How to Initialize 3D Vector in C++ STL?

Last Updated : 19 Nov, 2024

Initializing 3D vector refers to the process of assigning the initial values to the elements of 3D Vector. In this article, we will learn different methods to initialize the 3D vector in C++.

The simplest ways to initialize the 3D vector is by passing the elements inside the initializer list. This method is convenient for quick initialization when the number of items is less.

C++

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

int main() {

    // Initialize the 3D vector
    vector<vector<vector<int>>> v = {{{1, 2, 3}, {4, 5, 6}},
                                    {{7, 8, 9}, {10, 11, 12}}};

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

Output

Explanation: The elements specified in the initializer list are used as initial value of 3D vector.

Apart from the above method, C++ also provides other different methods to initialize a 3D vector depending on the situation. Some of them are:

Table of Content

By Default Value
Using std::fill()
Insert 2D Vector One by One
Using Another 3D Vector

By Default Value

The 3D vector can also be initialized with the default value at the time of declaration.

Syntax

vector<vector<vector<int>>> v(x, vector<vector<int>>(y, vector<int>(z, k)));

where x, y and z is the number of rows, number of column and depth of 3D vector respectively, and k is the default value by which we initialize the 3D vector.

C++

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

int main() {

    // Initialize 3D vector with default value 11
    vector<vector<vector<int>>> v(2, 
       vector<vector<int>>(2, vector<int>(3, 11)));

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

Output

Note: In this method, if we do not initialize the 3D vector with some default value, then by default it will be initialized by value of the int type which is 0.

Using fill() Function

The fill() function can also be used to initialize the 3D vector with any default value.

Syntax

fill(v.begin(), v.end(), vector<vector<int>>(y, vector<int>(z, k)));

Here y and z is the number of columns and depth of 3D vector v, and k is the default value by which we initialize 3D vector.

C++

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

int main() {
    vector<vector<vector<int>>> v(2, 
       vector<vector<int>>(2, vector<int>(3)));

    // Initialize 3D vector with default value 11
    fill(v.begin(), v.end(), 
     vector<vector<int>>(2, vector<int>(3, 11)));

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

Output

By Inserting 2D Vector One by One

The 3D vector can also be initialized by inserting the 2D vector one by one using vector push_back() method.

C++

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

int main() {
    vector<vector<vector<int>>> v;

    // Create the 2D vector 
    vector<vector<int>> v1(2, vector<int>(3, 11));
    vector<vector<int>> v2(2, vector<int>(3, 9));

    // Insert the 2D vector one by one
    v.push_back(v1);
    v.push_back(v2);

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

Output

Using Another 3D Vector

The 3D vector can also be initialized with another 3D vector by copying all elements with the help of copy constructor.

Syntax

vector<vector<vector<int>>> v1(v2);

where v1 and v2 is the name of 3D vector.