Prerequisite: Array Basics
In C/C++, multidimensional arrays in simple words as an array of arrays. Data in multidimensional arrays are stored in tabular form (in row major order). Below is the general form of declaring N-dimensional arrays:
Syntax of a Multidimensional Array:
data_type array_name[size1][size2]….[sizeN];
data_type: Type of data to be stored in the array.
Here data_type is valid C/C++ data type
array_name: Name of the array
size1, size2, …, sizeN: Sizes of the dimensions
3-D arrays are an array of Double dimensional arrays:
Syntax of a 3D array:
data_type array_name[x][y][z];
data_type: Type of data to be stored. Valid C/C++ data type.
For more details on multidimensional and, 3D arrays, please refer to the Multidimensional Arrays in C++ article.
Problem: Given a 3D array, the task is to dynamically allocate memory for a 3D array using new in C++.
Solution: In the following methods, the approach used is to make two 2-D arrays and each 2-D array is having 3 rows and 4 columns with the following values.
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X = No of 2D arrays.
Y = No of rows of each 2D array.
Z = No of columns of each 2D array.
Method 1: using single pointer – In this method, a memory block of size x*y*z is allocated and then the memory blocks are accessed using pointer arithmetic. Below is the program for the same:
C++
// C++ program to dynamically allocate // the memory for 3D array in C++ // using new operator #include <iostream> using namespace std; // Driver Code int main() { // Dimensions of the 3D array int x = 2, y = 3, z = 4; int count = 0; // Allocate memory blocks // of size x*y*z int* a = new int[x * y * z]; // Traverse the 3D array for (int i = 0; i < x; i++) { for (int j = 0; j < y; j++) { for (int k = 0; k < z; k++) { // Assign values to the // memory blocks created *(a + i * y * z + j * z + k) = ++count; } } } // Traverse the 3D array again for (int i = 0; i < x; i++) { for (int j = 0; j < y; j++) { for (int k = 0; k < z; k++) { // Print values of the // memory blocks created cout << *(a + i * y * z + j * z + k) << " "; } cout << endl; } cout << endl; } // Deallocate memory delete[] a; return 0; } |
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Method 2: using triple pointer – Below is the diagram to illustrate the concept:
Below is the program for the same:
C++
// C++ program to dynamically allocate // the memory for 3D array in C++ // using new operator #include <iostream> using namespace std; // Driver Code int main() { // Dimensions of the 3D array int x = 2, y = 3, z = 4; int count = 0; // Allocate memory blocks of size // x i.e., no of 2D Arrays int*** a = new int**[x]; for (int i = 0; i < x; i++) { // Allocate memory blocks for // rows of each 2D array a[i] = new int*[y]; for (int j = 0; j < y; j++) { // Allocate memory blocks for // columns of each 2D array a[i][j] = new int[z]; } } for (int i = 0; i < x; i++) { for (int j = 0; j < y; j++) { for (int k = 0; k < z; k++) { // Assign values to the // memory blocks created a[i][j][k] = ++count; } } } for (int i = 0; i < x; i++) { for (int j = 0; j < y; j++) { for (int k = 0; k < z; k++) { // Print values of the // memory blocks created cout << a[i][j][k] << " "; } cout << endl; } cout << endl; } // Deallocate memory delete[] a; return 0; } |
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