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Following are different ways to create a 2D array on heap (or dynamically allocate a 2D array).
In the following examples, we have considered ‘r‘ as number of rows, ‘c‘ as number of columns and we created a 2D array with r = 3, c = 4 and following values
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Method 1 :- Using a single pointer
#include <stdio.h> #include <stdlib.h> int main() { int r = 3, c = 4; int *arr = (int *)malloc(r * c * sizeof(int)); int i, j, count = 0; for (i = 0; i < r; i++) for (j = 0; j < c; j++) *(arr + i*c + j) = ++count; for (i = 0; i < r; i++) for (j = 0; j < c; j++) printf("%d ", *(arr + i*c + j)); /* Code for further processing and free the dynamically allocated memory */ return 0; }
Method 2 :- Using an array of pointers
#include <stdio.h> #include <stdlib.h> int main() { int r = 3, c = 4, i, j, count; int *arr[r]; for (i=0; i<r; i++) arr[i] = (int *)malloc(c * sizeof(int)); // Note that arr[i][j] is same as *(*(arr+i)+j) count = 0; for (i = 0; i < r; i++) for (j = 0; j < c; j++) arr[i][j] = ++count; // Or *(*(arr+i)+j) = ++count for (i = 0; i < r; i++) for (j = 0; j < c; j++) printf("%d ", arr[i][j]); /* Code for further processing and free the dynamically allocated memory */ return 0; }
Method 3 :- Using pointer to a pointer
#include <stdio.h> #include <stdlib.h> int main() { int r = 3, c = 4, i, j, count; int **arr = (int **)malloc(r * sizeof(int *)); for (i=0; i<r; i++) arr[i] = (int *)malloc(c * sizeof(int)); // Note that arr[i][j] is same as *(*(arr+i)+j) count = 0; for (i = 0; i < r; i++) for (j = 0; j < c; j++) arr[i][j] = ++count; // OR *(*(arr+i)+j) = ++count for (i = 0; i < r; i++) for (j = 0; j < c; j++) printf("%d ", arr[i][j]); /* Code for further processing and free the dynamically allocated memory */ return 0; }