Question

How can a 2D array be allocated using malloc() and a single pointer in C?

a) Using a single call to malloc() for total elements
b) Allocating rows first, then columns using malloc()
c) Using pointer arithmetic for 2D array allocation
d) Not possible with a single pointer

Answer 1

A 2D array in C can be allocated using malloc() with a single pointer by making a single call for the total elements and accessing the elements via pointer arithmetic. This efficient method avoids multiple malloc() calls and the use of double pointers.

Step-by-step explanation:

To allocate a 2D array in C using malloc() and a single pointer, you can follow the approach of using a single call to malloc() for the total number of elements. Here's how you can do it:

1. Determine the number of rows and columns needed for the 2D array.
2. Multiply the number of rows by the number of columns to get the total number of elements.
3. Allocate the total memory required for the 2D array using a single call to malloc(), casting the returned pointer to the desired element type.
4. Use pointer arithmetic to access array elements as though it is a 2D array.

For example, if you want an array of rows x columns integers, you would use:

int *array = (int *)malloc(rows * columns * sizeof(int));

To access the element at [i][j], you would use:

int value = *(array + i * columns + j);
This technique is often used due to its simplicity and efficiency, as it avoids the overhead of making multiple calls to malloc() and it avoids the need for an array of pointers as is typically used in a double-pointer 2D array allocation.