How to dynamically allocate a 2D array in C?

Last Updated : 10 Jan, 2025

Following are different ways to create a 2D array on the 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 the following values

 1 2 3 4
 5 6 7 8
 9 10 11 12

1) Using a single pointer and a 1D array with pointer arithmetic:
A simple way is to allocate a memory block of size r*c and access its elements using simple pointer arithmetic.

Output

1 2 3 4 
5 6 7 8 
9 10 11 12

2) Using an array of pointers
We can create an array of pointers of size r. Note that from C99, C language allows variable sized arrays. After creating an array of pointers, we can dynamically allocate memory for every row.

Output

1 2 3 4 5 6 7 8 9 10 11 12

3) Using pointer to a pointer
We can create an array of pointers also dynamically using a double pointer. Once we have an array pointers allocated dynamically, we can dynamically allocate memory and for every row like method 2.

Output

1 2 3 4 5 6 7 8 9 10 11 12

4) Using double pointer and one malloc call

Output

1 2 3 4 5 6 7 8 9 10 11 12

5) Using a pointer to Variable Length Array.

The dimensions of VLA are bound to the type of the variable. Therefore one form a pointer to an array with run-time defined shape.
The pointer has to be dereferenced before subscripting with syntax (*arr)[i][j].

Output