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

Prerequisite: Vector in C++

Vectors in C++ are the same as arrays with dynamic sizes having the ability to resize themselves, we can insert and remove elements from the end. 

3-D Vector

A 3D vector is a type of vector having 3 Dimensions means a vector storing a 2-D vector inside it, similar to a 2-D array.

There are a few methods to initialize a 3D vector these are:

1. Standard Initialization of a 3D vector
2. Initialization of a 3D vector with given dimensions.
3. Initialization of a 3D vector with some value

1. Standard Initialization of a 3D vector

Standard initialization of a 3D vector is a method where we initialize by declaring and then inserting elements using the push_back( ) function.

Syntax:

vector<vector<vector<data_type>>> vector_name;

Example:

C++

// C++ program to initialise
// 3D vector using Standard
// initialization of a 3D vector
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    // Initialising an empty 3D vector
    vector<vector<vector<int> > > v;

    // Adding values to the vector
    v.push_back({ { 1, 2, 3 }, { 3, 2, 1 } });
    v.push_back({ { 4, 5, 6 }, { 6, 5, 4 } });

    // Printing the 3d vector
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            for (int k = 0; k < v[i][j].size(); k++) {
                cout << v[i][j][k] << " ";
            }
            cout << endl;
        }
    }

    return 0;
}

Output

1 2 3 
3 2 1 
4 5 6 
6 5 4 

2. Initialization of a 3D vector with given dimensions

Given below is the syntax for initializing the 3D vector with a given size in C++. The initialized value is 0 by default and thus different values can be assigned by traversing through loops.

Syntax:

vector<vector<vector<data_type>>> vector_name(x, vector<vector<data_type>>(y, vector<data_type>(z)));

Here x, y, and z are dimensions.

Example:

C++

// C++ program to initialise
// 3D vector Initialization
// of a 3D vector with
// given dimensions
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    // Initialising a 3D vector with 0 as initial value
    vector<vector<vector<int> > > v(
        2, vector<vector<int> >(3, vector<int>(4)));

    // Printing the 3d vector
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            for (int k = 0; k < v[i][j].size(); k++) {
                cout << v[i][j][k] << " ";
            }
            cout << endl;
        }
    }

    return 0;
}

Output

0 0 0 0 
0 0 0 0 
0 0 0 0 
0 0 0 0 
0 0 0 0 
0 0 0 0 

3. Initialization of a 3D vector with some value

Initialization of 3D vector with some value in this method we are creating a vector with x,y, and z dimensions with some value inside it.

Syntax:

vector<vector<vector<data_type>>> vector_name(x, vector<vector<data_type>>(y, vector<data_type>(z,value)));

Example:

C++

// C++ program to initialise
// 3D vector Initialization of
// 3D vector with some value
#include <iostream>
#include <vector>
using namespace std;

int main()
{
    // Initialising a 3D vector with 0 as initial value
    vector<vector<vector<int> > > v(
        2, vector<vector<int> >(3, vector<int>(4, 2)));

    // Printing the 3d vector
    for (int i = 0; i < v.size(); i++) {
        for (int j = 0; j < v[i].size(); j++) {
            for (int k = 0; k < v[i][j].size(); k++) {
                cout << v[i][j][k] << " ";
            }
            cout << endl;
        }
    }

    return 0;
}

Output

2 2 2 2 
2 2 2 2 
2 2 2 2 
2 2 2 2 
2 2 2 2 
2 2 2 2