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
2D arrays are arrays of single-dimensional arrays.
Syntax of a 2D array:
data_type array_name[x][y];
data_type: Type of data to be stored. Valid C/C++ data type.
Below is the diagrammatic representation of 2D arrays:
For more details on multidimensional and 2D arrays, please refer to Multidimensional arrays in C++ article.
Problem: Given a 2D array, the task is to dynamically allocate memory for a 2D array using new in C++.
Solution: Following 2D array is declared with 3 rows and 4 columns with the following values:
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Note: Here M is the number of rows and N is the number of columns.
Method 1: using a single pointer – In this method, a memory block of size M*N 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 2D array in C++// using new operator#include <iostream>using namespace std;// Driver Codeint main(){ // Dimensions of the 2D array int m = 3, n = 4, c = 0; // Declare a memory block of // size m*n int* arr = new int[m * n]; // Traverse the 2D array for (int i = 0; i < m; i++) { for (int j = 0; j < n; j++) { // Assign values to // the memory block *(arr + i * n + j) = ++c; } } // Traverse the 2D array for (int i = 0; i < m; i++) { for (int j = 0; j < n; j++) { // Print values of the // memory block cout << *(arr + i * n + j) << " "; } cout << endl; } //Delete the array created delete[] arr; return 0;} |
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Method 2: using an array of pointer: Here an array of pointers is created and then to each memory block. Below is the diagram to illustrate the concept:
Below is the program for the same:
C++
// C++ program to dynamically allocate// the memory for 2D array in C++// using new operator#include <iostream>using namespace std;// Driver Codeint main(){ // Dimensions of the array int m = 3, n = 4, c = 0; // Declare memory block of size M int** a = new int*[m]; for (int i = 0; i < m; i++) { // Declare a memory block // of size n a[i] = new int[n]; } // Traverse the 2D array for (int i = 0; i < m; i++) { for (int j = 0; j < n; j++) { // Assign values to the // memory blocks created a[i][j] = ++c; } } // Traverse the 2D array for (int i = 0; i < m; i++) { for (int j = 0; j < n; j++) { // Print the values of // memory blocks created cout << a[i][j] << " "; } cout << endl; } // Delete the array created for (int i = 0; i < m; i++) // To delete the inner // arrays delete[] a[i]; delete[] a; // To delete the outer array // which contained the pointers // of all the inner arrays return 0;} |
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