 2nd row at position 2
v[1].insert(v[1].begin() + 2, 10);

for (const auto& i : v) {
    for (int j : i)
        cout << j << " ";
    cout << endl;
}
return 0;

}

Output

1 3 5 4 6 10 8 7 9 11

Using vector emplace()

The **vector emplace() method works similarly to vector insert(), but instead of copying an element, it constructs the element directly in the vector. This avoids unnecessary copies, improving performance.

C++ `

#include <bits/stdc++.h> using namespace std;

int main() { vector<vector> v = {{1, 3, 5}, {7, 9, 11}};

// Emplacing a new row at position 1
v.emplace(v.begin() + 1, vector<int>{4, 6, 8});

// Emplacing value into 2nd row at position 2
v[1].emplace(v[1].begin() + 2, 10);

for (const auto& i : v) {
    for (int j : i)
        cout << j << " ";
    cout << endl;
}
return 0;

}

Output

1 3 5 4 6 10 8 7 9 11

Using vector emplace_back()

The vector emplace_back() method is the emplacing counterpart of push_back(). It constructs the new element directly in the vector, avoiding extra copies.

C++ `

#include <bits/stdc++.h> using namespace std;

int main() { vector<vector> v = {{1, 3, 5}, {7, 9, 11}};

// Emplacing a new row at the end
v.emplace_back(vector<int>{4, 6, 8});

// Emplacing a value in the last row
v[2].emplace_back(10);

for (const auto& i : v) {
    for (int j : i)
        cout << j << " ";
    cout << endl;
}
return 0;

}

Output

1 3 5 7 9 11 4 6 8 10