Allocating 2-D Arrays on Heap
Explore how to allocate two-dimensional arrays dynamically on the heap by creating arrays of pointers to arrays. Understand the process of managing memory safely, including writing functions to allocate and deallocate matrices, and handling potential allocation failures to avoid memory leaks.
Introduction
We’ve seen that allocating one-dimensional arrays is pretty straightforward. To allocate one array of 15 doubles, we can write the following:
double arr = malloc(15 * sizeof(double));
Then we can use this array just like we use any other array:
arr[0] = 5.0; //to write to the array
double x = arr[1]; //to read from the array
The question is, how can we dynamically allocate arrays with higher dimensions? We’ll present a strategy called “arrays of pointers to arrays” for the two-dimensional case. This strategy can extend to three-dimensional arrays and beyond.
Matrix structure
To understand this technique, let’s inspect how a 3x4 matrix looks:
As per the image above, we can view the matrix as multiple arrays stacked on top of each other, and each array is one row. Therefore, a matrix or two-dimensional array is an array of arrays.
To dynamically allocate a matrix with n lines and m columns, imagine dynamically allocating n individual one-dimensional arrays, where each array will serve as a row. We know how to allocate one-dimensional arrays, so this is doable.
For example, if we assume a 3x4 matrix that stores integers, we can do:
malloc(4 * sizeof(int)) //allocate first row array
malloc(4 * sizeof(int)) //allocate second row array
malloc(4 * sizeof(int) //allocate third row array
malloc(4 *